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Article

C−C and C−H Bond Activation at Ruthenium(II): The Stepwise Degradation of a Neopentyl Ligand to a Trimethylenemethane Ligand

Supporting Info

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

Contribution from the Materials and Chemical Sciences Division, Lawrence Berkeley Laboratory, and the Department of Chemistry, University of California, Berkeley, California 94720

J. Am. Chem. Soc., 1997, 119 (46), pp 11244–11254

DOI: 10.1021/ja972131e

Publication Date (Web): November 19, 1997

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

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 (SiP₃)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.