Chiral Recognition in Silver(I) Olefin Complexes with Chiral Diamines. Resolution of Racemic Alkenes and NMR Discrimination of Enantiomers

The fragment [(chiral diamine)Ag]+ is a very useful reagent, both for the resolution of racemic alkenes and for the 1H or 13C NMR determination of the enantiomeric abundances of chiral olefinic compounds

Coordination of Olefins and N-Donor Ligands at the Fragment [2,6-Bis((diphenylphosphino)methyl)pyridine]- palladium(II). Synthesis, Structure, and Amination of the New Dicationic Complexes [Pd(PNP)(CH₂CHR)](BF₄)₂ (R = H, Ph)

Dicationic complexes of palladium(II) containing the tridentate ligand 2,6-bis((diphenylphosphino)methyl)pyridine (PNP) of the general formula [Pd(PNP)L](BF4)2 (L = MeCN, pyridine, C2H4, CH2CHPh) have been prepared from Pd(PNP)Cl2 by addition of 2 equiv of AgBF4 in the presence of an excess of the respective ligand L in CH2Cl2. The corresponding amine complex (L = NHMe2) was obtained by substitution of the acetonitrile from [Pd(PNP)(MeCN)](BF4)2 by NHMe2 at 0 °C. The complexes were characterized by 1H, 13C, and 31P NMR spectroscopy, and the molecular structure of the styrene complex was determined by X-ray diffraction analysis. The spectral and structural parameters of the complexes are discussed in comparison to those of the recently prepared Rh(I) analogues. Nucleophilic attack of secondary amines on the coordinated olefins gave the corresponding β-aminoethyl complexes from which, upon reductive degradation, the respective ethylamines were obtained, showing selective anti-Markovnikov addition in the case of the styrene complex

The First Class of Square-Planar Platinum(II) Complexes Containing Electron-Poor Alkenes. Rare Insertion of an Alkene into a Pt−Alkyl Bond^†

The first class of square-planar Pt(II) complexes bearing electron-poor alkenes, i.e., [PtMe(N,N-chelate)(η2-CH2CHCOR)]BF4 (R = H, NMe2, Me, OMe), is described. By using N,N ligands with suitable steric properties, it was possible to inhibit olefin dynamic processes in solution, thus allowing a thorough characterization of the complexes. Insertion of methyl acrylate into the Pt−Me bond provides a rare example of migratory insertion of an alkene into a Pt−alkyl bond

Coordination of Alkenes at a Highly Electrophilic Site. New Dicationic Platinum(II) Complexes: Synthesis, Structure, and Reactions with Nucleophiles^§

Dicationic platinum(II) alkene complexes [Pt(PNP)(alkene)](BF4)2 (alkene = ethylene, propene, 1-butene, Z- and E-2-butene, styrene, norbornene; PNP = 2,6-bis(diphenylphosphinomethyl)pyridine) have been prepared and characterized by 1H and 13C NMR spectroscopy, and the molecular structure of the ethylene complex has been determined by X-ray diffraction analysis. Nucleophilic attack at the coordinated double bond takes place more readily than for known neutral and monocationic species, and a variety of protic nucleophiles NuH (MeOH, H2O, aromatic amines) give the corresponding β-functionalized σ-alkyl complexes [Pt(PNP)(CHRCHR‘Nu)]BF4 also in the absence of auxiliary bases. In the case of the styrene derivatives an unusual decomposition pathway gives the stable alkenyl complex [Pt(PNP)(CHCHPh)]BF4. A competitive equilibrium process between substitution and addition was revealed by reacting ethylene with the isolated aniline complex [Pt(PNP)(PhNH2)](BF4)2. The nucleophilic addition product was found to be thermodynamically favored over the substitution product more than in the case of the analogous palladium complexes

Catalytic Hydroarylation of Olefins Promoted by Dicationic Platinum(II) and Palladium(II) Complexes. The Interplay of C−C Bond Formation and M−C Bond Cleavage

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

Coordination of Alkenes at a Highly Electrophilic Site. New Dicationic Platinum(II) Complexes: Synthesis, Structure, and Reactions with Nucleophiles^§

