Going for gold: The first thermally stable gold(III) hydride [(C N C)*AuH] is presented. It undergoes regioselective insertions with allenes to give gold(III) vinyl complexes, and reductive condensation with [(C N C)*AuOH] to the air-stable Au(II) product, [(C N C)*(2)Au(2)], with a short nonbridged gold-gold bond.
The gold(III) hydroxide κ(3)-(C^N^C)*Au(OH) reacts with C-H and N-H compounds and arylboronic acids to produce a range of perfluoroaryls, N-heterocyclic and alkynyl compounds in high yields; some of which show unexpectedly strong modulation of their photoluminescence from yellow to blue [(C^N^C)* = 2,6-(C(6)H(3)Bu(t))(2)pyridine].
The (PNP)Rh fragment (2) can be conveniently accessed by dissociation of L from the four-coordinate complexes (PNP)Rh(L) (L = SPri
2, 3; L = H2CCHBut, 10), which contain the tridentate PNP pincer ligand (2-iPr2P-4-Me-C6H4)2N−. A new and a more straightforward synthesis of 10 is reported, yielding 65% of 10 based on RhCl3(H2O)
x
. A number of new aryl halide oxidation addition products (AHOAP) of the general formula (PNP)Rh(Ar)(Hal) (Hal = Cl, Br, I) have been synthesized through oxidative addition (OA) reactions of meta- and para-substituted aryl halides with 3 or 10. The rotation about the Rh−Caryl bond is restricted, resulting in rotamers for the meta-substituted aryls that are distinct on the NMR spectroscopy time scale. Reactions of some aryl halides containing a p-NO2 or p-CO2Me with 3 or 10 led to the observation of products of C−H OA that are ostensibly stabilized by coordination to the NO2 or CO2Me group. Analogous C−H OA products were observed for the halide-free nitrobenzene and ethyl benzoate, as well. However, the C−H OA products are thermodynamically unstable with respect to the isomeric AHOAP, to which they convert upon thermolysis. A Hammett-style analysis of the relative electronic effects of the para substituents X in the OA reactions of p-HalC6H4X with 10 was carried out. The positive values of ρ obtained (ρ = 1.51(15) for Ar−Cl, ρ = 0.70(9) for Ar−Br, and ρ = 0.92(9) for Ar−I) illustrate the increase in the OA rate with increasing electron-withdrawing effect of X. Issues relating to the usefulness of the Hammett parameters in comparing various OA reactions are discussed. Comparison with analogous studies on the OA of aryl halides to Pd(0) complexes leads to the notion that the electronic effects have an impact on the rate similar to, but less pronounced than, that of the (PNP)Rh system, possibly indicative of an earlier transition state for the OA of aryl halides with (PNP)Rh.
Treatment of gold(III) pincer complexes (C∧N∧C)*AuX with trifluoroacetic acid (X = C6F5, thiophenyl, Me, Et) or of (C∧N∧C)*AuOAcF with AgOAcF/arylboronic
acids leads to the selective cleavage of a C–Au bond under
mild conditions to give the bidentate complexes (HC-C∧N)*Au(X)(OAcF) [(C∧N∧C)* = 2,6-(C6H3But)2pyridine].
Alkylation of (C∧N∧C)*Au(OAcF) with AlR3 (R = Me, Et) proved to be a high-yielding
route to gold(III) alkyls. Au–C cleavage significantly influences
reactivity, e.g., with boronic acids. The photoemission of the cleavage
product (HC-C∧N)*Au(C6H4F)(OAcF) is about an order of magnitude more intense than that of
its tridentate parent compound.
Reactions of a series of phenyl esters with a (PNP)Rh fragment have been studied. PhO(2)CPh only underwent C-H oxidative addition (OA). PhO(2)CCF(3) chiefly underwent acyl-oxygen OA. PhO(2)CBu(t) and PhO(2)CNEt(2) initially underwent OA of an ortho-C-H bond of the phenyl group but continued thermolysis led to the phenyl-oxygen OA products.
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