Metallacarborane chemistry of the hypho-[6,7-C2B6H13]− anion: Reaction with nickelocene and the formation of three multimetallic nickel–boron clusters

The reaction of the hypho-[6,7-C2B6H13]− anion (1) with nickelocene and an excess of ‘proton sponge’ (1,8-bis-(dimethylamino-naphthalene)) in boiling acetonitrile leads to the formation of a pair of isomeric trimetallic nickel–boron clusters, [6,7,8-(CpNi)3-1-CB5H6] (2) and [6,7,8-(CpNi)3-2-CB5H6] (3), in a combined yield of 55%. Isomer (2) had been previously prepared from nido-2-CB5H9 but in much lower yield. Isomer (3) is without precedent and has been characterized using multi-nuclear NMR spectroscopy and mass spectrometry. Isomer (3) undergoes conversion to (2) via heating in boiling toluene. In addition to this isomeric pair, an interesting nido dimetallacarborane of constitution [6,6′-(CpNi)2-7,7′-C2B6H8] (4) has been isolated from the same reaction in 5% yield and characterized by single-crystal X-ray diffraction analysis.