Carbonylmetallates as Versatile 2-, 4- or 6-Electron Donor Metalloligands in Transition-Metal Complexes and Clusters:...

Carbonylmetallates [m]^- , such as [MoCp(CO)₃ ]^- , [Mn(CO)₅ ]^- , [Co(CO)₄ ]^- , have long been successfully used in the preparation of hundreds of metal-metal bonded carbonyl complexes and clusters, in particular of the heterometallic type. We focus here on situations where [m]^- can be viewed as a terminal, doubly or even triply bridging metalloligand, developing metal-metal interactions with one, two or three metal centers M, respectively. With metals M from the Groups 10-12, it is not straightforward or even impossible to rationalize the structure of the resulting clusters by applying the well-known Wade-Mingos rules. A very simple but global approach is presented to rationalize structures not obeying usual electron-counting rules by considering the anionic building blocks [m]^- as metalloligands behaving formally as potential 2-, 4- or 6-electron donors, similarly to what is typically encountered with for example halido ligands. Qualitative and theoretical arguments by using DFT calculations highlight similarities between seemingly unrelated metal complexes and clusters and also entail a predicting power with high synthetic potential.