Iridium tricyclohexylphosphine

Pyridinethione-iridium tricyclohexylphosphine hydride systems and related systems... 

The stereochemistry of reduction by homogeneous catalysts is often controlled by functional groups in the reactant. Delivery of hydrogen occurs cis to a polar functional group. This behavior has been found to be particularly characteristic of an iridium-based catalyst that contains cyclooctadiene, pyridine, and tricyclohexylphosphine as ligands, known as the Crabtree catalyst 6 Homogeneous iridium catalysts have been found to be influenced not only by hydroxy groups, but also by amide, ester, and ether substituents.17... 

PENTAHYDRIDOBIS(TRICYCLOHEXYLPHOSPHINE)-IRIDIUM(V) AND TRIHYDRIDOTRIS(TRIPHENYLPHOS-PHINE)IRIDIUM(ni)... 

Tricyclohexylphosphine Complexes of Ruthenium, Rhodium, and Iridium and Their Reactivity Toward Gas Molecules... 

Since 1977 several papers on rhodium and iridium systems relevant to the present work have appeared (10-16). One of these by Vrieze s group (15), which reported partial dehydrogenation of tricyclohexylphosphine coordinated to iridium(I) and rhodium(I), overlapped with some of our studies which were reported almost simultaneously at a conference (17). 

Tricyclohexylphosphine was obtained from Strem Chemicals. Ruthenium, rhodium, and iridium trichlorides were obtained as trihydrates from Johnson, Matthey Limited. Iridium tetrachloride was obtained from Platinum Chemicals. The precursor complexes [RhCl(COD)]2 (57), [RhCl(COT)2]2 (58), [RhCl(C2H4)2]2 (59), [IrCl(COD)]2 (14), and [HIrCl2-(COD)]2 (31) were made according to the literature procedures. 

Trans -Carbonylchlorobis(tricyclohexylphosphine)iridium (I), IrCl(CO)(PCy3)2. Solid PCy3 (0.2 g) and LIrCl(COT)2]2 (0.1 g) were placed under a CO atmosphere. The mixture turned blackish green, but when 10 mL toluene was added the stirred mixture became lighter and after 2 hr it precipitated a yellow solid that was collected and washed with ethanol (80%). We found carbon, 54.2 hydrogen, 8.2. C37H660ClP2Ir requires carbon, 54.4 hydrogen, 8.2. 

Carbon ylchlorodihydridobis(tricyclohexylphosphine) iridium-(III), H2IrCl(CO)(PCy3)2, Complex 10. This complex was prepared from Complex 7 by the same procedure that 5 was prepared from 3. We found carbon, 54.6 hydrogen, 8.3. C37H6aOClP2Ir requires carbon, 54.3 hydrogen, 8.4. 

The complex has enjoyed relatively little use in organic synthesis. For iridium-catalyzed homogeneous hydrogenation of alkenes, Crabtree s iridium complex ((1,5-Cycloocta-diene)(tricyclohexylphosphine)(pyridine)iridium(I) Hexafluoro-phosphate) is generally preferred, although this readily prepared Ir complex is active. It is more reactive than its rhodium counterpart in the catalytic isomerization of butenyl- to allylsilanes. ... 

The next breakthrough was obtained when iridium was used instead of rhodium. This idea was inspired by results from Crabtree who had described an extraordinarily active Ir-tricyclohexylphosphine-pyridine catalyst that was able to hydrogenate even tetra-substituted C=C bonds. For the MEA imine hydrogenation very good ee values were obtained with an Ir-bdpp catalyst in the presence of iodide ions (ee 84% at 0°C) but the activity was disappointing. Turnover numbers (ton) of up to 10000 and tof numbers of 250/h (100 bar and 25 °C) but somewhat lower ee values were obtained with Ir-diop-iodide catalysts [10, 11], A major problem with these new Ir-diphosphine catalysts was an irreversible catalyst deactivation. 

Based on these results, we realized that the catafyst activity would be the critical issue. Therefore, F. Spindler, who was responsible for the project, was very much attracted 1 the results of Crabtree et aL who described an extraordinarily active Ir / tricyclohexylphosphine / pyridine catafyst that was able to hydrogenate even tetra substituted C=C bonds [11]. He decided to give iridium catafysts a try even though he was aware of their frist deactivation and... 

The olefin complexes of iron, nickel, rhodium, and iridium described in this chapter have found broad application in the synthesis of phosphine, phosphite, and carbonyl derivatives of these metals. In Chapter Two, the synthesis of another labile olefin complex, (ethylene)bis(tricyclohexylphosphine)nickel, is described as an initial step in synthesis of a complex of dinitrogen. 

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