Vertex-Fused Clusters Featuring a Flattened Butterfly

In an effort to exploit the reactive chalcogen centers (Se or S) of preformed metallaheteroboranes [Cp*Ta­(EPh)2{B4H8}] (Cp* = η5-C5Me5; 1, E = Se; 2, E = S) toward cluster growth reactions, we have carried out the photolysis of tantallaheteroboranes 1 and 2 with the group 6 metal carbonyls [M­(CO)5·THF] (M = Mo, W). The reactions yielded the vertex-fused metallaheteroborane clusters [{(CO)4M­(EPh)2}­Cp*Ta­{B4H8}] (3, E = Se, M = Mo; 4, E = Se, M = W; 5, E = S, M = Mo; 6, E = S, M = W). Clusters 3–6 comprise square-pyramidal {TaB4} and butterfly {TaME2} cores having a common Ta vertex. All of the butterfly cores of these fused metallaheteroboranes 3–6 are almost flat, in which the dihedral angle between the planes W1–S1–Ta1 and W1–S1′–Ta1 of 6 was observed to be 175.32°.