No abstract

Several levels of density functional theory, i.e., various combinations of exchange-correlation functionals and basis sets, have been employed to compute equilibrium geometries for a diverse set of 32 metal complexes from the first transition row, for which precise gas-phase geometries are known from electron diffraction or microwave spectroscopy. Most DFT levels beyond the local density approximation can reproduce the 50 metal-ligand bond distances selected in this set with reasonable accuracy, as assessed by mean and standard deviations of optimized vs observed values. The ranking of some popular functionals, ordered according to decreasing standard deviation, is BLYP ≈ HCTH > B3LYP > BP86 > TPSS ≈ TPSSh. Together with its hybrid variant, the recently introduced meta-GGA functional TPSS performs best of all tested functionals, with mean and standard deviations of -0.5 and 1.4 pm, respectively. Even smaller errors are found for a more compact but less diverse set of transition-metal mono- and dihalides, for which experimentally derived equilibrium geometries are available.

A series of monomeric arylpalladium(II) complexes LPd(Ph)X (L = 1-AdPtBu2, PtBu3, or Ph5FcPtBu2 (Q-phos); X = Br, I, OTf) containing a single phosphine ligand have been prepared. Oxidative addition of aryl bromide or aryl iodide to bis-ligated palladium(0) complexes of bulky, trialkylphosphines or to Pd(dba)2 (dba = dibenzylidene acetone) in the presence of 1 equiv of phosphine produced the corresponding arylpalladium(II) complexes in good yields. In contrast, oxidative addition of phenyl chloride to the bis-ligated palladium(0) complexes did not produce arylpalladium(II) complexes. The oxidative addition of phenyl triflate to PdL2 (L = 1-AdPtBu2, PtBu3, or Q-phos) also did not form arylpalladium(II) complexes. The reaction of silver triflate with (1-AdPtBu2)Pd(Ph)Br furnished the corresponding arylpalladium(II) triflate in good yield. The oxidative addition of phenyl bromide and iodide to Pd(Q-phos)2 was faster than oxidative addition to Pd(1-AdPtBu2)2 or Pd(PtBu3)2. Several of the arylpalladium complexes were characterized by X-ray diffraction. All of the arylpalladium(II) complexes are T-shaped monomers. The phenyl ligand, which has the largest trans influence, is located trans to the open coordination site. The complexes appear to be stabilized by a weak agostic interaction of the metal with a ligand C-H bond positioned at the fourth-coordination site of the palladium center. The strength of the Pd.H bond, as assessed by tools of density functional theory, depended upon the donating properties of the ancillary ligands on palladium.