Cp*TaCl2B4H8: synthesis, crystal structure and spectroscopic characterization of an air-stable, electronically unsaturated, chiral tantalaborane

Reaction between Cp*TaCl4 (Cp* = η5-C5H5) and BH3·thf at 40 °C yields the pale red electronically unsaturated cluster Cp*TaCl2B4H8 1 which despite having two electrons fewer than the seven pairs required for the observed square pyramidal geometry is stable in air; viewed as a cluster, 1 is the first example of an unsaturated cluster containing a single metal atom; viewed as a chiral 16-electron organometallic complex it is isoelectronic with Cp(C2B9H11)TaCl2 and Cp[(Me3Si)2C2B4H4]TaCl2.