Tetracobalt complexes with Co3 face-capping cycloheptatrienyl and cyclooctatetraene ligands

Abstract

The novel tetracobalt cluster complexes [Co4(CO)6(η5-C7H9) (μ3-C7H7)] (8) and [Co4(CO)6(η4-C8H8)(μ3-C8H8)] (9), which contain facial C(n)H(n) ligands, were obtained in high yield from [Co4(CO)12] (5) and cycloheptatriene or cyclooctatetraene, respectively, in boiling n-heptane. Treatment of 9 with [Fe(CO)5], cyclohexadiene or 6,6-diphenylfulvene gave the derivatives [Co4(CO)6(L)(μ3-C8H8)], 10 [L=CO)2], 11 (L=η4-C6H8), and 12 (L=η4-C5H4CPh2). The crystal structures of 8-11 were determined. The facial (face-capping) C7H7 ligand in 8 adopts a μ3-η3:η3 coordination mode to a Co3 face of the tetracobalt cluster. The coordination geometry of the facial C8H8 ligands in 9-11 can be viewed as within a continuum limited by μ3-η2:η3:η3 and μ3-η3:η3:η3. In solution, 8-12 are highly fluxional (rapid reorientation of the μ3-C(n)H(n) ligands, rapid haptotropic shifts involving the apical C(n)H(n) ligand in 9). The crystal packing of 8-11 has been examined in detail; the hydrogen atoms of the cycloheptatrienyl and cyclooctatetraene ligands take part in intra- and intermolecular hydrogen bonding interactions of the C-H···O type.