Synthesis and Crystal Structure of Novel 1,3-Heterobinuclear Complexes with an Unusual Cyclic C4R3 Bridging Ligand

Abstract

Pentacarbonyl(dimethylvinylidene)chromium, [(CO)5CrCCMe2] (1), reacts with the alkynyl complexes [Cp(CO)2FeCCR] (4a−e; R = nBu (a), Me (b), Ph (c), C6H4NO2-p (d), COOMe (e)), [Cp(CO){P(OMe)3}FeCCnBu] (6), [Cp(CO){PPh3}FeCCnBu] (8), and [Cp(PEt3)NiCCnBu] (19) by cycloaddition of the CC bond of the alkynyl complexes to the CC bond of 1 to give [(CO)5Cr C CR C(CMe2) Fe(CO)2Cp] (5a−e), [(CO)5Cr C C(nBu) C(CMe2) Fe(CO){P(OMe)3}Cp] (7), [(CO)5Cr C C(nBu) C(CMe2) Fe(CO){PPh3}Cp] (9), and [(CO)5Cr C C(nBu) C(CMe2) Ni(PEt3)Cp] (20), respectively. The analogous reaction of [(CO)5CrCC(CH2)5] (2) with 4a and 6 affords complexes with a spirocyclic bridging ligand: [(CO)5Cr C C(nBu) C{C(CH2)5} Fe(CO)2Cp] (10) and [(CO)5Cr C C(nBu) C{C(CH2)5} Fe(CO){P(OMe)3}Cp] (11). Cycloaddition of 4a to [(CO)5CrCCPh2] (3) yields [(CO)5Cr C C(nBu) C(CPh2) Fe(CO)2Cp] (12). The spectroscopic data of these novel 1,3-heterobinuclear complexes indicate the delocalized π-system Cr C C C M (M = Fe, Ni). X-ray structural analyses of the compounds 5e, 10, and 11 reveal a “butterfly” conformation. The puckering angle of the four-membered ring is 160.0° (5e), 143.9° (10), and 144.9° (11). Both C(sp2)−C(sp2) bonds are almost equal in length. All complexes exhibit negative solvatochromic behavior. The extent of the solvatochromic effect is strongly influenced by the substituents at C-2 and C-4 of the ring.