Square planar gold complexes

Both the cyanide, [Au(CN)2] , and fulminate, [Au(CNO)2] , ions contain linear gold(I) centres.387,388 A report that KAu(CN)2(2,2 -bipyridyl) contains square planar gold(I) has been disproved the bipy ligand is not coordinated to gold and the complex contains linear [Au(CN)2J ions. 390 AuCN is polymeric with a linear (—Au—CN—) Au— chain structure.391... 

In the complex oxides MAu02 (M = K or Rb) there are infinite chains with square planar gold(ffl) centres linked by ju2-oxo ligands, while M3Au03 are properly formulated M6[Au206] in which the anion is isostructural with [Au2CL].516,517... 

Dithiols give several stable square planar gold(III) complexes. Some complexes of biochemical interest are those derived from 2,3-dimercaptopropanol (BAL),230 dimercaptosuc-cinic acid249 and penicillamine.542 These are thought to have structures similar to that of the toluenedithiolate derivative (72).543 They can be prepared by reaction of [AuCLJ- with the dithiol and base or by oxidation of gold in the presence of the dithiol. 

The related complexes [Os3(CO)nX(AuPR3)] are thought to have structure (123),762,763,765,766 while the remarkable compound [ Os3( -H) (CO) 10 2( 4-Au)]-, prepared as the [N(PPh3)2]+ salt by reaction of (122 X = H) with [N(PPh3)2]Cl, has structure (124). This complex has square planar gold(I) bridging between the two Os3 clusters.767 The interaction between gold... 

Aza-analogues of oxygen compounds frequently show related reactivity patterns, and this is certainly seen in a comparison of the chemistry of imines and carbonyl compounds. For example, 1,3-diimines are readily deprotonated to yield the 1,3-diketonate analogues. The most frequent consequence of this is that reactions which are expected to yield 1,3-diimine complexes often lead to those of the deprotonated species. This is seen in the formation of the gold(m) complex of a deprotonated macrocycle in the reaction of 1,2-diaminoethane with 2,4-pentanedione in the presence of Na[AuCl4] (Fig. 5-4). The exact sequence of events in this reaction is not known, but note that the product is a square-planar gold(in) complex of the doubly-deprotonated macrocycle, rather than a gold(i) species ... 

Fig. 5. Experimental s-i(s) values (crosses) for gold(III) halide solutions compared with theoretical values (solid lines) calculated for square-planar AuX4 complexes.

A dinuclear selenide complex anion [Au2(M-Se)2(Se4)2] is the product of the reaction" between [AuCN] and Na2 Ses. Square-planar gold(IIl) complexes are readily formed by a variety of bidentate sulfur-donor ligands such as toluene-1,2-dithiolate, maleonitriledithiolate, and dithiocarbamate. On oxidation with CI2 or Br2, [ Au(S2CNR)2 2] forms Au -Au complexes, which may be oxidized further to an Au complex. 

Figure 3 Coordination geometries for gold(I) and gold(III) complexes examples of (a) negative, neutral and positively charged linear gold(l) complexes (b) trigonal and tetrahedral gold(l) complexes and(c) square-planar gold(lll) complexes (Et = ethyl Me = methyl Ph = phenyl SG = glutathionate-(S))...

Thus they resemble square-planar gold(III) systems, but one ligand is replaced by the Au—Au bond. The high electron density in this bond gives Mossbauer parameters rather similar to those for gold(III) complexes with one fewer soft ligand15. 

An interesting feature concerning the redox properties of the complex, [Au(dddt)2] (dddt = 5,6-dihydro-l,4-dithiine-2,3-dithiolate, 3), is that the one-electron oxidized product, [Au(dddt)2]°, can be isolated14. An X-ray analysis of the neutral complex reveals a square planar gold structure stacked in dimeric units as a result of intermolecular S-----S contacts. Extended Hlickel calculations predict that the odd electron resides pri-... 

The electrochemistry of a square-planar gold(III) complex with 2-(diphenylphosphino) benzenethiolate (21) was reported by Dilworth and coworkers35. Cyclic voltammetry experiments on [Au(21)2]BPh4 indicate a reversible redox couple at —0.862 V (vs the Fc/Fc+ reference couple) in 0.2 M [Bu4N]BF4/MeCN solution. Peak-to-peak separation of the redox waves was 84.2 mV and convolution methods were used to establish that the redox couple was reversible and involved the same number of electrons as the ferrocene/ferrocenium couple under identical conditions. The reductive scan was assigned... 

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