Synthesis and Structure of Dirhodium Analogue of Octaborane-12 and Decaborane-14

We present the results of our investigation of a thermally driven duster expansion of rhodaborane systems with BH3 center dot THF. Four novel rhodaborane dusters, for example, nido-[(CP*Rh)(2)-B6H10], 1; nido-[(CP*Rh)B9H13] 2; nido-[(CP*Rh)(2)-B8H21], 3; and nido-[(Cp*Rh)(3)B8H9(OH)(3)], 4 (Cp* = eta(5)-C5Me5), have been isolated from the thermolysis of [Cp*RhCl2](2) and borane reagents in modest yields. Rhodaborane 1 has a nido geometry and is isostructural with [B8H12]. The low temperature B-11 and H-1 NMR data demonstrate that compound 1 exists in two isomeric forms. The framework geometry of 2 and 3 is similar to that of [B10H14] with one BH group in 2 (3-position), and two BH groups in 3 (3, 4-positions) are replaced by an isolobal {Cp*Rh} fragment The 11 vertex cluster 4 has a nido structure based on the 12 vertex icosahedron, having three rhodium and eight boron atoms. In addition, the reaction of rhodaborane 1 with [Fe-2(CO)(9)] yielded a condensed duster [(Cp*Rh)(2){Fe(CO)(3)}(2)B6H10], 5. The geometry of 5 consists of [Fe2B2] tetrahedron and an open structure of [(Cp*Rh)(2)B-6], fused through two boron atoms. The accuracy of these results in each case is established experimentally by spectroscopic characterization in solution and structure determinations in the solid state.