![]() Noting that the calculated Cu-alkyne orbital interaction energies underestimate the degree of distortion suggests that some of the distortion of the Cu-bound alkyne may be due to geometrical constraints of that system. These calculations also provide further insight into the observed distortion of the Cu(I)-bound alkyne. For all three metals, σ-donation to the metal dominates, augmenting the electrophilicity of the alkyne, although the difference of the two bonding interactions is the largest for Au. Second-order perturbative analysis revealed that π-to-metal σ-donation is of the largest magnitude for Au (56.6 kcal/mol), as is metal-to-π* back-donation (13.3 kcal/mol). With these optimized geometries in hand, we turned to natural bond order calculations to investigate the nature of the metal-alkyne bond ( Table 2) (for similar studies, see refs. The same structural trends were observed in both the calculated and experimental geometries. The structures of 2 and 3 were trimmed and optimized similarly the experimental and calculated values are compared in Table 1. Importantly, this indicates that the geometry of the metal center in 1 is not significantly influenced by the constraints of crystallization. The experimental geometric features were well produced with the B3PW91/LANL2DZ(Au), LANL2DZdp(Si,P), ccpVDZ(C,H) level of theory ( Table 1). In contrast, the Cu(I) complex 3 is monomeric, with pseudo-trigonal planar geometry about copper.īeginning with the crystal structure of Au(I) complex 1, we initially simplified the structure to monomeric triphenylphosphine-metal-alkyne complex 1b ( Fig. †† Although, the dimeric structure of 1 and 2 was unexpected, it is not surprising considering the structure of the ligand and the preferred linear Au(I)-coordination geometry. The Au(I) and Ag(I) complexes 1 and 2 are structurally analogous dimers, both displaying pseudo-linear geometry about the metal. In all cases, solvent molecules and counterions are completely separated from the cationic metal centers. The structures of the complexes 1– 3 were firmly established by x-ray crystallographic analysis ( Figs. The corresponding Ag(I) and Cu(I) complexes were obtained in quantitative yields by the reaction of ligand 5 directly with cationic metal precursors. Crystals of complex 1 were obtained when a layered CH 2Cl 2/hexanes solution of 1 was allowed to stand at 0☌. This complex was converted into cationic phosphinegold(I) complex 1 in 98% yield by abstraction of the chloride with silver hexafluoroantimonate. To this end, reaction of alkynyl phosphine 5 with (dimethylsulfide)gold(I) chloride afforded the phosphinegold(I) chloride complex in 93% yield ( Fig. Although Au(I)-π-complexes have traditionally been difficult to isolate and characterize, we hypothesized that these difficulties might be overcome by employing a tethered phosphine-alkyne ligand.
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