Gallium Methylene

Despite the eminent importance of metal alkylidene species for organic synthesis and industrial catalytic processes, molecular homoleptic metal methylene compounds [M(CH2)(n)] as the simplest representatives, have remained elusive. Reports on this topic date back to 1955 when polymeric [Li-2(CH2)](n) and [Mg(CH2)](n) were accessed by pyrolysis of methyllithium and dimethylmagnesium, respectively. However, the insoluble salt-like composition of these compounds has impeded their application as valuable reagents. We report that rare-earth metallocene methyl complexes [(C5Me5)(2)Ln{(mu-Me)(2)GaMe2}] (Ln=Lu, Y) trigger the formation of homoleptic gallium methylene [Ga-8(mu-CH2)(12)] from trimethylgallium [GaMe3] (Me=methyl) via a cascade C-H bond activation involving the dodecametallic clusters [(C5Me5)(6)Ln(3)(mu(3)-CH2)(6)Ga-9(mu-CH2)(9)] as crucial intermediates. Such gallium methylene compounds feature a reversible [Ga-8(mu-CH2)(12)]/[Ga-6(mu-CH2)(9)] oligomer switch in donor solvents and act as Schrock-type methylene-transfer reagents.