Alkene isomerization by non-hydridic phosphine substituted ruthenium carbonyl carboxylates

Abstract

The behaviour of phosphine substituted ruthenium carbonyl carboxylates in the presence of hex-1-ene has been followed by IR and NMR spectroscopies. The complex Ru 4(CO) 8(MeCO 2) 4(PBu 3) 2 reacts at room temperature with a large excess of hex-1-ene giving the Ru 2(CO) 4(MeCO 2) 2(PBu 3)(hex-1-ene) compound. The same complex is formed from Ru 2(CO) 4(MeCO 2) 2(PBu 3) 2 and hex-1-ene at 80°C. Mononuclear Ru(CO) 2(MeCO 2) 2(PBu 3) 2 is not transformed under the same conditions. Catalytic tests performed at 80°C in the presence of Ru 4(CO) 8(MeCO 2) 4(PBu 3) 2 or Ru 2(CO) 4(MeCO 2) 2(PBu 3) 2 indicate that these complexes display almost the same catalytic activity in hex-1-ene isomerization in agreement with the formation of the same intermediate. Working in the presence of Ru 4(CO) 8(MeCO 2) 4(PBu 3) 2 at 80°C, an 85% conversion was obtained after 70 h. The isomeric olefins had a trans/ cis ratio of 4.5. A reaction scheme has been suggested to rationalise the behaviour of these complexes.