Organometallic and classical coordination sites in highly preorganized pyrazolate-based hybrid systems: The Mn/Ni case

Abstract

A series of unsymmetric heterodinuclear Mn/Ni complexes is reported in which an organometallic CpMn(CO)(2) fragment and a classical Werner-type nickel(II) subunit are arranged in close proximity by means of a bridging pyrazolate. The two metalloligand scaffolds (1 and 2) employed differ in the chelate size of the tripodal tetradentate (N-4) binding site for nickel. Molecular structures have been determined for (1-(H))Ni(NO3) (3), (2-H)Ni(NO3) (4), and (2-H)Ni(OAc) (5). Comparison with the molecular structures of the related Mn/Mn, Mn/ Co, and Mn/Zn systems confirms that structural flexibility is greater for the complexes based on ligand 2 due to the longer chelate arms. According to IR and UV/Vis spectroelectro-chemistry, oxidation of the heterobimetallic systems is highly localized at the organometallic manganese site. Structural and spectroscopic features as well as trends for the redox potentials of the Mn-I/Mn-II couple suggest that ligand variations at the nickel(II) Werner-type subunit exert only a small influence on the properties of the organometallic part. In contrast, reduction occurs at the nickel site and is strongly dependent on the anion present. The effects at the organometallic CpMn(CO)(2) subunit upon reduction of the proximate nickel ion are most pronounced for 5.