188906-89-0Relevant academic research and scientific papers
Competition between steric and electronic control of structure in Ru(CO)2L2L′ complexes
Ogasawara, Masamichi,Maseras, Feliu,Gallego-Planas, Nuria,Kawamura, Kazumori,Ito, Kazuhiko,Toyota, Koichiro,Streib, William E.,Komiya, Sanshiro,Eisenstein, Odile,Caulton, Kenneth G.
, p. 1979 - 1993 (2008/10/08)
Magnesium reduction of RuCl2(CO)2L2 in the presence of equimolar L in THF gives Ru(CO)2L3 (L = PPh3 (1), PMePh2 (2), PEt3 (3), PiPr2Me (4)). The corresponding reduction of RuCl2(CO)2(PEt3)2 in the presence of equimolar L′ (L′ = P(2-furyl)3 (5) or AsPh3 (6)) gives Ru(CO)2(PEt3)2L′ but gives a mixture of Ru(CO)2(PEt3)3-nLn (n = 0-3) species when L′ = PPh3. Comparisons show that 3 or 5 reacts slowly with L″ = (H)2, CO, or PhC≡CPh to form Ru(CO)2L″(PEt3)2 and free PEt3 or P(2-furyl)3 but rapidly with 4 or 6 to give the analogous products. The reaction of PhC≡CPh with Ru(CO)2(PEt3)2L′ is faster for L′ = PEt3 than for P(2-furyl)3. All of these reactions are proposed to take place by preliminary ligand loss of L′, this being slower for 3 and 5 than for 1, 4, and 6. Reaction of O2 with complexes containing the readily dissociated L′ species gives simply Ru(η2-O2)(CO)2L2, but for Ru(CO)2-(PEt3)3, this is accompanied by an apparent bimolecular electron transfer involving the intact complex to give Ru(CO)(CO3)(PEt3)3. X-ray structure determinations of Ru(CO)2(PEt3)3 (bis equatorial CO in trigonal bipyramid (TBP)), Ru(CO)2(PiPr2Me)3 (two isomers: bis axial CO in TBP and also square pyramidal), and Ru(η2-PhCCPh)(CO)2(PEt3)2 (cis carbonyls and trans phosphines) are reported. It is shown that all of the Ru(CO)2L3 species exist in solution as two isomers in rapid equilibrium. Ab initio MP2 calculations on the unhindered Ru(CO)2-(PH3)3 model shows a preference for a trigonal bipyramidal structure with only a weak preference for CO to be at the equatorial site. It is shown that this pattern cannot be generalized to all π-acid ligands since ethylene is calculated to have a strong preference for an equatorial site in a TBP. Integrated quantum chemical and molecular mechanics calculations on Ru(CO)2(PEt3)3 and Ru(CO)2(PiPr2Me)3 give structures in excellent agreement with the X-ray results and confirm that the geometry and relative energetic preference for the observed structural isomers is strongly influenced, or even dominated by, the steric effect of the phosphine ligands.
