| Abstract
| - The iridium allyl complex [PhB(CH2PiPr2)3]IrH(η3-C8H13) (3) undergoes facile β-hydride elimination of 1,3-cyclooctadiene, acting exclusively as a source of “[PhBP3‘]IrH2”. It reacts with secondary silanes (H2SiR2, with R = Et, Ph) to produce the silyl-capped trihydride complexes [PhBP3‘]Ir(H)3(SiHR2). At elevated temperatures, the Rh(I) complex [κ2-PhBP3‘]Rh(PMe3)2 (10) undergoes dissociation of both PMe3 ligands, accompanied by the reversible migration of a ligand methylene group from B to Rh.
- The synthesis, characterization, and reactivity of zwitterionic rhodium and iridiumcomplexes containing the tris(phosphino)borate ligand [PhB(CH2PiPr2)3]- ([PhBP3‘]-) arereported. The allyl complexes [PhBP3‘]IrH(η3-C8H13) (3) and [PhBP3‘]IrH(η3-C3H5) (4) wereprepared by reaction of [PhBP3‘]Li(THF) (2) with the corresponding [(alkene)2IrCl]2 complex.Complex 3 reacted with secondary silanes (H2SiR2, with R = Et, Ph) to give silyl-cappedtrihydride complexes of the type [PhBP3‘]IrH3(SiHR2) (R = Et, 5; Ph, 6) with concomitantβ-hydride elimination of 1,3-cyclooctadiene. Complex 5 underwent H/D exchange with D2 toincorporate deuterium into both the Ir−H and Si−H positions. The reaction of 5 with 1equiv of PMe3 resulted in elimination of Et2SiH2 to form the corresponding dihydride complex,[PhBP3‘]Ir(H)2(PMe3) (7). Complexes of the type [PhBP3‘]Ir(H)2(L) (L = PMe3, 7; PH2Cy, 8;CO, 9) could also be prepared directly by the reaction of 3 with L. The observed reactivityof [PhBP3‘]Ir complexes is compared with that of the related [PhB(CH2PPh2)3]- ([PhBP3]-)species. The Rh(I) complexes [κ2-PhBP3‘]Rh(PMe3)2 (10) and [PhBP3‘]Rh(CO)2 (11) are alsoreported. Variable-temperature 1H and 31P NMR experiments did not reveal evidence forκ2−κ3 interconversion for 10 and 11. However at elevated temperatures 10 was found toengage in a dynamic equilibrium process involving dissociation of the PMe3 ligands andreversible migration of a −CH2 group in the ligand backbone from B to Rh. The product ofthis migration, (12), was prepared independently by thereaction of 2 with [RhCl(C2H4)2]2 and was structurally characterized by X-ray crystallography.Complex 10 reacted with H2 to give the oxidative addition product [PhBP3‘]Rh(H)2(PMe3)(13). The reaction of 10 with 1 equiv of Ph2SiH2 resulted in loss of a ligand arm to give thebis(phosphino)borane complex [PhB(CH2PiPr2)2]Rh(H)2(SiHPh2)(PMe3) (14). Complex 11reacted with H2 in the presence of 1 equiv of Me3NO to give the oxidative addition product[PhBP3‘]Rh(H)2(CO) (15), with concomitant liberation of Me3N.
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