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Platinum(II) olefin compounds [PtMe(N,N′-imino, amide)(η2-olefin)] have been found to dimerize spontaneously in solution, yielding dinuclear complexes through an oxidative coupling. The extended conjugation within the molecules produces an intense blue color, and the properties of the compounds have been investigated through NMR spectroscopy, optical measurements, and theoretical calculations. The solid-state structure of a representative compound has been solved.

Novel coordinatively saturated platinum(II) compounds bearing C-linked carbohydrates were synthesized and characterized. The complexes exhibit bipyramidal trigonal geometry with a bidentate nitrogen ligand and ethylene in the equatorial plane. The axial positions are occupied by a halide ligand X and a D-galactose or D-glucose derivative, linked either via C1 or C6. The compounds were designed for evaluation of the biological activity because they combine the steady coordinative saturation, the beneficial action of the modular sugar moiety and the organometallic nature of the Pt-sugar linkage, which is expected to be stable in the biological media, until the target is reached. The newly synthesized molecules were stable in mixed DMSO/aqueous solvents, able to bind DNA in vitro and exhibited a selective cytotoxic activity on cancer cells through apoptosis activation.

Stable five-coordinate Pt(II) complexes have been highlighted as a promising and original platform for the development of new cytotoxic drugs. Their interaction with proteins has been scarcely studied. Here, the reactivity of the five-coordinate Pt(II) compound [Pt(I)(Me) (dmphen)(olefin)] (Me = methyl, dmphen = 2,9-dimethyl-1,10-phenanthroline, olefin = dimethylfumarate) with the model proteins hen egg white lysozyme (HEWL) and bovine pancreatic ribonuclease (RNase A) has been investigated by X-ray crystallography and electrospray ionization mass spectrometry. The X-ray structures of the adducts of RNase A and HEWL with [Pt(I)(Me)(dmphen)(olefin)] are not of very high quality, but overall data indicate that, upon reaction with RNase A, the compound coordinates the side chain of His105 upon releasing the iodide ligand, but retains the pentacoordination. On the contrary, upon reaction with HEWL, the trigonal bi-pyramidal Pt geometry is lost, the iodide and the olefin ligands are released, and the metal center coordinates the side chain of His15 probably adopting a nearly square-planar geometry. This work underlines the importance of the combined use of crystallographic and mass spectrometry techniques to characterize, in detail, the protein&ndash, metallodrug recognition process. Our findings also suggest that five-coordinate Pt(II) complexes can act either retaining their uncommon structure or functioning as prodrugs, i.e., releasing square-planar platinum complexes as bioactive species.

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)](SbF6)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)CH2CH(R)Ar](SbF6) or [M(PNP)CH(R)CH2Ar](SbF6) (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)PtCH2CH2−C6H2(OMe)3](BF4) 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.

This article describes a stereochemical study on five-coordinate complexes of PtII containing a prochiral alkene (E-R1O2CCH=CHCO2R1) and a prochiral sulfide R2SR3, of general formula [PtMe(R2SR3)(dmphen) (E-R1O2CCH=CHCO2R1)]BF4. Through mono- and two-dimensional NMR spectroscopy, it was demonstrated that there is mutual recognition between the prochiral ligands in the presence of aryl sulfides R2SAr, whose origin was also explained. The equilibrium constants of sulfide exchange were also evaluated, which are in full agreement with the σ-donor properties of the ligands.

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.

This review provides a survey of the key-class of Pt0 complexes of general formula [Pt(N,N′-chelate)(η2-olefin)]. The main spectroscopic, structural and chemical features are discussed, in terms of electronic and steric properties of the ancillary ligands. The versatile reactivity towards electrophiles is described as a very useful entry to PtII compounds with a wide assortment of ligands, such as halido, hydrido, hydrocarbyl, organometal, organoelement and carbene fragments, in some cases stabilised for the first time by the careful choice of the N,N′-ligand. Remarkably, the reactions can be an equilibrium, and their relevant thermodynamic parameters have also been collected, thus allowing a thorough discussion of the electronic and steric factors which affect its position.

Aiming to contribute to the design of new antitumoral drugs, we synthesized new hydrophilic Pt(II) complexes of general formula [PtCl 2 ( N , N ′)] containing nitrogen bidentate amine–imine and di-imine ligands derived from glucose. Some chemical properties were discussed. The X-ray molecular structure of [PtCl 2 (α- d -glucopyranoside-methyl-6-deoxy-6(2-(methylimino)methyl)pyridine) ( D ) was reported. [PtCl 2 (β- d -glucopyranosylimine- N -(2-pyridinylmethyl))] ( A ), which is well-soluble both in organic solvents and in water, was tested for cytotoxicity.

