Correlation between the Structure and Catalytic. Activity of [Cp*Rh(Substituted Bipyridine)] Complexes for NADH Regeneration

Supporting Information Correlation between the Structure and Catalytic Activity of [Cp*Rh(Substituted Bipyridine)] Complexes for NADH Regeneration Vinothkumar Ganesan, Dharmalingam Sivanesan and Sungho Yoon* Department of Bio & Nano Chemistry, College of Natural Sciences, Kookmin University, 861-1 Jeoungnung-dong, Seongbuk-gu, Seoul 136-702, Republic of Korea. S1

Contents 1. Synthesis of complex 2 S3-S4 2. Synthesis of complex 3 S4-S5 3. Synthesis of complex 4 S6-S7 4. Synthesis of complex 5 S7-S8 5. Reaction scheme and Kinetic studies of Rh-(H) and Rh-(Cp*-H) species generation S17 List of Figures Figure S1. UV-Visible absorption spectrum of 2-5 S11 Figure S2. Figure S3. Figure S4. Figure S5. 1 H NMR spectrum of 2 ([η 5 -Cp*Rh((3,3 -CH 2 OH-bpy))Cl]Cl) in CD 3 OD S13 1 H NMR spectrum of 3 ([η 5 -Cp*Rh((4,4 -CH 2 OH-bpy))Cl]Cl) in CD 3 OD S13 1 H NMR spectrum of 4 ([η 5 -Cp*Rh((5,5 -CH 2 OH-bpy))Cl]Cl) in CD 3 OD S14 1 H NMR spectrum of 5 ([η 5 -Cp*Rh((6,6 -CH 2 OH-bpy))Cl]Cl) in CD 3 OD S14 Figure S6. Cyclic Voltammogram of 2 and 5 S15 Figure S7. Cyclic Voltammogram of 3 and 4 S16 Figure S8. Kinetic traces of UV-Visible absorption spectra of 1 with HCO 2 Na S18 Figure S9. Kinetic traces of UV-Visible absorption spectra of 2 with HCO 2 Na S19 Figure S10. Kinetic traces of UV-Visible absorption spectra of 3 with HCO 2 Na S20 Figure S11. Kinetic traces of UV-Visible absorption spectra of 4 with HCO 2 Na S21 Figure S12. Kinetic traces of UV-Visible absorption spectra of 5 with HCO 2 Na S22 Figure S13. Space filling model of complex 2 (Figure 14A) and 5 (Figure 14B) S23 Figure S14. Figure S15. Figure S16. Figure S17. 1 H NMR spectrum of complex 2 in HCO 2 Na/D 2 O solution S24 1 H NMR spectrum of complex 3 in HCO 2 Na/D 2 O solution S25 1 H NMR spectrum of complex 4 in HCO 2 Na/D 2 O solution S26 1 H NMR spectrum of Rh-hydride species of 5 in HCO 2 Na/D 2 O solution S27 List of Tables Table S1. Summary of selected bond distances, bond angles and dihedral angle of 1-3, 5 S9 Table S2 Summary of X-ray Crystallographic information of 2 and 5 S10 Table S3. Summary of UV-Visible peaks and molar extinction coefficients. S12 Table S4. Summary of 1 H NMR spectra. S15 S2

Synthetic procedure of 2 Reagents: a). KMnO 4, Reflux, b). MeOH, Reflux, c). NaBH 4, EtOH, d). (Cp*Rh(μ-Cl)Cl) 2, MeOH, rt. Synthesis of [2,2'-bipyridine]-3,3'-dicarboxylic acid To a mixture of phenanthroline (1.20 g, 6.65 mmol) and NaOH (0.532 g, 13.3 mmol), H 2 O (52.5 ml) was added and stirred at room temperature. Then KMnO 4 (3.157 g, 19.9 mmol) was added pinch by pinch for 30 minutes and heated to 105 o C for 6 hours. The reaction mixture volume was reduced to half of its original volume and it was acidified with conc. HCl. Resulting light yellow solution was concentrated under reduced pressure and used as such in the next step without further purifications. Yield = 1.50 g (crude). Synthesis of dimethyl [2,2'-bipyridine]-3,3'-dicarboxylate To a mixture of [2,2'-bipyridine]-3,3'-dicarboxylic acid (0.560 g) in MeOH, conc. H 2 SO 4 (4 ml) was added drop by drop and refluxed at 80 o C for 24 hours. After that, ethanol was evaporated under reduced and diluted with saturated NaHCO 3, and this mixture was extracted with CH 2 Cl 2 (100 ml). The CH 2 Cl 2 layer was dried over Na 2 SO 4 and concentrated under reduced pressure. If afforded off white solid which was dried under high vacuum. Yield = 0.555 g (89%). 1 H NMR (500 MHz, cdcl 3 ) δ 8.78 (dd, J = 4.8, 1.7 Hz, 2H), 8.37 (dd, J = 7.9, 1.7 Hz, 2H), 7.45 (dd, J = 7.9, 4.8 Hz, 2H), 3.69 (s, 6H). Synthesis of [2,2'-bipyridine]-3,3'-diyldimethanol S3

