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[AuCl₄] has been studied under different conditions. Mono- ([N⁁CH⁁NH][AuCl₄]) and di-protonated salts ([HN⁁CH⁁NH][AuCl₄]₂), as well as an adduct, [(N⁁CH⁁N)(AuCl₃)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][AuCl₄] and [Au(N⁁C⁁N)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(N⁁C⁁N)(Cl)(PPh₃)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)(PPh₃)₂][PF₆] confirms that the ligand N⁁C⁁N is only σ-carbon bonded and the PPh₃ molecules are in a trans-arrangement. The pattern of the ³¹P{¹H}NMR spectrum of [Au(N⁁C⁁N)(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.