BINUCLEAR OXIDATIVE ADDITIONS OF SILANES TO [IR2(CO)3(PH2PCH2PPH2)2] TO YIELD SILYLENE-BRIDGED DIHYDRIDE COMPLEXES

The complex [Ir2(CO)3(dppm)2] (1; dppm = Ph2PCH2PPh2) reacts with the secondary silanes Me2SiH2, Et2SiH2, and Ph2SiH2 to give products of the form [Ir2(H)2(CO)2(μ-SiR2)(dppm)2] (R = Me (2), Et (3), Ph (4)). These silylene-bridged species are found to be fluxional at room temperature. Reaction of 1 with PhSiH3 yields [Ir2(H)2(CO)2(μ-SiHPh)(dppm)2] (5), which is not fluxional. The X-ray structures of 4 and 5 have been determined and show that both species have bridging silylene groups, terminal hydride ligands, and eis arrangements of the phosphine ligands about each metal center. Compound 4 displays a twisted configuration showing substantial steric interaction between the μ-diphenylsilylene group and the dppm phenyls, suggesting the genesis for fluxionality of this species. In contrast, species 5 appears to be relatively free of such steric encumbrance, with the phenyl group of the bridging phenylsilylene unit held away from the dppm phenyl groups. In this complex the dppm ligands are disposed in an eclipsed manner about the two metals. The similarities of the low-temperature1H and31P(1H) NMR spectra of 2 and 3 to those of 5 at room temperature indicate that a structure similar to that of 5 may be the low-temperature configuration adopted by the dialkylsilylene-bridged dimers. Complex 4 crystallizes with two THF solvent molecules in the trigonal space group P3121 with a = 13.295 (3) Å, c = 32.286 (4) Å, and Z = 3. This structure was refined to R-0.038 and Rw = 0.039 on the basis of 3288 unique observed reflections and 229 parameters varied. Complex 5 crystallizes with two THF solvent molecules in the monoclinic space group P21/c with a = 12.425 (3) Å, b = 20.282 (4) Å, c = 26.505 (3) Å, β = 97.61 (1)°, and Z = 4. This structure was refined to R = 0.061 and Rw= 0.087 on the basis of 4697 unique observed reflections and 334 parameters varied. © 1990, American Chemical Society. All rights reserved.