SYNTHESIS AND CRYSTAL-STRUCTURE OF NOVEL 1,3-HETEROBINUCLEAR COMPLEXES WITH AN UNUSUAL CYCLIC C(4)R(3) BRIDGING LIGAND

Pentacarbonyl(dimethylvinylidene)chromium, [(CO)(5)Cr=C=CMe(2)] (1), r eacts with the alkynyl complexes [Cp(CO)(2)FeC=CR] (4a-e; R = (n)Bu (a ), Me (b), Ph (c), C6H4NO2-p (d), COOMe (e)), [Cp(CO){P(OMe)(3)}FeC=C( n)Bu] (6), [Cp(CO){PPh(3)}FeC=C(n)Bu] (8), and [Cp(PEt(3))NiC=C(n)Bu] (19) by cycloaddition of the C=C bond of the alkynyl complexes to the C=C bond of 1 to give [(CO)(5)Cr-C-CR-C(CMe(2))-Fe(CO)(2)Cp] (5a-e), O )(5)Cr-C-C-((n)Bu)-C(CMe(2))-Fe(CO){P(OMe)(3)}Cp] (7), [(CO)(5)Cr-C-C( (n)Bu)-C(CMe(2))-Fe(CO)-{PPh(3)}Cp] (9), and [(CO)(5)Cr-C-C((n)Bu)-C(C Me(2))-Ni(PEt(3))Cp] (20), respectively. The analogous reaction of [(C O)(5)Cr=C=C(CH2)(5)] (2) with 4a and 6 affords complexes with a spiroc yclic bridging ligand: [(CO)(5)Cr-C-C((n)Bu)-C{C(CH2)(5)}-Fe(CO)(2)Cp] (10) and (5)Cr-C-C((n)Bu)-C{C(CH2)(5)}-Fe(CO){P(OMe)(3)}Cp] (11). Cyc loaddition of 4a to [(CO)(5)Cr=C=CPh(2)] (3) yields [(CO)(5)Cr-C-C((n) Bu)-C(CPH2)-Fe(CO)(2)Cp] (12). The spectroscopic data of these novel 1 ,3-heterobinuclear complexes indicate the delocalized pi-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 degrees (5e), 143.9 degrees (10), and 144 .9 degrees (11). Both C(sp(2))-C(sp(2)) bonds are almost equal in leng th. All complexes exhibit negative solvatochromic behavior. The extent of the solvatochromic effect is strongly influenced by the substituen ts at C-2 and C-4 of the ring.