Dr. Craig M. Davis, Associate Professor
202A Logan Hall, (513)-745-2066
Synthesis, Reactivity and Properties of Metallaborane Complexes
Many single-metal-atom, three-boron-atom clusters are known, but only a handful of two-metal-atom clusters have been reported in the literature; moreover, these were by-products of other reactions and not the results of planned syntheses. A rational synthetic approach to two-metal-atom clusters was sought. The two-tungsten-atom compound [(C5H5)W(CO)3]2 was selected as the metal reagent to react with [B3H8]-.
Formation of two-metal-atom clusters did not ensue; instead, clean, rapid, systematic borane-cage expansion was observed. Refluxing a 1:1 mixture of [B3H8]- and [(C5H5)W(CO)3]2 in toluene or dioxane lead to the rapid, quantitative conversion of [B3H8]- to B5H9. However, refluxing a 2:1 mixture of [B3H8]- and [CpW(CO)3]2 in the same solvents yielded [B9H14]- and [B11H14]- as the primary products.
Comparable reactions with the molybdenum analogue of the dimer [(C5H5)Mo(CO)3]2 have been conducted. Preliminary results (11B-NMR spectra) indicate the molybdenum dimer is not promoting cage expansion. We currently are attempting to separate and purify the products with column chromatography.
A second area of exploration will be to see if the tungsten dimer can induce single-boron species (BH3 or [BH4]-) to coalesce into clusters. We also plan to probe the interactions of [B3H8]- with the three-metal-atom molecules Fe3(CO)12 and Ru3(CO)12. Will their “multinuclear” (multiple metal atoms) nature cause cage expansion? Perhaps an unexpected series of reactions will occur.
1. Davis, C. M.; Klein, M. F.; Nicholson, K. T. “Organotransition-Metal-Mediated Borane- Cage Expansion.” Phosphorus, Sulfur Silicon Relat. Elem. 2001, 179, 123-128.