Synthesis and spectroscopic characterisation of binuclear molybdenum-rhenium complexes

Protonation of CpMo(eta(3)-C3H5)(CO)(2) followed by reactions with several diazole ligands produce the molybdenum half-sandwich complexes [CpMo(CO)(2)L-2](+) (L-2 = Bisimidazole (H(2)Biim), pyrazole (Hpz)(2), Cpz(4), and [Bpz(4)](-)) in good yields. Deprotonation of [CpMo(CO)(2)(H(2)Biim)](+) gives the anionic complex [CpMo(CO)(2)(Biim)](-). The structure of [CpMo(CO)(2)(H(2)Biim)][ReO4] was determined by X-ray single crystal analysis. The coordination geometry around the molybdenum atom in the complex cation [CpMo(CO)(2)(H(2)Biim)](+) can be described as a distorted square pyramid. The basal plane is defined by two nitrogen atoms of H(2)Biim bidentate ligand and two carbon atoms of carbonyl groups. The apical position is occupied by five carbon atoms of the eta(5)-C5H5 ligand. The Mo centre lies at 0.94(1) Angstrom from the basal plane in the apical direction. [CpMo(CO)(2)(Biim)](-) reacts with ClReO3 or MeReO3 (MTO) to give binuclear complexes of the formula [{CpMo(CO)(2)}(mu-Biim){Re(X)O-3}]Na (X = Cl, CH3) in quantitative yields. [CpMo(CO)(2)(mu-Cpz(4))][BF4] reacts with ClReO3 to yield [{CpMo(CO)(2)}(mu Cpz(4)){Re(Cl)O-3}][BF4]. The corresponding adduct [{CpMo(CO)(2)}(mu-Cpz(4)){Re(Cl)O-3}][BF4] can not be obtained in a pure form. The reaction of [Bpz(4)](-) with ClReO3 yield the known Bpz(4)ReO(3), with MeReO3 the sensitive [Bpz(4){Re(CH3)O-3}]K is obtained. Deprotonation of the molybdenocene complex [Cp2Mo(H(2)Biim)](2+) leads to the neutral compound Cp2Mo(Biim). The latter compound can be reacted with CH3ReO3 or ClReO3 to form [{Cp2Mo}(mu-Biim){Re(X)O-3}] (X = CH3, Cl). A Mo-95 NMR investigation shows the influence of the overall charge of the complex and the electron donor capability on the Mo centre. It is shown by Mo-95, O-17, H-1 NMR, and IR spectroscopy that the donor capability of the molybdenocene to the rhenium(VII) centre in the binuclear complexes is not very pronounced and can be compared to the strength of organic nitrogen donor complexes, e.g. 2,2'-bipyridyl. In donor solvents temperature dependent, rapid dynamic exchange processes can be observed. (C) 1998 Elsevier Science Ltd. All rights reserved.