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

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journal contribution
posted on 25.10.2019, 12:08 by Matthias Reiners, Ann Christin Fecker, Dirk Baabe, Matthias Freytag, Peter G. Jones, Marc D. Walter
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 μ244-(dmch)2 and μ244-(chd)2 units, respectively. In contrast, the isolation of [(η3-dmch)2Ni] (7) and [(η3-cod)2Ni] (8) proceeds in excellent yields. In addition, several Co­(I) complexes of the type [(η3-cod)­Co­(L3)] (L = PMe3; L2 = dppe/dmpe, L = PMe3/CO) were prepared, which feature low melting and sublimation/distillation points. These complexes may offer potential for ALD/CVD processes.