Bonding, Luminescence, Metallophilicity in Linear Au3 and Au2Ag Chains Stabilized by Rigid Diphosphanyl NHC Ligands

• Published in: Inorganic chemistry 2016-09, Vol.55 (17), p.8527-8542
• Main Authors: Ai, Pengfei, Mauro, Matteo, Gourlaouen, Christophe, Carrara, Serena, De Cola, Luisa, Tobon, Yeny, Giovanella, Umberto, Botta, Chiara, Danopoulos, Andreas A, Braunstein, Pierre
• Format: Article
• Language: English
• Subjects: Chemical Sciences; or physical chemistry; Theoretical and
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.6b01095

The heterofunctional and rigid ligand N,N′-diphosphanyl-imidazol-2-ylidene (PC NHC P; P = P­(t-Bu)2), through its phosphorus and two N-heterocyclic carbene (NHC) donors, stabilizes trinuclear chain complexes, with either Au3 or AgAu2 cores, and dinuclear Au2 complexes. The two oppositely situated PC NHC P (L) ligands that “sandwich” the metal chain can support linear and rigid structures, as found in the known tricationic Au­(I) complex [Au3(μ3-PC NHC P,κP,κC NHC,κP)2]­(OTf)3 (OTf = CF3SO3; [Au3 L 2]­(OTf)3; Chem. Commun. 2014, 50, 103–105) now also obtained by transmetalation from [Ag3(μ3-PC NHC P,κP,κC NHC,κP)2]­(OTf)3 ([Ag3 L 2]­(OTf)3), or in the mixed-metal tricationic [Au2Ag­(μ3-PC NHC P,κP,κC NHC,κP)2]­(OTf)3 ([Au2AgL 2]­(OTf)3). The latter was obtained stepwise by the addition of AgOTf to the digold­(I) complex [Au2(μ2-PC NHC P,κP,κC NHC)2]­(OTf)2 ([Au2 L 2 ]­(OTf)2). The latter contains two dangling P donors and displays fluxional behavior in solution, and the Au···Au separation of 2.8320(6) Å in the solid state is consistent with metallophilic interactions. In the solvento complex [Au3Cl2(tht)­(μ3-PC NHC P,κP,κC NHC,κP)]­(OTf)·MeCN ([Au3Cl2(tht)L]­(OTf)·MeCN), which contains only one L and one tht ligand (tht = tetrahydrothiophene), the metal chain is bent (148.94(2)°), and the longer Au···Au separation (2.9710(4) Å) is in line with relaxation of the rigidity due to a more “open” structure. Similar features were observed in [Au3Cl2(SMe2)L]­(OTf)·2MeCN. A detailed study of the emission properties of [Au3 L 2]­(OTf)3, [Au3Cl2(tht)L]­(OTf)·MeCN, [Au2 L 2]­(OTf)2, and [Au2AgL 2]­(OTf)3 was performed by means of steady state and time-resolved photophysical techniques. The complex [Au3 L 2]­(OTf)3 displays a bright (photoluminescence quantum yield = 80%) and narrow emission band centered at 446 nm with a relatively small Stokes’ shift and long-lived excited-state lifetime on the microsecond timescale, both in solution and in the solid state. In line with the very narrow emission profile centered in the violet-blue region, fabrication of organic light-emitting devices (OLEDs) comprising the [Au3 L 2]­(OTf)3 complex demonstrated its usefulness as a deep-blue emitter in solution-processed OLEDs. Electrochemical and Raman spectroscopic studies were also performed on [Au3 L 2]­(OTf)3. Experimental results were rationalized by means of Wave-Function Theory (WFT) and Density Functional Theory (DFT). MP2 calculations gave a satisfactory description of the stru