The Unusual Stability of Homoleptic Di- and Tetravalent Chromium Alkyls

Reaction of CrCl 3 (THF) 3 with 3 equiv of R−M [R = Me 3 CCH 2 ( a ), Me 3 SiCH 2 ( b )] afforded either the previously reported tetravalent homoleptic R 4 Cr ( 1a, b ) [M = MgCl] or the unprecedented divalent and tetranuclear homoleptic [R 2 Cr] 4 ( 2b ) [M = Li]. Both types of compounds display a remarkable chemical inertness toward proton transfer agents but readily react with ethylene.