Rhenium bimetallic complexes

The bimetallic complex [Re(CO)3Cl]jtbpq synthesized in this work showed the typical spectroscopic and electrochemical behavior based on analogous polypyridyl complexes of rhenium(l). Re(l) dn tpbq n charge transfer transition and ligand-field n- n transitions are observed. Typical redox behavior of this system consists of Re /Re oxidation and tpbq/tpbq reduction. Such electrochemical activity, particularly in the reductive region, is found ideal for catalytic processes such as CO reduction. IR-SEC studies have shown that the reduction process occurring at -0.50... 

The main routes for the synthesis of rhenium(II) compounds involve oxidation of rhenium(I) or the reduction of rhenium(III) complexes. Additionally a few examples are known where Re" species are formed during the cleavage of Re—Re bonds of bimetallic units. 

The electrochemical technique can be used also for direct synthesis of bimetallic alkoxides. For instance, the anodic dissolution of rhenium in the methanol-based electrolyte that already contained MoO(OMe)4, permitted to prepare with a good yield (60%) a bimetallic complex RevMov,02(OMe)7, with a single Re-Mo bond [904], Application of the same procedure permitted the preparation of complex alkoxide solutions with controlled composition for sol-gel processing of ferroelectric films [1777]. 

In addition to the bimetallic complexes of rhenium and alkaline metals formed as byproducts in the exchange reactions of rhenium halids with alkali alkoxides (such as, for example, LiReO(OPr )5 xLiCl(THF)2 [519]) there has been recently prepared a number ofbimetallic complexes ofrhenium and molybdenum, rhenium and tungsten, and rhenium and niobium [904, 1451]. The latter are formed either due to the formation of a metal-metal bond, arising due to combination of a free electron pair on rhenium (V) and a vacant orbital of molybdenum (VI) atom or via insertion of molybdenum or tungsten atoms into the molecular structure characteristic of rhenium (V and VI) oxoalkox-ides. The formation of the compounds with variable composition becomes possible in the latter case. 

The use of carbonyl complexes has enabled proper study of the role of rhenium in Pt-Re bimetallic catalysts used in the reforming of naphtha [57-60] and tailoring of the preparation of Pt-Ru bimetallic particles. Pt-Ru systems are of interest in developing electrodes for fuel cell applications [61]. 

The complex formation of tungsten alkoxides with the alkoxides of other metals than the alkali, bismuth, and rhenium (see Section 12.21) has not been investigated in detail, and therefore the major attention below will be paid to the description of the bimetallic alkoxides of molybdenum. 

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