Reactivity of 1,3-bis(2-pyridyl)benzene, N⁁CH⁁N, with gold(iii) chlorides: salts, adducts and cyclometalated pincer derivatives. Crystal and molecular structures of [HN⁁CH⁁N][AuCl4], [Au(N⁁C⁁N)Cl][PF6] and [Au(N⁁C⁁N)Cl(PPh3)2][PF6

Abstract

The reaction of 1,3-bis(2-pyridyl)benzene, N--CH--N, with H[AuCl(4)] has been studied under different conditions. Mono- ([N--CH--NH][AuCl(4)]) and di-protonated salts ([HN--CH--NH][AuCl(4)](2)), as well as an adduct, [(N--CH--N)(AuCl(3))(2)], have been isolated. Very rare cyclometalated pincer derivatives, [Au(N--C--N)Cl](+) have been obtained as different salts, either by transmetallation from the corresponding mercury(ii) derivative, [Hg(N--C--N)Cl], or by direct C-H activation. The structures in the solid state of [N--CH--NH][AuCl(4)] and [Au(N--C--N)Cl][PF(6)] have been solved by X-ray diffraction. Reaction of the pincer derivatives with PPh(3), dppm (bis(diphenylphosphino)methane) and dppe (1,2-bis(diphenylphosphino)ethane) occurs with displacement of the coordinated nitrogen atoms to afford [Au(N--C--N)(Cl)(PPh(3))(2)](+), [Au(N--C--N)(Cl)(dppm)(2)](+) and [Au(N--C--N)(Cl)(dppe)](+), respectively. The X-ray structure of [Au(N--C--N)(Cl)(PPh(3))(2)][PF(6)] confirms that the ligand N--C--N is only sigma-carbon bonded and the PPh(3) molecules are in a trans-arrangement. The pattern of the (31)P{(1)H}NMR spectrum of [Au(N--C--N)(Cl)(dppm)(2)](+), a pair of "triplets", deserves comments: the spectrum is not of the A(2)X(2) type but a case of a deceptively simple AA'XX' spin system.