1,3-HETEROBINUCLEAR CYCLOBUTENYLIDENE COMPLEXES WITH AN EXOCYCLIC C=C BOND: SYNTHESIS, STRUCTURE, AND SPECTROSCOPIC PROPERTIES

Pentacarbonyl(allenylidene)chromium and -tungsten, [(CO)5MCCCR2] (M=Cr, R=C6H4CH3-p(1a), C6H4OCH3 (1b); M=W, R=C6H4CH3-p (1c), react with the alkynyl complexes [Cp(CO)2FeCCR′] (R′ = nBu (2), Ph (4)), [Cp*(CO)2FeCCnBu] (6), [Cp(CO){P(OMe)3}-FeCCnBu] (8) and [Cp(PPh3)NiCCnBu] (10) by cycloaddition of the CC bond of the alkynyl complexes to the Cα=Cβ bond of the allenylidene ligand to give 3a–c), (5), (7), and respectively. The cycloaddition is highly selective. The spectroscopic data of these 1,3-heterobinuclear complexes indicate a delocalized π-system (M=Cr, W; Y=[Fe(CO)2Cp], [Fe(CO)(P{OMe}3)Cp], [Fe(CO)2Cp*], [Ni(PPh3)-Cp]). X-ray structural analyses of the compounds 3a, 9a, and 11c reveal a “butterfly” conformation of the four-membered ring. Its puckering angle is 142° (3a), 152° (9a), and 151° (11c). All Complexes exhibit a moderate to strong negative solvatochromic behavior. The extent of the solvatochromic effect depends on [(CO)5M] and Y and considerably decreases when C=CR2 is replaced by e.g. CMe2.