Pentacoordinate silicon complexes ligand exchange

Ligand Exchange via Coordinative Si-N Bond Cleavage and Pseudorotation in Neutral Pentacoordinate Silicon Complexes... 

Summary Introduction of a chiral ligand to a series of pentacoordinate silicon complexes led to the assignment of two intramolecular rate processes Si-N cleavage and pseudorotation. Linear correlations between and Si chemical shifts of the complexes, as well as between the latter and the N-methyl exchange barriers were attributed to variation in strength of N—>Si coordination. 

Penta- and hexacoordinate silicon complexes often show very complex ligand exchange reactions, which have been the subject of intense studies [2-5]. In the present paper we analyze the ligand exchange processes and H, N, and Si NMR chemical shifts of a series of pentacoordinate complexes in a search for a better understanding of the exchange mechanisms. Compounds 2a-2h were readily prepared by the reaction shown in Eq. 1. 

A complex system of equilibria of both Si-Cl vs. Si-N dismutation and intramolecular Si-N exchange was observed with NMR spectroscopy in Si(pz )4 and Si(pz )3Cl [106]. The reactirai of Me3Si(pz ) with H2SiCl2 leads to the xmexpected formation of a silicon complex with three silicon atoms [134]. The lateral silicon atoms are pentacoordinated the central silicon atom is hexacoordinated. Furthermore, it was found that the reactimi of HSiCl3 with 3,5-dimethylpyrazole in acetonitrile gives 3,5-dimethylpyrazolyl siUcmi complexes where one (96) or two molecules acetonitrile (97) have been inserted into the braid between silicon and the 3,5-dimethylpyrazolyl ligand (see Scheme 28) [134]. 

---