Photoreactions of chromium cyclodienyl complexes with alkynes: Double [5+2],homo[5+2] cycloaddition reactions

UV irradiation of the cycloheptadienyl complexes [(eta 5-C(7)H(8)R)Cr(CO)(3)SnPh(3)] (1a, R = H; 1b, R = C(Me)S(CH2)(3)S; 1c, R = CHPh(2)) or cyclohexadienyl complexes [(eta(5)-C(6)H(6)R)Cr(CO)(2)(NO)] (7, R = C(Me)S(CH2)(3)S) and 2 equiv of 2-butyne or 3-hexyne in toluene or n-hexane gave new tricyclic complexes 2, 5, and 8. These complexes arise from sequential [5 + 2] and homo[5 + 2] cycloadditions of two alkyne molecules to the eta 5-dienyl manifold forming 11-alkylidenetricyclo[5.3.1.0(4,10)]undeca or tricyclo[5.2.1.0(4,9)]deca-2,5-dien-10-yl ligands, respectively. Heating 2 in acetonitrile gave [Cr(CO)(3)(CH3CN)(3)] and the tricyclic organic compounds 3. UV irradiation of 1a and 1-phenyl-1-propyne or 1c and 2-butyne directly gave the organic compounds 4a,b and 5c, 6a,b, respectively, as mixtures of isomers. The adduct resulting from 1a and two molecules of 3-hexyne has been characterized by an X-ray diffraction study.