ÜbergangsmetallMethylen-Komplexe: XLVI. Metallzentrierte CC-Verknünpfung durch addition von alkinen an Metalldoppelbindungen

Abstract

Alkynes add readily to the metalmetal double bonds of the rhodium and cobalt complexes of composition [(η 5-C 5Me 5)M(μ-CO)] 2 (M = Rh, 1; M = Co, 6) with rapid CO insertion and concomitant formation of metallacyclic structures. While phenylacetylene ( 2a) and diphenylacetylene ( 2b) undergo addition/insertion reactions with the organorhodium precursor 1 and thus yield the dimetallacycles 3a and 3b, respectively, an isomeric mixture consisting of the corresponding rhodacycle 3c and the μ-ketenylmethylene complex 4 arises from treatment of 1 with the parent acetylene 2c. Compounds 3c and 4 reversibly interconvert in solution at ambient temperature. Regiospecific incorporation into the metal complex 1 is osserved with the unsymmetrically substituted alkyne 2a. The carboncarbon bonds formed during these alkyne reactions are irreversibly cleaved by sulfurdioxide which molecule causes ring expansion and thus produces novel metallacycles of type 5. The cobalt complex 6 and acetylene ( 2c) form the alkyne addition/insertion product 7c which, although structurally homologous with the rhodium derivative 3c, suffers from limited stability at room temperature; in solution, rapid and reversible (!) extrusion of acetylene is observed with the dicobaltacycle 7c. With the rhodium derivative 3c, this degradation reaction is less clean but nevertheless occurs under more drastic conditions. Insertion of sulfurdioxide supresses extrusion of acetylene in both the cobalt and the rhodium compounds 7c and 3c, respectively.