PI-OLEFIN-IRIDIUM COMPLEXES .24. PHOTOREACTIONS OF [CPM(C2H4)(2)] (M = RH, IR) WITH ALKYNES - GOOD SOURCE OF NEW PI-COMPLEXES

UV irradiation of [CpRh(C2H4)(2)] in pentane in the presence of alkyne s C2R2 [R = Me (a); Et (b)] gives a variety of products, and several c ompounds have been isolated by chromatography. The eta(4)-benzene comp lexes [CpRhC6R6] (2a,b) and the rhodacyclopentadienyl species [Cp2Rh2C 4R4] (3a,b) were obtained as main products. The isolable but highly re active complexes [CpRh(C2H4)(C2R2)] (1a,b) act as precursors for 3 and for hexaalkylbenzene, and by hydrolysis during chromatography also gi ve the 1-rhoda-2-oxa-cyclohexa-3,5-diene compounds [Cp2Rh2C4R4O] (6a,b ). Further isolated products are the bis(mu-vinyl) compound [Cp2Rh2(C2 H3)(C2HMe2)] (4a) as well as the eta(4)-butadiene species [CpRh{C4HR4- C5H4Rh(C2H4)(2)}] (5a) the formation of which involves the unusual C-H activation of a Cp moiety. From the reaction mixture formed by UV irr adiation of [CpIr(C2H4)(2)] in hexane only the mu-vinyl species [Cp2Ir 2(C2H3)(2)] (7) was isolated, while irradiation in the presence of but yne-2 yielded the eta(4)-hexamethylbenzene complex [CpIrC6Me6] (8). Th e compounds 2b, 3b, 5a, and 8 were characterised by X-ray crystal anal ysis.