REACTIONS OF [PDX2(DPPM)] COMPLEXES WITH GRIGNARD-REAGENTS

Reactions of [PdX2(dppm)] (X = Cl, Br) with a range of Grignard reagen ts have been investigated. Diorganopalladium complexes of the type [Pd R2(dppm)] were obtained in good yield with the bulky mesityl or trimet hylsilylmethyl groups, provided the reactions were performed using hig h Grignard:Pd ratios in ether solution. With the smaller R groups Me, Et, Bu, and CH2Ph, only the halide-bridged A-frame complexes [Pd2R2(mu -X)(mu-dppm)(2)](+) were formed, irrespective of the reaction conditio ns. Mixtures of chloride-and bromide-bridged complexes were produced w hen [PdCl2(dppm)] was treated with RMgBr, so [PdBr2(dppm)] was used as the starting material in certain cases. The mesityl derivative [Pd-2( C6H2Me3)(2)(mu-Br)(mu-dppm)(2)](+) could be obtained from the reaction of [PdBr2(dppm)] with 4 mol equiv of C6H2Me3MgBr in CH2Cl2 solution, but with Me3SiCH2MgCl mixtures of monomeric and dimeric complexes were obtained under these conditions. The A-frame complex [Pd-2(CH2SiMe3)( 2)(mu-Cl)(mu-ppm)(2)](+) was generated, however, by reaction of [Pd(CH 2SiMe3)(2)(dppm)] with 1 mol equiv of HCl. The A-frames were isolated as their PF6- salts. They were characterized by elemental analysis, NM R spectroscopy, and, in the case of [Pd-2(C6H2Me3)(2)(mu-Br)(mu-dppm)( 2)]PF6, X-ray crystallography. The molecular structure of the [Pd-2(C6 H2Me3)(2)(mu-Br)(mu-dppm)(2)](+) cation reveals that it adopts an elon gated boat conformation, with the dppm CH2 groups lying on the same si de of of the Pd2P4 framework as the bridging bromide. With the smaller aryl Grignards PhMgBr, p-tolylMgBr, or o-tolylMgCl, the diarylpalladi um species [PdAr2(dppm)] could be detected in solution at low temperat ures but at ambient temperature reductive coupling of the aryl groups occurred and the palladium(I) complexes [Pd2X2(mu-dppm)(2)] were forme d.