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.