Heterodinuclear M1M2 Complexes (M1=Ni, Pd, Pt; M2=Rh, Ir) Supported by a Tetradentate Phosphine Ligand and Their Application for Hydrosilylation

Abstract

AbstractA new series of cationic heterodinuclear complexes, [M1M2Cl2(meso‐dpmppp)(RNC)2]PF6 (M1=Ni, M2=Rh, R=tBu (1 a); M1=Pd, M2=Rh, R=tBu (2 a), Xyl (2 b); M1=Pt, M2=Rh, R=tBu (3 a), Xyl (3 b); M1=Pd, M2=Ir, R=tBu (4 a)), supported by a tetradentate phosphine ligand, meso‐Ph2PCH2P(Ph)(CH2)3P(Ph)CH2PPh2 (meso‐dpmppp), were synthesized by stepwise reactions of meso‐dpmppp with NiCl2 ⋅ 6H2O or MCl2(cod) (M=Pd, Pt), forming mononuclear metalloligands of [M1Cl2(meso‐dpmppp)], and with [M2Cl(cod)]2 (M2=Rh, Ir) and RNC (R=tBu, Xyl) in the presence of [NH4][PF6]. The related neutral PdRh complex, [PdRhCl3(meso‐dpmppp)(XylNC)] (5), was also prepared. The structures of 1–5 were determined by X‐ray analyses to contain two square planar d8 metal centers with face‐to‐face arrangement, where meso‐dpmppp supports M1 and M2 metal ions in cis/trans‐P,P coordination mode, combining cis‐{M1P2Cl2} and trans‐{M2P2(CNR)2} units. Complexes 1–4 showed an intence characteristic absorption around 422–464 nm derived from RhI→RNC MLCT transition (HOMO→LUMO+1), which are influenced by changing M1 (NiII, PdII, PtII) metal ions since HOMO composed of dσ* orbitals appreciably destabilized by changing M1 from Ni to Pd, and Pt. The electronic structures of 1 a–4 a were investigated on the basis of DFT calculations and NBO analyses to show weak but noticeable d8–d8 metallophilic interaction as empirical dispersion energy of 0.9–1.5 kcal/mol without M1–M2 covalent bonding interaction. In addition, 1–5 were utilized as catalysts for hydrosilylation of styrene, and the NiRh complex 1 a was found to show higher activity and chemo‐ and regioselectivity compared with 2–5.