Neutral and Cationic Complexes of Silicon(IV) Halides with Phosphine Ligands

[Image: see text] The reaction of SiI(4) and PMe(3) in n-hexane produced the yellow salt, [SiI(3)(PMe(3))(2)]I, confirmed from its X-ray structure, containing a trigonal bipyramidal cation with trans-phosphines. This contrasts with the six-coordination found in (the known) trans-[SiX(4)(PMe(3))(2)] (X = Cl, Br) complexes. The diphosphines o-C(6)H(4)(PMe(2))(2) and Et(2)P(CH(2))(2)PEt(2) form six-coordinate cis-[SiI(4)(diphosphine)], which were also characterized by X-ray crystallography, multinuclear NMR, and IR spectroscopy. Reaction of trans-[SiX(4)(PMe(3))(2)] (X = Cl, Br) with Na[BAr(F)] (BAr(F) = [B{3,5-(CF(3))(2)C(6)H(3)}(4)]) produced five-coordinate [SiX(3)(PMe(3))(2)][BAr(F)], but while Me(3)SiO(3)SCF(3) also abstracted chloride from trans-[SiCl(4)(PMe(3))(2)], the reaction products were six-coordinate complexes [SiCl(3)(PMe(3))(2)(OTf)] and [SiCl(2)(PMe(3))(2)(OTf)(2)] with the triflate coordinated. X-ray crystal structures were obtained for [SiCl(3)(PMe(3))(2)][BAr(F)] and [SiCl(2)(PMe(3))(2)(OTf)(2)]. The charge distribution across the silicon species was also examined by natural bond orbital (NBO) analyses of the computed density functional theory (DFT) wavefunctions. For the [SiX(4)(PMe(3))(2)] and [SiX(3)(PMe(3))(2)](+) complexes, the positive charge on Si decreases and the negative charge on X decreases going from X = F to X = I. Upon going from [SiX(4)(PMe(3))(2)] to [SiX(3)(PMe(3))(2)](+), i.e., removal of X(–), there is an increase in positive charge on Si and a decrease in negative charge on the X centers (except for the case X = F). The positive charge on P shows a slight decrease.