Polyhedral and Macropolyhedral Metal-Rich Cobaltaboranes: A 25-Vertex Hourglass-Shaped Cluster.

In an effort to break the single-cage 16-vertex supraicosahedral barrier, we have explored the reaction of [Cp*CoCl 2 ], 1 with [LiBH 4 ·THF], followed by thermolysis with [BH 3 ·SMe 2 ] [Cp* = η 5 -C 5 Me 5 ]. Although our objective to synthesize a high-nuclearity single-cage cluster was not achieved, we have isolated a 25-vertex macropolyhedral cluster [(Cp*Co) 5 Co 2 B 18 H 17 (CH 3 )S] ( 2 ). Cluster 2 is an exceptional fused hourglass-shaped macropolyhedral cluster composing two icosahedral cores ([Co 3 B 9 ] and [Co 4 B 8 ]) and three tetrahedral cores [Co 2 B 2 ]. Although the fusion in cluster 2 is very complex, it follows Mingos fusion formalism, leading to an attractive hourglass-shaped cluster. Through subtle changes in reaction conditions, two new cobaltaborane clusters, nido -4,5,7-[(Cp*Co) 3 B 7 H 11 ] ( 3 ) and nido -2,9-[(Cp*Co) 2 B 8 H 12 ] ( 4 ), have been isolated. The observed core geometries of clusters 3 and 4 are similar to the parent deltahedra [B 10 H 14 ] with ( n + 2) SEP (SEP = skeletal electron pair, n = no. of vertices). All the synthesized cobaltaboranes have been characterized in solution by ESI-mass, nuclear magnetic resonance spectroscopy, infrared spectroscopy and structurally solved by single-crystal X-ray diffraction analysis.