The coordinated olefin in dicationic platinum(II) and palladium(II) complexes [M(PNP)(olefin)](SbF6)2 (M = Pt, Pd; PNP = 2,6-bis(diphenylphosphinomethyl)pyridine; olefin = ethylene, propylene) reacts with β-dicarbonyl compounds (pentane-2,4-dione and methyl-3-oxobutanoate). If the proton released after the nucleophilic attack is trapped by a base, stable σ-alkyl derivatives [(PNP)M-CH2-CH(R)CH(Ac)COR′]SbF6 (R = H, Me; R′ = Me, OMe) are formed; otherwise the M−C σ-bond can be cleaved by the proton, in the rate-determining step of a catalytic cycle that leads to the alkylated dicarbonyl compound. The β-diketone is intrinsically more reactive than the β-ketoester, but in the catalytic reaction of the former an inhibition effect is observed in the case of the platinum catalyst.

Alkenes, alkynes, 1,2- and 1,3-dienes react with [MR(N-N)(MeCN)] + (M = Pt or Pd; R = hydrocarbyl group; NN = bidentate nitrogen ligand) to give R-substituted derivatives. The organic fragment is generally retained within the metal environment in η 1 or η 3 coordination, except in the reaction of alkenes with Pd (II) complexes. In this case, a free R-substituted alkene is produced via a relatively fast β-elimination process from a Pd-alkyl intermediate. Different regiochemistries are detected in the reaction between monosubstituted olefins (propene or styrene) and homologous Pt and Pd complexes. The Pt-C bond is always formed with the terminal unsubstituted alkene carbon, while a preference toward the internal carbon, particularly if phenyl-substituted, is observed with Pd species. Neutral [MClR(N-N)] are markedly less reactive. In this case, when M = Pt, the unsaturated organic substrate generally adds to the metal affording fairly stable tbp five-coordinate complexes.

Coordinatively saturated carbene complexes of platinum(II) have been obtained by oxidative addition of [ClCHNMe2]Cl to Pt(0) precursors. The cationic products of general formula [PtCl(CHNMe2)(N,N-chelate)(olefin)]Cl have been characterized through NMR spectroscopy and for [PtCl(CHNMe2)(2,9-Me2-1,10-phen)(Z-MeO2CCHCHCO2Me)]Cl by X-ray diffractometry. The latter species reacts with nucleophiles affording dimethylformamide and the corresponding Pt(0) precursor [Pt(2,9-Me2-1,10-phen)(Z-MeO2CCHCHCO2Me)]. Attempts to obtain related complexes containing carbene groups PtCHY without a heteroatom in α-position (Y = CO2Et, CO2NMe2, CN) have led to the isolation of complexes of formula [PtR(dmphen){η1,η2-CH(Y)O2CCHCHCO2Me}] (R = Me, Ph), formally derived from an intramolecular nucleophilic addition to a carbene intermediate. The X-ray structure of a representative product, [PtMe(dmphen){η1,η2-CH(CO2Et)O2CCHCHCO2Me}], is reported.

Three cationic five-coordinate platinum(II) complexes bearing alkylmercury fragments as “ligands” have been isolated. The complexes of general formula [Pt(HgR)H2O(dmphen)(Z-R′O2CCH = CHCO2R′] (BF4) ( dmphen = 2,9- dimethyl -1,10- phenanthroline ; R, R ′ = Me ; = R = Me, R ′ = t Bu, R ′ = Me ) are stabilized by the factors operating in related neutral species. Two of the new complexes slowly demercuriate in solution, affording the mononuclear complexes [ Pt(Me)(H 2 O)(dmphen)(Z- R ′ O 2 CCH = CHCO 2 R ′)]( BF 4 ) ( R ′ = Me or t Bu . When R = t Bu , a slow redistribution is observed, yielding the trinuclear cluster [{Pt(dmphen)(Z-MeO2CCH = CHCO2Me(H2O)}2Hg](BF4)2. The structure of this complex has been determined by X-ray analysis.

Trigonal bipyramidal olefin-platinum complexes of the title chiral diamine (mestien) have been synthetized and their stereochemistry has been investigated by H-1 and C-13 NMR spectroscopy. The molecular structure of the complex PtClMe ((E)-ClCH = CHCl) (mestien) has been determined by X-ray diffraction analysis. The coordinated nitrogen atoms display a single configuration, and a high enantioface selectivity is observed in the coordination of prochiral olefins having a moderate lateral bulk. The selectivity can be correlated to the conformation adopted by the diamine ligand, which shows a remarkable similarity to those calculated for a proposed intermediate in the enantioselective dihydroxylation of olefins by osmium tetraoxide.