TETRACOBALT COMPLEXES WITH CO-3 FACE-CAPPING CYCLOHEPTATRIENYL AND CYCLOOCTATETRAENE LIGANDS

The novel tetracobalt cluster complexes [CO4(CO)(6)(eta(5)-C7H9)(mu(3) -C7H7)] (8) and [CO4(CO)(6)(eta(4)-C8H8)(mu(3)-C8H8)] (9), which conta in facial CnHn ligands, were obtained in high yield from [Co-4(CO)(12) ] (5) and cycloheptatriene or cyclooctatetraene, respectively, in boil ing n-heptane. Treatment of 9 with [Fe(CO)(5)], cyclohexadiene or 6,6- diphenylfulvene gave the derivatives [CO4- (CO)(6)(L)(mu(3)C(8)H(8))], 10 [L = (CO)(2)], 11 (L = eta(4)-C6H8), and 12 (L=eta(4)-C5H4CPh2). T he crystal structures of 8-11 were determined. The facial (face-cappin g) C7H7 ligand in 8 adopts a mu(3)-eta(2):eta(3):eta(3) coordination m ode to a Co-3 face of the tetracobalt cluster. The coordination geomet ry of the facial C8H8 ligands in 9-11 can be viewed as within a contin uum limited by mu(3)- eta(2):eta(3):eta(3) and mu(3)-eta(3) eta(3) eta (3). In solution, 8-12 are highly fluxional (rapid reorientation of th e mu(3)-CnHn ligands, rapid hapto-tropic shifts involving the apical C nHn ligand in 9). The crystal packing of 8-11 has been examined in det ail; the hydrogen atoms of the cycloheptatrienyl and cyclooctatetraene ligands take part in intra-and intermolecular hydrogen bonding intera ctions of the C-H ... O type.