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

The synthesis and characterization of a series of Ni, Co, and Fe complexes bearing a tridentate bis(phosphino)silyl ligand (κ 3 -(2-Ph 2 PC 6 H 4 ) 2 SiMeH, [PSiP]-H, 1 ) are reported. 1 reacted with Ni(PMe 3 ) 4 to afford the mononuclear nickel(0) complex [η 2 (Si–H)-PSiP]Ni(PMe 3 ) ( 2 ). The halogeno nickel complexes [PSiP]Ni(X)(PMe 3 ) (X = Cl ( 3 ), Br ( 4 ), I ( 5 )) were synthesized in the reactions of 2 with Me 3 SiCl or MeHSiCl 2, EtBr, and MeI. Complex 2 underwent ligand substitution of PMe 3 by CO to give [η 2 (Si–H)-PSiP]Ni(CO) ( 6 ). Complex 3 reacted with NaOMe to deliver [PSiP]Ni(OMe)(PMe 3 ) ( 7 ) through anionic ligand substitution, while the neutral ligand replacement of PMe 3 by CO in 3 afforded the rare hexacoordinate 20-electron nickel(II) complex [PSiP]Ni(Cl)(CO) 2 ( 8 ). Unexpectedly, reaction of 1 with NiMe 2 (PMe 3 ) 3 produced the tetracoordinate nickel(0) complex [Me 2 PSiP] 2 Ni ( 9 ). The complex [Me 2 PSiP]Ni(CO) 2 ( 10 ) was acquired from 9 after the substitution of one [PSiP] ligand by two carbonyl ligands. 1 reacted with Co(PMe 3 ) 4 or CoCl(PMe 3 ) 3 to afford the hydrido cobalt(II) complex [PSiP]CoH(PMe 3 ) ( 11 ) or hydrido cobalt(III) complex [PSiP]Co(H)(Cl)(PMe 3 ) ( 13 ). Complex 12, [PSiP]Co(H)(I)(PMe 3 ), 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(PMe 3 ) 2 ( 14 ) via reductive elimination. The simple anhydrous inorganic salt NiCl 2 or CoCl 2 could also react with 1 in the presence of PMe 3 to form the corresponding silyl complexes 3 and [PSiP]Co(Cl)(PMe 3 ) ( 15 ) via Si–H bond cleavage. 1 reacted with Fe(PMe 3 ) 4 to form the hexacoordinate octahedral hydrido iron(II) complex [PSiP]Fe(H)(PMe 3 ) 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.