Discrete Singular Metallophilic Interaction in Stable Large 12-Membered Binuclear Silver and Gold Metallamacrocycles of Amido-Functionalized Imidazole and 1,2,4-Triazole-Derived N-Heterocyclic Carbenes

Abstract

Metallophilic interactions were observed in four pairs of 12-membered metallamacrocyclic silver and gold complexes of imidazole-derived N-heterocyclic carbenes (NHCs), [1-(R¹)-3-N-(2,6-di-(R²)-phenylacetamido)-imidazol-2-ylidene]₂M₂ [R¹ = p-MeC₆H₄, R² = Me, M = Ag (1b) and Au (1c); R¹ = Me, R² = i-Pr, M = Ag (2b) and Au (2c); R¹ = Et, R² = i-Pr, M = Ag (3b) and Au (3c)], and a 1,2,4-triazole-derived N-heterocyclic carbene (NHC), [1-(i-Pr)-4-N-(2,6-di-(i-Pr)-phenylacetamido)-1,2,4-triazol-2-ylidene]₂M₂ [M = Ag (4b) and Au (4c)]. The X-ray diffraction, photoluminescence, and computational studies indicate the presence of metallophilic interactions in these complexes, which are significantly influenced by the sterics and the electronics of the N-amido substituents of the NHC ligands. The argentophilic interaction in the silver 1b-4b complexes was stronger than the aurophilic interaction in the gold 1c-4c complexes, with the metallophilic interaction decreasing in the order 4b > 1b > 1c > 4c > 3b > 3c > 2b > 2c. The 1b-4b complexes were synthesized from the corresponding amido-functionalized imidazolium chloride 1a-3a and the 1,2,4-triazolium chloride 4a salts upon treatment with Ag₂O. The reaction of 1b-4b complexes with (Me₂S)AuCl gave the gold 1c-4c complexes.

Figure 1

Twelve-membered metallamacrocyclic silver 1b–4b and gold 1c–4c complexes exhibiting discrete metallophilic interactions.

Scheme 1. Synthetic Route to Amido-Functionalized Ag–NHC 1b–4b and Au–NHC 1c–4c Complexes

Figure 2

ORTEP of 4b with thermal ellipsoids shown at the 50% probability level. Hydrogen atoms and cocrystallized CH₃CN molecules are omitted for clarity. Selected bond lengths (Å) and angles (°): Ag(1)···Ag(2) 2.9974(8), Ag(1)–C(1) 2.054(8), Ag(1)–N(8) 2.125(6), C(1)–N(1) 1.382(10), C(1)–N(3) 1.361(10), C(1)–Ag(1)–N(8) 176.1(3), C(1)–Ag(1)–Ag(2) 100.7(2), N(1)–C(1)–N(3) 100.7(7), N(3)–C(1)–Ag(1) 132.3(6), and N(1)–C(1)–Ag(1) 127.0(6).

Figure 3

ORTEP of 4c with thermal ellipsoids shown at the 50% probability level. Hydrogen atoms and cocrystallized H₂O molecule were omitted for clarity. Selected bond lengths (Å) and angles (°): Au(1)···Au(2) 3.5640(5), Au(1)–C(1) 1.975(4), Au(1)–N(8) 2.031(3), C(1)–N(1) 1.330(5), C(1)–N(2) 1.361(5), C(1)–Au(1)–N(8) 172.00(14), N(1)–C(1)–N(2) 103.4(3), N(2)–C(1)–Au(1) 130.5(3), and N(1)–C(1)–Au(1) 126.1(3).

Figure 4

Comparison of the emission spectra of the ligand (1a), the Ag–NHC complex (1b), and the Au–NHC complex (1c) in CHCl₃ at room temperature (excitation at 242 nm), in which the peak representing the M···M interaction is designated by an asterisk (*) in the plot. (^#Overtone of excitation at 242 nm).

Figure 5

Comparison of the emission spectra (expanded) of the ligand (1a), the Ag–NHC complex (1b), and the Au–NHC complex (1c) in the solid state at room temperature (excitation at 242 nm), in which the peak representing the M···M interaction is designated by an asterisk (*) in the plot.

Figure 6

AIM computed topological diagrams for different complexes (a) 1b, (b) 2b, (c) 3b, (d) 4b, (e) 1c, (f) 2c, (g) 3c, and (h) 4c. (Color code: yellow, ring critical point and green, cage critical point).

Figure 7

NCI plots of complexes (a) 1b, (b) 2b, (c) 3b, (d) 4b, (e) 1c, (f) 2c, (g) 3c, and (h) 4c and RDG scatter plots of complexes (a′) 1b, (b′) 2b, (c′) 3b, (d′) 4b, (e′) 1c, (f′) 2c, (g′) 3c, and (h′) 4c.

Figure 8

Electron localization function (ELF) color-filled maps of complexes (a) 1b, (b) 2b, (c) 3b, (d) 4b, (e) 1c, (f) 2c, (g) 3c, and (h) 4c.