Bis(arylimido)Cr(VI) dialkyls lacking beta-hydrogen decompose by alpha-hydrogen abstraction and, upon trapping with triphenylphosphine, yield isolable alkylidene complexes. Two such complexes, namely (ArN)(2)Cr=CHR(PPh3) (R = Bu-t, SiMe3), have been structurally characterized. The coordinatively unsaturated alkylidene intermediates are highly reactive; they effect C-H activation of saturated hydrocarbons and they react with olefins to produce metallacyclobutanes.