While several gold(I) complexes of the type (L)AuX (X = Cl, Br) are known to undergo oxidative addition of elemental chlorine and bromine (X2), respectively, to give the corresponding gold(III) complexes (L)AuX3, the addition of iodine to (iodo)gold(I) compounds is strongly ligand-dependent, suggesting a crucial threshold in the oxidation potentials. A systematic investigation of this particular oxidative addition of iodine using a large series of tertiary phosphines as ligands L has shown that both electronic and steric effects influence the course of the reaction. The reactions were followed by 31P NMR spectroscopy and the products crystallized from dichloromethane–pentane solutions. Complexes with small triakylphosphines (PMe3, PEt3) are readily oxidized, while those with more bulky ligands (PiPr3, PtBu3) are not. With L taken from the triarylphosphine series [PPh3, P(2-Tol)3, P(3-Tol3), P(4-Tol)3] no oxidation takes place at all, but mixed alkyl/aryl-phosphines [PMenPh3−n] induce oxidation for n
				= 3 and 2, but not for n
				= 1 and 0. However, in cases where no oxidation of the gold atoms is observed, the synthons may crystallize as adducts with molecular iodine of the polyiodide type instead, which have an iodine rich stoichiometry. This fact explains inconsistent reports in the literature. The metal atoms in (L)AuI coordination compounds with L representing a tri(heteroaryl)phosphine [P(2-C4H3E)3, E = O, S], a phosphite [P(OR)3] or a trialkenylphosphine [PVi3] are all not subject to oxidative addition of iodine. The dinuclear complex of the ditertiary phosphine Ph2PCH2PPh2, (dppm)(AuI)2, gives an iodine adduct (without oxidation of the metal atoms), but with 1,2-Ph2P(C6H4)PPh2
				(dppbe) an ionic complex [(dppbe)AuI2]+I3− with a chelated gold(III) centre is obtained. The gold(I)
				bromide complexes with tertiary phosphines are readily oxidized by bromine to give the corresponding gold(III) tribromide complexes, as demonstrated for (BzMePhP)AuBr and (Ph3P)AuBr. With (dppm)(AuBr)2 the primary product with mixed oxidation states was also isolated: (dppm)AuBr(AuBr3). The crystal structures of the following representative examples and reference compounds have been determined: (Me3P)AuI3, (Me2PhP)AuI3, (iPr3P)AuI·1.5I2, (Ph3P)AuI·I2, {[(2-Tol)3P]AuI}2·I2, [(2-Tol)3P]AuI, (dppm)(AuX)2
				(with X = Br, I), (dppm)AuBr(AuBr3) and [(dppbe)AuI2]+I3−. The structures are discussed focusing on the steric effects. It appears that e.g. the reluctance of (Ph3P)AuI to add I2 is an electronic effect, while that of (iPr3P)AuI has its origin in the steric influence of the ligand.

Governing the oxidative addition of iodine to gold(I) complexes by ligand tuning

The question raised in the title of this progress report is answered point for point with an emphatic “yes”: Ranging from metallic gold, via clusters of gold atoms in low valence states, compounds of AuI, AuII, AuIII, and AuV, organogold derivatives, ylide and carbene complexes, to the catalytic activity of gold it embraces a long-neglected area of chemistry holding promise of many a discovery.

Is Gold Chemistry a Topical Field of Study

Einige ein- und zweikernige Komplexe von AuCl und AuCl3 mit mono- und difunktionellen Thioathern wurden hergestellt. Gold(I)-Zentren addieren nur jeweils einen Thioatherliganden, tauschen diesen aber in Losung sehr rasch gegen uberschussigen Liganden aus. Dies gilt auch fur potentielle Chelatliganden. Fur die Gold(III)-Komplexe wird eine ionische Struktur vorgeschlagen. Die Verbindungen sind fur therapeutische Zwecke von Interesse.



Organogold Chemistry, XII. Complexes of Gold(I) and Gold(III) Halides with Thioethers



A series of mono- and binuclear complexes of AuCl and AuCl3 with mono- and difunctional thioethers have been prepared. In all cases gold(I) centers are adding only one thioether, which in solution is in very rapid exchange with excess ligand, however. This is also true with potential chelating ligands. For the gold(III) complexes an ionic structure is proposed. The compounds are of interest for therapeutic uses.

Organogold‐Chemie, XII. Komplexe von Gold(I)‐ und Gold(III)‐halogeniden mit Thioäthern

Synthesis, Structure, and Reactions of a Binuclear Gold(I)−Gold(III) Complex Containing Bridging and Bidentate (2-Diphenylphosphino-6-methyl)phenyl Groups.

Tris[(trimethylphosphane)gold(I)]sulfonium tetrafluoroborate (1) has been prepared from the corresponding oxonium salt [(Me3P)Au]3O+ BF-4 and bis(trimethylsilyl) sulfide, (Me3Si)2S. The analogous triisopropylphosphane and methyldiphenylphosphane complexes (2, 3) have been obtained in a similar way. The products are stable crystalline solids, the structure of which has been determined by X-ray methods. They are composed of independent tetrafluoroborate anions and pyramidal tri(gold)sulfonium cations, which are aggregated to form dimeric units (as in 3) or even strings of dimers (as in 1). It is only in complex 2 that steric effects, originating from the bulky phosphane ligands, prevent the building of supra-molecular (supracationic) aggregates. In the independent pyramidal cations of 2 only short intracationic Au…Au contacts have been detected. These are complemented by intercationic gold-gold contacts of similar length in the structures of 1 and 3. - In the preparation of complex 1, the species [(Me3P)Au]4S2+ (BF-4)2 (4) with hypercoordinate sulfur atoms has also been detected by mass spectroscopy.

D.R. Williamson

Papers

Gold-halogen stretching frequencies