To a solution of dimethyl [2,2'-bipyridine]-3,3'-dicarboxylate (0.350 g, 1.28 mmol) in EtOH, NaBH 4 (0.291 g, 7.71 mmol) was added and heated to 75 80 o C for 12 hours. After removing the EtOH, NaBH 4 was quenched with saturated NH 4 Cl and extracted with ethyl acetate(125 ml). The organic layer was dried over Na 2 SO 4 and concentrated on a rotavapor and it gave white solid. Yield = 0.201 g (72%). 1 H NMR (500 MHz, Acetone-D 6 ) δ 8.47 8.45 (m, 2H), 7.95 7.93 (m, 2H), 7.38 (ddd, J = 7.7, 4.8, 1.4 Hz, 2H), 4.34 (s, 4H). Synthesis of [η 5 -Cp*Rh((3,3 -CH 2 OH-bpy))Cl]Cl To a methanol(2ml) solution of [2,2'-bipyridine]-3,3'-diyldimethanol (0.027 g, 0.129 mmol), {η 5 -Cp*Rh(μ-Cl)Cl} 2 (0.040 g, 0.064 mmol) was added under N 2 atmosphere. The color of the reaction mixture slowly turned to orange yellow from reddish brown. After 3h stirring at room temperature, the volume was reduced; upon addition of diethyl ether(15 ml) precipitate was formed. Yield = 0.057 g. 1 H NMR (500 MHz, CD 3 OD) δ 8.97 (d, J = 4.8 Hz, 2H), 8.42 (dd, J = 8.0, 1.4 Hz, 2H), 7.90 (dt, J = 11.6, 5.8 Hz, 2H), 4.62 (s, 4H), 1.67 (s, 15H). Synthetic procedure of 3 Reagents: a). SOCl 2, Et 3 N/EtOH reflux, b).nabh 4, MeOH/THF, c).(cp*rh(μ-cl)cl) 2, MeOH, rt, Synthesis of Diethyl 2,2 -bipyridyl-4,4 -dicarboxylate 2,2 -bipyridyl-4,4 -dicarboxylic acid (0.200g) and SOCl 2 (6.00 ml) were refluxed under N 2 atmosphere for 12 h at 90 C. The excess SOCl 2 was removed from the reaction mixture by distillation and the residue was dried under reduced pressure to afford a yellow solid. Yield: 0.215 g (93%). The yellow solid, 2,2 -bipyridyl-4,4 -dicarbonyl dichloride (0.220 g, 0.803 mmol) S4

