Bimetallic zwitterions

Disproportionation of bimetallic fulvalene carbonyl complexes to bimetallic zwitterions... 

Despite the formal similarity of the reaction, the mechanism of Cp2ZrCl2-catalyzed ethylalumination [64] with AlEt3 is different from that of either methylalumination with AlMe3 or ethylalumination with Et2AlCl [62]. The involvement of dimetallic species was confirmed by NMR spectroscopy as well as deuterolysis (Scheme 8.31). The proposed mechanism features an interesting zwitterionic bimetallic species, in which the zirconium center is cationic. A highly instructive treatise on the mechanistic pathways of carbometalation is presented in [65],... 

Serendipitous formation of bimetallic complexes 55, 56 with a /7 -coordi-nated phosphonio-benzophospholides was observed in the reaction of the zwitterion 26 with [M2(CO)io] (M=Mn, Re) [43]. Complexes 56a,b were characterised by spectroscopic data and single-crystal X-ray diffraction studies whose results pointed to a low degree of d(M) r (L) charge-transfer and thus low metallacycle character, suggesting that, similar as in the copper r-complex 51, the coordinated double bond acts predominantly as n-donor rather than an as n-acceptor [43]. 

Complexes like 139 have been prepared and contain planar four-coordinate carbon atoms." " The zwitterionic early-late transition metal bimetallic species 140 has been synthesised and characterised. Little information about the structure, other than connectivity, could be inferred due to the poor nature of the crystallographic data." Heterobimetallic compounds such as 141 have been synthesised and fully characterised. Strong negative solvatachroism was observed along with high first-order hyperpolarisability The compound 142 has been prepared and crystallographically characterised. The role of planar... 

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