Supplementary Figures

Transcription

1 Supplementary Figures Supplementary Figure 1. Cp*Ir III complexes screened for the conversion of glycerol into lactic acid. Catalyst TON Supplementary Figure 2. Activity of Cp*Ir III complexes for the conversion of glycerol into lactic acid.

2 Supplementary Figure 3. TONs a function of time calculated by hydrogen evolution measurements in a gas-burette before and after successive addition of Hg(0) and PPh 3 (TOF = turnover frequency = TON/t). Supplementary Figure 4. Post-catalytic 1 H NMR hydride region using precursors 6 (A), 15 (B) and 16 (C).

3 Supplementary Figure 5. 2D-COSY experiment of the in situ NMR reaction of 16 with KOH (14 equiv.) in methanol under argon. Supplementary Figure 6. 2D-COSY experiment of the in situ NMR reaction of 15 with KOH (14 equiv.) in methanol under H 2 (1 bar).

4 Supplementary Figure 7. 2D-COSY experiment of the in situ NMR reaction of 16 with KOH (14 equiv.) in methanol under H 2 (1 bar). Supplementary Figure 8. Mass spectrometry spectrum (FT-ICR) after the in situ NMR reaction between 16 and KOH. Conditions: 16 (7 mg, mmol), KOH (10 mg, 0.18 mmol), methanol (0.7 ml), 60 ºC, 16 h, argon.

5 Supplementary Figure 9. Mass spectrometry spectrum (FT-ICR) after the in situ NMR reaction between 16 and KOH. Conditions: 16 (7 mg, mmol), KOH (10 mg, 0.18 mmol), iso-propanol (0.7 ml), 80 ºC, 16 h, argon. Supplementary Figure 10. Mass spectrometry spectrum (FT-ICR) a dichloromethane extract after the reaction between 16 and KOH. Conditions: 16 (20 mg, mmol), KOH (29 mg, 0.52 mmol), methanol (1.5 ml), 60 ºC, 4 h, argon. The reaction mixture was evaporated to dryness, washed with Et 2 O and the residue extracted with dichloromethane (3mL) under argon.

6 Supplementary Figure 11. Mass spectrometry spectrum (FT-ICR) an Et 2 O extract after the reaction between 16 and KOH. Conditions: 16 (20 mg, mmol), KOH (29 mg, 0.52 mmol), methanol (1.5 ml), 60 ºC, 4 h, argon. The reaction mixture was evaporated to dryness and the residue extracted with Et 2 O (3mL) under argon.

7 Supplementary Figure 12: Gas-burette setup used for monitoring reaction

8 Supplementary Figure 13. ORTEP diagrams of the cationic portions of compounds 16, 17 and % thermal ellipsoids are shown. Solvent molecules and hydrogen atoms, except those directly bound to iridium, have been omitted for clarity.

9 Supplementary Figure H and 13 C{ 1 H} NMR spectra of compound 15.

10 Supplementary Figure H and 13 C{ 1 H} NMR spectra of compound 16.

11 Supplementary Figure H NMR spectrum of compound 17.

12 Supplementary Figure 17. 2D-HSQC and HMBC spectra of compound 17.

13 Supplementary Figure C{ 1 H} NMR spectrum of compound 17. Supplementary Figure H NMR spectrum after a typical catalytic reaction. Reaction conditions: glceryol/water (94/6; 2 g), 24 h, 115 ºC, 5 μmol 16, N 2.

14 Supplementary Tables Supplementary Table 1. Catalytic activity if IrCl 3 and iridium heterogeneous forms. Entry Catalyst TON 1 IrCl IrO Ir/C Ir(0) (2-3nm) 281 Supplementary Table 2. Poisoning experiments with Hg(0) and PPh 3. Entry Catalyst Additivve TON 1 6 Hg(0) Hg(0) Hg(0) PPh PPh PPh Supplementary Table 3. Optimization of conditions for the conversion of crude glycerol into lactic acid. Entry Glycerol H 2 O KOH 16 (ml) (ml) (equiv.) (mol%) Flask type t (h) T (ºC) Conv. 1 a Pear % Pear % none Pear % 4 b Cylindrical % 5 b Cylindrical % Pear % Pear % Cylindrical % Cylindrical % a Average over multiple experiments; b no stirring.

