In chemistry, a metallaborane is a compound that contains one or more metal atoms and one or more boron hydride.  These compounds are related conceptually and often synthetically to the boron-hydride clusters by replacement of BH units with metal-containing fragments.  Often these metal fragments are derived from metal carbonyls or cyclopentadienyl complexes. Their structures can often be rationalized by polyhedral skeletal electron pair theory.  The inventory of these compounds is large, and their structures can be quite complex.