Dynamic Behavior of the P₇^3- Cluster and Its Derivatives with Main-Group and Transition Metal Fragments

The mobility of main-group and transition metal fragments on the surface of a phosphorus cluster, P₇^3-, has been explored using density functional theory. The naked P₇^3- cluster undergoes rapid exchange of apical, bridging, and basal sites via the concerted making and breaking of P-P bonds, but the presence of substituents linking two of the phosphorus sites blocks some of the available pathways. In the boron-substituted cluster [P₇(9-BBN)]^2- (9-BBN = 9-borabicyclo[3.3.1]nonane), the boron center can move between the three bridging P centers via a "merry-go-round" pathway, where significant B═P double bond character stabilizes the three-coordinate boron at the transition state. The migration of transition metal fragments such as [Pt(H{(PPh₃)]⁺, in contrast, is more restricted because the corresponding "merry-go-round" transition states are very high in energy. The [P₇(9-BBN)]^2- cluster has been shown to be an effective catalyst for the hydroboration of carbonyl compounds, where the lability of the boron center highlighted here may play an important role in allowing the substrate to access binding sites.