Cluster Growth Reactions: Structures and Bonding of Metal-Rich Metallaheteroboranes Containing Heavier Chalcogen Elements.

In an effort to synthesize cobalt-rich metallaheteroboranes from decaborane(14) analogues, we have studied the reaction of 10-vertex nido -[(Cp*Co) 2 B 6 H 6 E 2 ] (Cp* = η 5 -C 5 Me 5 , 1 : E = Se and 2 : E = Te) with [Co 2 (CO) 8 ] under thermolytic conditions. All of these reactions yielded face-fused clusters, [(Cp*Co) 2 B 6 H 6 E 2 {Co(CO)}(μ-CO){Co 3 (CO) 6 }] ( 3 : E = Se and 4 : E = Te). Further, when clusters 3 and 4 were treated with [Co 2 (CO) 8 ], they underwent further cluster buildup reactions leading to the formation of 16-vertex doubly face-fused clusters [(Cp*Co) 2 B 6 H 6 E 2 {Co 2 (CO) 2 }(μ-CO) 2 {Co 4 (CO) 8 }] ( 5 : E = Se and 6 : E = Te). Cobaltaheteroboranes 3 and 4 comprise one icosahedron {Co 4 B 6 E 2 } and one square pyramidal {Co 3 B 2 } moiety, whereas 5 and 6 are made with one icosahedron {Co 4 B 6 E 2 } and two square pyramidal {Co 3 B 2 } cores. In an attempt to generate heterometallic metal-rich clusters, we have explored the reactivity of decaborane(14) analogue nido -[(Cp*Co) 2 B 7 TeH 9 ] ( 7 ) with [Ru 3 (CO) 12 ] at 80 °C, which afforded face-fused 13-vertex cluster [(Cp*Co) 2 B 7 H 7 Te{Ru 3 (CO) 8 }] ( 8 ). Cluster 8 is a rare example of a metal-rich metallaheteroborane in which one icosahedron {Co 2 Ru 2 B 7 Te} and a tetrahedron {Ru 2 B 2 } units are fused through a common {RuB 2 } triangular face. Further, the treatment of nido -[(Cp*Co) 2 B 6 S 2 H 4 (CH 2 S 2 )] ( 9 ) with [Fe 2 (CO) 9 ] afforded 11-vertex nido -[(Cp*Co) 2 B 6 S 2 H 4 (CH 2 S 2 ){Fe(CO) 3 }] ( 10 ). The core structure of 10 is similar to that of [C 2 B 9 H 11 ] 2- with a five-membered pentahapto coordinating face. All of the synthesized metal-rich metallaheteroboranes have been characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy, IR spectroscopy, ESI-MS, and structurally solved by single-crystal X-ray diffraction analysis. Furthermore, theoretical investigations gave insight into the bonding of such higher-nuclearity clusters containing heavier chalcogen atoms.