Complexes gold amidinate

Figure 1.9 Structure of the trinuclear and dinuclear gold amidinate complexes.

Gold in the oxidation state +1 also tends to form dinuclear complexes with bridging amidinate ligands. A typical example is Au2[HC(NC6H3Me2-2,6)2]2 (cf. Section Oxidative addition of iodomethane to the dinuclear gold(I)... 

Theoretical studies by Pyykkb in 1998 for [M2(NHCHNH)2] systems, M=Cu, Ag, and Au, predicted the M-M distances at the MP2 level [8]. Experimentally, systems containing amidinate ligands were known with Cu and Ag but unknown with Au. The results for the models containing silver and copper are close to the X-ray structures of [M2(ArNC(H)NAr)2], Ar=C6H4-4-Me and M=Ag, Cu. The Ag-Ag distance is 2.705 and 2.712 A and the Cu-Cu distance is 2.497 and 2.528 A at the experimental and theoretical level. Table 1.1. The hypothetical dinuclear gold(I) amidinate compound was calculated to have an Au-Au distance at the MP2 level of 2.728 A [8]. The dinuclear gold(I) amidinate complex now known proves the predicted Au-Au distance to be rather good. 

The structural arrangement of group 11 amidinate complexes is determined by the substituents on the amidinate aryl groups as well as on the NCN carbon [14,19]. The electronic vs. steric effect of the substituents on the molecular arrangement of gold(I) amidinate complexes have been studied in detail in the Fackler laboratory. 

Figure 1.2 Amidine ligands used in the synthesis of terta-, tri-, and dinuclear gold complexes.

Tetranudear gold(I) amidinate complexes are synthesized by the reaction of Au(THT)Cl with the potassium or sodium salt of the amidinate ligand in THF, Figure 1.4. Syntheses involving various substituted amidinates resulted in tetra-nuclear gold(I) clusters, [Au4(ArNC(H)NAr)4]. The C-functionalized substituted amidine ligands, ArNC(Ph)NHAr and ArNC(Me)NHAr, Ar=-QH5, were synthesized and reacted with Au(THT)Cl after deprotonation. Only tetranudear clusters were isolated. 

Oxidative-Addition Reactions to the Dinuclear Gold(l) Amidinate Complex 9... 

Figure 1.13 Synthesis of gold(ll) amidinate complexes by oxidative-addition to the dinuclear gold(l) amidinate.

The reaction of the dinuclear gold(I) amidinate complex, [Au2(2,6-Me2Ph-form)2], with Hg(CN)2 (1 2 stoichiometry) in THF forms a 2D coordination polymer, [Au2(2,6-Me2Ph-form)2]-2Hg(CN)2 2THF, not the expected oxidative-addition product of the type formed vdth the ylides. White crystals and a yellow powder are formed. 

The behavior of Hg(CN)2 toward the dinuclear gold(I) amidinate complexes requires comment. In the case of the dinuclear gold(I) ylide, oxidation of the Au(I) to Au(II) resulted in the formation of a reduced mercury(O) product. Figure 1.19(a) [36]. In the mercury(II) cyanide reaction with the dinuclear gold(I) dithiophosphinate. Figure 1.19(b), the stability of the gold(I)-carbon bond compared... 

The differences observed in the chemistry of these dinuclear gold(I) amidinate complexes compared with dinuclear gold(I) complexes with sulfur and carbon ligands may be understood by examining their respective highest occupied molecular orbital (HOMO)s and lowest unoccupied molecular orbital (LUMO)s of the species. 

Gold(I) ylides are oxidized in 0.1 M [Bu4N]BF4/THFat low potentials of +0.11 and + 0.23 V vs. Ag/AgCl (quasi-reversible). The dinuclear amidinate oxidizes under the same conditions at + 1.24 V vs. Ag/AgCl (reversible). These large differences in chemical character of the dinuclear gold(I) complexes appear to explain the widely different behavior of these compounds and especially toward the reaction with mercury cyanide. 

Density functional theory (D FT) modeling calculations show that a dinuclear gold(I) amidinate complex is less stable than the tetranuclear gold(I) amidinate cluster, [Au4(HNC(H)NH)4]. However, replacing C by Si in the backbone reduces ring strain and makes the energies similar. Figures 1.21 and 1.22 [39]. 

Reacting the amidinate salt, K[4-MePh-form], with the dinuclear gold(I) complex, [Au2(2,6-Me2Ph-form)2], in a 1 1 stoichiometry in THF forms the dinuclear-tetra-nuclear complex [Au2(2,6-Me2Ph-form)2][Au4(4-MePh-form)4]-2THF, Figure 1.24, with one tetranuclear and one dinuclear molecule in the same unit cell. Adjusting the reaction ratio to 2 1 formed the tetranuclear complex [Au4(4-MePh-form)4j. 

Abdou, H.E., Mohamed, A.A. and Fackler, J.P. Jr (2004) Oxidative addition of methyl iodide to dinuclear Gold(I) amidinate complex schmidbaur s breakthrough reaction revisited with amidinates. ZeitschriJiJurNaturforschungB. A Journal of Chemical Sciences, 59, 1480-1482. 

Mohamed, A.A., Abdou, H.E. and Fackler, J.P. Jr (2006) Mercury(ll) cyanide coordination polymer with dinuclear gold (1) amidinate. Structure of the 2-D [Au2(2,6-Me2-formamidinate)2]-2Hg (CN)2 2THF complex. Inorganic Chemistry, 45, 11-12. 

Abdou, H. (2006) PhD. Thesis New Chemistry with Gold-Nitrogen Complexes Synthesis and Characterization of Tetra-, Tri-, and Dinuclear Gold(I) Amidinate Complexes. Oxidative-Addition to the Dinuclear Gold (I) Amidinate, A M University, Texas. 

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