The Unusual Stability of Homoleptic Di- and Tetravalent Chromium Alkyls

Reaction of CrCl3(THF)3 with 3 equiv of R−M [R = Me3CCH2 (a), Me3SiCH2 (b)] afforded either the previously reported tetravalent homoleptic R4Cr (1a, b) [M = MgCl] or the unprecedented divalent and tetranuclear homoleptic [R2Cr]4 (2b) [M = Li]. Both types of compounds display a remarkable chemical inertness toward proton transfer agents but readily react with ethylene.