was dissolved in ethanol (15 ml) at 0 C and triethylamine (0.223 ml, 1.60 mmol) was added. The temperature was slowly increased to room temperature and the reaction was refluxed for 5 h. Ethanol was removed under reduced pressure and the residue was diluted with dichloromethane and deionized water. The separated organic layer was dried over Na 2 SO 4 and concentrated on a rotavapor to afford white solid. Yield: 0.220g (90%). 1 H NMR (CDCl 3 ) δ 8.95 (s, 2H), 8.65 (d, 2H), 4.45 (q, 2H), 1.45 (t, 3H). Synthesis [2,2'-bipyridine]-4,4'-diyldimethanol (4,4 -CH 2 OH-bpy) To a solution of diethyl 2,2 -bipyridyl-4,4 -dicarboxylate (0.200g, 0.666 mmol) in ethanol (20 ml), NaBH 4 (0.580 g, 16.0 mmol) was added. This mixture was refluxed at 80 C for 10 h. The progress of the reaction was monitored by thin layer chromatography. After completion, the reaction was diluted with saturated NH 4 Cl (25 ml) and extracted twice with ethyl acetate(60ml). The combined ethyl acetate layers were dried over Na 2 SO 4 and concentrated under reduced pressure to yield the desired product as a white solid. Yield: 0.120g (83%). 1 H NMR (DMSO-d 6 ) δ 7.80(d, 2H), 7.42(s, 2H), 6.60(d, 2H), 3.95(s, 4H); 13 C NMR (DMSO-d 6 ) δ 154.9, 147.95, 120.45, 177.97, 61.37; FT-IR (KBr, cm -1 )3369 (s), 3194 (m), 2877 (m), 2819 (m), 2735 (m), 2634 (w), 1598(s), 1556 (s), 1456 (s), 1381 (s), 1308(m), 1234 (m), 1207 (w), 1049 (s), 996 (s), 906 (m), 821 (m), 758 (m), 652 (w), 605 (w). Synthesis of [η 5 -Cp*Rh(4,4 -CH 2 OH-bpy)Cl]Cl To a methanol(2ml) solution of [2,2'-bipyridine]-4,4'-diyldimethanol (0.027 g, 0.129 mmol), {η 5 -Cp*Rh(μ-Cl)Cl} 2 (0.040 g, 0.064 mmol) was added under N 2 atmosphere. The color of the reaction mixture slowly turned to orange yellow from reddish brown. After 3h stirring at room temperature, the volume was reduced to 1 ml; upon addition of diethyl ether(10 ml) precipitate was formed. Suitable single crystals for X-ray diffraction analysis were obtained from MeOH and diethyl ether by vapor diffusion. Yield (0.061 g, 92%). 1 H NMR (CD 3 OD) δ 8.91(d, 2H), 8.50(s, 2H), 7.85(d, 2H), 4.90 (s, 4H), 1.72(s, 15H); 13 C NMR (CD 3 OD) δ 157.24, 154.51, 151.71, 125.40, 120.59, 97.53, 61.70, 7.72; FT-IR (KBr, cm -1 ) 3522 (m), 3274 (s), 3063 (s), 3063 (s), 2893 (w), 2835 (w), 2629 (w), 1619 (s), 1561(s), 1488 (s), 1413 (s), 1292(s), 1239 (s), 1160 (w), 1070 (s), 1022 (m), 896 (m), 826 (w), 605 (w); LC/MS (ESI): m/z 489.10 [η 5 -Cp* Rh(bpy- OH)Cl] +. S5

Synthetic procedure of 4 Reagents: a).h 2 SO 4 /EtOH reflux, b).nabh 4, MeOH/THF, c).[cp*rh(μ-cl)cl] 2, MeOH, rt, Synthesis of diethyl [2,2'-bipyridine]-5,5'-dicarboxylate To a mixture of [2,2'-bipyridine]-5,5'-dicarboxylic acid (0.532 g) in EtOH (20 ml), conc. H 2 SO 4 (3 ml) was added drop by drop and refluxed at 80 o C for 12 hours. After that, methanol was evaporated under reduced and diluted with saturated NaHCO 3, and this mixture was extracted with CH 2 Cl 2 (90 ml). The CH 2 Cl 2 layer was dried over Na 2 SO 4 and concentrated under reduced pressure. If afforded off white solid which was dried under high vacuum. Yield = 0.615 g (94 %). 1 H NMR (400 MHz, CDCl 3 ) δ 9.31 (dd, J = 2.1, 0.8 Hz, 2H), 8.59 (dd, J = 8.3, 0.8 Hz, 2H), 8.45 (dd, J = 8.3, 2.1 Hz, 2H), 4.47 (q, J = 7.1 Hz, 4H), 1.46 (t, J = 7.1 Hz, 6H). Synthesis of [2,2'-bipyridine]-5,5'-diyldimethanol To a solution of diethyl [2,2'-bipyridine]-5,5'-dicarboxylate (0.502 g, 1.77 mmol) in EtOH, NaBH 4 (1.00 g, 26.01 mmol) was added and heated to 75 80 o C for 12 hours. After removing the EtOH, NaBH 4 was quenched with saturated NH 4 Cl and extracted with ethyl acetate(150 ml). The organic layer was dried over Na 2 SO 4 and concentrated on a rotavapor and it gave white solid. Yield = 0.210 g (58%). 1 H NMR (400 MHz, CD 3 OD) δ 8.65 (s, 2H), 8.29 (d, J = 8.1 Hz, 2H), 7.94 (dd, J = 8.2, 2.0 Hz, 2H), 4.74 (s, 4H). Synthesis of [η 5 -Cp*Rh(5,5 -CH 2 OH-bpy)Cl]Cl S6

