Supplementary Information

Transcription

1 Supplementary Information General procedures. All manipulations were performed under a nitrogen atmosphere by standard Schlenk techniques or in an M. Braun glove box maintained at or below 1 ppm of O 2 and H 2 O. Glassware was dried at 150 C overnight. NMR data were recorded on a Bruker Avance 400 spectrometer (400 MHz) at 22 C. All peaks in the NMR spectra are referenced to residual C 6 D 5 H at δ 7.16 ppm. In parentheses are listed: T 2 values in ms calculated as (π ν 1/2 ) -1, 1 integrations and assignments. In some cases, it was not possible to determine integrations and T 2 values because of peak overlap. UV-vis spectra were measured on a Cary 50 spectrophotometer, using screw-cap cuvettes. Solution magnetic susceptibilities were determined by the Evans method. 2 Elemental analyses were determined by Desert Analytics, Tucson, AZ. Pentane, diethyl ether and toluene were purified by passage through activated alumina and "deoxygenizer" columns from Glass Contour Co. (Laguna Beach, CA). Deuterated benzene was first dried over CaH 2, then over Na/benzophenone, and then vacuum transferred into a storage container. Before use, an aliquot of each solvent was tested with a drop of sodium benzophenone ketyl in THF solution. Celite was dried overnight at 200 C under vacuum. The compounds LFeCl, 3 KBEt 3 H, 4 and Cp* 2 Zr(H) 5 2 were prepared by published procedures. 3-Hexyne and 2-butyne were obtained from Aldrich, degassed, vacuum transferred to a new container, and stored in the glovebox at -35 C. Naphthalene was purified by vacuum sublimation, and 4-tert-butylpyridine dried over molecular sieves. Azobenzene was dissolved in pentane, dried over molecular sieves, filtered through Celite then dried in vacuo. LiNHPh was prepared by reaction of distilled aniline with n BuLi in pentane. Temperatures in the NMR probe were calibrated using standard MeOD (<20 C) or DOCH 2 CH 2 OD (>20 C) samples. 6 Preparation of [LFeH] 2 1. From KBEt 3 H: LFeCl (1.00 g, 1.69 mmol) was dissolved in toluene (30 ml) in a Schlenk flask to give a red solution. A clear solution of KBEt 3 H (233 mg, 1.69 mmol) in toluene (10 ml) was added, resulting in the immediate formation of a very dark red solution. The reaction mixture was stirred at room temperature for 45 min, and the volatile materials removed in vacuo. The residue was washed with pentane until clear, removing a small amount of a bright red impurity. The residue was stirred with toluene (20 ml) S-1

2 overnight, and then filtered through Celite to give a dark red solution. This solution was then reduced in volume to ca. 8 ml, warmed to dissolve the product, and then cooled to 35 C. Very dark red crystals (682 mg) were isolated. A second crop (56 mg) was obtained after reducing the solvent to ca. 3 ml and cooling to -35 C. Total yield is 738 mg, 78%. It is critical that the reaction is not stirred for too long because [LFeH] 2 reacts with the BEt 3 byproduct. 2. From Cp* 2 Zr(H) 2 : This procedure has not been optimized. To a red slurry of LFeCl (350 mg, 590 µmol) in Et 2 O (8 ml) was added a yellow solution of Cp* 2 Zr(H) 2 (215 mg, 590 µmol). The reaction was stirred overnight to give a dark red solution. The solvent was reduced to ca. 4 ml, and the solution cooled to -35 C. A dark red solid (115 mg, 35%) was isolated. The complex [LFeH] 2 dissolves slowly in toluene, benzene, THF and Et 2 O. It is very slightly soluble in pentane. The 1 H NMR spectrum as a function of temperature is shown in Figure S1a, and the equilibrium populations and magnetic moment as a function of temperature are shown in Figure S1b. 1 H NMR ([LFeH] 2, 22 C, C 6 D 6 ) δ 70, 22, 14, 12, 10, 6, 3, 1, -8, -11, -23, -27, -28, -33, -39, -52, H NMR (LFeH, 22 C, C 6 D 6 ) δ 43 (2, 18H, C(CH 3 ) 3 ); -2 (4, 4H, m-h); -13 (3, 12H, CH(CH 3 ) 2 ); -112 (2, 2H, p-h); -117 (0.2, 4H, CH(CH 3 ) 2 ); -126 (0.4, 12H, CH(CH 3 ) 2 ). Anal. Cald. for C 70 H 108 N 4 Fe 2 C 75.25, H 9.74, N Found C, 75.11, H 9.62, N IR and resonance Raman spectra did not give any characteristic peaks for the iron-hydride functionality. S-2

3 Figure S1. (a) Top: 1H NMR spectrum of [LFeH]2 in C7D8 as a function of temperature. [Fe] = 25.7 mm. Inset shows the 1H NMR spectrum of LFeMe.7 (b) Bottom: Plot of µeff (z) and monomer ( ) and dimer (T) populations for [LFeH]2 as a function of temperature. [Fe] = 49 mm at 303 K. S-3

4 Preparation of LFe(H)(4- t Bupy). A mixture of [LFeH] 2 (50 mg, 45 µmol) and Et 2 O (8 ml) was stirred until the solid had completely dissolved (30 min), and a solution of 4-tert-butylpyridine (13 µl, 90 µmol) in Et 2 O (3 ml) was slowly added over the course of 15 min. The initial dark red color of the solution lightened considerably. After another 10 min stirring at room temperature, the volatile materials were removed in vacuo. The resulting red solid was redissolved in pentane (4 ml), and the product crystallized at 35 C as bright red crystals (30 mg, 50%). It has not been possible to obtain accurate elemental analysis for this compound; 1 H NMR spectra suggest that it contains some [LFeH] 2. This probable equilibrium is under investigation. 1 H NMR (22 C, C 6 D 6 ) δ 24, 22, 10, 5, -2, -5, -7, -12, -17, -54, -93. Preparation of LFeC(Et)=C(H)Et. 3-Hexyne (17 µl, 151 µmol) was added via a syringe to a slurry of [LFeH] 2 (80 mg, 72 µmol) in Et 2 O (6 ml). Over the course of 1 h, the dark red solution became orange in color, and the solid dissolved. The volatile materials were then removed in vacuo. The orange solid was redissolved in warm pentane (2 ml), and crystallized at 35 C, giving orange crystals (69 mg, 75%). 1 H NMR (22 C, C 6 D 6 ) δ 125 (0.3, 1H, backbone CH), 94 (0.4, 2H, CH 2 CH 3 ), 65 (0.6, 3H, CH 2 CH 3 ), 45 (0.6, 18 H, C(CH 3 ) 3 ), 5 (0.9, 3H, CH 2 CH 3 ), 3 (0.9, 4H, m-h), -25 (0.9, 12H, CH(CH 3 ) 2 ), -105 (4H, CH(CH 3 ) 2 ), -107 (0.8, 2H, p-h), -133 (0.3, 12H, CH(CH 3 ) 2 ), -208 (0.1, 1H, =CH(Et)). µ eff (Evans, C 6 D 6 ) 5.4(3) BM. Anal. Calcd. for C 41 H 64 N 2 Fe C 76.85, H 10.07, N Found C, 75.48, H 10.28, N Preparation of LFeN(Ph)NHPh. 1. From [LFeH] 2 : An orange solution of azobenzene (20 mg, 107 µmol) in Et 2 O (2 ml) was added to a dark red slurry of [LFeH] 2 (60 mg, 54 µmol) in Et 2 O (6 ml). A red solution was formed over the course of an hour. The volatile materials were removed in vacuo and the residue extracted with pentane and filtered through Celite. The volume was reduced to 2 ml, and the solution was cooled to 35 C to give red crystals (46 mg, 58%). 2. From LFeCl: A 20 ml scintillation vial was charged with LFeCl (150 mg, 253 µmol), azobenzene (46 mg, 253 µmol) and Et 2 O (10 ml). A solution of KBEt 3 H (35 mg, 253 µmol) in Et 2 O (2 ml) was added S-4

