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 [Li2 (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 [(C5 Me5 )2 Ln{(μ-Me)2 GaMe2 }] (Ln=Lu, Y) trigger the formation of homoleptic gallium methylene [Ga8 (μ-CH2 )12 ] from trimethylgallium [GaMe3 ] (Me=methyl) via a cascade C-H bond activation involving the dodecametallic clusters [(C5 Me5 )6 Ln3 (μ3 -CH2 )6 Ga9 (μ-CH2 )9 ] as crucial intermediates. Such gallium methylene compounds feature a reversible [Ga8 (μ-CH2 )12 ]/[Ga6 (μ-CH2 )9 ] oligomer switch in donor solvents and act as Schrock-type methylene-transfer reagents.