Novel Class of Heterometallic
Cubane and Boride Clusters
Containing Heavier Group 16 Elements
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Abstract
Thermolysis of an in situ generated intermediate, produced
from
the reaction of [Cp*MoCl<sub>4</sub>] (Cp* = η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>) and [LiBH<sub>4</sub>.THF], with excess Te
powder yielded isomeric [(Cp*Mo)<sub>2</sub>B<sub>4</sub>TeH<sub>5</sub>Cl] (<b>2</b> and <b>3</b>), [(Cp*Mo)<sub>2</sub>B<sub>4</sub>(μ<sub>3</sub>-OEt)TeH<sub>3</sub>Cl] (<b>4</b>), and [(Cp*Mo)<sub>4</sub>B<sub>4</sub>H<sub>4</sub>(μ<sub>4</sub>-BH)<sub>3</sub>] (<b>5</b>). Cluster <b>4</b> is a notable example of a dimolybdaoxatelluraborane cluster where
both oxygen and tellurium are contiguously bound to molybdenum and
boron. Cluster <b>5</b> represents an unprecedented metal-rich
metallaborane cluster with a cubane core. The dimolybdaheteroborane <b>2</b> was found to be very reactive toward metal carbonyl compounds,
and as a result, mild pyrolysis of <b>2</b> with [Fe<sub>2</sub>(CO)<sub>9</sub>] yielded distorted cubane cluster [(Cp*Mo)<sub>2</sub>(BH)<sub>4</sub>(μ<sub>3</sub>-Te){Fe(CO)<sub>3</sub>}] (<b>6</b>) and with [Co<sub>2</sub>(CO)<sub>8</sub>] produced the
bicapped pentagonal bipyramid [(Cp*MoCo)<sub>2</sub>B<sub>3</sub>H<sub>2</sub>(μ<sub>3</sub>-Te)(μ-CO){Co<sub>3</sub>(CO)<sub>6</sub>}] (<b>7</b>) and pentacapped trigonal prism [(Cp*MoCo)<sub>2</sub>B<sub>3</sub>H<sub>2</sub>(μ<sub>3</sub>-Te)(μ-CO)<sub>4</sub>{Co<sub>6</sub>(CO)<sub>8</sub>}] (<b>8</b>). The geometry
of <b>8</b> is an example of a heterometallic boride cluster
in which five Co and one Mo atom define a trigonal prismatic framework.
The resultant trigonal prism core is in turn capped by two boron,
one Te, and one Co atom. In the pentacapped trigonal prism unit of <b>8</b>, one of the boron atoms is completely encapsulated and bonded
to one molybdenum, one boron, and five cobalt atoms. All the new compounds
have been characterized in solution by IR, <sup>1</sup>H, <sup>11</sup>B, and <sup>13</sup>C NMR spectroscopy, and the structural types
were unambiguously established by crystallographic analysis of <b>2</b> and <b>4</b>–<b>8</b