5 to yield a dark red solution. After stirring at room temperature for 2 h, the solution was filtered through Celite to give a red solution. The volume was reduced to 6 ml, and the solution was cooled to 35 C to give red crystals in two crops (140 mg, 75%). 1 H NMR (22 C, C 6 D 6 ) δ 169 (0.1, 1H, backbone CH), 118 (0.3, 1H), 45 (1.1, 18H, C(CH 3 ) 3 ), 41 (1H), 30 (0.3, 1H), 17 (0.2, 1H), -8 (2, 2H, o/m-h), -9 (2, 2H, o/m-h), -21 (0.2, 1H), -25 (2, 6H, CH(CH 3 ) 2 ), -31 (2, 6H, CH(CH 3 ) 2, -47 (2, 1H, hydrazido p-h), -93 (0.2, 6H, CH(CH 3 ) 2, -98 (1, 2H, diketiminate p-h), -182 (8H, CH(CH 3 ) 2 and CH(CH 3 ) 2 ). µ eff (Evans, C 6 D 6 ) 5.1(3) BM. Due to the thermal instability of the solid, we have not been able to obtain successful elemental analysis. Thermolysis of LFeN(Ph)NHPh. A screw-cap NMR tube was charged with LFeN(Ph)NHPh (9.8 mg) and C 6 D 6 (418 µmol). The solution was heated at 80 C and the reaction was monitored by 1 H NMR spectroscopy. After one hour, 1 H NMR showed the formation of a product with an 1 H NMR spectrum identical to LFeNHPh. (There were other minor iron-containing products; their identity is under investigation.) The reaction mixture was passed through an activated alumina column to yield an orange solution. The solvent was removed in vacuo to yield orange PhNNPh. 1 H NMR (CDCl 3, 22 C) δ 7.94 (m, 2H), 7.51 (m, 3H). GC/MS (EI) 182; the fragmentation pattern matches that found online at Independent preparation of LFeNHPh. A slurry of LiNHPh (17 mg, 169 µmol) in Et 2 O (2 ml) was added to a red solution of LFeCl (100 mg, 169 µmol) in Et 2 O (6 ml). The solution became orange in color with the formation of a white precipitate. After stirring at room temperature for one hour, the solution was filtered through Celite to give an orange solution. The volume was reduced to 4 ml, and the solution was cooled to 35 C to give orange-red crystals (45 mg, 41%). 1 H NMR (22 C, C 6 D 6 ) δ 97 (0.4, 1H, backbone CH), 88 (0.3, 2H, NHPh m-h), 41 (0.7, 18H, C(CH 3 ) 3 ), 3 (2.2, 4H, m-h), -25 (2, 12H, CH(CH 3 ) 2 ), -54 (2, 1H, NHPh p-h), -101 (0.1, 4H, CH(CH 3 ) 2 ), (2H, p-h), -116 (12H, CH(CH 3 ) 2 ). µ eff (Evans, C 6 D 6 ) 5.5(3) BM. Anal. Cald. for C 41 H 59 N 3 Fe: C 75.79, H 9.15, N Found C, 74.32, H 9.41, N S-5

6 Kinetics Experiments. 1. [LFeH] 2 + 2EtCCEt: An accurately weighed sample of [LFeH] 2 (10-13 mg) was placed in a J. Young resealable NMR tube with an accurately weighed aliquot of C 7 D 8 (ca. 450 mg). An internal reference consisting of a capillary containing a solution of LFeCl (1.97 µmol) in C 7 D 8 was added. The tube was closed, and sonicated (ca. 5 min) to completely dissolve the complex. The tube was then connected to the vacuum line, the solution frozen and the headspace evacuated. An appropriate amount of alkyne was condensed into the tube. The solution was thawed, and the NMR tube placed into the NMR probe that was already equilibrated at the required temperature. After the sample had equilibrated for 5 min, 1 H NMR spectra were recorded at preset times using an automated program. After Fourier transform, phasing, calibrating and integrating each spectrum, a plot of normalized [LFeH] 2 concentration (y) vs. time (M0) was used to find the best fit to the general, integrated equation: y = m1 + m2*exp(-m0*m3), where m1, m2 and M3 are variables, M3 being the first order rate constant. For this purpose, KaleidaGraph 3.51 was used. A representative curve (Figure S2) and the final Eyring plot (Figure S3) are shown. The vinyl complex was the only observed iron product. Because of the steep dependence of the reaction rate on temperature, it was only practical to monitor the reaction between 277 and 299 K. Table S1. Observed rate of hydride consumption by EtCCEt in C 6 D 6 at 288K in C 6 D 6. Entry [EtCCEt] / mm k obs / 10-4 s (2) (2) (2) S-6

7 y = m1 + m2 * (exp(-m0*m3)) Value Error m e m m e-05 Chisq e-07 NA R NA [LFeH] 2 / mm t / s Figure S2. Plot of [[LFeH] 2 ] vs time for the reaction with 3-hexyne (52 mm) at 298 K. [Fe] = 35.0 mm y = m1 + m2 * M0 Value Error m m Chisq NA R NA ln(k/t) /T Figure S3. Eyring plot for the reaction of 3-hexyne with [LFeH] 2. S-7

8 2. LFeN(Ph)NHPh LFeNHPh PhNNPh: An accurately weighed sample of LFeN(Ph)NHPh (10-13 mg) was placed in a J. Young resealable NMR tube with an accurately weighed aliquot of C 6 D 6 (ca. 450 mg). An internal reference consisting of a capillary containing a solution of CoTp* 2 in C 7 D 8 was added. The NMR tube placed into the NMR probe that was already equilibrated at the required temperature. After the sample had equilibrated for 2 min, 1 H NMR spectra were recorded at preset times using an automated program. After Fourier transform, phasing, calibrating and integrating each spectrum, a plot of normalized LFeN(Ph)NHPh concentration (y) vs. time (M0) was used to find the best fit to the general, integrated equation: y = m1 + m2*exp(-m0*m3), where m1, m2 and M3 are variables, M3 being the first order rate constant. For this purpose, KaleidaGraph 3.51 was used. A representative curve (Figure S4) for the hydrazido cleavage reaction is shown. There were minor amounts of iron-containing products other than LFeNHPh formed; their identity is under investigation. 70 [LFe(N(Ph)N(H)Ph)] / mm y = m1 + m2 * (exp(-m0*m3)) Value Error m m m e -05 Chisq NA R NA Time / s Figure S4 Plot of [LFe(N(Ph)NHPh] vs time at 358 K. [Fe] = 61.0 mm S-8

9 Table S2. Observed rate of LFeN(Ph)NHPh decomposition in C 6 D 6 at 358 K. Entry [LFeN(Ph)N(H)Ph] / mm k obs / 10-4 s (2) (2) (3) Equilibrium Measurements. A sample of [LFeH] 2 (4.9 mg, 4.4 µmol) was placed in a resealable NMR tube with an aliquot of C 7 D 8 (389 mg). An internal reference consisting of a capillary containing a solution of CoTp* 2 (6.4 mm in C 7 D 8 ) was added. The tube was closed and sonicated (ca. 5 min) to completely dissolve the iron complex. Sample equilibration at each temperature was confirmed by recording the 1 H NMR spectrum every 5 min until no change was observed. Thermal equilibration was found to be complete within 10 min at each temperature. Thermodynamic parameters ( H = 72(2) kj/mol; S = 247(4) J/K mol) were obtained from a van t Hoff plot over the range K (Figure S5) ln(k) 0-2 y = m1 + m2 * M0 Value Error m m Chisq NA R NA /T Figure S5 van t Hoff plot for the equilibrium 2LFeH [LFeH] 2. [Fe] = 20 mm at 20 C. S-9

10 Magnetic Moment Measurements. A sample of [LFeH] 2 (13.1 mg, 11.7 µmol) was placed in an NMR tube (connected to a ground glass joint) with an aliquot of C 7 D 8 (412 mg). An internal reference consisting of a capillary containing a solution of LFeCl (1.97 µmol) in C 7 D 8 was added. The tube was connected to the vacuum line, frozen, flame-sealed and sonicated to completely dissolve the iron complex. Magnetic moments were determined by the Evans method. 2 Sample equilibration at each temperature was confirmed by recording the 1 H NMR spectrum every 5 min until no change was observed. Thermal equilibration was complete within 10 min at each temperature. Molecular Weight Determinations. A mixture of [LFeH] 2 (1.8 mg) and naphthalene (185 mg) was heated until an orange solution formed. After cooling, an aliquot of the orange solid was placed in capillary which was then plugged with silicone grease and flame sealed. Melting point depressions, compared to that of authentic naphthalene, were measured on a Thomas Hoover melting point apparatus, using a VWR Precision 0.01 Thermometer equipped with a Pt-100Ω sensor. Molecular weights were determined using the formula: molecular weight = K w 1000/ T W, where K = 4.9 for naphthalene, w = mass of iron complex, W = mass naphthalene and T = temperature depression. 8 Table S3. Observed melting point depressions and corresponding molecular weights. Entry T / C MW S-10

