C-C and C-H bond activation at ruthenium(II): The stepwise degradation of a neopentyl ligand to a trimethylenemethane ligand

Kristopher McNeill, Richard A. Andersen, Robert G. Bergman

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Abstract

Ruthenacyclobutane complexes (SiP3)(PMe3)Ru(CH2EMe2CH2) (SiP3 = MeSi(CH2PMe2)3; 1, E = C; 2, E = Si) were synthesized from (SiP3)(PMe3)RuCl2 (3) and 2 equiv of the Grignard reagents, Me3ECH2MgCl. Metallacycle 1 was found to reversibly interconvert with the allyl complex (SW)Ru(Me)(η3-CH2CMeCH2) (4) and PMe3 when heated above 75°C. From the results of kinetic studies and thermolysis of labeled material, the interconversion is proposed to take place by reversible β-methyl elimination/insertion. Conversion of 1 to 4 is an endothermic process (ΔH°= 14.3 ± 1.1 kcal mol-1), but it is entropically favorable (ΔS°= 40.9 ± 2.8 cal K-1 mol-1) due to the loss of the PMe3 ligand. Activation parameters for the β-insertion were determined to be ΔH≠ = 26.0 ± 1.2 kcal mol-1 and ΔS≠ = -10.5 ± 0.9 cal K-1 mol-1. Allyl complex 4 has been isolated as a mixture of isomers (7:1 endo:exo). The mechanism of interconversion of 4(endo) and 4(exo) was determined by 1H{31P} NMR spectroscopy (EXSY) to be a process involving a stereochemically rigid, square-pyramidal η1-intermediate. Thermolysis of 4 leads to loss of CH4 and the production of the trimethylenemethane complex (SiP3)Ru(η4-C(CH2)3) (7). The solid state structures of 1 and 7 were determined by X-ray diffraction.

Original languageEnglish (US)
Pages (from-to)11244-11254
Number of pages11
JournalJournal of the American Chemical Society
Volume119
Issue number46
DOIs
StatePublished - Nov 19 1997

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