X-Ray structural studies of the two redox-related pairs [Cr(CO)2(η-PhC![[triple bond, length half m-dash]](http://hg.y866.cn/compound/lib/scimg/usr/1/CC9960002583.jpg)
CPh)(η6-C6HMe5)]0/1+ and [Mo(CO)2(η-PhCPh)(Tp′)]0/1+[Tp′= hydrotris(3,5-dimethyl-pyrazolyl)borate] are consistent with the HOMO of the d6, Cr0 alkyne complex being an antibonding M–alkyne π⊥ orbital.