11 X-ray Structural Determinations of [LFeH] 2, LFeC(Et)=C(Et)H, LFe(H)( t Bupy), LFeN(Ph)NHPh and LFeNHPh. Crystalline samples of the three complexes were grown in the glove box from saturated toluene ([LFeH] 2 ) or pentane (LFe(H)( t Bupy), LFeC(Et)=C(Et)(H), LFeN(Ph)NHPh and LFeNHPh) solutions at -35 C. The crystals were rapidly mounted under Paratone-8277 onto glass fibers, and immediately placed in a cold nitrogen stream at -80 C on the X-ray diffractometer. The X-ray intensity data were collected on a standard Bruker-axs SMART CCD Area Detector System equipped with a normal focus molybdenum-target X-ray tube operated at 2.0 kw (50 kv, 40 ma). A total of 1321 frames of data (1.3 hemispheres) were collected using a narrow frame method with scan widths of 0.3 in ω and exposure times of 30 sec/frame for [LFeH] 2 and LFe(H)( t Bupy), and 60s/frame for LFeC(Et)=C(Et)H, LFeN(Ph)NHPh and LFeNHPh, using a detector-to-crystal distance of 5.09 cm. The total data collection time was approximately 12 hours for 30 sec data and 26 hours for 60 sec data. Frames were integrated to a maximum 2θ angle of 56.5 for [LFeH] 2, LFe(H)( t Bupy), LFeN(Ph)NHPh, and LFeNHPh and 46.5 (due to a lack of observed data <0.9 Å) for LFeC(Et)=C(Et)H with the Bruker-axs SAINT program. Laue symmetry revealed monoclinic crystal systems for [LFeH] 2 and LFe(H)( t Bupy), a triclinic crystal system for LFeC(Et)=C(Et)H and orthorhombic crystal systems for LFeN(Ph)NHPh and LFeNHPh. The final unit cell parameters (at -80 C) were determined from the least-squares refinement of three dimensional centroids of >5000 reflections for each crystal. Data were corrected for absorption with the SADABS 9 program. The space groups were assigned as C2/c (#15) for [LFeH] 2, P1 (#2) for LFeC(Et)=C(Et)H, and P2 1 /c (#14) for LFe(H)( t Bupy), Pbca for LFeN(Ph)NHPh, Pca2 1 for LFeNHPh and the structures were solved by direct methods using Sir92 10 (WinGX v ) and refined employing full-matrix least-squares on F 2 (Brukeraxs, SHELXTL-NT, 11 version 5.10). For [LFeH] 2, there is one full molecule in the asymmetric unit (Z = 8) and diffuse solvent that was not assignable. Therefore solvent areas were removed with the SQUEEZE (WinGX v ) program, 12 and H1 was located and its position and thermal parameter was refined. However, the residual value of suggests that the Fe H values may not be trustworthy. Z values were as expected for one full molecule per asymmetric unit in both LFeC(Et)=C(Et)H (Z = 2) and LFe(H)( t Bupy) (Z = 4). For LFeN(Ph)NHPh solvent areas (these most closely resembled two pentane S-11

12 molecules, one on an inversion center) were removed with the SQUEEZE (WinGX v ) program. All non-h atoms for the complexes were refined with anisotropic thermal parameters. For all three complexes, hydrogen atoms were included in idealized positions with the exception of H(1) in [LFeH] 2, H(24b) in LFeN(Ph)N(H)Ph, H(1) in LFe( t Bupy)H, and H(1) in LFeNHPh. The structures refined to goodness of fit (GOF) 12 values and final residuals 13 found in the tables below. ORTEP plots for LFeC(Et)=C(Et)H and LFeNHPh are shown in Figures S6 and S7. S-12

13 Figure S6. ORTEP plot of LFeC(Et)C(H)Et, themal ellipsoids shown at 50% probability. Figure S7. ORTEP plot of LFeNHPh, thermal ellipsoids shown at 50% probability. S-13

14 References 1 (a) Ming, L.-J. In Physical Methods in Bioinorganic Chemistry; Que, L., Jr., Ed.; University Science Books: Sausalito, 2000; pp (b) Holland, P.L.; Cundari, T.R.; Perez, L.L.; Eckert, N.A.; Lachicotte, R.J. J. Am. Chem. Soc. 2002, 124, Schubert, E. M. J. Chem. Ed. 1992, 69, (a) Smith, J.M.; Lachicotte, R.J.; Holland, P.L. Chem. Commun. 2001, (b) Smith, J.M.; Lachicotte, R.J.; Holland, P.L. Organometallics 2002, 21, Fryzuk, M.D.; Lloyd, B.R.; Clentsmith, G.K.B.; Rettig, S.J. J. Am. Chem. Soc. 1994, 116, Schock, L.E.; Marks, T.J. J. Am. Chem. Soc. 1988, 110, Amman, C.; Meier, P.; Merbach, A. E. J. Magn. Reson. 1982, 46, Andres, H.; Bominaar, E.M.; Smith, J.M.; Eckert, N.A.; Holland, P.L.; Münck, E. J. Am. Chem. Soc. 2002, 124, Pasto, D.J.; Johnson, C.R. Laboratory Text for Organic Chemistry; Prentice-Hall: Englewood Cliffs, 1979; pp The SADABS program is based on the method of Blessing; see Blessing, R.H. Acta Crystallogr., Sect A 1995, 51, A. Altomare, G. Cascarano, C. Giacovazzo and A. Gualardi (1993) J. Appl. Cryst. 26, SHELXTL NT: Structure Analysis Program, version 5.10; BRUKER-axs: Madison, WI, SQUEEZE: Spek, A. L. Acta Cryst. 1990, A46, C34. / 2 2 [ [ ] ( )] [ [ ] [ ( ) ]] 13 ( o c) G OF = w F F / n p, where n and p denote the number of data and parameters 14 R1 = ( Fo F c ) / Fo ; wr w ( F F ) / w / 2 = o c F o where w = 1 / [ σ ( Fo) + ( a P) + b P] and = [( o) + c] P Max; 0,F 2 F / 3 S-14

15 Table S3. Crystal data and structure refinement for [LFeH]2. Identification code Empirical formula holjs39 C35 H54 Fe N2 Formula weight Temperature Wavelength Crystal system Space group 193(2) K A Monoclinic C2/c deg. Unit cell dimensions a = (2) A alpha = 90 deg. b = (11) A beta = (2) c = (3) A gamma = 90 deg. Volume, Z (12) A^3, 8 Density (calculated) Absorption coefficient Mg/m^ mm^-1 F(000) 2432 Crystal size Theta range for data collection Limiting indices 0.10 x 0.16 x 0.20 mm 1.67 to deg. -17<=h<=26, -13<=k<=13, -28<=l<=28 Reflections collected Independent reflections 5131 [R(int) = ] Reflections >2Sig(I) 4622 Absorption correction Empirical; SADABS Max. and min. transmission and Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 5131 / 0 / 361 S-15

16 Goodness-of-fit on F^ Final R indices [I>2sigma(I)] R1 = , wr2 = R indices (all data) R1 = , wr2 = Largest diff. peak and hole and e.a^-3 Table S4. Atomic coordinates ( x 10^4) and equivalent isotropic displacement parameters (A^2 x 10^3) for [LFeH]2. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. x y z U(eq) Fe(1) 554(1) 9457(1) 2849(1) 30(1) N(1) 1277(2) 8664(4) 2820(2) 32(1) N(2) 1007(2) 10408(5) 3482(2) 35(1) C(11) 2428(3) 8531(7) 3098(4) 58(2) C(21) 1820(3) 9080(6) 3054(3) 39(2) C(31) 1902(3) 10110(6) 3326(3) 43(2) C(41) 1571(3) 10729(6) 3553(3) 39(2) C(51) 1899(3) 11775(7) 3856(3) 47(2) C(61) 2741(5) 9273(9) 2814(6) 121(6) C(71) 2802(4) 8405(11) 3710(5) 115(5) C(81) 2415(4) 7394(7) 2846(4) 63(3) C(91) 2573(4) 11597(8) 4169(4) 75(3) C(101) 1831(4) 12610(7) 3396(4) 59(2) C(111) 1666(4) 12332(8) 4265(4) 70(3) C(12) 1159(3) 7643(6) 2519(3) 42(2) C(22) 1100(3) 6672(6) 2779(4) 47(2) C(32) 992(4) 5709(7) 2471(5) 74(3) C(42) 932(4) 5704(10) 1931(6) 84(4) C(52) 969(4) 6655(9) 1681(4) 68(3) C(62) 1078(3) 7651(7) 1954(4) 51(2) C(72) 1143(3) 6661(7) 3373(4) 60(3) C(82) 521(4) 6486(9) 3394(5) 82(3) C(92) 1574(5) 5794(9) 3719(5) 99(4) C(102) 1088(4) 8694(9) 1649(4) 63(3) C(112) 1558(5) 8679(12) 1371(5) 117(5) C(122) 475(5) 8913(10) 1206(4) 92(4) C(13) 754(3) 10718(6) 3887(3) 36(2) C(23) 289(4) 11448(6) 3779(3) 42(2) C(33) 72(4) 11692(8) 4192(3) 62(3) S-16

