Synthesis and Characterization of Ambient Temperature Stable Organopalladium(IV) Complexes, Including Aryl-, hl-Allyl-, Ethylpalladium(IV), and Pallada(IV)cyclopentane Complexes. Structures of the Poly(pyrazo1-l-y1)borate Complexes PdMe3{(pz)sBH} and PdMe3{(pz)4B} and Three Polymorphs of PdMe2Et{(pz)3BH}

Abstract

The palladium(I1) complexes PdMe2(tmeda), PdMePh(tmeda), and Pd(CH2CH2CH2CH2)(tmeda) (tmeda = tetramethylethylenediamine) react with potassium tris(pyrazo1-l-y1)borate and organohalides RX in acetone to form the octahedral palladium(IV) complexes PdMeRR”{(pz)3BH}(R = Me, Ph) and Pd(CH2CH2CH2CH2)R"{(pz)3BH} (R"X = MeI, EtI, PhCH2Br, CH2=CHCH2I). The complexes are stable in the solid state and in solution at ambient temperature, PdMe3{(pz)3BH} is more stable than the iodide salt of isoelectronic [PdMe3{(pz)3CH}]+, and the aryl- and hl-propenylpalladium(IV) complexes are the first examples of aryl and allylpalladium(IV) complexes that are stable above 0 C. The tris(pyrazo1-l-y1)borate ligand considerably enhances the stability of palladium(IV) complexes when compared with related neutral donor ligands. The ethylpalladium(IV) complexes have stabilities in solution similar to that of the most stable ethylpalladium(I1) complexes reported. The complex PdMe3 {(pz)4B} (2) as been prepared, and structural studies of this complex and PdMe2R"{(pz)3BH} [R"= Me (l), Et (3)] completed, allowing the first comparison of structural parameters of ethylpalladium(II, IV) complexes and of PdMe3{(pz)3BH} with the “isoelectronic” cation [PdMe3{(pz)3CH}]+. Three polymorphs of PdMe2Et{(pz)3BH} were examined: complex 3a is ordered, but the other polymorphs exhibit disordering in the conformation of the ethyl group (3b) and in the position of the ethyl group and one of the methyl groups (3c).