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

Abstract

Sterically hindered pentacoordinate tert‐butylsiliconium halide complexes undergo methyl halide elimination. The products have one covalent and one dative NSi bond, both in the unprecedented equatorial position. A complete pseudorotation coordinate is demonstrated with suitable crystal structures.

Donor-Stabilized Silyl Cations. 8. Carbon−Carbon Bond Formation through a Novel Interchelate Molecular Rearrangement in Pentacoordinate Siliconium-Ion Salts1

“…The reaction is quite general and is not restricted to isopropylideneimino complexes 2 , as demonstrated by the variety of differently substituted diiminosiliconium complexes listed in Table , including the cyclopentylideneimino complexes 6 → 7 (eq 4). This skeletal rearrangement is another case of the unusual reactivity of siliconium ion salts, following the reported methyl halide elimination (eq 1) . It is interesting to note that in both of these reactions one of the N→Si dative bonds is converted to a regular covalent bond (evidenced by the tricoordinate nitrogen).…”

“…Within the chemistry of hypercoordinate silicon complexes, which has attracted considerable interest recently, the least studied subgroup consists of pentacoordinate siliconium ion salts. 2d, These were described as highly reactive; 3c,d however, little has been reported about their reactions. We have developed a straightforward synthesis for pentacoordinate siliconium ion salts ( 1 ) and have reported that sterically congested 1 (X = t -Bu, cyclohexyl) undergoes facile nucleophilic attack by the halide anion at one of the N -methyl groups, to eliminate methyl halide (eq 1) …”

A Disilane with a Hypercoordinate Silicon Atom: Coordination of an Imine Ligand versus Si−Si Bond Splitting

“…The Si−N bond [Si1−N1 1.888(1) Å] in 4 is much shorter than in most other examples of neutral pentacoordinate Si complexes with a N→Si dative bond. A neutral pentacoordinate silicon complex with a notable short dative N→Si bond [1.9496(9) Å] was reported by Kost et al The Si−Si distance in 4 [2.3532(6) Å] is in the range of common disilane bond lengths (compare to 2.358(1) Å in 1 4 ). Surprisingly, the Si−C bonds [Si1−C21 1.866(2) Å, Si2−C22 1.865(2) Å] have the same length despite the different coordination numbers of the silicon atoms.…”

Competitive Molecular Rearrangements in Hexacoordinate Cyano-Silicon Dichelates

“…Hexacoordinate silicon dichelates based on hydrazide ligands and sharing the SiN 2 O 2 XY ligand environment (X, Y = alkyl, halogen) react in a variety of ways,1p all of which lead from hexa- to pentacoordination, and usually reduce the number of dative N−Si bonds from two to one. These reactions include equilibrium ionic dissociation 2 and methyl halide elimination, and when the donor group is a ketene−imine, an internal aldol-type condensation between the imine functions takes place . In the present work a new reaction of this family has been studied, the 1,3-shift of a cyano monodentate ligand from silicon to the imino carbon.…”