To a methanol(2ml) solution of [2,2'-bipyridine]-5,5'-diyldimethanol (0.013 g, 64.7 μmol), {η 5 - Cp*Rh(μ-Cl)Cl} 2 (0.020 g, 32.3 μmol) was added under N 2 atmosphere. The color of the reaction mixture slowly turned to orange yellow from reddish brown. After 3h stirring at room temperature, the volume was reduced to 1 ml; upon addition of diethyl ether(10 ml) precipitate was formed. Yield (0.061 g, 92%). 1 H NMR (500 MHz, CD 3 OD) δ 8.96 (s, 2H), 8.48 (d, J = 8.3 Hz, 2H), 8.18 (dd, J = 8.3, 1.8 Hz, 2H), 4.85 (s, 4H), 1.73 (s, 15H). Synthetic procedure of 5 Reagents: a).h 2 SO 4 /EtOH reflux, b).nabh 4, MeOH/THF, c).[cp*rh(μ-cl)cl] 2, MeOH, rt, Synthesis of diethyl [2,2'-bipyridine]-6,6'-dicarboxylate To a mixture of [2,2'-bipyridine]-6,6'-dicarboxylic acid (0.200 g) in EtOH (20 ml), conc. H 2 SO 4 (3 ml) was added drop by drop and refluxed at 110 o C for 12 hours. After that, ethanol was evaporated under reduced pressure and diluted with saturated Na 2 CO 3, and this mixture was extracted with CH 2 Cl 2 (90 ml). The CH 2 Cl 2 layer was dried over Na 2 SO 4 and concentrated under reduced pressure. If afforded off white solid which was dried under high vacuum. Yield = 0.182 g (73.7%). 1 H NMR (400 MHz, CDCl 3 ) δ 8.76 (dd, J = 7.9, 1.1 Hz, 2H), 8.14 (dd, J = 7.7, 1.1 Hz, 2H), 7.98 (t, J = 7.8 Hz, 2H), 4.49 (q, J = 7.1 Hz, 4H), 1.46 (t, J = 7.1 Hz, 6H). Synthesis of [2,2'-bipyridine]-6,6'-diyldimethanol To a solution of diethyl [2,2'-bipyridine]-6,6'-dicarboxylate (0.184 g, 0.612 mmol) in THF, NaBH 4 (349 mg, 9.19 mmol) was added followed by 3 ml of MeOH and heated to 75 80 o C for 12 hours. After removing the THF, NaBH 4 was quenched with saturated NH 4 Cl and extracted S7

with ethyl acetate(150 ml). The organic layer was dried over Na 2 SO 4 and concentrated on a rotavapor to yield a white solid. Yield = 0.12 g (90.5%). 1 H NMR (400 MHz, CD 3 OD) δ 8.23 (d, J = 7.8 Hz, 2H), 7.90 (t, J = 7.8 Hz, 2H), 7.53 (d, J = 7.7 Hz, 2H), 4.78 (s, 4H). Synthesis of [η 5 -Cp*Rh(6,6 -CH 2 OH-bpy)Cl]Cl To a methanolic solution of [2,2'-bipyridine]-6,6'-diyldimethanol (0.074 g, 0.342 mmol), {η 5 - Cp*Rh(μ-Cl)Cl} 2 (0.1057 g, 0.1711 mmol) was added under N 2 atmosphere. The color of the reaction mixture slowly turned to orange yellow from reddish brown. After 4h stirring at room temperature, the volume was reduced to 1 ml; upon addition of diethyl ether(10 ml) yellow precipitate was formed. Suitable single crystals for X-ray diffraction analysis were obtained from MeOH and diethyl ether by vapor diffusion. Yield (0.170 g, 94.5%). 1 H NMR (500 MHz, CD 3 OD) δ 8.49 (d, J = 7.8 Hz, 1H), 8.31 (t, J = 7.9 Hz, 1H), 8.06 (d, J = 7.8 Hz, 1H), 5.05 (dd, J = 48.0, 15.8 Hz, 2H), 1.48 (s, 15H). S8