17 C(43) 304(5) 11202(9) 4700(4) 72(3) C(53) 735(4) 10439(10) 4802(3) 70(3) C(63) 978(4) 10161(6) 4403(3) 43(2) C(73) 11(4) 12032(8) 3230(3) 55(2) C(83) -651(4) 11797(11) 2970(4) 89(4) C(93) 118(6) 13277(9) 3293(5) 100(4) C(103) 1436(4) 9232(8) 4527(4) 66(3) C(113) 2013(5) 9498(11) 5021(5) 124(5) C(123) 1190(5) 8151(9) 4643(5) 106(4) Table S5. Bond lengths [A] and angles [deg] for [LFeH]2. Fe(1)-N(2) 1.990(5) Fe(1)-N(1) 2.022(6) Fe(1)-Fe(1)# (19) N(1)-C(21) 1.328(9) N(1)-C(12) 1.445(9) N(2)-C(41) 1.361(9) N(2)-C(13) 1.456(9) C(11)-C(81) 1.532(12) C(11)-C(71) 1.531(14) C(11)-C(61) 1.535(14) C(11)-C(21) 1.577(11) C(21)-C(31) 1.422(10) C(31)-C(41) 1.383(10) C(41)-C(51) 1.558(10) C(51)-C(101) 1.539(11) C(51)-C(111) 1.541(11) C(51)-C(91) 1.544(12) C(12)-C(22) 1.400(11) C(12)-C(62) 1.420(11) C(22)-C(32) 1.395(12) C(22)-C(72) 1.521(12) C(32)-C(42) 1.366(15) C(42)-C(52) 1.354(15) C(52)-C(62) 1.385(12) C(62)-C(102) 1.508(13) C(72)-C(92) 1.526(12) C(72)-C(82) 1.536(12) C(102)-C(122) 1.530(12) C(102)-C(112) 1.558(12) C(13)-C(23) 1.378(10) C(13)-C(63) 1.428(10) C(23)-C(33) 1.396(10) C(23)-C(73) 1.520(11) S-17

18 C(33)-C(43) 1.375(12) C(43)-C(53) 1.347(13) C(53)-C(63) 1.413(12) C(63)-C(103) 1.534(12) C(73)-C(83) 1.515(13) C(73)-C(93) 1.542(14) C(103)-C(123) 1.523(14) C(103)-C(113) 1.546(14) N(2)-Fe(1)-N(1) 95.3(2) N(2)-Fe(1)-Fe(1)# (17) N(1)-Fe(1)-Fe(1)# (16) C(21)-N(1)-C(12) 123.0(6) C(21)-N(1)-Fe(1) 121.3(5) C(12)-N(1)-Fe(1) 115.7(4) C(41)-N(2)-C(13) 119.5(6) C(41)-N(2)-Fe(1) 119.8(5) C(13)-N(2)-Fe(1) 120.6(4) C(81)-C(11)-C(71) 105.7(8) C(81)-C(11)-C(61) 105.2(8) C(71)-C(11)-C(61) 111.1(9) C(81)-C(11)-C(21) 118.9(7) C(71)-C(11)-C(21) 107.0(7) C(61)-C(11)-C(21) 108.9(8) N(1)-C(21)-C(31) 120.0(7) N(1)-C(21)-C(11) 127.2(7) C(31)-C(21)-C(11) 112.7(7) C(41)-C(31)-C(21) 134.7(7) N(2)-C(41)-C(31) 119.4(7) N(2)-C(41)-C(51) 126.9(7) C(31)-C(41)-C(51) 113.6(6) C(101)-C(51)-C(111) 106.9(7) C(101)-C(51)-C(91) 107.3(7) C(111)-C(51)-C(91) 106.1(7) C(101)-C(51)-C(41) 104.8(6) C(111)-C(51)-C(41) 117.9(6) C(91)-C(51)-C(41) 113.2(7) C(22)-C(12)-C(62) 120.8(7) C(22)-C(12)-N(1) 120.1(7) C(62)-C(12)-N(1) 119.1(7) C(32)-C(22)-C(12) 117.7(9) C(32)-C(22)-C(72) 120.7(9) C(12)-C(22)-C(72) 121.6(7) C(42)-C(32)-C(22) 121.8(10) C(52)-C(42)-C(32) 119.8(10) C(42)-C(52)-C(62) 122.5(10) C(52)-C(62)-C(12) 117.3(9) C(52)-C(62)-C(102) 120.3(9) S-18

19 C(12)-C(62)-C(102) 122.3(7) C(22)-C(72)-C(92) 112.8(9) C(22)-C(72)-C(82) 109.8(7) C(92)-C(72)-C(82) 110.2(8) C(62)-C(102)-C(122) 110.5(9) C(62)-C(102)-C(112) 113.1(8) C(122)-C(102)-C(112) 108.4(8) C(23)-C(13)-C(63) 119.9(7) C(23)-C(13)-N(2) 123.1(6) C(63)-C(13)-N(2) 116.8(7) C(13)-C(23)-C(33) 119.2(7) C(13)-C(23)-C(73) 122.8(6) C(33)-C(23)-C(73) 118.0(7) C(43)-C(33)-C(23) 121.3(9) C(53)-C(43)-C(33) 120.2(9) C(43)-C(53)-C(63) 121.3(9) C(53)-C(63)-C(13) 117.9(8) C(53)-C(63)-C(103) 119.0(8) C(13)-C(63)-C(103) 123.0(7) C(83)-C(73)-C(23) 111.3(8) C(83)-C(73)-C(93) 110.0(9) C(23)-C(73)-C(93) 111.3(8) C(123)-C(103)-C(63) 112.3(8) C(123)-C(103)-C(113) 108.2(8) C(63)-C(103)-C(113) 112.2(9) Symmetry transformations used to generate equivalent atoms: #1 -x,y,-z+1/2 Table S6. Anisotropic displacement parameters (A^2 x 10^3) for [LFeH]2. The anisotropic displacement factor exponent takes the form: -2 pi^2 [ h^2 a*^2 U h k a* b* U12 ] U11 U22 U33 U23 U13 U12 Fe(1) 27(1) 32(1) 32(1) -4(1) 14(1) -2(1) N(1) 28(3) 31(3) 35(3) -1(3) 11(3) -5(3) N(2) 32(3) 37(3) 31(3) -8(3) 7(3) -5(3) C(11) 28(4) 59(6) 90(7) -19(5) 26(5) -8(4) C(21) 40(5) 39(4) 46(5) 0(4) 24(4) -8(4) C(31) 33(4) 45(5) 52(5) -14(4) 18(4) -14(4) C(41) 39(4) 37(5) 37(4) 3(4) 8(4) -3(4) C(51) 46(5) 51(5) 50(5) -17(4) 23(4) -14(4) S-19

