Alkylidene dynamics in the cluster complex Cp ∗Rh(CpCo) 2(CO) 2(μ-CH 2): Observation of an intermediate containing a μ3-methylidene ligand

Abstract

The dynamic behaviour of the methylidene ligand in the triangular cluster complex, Cp ∗Rh(CpCo) 2(CO) 2(μ-CH 2) 3, has been investigated using multidimensional NMR techniques. Two distinct processes have been identified whereby the methylidene ligand moves between bridging different metal-metal bonds in the complex: (1) methylidene jumps from a RhCo bond to the CoCo bond and (2) degenerate methylidene jumps between the two RhCo bonds of the metal triangle. An intermediate has been observed for the latter process. Based on 1H and 13C NMR data, we propose that the methylidene ligand in this intermediate occupies a triply-bridging coordination position above the metal triangle, simultaneously interacting with all three metal atoms in the complex. To our knowledge, this is the first observation of an intermediate involved in the dynamic behaviour of an alkylidene ligand. Furthermore, it is only the second example of a μ 3-methylidene ligand to be reported. The implications of these results in the areas of alkylidene mobility on metal surfaces and catalysis are discussed.