Reactivity of 1,3-bis(2-pyridyl)benzene, NCHN, with gold(III) chlorides: salts, adducts and cyclometalated pincer derivatives. Crystal and molecular structures of [HNCHN][AuCl4], [Au(NCN)Cl][PF6] and [Au(NCN)Cl(PPh3)2][PF6]

The reaction of 1,3-bis(2-pyridyl)benzene, NCHN, with H[AuCl4] has been studied under different conditions. Mono- ([NCHNH][AuCl4]) and di-protonated salts ([HNCHNH][AuCl4]2), as well as an adduct, [(NCHN)(AuCl3)2], have been isolated. Very rare cyclometalated pincer derivatives, [Au(NCN)Cl]+ have been obtained as different salts, either by transmetallation from the corresponding mercury(ii) derivative, [Hg(NCN)Cl], or by direct C-H activation. The structures in the solid state of [NCHNH][AuCl4] and [Au(NCN)Cl][PF6] have been solved by X-ray diffraction. Reaction of the pincer derivatives with PPh3, dppm (bis(diphenylphosphino)methane) and dppe (1,2-bis(diphenylphosphino)ethane) occurs with displacement of the coordinated nitrogen atoms to afford [Au(NCN)(Cl)(PPh3)2]+, [Au(NCN)(Cl)(dppm)2]+ and [Au(NCN)(Cl)(dppe)] +, respectively. The X-ray structure of [Au(NCN)(Cl)(PPh 3)2][PF6] confirms that the ligand NCN is only σ-carbon bonded and the PPh3 molecules are in a trans-arrangement. The pattern of the 31P{1H}NMR spectrum of [Au(NCN)(Cl)(dppm)2]+, a pair of "triplets", deserves comments: the spectrum is not of the A2X2 type but a case of a deceptively simple AA'XX' spin system.