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Solution behavior and structural diversity of bis(dialkylphosphino)methane complexes of palladium

TitleSolution behavior and structural diversity of bis(dialkylphosphino)methane complexes of palladium
Publication TypeJournal Article
Year of Publication2003
AuthorsPamplin, CB, Rettig, SJ, Patrick, BO, James, BR
JournalInorganic Chemistry
Volume42
Pagination4117-4126
Date PublishedJun
Type of ArticleArticle
ISBN Number0020-1669
Keywordsbis(diphenylphosphino)methane, DIMERIC COMPLEXES, DPM, HYDROGEN-SULFIDE, LIGANDS, MECHANISTIC ASPECTS, METAL-METAL BONDS, MOLECULAR-STRUCTURE, RAY CRYSTAL-STRUCTURE, RHODIUM(I)
Abstract

The preparation of dipalladium complexes containing sterically nondemanding diphosphine (P-P) ligands of the type R2PCH2PR2 where R = Me (dmpm) or Et (depm) is reported. Variable-temperature H-1 NMR spectra of the Pd-2(1) complexes Pd2X2(dMPM)(2) (X = Cl, Br, or I; the P-P ligands in the Pd-2 complexes are always bridged, but for convenience, the mu-symbol is omitted) show the complexes to be fluxional in solution, the barriers to a ring-flipping process being DeltaGdouble dagger = 37.9, 39.0, and 43.2 +/- 0.9 kJ mol(-1) for the chloro, bromo, and iodo complexes, respectively. Treatment of Pd2X2(P-P)(2) (X = Cl or Br) with X-2 generates the stable, face-to-face Pd-2(II) derivatives trans-Pd2X4(P-P)(2), while oxidation of Pd2I2(P-P)(2) complexes with I-2 generates a new type of symmetrically di-iodo-bridged, five-coordinate complexes Pd2I2(mu-I)(2)(dmpm)(2) and Pd2I2(mu-I)(2)(depm)(2). The molecular crystal structures of four dipalladium(II) complexes are described: trans-Pd2Cl4(dmpm)(2).2CHCl(3), trans-Pd2Br4(dmpm)(2), trans-Pd2Cl4(depm)(2), and Pd2I2(mu-I)(2)(dmpm)(2). Solution NMR and UV-vis absorption spectra are consistent with the solid-state structures determined by X-ray diffraction. The stability of the dimeric Pd(II) complexes is attributed primarily to ligand steric factors.

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