Maria Elena Cucciolito

Cationic platinum(II) - or palladium(II)-carbyl complexes and unsaturated substrates: a facile way to C-C bond formation

Abstract 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.

On the stabilization of five-coordinate trigonal-bipyramidal palladium(II) species. Crystal structure of (2,9-dimethyl-1,10-phenanthroline)methylchloropalladium(II)

Abstract The role of the steric requirements of the NN′ chelate ligand in the stabilization of trigonal-bipyramidal [Pd(NN′)(olefin)RX] complexes is discussed. The crystal structure of the precursor (2,9-dimethyl-1,10,phenanthroline)methylchloropalladium(II) (1a) has been determined. The molecule adopts a significantly distorted square-planar coordination geometry in order to accomodate the crowding in the coordination plane. The most significant distortions involves the coordinated methyl group and the dimethylphenanthroline molecule, whose mean plane lies out of the coordination plane by 39.3°. There is ready CO insertion into the PdMe bond of 1a to give an acyl derivative. The formation of a five-coordinate acyl derivative by subsequent uptake of an olefin also illustrates the importance of the steric effects of NN′ ligands.

Novel chiral diimines and diamines derived from sugars in copper-catalysed asymmetric cyclopropanation

Abstract New chiral diimino and diamino ligands derived from α- d -mannose and α- d -glucose are described. The ligands are obtained by introducing the appropriate nitrogen functions at C(2) and C(3) of the sugar rings. The ability of the new chelates to promote the asymmetric copper(I)-catalysed cyclopropanation of styrene has been investigated. The nature of both the sugars and the chelates is crucial in determining the enantioselectivity of the reaction.

Preparation and catalytic properties of palladium(0) and rhodium(I) complexes containing new chiral P,N-ligands derived from carbohydrates

Abstract New chiral P,N-chelates o-Ph2PC6H4CHNR (R=carbohydrate residue) derived from d -glucose and d -mannose were described. The synthesis of palladium(0) and rhodium(I) complexes of respective formula [Pd(P,N-chelate)(fumarodinitrile)] and [Rh(1,5-cyclooctadiene)(P,N-chelate)]BF4 was performed. It was found that the ligands effectively discriminate between the enantioface of fumarodinitrile in the Pd(0) species, prompting up to 100% diastereomeric excess when R is a 2,3,4-tri-O-acetylated glucoside moiety linked to N through C6. The catalytic activity of the complexes towards allylic alkylation and olefin hydroboration was also examined.

Coordination modes of cis-P, P'-diphenyl-1,4-diphospha-cyclohexane to metal ions of Groups 9 and 10

Abstract Complexes of a tertiary diphosphine with cyclic core, cis - P , P ′-diphenyl-1,4-diphospha-cyclohexane (dpdpc), with metal ions of Groups 9 and 10 have been prepared and characterised. In neutral M(0) or M(II) (M=Pt, Pd) complexes the diphosphine acts as a bridge affording polynuclear products. Instead, in cationic mononuclear Pt(II) and Pd(II) species a clear preference for chelation of dpdpc is observed. Also the cation [Ni(dpdpc) 2 Cl] + contains the two dpdpc moieties as chelates. The molecular and crystal structure of [Ni(dpdpc) 2 Cl] 2 (NiCl 4 ) discloses a significantly small bite angle of the chelate and interaction of near phenyl rings pertaining to opposite dpdpc moieties. Coordination of dpdpc to cobalt prompts its oxidation to the corresponding P , P ′-dioxide.

Resolution of Allylic Alcohols via Copper(I) Complexes with a Chiral Diamine

Abstract By using the Corey diamine 1,2-diphenyl-N,N′-bis[(2,4,6-trimethylphenyl)methyl]-1,2-diaminoethane, Copper(I) olefin complexes are prepared. When the olefin is a racemic allylic alcohol, selective coordination of one enantiomer is observed. Cleavage with aqueous HCl or NaCN allows a two-steps resolution affording excellent enantiomeric excess.

Bi- and trinuclear cationic complexes involving bonds between mercury and five-coordinate platinum(II). Molecular structure of [{Pt(2,9-dimethyl-1,10-phenanthroline)-(Z-MeO2CCH = CHCO2Me)(H2O)}2 Hg](BF4)2

Abstract Three cationic five-coordinate platinum(II) complexes bearing alkylmercury fragments as “ligands” have been isolated. The complexes of general formula [Pt(HgR)H 2 O( dmphen )( Z -R′O 2 CCH = CHCO 2 R′] (BF 4 ) ( 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 -MeO 2 CCH = CHCO 2 Me(H 2 O)} 2 Hg](BF 4 ) 2 . The structure of this complex has been determined by X-ray analysis.

A hydrophilic chiral diamine from d-glucose in the Rh(I) catalysed asymmetric hydrogenation of acetophenone

Abstract A strategy for the synthesis of a new hydrophilic chiral diamine derived from α- d -glucose is described. The compound is obtained by introducing proper nitrogen functions at C2 and C3 positions of the sugar ring, and by deprotecting positions 4 and 6. The efficiency of the ligand in the Rh(I)-catalysed hydrogenation of acetophenone has been examined by using isopropanol and ethanol as hydrogen sources. The secondary alcohol has been obtained in ees up to 50%.

Nucleophilic Attack of Carbanions on Cationic Platinum(II) Nitrile Complexes Affording Stable η1-Imine Enol and η1-Enamine Coordinated Fragments

Cationic nitrile platinum(II) complexes of formula [PtMe(RCN)(bipy)]+ undergo nucleophilic addition of carbanions −CH(COX)(COY) (X, Y= Me, OMe), −CH(CO2Me)CN and −CH(CN)2 to afford neutral products. According to the nature of the nucleophile, the organic ligand fragment displays either an imino enol or an enamine isomeric structure. The Pt−N bond can be cleaved upon reaction with acids with formation of the corresponding β-enaminodione.

Stability and reactivity of thecis-PtIIR(alkyne) fragment(R = alkyl): an unprecedented rearrangement to form thePtII(η3-allyl) moiety

The complexes [PtR(η 2 -E-MeO 2 CCH CHCO 2 Me)(phen)] + BF 4 - (R = Me 1a or Et 1b; phen = 1,10-phenanthroline) reacted with alkynes yielding the corresponding products [PtR(η 2 -alkyne)(phen)] + BF 4 - 2. These can be isolated in the case of disubstituted electron-rich alkynes, while the electron-poor MeO 2 CCCCO 2 Me inserted into the Pt–R bond leading to the corresponding σ-vinyl derivative. Type 2 complexes containing alk-1-ynes undergo an unprecedented rearrangement to form stable [Pt(η 3 -allyl)(phen)] + BF 4 - products. Mechanistic aspects of the reaction are discussed.