A gold exchange: a mechanistic study of a reversible, formal ethylene insertion into a gold(III)-oxygen bond.

The Au(III) complex Au(OAc(F))2(tpy) (1, OAc(F) = OCOCF3; tpy = 2-p-tolylpyridine) undergoes reversible dissociation of the OAc(F) ligand trans to C, as seen by (19)F NMR. In dichloromethane or trifluoroacetic acid (TFA), the reaction between 1 and ethylene produces Au(OAc(F))(CH2CH2OAc(F))(tpy) (2). The reaction is a formal insertion of the olefin into the Au-O bond trans to N. In TFA this reaction occurs in less than 5 min at ambient temperature, while 1 day is required in dichloromethane. In trifluoroethanol (TFE), Au(OAc(F))(CH2CH2OCH2CF3)(tpy) (3) is formed as the major product. Both 2 and 3 have been characterized by X-ray crystallography. In TFA/TFE mixtures, 2 and 3 are in equilibrium with a slight thermodynamic preference for 2 over 3. Exposure of 2 to ethylene-d4 in TFA caused exchange of ethylene-d4 for ethylene at room temperature. The reaction of 1 with cis-1,2-dideuterioethylene furnished Au(OAc(F))(threo-CHDCHDOAc(F))(tpy), consistent with an overall anti addition to ethylene. DFT(PBE0-D3) calculations indicate that the first step of the formal insertion is an associative substitution of the OAc(F) trans to N by ethylene. Addition of free (-)OAc(F) to coordinated ethylene furnishes 2. While substitution of OAc(F) by ethylene trans to C has a lower barrier, the kinetic and thermodynamic preference of 2 over the isomer with CH2CH2OAc(F) trans to C accounts for the selective formation of 2. The DFT calculations suggest that the higher reaction rates observed in TFA and TFE compared with CH2Cl2 arise from stabilization of the (-)OAc(F) anion lost during the first reaction step.

Di-µ-chlorido-bis-[(2,2'-bipyridine-5,5'-dicarb-oxy-lic acid-κ(2)N,N')chloridocopper(II)] dimethyl-formamide tetra-solvate.

In the title compound, [Cu(2)Cl(4)(C(12)H(8)N(2)O(4))(2)]·4C(3)H(7)NO, which contains a chloride-bridged centrosymmetric Cu(II) dimer, the Cu(II) atom is in a distorted square-pyramidal 4 + 1 coordination geometry defined by the N atoms of the chelating 2,2'-bipyridine ligand, a terminal chloride and two bridging chloride ligands. Of the two independent dimethyl-formamide mol-ecules, one is hydrogen bonded to a single -COOH group, while one links two adjacent -COOH groups via a strong accepted O-H⋯O and a weak donated C(O)-H⋯O hydrogen bond. Two of these last mol-ecules and the two -COOH groups form a centrosymmetric hydrogen-bonded ring in which the CH=O and the -COOH groups by disorder adopt two alternate orientations in a 0.44:0.56 ratio. These hydrogen bonds link the Cu(II) complex mol-ecules and the dimethyl-formamide solvent mol-ecules into infinite chains along [-111]. Slipped π-π stacking inter-actions between two centrosymmetric pyridine rings (centroid-centroid distance = 3.63 Å) contribute to the coherence of the structure along [0-11].