The intermolecular alkoxylation of alkynes is the oldest application of cationic gold(I) catalysts; however, no systematic experimental data about the role of the anion are available. In this contribution, the role of the anion in this catalytic reaction as promoted by a N-heterocyclic carbene-based gold catalyst, [(NHC)AuX] (X=BARF(-) , BF4 (-) , OTf(-) , OTs(-) , TFA(-) , or OAc(-) ) is analyzed, through a combined experimental (NMR spectroscopy) and theoretical (DFT calculation) approach. The most important factor seems to be the ability to abstract the proton from the methanol during the nucleophilic attack, and such ability is related to the anion basicity. On the other hand, too high coordination power or basicity of the anion worsens the catalytic performance by preventing alkyne coordination or by forming too much free methoxide in solution, which poisons the catalyst. The intermediate coordinating power and basicity of the OTs(-) anion provides the best compromise to achieve efficient catalysis.

Herein, we synthesized and characterized through NMR and X-ray techniques a new set of [(NHC)-Au-X] complexes (NHC = 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene), differing in the counterion X (X = OMs , NO3 , ClO4 , 2,2,3,3,4,4,5,5,6,6,7,7,7-tridecafluoroheptanoate (PFHp )). All of these complexes, together with those already known having NTf2 and phthalimide (ptm ) as counterions, were tested as catalysts in the methoxylation of 3-hexyne. The results were analyzed together with those obtained previously. The values of activation parameters (Delta H-? and Delta S-?) for different anions are also reported. The overall catalytic and kinetic evidence, together with an extensive computational work, confirm the general mechanistic picture given recently in which the anion plays an active role in all steps of the reaction mechanism: pre-equilibrium, nucleophilic attack, and protodeauration. Medium-coordinating anions (OMs , OTs ) containing a highly symmetric anchoring group give the best catalytic performances. This is due to the following reasons: (a) the pre-equilibrium is shifted toward the outer sphere ion pair, (b) their characteristic basicity promotes the nucleophilic attack, and (c) the possible paths leading to the deactivation of the catalyst are inhibited. These highly symmetric tridentate anions destabilize the unreactive tricoordinated gold species, which instead may be formed by anions with a planar anchoring group, such as PFHp and TFA . A general trend between coordinating ability and catalytic performances in the alkoxylation of alkynes may be established only when the geometric features of the anion are taken into account. The role of the anion has been also investigated in connection with the nature of the nucleophile. In particular, when the alcohol is a poor nucleophile, a large difference in reactivity is observed, while the use of suitably functionalized alcohols, which may contribute to polarizing the -OH bond through intramolecular interactions, flattens the anion effect

This article describes the synthesis and characterization of novel cationic five-coordinate Pt(II) complexes containing nitrogen sugar-based ligands. The cytotoxicity of the complexes was evaluated on different cell lines with the expectation that both the coordinative saturation and the sugar moiety cooperate to enhance their biological activity. In fact, the complexes resulted to be more active than cisplatin but still with little selectivity. They activate the apoptosis pathway. Binding of representative compounds with DNA was studied by ethidium bromide displacement assay and circular dichroism. Binding to model proteins was also investigated; the X-ray structure of the adduct formed in the reaction between a representative compound and the model protein bovine pancreatic ribonuclease was obtained. The structure discloses an unprecedented interaction between a five-coordinate Pt(II) moiety and a His side chain.

The coordinated olefin in dicationic platinum(II) and palladium(II) complexes [M(PNP)(olefin)](SbF 6 ) 2 (M ) Pt, Pd; PNP ) 2,6-bis(diphenylphosphinomethyl)pyridine; olefin ) ethene, propene) is electrophilic enough to react with benzene rings activated by methoxy substituents. If the proton released by the aromatic ring is trapped by a base, stable σ-alkyl derivatives of the type [M(PNP)CH 2 CH(R)Ar](SbF 6 ) or [M(PNP)CH(R)CH 2 Ar](SbF 6 ) (R ) H, Me) are formed; otherwise the M-C σ-bond can be cleaved by the proton, setting up a catalytic cycle that leads to the alkylated aromatic compound. The molecular structure of the σ-alkyl derivative [(PNP)PtCH 2 CH 2 -C 6 H 2 (OMe) 3 ](BF 4 ) has been determined by X-ray diffraction analysis, and the factors affecting the mechanism and the rates of the catalytic reaction have been qualitatively investigated and rationalized, showing that the rates of C-C bond formation and M-C bond cleavage are inversely correlated.

The dicationic palladium(II) and platinum(II) complexes [(PNP)M(C2H4)](BF4)2 (1a, M = Pt; 1b, M = Pd; PNP = 2,6-bis((diphenylphosphino)methyl)pyridine) and [(PPP)Pt(C2H4)](BF4)2 (7; PPP = triphos) catalyze a cross-coupling reaction of ethylene with tri- and tetrasubstituted olefins, which can lead to both hydrovinylation and cyclopropanation products. The product ratio is strongly affected by the choice of the ligand and of the metal, the two limiting cases being 1a and 7, which selectively give the hydrovinylation and the cyclopropanation products, respectively.