15 Supplementary Table 4. Catalytic activity of iridium precursors 3, 12 and 16 in the presence of [1,3-dimethylimidazolium]BF 4. Reaction conditions: neat glycerol (6 ml), iridium precursor (3 μmol), KOH (2.68 g), 115 ºC, 15 h. Entry Catalyst Imidazolium (equiv.) TON

16 Supplementary Table 5. Crystal data and structure refinement for compound 16. Crystal data C 12 H 16 IrN 4 O 2 BF 4 Z = 4 M r = F(000) = 1000 Orthorhombic, Pccn D x = Mg m -3 a = (5) Å b = (5) Å c = (9) Å = = 90 = 7.77 mm -1 = 90 = 90 V = (16) Å 3 Data collection Rigaku R-AXIS RAPID imaging plate diffractometer Mo K radiation, = Å Cell parameters from reflections T = 93 K Prism, colorless mm Radiation source: fine-focus sealed tube R int = reflections with I > 2 (I) Graphite Monochromator max = 27.5, min = 3.2 Absorption correction: multi-scan Jacobson, R. (1998) Private Communication h = T min = 0.333, T max = k = measured reflections l = independent reflections Refinement Refinement on F 2 Least-squares matrix: full R[F 2 > 2 (F 2 )] = wr(f 2 ) = S = 1.13 Primary atom site location: structureinvariant direct methods Secondary atom site location: difference Fourier map Hydrogen site location: inferred from neighbouring sites H-atom parameters constrained 1987 reflections ( / ) max = parameters ρ max = 1.43 e Å restraints ρ min = e Å -3 w = 1/[ 2 (F o 2 ) + (0.0192P) P] where P = (F o 2 + 2F c 2 )/3

17 Supplementary Table 6. Crystal data and structure refinement for compound 17. Crystal data C 47 H 38 BF 24 IrN 6 Z = 4 M r = F(000) = 1320 Triclinic, P-1 D x = Mg m -3 a = (10) Å b = (11) Å c = (11) Å = = (5) = 2.72 mm -1 = (6) = (6) V = (3) Å 3 Data collection Rigaku R-AXIS RAPID imaging plate diffractometer Mo K radiation, = Å Cell parameters from reflections T = 150 K Block, colorless mm Radiation source: fine-focus sealed tube R int = reflections with I > 2 (I) Graphite Monochromator max = 25.0, min = 3.0 Absorption correction: multi-scan Jacobson, R. (1998) Private Communication h = T min = 0.613, T max = k = measured reflections l = independent reflections Refinement Refinement on F 2 Least-squares matrix: full R[F 2 > 2 (F 2 )] = wr(f 2 ) = S = 1.04 Primary atom site location: structureinvariant direct methods Secondary atom site location: difference Fourier map Hydrogen site location: inferred from neighbouring sites H-atom parameters constrained 9043 reflections ( / ) max = parameters ρ max = 1.35 e Å -3 2 restraints ρ min = e Å -3 w = 1/[ 2 (F o 2 ) + (0.0192P) P] where P = (F o 2 + 2F c 2 )/3

18 Supplementary Table 7. Crystal data and structure refinement for compound 18. Crystal data C 49 H 40 BCl 2 F 24 IrN 6 O Z = 2 M r = F(000) = 1432 Triclinic, P-1 D x = Mg m -3 a = (13) Å b = (14) Å c = (2) Å = = (6) = 2.50 mm -1 = (6) = (5) V = (5) Å 3 Data collection Rigaku R-AXIS RAPID imaging plate diffractometer Mo K radiation, = Å Cell parameters from reflections T = 223 K Block, colorless mm Radiation source: fine-focus sealed tube R int = reflections with I > 2 (I) Graphite Monochromator max = 25.3, min = 3.2 Absorption correction: multi-scan Jacobson, R. (1998) Private Communication h = T min = , T max = k = measured reflections l = independent reflections Refinement Refinement on F 2 Least-squares matrix: full R[F 2 > 2 (F 2 )] = wr(f 2 ) = S = 1.07 Primary atom site location: structureinvariant direct methods Secondary atom site location: difference Fourier map Hydrogen site location: inferred from neighbouring sites H-atom parameters constrained reflections ( / ) max = parameters ρ max = 1.89 e Å restraints ρ min = e Å -3 w = 1/[ 2 (F o 2 ) + (0.0192P) P] where P = (F o 2 + 2F c 2 )/3

