Tris(3,5-dimethylpyrazolyl)methane-Based Heterobimetallic Complexes that Contain Zn- and Cd-Transition-Metal Bonds: Synthesis, Structures, and Quantum Chemical Calculations

Reactions of the tris(3,5-dimethylpyrazolyl)methanide amido complexes [M'{C(3,5-Me(2)pz)(3)}{N(SiMe3)(2)}] (M'=Mg (1a), Zn (1b), Cd (1c); 3,5-Me(2)pz=3,5-dimethylpyrazolyl) with two equivalents of the acidic Group 6 cyclopentadienyl (Cp) tricarbonyl hydrides [MCp(CO)(3)H] (M=Cr (2a), Mo (2b)) gave different types of heterobimetallic complex. In each case, two reactions took place, namely the conversion of the tris(3,5-dimethylpyrazolyl) methanide ligand (Tpmd*) into the -methane derivative (Tpm*) and the reaction of the acidic hydride M-H bond with the M'-N(SiMe3)(2) moiety. The latter produces HN(SiMe3)(2) as a byproduct. The Group 2 representatives [Mg(Tpm*){MCp(CO)(3)}(2)(thf)] (3a/b) form isocarbonyl bridges between the magnesium and chromium/molybdenum centres, whereas direct metal-metal bonds are formed in the case of the ions [Zn(Tpm*){MCp(CO)(3)}](+) (4a/b; [MCp(CO)(3)](-) as the counteranion) and [Cd(Tpm*){MCp(CO)(3)}(thf)](+) (5a/b; [Cd{MCp(CO)(3)}(3)](-) as the counteranion). Complexes 4a and 5a/b are the first complexes that contain Zn-Cr, Cd-Cr, and Cd-Mo bonds (bond lengths 251.6, 269.8, and 278.9 pm, respectively). Quantum chemical calculations on 4a/b* (and also on 5a/b*) provide evidence for an interaction between the metal atoms.