Vinyliden-Übergangsmetallkomplexe XXX. Reaktionen von acetato- und trifluoracetato-rhodium(I)-komplexesn mit 1-alkinen: Ein beispiel für die balance zwischen isomeren π-alkin-alkinyl(hydrido)- und vinyliden-metallverbindungen

Abstract

The rhodium complex [Rh(η2-O2CCF3)(PiPr3)2] (2) reacts with 1-alkynes at −20°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(η1-O2CCF3)(HC≡CR)(PiPr3)2] (6–8) and [RhH(C≡CR)(η2-O2CCF3)(PiPr3)2] (9,10), rearrange to give the isomeric vinylidene-rhodium(I) compounds trans-[Rh(η1-O2CCF3)(CCHR)(PiPr3)2] (11–14). Analogous acetatorhodium(I) and -rhodium(III) complexes, trans-[Rh(η1-O2CCH3)(HC≡CR)(PiPr3)2] (16,17), [RhH(C≡CR)(η2-O2CCH3)(PiPr3)2] (18,19) and trans-[Rh(η1-O2CCH3)(CCHR)(PiPr3)2] (23,24) were prepared via similar routes. Compound18 (RPh) reacts with CO at −78°C to give [RhH(C≡CPh)(η1-O2CCH3)(CO)(PiPr3)2] (20) which at room temperature loses CH3CO2H to yield trans-[Rh(C≡CPh)(CO)(PiPr3)2] (21). The dihydrido complexes [RhH2-(η2-O2CR)(PiPr3)2] (4,5) have also been used as starting materials for the synthesis of alkynyl(hydrido)rhodium(III) and vinylidenerhodium(I) derivatives. From compound5 (RCH3) and HC≡CR (R H, Ph), the alkynl(ethene) complexes trans-[Rh(C≡CR)(C2H4)(PiPr3)2] (29,30) have been prepared. The related four-coordinate alkynyl(vinylidene)rhodium(I) compounds trans-[Rh(C≡CR)(CCHR)(PiPr3)2] (33,34) were obtained from trans-[Rh(η1-O2CCH3)(HC≡CCO2Me)(PiPr3)2] (17) as well as [RhH(C≡CPh)(η2-O2CCH3)(PiPr3)2] (18) and HC≡CR in presence of base. The unusual alkynyl(vinyl)rhodium(III) complex32 is accessible along four routes, from33 (RCO2Me) or from one of the isomers17, 26, 28 and HC≡CCO2Me.