19 Supplementary Methods General experimental details. Organic solvents were purified by passing over activated alumina with dry N 2. All chemicals were purchased from major commercial suppliers and used as received. Syntheses of iridium complexes were performed under an inert atmosphere of dry N 2 using standard Schlenk techniques. Compounds 1-10, 1 11, and 14 4 were synthesized by previously reported procedures. Synthesis of compound 12, [Ir(CO) 2 Cl] 2. This known material was prepared in a similar manner to the previously reported synthesis. 5 [Ir(COD)Cl] 2 (50 mg, mmol) was added to a 100 ml round bottom Schlenk flask with a magnetic stir bar, then evacuated and purged with carbon monoxide. Dry dichloromethane (20 ml) was added under carbon monoxide atmosphere and the reaction mixture stirred at room temperature for 1 hour with CO bubbled through the solution via a long needle. The solution turned from dark red-orange to blue-black in minutes. The solution was allowed to settle and a dark blue precipitate began to form. This fine precipitate was isolated by decanting off the yellow-orange solution from the dark product and was washed with additional dichloromethane (2 x 10 ml) yielding a very fine blue-black powder (12 mg, 14 % yield). The infrared spectrum matches the reported bands at 2081 and 2006 cm -1. Identification of reaction intermediates. A number of experiments with low base loadings were carried out with iridium precursors 6, 15 and 16. In a general procedure a screw-capped NMR tube was charged with the corresponding iridium catalyst (0.013 mmol), KOH (10 mg, 0.18 mmol) and 0.8 ml of a previously deoxygenated mixture of glycerol/h 2 O (1:1) under argon. The NMR tube was heated at 60 ºC for 16 hours and 1 H

20 NMR analysis of the reaction mixture was carried out after addition of sodium [D] 4-2,2,3,3-(3-trimethylsilyl)propionate as internal standard. The identification of reaction products was undertaken by addition of authentic samples (sodium formate, formaldehyde, sodium acetate, ethyleneglycol, 1,2-propanediol, glyceraldehyde, dihydroxyacetone, acetol, pyruvaldehyde, sodium pyruvate, glyceric acid and lactic acid). Conversion of reaction intermediates under catalytic conditions. A number of experiments were carried under standard catalytic conditions (8M KOH, 115 ºC, 16 h) but using glyceraldehyde (GAL), dihydroxyacetone (DHA), 1,2-propanediol (PDO) or lactic acid (LA) instead of glycerol. In a general procedure, a Schlenk flask was charged with the organic substrate (GAL or DHA, 0.35 mmol; PDO or LA, 1mmol), KOH (8M) and previously deoxygenated water (0.3 ml) under argon. The reaction mixture was heated at 115 ºC for 16 hours under nitrogen, then D 2 O (1 ml) and [D] 4-2,2,3,3-(3- trimethylsilyl)propionate as internal standard were added. The reaction mixture was analyzed by 1 H NMR spectroscopy with addition of authentic samples as described previously. Isolation of compounds 17 and 18. Several experiments were undertaken with the aim of isolating iridium species derived from 16 under conditions somewhat relevant to the catalytic process. After many attempts using variable amounts of 16, KOH (from 1 to 100 equiv. with respect to iridium) and solvents (MeOH, H 2 O, glycerol, i PrOH and their mixtures), we succeeded in isolating compounds 17 and 18 in low yields. Crystals of 17 and 18 were only isolated after exchanging the counterion BF - 4 by the bulkier BAr F - (BAr F = [B(3,5-C 6 H 3 (CF 3 ) 2 ) 4 ]) anion. Compound 17. A Schlenk flask was charged with 16 (20 mg, mmol), KOH (29 mg, 0.70 mmol) and NaBAr F (84 mg,

