Fine-Tuning the Basicity of Metal Complexes: Reversible Oxidative Addition of Se−Se Bonds to Platinum(II) Precursors

The oxidative addition of diselenides to novel platinum(II) precursors affording octahedral platinum(IV) products was investigated. The properties of the substituents on Pt were finely tailored in order to prompt easy reversibility of the reaction. This allowed the achievement of the first example of equilibrium of oxidative addition of an E−E bond (E = chalcogen) to a Pt(II) precursor. The equilibrium constants could be evaluated by NMR spectroscopy, and the results were preliminarily rationalized in terms of steric and electronic factors

[PtR(η²-olefin)(N-N)]⁺ Complexes Containing the Olefin and the Alkyl Ligand in a <i>cis</i> Arrangement. Preparation, Structural Characterization, and Olefin Stereochemistry

Cationic Pt(II) complexes containing an alkyl and an olefin in cis positions are described. The compounds (1) of general formula [PtR(N-N)(olefin)]BF4 are obtained either through oxidative addition of the trialkyloxonium salt R3O+BF4- to the appropriate three-coordinate precursor [Pt(N-N)(olefin)] or by substitution of an alkene for the chloride in [PtR(Cl)(N-N)] complexes. The complexes are involved in a dynamic process involving the alkene ligand. The rate of alkene exchange is strongly influenced by the steric hindrance of the N-N ligand above and below the coordination plane. This feature also controls the stereochemistry of alkene coordination. Thus, for type 1 derivatives of α-olefins containing the highly crowded diacetyl bis(di-isopropylphenylimine), only one enantiomeric couple has been detected in the temperature range 203−328 K, and its geometry has been tentatively assigned. Finally, the X-ray crystal structure of a representative complex has been determined

Organometallics in Water: Three-Coordinate [Pt⁰(N,N-chelate)(η²-olefin)] Complexes Containing New Chiral Ligands Based on α-d-Mannose

New bidentate nitrogen ligands based on α-D-mannose were prepared and investigated by preparing a family of platinum(0) complexes of formula [Pt(N,N-chelate)(η2-olefin)]. The ability of one N,N-chelate to induce a stereoselective reaction in water was assessed

Oxidative Additions of E−E Bonds (E = Chalcogen) to Group 10 Metals: “Tunable” Cleavage of Se−Se Bonds by Pt(0) Complexes

Oxidative Additions of E−E Bonds (E = Chalcogen) to Group 10 Metals:  “Tunable” Cleavage of Se−Se Bonds by Pt(0) Complexe

First Coordinatively Saturated Carbene Complexes of Platinum(II): Synthesis, Structure, and Reactivity

Coordinatively saturated carbene complexes of platinum(II) have been obtained by oxidative addition of [ClCHNMe2]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-MeO2CCHCHCO2Me)]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-MeO2CCHCHCO2Me)]. Attempts to obtain related complexes containing carbene groups PtCHY 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)O2CCHCHCO2Me}] (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)O2CCHCHCO2Me}], is reported

Organometallics in Water: Three-Coordinate [Pt⁰(N,N-chelate)(η²-olefin)] Complexes Containing New Chiral Ligands Based on α-d-Mannose

New bidentate nitrogen ligands based on α-D-mannose were prepared and investigated by preparing a family of platinum(0) complexes of formula [Pt(N,N-chelate)(η2-olefin)]. The ability of one N,N-chelate to induce a stereoselective reaction in water was assessed

Binuclear Complexes of Bis-Chelating Ligands Based on [1,4]Dioxocino[6,5-<i>b</i>:7,8-<i>b</i>′]dipyridine Moieties

Ligands based on a [1,4]dioxocino[6,5-b:7,8-b′]dipyridine (doxpy) core were prepared and characterized. They all present two equal chelating moieties each one including one N, O, or S donor in addition to a pyridinic nitrogen. These ligands displayed high selectivity for the formation of binuclear complexes. At least one d8 ion (PdII or PtII) complex was prepared for each type of ligand. The stereochemical behavior of the ligands is discussed on the basis of NMR spectra. Stable atropoisomers were obtained in the case of N-oxides or in case chiral centers were introduced in the ethereal bridge. As for the complexes, stable enantiomers appear to be in principle attainable for all the new compounds. A test on the cooperative ability of two PdII centers has been grounded on the microstructure of the styrene/CO copolymer catalytically produced by a binuclear pyridine-imino complex. In fact, comparison with the microstructure of the copolymers produced by related single-site mono- and (open-chain) binuclear catalysts reveals significant difference, thus giving indication of possible synergic metal activity

