VINYLIDENE TRANSITION-METAL COMPLEXES .30. REACTIONS OF ACETATO AND TRIFLUOROACETATO RHODIUM(I) COMPLEXES WITH 1-ALKYNES - BALANCE BETWEEN ISOMERIC PI-ALKYNE, ALKYNYL(HYDRIDO) AND VINYLIDENE METAL-COMPOUNDS

The rhodium complex [Rh(eta(2)-O2CCF3)(PiPr(3))(2)] (2) reacts with 1-alkynes at - 20 degrees C in pentane to give either four-coordinate alkynerhodium(I) or six-coordinate alkynyl(hydrido)rhodium(III) derivatives. On heating, both types of complexes, trans-[Rh(eta(1)-O2CCF3)(HC=CR)(PiPr(3))(2)] (6-8) and [RhH(C=CR)(eta(2)-O2CCF3)(PiPr(3))(2)] (9,10), rearrange to give the isomeric vinylidenerhodium(I) compounds trans-[Rh(eta(1)-O2CCF3)(=C=CHR)(PiPr(3))(2)] (11-14). Analogous acetatorhodium(I) and -rhodium(III) complexes, trans-[Rh(eta(1)-O2CCH3)(HC=CR)(PiPr(3))(2)] (16,17), [RhH(C=CR)(eta(2)-O2CCH3)(PiPr(3))(2)] (18,19) and trans-[Rh(eta(1)-O2CCH3)(=C=CHR)(PiPr(3))(2)] (23,24) were prepared via similar routes. Compound 18 (R = Ph) reacts with CO at - 78 degrees C to give [RhH(C=CPh)(eta(1)-O2CCH3)(CO)(PiPr(3))(2)] (20) which at room temperature loses CH3CO2H to yield trans-[Rh(C=CPh)(CO)(PiPr(3))(2)] (21). The dihydrido complexes [RhH2-(eta(2)-O(2)CR)(PiPr(3))(2)] (4,5) have also been used as starting materials for the synthesis of alkynyl(hydrido)rhodium(III) and vinylidenerhodium(I) derivatives. From compound 5 (R = CH3) and HC=CR (R = H, Ph), the alkynyl(ethene) complexes trans-[Rh(C=CR)(C2H4)(PiPr(3))(2)] (29,30) have been prepared. The related four-coordinate alkynyl(vinylidene)rhodium(I) compounds trans-[Rh(C=CR)(=C=CHR)(PiPr(3))(2)] (33,34) were obtained from trans-[Rh(eta(1)-O2CCH3)(HC=CCO(2)Me)(PiPr(3))(2)] (17) as well as [RhH(C=CPh)(eta(2)-O2CCH3)(PiPr(3))(2)] (18) and HC=CR in presence of base. The unusual alkynyl(vinyl)rhodium(III) complex 32 is accessible along four routes, from 33 (R = CO(2)Me) or from one of the isomers 17, 26, 28 and HC=CCO(2)Me.