Multinuclear copper(I) and silver(I) amidinate complexes: synthesis, luminescence, and CS2 insertion reactivity

Dinuclear Cu(I) and Ag(I) complexes, Cu2[(2,6-Me2C6H3N)2C(H)]2, 1, Ag2[(2,6-Me2C6H3N)2C(H)]2, 2, Cu2[2,6-(i)Pr2C6H3N)2C(H)]2, 3, and Ag2[(2,6-(i)Pr2C6H3N)2C(H)]2, 4, were synthesized from reactions of [Cu(NCCH3)4][PF6] with Na[(2,6-R2C6H3N)2C(H)] and AgO2CCH3 with [Et3NH][(2,6-R2C6H3N2C(H)], R = Me, (i)Pr. Carbon disulfide was observed to insert into the metal-nitrogen bonds of 1 to produce Cu4[CS2(2,6-Me2C6H3NC(H)═NC6H3Me2)]4, 5, with a Cu4S8 core, which represents a rare transformation of dinuclear to tetranuclear species. Insertion is also observed with 2 and CS2, with the product likely being polymeric, 6. With the (i)Pr-derivatives, CS2 insertion was also observed, albeit at much slower rate, with 3 and 4 producing hexanuclear clusters, M6[CS2(2,6-Me2C6H3NC(H)═NC6H3Me2)]6, M = Cu, 7; Ag, 8. Complexes 1 and 5 display green luminescence, a feature not shared by their Ag(I) analogs nor with 3. Notably, oxygen acts as a collisional quencher of the luminescence from 1 and 5 at a rate faster than most metal-based quenchometric O2 sensors. For example, we find that complex 1 can be rapidly and reversibly quenched by oxygen, presenting a nearly 6-fold drop in intensity upon switching from nitrogen to an aerated atmosphere. The results here provide a platform from which further group 11 amidinate reactivity can be explored.