Chemical reactivity dinuclear complexes

There is a large number of heteroleptic dithiolene complexes—complexes that contain at least one dithiolene and at least one other ligand. This chapter is focused on mononuclear and relatively simple dinuclear complexes. The electrochemistry of heteroleptic dithiolene complexes is only briefly discussed in view of the limited amount of data available. Oxodithiolene complexes are often studied as structural models for Mo and W enzymes and are reviewed in Chapter 10 in this volume (113). Focused here is the chemical reactivity of selected types of heteroleptic dithiolene complexes. 

This group demonstrated that both dinuclear complexes 38 and 40 exhibit a remarkably better activity than the mononuclear complexes 39 and 41 at equivalent metal-catalyst concentrations (Table 22.19). The reaction was evaluated/tested against the Monsanto catalyst [Rhl2(CO)2l used in industrial processes, which is formed in situ from [ RhCl(CO)2 2]. In the carbonylation of methanol, 38 outperformed the Monsanto catalyst, whereas 40 demonstrated a similar turnover number. The exceptionally good reactivity could be explained by the formation of thermally stable metal chelate complexes, due to the ort/ o-carborane(12) backbone. NMR spectra of the residue at the end of the reaction showed a high content of phosphine bound to rhodium with a retained bimetallic structure, indicated by the chemical shifts and coupling constants. 

The reactivity of dinuclear anionic hydroxo complexes of the type [ R2M(pi-OH) 2]2- (M = Ni, Pd, or Pt) toward weak acids as pyrazoles was studied extensively. The chemical behavior is consistent with the high-field proton resonances of the OH bridges (65, 66). The (/i-hydroxo)(/r-pyrazolate) or bis(jt-pyrazolate) complexes (the latter are described in Section III.C) were obtained, depending on the reactants molar ratio (M/Hpz = 1 or 2, respectively) (60-65) (Table VII). 

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