Irreversible Rearrangement in Hexacoordinate Silicon Complexes:  From Neutral Bis(N→Si) Chelates to Mono(N→Si) Zwitterionic λ⁶-Silicates

Abstract

The reaction of (chloromethyl)trichlorosilane (7) with O-trimethylsilylated N,N-dimethylhydrazides yields initially under kinetic control, in nearly quantitative yields, a neutral hexacoordinate bis(NfSi) chelate, bis(N-(dimethylamino)acylimidato-N,O)chloro(chloromethyl)silicon(IV) (8a-c). Upon heating, the octahedral complexes 8 are quantitatively and irreversibly converted to the isomeric hexacoordinate chelates zwitterionic λ 6 -silicates 9a-c, (N-(dimethylamino). This molecular rearrangement is rather unusual, since it involves chelatering expansion from the common five-membered ring to a six-membered ring in the thermodynamically favored product 9. 8b and 9b were characterized by X-ray crystal analyses and in solution by their 1 H, 13 C, and 29 Si NMR spectra. The analogous compounds 8a,c and 9a,c were characterized by the respective analogy of their NMR spectra. Both 8b and 9b have slightly distorted octahedral geometries around the central silicon atom. Both series of chelates 8 and 9 undergo ligand-site exchange processes, observed by the coalescence of signals due to diastereotopic N-methyl and/or CH 2 groups. Each compound (of both series) undergoes two consecutive rate processes: in 8 this sequence of exchange processes is analogous to previously reported stereomutations through a bicapped-tetrahedral intermediate or transition state; in 9 the first (lower barrier) process is a nitrogen-silicon dissociationrecombination, and the high-barrier process is an inversion of configuration at the silicon center.We have recently utilized the reaction of O-(trimethylsilyl)-N,N-dimethylhydrazides (1) with polyhalosilanes as a convenient method for the synthesis of a variety of different penta-and hexacoordinate silicon complexes with NfSi coordination (eq 1). 1-9 1 functions as a precursor for five-membered NfSi chelate rings.On the other hand, when 1 was allowed to react with (chloromethyl)dimethylchlorosilane (4; eq 2), OfSi coordinated complexes with five-and six-membered chelate cycles (6 and 5, respectively) were obtained. 10-13 † Ben-Gurion University. Kalikhman, I.; Krivonos, S.; Stalke, D.; Kottke, T. J. Am. Chem. Soc. 1998, 120, 4209. (7) Mozzhukhin, A. O.; Antipin, M. Yu.; Struchkov, Yu. T.; Gostevskii, B. A.; Kalikhman, I. D.; Pestunovich, V. A.; Voronkov, M. G. Bannikova, O. B.; Petuchov, L. P.; Pestunovich, V. A.; Voronkov, M. G. Dokl. Akad. Nauk SSSR 1986, 287, 870. (11) Kalikhman, I. D.; Pestunovich, V. A.; Gostevskii, B. A.; Bannikova, O. B.; Voronkov, M. G. J. Organomet. Chem. 1988, 338, 169. (12) Macharashvili, A. A.; Shklover, V. E.; Struchkov, Yu. T.; Gostevskii, B. A.; Kalikhman, I. D.; Bannikova, O. B.; Voronkov, M. G.; Pestunovich, V. A.

Donor-Stabilized Silyl Cations 4: N-Isopropylidene Hydrazides, Novel Bidentate Ligands for Penta- and Hexacoordinate Silicon Chelates1

“…The crystal structure stands in sharp contrast to the analogous chelate 5 with the N -(dimethylamino)acylimidato- N ‘ , O ligand, in which the bromo ligands are cis to each other (Figure , Table ) . The cis structure is characteristic of this class of compounds, and numerous similar structures have been reported . This appears to be the first report of a trans geometry in a neutral intramolecular hexacoordinate silicon bis-chelate.…”

Synthesis and Reactivity of Martin’s Spirosilane-Derived Chloromethylsilicate

“…One can wonder if such a structure can rearrange via ring expansion, driven by a favorable strain release, to form a new tetravalent species with a six-membered ring (Scheme 3). This behavior, related to a sila-Matteson rearrangement [21][22][23], has already been observed for isolable pentacoordinate [24] and hexacoordinate chloromethylsilicates [25]. O-Migration, N-migration and C-migration have been reported and are usually triggered by thermal conditions when the hypercoordinate species are isolable.…”

Neutral and Cationic Bis-Chelate Monoorganosilicon(IV) Complexes of 1-Hydroxy-2-pyridinone

“…There are currently no other crystallographically characterized hexacoordinate complexes with Si CO 4 X (X = halide) ligand cores. Of the 13 known complexes having Si CClN 2 O 2 frameworks, 4 have dissociated chloride ions and 9 have Si–Cl bonds ranging from 2.188 to 2.384 Å …”