Ligand stereochemistry of metal clusters containing π-bonded ligands

The dummy atom formalism, originally proposed by Doman, Landis, and Bosnich for metallocenes, has been generalized in order to deal with any kind of π-bonding ligands and cluster faces (which can also be seen as polyhapto moieties). A modified VESCF approach has been used to derive a general force field for η(n)-coordinated π-bonding ligands whose performances are comparable with those of the best current force fields for cyclopentadienyl derivatives but can be used also for μ3-η2:η2:η2 and even complex coordination modes. This approach, which can be considered a further step in the building up of a general force field for metal (carbonyl) clusters, has been tested by rationalizing the dynamic stereochemistry in solution of two classes of triangular clusters: M3L3(CO)3 (M = Co, Rh, Ir; L = η5-Cp, η5-Cp*, η5-Ind) and Co3(η5-Cp)3(μ3-η2:η2:η2-RR'C6H4) (R = R' = H, Me, Et and R = Me, Et, (i)Pr; R' = H).