Ruthenium Allenylidene and Allylcarbene Complexes from 1,6-Diyne

Abstract

Reactions of the four 1,6-diynes 1−3 and 7, each with one terminal propargylic alcohol and one internal triple bond containing Me3Si groups, with [Ru]−Cl ([Ru] = Cp(PPh3)2Ru) led to two types of products. In the first type, only the propargylic group is involved in the reaction leading to vinylidene, allenylidene, or acetylide complexes. A C−C bond formation of two triple bonds in 1,6-diynes gave allylcarbene products of the second type. The reaction of 1 with [Ru]−Cl yielded only the first type, giving a mixture of two cationic complexes; the allenylidene complex 8 and the phosphonium acetylide complex 9, the latter resulting from further addition of a phosphine molecule to Cγ of 8. The same reaction in the presence of excess phosphine gave 9 only. However, with an additional methyl group, the 1,6-diyne 2 reacted with [Ru]−Cl to give the allylcarbene complex 11 also with a phosphonium group on the ligand. The reaction proceeds by a cyclization reaction involving two triple bonds on the metal accompanied by a migration of a phosphine ligand to Cα. In both reactions strong affinity between alkyne and phosphine was observed, resulting in formations of P−C bonds with different regioselectivity. Addition of HCl to 11 transforms the five-electron-donor allylcarbene ligand to the four-electron-donor diene ligand along with formation of a Ru−Cl bond, giving complex 12 in high yield. From the reaction of [Ru]−Cl with diyne 3 containing a tert-butyl group at the propargylic carbon, both the allenylidene complex 13 and the allylcarbene complex 14 were obtained. The reaction of diyne 7 with [Ru]−Cl also gave both types of complexes, namely the vinylidene complex 16 and the allylcarbene complex 17. Crystal structures of complexes 9, 11, 12, and 16 have been determined by single-crystal X-ray diffraction analysis