21 0.094 mmol) under argon and the mixture suspended in dry MeOH (1.5 ml). The reaction was stirred at 60 ºC for 4 h, then filtered by cannula and evaporated under reduced pressure. The residue was redissolved in dichloromethane (1.5 ml), layered with pentane and the Schlenk kept at -20 ºC. After several days colorless crystals covered by greenish oil appeared and were washed several times with diethyl ether. Analysis of the mother liquor and oily fraction revealed a complex mixture of iridium hydrides (more than 5 different species). X-ray diffraction studies and 1 H and 13 C{ 1 H} NMR spectroscopic analysis demonstrated the molecular structure of compound 17, whose yield was calculated by 1 H NMR using an internal standard (Yield = 8 %). 1 H NMR (600 MHz, CD 2 Cl 2 ): δ 6.81 (s, 4 H, NCHCHN), 6.80 (s, 2 H, NCHCHN), 6.72 (s, 2 H, NCHCHN), 6.42 (s, 4 H, NCHCHN), 4.23 (s, 6 H, NCH 3 ), 4.00 (s, 12 H, NCH 3 ), 2.91 (s, 18 H, NCH 3 ), (s, 2 H, Ir H), (s, 2 H, Ir H). 13 C{ 1 H} NMR (151 MHz, CD 2 Cl 2 ): δ = (Ir=C), (Ir=C), (NCHCHN), (NCHCHN), (NCHCHN), (NCHCHN), 41.3 (NCH 3 ), 40.4 (NCH 3 ), 39.6 (NCH 3 ), 38.3 (NCH 3 ). HRMS (FT-ICR, m/z): [(M H 2 )/2] + calcd. for C 15 H 24 IrN 6, ; found, Compound 18. A Schlenk flask was charged with 16 (100 mg, mmol) and KOH (145 mg, 2.59 mmol) under argon and the reaction mixture suspended in dry MeOH (10 ml) and stirred at 60 ºC for 16 h. The solution was filtered via cannula to a Schlenk containing NaBAr F (300 mg, 0.34 mmol) and the mixture stirred at room temperature for 2 h, then evaporated under vacuum. The residue was extracted with diethyl ether (10 ml) under argon, concentrated, layered with pentane and kept in the freezer at -20 ºC. Compound 18 was isolated as tiny colorless crystal plates (yield calculated by 1 H NMR with internal standard; yield = 9 %). 1 H NMR (600 MHz, CD 2 Cl 2 ): δ 6.95 (s, 4 H, NCHCHN), 6.93 (s, 2 H, NCHCHN), 3.66 (s, 6 H, NCH 3 ), 3.37 (s, 12 H, NCH 3 ), -9,02 (d, 1 H, 2 J HH = 2.8 Hz, Ir-H), (d, 1 H, 2 J HH =

22 2.8 Hz, Ir-H). FT-IR (solid): ν (CO) = 2020 cm -1. HRMS (FT-ICR, m/z): [M] + calcd. for C 16 H 26 IrN 6 O, ; found, Screening of Cp*Ir III precatalysts. A small library of Cp*Ir III complexes (Supplementary Figure 1) was screened for the conversion of glycerol into lactic acid (Supplementary Table 1). The general catalytic procedure described in the Methods section of the manuscript was employed (3 ml neat glycerol, mol% Ir, 115 ºC, KOH 8M, 15 h). TONs were calculated by 1 H NMR analysis using sodium acetate or sodium [D] 4-2,2,3,3-(3-trimethylsilyl)propionate as internal standards. Homogeneity assays. (A) Screening of heterogeneous and simple iridium precursors. Several heterogeneous iridium precursors (IrO 2, Ir/C and freshly prepared 2-3nm iridium nanoparticles 1 ), as well as IrCl 3, were tested for the conversion of glycerol into lactic acid under the same conditions described in the Methods section of the manuscript (3 ml neat glycerol, mol% Ir, 115 ºC, KOH 8M, 15 h). (B) Poisoning Experiments. Catalytic runs with catalysts 6, 15 and 16 were carried out in the presence of mercury under otherwise identical conditions as in the Methods section of the manuscript (3 ml neat glycerol, mol% Ir, 115 ºC, KOH 8M, 15 h). No decrease in activity was recorded for any of the reactions (Supplementary Table 2, entries 1-3). In contrast, addition of PPh 3 (50 mg, 50 equiv.) under identical conditions resulted in a dramatic decay of TONs for the three catalysts (entries 4-6). An additional poisoning experiment was carried out in the gas-burette (Supplementary Figure 3) where TONs were calculated by measuring the evolved hydrogen gas. Initially the reaction was carried out under standard conditions for gas-burette experiments (vide infra) using neat glycerol (3mL), catalyst 16 (0.8mg, mol%) and KOH (1.34 g) at 115 ºC. After one hour several drops of Hg(0) were added under argon and the mixture was stirred at 60 ºC for 30 min. Then the temperature was increased to 115 ºC

