Synthesis and Reactivity of Silyl Iron, Cobalt, and Nickel Complexes Bearing a [PSiP]-Pincer Ligand via Si–H Bond Activation

Abstract

The synthesis and characterization of a series of Ni, Co, and Fe complexes bearing a tridentate bis(phosphino)silyl ligand (κ3-(2-Ph2PC6H4)2SiMeH, [PSiP]-H, 1) are reported. 1 reacted with Ni(PMe3)4 to afford the mononuclear nickel(0) complex [η2(Si–H)-PSiP]Ni(PMe3) (2). The halogeno nickel complexes [PSiP]Ni(X)(PMe3) (X = Cl (3), Br (4), I (5)) were synthesized in the reactions of 2 with Me3SiCl or MeHSiCl2, EtBr, and MeI. Complex 2 underwent ligand substitution of PMe3 by CO to give [η2(Si–H)-PSiP]Ni(CO) (6). Complex 3 reacted with NaOMe to deliver [PSiP]Ni(OMe)(PMe3) (7) through anionic ligand substitution, while the neutral ligand replacement of PMe3 by CO in 3 afforded the rare hexacoordinate 20-electron nickel(II) complex [PSiP]Ni(Cl)(CO)2 (8). Unexpectedly, reaction of 1 with NiMe2(PMe3)3 produced the tetracoordinate nickel(0) complex [Me2PSiP]2Ni (9). The complex [Me2PSiP]Ni(CO)2 (10) was acquired from 9 after the substitution of one [PSiP] ligand by two carbonyl ligands. 1 reacted with Co(PMe3)4 or CoCl(PMe3)3 to afford the hydrido cobalt(II) complex [PSiP]CoH(PMe3) (11) or hydrido cobalt(III) complex [PSiP]Co(H)(Cl)(PMe3) (13). Complex 12, [PSiP]Co(H)(I)(PMe3), could be obtained from the reaction of MeI with 11 or 13. Treatment of 13 with 1 equiv of MeLi or n-BuMgBr in THF resulted in the clean formation of cobalt(I) complex [PSiP]Co(PMe3)2 (14) via reductive elimination. The simple anhydrous inorganic salt NiCl2 or CoCl2 could also react with 1 in the presence of PMe3 to form the corresponding silyl complexes 3 and [PSiP]Co(Cl)(PMe3) (15) via Si–H bond cleavage. 1 reacted with Fe(PMe3)4 to form the hexacoordinate octahedral hydrido iron(II) complex [PSiP]Fe(H)(PMe3)2 (16). The molecular structures of complexes 2–5, 10, 12, 13, 15, and 16 were determined by X-ray single crystal diffraction. 16 has excellent catalytic reactivity for the reduction of aldehydes and ketones.