20 C(61) 80(8) 81(8) 256(17) -31(10) 124(10) -21(7) C(71) 52(6) 132(11) 111(9) -63(9) -29(6) 39(7) C(81) 29(4) 69(6) 86(7) -1(5) 14(5) 24(4) C(91) 61(6) 65(7) 84(7) -26(6) 9(5) -18(5) C(101) 71(6) 42(5) 68(6) -14(5) 30(5) -20(5) C(111) 85(7) 64(6) 70(6) -32(5) 38(6) -42(6) C(12) 26(4) 39(5) 57(5) -20(4) 10(4) 5(3) C(22) 24(4) 39(5) 67(6) -6(4) 3(4) -3(4) C(32) 38(5) 35(5) 130(10) -20(6) 7(6) 0(4) C(42) 37(5) 79(9) 120(10) -58(8) 8(6) -1(6) C(52) 46(6) 76(7) 80(7) -36(6) 21(5) 8(5) C(62) 22(4) 62(6) 65(6) -18(5) 10(4) 18(4) C(72) 34(5) 34(5) 96(7) 17(5) 6(5) -5(4) C(82) 58(6) 77(7) 106(9) 14(6) 24(6) 2(6) C(92) 65(7) 75(8) 141(11) 46(7) 20(7) 18(6) C(102) 55(6) 86(7) 53(5) -8(5) 25(5) 22(5) C(112) 91(9) 179(14) 105(9) 32(10) 66(8) 42(9) C(122) 85(8) 131(10) 61(6) -9(7) 28(6) 44(7) C(13) 41(4) 43(5) 25(4) -3(3) 16(3) -11(4) C(23) 53(5) 48(5) 34(4) -6(4) 27(4) -3(4) C(33) 67(6) 86(7) 44(5) -9(5) 32(5) 13(5) C(43) 75(7) 109(9) 40(5) -9(6) 31(5) 2(7) C(53) 75(7) 100(8) 35(5) -5(5) 20(5) -16(7) C(63) 51(5) 41(5) 35(4) 0(4) 14(4) -9(4) C(73) 61(6) 75(7) 34(5) 5(4) 23(4) 26(5) C(83) 67(7) 148(11) 57(6) 19(7) 28(6) 31(7) C(93) 152(12) 65(7) 96(9) 29(6) 61(8) 51(8) C(103) 68(6) 77(7) 45(5) 19(5) 12(5) 14(5) C(113) 75(8) 113(10) 140(11) 54(10) -14(8) -2(8) C(123) 100(9) 77(8) 123(10) 22(8) 20(8) 5(7) Table S7. Hydrogen coordinates ( x 10^4) and isotropic displacement parameters (A^2 x 10^3) for [LFeH]2. x y z U(eq) H(1) 150(30) 9380(60) 2360(30) 70(30) H(31A) H(61A) H(61B) H(61C) H(71A) H(71B) S-20

21 H(71C) H(81A) H(81B) H(81C) H(91A) H(91B) H(91C) H(10A) H(10B) H(10C) H(11A) H(11B) H(11C) H(32A) H(42A) H(52A) H(72A) H(82A) H(82B) H(82C) H(92A) H(92B) H(92C) H(10D) H(11D) H(11E) H(11F) H(12A) H(12B) H(12C) H(33A) H(43A) H(53A) H(73A) H(83A) H(83B) H(83C) H(93A) H(93B) H(93C) H(10E) H(11G) H(11H) H(11I) H(12D) H(12E) H(12F) S-21

22 Table S8. Crystal data and structure refinement for LFe(H)(4-tBupy). Identification code Empirical formula holjs71 C44 H67 Fe N3 Formula weight Temperature Wavelength Crystal system, space group 193(2) K A Monoclinic, P2(1)/c deg. Unit cell dimensions a = (7) A alpha = 90 deg. b = (11) A beta = (1) c = (11) A gamma = 90 deg. Volume (4) A^3 Z, Calculated density 4, Mg/m^3 Absorption coefficient mm^-1 F(000) 1512 Crystal size Theta range for data collection Limiting indices 0.53 x 0.30 x 0.21 mm 1.56 to deg. -16<=h<=16, -23<=k<=18, -26<=l<=21 Reflections collected / unique / [R(int) = ] Completeness to theta = % Absorption correction Empirical Max. and min. transmission and Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters / 0 / 454 Goodness-of-fit on F^ S-22

23 Final R indices [I>2sigma(I)] R1 = , wr2 = R indices (all data) R1 = , wr2 = Largest diff. peak and hole and e.a^-3 Table S9. Atomic coordinates ( x 10^4) and equivalent isotropic displacement parameters (A^2 x 10^3) for LFe(H)(4-tBupy). U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. x y z U(eq) Fe(1) 2777(1) 2581(1) 1603(1) 32(1) N(21) 1108(1) 2545(1) 1052(1) 34(1) N(13) 3215(1) 1474(1) 1477(1) 37(1) N(11) 3295(1) 3065(1) 834(1) 32(1) C(51) 741(2) 2655(1) 348(1) 34(1) C(61) -510(2) 2660(1) -141(1) 43(1) C(41) 1516(2) 2785(1) -40(1) 35(1) C(31) 2644(2) 2999(1) 146(1) 33(1) C(22) 5366(2) 3214(1) 1366(1) 41(1) C(14) 2978(2) 1171(1) 824(1) 39(1) C(23) 125(2) 1668(1) 1622(1) 47(1) C(12) 4289(2) 3523(1) 1059(1) 35(1) C(21) 3071(2) 3096(1) -522(1) 40(1) C(13) 430(2) 2395(1) 1515(1) 40(1) C(103) 527(2) 3761(1) 1846(1) 52(1) C(64) 4543(2) -661(1) 1173(1) 56(1) C(24) 3364(2) 493(1) 700(1) 42(1) C(62) 4174(2) 4294(1) 1012(1) 42(1) C(63) 182(2) 2977(1) 1914(1) 47(1) C(44) 4260(2) 391(1) 1942(1) 43(1) C(54) 3843(2) 1069(1) 2028(1) 41(1) C(34) 4039(2) 80(1) 1268(1) 41(1) C(102) 3027(2) 4663(1) 750(1) 49(1) C(111) -685(2) 2016(2) -675(1) 57(1) C(72) 5575(2) 2395(1) 1461(1) 47(1) C(101) -725(2) 3391(2) -557(1) 56(1) C(71) -1426(2) 2600(2) 227(1) 53(1) C(32) 6300(2) 3679(1) 1586(1) 52(1) C(33) -460(2) 1547(2) 2117(1) 60(1) C(82) 5985(2) 2194(1) 2254(1) 56(1) S-23

24 C(42) 6196(2) 4426(1) 1516(1) 55(1) C(73) 390(2) 1004(1) 1236(1) 56(1) C(43) -732(2) 2115(2) 2494(1) 66(1) C(53) -413(2) 2813(2) 2397(1) 61(1) C(81) 2336(2) 3636(2) -1066(1) 68(1) C(11) 4291(2) 3355(2) -380(1) 67(1) C(123) 1275(2) 4065(2) 2566(1) 64(1) C(52) 5145(2) 4727(1) 1237(1) 52(1) C(91) 3000(3) 2337(2) -862(2) 71(1) C(92) 6428(2) 2119(2) 1098(2) 66(1) C(122) 3015(3) 5323(2) 258(1) 72(1) C(93) 1161(2) 465(2) 1765(2) 79(1) C(83) -676(2) 591(2) 787(2) 76(1) C(112) 2667(2) 4907(2) 1385(1) 70(1) C(113) -483(3) 4279(2) 1553(2) 85(1) C(84) 4187(3) -920(2) 405(2) 100(1) C(94) 5834(3) -562(2) 1391(2) 100(1) C(74) 4255(5) -1225(2) 1640(3) 146(2) Table S10. Bond lengths [A] and angles [deg] for LFe(H)(4-tBupy). Fe(1)-N(11) (14) Fe(1)-N(21) (16) Fe(1)-N(13) (16) Fe(1)-H(1) 1.740(18) N(21)-C(51) 1.332(2) N(21)-C(13) 1.446(2) N(13)-C(14) 1.343(2) N(13)-C(54) 1.345(2) N(11)-C(31) 1.349(2) N(11)-C(12) 1.447(2) C(51)-C(41) 1.425(3) C(51)-C(61) 1.560(3) C(61)-C(71) 1.536(3) C(61)-C(101) 1.542(3) C(61)-C(111) 1.544(3) C(41)-C(31) 1.398(3) C(31)-C(21) 1.573(2) C(22)-C(32) 1.398(3) C(22)-C(12) 1.411(3) C(22)-C(72) 1.517(3) C(14)-C(24) 1.375(3) C(23)-C(33) 1.402(3) C(23)-C(13) 1.411(3) C(23)-C(73) 1.518(3) S-24

