Gold complexes ylides

A related dinuclear species 77, recently described, constitutes the first dinuclear gold(I) complex with heterobridged phosphor-1,1 -dithiolato moieties and bis(ylide) bridging ligands [ 102]. It is obtained by reaction between [ AuS2PPh2] and the diylide gold complex 74 (R=Me). No intermolecular Au-Au interaction is observed in 77 but the oxidative addition of chlorine to the product leads to a new complex 78 in which a single bond is formed between the two Au(II) centers (Scheme 26). 

The compound 86 constitutes an interesting compound in which a bis keto-ylide coordinates both a palladium (through an aryl and an ylidic carbon) and a mercuric center (through an yfidic carbon) [89,110]. This C,C,C-terdentate coordination has also been observed with gold complexes. 

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... 

Figure 1.19 Schematic representation of the reactions between Hg(CN)2 and the (a) dinuclear gold(l) ylide with loss of Hg(0), (b) dinuclear gold(l) dithiophosphinate with los of AuCN, and with (c) dinuclear Au(l) 2,6-Me2formamidinate complexes.

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. 

Scheme 11 Gold(III) and mixed Gold(I)/Gold(III) ylide complexes.

Phosphonium ylides, which can be written in the two familiar canonical forms, are available with a wide variety of substituents both at the phosphorus and at the carbon atoms (Scheme 30). In gold complexes, without any exceptions, they function as two-electron donors, as proposed by the dipolar form to give discrete Au-C cr-bonds (771, monohapto). No side-on, 7r-coordination (t 2), as might be expected out of the ylene form, has been observed to date. 

Scheme 1.3 Synthesis of polynuclear gold(II) ylide complexes.

The chemistry of metal-gold-containing ylide bimetallic complexes based on methylenethiophosphinate ligand was developed by Fackler and coworkers [34—39]. The chemical similarities of Au(I) and Hg(II) ions were used to synthesize a series of complexes, as shown in Scheme 4.2. 

Table 4.2 Selected molecular parameters for gold-mercury ylide complexes.

Gold(I) ylide complexes of various types have been prepared (45). Reactions of [AuCIL] complexes with ylides led initially to monoylide species (49), but displacement of L also occurred with excess ylide [Eq. (16)]. Analogous compounds with one or two a-silyl groups were also obtained. 

Six gold(I) ylide complexes of the types described above have been tested for use in arthritis therapy (55), but only one showed an activity comparable to standard chrysotherapeutic agents. The separation between toxic and therapeutic doses was too narrow, but this is clearly an area where further study could be of immense value. 

The majority of gold(I) ylide complexes prepared have been of a binu-clear constitution. The first compound of this type was obtained (56) when [Au(CH2PMe3)2]Cl was allowed to stand in the presence of the ylide for seven days [Eq. (19)]. The 3IP-NMR spectrum showed only one signal, indicating that the two phosphorus centers were in identical environments, and the H-NMR spectrum exhibited two doublets with 2/(P—CH3) and 2J(P—CH2) having the same sign. Thus the symmetrical structure depicted in Eq. (19) was invoked, and the presence of two onium centers adjacent to the Au—C bonds was believed to stabilize this unlikely species. 

Stepwise addition of halogens to the trimeric complex, [Au C(OMe)= NMe ]3 produced (155) three complexes Au3 C(OMe)=NMe 3X ] (n = 2,4,6) by consecutive oxidation of the three gold(I) centers. Binuclear gold(I) ylide complexes, however, underwent (56) consecutive oxidative addition of X2 to give formal gold(II) and finally gold(III) products [Eq. (49)]. Crystal structure (188) and spectroscopic (56. 189, 190) data have... 

Similar to the abovementioned silver nhc coordination compounds, carbene chemistry has also been dominant in the field of gold organometallic chemistry. Noteworthy examples include a Au(PPh3)-compound derived from tetraaminoallene, that can be rationalised in terms of a dicarbene with ylide character and which, owing to the electron-rich character of the central carbon atom, offers the potential for dimetallation products.108 Non-activated allenes and alkynes have been found by Lavallo to be readily aminated by cationic carbene gold complexes.109 For this purpose, a 2,6-diisopropylphenyl functionalized cyclic alkylaminocarbene gold(I) complex... 

As part of a wider study of the chemistry of ferrocene derivatives containing organophosphorus groups, Laguna and co-workers have prepared and structurally characterised ylide complex (57). Other gold complexes containing coordinated ylides reported include mononuclear species (58), (59) and di-nuclear complex (60) which were obtained from the reactions of the ylides or... 

Bimetallic gold-silver complexes may be prepared from gold bis(ylide) species such as [Au(CH2PPh3)2]ClC>4 and AgC104 (leading to neutral clusters, equation 54) or... 

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