23 and the evolution of H 2 monitored for one hour without decrease in catalytic activity. 50 equiv. of PPh 3 were subsequently added under argon and the mixture was stirred for 20 min at 60 ºC. Afterwards the solution was heated to 115 ºC and gas evolution measurements were restored, revealing a considerable reduction of catalytic activity. Screening conditions for conversion of crude glycerol from biodiesel industry. (A) Optimization of conditions for crude glycerol conversion. Crude glycerol (68.1% glycerol, 0.83% methanol, 6.1% water, 5.0% ash, 20.8% organic impurities) was obtained from Greenleaf Biofuels, LLC, and was heated to 80 C immediately prior to use to lower viscosity. Varying amounts of water were added and the flask type was varied to achieve optimal stirring and prevent excessive foam formation. In the optimized procedure (CO) 2 Ir(IMe) 2 BF 4 (16) (12 mg, 0.6 mol%), KOH (430 mg, 2.05 equivalents), and a stir bar were added to a 100 ml pear shaped flask coupled to a condenser. The flask was charged with N 2, and crude glycerol (0.5 ml, mol glycerol) and water (0.3 ml) were then added and the reaction mixture heated to 130 C with stirring at 60 RPM. After 24 hours, the flask was removed from heat, and deuterium oxide (3 ml) and sodium [D] 4-2,2,3,3-(3-trimethylsilyl)propionate (4 mg, internal standard) were added immediately with stirring. The reaction was analyzed by NMR and conversion and selectivity were determined by integration against the internal standard (Supplementary Table 3). (B) Un-optimized procedure for isolation of lactic acid from crude glycerol reaction. Pure Lactic acid was isolable from the reaction mixture by means of a simple extraction procedure. The reaction mixture from crude glycerol conversion was acidified to ph 1.5 with HCl (1M), then water (100 ml) and decolorizing charcoal were added and the slurry was stirred for 15 minutes. The mixture was then passed through a frit layered with celite. The clear, colorless filtrate was extracted with 2-butanol (2 x 150 ml), and the organic layer was concentrated in vacuo.

24 The resulting residue was taken up in water (2.5 ml), and filtered through a Pasteur pipette layered with celite and decolorizing charcoal, yielding a clear colorless liquid (pure by NMR, 60% yield). In agreement with prior studies, we occasionally observed the formation of lactic acid oligomers by NMR when water content was low, and these could be cleaved to lactic acid by heating at 100 C in excess KOH for 10 minutes and re-acidifying. Post-catalytic 1 H NMR spectra. Three catalytic experiments were carried out with higher loadings of precursors 6, 15 and 16 to facilitate the identification of iridium species after catalysis (Supplementary Figure 4). A modified version of the general procedure described in the Methods section of the manuscript was employed: iridium precursor (0.038 mol%; 6, 10 mg, 15, 9.1 mg, 16, 8.2 mg), glycerol/h 2 O (0.5/0.4 ml), KOH (420 mg), 115 ºC, 16h. The hydride regions of the 1 H NMR spectra depicted in Figure S4 exhibit different resonances for each of the three precursors. This might indicate that different active species are responsible for catalytic turnover in 6, 15 and 16, although we defer a more definitive proposal on the nature of the active catalyst(s). Nevertheless, the major hydride signal resulting from 6 was due to cationic monohydride [Cp*Ir(IMe) 2 H] +, a complex already reported by us in a prior study. This compound was tested for catalysis under standard conditions and exhibited a considerably lower activity in comparison to chloride 6, which is evidence against its role as a catalytically relevant intermediate. 6 For the sake of comparison and with the aim of isolating hydride species relevant to catalysis we carried out a number of in situ NMR experiments with precursors 15 and 16. Methanol was used in place of glycerol to prepare these samples because residual glycerol was not compatible with the mass spectrometry instrumentation available to us. These reactions in methanol provided species with 1 H NMR resonances in the hydride region identical to those observed in

