BINUCLEAR METAL-COMPLEXES OF A DOUBLY BRIDGED CYCLOPENTADIENYL LIGAND

Binuclear metal complexes derived from the doubly bridged cyclopentadiene system 2,2,8,8-tetramethyl-2,8-disilatricyclo[7.3.0.0(3,7)]dodeca-3,5,9,11-tetraene (LH2) are examined. This compound is deprotonated with 2 equiv of 1-butyllithium to form the dilithio salt LLi2 (2). Reaction of 2 with trimethyltin chloride yields (Me3Sn)2L (3). The analogous reaction with Cp*RuCl (Cp* = C5Me5) gives the binuclear ruthenocene (Cp*Ru)2L (4). By cocomplexation of 2 and Cp*Li with iron(II) chloride, the binuclear ferrocene (Cp*Fe)2L (5) is obtained. Reaction of LH2 with octacarbonyldicobalt leads to the formation of [(CO)2Co]2L (6). The analogous reaction with pentacarbonyliron yields a mixture of products, from which [(CO)2Fe]2L (Fe-Fe) (7) is isolated. The stereochemistry of complexes 3-7 is investigated by IR and NMR spectroscopy. Single-crystal X-ray structure determinations are performed for 5 and 6. The structure investigations on 5 show a trans arrangement of the two Cp*Fe units. The ligand L is not planar. The unit cell contains two independent molecules, whose bonding parameters are essentially identical (crystal system triclinic; space group P1BAR; a = 8.7443 (13), angstrom, b = 18.561 (3) angstrom, c = 20.576 (4) angstrom; alpha = 89.340 (13)-degrees, beta = 89.160 (13)-degrees, gamma = 78.300 (12)-degrees; Z = 4). The structure investigations on the cis isomer of 6 also show a nonplanar ligand L (crystal system monoclinic; space group P2(1)/n; a = 10.496 (2) angstrom, b = 13.380 (2) angstrom, c = 14.537 (6) angstrom; beta = 92.96 (3)-degrees; Z = 4). The flexibility of L is estimated, and the potential of its binuclear complexes for catalytic processes is discussed.