Formation of metallocycloimides from the reactions of isocyanates with a neutral transition metal carbonyl

Abstract

Abstract : The nucleophilic carbonyl complex (W(eta-C5H5)2(CO)) (1) reacts readily with the isocyanates OCNR (R = CH3, Ph) in pentane to give the first reported metallocycloimides (W(eta-C5H5)2(C(O)N(CH3)C(O))) (2) and (W(eta-C5H5)2(C(O)N(Ph)C(O))) (3). It is suggested that the reaction involves initial eta 1-C coordination of an isocyanate to give a zwitterionic intermediate in which the ligands are simultaneously activated in opposite senses, and that nucleophilic attack by the heteroallene on the electrophilic carbonyl then gives a metallocycloimide. Complex 2 has been structurally characterized by a single crystal X-ray diffraction study (monoclinic space group P2 sub 1/m, with Z = 2; a = 7.6586 A, b = 8.6718 A, c = 9.6557 A; Beta = 101.45 deg; d calc = 2.20 g/cc; R = 2.20 % and R sub w = 2.19 %) which establishes that the metallocycloimide group is essentially planar. Both 2 and 3 are moderately water sensitive, regenerating 1 at 55 C and ambient temperatures respectively. Complex 1 in toluene does not react with 1.7 atmospheres of CO2 at temperatures up to 85 C.