Synthesis and Characterization of Trigonal-Bipyramidal Platinum(II) Olefin Complexes with Chalcogenide Ligands in Axial Positions. X-ray Molecular Structures of [Pt(SMe)₂(dmphen)(diphenyl fumarate)], Its Cationic Dipositive Derivative [Pt(SMe₂)₂(dmphen)(diphenyl fumarate)][BF₄]₂, and Free Diphenyl Fumarate

The oxidative addition of RE−ER molecules (E = O, R = H, C(O)Ph, C(O)Me; E = S, Se, Te, R = Me, Ph) to Pt(0) precursors [Pt(N,N-chelate)(olefin)] (1:  N,N-chelate = e.g. 2,9-dimethyl-1,10-phenanthroline; olefin = maleic or fumaric ester) has been studied. Symmetrical cleavage of the E−E bonds affords unprecedented trigonal-bipyramidal Pt(II) complexes of the formula [Pt(ER)2(N,N-chelate)(olefin)] (2). Products of type 2, which have been characterized through 1H and 13C NMR spectroscopy, contain chalcogenide ligands in the axial positions. The reactivity of the new compounds has also been investigated. Thus, Pt−OH fragments generated by the addition of H2O2 are acetylated by acetic anhydride. Furthermore, S, Se, and Te coordinated to Pt are readily methylated by trimethyloxonium tetrafluoroborate, affording the first examples of dipositive coordinatively saturated platinum(II) cations (3). The structures of the related neutral [Pt(SMe)2(2,9-dimethyl-1,10-phenanthroline)(diphenyl fumarate)] and cationic [Pt(SMe2)2(2,9-dimethyl-1,10-phenanthroline)(diphenyl fumarate)][BF4]2 compounds have been determined by X-ray diffraction together with that of the free diphenyl fumarate ligand

Addition−Elimination Equilibria Involving 16e^- Platinum(0) and 18e^- Platinum(II) Complexes

The addition−elimination equilibrium involving a platinum(0) nucleophile [Pt(N,N‘-chelate)(olefin)] (1), an organometal electrophile RmMXn (M = Hg, Sn; X = Cl, Br, I; R = hydrocarbyl group), and the corresponding five-coordinate adduct [PtX(MRmXn-1)(N,N‘-chelate)(olefin)] (2) has been investigated. The influence on the equilibrium of the groups bonded to the electrophilic center and of the ligands bonded to platinum has been evaluated. It has been found that the adduct is stabilized by the presence of electron-donor olefins on platinum and of electron-withdrawing groups on the electrophilic metal. It has also been found that the influence of the halide moving onto platinum can be rationalized in terms of the relative softness of the two metals involved in the equilibrium. The X-ray molecular structures of [Pt(dmphen)(E-MeO2CCHCHCO2Me)] (1k, dmphen = 2,9-Me2-1,10-phenanthroline) and of the related addition product [PtCl(SnMe2Cl)(dmphen)(E-MeO2CCHCHCO2Me)] (2i) have been determined for a better understanding of the influence of steric and bonding features

Mechanism of Silver-Promoted Ligand Metathesis in Square-Planar Complexes of d⁸ Ions. Kinetics of Formation and Molecular Structures of a Trinuclear Intermediate [(Me)(N−N)Pt(μ-Cl)Ag(μ-Cl)Pt(N−N)(Me)]⁺ and Its Dinuclear Evolution Product [(Me)(N−N)Pt(μ-Cl)Pt(N−N)(Me)]⁺ (N−N = ArNC(Me)C(Me)NAr, Ar = 2,6-(<i>i</i>-Pr)₂C₆H₃)

The silver-assisted ligand methatesis reaction involving a platinum(II) complex of formula [PtClMe(N,N-chelate)] with acetonitrile has been investigated. By using a suitably hindered N,N-chelate, an otherwise hardly detectable trinuclear species has been isolated and characterized through X-ray diffractometry. The trinuclear cation consists of two nearly orthogonal [PtCl(Me)(N,N-chelate)] square-planar units entrapping an Ag+ cation through the chloride ligands that, acting as bidentate, form a linear AgCl2 unit with two nonequivalent Ag−Cl bonds. The residual acidity of the silver cation is satisfied by one secondary Ag−Pt interaction [Ag−Pt(1) = 2.82 Å] in which the platinum atom acts as a donor. Kinetic studies have demonstrated that the silver assistance operates both through a simple associative step and through a pathway in which the above trinuclear complex is an active intermediate. In a noncoordinating solvent the latter species evolves with AgCl loss and formation of a dinuclear Pt,Pt complex showing a rare single chloride bridge