25 C(12)-C(62) 1.412(3) C(21)-C(91) 1.525(3) C(21)-C(81) 1.532(3) C(21)-C(11) 1.536(3) C(13)-C(63) 1.411(3) C(103)-C(63) 1.510(4) C(103)-C(123) 1.537(3) C(103)-C(113) 1.537(3) C(64)-C(74) 1.493(4) C(64)-C(84) 1.512(4) C(64)-C(34) 1.524(3) C(64)-C(94) 1.546(4) C(24)-C(34) 1.394(3) C(62)-C(52) 1.399(3) C(62)-C(102) 1.521(3) C(63)-C(53) 1.406(3) C(44)-C(54) 1.371(3) C(44)-C(34) 1.388(3) C(102)-C(112) 1.519(3) C(102)-C(122) 1.539(3) C(72)-C(82) 1.528(3) C(72)-C(92) 1.538(3) C(32)-C(42) 1.369(3) C(33)-C(43) 1.375(4) C(42)-C(52) 1.371(3) C(73)-C(93) 1.535(3) C(73)-C(83) 1.547(3) C(43)-C(53) 1.363(4) N(11)-Fe(1)-N(21) 97.36(6) N(11)-Fe(1)-N(13) (6) N(21)-Fe(1)-N(13) 99.53(6) N(11)-Fe(1)-H(1) 126.1(6) N(21)-Fe(1)-H(1) 124.9(6) N(13)-Fe(1)-H(1) 103.5(6) C(51)-N(21)-C(13) (16) C(51)-N(21)-Fe(1) (12) C(13)-N(21)-Fe(1) (11) C(14)-N(13)-C(54) (17) C(14)-N(13)-Fe(1) (12) C(54)-N(13)-Fe(1) (14) C(31)-N(11)-C(12) (15) C(31)-N(11)-Fe(1) (12) C(12)-N(11)-Fe(1) (11) N(21)-C(51)-C(41) (17) N(21)-C(51)-C(61) (16) C(41)-C(51)-C(61) (16) C(71)-C(61)-C(101) (18) S-25

26 C(71)-C(61)-C(111) (19) C(101)-C(61)-C(111) (18) C(71)-C(61)-C(51) (16) C(101)-C(61)-C(51) (18) C(111)-C(61)-C(51) (17) C(31)-C(41)-C(51) (17) N(11)-C(31)-C(41) (16) N(11)-C(31)-C(21) (16) C(41)-C(31)-C(21) (16) C(32)-C(22)-C(12) 119.0(2) C(32)-C(22)-C(72) (18) C(12)-C(22)-C(72) (18) N(13)-C(14)-C(24) (18) C(33)-C(23)-C(13) 118.3(2) C(33)-C(23)-C(73) 117.5(2) C(13)-C(23)-C(73) (18) C(22)-C(12)-C(62) (18) C(22)-C(12)-N(11) (17) C(62)-C(12)-N(11) (17) C(91)-C(21)-C(81) 109.7(2) C(91)-C(21)-C(11) 106.2(2) C(81)-C(21)-C(11) 106.1(2) C(91)-C(21)-C(31) (17) C(81)-C(21)-C(31) (16) C(11)-C(21)-C(31) (17) C(63)-C(13)-C(23) (18) C(63)-C(13)-N(21) (19) C(23)-C(13)-N(21) (18) C(63)-C(103)-C(123) 111.6(2) C(63)-C(103)-C(113) 112.9(2) C(123)-C(103)-C(113) 108.6(2) C(74)-C(64)-C(84) 110.3(3) C(74)-C(64)-C(34) 110.4(2) C(84)-C(64)-C(34) 113.1(2) C(74)-C(64)-C(94) 109.8(3) C(84)-C(64)-C(94) 105.8(3) C(34)-C(64)-C(94) 107.3(2) C(14)-C(24)-C(34) (19) C(52)-C(62)-C(12) (19) C(52)-C(62)-C(102) (19) C(12)-C(62)-C(102) (19) C(53)-C(63)-C(13) 117.9(2) C(53)-C(63)-C(103) 119.1(2) C(13)-C(63)-C(103) (18) C(54)-C(44)-C(34) (18) N(13)-C(54)-C(44) (19) C(44)-C(34)-C(24) (19) C(44)-C(34)-C(64) (18) S-26

27 C(24)-C(34)-C(64) (19) C(112)-C(102)-C(62) (18) C(112)-C(102)-C(122) 109.9(2) C(62)-C(102)-C(122) 112.6(2) C(22)-C(72)-C(82) (19) C(22)-C(72)-C(92) 112.4(2) C(82)-C(72)-C(92) (19) C(42)-C(32)-C(22) 121.8(2) C(43)-C(33)-C(23) 121.5(3) C(32)-C(42)-C(52) 119.2(2) C(23)-C(73)-C(93) 111.1(2) C(23)-C(73)-C(83) 113.0(2) C(93)-C(73)-C(83) 108.8(2) C(53)-C(43)-C(33) 119.8(2) C(43)-C(53)-C(63) 122.0(2) C(42)-C(52)-C(62) 121.9(2) Table S11. Anisotropic displacement parameters (A^2 x 10^3) for LFe(H)(4- tbupy). The anisotropic displacement factor exponent takes the form: -2 pi^2 [ h^2 a*^2 U h k a* b* U12 ] U11 U22 U33 U23 U13 U12 Fe(1) 31(1) 41(1) 26(1) 5(1) 11(1) 8(1) N(21) 30(1) 48(1) 27(1) 5(1) 13(1) 7(1) N(13) 36(1) 42(1) 35(1) 8(1) 12(1) 6(1) N(11) 31(1) 38(1) 29(1) 5(1) 12(1) 8(1) C(51) 30(1) 44(1) 29(1) 2(1) 10(1) 8(1) C(61) 31(1) 67(1) 30(1) 4(1) 8(1) 8(1) C(41) 36(1) 47(1) 24(1) 4(1) 11(1) 10(1) C(31) 36(1) 35(1) 30(1) 6(1) 15(1) 10(1) C(22) 35(1) 50(1) 41(1) 2(1) 15(1) 1(1) C(14) 37(1) 44(1) 36(1) 10(1) 10(1) 6(1) C(23) 31(1) 74(2) 36(1) 14(1) 11(1) 0(1) C(12) 39(1) 40(1) 30(1) 4(1) 14(1) 2(1) C(21) 41(1) 52(1) 31(1) 6(1) 18(1) 6(1) C(13) 27(1) 69(1) 25(1) 8(1) 9(1) 8(1) C(103) 49(1) 74(2) 36(1) -6(1) 17(1) 19(1) C(64) 63(2) 39(1) 58(1) 1(1) 6(1) 14(1) C(24) 42(1) 43(1) 38(1) 2(1) 8(1) 2(1) C(62) 50(1) 44(1) 33(1) 6(1) 15(1) 3(1) C(63) 29(1) 83(2) 26(1) 3(1) 8(1) 13(1) C(44) 44(1) 42(1) 40(1) 12(1) 7(1) 6(1) S-27

28 C(54) 41(1) 46(1) 35(1) 8(1) 11(1) 5(1) C(34) 37(1) 37(1) 47(1) 6(1) 11(1) 2(1) C(102) 58(1) 41(1) 45(1) 6(1) 13(1) 10(1) C(111) 43(1) 83(2) 42(1) -8(1) 11(1) -5(1) C(72) 31(1) 50(1) 59(1) -1(1) 12(1) 6(1) C(101) 40(1) 80(2) 45(1) 16(1) 10(1) 23(1) C(71) 27(1) 93(2) 38(1) 3(1) 8(1) 8(1) C(32) 38(1) 62(1) 55(1) 4(1) 15(1) -3(1) C(33) 38(1) 102(2) 42(1) 22(1) 14(1) -4(1) C(82) 45(1) 55(1) 65(2) 9(1) 14(1) 7(1) C(42) 50(1) 61(2) 58(1) 4(1) 19(1) -14(1) C(73) 47(1) 65(2) 63(2) 17(1) 25(1) -4(1) C(43) 37(1) 130(3) 35(1) 12(1) 17(1) -2(1) C(53) 37(1) 117(2) 30(1) -3(1) 14(1) 13(1) C(81) 73(2) 92(2) 47(1) 30(1) 32(1) 23(2) C(11) 53(1) 113(2) 44(1) 3(1) 30(1) -8(1) C(123) 50(1) 87(2) 52(1) -9(1) 12(1) 10(1) C(52) 70(2) 42(1) 47(1) 6(1) 23(1) -6(1) C(91) 106(2) 65(2) 69(2) -12(1) 66(2) -1(2) C(92) 46(1) 79(2) 73(2) -11(1) 18(1) 17(1) C(122) 94(2) 66(2) 63(2) 26(1) 34(2) 34(2) C(93) 65(2) 73(2) 107(2) 41(2) 38(2) 7(1) C(83) 72(2) 79(2) 81(2) 2(2) 28(2) -18(2) C(112) 71(2) 84(2) 64(2) 20(1) 33(1) 24(2) C(113) 76(2) 95(2) 65(2) -11(2) -7(2) 35(2) C(84) 116(3) 73(2) 91(2) -24(2) 4(2) 37(2) C(94) 72(2) 95(2) 116(3) -34(2) 6(2) 32(2) C(74) 253(6) 49(2) 173(4) 30(2) 120(4) 36(3) Table S12. Hydrogen coordinates ( x 10^4) and isotropic displacement parameters (A^2 x 10^3) for LFe(H)(4-tBupy). x y z U(eq) H(41) H(14) H(103) H(24) H(44) H(54) H(102) H(11A) H(11B) S-28

