Beiträge zur chemie der halogensilan-addukte XV. 2,2′-bipyridin- und 1,10-phenanthrolin-komplexe von halogendisilanen und Si3Cl8

A series of mono-bipy and -phen complexes (bipy = bipyridine, phen = phenanthroline) of the perhalodisilanes, Si₂F₆, Si₂Cl₆ and Si₂Br₆, mixed methylhalodisilanes (Si₂Me_nX_6?n, X = Cl, I; n = 2,3) and Si₃Cl₈ · bipy have been prepared by reaction of the components, and have been characterized. $\text{1}\text{1}$ complexes are obtained exclusively.The structures of all complexes involve coordination of the base to the more acidic silicon and perpendicular alignment of the SiSi axis on the plane of the ligand. This may be rationalised in terms of steric requirements of the different groups, the more demanding groups occupying the sterically more favorable positions vertical to the plane of the ligand. For Si₃Cl₈ · bipy, spectroscopic and chemical evidence suggests bipy-coordination to the center silicon. PMR investigations of the dissociation equilibria of the complexes in solution led to determination of the heats of formation of four of the complexes and to a qualitative estimation of the relative acceptor strengths of several disilanes. Contrary to expectation, silyl groups increase the acceptor strength of silicon considerably and in the order SiMe₃ < SiMe₂Cl < SiMeCl₂ < SiCl₃. The effect of a SiMe₃, substituent group may be compared to that of Cl. Methylchlorosilyl groups may exceed the effect of Cl as indicated by the increase in acceptor strength in the sequence (R =) Me < Ci < SiMe₂Cl < SiMeCl₂ for the acceptor RSiCl₂Me. Si₃Cl₈ is the strongest acceptor in the series. Assuming the structural suggestion for Si₃Cl₈ · bipy (center coordination) to be correct an increase in acceptor strength is indicated in the sequence SiCl₃(Si₂Cl₅) < SiCl₂(SiCl₃)₂ (Si = coordinating center). This may be interpreted mainly in terms of charge accepting capacity of the polarisable silyl groups. Another interesting sequence of acceptor strengths measured in this work is 1,1,2-Si₂Me₃F₃, 1,2-Si₂Me₂F₄ < Si₂Me₃Cl₃ < 1,2-Si₂Me₂Cl₄, showing fluorodisilanes to be weaker acceptors than chlorodisilanes. This result is compared to the heats of formation of SiX₄ · 2py complexes.