METAL ATOMS IN THE SYNTHESIS OF METAL CLUSTERS .8. ON THE REACTION OFSTERICALLY DEMANDING CYCLOPENTADIENE LIGANDS WITH COBALT ATOMS - SYNTHESIS, CRYSTAL-STRUCTURE, SPECTROSCOPIC BEHAVIOR, AND REACTIVITY OF DINUCLEAR, TRINUCLEAR AND TETRANUCLEAR HYDRIDE CLUSTERS OF COBALT

The metal-vapor reactions of Co atoms with 1,3-tBu(2)CpH (1a), 1,3-tBu (2)CpH (1a), 1,2,4-tBu(3)CpH (1b) and EtMe(4)CpH (1c) are described. W ith 1a the two mononuclear complexes 5)-tBu(2)Cp)(eta(4)-tBu(2)-1,3-cy clopentadiene)Co] (2a) and [(eta(5)-tBu(2)Cp)(2)Co] (3a) were isolated , together with the dinuclear cobalt cluster [{(eta(5)-tBu(2)Cp)Co}H-2 (3)] (4a) and trace amounts of the tetranuclear cluster [{(eta(5)-tBu( 2)Cp)CoH}(4)] (5a). The molecular structures of 3a and 4a were determi ned by X-ray diffraction. Reaction of 1b with Co atoms afforded a sing le product, the dinuclear cluster [{(eta(5)-tBu(3)Cp)Co}H-2(3)] (4b), whose molecular structure was determined by single-crystal X-ray diffr action. Both, 4a and 4b exhibit extremely short Co- Co distances [2.24 4(1) (4a) and 2.242(1) Angstrom (4b)], as found for the Me(5)Cp analog [{(eta(5)-Me(5)Cp)Co}H-2(3)] (4c). Reaction of an isomeric mixture of Me(4)EtCpH (1c) with Co atoms furnished the mononuclear sandwich -Me( 4)EtCp)(eta(4)-Me(4)Et-1,3-cyclopentadiene)Co] (2b), the trinuclear hy dridocobalt cluster [{(eta(5)-Me(4)EtCp)Co}H-3(4)] (6a) and the tetran uclear hydridocobalt cluster [{(eta(5)-Me(4)EtCp)Co}H-4(4)] (5c). The molecular structure of 5c was determined by X-ray crystallography and revealed a tetrahedral arrangement of the cobalt atoms. The electroche mical behavior of the dinuclear complexes 4a-4c was studied by cyclic voltammetry, Reversible redox couples were found for all three compoun ds, with a correlation between the degree of alkyl substitution and th eir respective cathodic shifts. Compounds 4a and 4b react with CO to y ield the mononuclear and dinuclear complexes [(eta(5)-Cp(R))Co(CO)(2)] (R = 1,3-tBu(2), 1,2,4-tBu(3)) (7a and 7b) as well as [{(eta(5)-Cp(R) )Co}(2)(CO)(2)] (8a and 8b). Reaction of the trinuclear hydridocobalt cluster 6a and its Me(5)Cp analog 6b with AgBF4 in the presence of PEt (3) yielded the heteronuclear clusters [{eta(5)-Me(4)Cp(R))Co}3AgP(Et) (3)H-4](+)[BF4](-) (R = Et, Me) (9a and 9b). 9a was structurally chara cterized by X-ray crystallography.