Synthesis and structures of hydride-bridged palladium A-frame complexes

A series of hydride-bridged palladium A-frame complexes [Pd2R2(μ-H)(μ-dppm)2]PF6 has been prepared by reaction of [Pd2Cl2(μ-dppm)2] with 2 equiv. of a Grignard reagent, followed by addition of CBr4, NaBH4 and TlPF6. The mixed palladium–platinum species [PdPtR2(μ-H)(μ-dppm)2]PF6 were generated analogously from [PdPtCl2(μ-dppm)2], whereas the unsymmetrical dipalladium derivatives [Pd2(Mes)R(μ-H)(μ-dppm)2]PF6 were produced from the reaction of [Pd(Mes)(dppm)2]X with [Pd2R2(μ-Cl)2(AsPh3)2], followed by treatment with NaBH4. The complexes were characterized by elemental analysis, 1H and 31P NMR spectroscopy. The solid-state structures of [Pd2(C6H4Me-4)2(μ-H)(μ-dppm)2]BH3CN (1a) (obtained as its BH3CN− salt when NaBH3CN was used instead of NaBH4), [PdPt(C6H4Me-4)2(μ-H)(μ-dppm)2]PF6 (2a), [Pd2(Mes)Et(μ-H)(μ-dppm)2]PF6 (3b), [Pd2(Mes)Ph(μ-H)(μ-dppm)2]PF6 (3c) and [EtPt(μ-H)(μ-dppm)2PdMe]PF6 (4) have been determined by X-ray crystallography. 3c adopts an elongated boat conformation in the solid state, whereas the others exist in the chair form. The unsymmetrical cations 2a and 4 containing smaller organic substituents are disordered in the solid state, whereas the mesityl-containing derivatives 3b and 3c are not.