Physical studies on solutions of zerovalent nickel, palladium, and platinum complexes containing ethylene and arylphosphine ligands (L = P(C6H5)3, POC6H4CH3)3, or P(m-C6H4CH3)3) are reported. The ML4 complexes are substantially dissociated into ML3 and L at 25°; the PtL4 complexes have, however, been detected by 31P nmr at -90°. No dissociation of ML3 or (C2H4)ML2 complexes was detected. Equilibrium constants in benzene at 25°are reported for MLg + C2H4 (C2H4)ML2 + L and found to be 300, 0.12, and 0.013 for M = Ni,
Stable solid adducts of substituted pyridines (Rpy) with HSiCl(3) and HSiCl(2)Me were prepared in high yields under aprotic and anaerobic conditions at room temperature. The octahedral complexes of HSiCl(3) underwent dismutation reactions in polar solvents. In contrast, the HSiCl(2)Me(Rpy)(2) adducts were not susceptible to dismutation under comparable conditions, but they tended to dissociate more easily because of the reduced Lewis acidity of HSiCl(2)Me relative to HSiCl(3). The bonding between silicon and its surrounding ligands is highly ionic, as can be seen from QTAIM and charge distribution analyses. (29)Si CP/MAS spectra in combination with quantum-chemical calculations show that the lowest shielding is along the Cl-Si-Cl axis. The other two components of the shielding tensor are oriented along the N-Si-N and H-Si-Cl/Me axes. It is known that many reactions of (hydrido)chlorosilanes are catalyzed by pyridine bases. Therefore, the results presented here provide a basis for better control of these reactions, especially chlorine substitution and hydrosilylation.
The tridentate title ligand was found to act as an (NeqNaxOeq) = (Namide,Nimine,Ophenolate) ligand as well
as an (NaxNeqOax) ligand in pentacoordinate silicon complexes depending on the substituents at the Si
atom. Its two notably different coordination modes in (NeqNaxOeq)Si(CH2)3 and (NaxNeqOax)SiPhMe were
studied with X-ray structure analysis as well as 29Si CP/MAS NMR spectroscopy together with quantum
chemical calculations of geometry and NMR chemical shielding tensors.
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