Synthesis and Characterization of a New Series of Gold (I) and Silver (I) N-Heterocyclic Carbene (NHC) Complexes

Abstract

Synthesis and characterization of different Au(I) and Ag(I) complexes are described. Treatment of 1-methylimidazole with various bromophthalimide linkers produces [H(CH3im(CH2)nphth)]+, (n=1−5), as an off-white powder in good yield. Further treatment of [H(CH3im(CH2)nphth)]+, (n=2-5), with excess N2H4 in refluxing acetonitrile forms [H(CH3im(CH2)nNH2)]+, (n=2-5), as yellow oil. Reaction of [H(CH3im(CH2)nNH2)]+, (n=2-5), with Au(tht)Cl in the presence of 1.0 M NaOH followed by treatment with excess NH4PF6 forms [Au(CH3im(CH2)nNH3)2](PF6)3, (n=2-5), as an off-white powder. Deprotonation of [Au(CH3im(CH2)nNH3)2](PF6)3, (n=2-5), with Ag2O produces dimeric and polymeric mixed metal complexes. Similarly, treatment of [Au(CH3im(CH2)nNH3)2](PF6)3, (n=2-5), with Ag2O forms dimeric and polymeric silver complexes. As expected, in these complexes the metal-metal separation increases as the length of the linker increases. The alkylation of the propylene linker ligand precursor with two equivalents of 2- (chloromethyl)pyridine forms the hydrochloride salt, [H(CH3im(CH2)3NH(CH2py)2)] (PF6)Cl in good yield. Reaction of [H(CH3im(CH2)3NH(CH2py)2)](PF6)Cl with Au(tht)Cl in the presence of NaOH produces [Au(CH3im(CH2)3N(CH2py)2)2Na](PF6)2. Further treatment of the sodium encapsulated gold complex with excess NH4PF6 protonates the pyridyl nitrogen atoms to form the "proton sponge-like" complex [Au(CH3im(CH2)3N(CH2py)2H)2](PF6)3. Upon deprotonation of the "proton sponge-like" complex with K2CO3, a potassium ion is encapsulated to produce [Au(CH3im(CH2)3N(CH2py)2)2K](PF6)2. Whereas, deprotonation of the "proton spongeii like" complex with Ag2O produces a polymeric {[AuAg(CH3im(CH2)3N(CH2py)2)2] PF6}n in good yield. Treatment of the [H(pyCH2)2im)]BF4 with excess Cu2O produces the trimetallic [Cu3((pyCH2)2im)3](BF4)3, cluster with considerably short Cu−Cu separation of 2.5090(8) Å. Further treatment of the trimetallic copper(I) cluster with Au(tht)Cl forms the chloride bridged heterometallic complex with Cu−Au separation of 2.7467 (15) Å. Likewise, treatment of the ligand precursor [H(CH3COOpyCH2)2im)]BF4, with excess Ag2O produces triangulo-Ag3 cluster, with a Ag***Ag contact of 2.8624(9) Å.