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

Pentacarbonyl(allenylidene)chromium and -tungsten, [(CO)(5)-M=C=C=CR(2 )] (M=Cr, R=C6H4CH3-p (1a), C6H4OCH3 (1b); M=W, R=C6H4CH3-p (1c)), rea ct with the alkynyl complexes [Cp(CO)(2)Fe-C=CR'] (R'=nBu (2), Ph (4)) , [Cp(CO)(2)Fe-C=CnBu] (6), [Cp(CO){P(OMe)(3)}-Fe-C=CnBu] (8) and [Cp (PPh(3))Ni-C=CnBu] (10) by cycloaddition of the C=C bond of the alkyny l complexes to the C-alpha=C-beta bond of the allenylidene ligand to g ive [(CO)(5)M - C - C(nBu)- C(C=CR(2))- Fe(CO)(2)Cp] (3a-c), [(CO)(5)C r - C - C-(Ph)- C(C=CR(2))- Fe(CO)(2)Cp] (5), [(CO)(5)Cr - C - C(nBu)- C-(C=CR(2))- Fe(CO)(2)Cp] (7), [(CO)(5)-M - C - C(nBu)- C(C=CR(2))- Fe(CO){P(Ome)(3)}Cp] (91-c), and [(CO)(5)M - C - C-(nBu)- C(C=CR(2))- Ni(PPh(3))Cp] (11a-c), respectively. The cycloaddition is highly selec tive. The spectroscopic data of these 1,3-heterobinuclear complexes in dicate a delocalized pi-system [(CO)(5)M - C - C - C - Y] (M=Cr, W; Y= [Fe(CO)(2)Cp], [Fe(CO)(P{OMe}(3))Cp], [Fe(CO)(2)Cp], [Ni(PPh(3))-Cp]) . X-ray structural analyses of the compounds 3a, 9a, and 11c reveal a ''butterfly'' conformation of the four-membered ring. Its puckering an gle is 142 degrees (3a), 152 degrees (9a), and 151 degrees (11c). All complexes exhibit a moderate to strong negative solvatochromic behavio r. The extent of the solvatochromic effect depends on [(CO)(5)M] and Y and considerably decreases when C=CR(2) is replaced by e.g. CMe(2).