NEW SYNTHETIC ROUTES TO HOMONUCLEAR COBALT HYDRIDE CLUSTERS

Several homonuclear cobalt hydride clusters are accessible by reacting the complexes (eta(5)-Cp(R))Co(eta(2)-ethene)2 (R = H-5, Me(5)) 3, 4 with (C2H5)(2)AlH followed by alcoholysis of the crude reaction mixtures. Depending on the degree of alkyl substitution, different nuclearities of the resulting clusters have been observed. In the case of the pentamethyl substituted derivative (eta(5)-Cp*)Co(eta(2)-ethene) 4 a mixture of di-, tri- and tetranuclear cobalt hydride clusters namely [(eta(5)-CP*)Co]H-2(3) 1, [(eta(5)-Cp*)Co]H-3(4) 2 and [(eta(5)-Cp*)Co]H-4(4) 7 were formed and separated by repeated crystallization. When reacting the parent compound (eta(5)-Cp)Co(eta(2)-ethene) 3 with (C2H5)(2)AlH and quenching the reaction mixture with alcohol at low temperature, the tetranuclear cobalt cluster [(eta(5)-CP)Co]H-4(4) 5 is the main product. Aside from this, trace amounts of the cobalt alkylidine cluster [(eta(5)-Cp)Co](4) mu-[C(CH3)]H 6 were formed as detected by mass spectrometry. For the first time a direct synthesis of [(eta(5)-Cp**)Co]H-3(4) 10 and [(eta(5)-Cp**)Co]H-4(4) 11 was achieved by reaction of cobalt atoms with tetramethyl-ethyl-1,3-cyclopentadiene (mixture of isomers) in methylcyclohexane at -120 degrees C. However, the main product of this metal atom reaction is the mononuclear cobalt sandwich compound (eta(5)-Cp**)Co(eta 4-tetramethyl-ethyl-1,3-cyclopentadiene) 9 as a mixture of isomers. The trinuclear cobalt alkylidine cluster [(eta(5)-CP*)Co](3) mu(3)-[C(CH3)](2) 8 is formed when reacting (eta(5)-Cp(R))Co(eta(2)-ethene)2 3 with equimolar amounts of di-isobutyl-aluminium-hydride or the borabicyclus 9-BBN.