Comproportionation of the palladium(0) compound Pd(PMe3)4 with the palladium(II) hexafluoroacetylacetonate compound Pd(hfac)2 or [Pd(hfac)(PMe3)2] [hfac] gives the novel palladium(I) dimer [Pd2(PMe3)6] [hfac]2 (1). The analogous mixed-metal complex [PdPt(PMe3)6] [hfac]2 (2) can be prepared similarly. The and 31P NMR spectra are consistent with structures in which the two metal centers are connected by a metal-metal bond and the six terminal PMe3 ligands complete two mutually perpendicular square-planar coordination environments; the hfac groups are not attached to the metal centers and instead serve as counterions for the [M2(PMe3)6]2+ cations. This structure has been established by X-ray crystallography for the dipalladium(I) compound; the cation has 2-fold crystallographic symmetry, and the Pd-Pd distance is 2.598(1) Á. The average Pd-P distances to the equatorial PMe3 groups cis to the Pd-Pd bond are 2.342(1) Å while the Pd-P distances to the axial PMe3 groups trans to the Pd-Pd bond are slightly longer at 2.371(1) Å; the lengthening of the axial Pd-P bonds may be ascribable to the larger trans influence of the metal-metal bond. The axial phosphine ligands in 1 can be replaced by treatment with LiCl or Nal in tetrahydrofuran to afford the nonionic dinuclear complexes Pd2(PMe3)4Cl2 and Pd2(PMe3)4I2. Surprisingly, thermolysis of 1 at 100 °C and 10−3 Torr yields the palladium(II) methyl complex [PdMe(PMe3)3]- [hfac]; the methyl group attached to palladium in this product evidently arises via P-C bond cleavage of a PMe3 ligand. This result constitutes the first example of the isolation of a metal alkyl complex via P-C bond cleavage of a unidentate alkylphosphine. Analogously, thermolysis of 2 at 140 °C and 10−3 Torr yields a mixture of [PdMe-(PMe3)3] [hfac] and the platinum(II) methyl complex [PtMe(PMe3)3][hfac], These results are relevant to the incorporation of phosphorus and carbon impurities into metal films grown by metal-organic chemical vapor deposition from PMe3-containing precursors. Crystal data for 1 at −75 °C: monoclinic, space group C2/c, a = 25.499(6) Å, b = 9.791 (2) Å,c = 18.424(5) Å,β = 106.85(2)°, F= 4402(26) Å3, Z = 4, RF= 0.032, RwF = 0.033 for 241 variables and 3054 reflections with I > 2.58 (7)σ.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry