Boron-based transition metal clusters

It should be clear from the discussion of Section 2 that all of these clusters can be unstable with respect to cluster degradation in the presence of Lewis bases with the formation of saturated fragment species (see Boron Hydrides and Polynuclear Organometallic Cluster Complexes). Thus, in the presence of an excess of phosphine, the reaction of [HFe3(CO)9(/u-H)2BH] changes from that shown in equation (10) to that shown in equation (12). The mononuclear boron and iron products demonstrate that both transition metal and main group element vertices are removed by base and the cluster is degraded. ... 

Before considering organometallic clusters, we will find it useful to examine the capacity of boron to form clusters. The types of orbital interactions involved in boron-based clusters will provide useful background to understand the types of interactions that occur in organometallic clusters containing transition metals. 

Metallacarboranes are cluster compounds in which the cluster vertices comprise one or more metal atoms (main group metal, transition metal or rare earth [lanthanide or actinide] metal), one or more (most often two) carbon atoms, and boron atoms, the last usually in the majority. The total number of cluster vertices may vary but the vast majority of metallacarboranes have between 6 and 14 vertices moreover, the cluster may be either open or closed. However, the single largest group of metallacarboranes has 12 vertices and is structurally based on the closed icosahedron, 1. 

---