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

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Group 9 and 10 mixed-metal complexes, [M1M2Cl2(meso-dpmppp)(RNC)2][PF6] were synthesized. Their electronic structures and d8-d8 interaction were investigated. In addition, they were utilized for catalytic hydrosilylation of styrene. Among them, the NiRh complex was found to show higher activity and chemo- and regioselectivity compared with the other complexes.


Abstract

A new series of cationic heterodinuclear complexes, [M1M2Cl2(meso-dpmppp)(RNC)2]PF6 (M1=Ni, M2=Rh, R= t Bu (1 a); M1=Pd, M2=Rh, R= t Bu (2 a), Xyl (2 b); M1=Pt, M2=Rh, R= t Bu (3 a), Xyl (3 b); M1=Pd, M2=Ir, R= t Bu (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= t Bu, Xyl) in the presence of [NH4][PF6]. The related neutral PdRh complex, [PdRhCl3(meso-dpmppp)(XylNC)] (5), was also prepared. The structures of 15 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 14 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 a4 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, 15 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 25.

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