Thermally triggered reductive elimination of bromine from Au(iii) as a path to Au(i)-based coordination polymers

摘要

Four new [AuBr_2(CN)_2]--based coordination polymers, Zn(pyz)(NCMe)_2[AuBr_2(CN)_2] _2 (1; pyz = pyrazine), Co(pyz)[AuBr_2(CN)_2] _2·H_2O (2) and [M(bipy)_2(AuBr _2(CN)_2)][nBu_4N][AuBr _2(CN)_2]_2 (bipy = 4,4′-bipyridine), where M = Co (5) and Zn (6), were synthesized and three of them structurally characterized. 1 forms 1-D chains connected by pyz ligands while isostructural 5 and 6 form 3-D frameworks via [AuBr2(CN)2]- and bipy linkers. Aqueous suspensions of 2, 5 and 6 or their precursors in situ (preferred) were heated hydrothermally to 125 °C, triggering the reductive elimination of bromine from the Au(iii) centres, which yielded the [Au(CN) _2]~--based coordination polymers M(pyz)[Au(CN) _2]_2, where M = Zn (3) or Co (4) and Zn(bipy)[Au(CN) _2][Au{Br_(0.68)(CN)_(0.32)}CN] (7), or a mixture of cyanoaurate(i)-containing products in the case of 5 and 6. The structural characterization of 3 revealed a [Au(CN)_2]~-/pyz-based framework similar to previously reported Cu(pyz)[Au(CN)_2] _2, whereas 7 formed an intricate network consisting of individual 2-D networks held together by Au?Au interactions and featuring the rare [AuBrCN]~- unit. The kinetics of the thermally-induced reductive elimination of Br_2 from K[AuBr_2(CN)_2] in 1-BuOH yielded a t of approx. 10 min to 4 h from 98 to 68 °C, and activation parameters of ΔH~? = 131(15) kJ mol~(-1) and ΔS~? = 14.97(4) kJ K~(-1)mol~(-1), indicating that the elimination of the halogen provides the highest barrier to activation.