Abstract
A review. The research of Kreisel et al. who aimed to achieve metal-metal bond shortening by using a noninnocent ligand is reviewed with commentary and refs. According to DFT calcns. at the BLYP/6-311g level and natural resonance theory anal., the bonding in the compd. appears to involve five occupied MOs with significant Cr-Cr bonding character, raising the possibility of a quintuple bond description in agreement with the extremely short metal-metal distance. However, the difficulty in using noninnocent ligands such as the RNCHCHNR system concerns the identification of bonding orbitals. The MOs making up the multiple bonding may be considerably delocalized, rendering the classical concept of metal- metal bonding with little covalent contributions from the ligands less straightforward. Nevertheless, on the way to the half-century mark for recognized transition metal-metal multiple bonding, it seems that there is still ample room for isolation of novel metal-metal bonded species with remarkable (and unpredicted) compns. and unusual properties. on SciFinder(R)
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