29 H(11C) H(72) H(10A) H(10B) H(10C) H(71A) H(71B) H(71C) H(32) H(33) H(82A) H(82B) H(82C) H(42) H(73) H(43) H(53) H(81A) H(81B) H(81C) H(11D) H(11E) H(11F) H(12A) H(12B) H(12C) H(52) H(91A) H(91B) H(91C) H(92A) H(92B) H(92C) H(12D) H(12E) H(12F) H(93A) H(93B) H(93C) H(83A) H(83B) H(83C) H(11G) H(11H) H(11I) H(11J) H(11K) H(11L) S-29

30 H(84A) H(84B) H(84C) H(94A) H(94B) H(94C) H(74A) H(74B) H(74C) H(1) 3333(15) 2729(10) 2520(10) 29(5) S-30

31 Table S13. Crystal data and structure refinement for LFeC(Et)CHEt. Identification code holjs58 Empirical formula C41 H64 Fe N2 Formula weight Temperature 193(2) K Wavelength Å Crystal system Triclinic Space group P-1 Unit cell dimensions a = (7) Å a= (10). b = (9) Å b= (10). c = (12) Å g = (10). Volume (2) Å 3 Z 2 Density (calculated) Mg/m 3 Absorption coefficient mm -1 F(000) 700 Crystal size 0.16 x 0.18 x 0.18 mm 3 Theta range for data collection 1.78 to Index ranges -12<=h<=12, -16<=k<=16, -18<=l<=22 Reflections collected Independent reflections 8407 [R(int) = ] Completeness to theta = % Absorption correction Empirical Max. and min. transmission and Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 8407 / 0 / 413 Goodness-of-fit on F Final R indices [I>2sigma(I)] R1 = , wr2 = R indices (all data) R1 = , wr2 = Largest diff. peak and hole and e.å -3 S-31

32 Table S14. Atomic coordinates ( x 10 4 ) and equivalent isotropic displacement parameters (Å 2 x 10 3 ) for LFeC(Et)CHEt. U(eq) is defined as one third of the trace of the orthogonalized U ij tensor. x y z U(eq) Fe(1) 7386(1) 2304(1) 2681(1) 29(1) N(11) 8366(3) 1213(2) 2825(1) 26(1) N(21) 8293(3) 2819(2) 1725(1) 28(1) C(11) 9841(3) 23(3) 2409(2) 33(1) C(21) 9212(3) 972(2) 2342(2) 27(1) C(31) 9562(4) 1552(3) 1681(2) 34(1) C(41) 9202(4) 2415(3) 1386(2) 32(1) C(51) 9978(5) 2885(4) 672(2) 51(1) C(61) 8956(5) -973(3) 1695(2) 59(1) C(71) 11484(5) 508(4) 2357(4) 74(2) C(81) 9697(4) -532(3) 3175(2) 42(1) C(91) 11527(8) 3290(15) 891(8) 311(11) C(101) 9599(18) 1841(9) 11(5) 263(9) C(111) 9451(10) 3597(11) 218(5) 212(6) C(12) 8049(3) 805(2) 3569(2) 27(1) C(22) 6698(3) -129(3) 3581(2) 30(1) C(32) 6330(4) -372(3) 4331(2) 40(1) C(42) 7245(4) 271(3) 5043(2) 43(1) C(52) 8600(4) 1174(3) 5022(2) 40(1) C(62) 9037(3) 1457(3) 4297(2) 31(1) C(72) 5675(3) -862(3) 2804(2) 36(1) C(82) 5309(4) -2172(3) 2771(3) 52(1) C(92) 4238(4) -679(3) 2682(2) 45(1) C(102) 10541(4) 2410(3) 4281(2) 38(1) C(112) 11756(4) 2502(4) 4970(2) 51(1) C(122) 10465(5) 3596(3) 4272(3) 58(1) C(13) 7727(4) 3626(3) 1450(2) 32(1) C(23) 6404(4) 3196(3) 871(2) 40(1) C(33) 5771(5) 3967(4) 688(2) 53(1) C(43) 6394(5) 5124(4) 1069(3) 58(1) C(53) 7675(5) 5523(3) 1627(2) 50(1) S-32

33 C(63) 8368(4) 4800(3) 1837(2) 37(1) C(73) 5636(4) 1919(3) 478(2) 50(1) C(83) 4363(6) 1270(4) 898(3) 80(2) C(93) 5092(7) 1756(5) -438(3) 89(2) C(103) 9740(4) 5287(3) 2494(2) 45(1) C(113) 9367(5) 5650(4) 3308(2) 62(1) C(123) 10999(5) 6343(4) 2292(3) 77(1) C(14) 6460(6) 3333(4) 4782(3) 70(1) C(24) 5583(4) 2358(3) 4076(2) 43(1) C(34) 5918(4) 2700(3) 3253(2) 36(1) C(44) 5230(4) 3294(3) 2894(3) 51(1) C(54) 4088(5) 3703(4) 3171(3) 69(1) C(64) 4500(8) 4956(5) 3183(4) 104(2) S-33

34 Table S15. Bond lengths [Å] and angles [ ] for LFeC(Et)CHEt. Fe(1)-N(11) 1.988(2) Fe(1)-N(21) 1.990(2) Fe(1)-C(34) 2.021(3) N(11)-C(21) 1.328(4) N(11)-C(12) 1.434(3) N(21)-C(41) 1.346(4) N(21)-C(13) 1.433(4) C(11)-C(71) 1.519(5) C(11)-C(81) 1.533(4) C(11)-C(61) 1.536(5) C(11)-C(21) 1.557(4) C(21)-C(31) 1.409(4) C(31)-C(41) 1.393(4) C(41)-C(51) 1.557(4) C(51)-C(91) 1.404(8) C(51)-C(111) 1.447(7) C(51)-C(101) 1.519(10) C(12)-C(22) 1.404(4) C(12)-C(62) 1.418(4) C(22)-C(32) 1.394(4) C(22)-C(72) 1.513(4) C(32)-C(42) 1.370(5) C(42)-C(52) 1.392(5) C(52)-C(62) 1.385(4) C(62)-C(102) 1.516(4) C(72)-C(92) 1.523(4) C(72)-C(82) 1.540(5) C(102)-C(122) 1.529(5) C(102)-C(112) 1.532(5) C(13)-C(63) 1.407(5) C(13)-C(23) 1.413(5) C(23)-C(33) 1.389(5) C(23)-C(73) 1.517(5) C(33)-C(43) 1.386(6) S-34

35 C(43)-C(53) 1.367(6) C(53)-C(63) 1.390(5) C(63)-C(103) 1.517(5) C(73)-C(83) 1.519(6) C(73)-C(93) 1.540(6) C(103)-C(113) 1.531(6) C(103)-C(123) 1.537(5) C(14)-C(24) 1.512(6) C(24)-C(34) 1.538(5) C(34)-C(44) 1.339(5) C(44)-C(54) 1.513(5) C(54)-C(64) 1.468(7) N(11)-Fe(1)-N(21) 94.18(10) N(11)-Fe(1)-C(34) (11) N(21)-Fe(1)-C(34) (11) C(21)-N(11)-C(12) 127.5(2) C(21)-N(11)-Fe(1) (19) C(12)-N(11)-Fe(1) (17) C(41)-N(21)-C(13) 127.4(2) C(41)-N(21)-Fe(1) (19) C(13)-N(21)-Fe(1) (18) C(71)-C(11)-C(81) 106.1(3) C(71)-C(11)-C(61) 110.0(3) C(81)-C(11)-C(61) 106.3(3) C(71)-C(11)-C(21) 110.9(3) C(81)-C(11)-C(21) 117.1(2) C(61)-C(11)-C(21) 106.3(3) N(11)-C(21)-C(31) 120.7(3) N(11)-C(21)-C(11) 125.5(2) C(31)-C(21)-C(11) 113.8(2) C(41)-C(31)-C(21) 132.9(3) N(21)-C(41)-C(31) 121.2(3) N(21)-C(41)-C(51) 124.1(3) C(31)-C(41)-C(51) 114.6(3) C(91)-C(51)-C(111) 116.0(7) S-35

