Reactions of Tantalum Alkylidene Complexes with Silanes. Synthesis and Characterization of Novel Metallasilacyclodiene Complexes and Kinetic and Mechanistic Studies of Their Formation

Abstract

The reactions of tantalum alkylidene complexes (RCH 2 ) 3 Ta(L)dCHR (1) and RCH 2 Ta(L) 2 -[dCHR] 2 (3) (R ) SiMe 3 , L ) PMe 3 ) with phenylsilanes H 2 SiR′Ph (R′ ) Me, Ph) and (PhSiH 2 ) 2 -CH 2 were found to produce bis(silyl)-substituted alkylidene complexes (RCH 2 ) 3 TadCR-(SiHR′Ph) (4) and novel metallasilacyclobutadiene and metalladisilacyclohexadiene complexes. Reaction of the mixed-ligand trimethylsilylmethyl neopentylidene complex RCH 2 Ta(L) 2 [d CHBu t ] 2 ( 6) with H 2 SiMePh also yielded a metallasilacyclobutadiene complex, but reaction of the neopenyl neopentylidene complex Bu t CH 2 Ta(L) 2 [dCHBu t ] 2 (2) with H 2 SiMePh yielded unidentified products. Deuterium-labeling and kinetic studies of the conversion of 1 f 4 were found to be consistent with a dissociative mechanism. The structures of the novel metallacyclic complexes 5a, 5b, 7, and 8 were determined by X-ray crystallography.

Reaction of a Tungsten Alkylidyne Complex with a Chelating Diphosphine. α-Hydrogen Migration in the Intermediates and Formation of an Alkyl Alkylidene Alkylidyne Complex

“…These observations are consistent with a “pinwheel” anti , syn conformation for 4b with two inequivalent alkylidene ligands (Chart ). Such a conformation was also observed for W(CH 2 SiMe 3 ) 3 (CSiMe 3 )(PMe 3 ) ( 2a ) , and Ta(CH 2 EMe 3 )(CHEMe 3 ) 2 (PMe 3 ) 2 (E = C, Si) . In the 13 C NMR spectrum of 4b , two doublets at 256.7 and 254.7 ppm ( 2 J P−C = 12.5 Hz for both) are observed for the two alkylidene ligands in 4b .…”

Tungsten Alkyl Alkylidyne and Bis-alkylidene Complexes. Preparation and Kinetic and Thermodynamic Studies of Their Unusual Exchanges

“…Although the exchange of α-H atoms is a fundamental dynamic process in these archetypical d 0 alkylidene and alkylidyne complexes, there is, to our knowledge, only one direct observation of such an exchange between bis-alkylidene and alkylidyne tautomers. 1a-j, Alkylidyne complex (Bu t CH 2 ) 2 W(⋮CBu t )(SiBu t Ph 2 ) ( 4a ), a silyl analogue of (Bu t CH 2 ) 3 W⋮CBu t , was found to be in an equilibrium with its silyl bis-alkylidene tautomer (Me 3 CCH 2 )W(CHCMe 3 ) 2 (SiBu t Ph 2 ) ( 4b ) (eq 1) 1i,3a,5b,

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Transition metal alkylidene complexes. Pathways in their formation and tautomerization between bis-alkylidenes and alkyl alkylidynes

“…Silicon is known to stabilize an adjacent carbon-metal bond (Scheme 16) [61]. Complexes with eCH 2 SiMe 3 and/or ]CHSiMe 3 ligands have shown unique chemistry [30,34].…”