VINYLIDENE TRANSITION-METAL COMPLEXES .34. THE PREPARATION AND STRUCTURE OF NEUTRAL VINYLIDENE AND ALLENYLIDENE RUTHENIUM(II) COMPOUNDS OF THE HALF-SANDWICH TYPE CONTAINING (I)PR(2)PCH(2)CO(2)ME AS SUPPORTING LIGAND

The reaction of the tetrameric compound [CP*RU(mu(3)-Cl)](4) (1; CP* = C(5)Me(5)) with (i)Pr(2)PCH(2)CO(2)Me gives the monomeric species [Cp*RuCl{kappa(2)(P, O)-(i)Pr(2)PCH(2)CO(2)Me}] (2) which is an excellent starting material for the synthesis of neutral half-sandwich type ruthenium complexes containing substituted vinylidenes and allenylidenes as ligands. Compound 2 reacts with HC=CCO(2)Me to give [Cp*RuCl(=C=CHCO(2)Me)(Pr-i(2) PCH(2)CO(2)Me)] (4), and the corresponding reaction of 2 with HC=CCPh(2)- OH affords [Cp*RuCl(=C=CHCPh(2)OH)((Pr2PCH2CO)-Pr-i(2)Me)] (5) which on treatment with acidic alumina yields [Cp*RuCl(=C= C=CPh(2))((i)Pr(2)PCH(2)CO(2)Me)] (6). In contrast, the reaction of 2 with Me(3)SiC=CCO(2)Et gives, instead of an alkyne or vinylidene ruthenium derivative, the cyclobutadiene complex [Cp*RuCl{eta(4)-C-4(SiMe(3))(2)(CO(2)Et)(2)}] (7) which is accessible also from 1 and Me(3)SiC=CCO(2)Et in almost quantitative yield. The crystal and molecular structures of 2 and 4 have been determined.