Table S1: Comparison of selected bond distances, bond angles and dihedral angle of catalyst 1-3, 5 1 [21] 2 3 [9b] 5 Bond distance Rh1-Cl1 2.385(2) 2.397(16) 2.363(3) 2.387(18) Rh1-N1 2.100(5) 2.114(5) 2.109(9) 2.117(4) Rh1-N2 2.100(5) 2.103(5) 2.116(9) 2.117(4) Rh1-C11 2.141(6) 2.165(6) 2.132(18) 2.161(5) Rh1-C12 2.141(6) 2.168(6) 2.118(17) 2.161(5) Rh1-C13 2.146(6) 2.137(6) 2.111(19) 2.171(5) Rh1-C14 2.178(10) 2.158(5) 2.115(17) 2.143(7) Rh1-C15 2.146(6) 2.156(6) 2.138(17) 2.171(5) Bond Angle N1-Rh1-N2 75.3 77.1 76.9 77.0 N1-Rh1-Cl1 86.3 84.3 88.3 90.2 N2-Rh1-Cl1 86.3 89.1 87.4 90.2 Dihedral Angle θ1 172.27 176.77 172.50 154.48 θ2 2.50 31.58 6.56 16.38 θ1 = dihedral angle between the planes N1-C5-C6-N2 and Rh1-N1-N2 θ2 = dihedral angle between N1 pyridine and N2 pyridine ring of the bipyridine S9

Table S2. Summary of X-ray Crystallographic information of 2 and 5. Compound 2 5 Empirical formula C 22 H 27 Cl 2 N 2 O 2 Rh C 22 H 2 Cl 2 N 2 O 2 Rh 0.5 H 2 O Formula weight 525.27 534.27 T (K) 193(2) 200(2) λ (A ) 0.71073 0.71073 Crystal system Monoclinic Orthorhombic Space group P2(1) Pnnm Unit cell dimensions a (A ) 7.9789(4) 17.9947(9) b (A ) 12.2208(5) 8.4463(4) c (A ) 11.6751(5) 15.7807(8) 90 90 101.379(2) 90 90 90 V (Å 3 ) 1116.04(9) 2398.5(2) Z 2 4 D calc (Mg/m 3 ) 1.563 1.480 Absorption coefficient (mm -1 ) 1.025 0.957 Crystal size (mm 3 ) 0.29 x 0.20 x 0.06 0.45 x 0.37 x 0.24 θ range (deg) 2.44 to 28.34. 1.72 to 26.50. Reflections collected 23859 14597 Independent reflections 5529 [R(int) = 0.0530] 2574 [R(int) = 0.0406] No of parameters 269 148 Absorption correction Semi-empirical from equivalents Semi-empirical from equivalents Refinement method Full-matrix least-squares on F 2 Full-matrix least-squares on F 2 Goodness-of-fit on F 2 1.092 1.162 Final R indices [I >2σ (I)] R1 = 0.0486, wr2 = 0.1245 R1 = 0.0505, wr2 = 0.175 R indices (all data) R1 = 0.0647, wr2 = 0.1399 R1 = 0.0853, wr2 = 0.2236 Largest diff. peak and hole 3.423 and -0.922 e.å -3 1.464 and -1.800 e.å -3 R1 = Σ F o - F c / Σ F o ; wr2 = {Σ[w( F o 2 F c 2 ) 2 ]/ Σ[w F o 2 2 ]} 1/2 S10

Absorbance 1.5 1.2 Catalyst 1 Catalyst 2 Catalyst 3 Catalyst 4 Catalyst 5 0.9 0.6 0.3 0.0 250 300 350 400 450 500 (nm) Figure S1. UV-Visible absorption spectrum of catalyst 1-5 in aqueous solution (35 μm) S11

