CHLOROTRIS(TRIPHENYLPHOSPHINE)IRIDIUM(I) AND RELATED COMPLEXES . OXIDATIVE ADDITION REACTIONS AND HYDROGEN ABSTRACTION FROM COORDINATED LIGAND

The preparation, properties, and reactions of a series of complexes of general formula IrClL3 are described, where L is (C6H5)3P, (C6D5)3P, (o-DC6H4)3P, (p-FC6H4)3P, (p-CH3OC6H4)3P, (p-CH3C6H4)3P, (C6H5)3As, and (C6H5)3Sb. The complex IrCl(Ph3P)3 differs from the analogous rhodium compound in two principal ways: (i) triphenylphosphine is not so readily lost in solution; (ii) the reaction with hydrogen is irreversible and occurs without displacement of triphenylphosphine, so that IrCl(Ph3P)3 does not function as a homogeneous hydrogenation catalyst. Reactions with CO, PF3, NO, and HCl are described. Reaction of IrCl(Ph3P)3 with chlorine gives initially an iridium(III) complex IrCl3(Ph3P)2, which appears to be five-coordinate in solution, and with excess chlorine or nitrosyl chloride the iridium(IV) complex IrCl4(Ph3P)2 is formed. This and the analogous triphenylarsine complex are characterized by far-infrared, magnetic susceptibility, and esr measurements. Metal-chlorine stretching frequencies are reported for the new compounds and used where possible to assign stereochemistries. Unlike their rhodium analogs, the iridium(I) complexes IrClL3 isomerize on heating in solvents to octahedral hydrido aryls of iridium(III), the stereochemistry of which is inferred from infrared and proton nmr measurements. It is shown that the isomerization arises by transfer of one hydrogen atom from the ortho position of an aromatic ring of the coordinated ligand to the metal, with the formation of a metal-carbon σ bond at the ortho position. In the triarylphosphine series, the rate of isomerization depends on the substituent para to phosphorus in the order F < H < OCH3 < CH3. On the basis of the small kinetic isotope effect, a three-center mechanism is suggested for the hydrogen transfer. The reactions of the hydrides are generally similar to but slower than those of the parent iridium(I) complexes. Some of these reactions apparently proceed via the iridium(I) complex formed by return of the hydrogen to the ligand. The iridium(I)-iridium(III) tautomerism is compared with similar situations involving Fe(0)-Fe(II) and Ru(0)-Ru(II), and a brief analogy is drawn with metal-catalyzed H-D exchanges in aromatic hydrocarbons.