Coinage Metal Complexes of Bis‐Alkynyl‐Functionalized N‐Heterocyclic Carbenes: Reactivity, Photophysical Properties, and Quantum Chemical Investigations

Abstract

Bis-phenylpropynyl-functionalized imidazolium salts and their corresponding gold and copper N-heterocyclic carbene (NHC) complexes were prepared in order to investigate their potential application for the synthesis of heterometallic coinage metal compounds. By transmetalation reactions with different precious metal sources, including copper and silver phenylacetylides [MCCPh] (M=Cu, Ag), polynuclear compounds were obtained, which were further investigated for their photoluminescence properties. Additionally, one gold NHC complex was post-functionalized by autocatalytic hydration of the alkynyl side chains. Time-dependent DFT investigations of singlet electronic excitations in representative complexes revealed excited states of diverse character, as determined by the specific complex structure and metallophilic interactions.

Flexible and Versatile Pincer-Type PGeP and PSnP Ligand Frameworks

“…A single resonance for the ethylene backbone is observed at 3.49 ppm suggesting a symmetric conformation in solution. This assumption is strengthened by the 13 C{ 1 H} NMR spectrum in which triplets are observed for aromatic carbon atoms caused by virtual coupling to the 31 P nuclei. Indeed, the 31 P{ 1 H} spectrum of 1 reveals a singlet at -21.1 ppm proving that both phosphine units are isochronous and that σv-symmetry is maintained in solution.…”

“…The other two phosphorus resonances couple to each other and appear as doublets with associated 195 Pt satellites. No tin satellites are observed and the 119 Sn spectrum has one resonance at 132.6 ppm, but neither 31 P nor 195 Pt coupling could be resolved.…”

“…Additionally, CP-MAS NMR spectra were recorded for 2 and 4 (see SI for details). In the crystal structure of 2, the two phosphorus atoms in each molecule are inequivalent and therefore give separate peaks in 31 P spectrum both of which exhibit 117/119 Sn satellites ( 1 JP-Sn = 1423 Hz and 1 JP-Sn = 1436 Hz). The 119 Sn spectrum has one resonance which appears as a triplet due to coupling to the two 31 P nuclei.…”

“…Complex 4 contains two different phosphorus and tin environments, which are reflected in the 119 Sn and 31 P spectra, each of which contain two resonances. For 119 Sn, the chemical shifts account for -272.3 ppm and -296.5 ppm, whereas 31 We next felt inclined to investigate the coordination behavior of the phosphine-functionalized heavier carbene analogues towards coinage metal salts. Upon reaction of [(PNNP)Ge] 1 with one equivalent CuCl in toluene and subsequent concentration of the clear colorless solution, single crystals were directly obtained from the mother liquor and subjected to X-ray structural analysis (Scheme 3).…”

“…[19][20][21][22][23][24] However, so far they are limited to ECE or ENE systems (E = Si, Ge) and only very recently, the first phosphine-functionalized germylene and stannylene ligands and their applications have been reported. [25][26][27][28] Given that polydentate carbene ligands and their polymetallic complexes often feature interesting properties such as photoluminescent behavior, [29][30][31] we were interested in substituting the carbene carbon atom by its heavier analogues and explore the properties of such compounds. Thereby, we used a PNHNHP proligand developed by Thomas and co-workers (pictured in Scheme 1), whose synthesis is straightforward, feasible on a multi-gram scale and has been extensively investigated.…”