DINUCLEAR, TRINUCLEAR, AND TETRANUCLEAR CYCLOBUTENYLIDENE COMPLEXES

Pentacarbonyl(dimethylvinylidene)chromium, [(CO)(5)Cr=C=CMe2] (1), rea cts with the butadiynyl complexes [Cp(CO)(2)FeC=CC=CR] [2; R = SiMe3 ( a), nBu (b), Ph (c)] and [Cp(CO)(PPh3)FeC=CC=CSiMe3](3a) by regiospeci fic cycloaddition of the C-alpha=C-beta bond of the butadiynyl complex es to the C=C bond of 1 to form the 1,3-heterobinuclear cyclobutenylid ene complexes 4a-c and 5a with an alkynyl substituent at C-2 of the br idging ring. Desilylation of the 2-C=CSiMe3 substituent in 4a and 5a w ith tetrabutylammonium fluoride affords the 2-C=CH-substituted complex es 6 and 7. Complex 4a reacts with HNMe2 and HN(CH2)(5) by substitutio n of NR2 for the 3-Fe(CO)(2)Cp fragment to form the corresponding 3-am inocyclobutenylidene complexes 10 and 11. Sequential reactions of 4a w ith [nBu(4)N]F and nBu(3)SnNEt(2) give the trinuclear 2-C=CSnnBu(3)-su bstituted complex 12. Coupling of 12 with C6H4I2-p yields the 2-C=CC6H 4I-p-substituted complex 13. Coupling of 7 with C6H4I2-p yields a mixt ure of the mono-coupling product 14 and the tetranuclear C=CC6H4-C=C-b ridged bis(cyclobutenylidene) complex 15. Coupling of 7 with trans-[(E t3P)(2)MCl2] in the presence of CuI/[Pd(PPh3)(4)] gives the trinuclear 2-C=C-M(PEt3)(2)X-substituted complexes 16 (M = Pd, X = I) and 17 (M = Pt, X = Cl). The spectroscopic data as well as the results of the Xr ay-structural analysis of 5a indicate strong electronic communication between the metal centers. In the solid state, 5a exhibits a ''butterf ly'' conformation.