Dicationic platinum(II) alkene complexes [Pt(PNP)(alkene)](BF4)2 (alkene = ethylene, propene, 1-butene, Z- and E-2-butene, styrene, norbornene; PNP = 2,6-bis(diphenylphosphinomethyl)pyridine) have been prepared and characterized by 1H and 13C NMR spectroscopy, and the molecular structure of the ethylene complex has been determined by X-ray diffraction analysis. Nucleophilic attack at the coordinated double bond takes place more readily than for known neutral and monocationic species, and a variety of protic nucleophiles NuH (MeOH, H2O, aromatic amines) give the corresponding β-functionalized σ-alkyl complexes [Pt(PNP)(CHRCHR‘Nu)]BF4 also in the absence of auxiliary bases. In the case of the styrene derivatives an unusual decomposition pathway gives the stable alkenyl complex [Pt(PNP)(CHCHPh)]BF4. A competitive equilibrium process between substitution and addition was revealed by reacting ethylene with the isolated aniline complex [Pt(PNP)(PhNH2)](BF4)2. The nucleophilic addition product was found to be thermodynamically favored over the substitution product more than in the case of the analogous palladium complexes

Chiral Diamine−Silver(I)−Alkene Complexes: A Quantum Chemical and NMR Study

The ability of chiral diamine silver complexes to bind chiral and prochiral alkenes has been analyzed in detail. The stereoselectivity in binding of alkenes to a chiral ethanediamine silver complex has been investigated by NMR. The low-energy conformations of several small model complexes have been explored by DFT methods. By successive substitution of the computational model complexes, it has been possible to elucidate the role of each amine substituent in achieving successful discrimination of alkenes. The conformational space has been fully explored using small model systems, allowing an unbiased calculation of stereoselectivities that match well the experimental results. For a chiral allylic alcohol substrate, the correct stereoselectivity was obtained only when the structures were optimized with a continuum representation of the solvent. The discrepancy between gas phase and solution data is found to result from a competition between internal stabilization and solvation of the OH group of the substrate

Molybdenum-Catalyzed Allylic Substitution. Influence of 1,10-Phenanthroline Ligands on Reactivity and Selectivity

Some new allylmolybdenum complexes containing 1,10-phenanthroline or 2,9-dimethyl-1,10-phenanthroline as ligand have been synthesized and shown to have different geometries by NMR and X-ray diffraction analysis. The geometries of the complexes were elucidated by NMR techniques and confirmed by X-ray diffraction analysis. The catalytic activity and the influence on regio- and stereocontrol in the alkylation of allylic acetates have been investigated. The 2,9-dimethyl-1,10-phenanthroline complex was found to be a very efficient catalyst for selective conversion of (Z)-allyl acetates into (Z)-products

Chiral Diamine−Silver(I)−Alkene Complexes: A Quantum Chemical and NMR Study

The ability of chiral diamine silver complexes to bind chiral and prochiral alkenes has been analyzed in detail. The stereoselectivity in binding of alkenes to a chiral ethanediamine silver complex has been investigated by NMR. The low-energy conformations of several small model complexes have been explored by DFT methods. By successive substitution of the computational model complexes, it has been possible to elucidate the role of each amine substituent in achieving successful discrimination of alkenes. The conformational space has been fully explored using small model systems, allowing an unbiased calculation of stereoselectivities that match well the experimental results. For a chiral allylic alcohol substrate, the correct stereoselectivity was obtained only when the structures were optimized with a continuum representation of the solvent. The discrepancy between gas phase and solution data is found to result from a competition between internal stabilization and solvation of the OH group of the substrate

Chiral Diamine−Silver(I)−Alkene Complexes: A Quantum Chemical and NMR Study

The ability of chiral diamine silver complexes to bind chiral and prochiral alkenes has been analyzed in detail. The stereoselectivity in binding of alkenes to a chiral ethanediamine silver complex has been investigated by NMR. The low-energy conformations of several small model complexes have been explored by DFT methods. By successive substitution of the computational model complexes, it has been possible to elucidate the role of each amine substituent in achieving successful discrimination of alkenes. The conformational space has been fully explored using small model systems, allowing an unbiased calculation of stereoselectivities that match well the experimental results. For a chiral allylic alcohol substrate, the correct stereoselectivity was obtained only when the structures were optimized with a continuum representation of the solvent. The discrepancy between gas phase and solution data is found to result from a competition between internal stabilization and solvation of the OH group of the substrate