Donor-Stabilized Silyl Cations. 5. Comparison between Mono- and Binuclear Siliconium Chelates¹

Abstract

Binuclear hexacoordinate silicon chelates have been prepared and shown to have octahedral structure by X-ray crystallography. Their ionization in CD2Cl2 solution has been studied by 29Si NMR spectroscopy. Only one Si−Cl bond in 5a−c ionizes at low temperature to form the monosiliconium bis-chelates 11a−c. Use of a more acidic solvent, CHFCl2, facilitated the second ionization step to the disiliconium dichloride 12c. Replacement of the chloro ligands by better leaving groups (triflate, bromide, or iodide) caused complete ionization (7a−c, 8c, 9c) at room temperature. Crystal structure analyses of the binuclear siliconium triflates 7a,b show a square-pyramid geometry around the silicon atoms, with the ethylene bridge at the apex.

Hypercoordinate Silicon Complexes Based on Hydrazide Ligands. A Remarkably Flexible Molecular System

“…Even formation of dications has been reported in dinuclear silicon complexes 17 and 18 , where the formal positive charges are separated from each other by only three bonds. Ionization is facile in the dichloro complex 17 , with oxygen donors, but requires replacement of the chloro ligands by the more effective anions (Br, I, TfO) in 18 , with its Me 2 N ligands …”

An Unexpected, Sterically Driven, Methyl Halide Elimination in Pentacoordinate Siliconium Halide Salts: Silicon Complexes with Equatorial Nitrogen Coordination

“…This is the common geometry for pentacoordinate bischelates with two nitrogen donor ligands 8. The N‐Si‐N angle gradually decreases along the series, while the O‐Si‐O angle increases, via a distorted TBP ( 2 a , ∼65 % TBP1→SP),6c through pure square planar (SP) geometry ( 8 ; evidenced by the N‐Si‐N≃O‐Si‐O angles),6e then through another distorted TBP with axiallike oxygen ligands ( 6 a ), and finally to the TBP2 geometry of 7 b , which is essentially an inverted TBP in which axial and equatorial groups have exchanged their positions. Throughout this process the t Bu group acts as a “pivot” for the pseudorotation.…”

5 Carbon, silicon, germanium, tin and lead

“…108 Similar ionisation processes are also seen in the corresponding complexes of N-isopropylidene-NЈ-(O-trimethylsilyl) hydroxides, 109 and linked dinuclear complexes. 110 The coordination chemistry of dialkylhydroxylamides has been expanded by the report of the preparation of Ge(ONMe 2 ) from germanium() chloride and the lithium salt of dimethylhydroxylamide. The complex exhibits a "4 ϩ 4" coordination geometry with short contacts to the oxygen atoms and longer contacts to the nitrogen atoms.…”