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 (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.

Activation of Molecular Hydrogen and Oxygen by PSiP Complexes of Cobalt

“…While the one electron reduction of Co II halide complexes proved facile, access to Co III species supported by Cy‐PSiP ligation was significantly more challenging. This is in contrast to observations by Sun and co‐workers, who have reported on readily isolable Co III complexes supported by closely related diphenylphosphino PSiP derivatives. Attempted oxidative addition reactions involving (Cy‐PSiP)Co(PMe 3 )N 2 were generally unsuccessful, with the sole exception of H 2 , which reacted to afford the dihydride complex (Cy‐PSiP)Co(PMe 3 )(H) 2 .…”

“…The X‐ray crystal structure of 1‐PMe 3 revealed that this complex adopts distorted trigonal bipyramidal geometry in the solid state, with the chloride ligand and the silyl donor bound in the apical positions, and the phosphines occupying the equatorial positions. This is in contrast to the structure of (Ph‐PSiP)CoCl(PMe 3 )[10a] and the related bis(diphenylphosphanyl)silyl complex [κ 3 ‐C 6 H 4 (Ph 2 PCH 2 N) 2 SiMe]CoI(PMe 3 ),[10b] in which the PMe 3 ligand is coordinated in the apical position trans to Si. Solution magnetic moment measurements for 1‐PMe 3 and 2‐PMe 3 (room temperature, [D 6 ]benzene) resulted in µ eff values of 1.89 and 1.65 µ B , respectively, consistent with an S = 1/2 magnetic ground state in each case.…”

“…Kim, Lee and co‐workers reported on the conversion of [ i Pr‐P(η 1 ‐SiH)P]CoBr 2 to ( i Pr‐PSiP)CoBr in the presence of base,[4i] and Nishibayashi and co‐workers reported on the synthesis of (Cy‐PSiP)Co(PR 3 )N 2 species and their activity in catalytic N 2 reduction. [4k], …”

Lewis acid promoted dehydration of amides to nitriles catalyzed by [PSiP]‐pincer iron hydrides

“…This indicates that two PMe 3 ligands are chemically different. The spectroscopic characteristics are comparable with those of complex 1 . In the 31 P NMR spectrum of 4 a “dt” peak at 1.7 and a multiplet peak at 6.3 ppm for the two PMe 3 ligands and a doublet at 88.7 ppm for –P i Pr 2 groups were recorded in the integral ratio of 1 (PMe 3 ): 1 (PMe 3 ): 2 (‐P i Pr 2 ).…”

“…Complexes 1–3 were prepared according to the literature procedures . Complex 4 was obtained from the combination of bis( o ‐(diisopropylphosphino)phenyl)methylsilane with Fe (PMe 3 ) 4 in THF at 0 °C under Ar atmosphere (Scheme ).…”