Unique ring-methyl deprotonation of η4-1,2-dimethyl-3,4-di(tert-butyl)cyclobutadiene complexes of palladium(II) bearing phosphine ligand

We report unique ring-methyl deprotonation of an η4-cyclobutadiene complex [PdCl2(η4-C4 tBu2Me2)]2 (1). Reaction of 1 with 2 equiv. of triphenylphosphine in the presence of triethylamine afforded an exo-methylene-η3-cyclobutenyl palladium complex [Pd(μ-Cl)(η3-C4(CH2)(tBu)2Me)(PPh3)]2 (3) in quantitative yield. The reaction of complex 1 with 2 equiv. of DPPE gave a cationic complex [Pd(η3-C4(CH2)(tBu)2Me)(DPPE)][Cl] (4a) with the release of HCl. Upon treated with triethylamine and AgOTf, a cationic complex [Pd(η3-C4(CH2)(tBu)2Me)(DPPE)][OTf] (4b) was isolated as yellow microcrystalline solids. The cationic exo-methylene-η3-cyclobutenyl structure of 4 was revealed by spectral data together with a crystallographic study for complex 4a.