Synthesis and structure of dirhodium analogue of octaborane-12 and decaborane-14

Abstract

We present the results of our investigation of a thermally driven cluster expansion of rhodaborane systems with BH₃·THF. Four novel rhodaborane clusters, for example, nido-[(Cp*Rh) ₂B₆H₁₀], 1; nido-[(Cp*Rh)B₉H₁₃], 2; nido-[(Cp*Rh)₂B₈H₁₂], 3; and nido-[(Cp*Rh) ₃B₈H₉(OH)₃], 4 (Cp* = η⁵-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 ¹¹B and ¹H 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 [Fe₂ (CO)₉] yielded a condensed cluster [(Cp*Rh)₂{Fe(CO)₃}₂B₆H₁₀], 5. The geometry of 5 consists of [Fe₂B₂] tetrahedron and an open structure of [(Cp*Rh)₂B₆], 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.