Table S3. Summery of UV-Visible absorbance and molar extinction coefficient. Complex λ max (nm) ε (M -1 cm -1 ) 1 231 251 305 313 370 31000 20200 15050 15200 2500 2 233 310 375 26700 6300 2750 230 39200 3 302 15100 311 15150 370 2600 4 231 255 312 321 375 31500 19600 17850 18600 2500 5 235 260 317 327 370 24100 12200 10650 10800 2150 S12

Figure S2. 1 H NMR spectrum of 2 ([η 5 -Cp*Rh((3,3 -CH 2 OH-bpy))Cl]Cl) in CD 3 OD Figure S3. 1 H NMR spectrum of 3 ([η 5 -Cp*Rh((4,4 -CH 2 OH-bpy))Cl]Cl) in CD 3 OD S13

Figure S4. 1 H NMR spectrum of 4 ([η 5 -Cp*Rh((5,5 -CH 2 OH-bpy))Cl]Cl) in CD 3 OD Figure S5. 1 H NMR spectrum of 5 ([η 5 -Cp*Rh((6,6 -CH 2 OH-bpy))Cl]Cl) in CD 3 OD S14

Table S4. Summery of 1 H NMR spectra of catalyst 1-5 Complex Cp* Protons (ppm) -CH 2 OH (ppm) 1 1.74-2 1.66 4.58 3 1.72 4.90 4 1.74 4.90 5 1.48 5.05 S15

10 Complex 2 Complex 5 0 I ( -10-20 -30-40 -1.00-0.75-0.50-0.25 0.00 P (V) vs Ag/AgCl Figure S6. Cyclic voltammogram of complex 2(plain line) and 5(dot line), (2 mm) in 0.1 M Tris/HCl buffer (ph 7.5) at a glassy carbon cathode at the scan rate of 100 mv/s. 10 Complex 3 Complex 4 0 I ( -10-20 -30-1.00-0.75-0.50-0.25 0.00 P (V) vs Ag/AgCl Figure S7. Cyclic voltammogram of complex 3(plain line) and 4(dot line), (2 mm) in 0.1 M Tris/HCl buffer (ph 7.5) at a glassy carbon cathode at the scan rate of 100 mv/s. S16

Scheme S1. Kinetic studies of Rhodium-hydride species generation 1=R=H (bpy), 2=3,3 -CH 2 OH, 3=4,4 -CH 2 OH, 4=5,5 -CH 2 OH, 5=6,6 -CH 2 OH Procedure: To a degassed phosphate buffer solution (ph 7.2) of HCO 2 Na (0.35 M, 2.50 ml) was added 35.0 μm aliquot(70.0 μl) of Rh complex stock solution in an airtight UV-cuvette maintained at 300 K. The UV-Visible spectra were recorded under time based kinetic mode till the saturation of the reaction. The reaction was followed based on the UV-Visible absorbance changes at 287 nm for complex 2 and 5, 286 nm for complex 4 and 281 nm for complex 3. The rate constants were obtained by best exponential fitting of the absorbance data versus time using the following exponential fitting equation y = y 0 + A*exp(k*x), where k obs = -k. S17

Absorbance Absorbance 1.0 0.48 0.8 0.6 0.42 0.36 0.30 Fitting equation: y = y 0 + A*exp(k*x) y = 0.4699-0.2614*exp(-0.00641*t) R 2 = 0.9992 k obs = 6.41 x 10-3 sec -1 0.4 0.2 0.24 0 250 500 750 1000 1250 Time (sec) 0.0 300 400 500 600 (nm) Figure S8. Kinetic traces of UV-Visible absorption spectrum during the reaction of 1(35.0 μm, 2.50 ml) with 0.35 M HCO 2 Na in argon saturated aqueous phosphate buffer solution (ph 7.2) at 300 K. (Inset) Plot of [([η4-cp*-h)rh(bpy)] + species generation followed at 280 nm versus time and curve fitting for k obs calculation. S18