36 C(91)-C(51)-C(101) 102.7(9) C(111)-C(51)-C(101) 99.7(7) C(91)-C(51)-C(41) 110.4(4) C(111)-C(51)-C(41) 118.5(4) C(101)-C(51)-C(41) 107.2(4) C(22)-C(12)-C(62) 121.1(3) C(22)-C(12)-N(11) 120.0(3) C(62)-C(12)-N(11) 118.3(3) C(32)-C(22)-C(12) 118.0(3) C(32)-C(22)-C(72) 120.7(3) C(12)-C(22)-C(72) 121.3(3) C(42)-C(32)-C(22) 121.9(3) C(32)-C(42)-C(52) 119.5(3) C(62)-C(52)-C(42) 121.5(3) C(52)-C(62)-C(12) 117.9(3) C(52)-C(62)-C(102) 121.1(3) C(12)-C(62)-C(102) 121.0(3) C(22)-C(72)-C(92) 111.6(3) C(22)-C(72)-C(82) 112.1(3) C(92)-C(72)-C(82) 109.6(3) C(62)-C(102)-C(122) 111.9(3) C(62)-C(102)-C(112) 113.3(3) C(122)-C(102)-C(112) 110.3(3) C(63)-C(13)-C(23) 120.6(3) C(63)-C(13)-N(21) 119.7(3) C(23)-C(13)-N(21) 119.1(3) C(33)-C(23)-C(13) 118.3(3) C(33)-C(23)-C(73) 119.8(3) C(13)-C(23)-C(73) 121.9(3) C(43)-C(33)-C(23) 121.4(4) C(53)-C(43)-C(33) 119.4(3) C(43)-C(53)-C(63) 122.1(4) C(53)-C(63)-C(13) 118.2(3) C(53)-C(63)-C(103) 119.2(3) C(13)-C(63)-C(103) 122.6(3) C(23)-C(73)-C(83) 110.7(3) S-36

37 C(23)-C(73)-C(93) 112.5(4) C(83)-C(73)-C(93) 110.8(4) C(63)-C(103)-C(113) 110.8(3) C(63)-C(103)-C(123) 112.4(3) C(113)-C(103)-C(123) 108.8(4) C(14)-C(24)-C(34) 113.1(3) C(44)-C(34)-C(24) 119.5(3) C(44)-C(34)-Fe(1) 117.8(3) C(24)-C(34)-Fe(1) 122.7(2) C(34)-C(44)-C(54) 129.6(4) C(64)-C(54)-C(44) 113.0(4) S-37

38 Table S16. Anisotropic displacement parameters (Å 2 x 10 3 )for LFeC(Et)CHEt. The anisotropic displacement factor exponent takes the form: -2p 2 [ h 2 a* 2 U h k a* b* U 12 ] U 11 U 22 U 33 U 23 U 13 U 12 Fe(1) 34(1) 31(1) 30(1) 10(1) 11(1) 19(1) N(11) 29(1) 27(1) 25(1) 7(1) 5(1) 14(1) N(21) 35(1) 29(1) 24(1) 7(1) 5(1) 17(1) C(11) 38(2) 38(2) 37(2) 12(1) 11(1) 25(1) C(21) 29(1) 28(1) 25(1) 4(1) 3(1) 14(1) C(31) 43(2) 40(2) 31(2) 11(1) 14(1) 26(2) C(41) 42(2) 36(2) 24(1) 10(1) 10(1) 19(1) C(51) 75(3) 70(2) 39(2) 30(2) 33(2) 50(2) C(61) 98(3) 51(2) 41(2) 2(2) 4(2) 48(2) C(71) 49(2) 82(3) 127(4) 60(3) 41(3) 48(2) C(81) 58(2) 46(2) 41(2) 16(2) 10(2) 37(2) C(91) 75(5) 630(30) 284(14) 378(18) 101(7) 108(10) C(101) 620(30) 170(9) 140(8) 97(7) 258(13) 241(14) C(111) 200(9) 448(18) 179(8) 262(11) 159(7) 243(11) C(12) 32(1) 29(1) 26(1) 9(1) 8(1) 17(1) C(22) 32(2) 29(2) 36(2) 9(1) 10(1) 16(1) C(32) 38(2) 40(2) 49(2) 23(2) 19(2) 18(2) C(42) 53(2) 53(2) 33(2) 20(2) 19(2) 27(2) C(52) 53(2) 46(2) 26(2) 10(1) 7(1) 24(2) C(62) 35(2) 34(2) 29(2) 8(1) 6(1) 18(1) C(72) 32(2) 31(2) 46(2) 9(1) 10(1) 11(1) C(82) 48(2) 35(2) 72(3) 6(2) 5(2) 16(2) C(92) 34(2) 42(2) 56(2) 6(2) 1(2) 14(2) C(102) 40(2) 41(2) 28(2) 2(1) 3(1) 11(1) C(112) 41(2) 67(3) 42(2) 2(2) 1(2) 22(2) C(122) 57(2) 39(2) 64(3) 11(2) -4(2) 8(2) C(13) 41(2) 37(2) 29(2) 13(1) 11(1) 23(1) C(23) 46(2) 49(2) 32(2) 12(1) 5(1) 25(2) C(33) 55(2) 69(3) 48(2) 23(2) 5(2) 39(2) C(43) 74(3) 63(3) 64(3) 33(2) 17(2) 50(2) C(53) 69(3) 36(2) 56(2) 18(2) 18(2) 30(2) S-38

39 C(63) 45(2) 34(2) 39(2) 14(1) 14(1) 19(1) C(73) 55(2) 53(2) 41(2) -1(2) -5(2) 27(2) C(83) 74(3) 54(3) 94(4) 3(3) 14(3) 11(2) C(93) 110(4) 98(4) 47(3) -18(3) -28(3) 51(4) C(103) 49(2) 32(2) 50(2) 10(2) 6(2) 13(2) C(113) 83(3) 47(2) 48(2) -2(2) 4(2) 24(2) C(123) 59(3) 64(3) 90(4) 26(3) 12(3) 3(2) C(14) 83(3) 74(3) 47(2) 5(2) 20(2) 25(3) C(24) 50(2) 40(2) 48(2) 13(2) 22(2) 24(2) C(34) 40(2) 32(2) 43(2) 10(1) 16(1) 18(1) C(44) 57(2) 53(2) 63(2) 27(2) 32(2) 35(2) C(54) 75(3) 71(3) 100(4) 42(3) 47(3) 54(3) C(64) 141(6) 81(4) 145(6) 45(4) 79(5) 82(4) S-39

40 Table S17. Hydrogen coordinates ( x 10 4 ) and isotropic displacement parameters (Å 2 x 10 3 ) for LFeC(Et)CHEt. x y z U(eq) H(31A) H(61A) H(61B) H(61C) H(71A) H(71B) H(71C) H(81A) H(81B) H(81C) H(91A) H(91B) H(91C) H(10A) H(10B) H(10C) H(11A) H(11B) H(11C) H(32A) H(42A) H(52A) H(72A) H(82A) H(82B) H(82C) H(92A) H(92B) H(92C) H(10D) S-40

41 H(11D) H(11E) H(11F) H(12A) H(12B) H(12C) H(33A) H(43A) H(53A) H(73A) H(83A) H(83B) H(83C) H(93A) H(93B) H(93C) H(10E) H(11G) H(11H) H(11I) H(12D) H(12E) H(12F) H(14A) H(14B) H(14C) H(24A) H(24B) H(44A) H(54A) H(54B) H(64A) H(64B) H(64C) S-41

42 Table S18. Crystal data and structure refinement for LFeN(Ph)NHPh. Identification code holjs77 Empirical formula C47 H64 Fe N4 Formula weight Temperature 193(2) K Wavelength Å Crystal system Orthorhombic Space group Pbca Unit cell dimensions a = (6) Å a= 90. b = (13) Å b= 90. c = (3) Å g = 90. Volume (10) Å 3 Z 8 Absorption coefficient mm -1 F(000) 3200 Crystal size 0.20 x 0.22 x 0.30 mm 3 Theta range for data collection 1.71 to Index ranges -11<=h<=12, -25<=k<=31, -59<=l<=59 Reflections collected Independent reflections [R(int) = ] Completeness to theta = % Absorption correction Empirical Max. and min. transmission and Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters / 0 / 503 Goodness-of-fit on F Final R indices [I>2sigma(I)] R1 = , wr2 = R indices (all data) R1 = , wr2 = Largest diff. peak and hole and e.å -3 S-42