Laser flash photolysis and matrix isolation studies of Ru[R2PCH2CH2PR2]2H 2 (R = C2H5, C6H5, C2F5): Control of oxidative addition rates by phosphine substituents

Article abstract of DOI:10.1021/ja00145a016

The photochemistry of ruthenium hydrides Ru(depe)₂H₂, cis-Ru(dppe)₂H₂ and cis-Ru(dfepe)₂H₂ [depe = Et₂PCH₂CH₂PEt₂, dppe = Ph₂PCH₂CH₂PPh₂, dfepe = (C₂F₅)₂PCH₂CH₂P(C ₂F₅)₂] has been studied by matrix isolation at 12 K and laser flash photolysis at ambient temperature. Both techniques yield the 4-coordinate 16-electron RuP₄ species. The ethyl and phenyl species, Ru(depe)₂ and Ru(dppe)₂, exhibit very similar UV-visible spectra to Ru(dmpe)₂ [Ru(depe)₂ 475, 580, 735 nm; Ru(dppe)₂ 465, 550, 760 nm in solution]. The spectrum of Ru(dfepe)₂ is blue-shifted relative to the others (380, 450, 620 nm). The comparison of the spectra with that of [Rh(dppe)₂]⁺ conclusively establishes a square-planar structure for Ru(depe)₂ and Ru(dppe)₂. The rates of reaction with added ligands are extremely sensitive to substituent. The rate constants for reaction with H₂ are Ru(dfepe)₂ 2.0 × 10⁵, Ru(dppe)₂ 2.4(2) × 10⁷, Ru(depe)₂ 4.0(4) × 10⁸ dm³ mol^-1 s^-1 compared to 6.8 × 10⁹ dm³ mol^-1 s^-1 for Ru(dmpe)₂. For reaction with CO, the rate constants are Ru(dfepe)₂ 1.1 × 10⁴, Ru(dppe)₂ 1.0(2) × 10⁷, Ru(depe)₂ 9.1(7) × 10⁷ dm³ mol^-1 s^-1 compared to 4.6 × 10⁹ dm³ mol^-1 s^-1 for Ru(dmpe)₂. Thus reactivity increases in the order Ru(dfepe)₂ < Ru(dppe)₂ < Ru(depe)₂ < Ru(dmpe)₂ with an overall span of a factor of 34 000 for reaction with H₂ and 418 000 for reaction with CO. The rate constants for reaction of Ru(depe)₂ with C₂H₄ and Et₃SiH, and for reaction of Ru(dppe)₂ with C₂H₄ have also been determined.