Supraicosahedral Polyhedra in Metallaboranes: Synthesis and Structural Characterization of 12‑, 15‑, and 16-Vertex Rhodaboranes

Syntheses
and structural characterization of supraicosahedral rhodaborane
clusters are reported. Reaction of [(Cp*RhCl2)2], (Cp* = η5-C5Me5) with [LiBH4·thf] followed by thermolysis with excess of [BH3·thf] afforded 16-vertex closo-[(Cp*Rh)3B12H12Rh­{Cp*RhB4H9}], 1, 15-vertex [(Cp*Rh)2B13H13], 2, 12-vertex [(Cp*Rh)2B10Hn(OH)m],
(3a: n = 12, m = 0; 3b: n = 9, m = 1; 3c: n = 8, m = 2) and 10-vertex
[(Cp*Rh)3B7H7], 4, and
[(Cp*Rh)4B6H6], 5. Cluster 1 is the unprecedented 16-vertex cluster, consists of a sixteen-vertex
{Rh4B12} with an exo-polyhedral
{RhB4} moiety. Cluster 2 is the first example
of a carbon free 15-vertex supraicosahedral metallaborane, exhibits
icosihexahedron geometry (26 triangular faces) with three degree-six
vertices. Clusters 3a-c have 12-vertex isocloso geometry, different from that of icosahedral one.
Clusters 4 and 5 are attributed to the 10-vertex isocloso geometry based on 10-vertex bicapped square antiprism
structure. In addition, quantum-chemical calculations with DFT methods
at the BP86 level of theory have been used to provide further insight
into the electronic structure and stability of the optimized structures
which are in satisfactory agreement with the structure determinations.
All the compounds have been characterized by IR, 1H, 11B, 13C NMR spectroscopy in solution, and the solid
state structures were established by crystallographic analysis of
compounds 1–5.