Reaction of the electron-rich derivative cis-[Pt(Me) 2 (DMSO) 2 ] with 2,2′-bipyridine (L) affords the mononuclear "rollover" N′,C(3) cyclometalate [Pt(L-H)(Me)(DMSO)] (1a) or the unusual dinuclear species [Pt 2 (µ-L-2H)(Me) 2 (DMSO) 2 ] (2a), depending on the Pt/L molar ratio. The latter complex, 2a, can be obtained either directly from cis-[Pt(Me) 2 (DMSO) 2 ] or by a two-step process through complex 1a. The synthesis of 2a implies a double C-H bond activation, with loss of two molecules of methane: the 2-fold deprotonated 2,2′-bipyridine links two [Pt(Me)(DMSO)] fragments, acting as a π-delocalized C,N∧N,C eight-electron donor. From 1a and 2a displacement of DMSO with two-electron-donor ligands such as PPh 3 , (b), CO (c), and 3,5-Me 2 py (d) gives two series of complexes, 1b-d and 2b-d, respectively. Reaction of 1a and 2a with HCl affords the corresponding chlorides [Pt(L-H)(Cl)(DMSO)] (3a) and [Pt 2 (µ-L-2H)(Cl) 2 (DMSO) 2 ] (4a), from which complexes 3b-d and 4b,d can be obtained by substitution of DMSO. The crystal structures of the mono-and dinuclear complexes [Pt(L-H)(Cl)(PPh 3 )] (3b) and [Pt 2 (µ-L-2H)(Cl) 2 (PPh 3 ) 2 ] (4b) have been solved by X-ray diffraction. Protonation of the uncoordinated nitrogen atom in 1a can be achieved by reaction with 18-crown-6 • HBF 4 : [Pt(L*)(Me)(DMSO)][BF 4 ] (5), where the zwitterionic ligand L* is still N′-C(3) bonded to platinum(II), can be isolated in the solid state. Taking advantage of the two-step approach used for the synthesis of complex 2a, unsymmetric species where the platinum atoms are in different environments, e.g. [(DMSO)(Cl)Pt(µ-L-2H)Pt-(Me)(DMSO)] (6), [(PPh 3 )(Me)Pt(µ-L-2H)Pt(Me)(DMSO)] (7), and [(CO)(Cl)Pt(µ-L-2H)Pt(Me)(DMSO)] (8), can be prepared in good yields. Attempts to build up a platinum(II)-gold(III) species by reaction of 3a with Na[AuCl 4 ] failed: no platinum-gold derivative was obtained but a platinum(IV) complex, [Pt(L-H)(Cl) 3 (DMSO)] (9), likely due to the strong oxidative capability of gold(III).

The relevance of cis and trans influences of some anionic ligands X and Y in cis-[PtX(2)(PPh(3))(2)] and cis-[PtXY(PPh(3))(2)] complexes have been studied by the X-ray crystal structures of several derivatives (X(2) = (AcO)(2) (3), (NO(3))(2) (5), Br(2) (7), I(2) (11); and XY = Cl(AcO) (2), Cl(NO(3)) (4), and Cl(NO(2)) (13)), density functional theory (DFT) calculations, and one bond Pt-P coupling constants, (1)J(PtP). The latter have allowed an evaluation of the relative magnitude of both influences. It is concluded that such influences act in a cooperative way and that the cis influence is not irrelevant when rationalizing the (1)J(PtP) values, as well as the experimental Pt-P bond distances. On the contrary, in the optimized geometries, evaluated through B3LYP/def2-SVP calculations, the cis influence was not observed, except for compounds ClPh (21), Ph(2) (22), and, to a lesser extent, Cl(NO(2)) (13) and (NO(2))(2) (14). A natural bond order analysis on the optimized structures, however, has shown how the cis influence can be related to the s-character of the Pt hybrid orbital involved in the Pt-P bonds and the net atomic charge on Pt. We have also found that in the X-ray structures of cis-[PtX(2)(PPh(3))(2)] complexes the two Pt-X and the two Pt-P bond lengths are different each other and are related to the conformation of the phosphine groups, rather than to the crystal packing, since this feature is observed also in the optimized geometries.

