Carbon–hydrogen activation of ketones by 2-phenylazophenylgold(III) complexes to give ketonylgold(III) complexes

Abstract

Complexes [AuR(acac-C)Cl]{R = pap (C₆H₄NNPh-2)1a or mpap [C₆H₃(NNC₆H₄Me-4)-2-Me-5]1b; Hacac = acetylacetone} or ‘AuR(Cl)(OClO₃)’(R = pap 2a or mpap 2b) react with various ketones MeC(O)R′ to give [AuR{CH₂C(O)R′}Cl][R = pap, R′= Et 3, Prⁿ4, Prⁱ5, Buⁱ6 or C₆H₂(OMe)₃-3,4,5 7; R = mpap, R′= Me 8]. Whereas 1a does not react with MeC(O)CH₂Cl, 2a gives a mixture of the expected [Au(pap){CH₂C(O)CH₂Cl}Cl] and [Au(pap)Cl₂]. However, other ketones [R′C(O)R″](R′= Me; R″= Ph, CH₂CH, trans-PhCHCH or MeCO; R′= R″= CH₂Cl or Et) or 2-methylcyclohexanone do not react at room temperature with 2a. The reactions of 2a with other species containing activated methyl groups [MeCO₂Et, MeC(O)NH₂ or MeCN] either do not occur or give products in which there is no carbon–hydrogen activation. Thus, 2a reacts with dimethyl sulfoxide (dmso) to give the first organogold(III) complex with this ligand, [Au(pap)(dmso)₂][ClO₄]₂9. It reacts with NaI to give [Au(pap)Cl(I)]10. Complex 8 reacts with NaClO₄·H₂O and pyridine (py) or 2,2′-bipyridine (bipy) to give [Au(mpap){CH₂C(O)Me}L]ClO₄(L = py 11 or bipy 12). The following reactions were also studied: [Au(pap)Cl(acac-C)]+ PPh₃ or AgClO₄ to give [Au(pap)Cl(acac-C)(PPh₃)]13 or [Au(pap)(acac-O,O′)]ClO₄14, respectively. Complexes 13 and 14 do not give an acetonyl complex with acetone; 14 is the first cationic acetylacetonatogold(III) complex. A plausible reaction pathway is proposed for ketone carbon–hydrogen activation starting from complexes 2. Low-temperature crystal structures were determined for [Au(mpap)Cl₂][space group P, a= 7.902(2), b= 9.527(2), c= 10.378(3)Å, α= 86.77(2), β= 77.32(2), γ= 67.42(2)°, R= 0.024] and 11[space group P2₁/n, a= 8.693(5), b= 15.800(8), c= 16.489(8)Å, β= 94.51(4)°, R= 0.027]. The latter is the first crystal structure of an acetonylgold(III) complex, and it could be shown conclusively that the CH₂C(O)Me group is bonded through the carbon atom. Both structures show the expected square-planar co-ordination around the gold atom, with some distortion from the narrow chelate rings. In the first complex the higher trans influence of the aryl group leads to a lengthening of the trans Au–Cl bond (2.347 Å) with respect to the cis bond (2.274 Å).