Synthesis and spectroscopic characterisation of binuclear molybdenum-rhenium complexes

Abstract

Protonation of CpMo( η 3-C 3H 5)(CO) 2 followed by reactions with several diazole ligands produce the molybdenum half-sandwich complexes [CpMo(CO) 2L 2] + (L 2 = Bisimidazole (H 2Biim), pyrazole (Hpz) 2, Cpz 4, and [Bpz 4] −) in good yields. Deprotonation of [CpMo(CO) 2(H 2Biim)] + gives the anionic complex [CpMo(CO) 2(Biim)] −. The structure of [CpMo(CO) 2(H 2Biim)][ReO 4] was determined by X-ray single crystal analysis. The coordination geometry around the molybdenum atom in the complex cation [CpMo(CO) 2(H 2Biim)] + can be described as a distorted square pyramid. The basal plane is defined by two nitrogen atoms of H 2Biim bidentate ligand and two carbon atoms of carbonyl groups. The apical position is occupied by five carbon atoms of the η 5-C 5H 5 ligand. The Mo centre lies at 0.94(1) Å from the basal plane in the apical direction. [CpMo(CO) 2(Biim)] − reacts with ClReO 3 or MeReO 3 (MTO) to give binuclear complexes of the formula [{CpMo(CO) 2}(μ-Biim){Re(X)O 3}]Na (X = Cl, CH 3) in quantitative yields. [CpMo(CO) 2(μ-Cpz 4)][BF 4] reacts with ClReO 3 to yield [{CpMo(CO) 2}(μ-Cpz 4){Re(Cl)O 3}][BF 4]. The corresponding adduct [{CpMo(CO) 2}(μ-Cpz 4){Re(Cl)O 3}][BF 4] can not be obtained in a pure form. The reaction of [Bpz 4] − with ClReO 3 yields the known Bpz 4ReO 3, with MeReO 3 the sensitive [Bpz 4{Re(CH 3)O 3}]K is obtained. Deprotonation of the molybdenocene complex [Cp 2Mo(H 2Biim)] 2+ leads to the neutral compound Cp 2Mo(Biim). The latter compound can be reacted with CH 3ReO 3 or ClReO 3 to form [{Cp 2Mo}(μ-Biim){Re(X)O 3}] (X = CH 3, Cl). A 95Mo 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 95Mo, 17O, 1H 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.