The cis influence of a series of anionic ligands X and Y has been evaluated through the magnitude of the Pt-P coupling constants for compounds of formula trans-[PtXY(PPh(3))(2)]. The order of decreasing cis influence was found to be I > Cl > SePh approximately SPh approximately SEt > NO(3) > AcO approximately NO(2) > H > Me > Ph > mtc (mtc = N,N-dimethylmonothiocarbamato-S); moreover, the cis influences of the various ligands was found to be additive. The X-ray structures of three representative compounds (t-: X = Cl, Y = NO(3); t-: X = Cl, Y = AcO and t-: X = Y = NO(2)) have also been determined.

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Novel gold(III) pyridinyl-oxazoline cationic complexes [Au(pyoxR)Cl2][X] [pyoxR = (S)-4-R-2-(pyridin-2-yl)-4,5-dihydrooxazole, with R = iPr, Bn, and (R)-4-phenyl-2-(pyridin-2-yl)-4,5-dihydrooxazole; X = PF6, AuCl4, or mixtures of the two anions] were synthesized and structurally characterized. Reaction of the adducts with NaOAc in aqueous solution afforded the neutral complexes [Au(N,N′,O)Cl] of the deprotonated ligands N-(1-hydroxy-3-R-2-yl)pyridine-2-carboxamide (R = iPr, Ph), N,N′H,OH, resulting from ring-opening of the bound pyox ligand by hydroxide ions and incorporation of hydroxide into the ring-opened products. Reaction of [Au(N,N′,O)Cl] (R = iPr) with HX (X = Cl, BF4, OTf) in aqueous solution resulted in protonation of the coordinated alkoxo group and its displacement from the coordination sphere to give the adducts [Au(N,N′,OH)ClX] (X = OTf, Cl) or the aquo complex [Au(N,N′,OH)(OH2)Cl]+ (X = BF4). Crystal structure characterizations were carried out on both [Au(N,N′,O)Cl] and [Au(N,N′,OH)Cl2] (R = iPr). Equimolar mixtures of the ring-opened derivative [Au(N,N′,O)Cl] (R = iPr) and either silver salts or HBF4 were found to promote, under mild conditions, polymerization of styrenes.

cis-[Pt(R) 2 (DMSO) 2 ] (R ) Me, Ph) reacts with 6,6′-diphenyl-2,2′-bipyridine (H 4 L) in a 2:1 molar ratio, giving the unusual, very slightly soluble dinuclear complex [Pt 2 (L)(DMSO) 2 ] (1). The reaction implies activation of four C-H bonds: in 1 a fourfold deprotonated H 4 L links two Pt-DMSO fragments acting as a delocalized C,N,C∧C,N,C 12-electron donor. From 1 more soluble dinuclear [Pt 2 (L)(L′) 2 ] (L′ ) bulky 2-electron donors such as PR 3 and substituted pyridines) species, 2-6, and polynuclear) species, 7-9, have been obtained by substitution of the DMSO ligands. DMSO can also be displaced from 1 by CO, both in solution and in the solid state, to give the flat and completely insoluble complex [Pt 2 (L)(CO) 2 ] (10). The structures of [Pt 2 (L)(3,5-Me 2 -Py) 2 ] (5) and {Pt 2 (L)(dppe)} 2 (8) have been determined by singlecrystal X-ray diffraction analysis, while a powder X-ray diffraction analysis has been performed on complex 10, [Pt 2 (L)(CO) 2 ]. With a 1:1 Pt:L molar ratio a mononuclear complex, [Pt(H 2 L)(DMSO)] (11), is obtained, where the twofold deprotonated ligand is C,N,C coordinated. Also, the DMSO can be displaced from 11 by neutral ligands, L′, such as CO, PPh 3 , and 3,5-Me 2 -py to give [Pt(H 2 L)(L′)] (12-14). Compounds 11-14 further react with cis-[Pt(R) 2 (DMSO) 2 ] to give dinuclear complexes. This two-step approach allows us to obtain species with different ligands around each platinum atom, [Pt 2 (L)(L′)(L′′)] (15-18).

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