Cobalt and Nickel Compounds with Pentadienyl and Edge-Bridged Pentadienyl Ligands: Revisited

A series of Co(I), Co(II), and Ni(II) compounds were prepared by employing the open pentadienyl 2,4-(Me3C)2C5H5 (Pdl′) and some edge-bridged variants (ePdl) such as 6,6′-dimethylcyclohexadienyl (dmch), cycloheptadienyl (chd), and cyclooctadienyl (cod). The sterically encumbered Pdl′ ligand allowed the first synthesis of an open cobaltocene derivative [(η3-Pdl′2)Co] (1), which adopts a low-spin configuration and features two η3-coordinate Pdl′ units. For Ni(II), the heteroleptic derivative [(η3-Pdl′)Ni(acac)] (2) and the open nickelocene [(η3-Pdl′2)Ni] (3) were isolated. Complex 3 is isostructural to its Co analogue (1). The reactivity patterns, however, change when similar reactions are performed with the edge-bridged pentadienyl derivatives (ePdl = dmch, chd, and cod). For [Co(acac)2] the reaction with K(dmch) and K(chd) resulted in reduction of Co(II) to Co(I), concomitant with ligand coupling to form bridging Co(I) complexes 5 and 6 with μ2-η4:η4-(dmch)2 and μ2-η4:η4-(chd)2 units, respectively. In cont...