Absorbance Absorbance 1.0 0.30 0.8 0.6 0.27 0.24 Fitting equation: y = y 0 + A*exp(k*x) y = 0.3050-0.1556*exp(-0.00329*t) R 2 = 0.9996 k obs = 3.29 x 10-3 sec -1 0.21 0.4 0.2 0.18 0 300 600 900 1200 1500 1800 Time (sec) 0.0 300 400 500 600 (nm) Figure S9. Kinetic traces of UV-Visible absorption spectrum during the reaction of 2(35.0 μm, 2.50 ml) with 0.35 M HCO 2 Na in argon saturated aqueous phosphate buffer solution (ph 7.2) at 300 K. (Inset) Plot of Rh-hydride species generation followed at 287 nm versus time and curve fitting for k obs calculation. S19

Absorbance Absorbance 1.0 0.60 0.8 0.6 0.54 0.48 0.42 Fitting equation: y = y 0 + A*exp(k*x) y = 0.5937-0.2727*exp(-0.00676*t) R 2 = 0.9997 k obs = 6.76 x 10-3 sec -1 0.4 0.36 0.2 0 200 400 600 800 Time (sec) 0.0 300 400 500 600 nm) Figure S10. Kinetic traces of UV-Visible absorption spectrum during the reaction of 3 (35.0 μm, 2.50 ml) with 0.35 M HCO 2 Na in argon saturated aqueous phosphate buffer solution (ph 7.2) at 300 K. (Inset) Plot of Rh-hydride species generation followed at 281 nm versus time and curve fitting for k obs calculation. S20

Absorbance Absorbance Absorbance 1.0 0.42 0.8 0.6 0.36 0.30 Fitting equation: y = y 0 + A*exp(k*x) y = 0.4211-0.2273*exp(-0.00704*t) R 2 = 0.9998 k obs = 7.04 x 10-3 sec -1 0.42 0.24 0.4 0.36 0 180 360 540 720 900 Time (sec) 0.30 0.2 0.24 0.0 300 400 500 600 nm) 0 Figure S11. Kinetic traces of UV-Visible absorption spectrum during the reaction of 4 (35.0 μm, 2.50 ml) with 0.35 M HCO 2 Na in argon saturated aqueous phosphate buffer solution (ph 7.2) at 300 K. (Inset) Plot of Rh-hydride species generation followed at 286 nm versus time and curve fitting for k obs calculation. S21

Absorbance Absorbance 1.0 0.42 0.39 0.8 0.6 0.36 0.33 0.30 Fitting equation: y = y 0 + A*exp(k*x) y = 0.3991-0.1299*exp(-0.00325*t) R 2 = 0.9714 k obs = 3.25 x 10-3 sec -1 0.27 0.4 0.24 0 800 1600 2400 3200 Time (sec) 0.2 0.0 300 400 500 600 nm) Figure S12. Kinetic traces of UV-Visible absorption spectrum during the reaction of 5 (35.0 μm, 2.50 ml) with 0.35 M HCO 2 Na in argon saturated aqueous phosphate buffer solution (ph 7.2) at 300 K. (Inset) Plot of Rh-hydride species generation followed at 287 nm versus time and curve fitting for k obs calculation. S22

A) B) Figure S13. Space filling model of complex 2 (Figure 14A) and 5 (Figure 14B) S23

Figure S14. 1 H NMR spectrum of complex 2 (15.0 mm, 0.50 ml) measured upon reaction with HCO 2 Na in D 2 O under inert condition at room temperature. Ratio of Catalyst to HCO 2 Na is 25. S24

Figure S15. 1 H NMR spectrum of complex 3 (15.0 mm, 0.50 ml) measured measured upon reaction with HCO 2 Na in D 2 O under inert condition at room temperature. Ratio of Catalyst to HCO 2 Na is 25. Because of the deuteration, Cp*-H proton is not observed. S25

Figure S16. 1 H NMR spectrum of complex 4 (15.0 mm, 0.50 ml) measured measured upon reaction with HCO 2 Na in D 2 O under inert condition at room temperature. Ratio of Catalyst to HCO 2 Na is 25. Because of the deuteration, Cp*-H proton is not observed. S26

Figure S17. 1 H NMR spectrum of Rh-hydride complex of catalyst 5 (15.0 mm, 0.50 ml) measured measured upon reaction with HCO 2 Na in D 2 O under inert condition at room temperature. Ratio of Catalyst to HCO 2 Na is 25. S27