one R' is other than hydrogen on at least one (C5 R'4), R is a germanium, silicon, phosphine or amine radical substituting on and bridging two (C5 R'4) rings, each Q which can be the same or different is an aryl, alkyl, alkenyl, alkylaryl, or arylalkyl radical having from 1 to 20 carbon atoms or halogen, and Q' is an alkylidene radical having from 1-20 carbon atoms. 3.