25 preliminary experiments in glycerol. This allowed us to compare one sample consistently across all characterization methods. First, we carried out two parallel experiments with 15 (7.7 mg, mmol) and 16 (7 mg, mmol) in screw-capped NMR tubes charged with KOH (10 mg, 0.18 mmol) and methanol (0.7 ml) under argon. Whereas no transformation was observed for 15 after 16 hours at 60 ºC, compound 16 gave rise to a mixture of products evidenced by complex aromatic and hydridic regions in 1 H NMR analysis (Figure S5). Since hydrogen gas is generated in the conversion of glycerol into lactic acid, we carried out the same experiments in the presence of H 2 (1 bar) in J. Young NMR tubes. After 12 hours at 60 ºC, both complexes 15 and 16 led to a number of species characterized by a complicated pattern of resonances in the hydridic region of the 1 H NMR spectra (Supplementary Figures 6 and 7). Effects of the addition of [1,3-dimethylimidazolium]BF 4. A number of experiments in which additional equivalents of [1,3-dimethylimidazolium]BF 4 were added to Ir precursors containing no NHC (12), one NHC (3) or two NHCs (16) were performed using the general procedure described in the Methods section of the manuscript (Supplementary Table 4). General procedure for gas-burette monitoring of reactions. The burette setup pictured below (Supplementary Figure 12) was used to measure H 2 gas evolved during the reaction. Before each run, all ground glass joints were cleaned and thoroughly regreased to ensure an air-tight system. A Schlenk tube was charged with a stir bar, iridium catalyst ( mol%) and KOH ( equivalents) and attached to the burette condenser. The system was then evacuated and backfilled with argon 3-5 times, and glycerol ( ml) pre-heated to 60 C was added under a positive flow of argon. The reaction flask was then heated to 115 C. Once the KOH was dissolved, the

26 Schlenk flask was closed to the argon line and the condenser was opened to the burette by means of a 3-way stopcock. The water level was recorded as a function of time and the Van der Waals equation shown below was used to convert gas volume to moles of H 2. After stopping the reaction, the number of moles of gas produced was compared with the amount of lactate detected by NMR with an internal standard, and >90% agreement was observed in all cases. =23.96 a = T = 292 K p = 101,325 Pa Crystallographic details. Low-temperature diffraction data (ω scans) were collected on either a Rigaku R-AXIS RAPID diffractometer coupled to a RAXIS RAPID imaging plate detector with Mo Kα radiation (λ = Å) at 150K or a Rigaku Mercury275R CCD (SCX mini) diffractometer using filtered Mo Kα radiation (λ = Å) at 223K. The data frames were processed and scaled using the Rigaku CrystalClear software. The data were corrected for Lorentz and polarization effects. All structures were solved by direct methods using SHELXS and refined against F 2 on all data by full-matrix least squares with SHELXL-97. All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were included into the model at geometrically calculated positions and refined using a riding model, except for those bound to iridium which were located in the Fourier difference electron density map and their Ir-H bond distances restrained using DFIX instruction. The isotropic displacement

27 parameters of all hydrogen atoms were fixed to 1.2 times the U value of the atoms to which they are linked (1.5 times for methyl groups). All disorders were refined with the help of similarity restraints on displacement parameters (SIMU and DELU instructions).

28 Supplementary References 1 Hintermair, U., Campos, J., Brewster, T. P., Pratt, L. M., Schley, N. D. & Crabtree, R. H. Hydrogen-Transfer Catalysis with Cp*Ir III Complexes: The Influence of the Ancillary Ligands. ACS Catal. 4, (2014). 2 Herde, J. L., Lambert, J. C. & Senoff, C. V. Cyclooctene and 1,5-Cyclooctadiene Complexes of Iridium(I). Inorg. Synth. 15, (1974). 3 Voutchkova, A. M., Appelhans, L. N., Chianese, A. R. & Crabtree, R. H. Disubstituted Imidazolium-2-Carboxylates as Efficient Precursors to N-Heterocyclic Carbene Complexes of Rh, Ru, Ir, and Pd J. Am. Chem. Soc. 127, (2005). 4 Zinner, S. C., Rentzsch, C. F., Herdtweck, E., Herrmann, W. A. & Kuhn, F. E. N- heterocyclic carbenes of iridium(i): ligand effects on the catalytic activity in transfer hydrogenation. Dalton Trans. 35, (2009). 5 Roberto, D., Cariati, E., Psaro, R. & Ugo, R. Formation of [Ir(CO) 2 Cl] x (x = 2, n) Species by Mild Carbonylation of [Ir(cyclooctene) 2 Cl] 2 Supported on Silica or in Solution: A New Convenient Material for the Synthesis of Iridium(I) Carbonyl Complexes. Organometallics 13, (1994). 6 Campos, J., Hintermair, U., Brewster, T. P., Takase, M. K. & Crabtree, R. H. Catalyst Activation by Loss of Cyclopentadienyl Ligands in Hydrogen Transfer Catalysis with Cp*IrIII Complexes. ACS Catal. 4, (2014).