Mononuclear Gold II Complexes

Mononuclear gold(II) complexes, consistent with a d9 configuration, must be paramagnetic (peff= 1-79 MB) and show a hyperfine four-line EPR signal, in accordance with the nuclear spin of 197Au (I = 3/2). These two properties are evidence ofa real gold(II) complex in addition to their stoichiometry. 

In 1992 Herring et al. gave clear EPR and magnetic evidence for Au2+, as a species present in partially-reduced Au(S03F)3 and as a solvated ion in the strong protonic 

In this complex, xenon functions as a a-donor toward Au2+. This is reflected in the calculated charge distribution within the cation, where the main part of the positive charge resides in the xenon atoms. Relativity plays a large role in stabilizing this and other predicted Au-Xe compounds about half of the Au-Xe bonding energy comes from relativistic effects [279]. 

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The first evidence for mononuclear gold(II) complexes was obtained during a study of the reaction (57). 

The electronic configuration of Au is [Xe]4E 5d , and, hence, the mononuclear gold(II) complexes are paramagnetic... 

Fig. 7 Resonance Raman spectra of (a) the mononuclear Ru(II) complex and (b) the homo-binuclear Ru(II)/Ru(II) complex 355 nm in CH3CN (solvent subtracted) and (c) overlay of SERS spectra of the mononuclear Ru(II) complex (thick line) with that of the homo-binuclear Ru(II)/Ru(II) complex (thin line) at 785 nm (on gold colloid, self-aggregated). ...

Other cases of transition-metal ion binding to the imidazole ring N9 atom of the purine ligand have been reported in the monomer [TiCl(cp)2(pur-KA )] (cp is the cyclopentadienyl anion) with a purinate monoanion" and a series of neutral dinuclear and mononuclear gold(I) complexes with phosphine and purin-9-ate synthesized under basic conditions. There are reported examples of Mn(II) binding to N donor sites of nueleobases in biopolymeric systems, but coordinative Mn-N linkages involving isolated nueleobases, as seen in... 

Thus, the abstraction of the chlorine atom in [Au(QF5)2Cl(dppm)j [175] provides a mononuclear gold(I II) derivative with the diphosphine acting as a chelate ligand, which is an excellent starting material in the synthesis of dinuclear or polynuclear methanide and methanidiide complexes after deprotonation of the dppm ligand (first deprotonation with HNa and the second with acetylacetonate gold(I) derivatives) [198-201] (Scheme 3.3)... 

The coordination chemistry of tertiary phosphine-functionalized calix[4]arenes have been described.279 Treatment of a bis(diphenylphosphino) or bis(dimethylphosphino) derivative of calix[4]arene with [PtCl2(COD)] leads to the formation of the corresponding dichloroplatinum(II) complex. The related diplatinum(II) species has also been reported with the tetrafunctionalized calix[4]arene.280 The mononuclear derivative is susceptible to oligomerization if the two free phosphine ligands are not oxidized or complexed to another metal center such as gold(I).279 The platinum(II) coordination chemistry of a mono-281 and diphosphite282 derived calix[ ]arene (n = 4 and 6, respectively) has also been described. 

In 1959, the coordinated mercaptide ion in the gold(III) complex (4) was found to undergo rapid alkylation with methyl iodide and ethyl bromide (e.g. equation 3).9 The reaction has since been used to great effect particularly in nickel(II) (3-mercaptoamine complexes.10,11 It has been demonstrated by kinetic studies that alkylation occurs without dissociation of the sulfur atom from nickel. The binuclear nickel complex (5) underwent stepwise alkylation with methyl iodide, benzyl bromide and substituted benzyl chlorides in second order reactions (equation 4). Bridging sulfur atoms were unreactive, as would be expected. Relative rate data were consistent with SN2 attack of sulfur at the saturated carbon atoms of the alkyl halide. The mononuclear complex (6) yielded octahedral complexes on alkylation (equation 5), but the reaction was complicated by the independent reversible formation of the trinuclear complex (7). Further reactions of this type have been used to form new chelate rings (see Section 7.4.3.1). 

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