The effect of the catalyst structure on the stereoselectivity of CO/vinyl arene copolymerization has been studied with the aim of developing catalytic systems able to improve the yields while maintaining the high degree of copolymer isotacticity previously obtained using achiral nitrogen ligands. Aryl alpha-diimine ligands having extended aromatic rings (Ar)(2)DABMe(2), with Ar = 1-C10H7 (e), 1-C14H9 (f), 9-C14H9 (g), have been synthesized, and alpha-diimine coordination to cationic methylpalladium complexes has been investigated in solution, by means of NMR spectroscopy, and in the solid state for [Pd(Me)(NCMe)((9-C14H9)(2)DABMe(2))][PF6] (2g). The performance of these catalysts in CO/vinyl arene copolymerization, under mild conditions, was analyzed in terms of productivity and degree of stereoregularity of the resulting polyketones. In comparison with previous results, a remarkable enhancement in the yield of isotactic copolymer was observed using the new achiral 9-anthryl alpha-diimine ligand g, confirming that the ortho disubstitution and the extended aromatic rings play key roles in obtaining good stereoselectivity and good productivity. To perform a structural analysis of the first steps of the CO/p-methylstyrene copolymerization, complex [Pd(Me)(CO)((9-C14H9)(2)DABMe(2))][BAr'(4)] (3g) was used as a starting point: NMR investigation reveals the stereoselective formation of the olefin/CO/olefin insertion product (6g), which prevalently exists in solution in only one diastereoisomeric form, thus justifying the observed high polymer isotacticity.

A series of cationic palladium complexes of general formula [Pd(Me)(MeCN)(N-N)][PF(6)] (N-N = (phen) 1 a, 4,7-dichloro-1,10-phenanthroline (4,7-Cl(2)-phen) 2 a, 4,7-diphenyl-1,10-phenanthroline (4,7-Ph(2)-phen) 3 a, 4-methyl-1,10-phenanthroline (4-Me-phen) 4 a, 4,7-dimethyl-1,10-phenanthroline (4,7-Me(2)-phen) 5 a, 5,5,6,6-tetrafluoro-5,6-dihydro-1,10-phenanthroline (F(4)-phen) 6 a, containing different substituted phenanthroline ligands, have been prepared from the corresponding neutral chloro derivatives [Pd(Me)(Cl)(N-N)], (1 b-6 b). The X-ray crystal structure of [Pd(Cl)(2)(4,7-Cl(2)-phen)] (2 b') was determined. DFT calculations show that the electron density on the metal is tuned by the substituents on the ligands. The catalytic behavior of complexes 1 a-6 a in the CO/styrene and CO/p-Me-styrene copolymerizations was studied in detail, showing that the generated catalysts are active for at least 90 h, yielding copolymers of high molecular weight. A firm correlation between the electron density on palladium on the one hand and the catalytic activity of the complexes and the molecular weight and the stereochemistry of the polyketones synthesized on the other hand has been established: the catalyst containing the F(4)-phen is thus far the most active among those tested, yielding the syndiotactic CO/styrene copolymer with a stereoregularity of 96 % (uu triad) and with an M(w) value of 1 000 000.

Palladacyclic compounds [Pd(C6H4(C6H5C=O)C=N-R)(N-N)] [X] (R = Et, Pr-i, 2,6-(Pr2C6H3)-Pr-i; N-N=bpy=2,2'-bipyridine, or 1,4-(o,o'-dialkylaryl)-1,4-diazabuta-1,3-dienes; [X](-)=[BF4](-) or [PF6](-)) were synthesized from the dimers [(Pd(C6H4(C6H5C=O)C=N-R)(mu-Cl)}2] and N-N ligands. Their interionic structure in CD2Cl2 was determined by means of F-19,H-1-HOESY experiments and compared with that in the solid state derived from X-ray single-crystal studies. [Pd(C6H4(C6H5C=O)C=N-R)(N-N)[X] complexes were found to copolymerize CO and p-methylstyrene affording syndiotactic or isotactic copolymers when bpy or 1,4-(o,o'-dimethylaryl)-1,4-diazabuta-1,3-dienes were used, respectively. The reactions with CO and p-methylstyrene of the bpy derivatives were investigated. Two intermediates derived from a single and a double insertion of CO into the Pd-C bonds were isolated and completely characterized in solution.

The catalytic activity and stereoselectivity of complexes [Pd(eta(1),eta(2)-C(8)H(12)OMe)(Ar--N==C(R')--C(R')==N--Ar)]X in the copolymerization of CO and p-methylstyrene have been correlated with their interionic structure in solution and in the solid state, as determined by (19)F,(1)H-HOESY NMR spectroscopy and X-ray diffraction studies, respectively. The highest productivity is obtained with unhindered diimine ligands bearing electron-donating substituents and with the least coordinating counterion. Copolymers with a microstructure ranging from atactic to predominantly isotactic are obtained. The degree of isotacticity increases as the steric hindrance in the apical positions and the coordinating ability of the counterion increase. The counterion is located close to the diimine in both solution and the solid state but it moves toward the palladium as the steric hindrance in the apical positions decreases. When the latter is small the counterion competes with the substrate for apical coordination, and consequently it affects the productivity. In the case of ortho-dimethyl-substituted ligands the counterion is confined in the back, above the N==C(R')--C(R')==N moiety, and does not affect the productivity. However, it contributes to increasing the stereoregularity of the copolymer by making the aryl moieties more rigid. With R'=Me and Ar=o-Me(2)C(6)H(3) an ll of 81 % and 72 % was obtained with X(-)=CF(3)SO(3) (-) or BArF(-), respectively. The isotacticity of the copolymers produced by ortho-monosubstituted catalysts depends greatly on the counterion and ranges from 30 % to 59 % with X(-)=BArF(-) and X(-)=CF(3)SO(3) (-), respectively, with Ar=o-EtC(6)H(4) and R'=Me. Based on the interionic structural results, this effect can be explained by a greater reduction of the copolymerization rate of C(s)-symmetric isomers with respect to their C(2)-symmetric counterparts.

The catalytic behavior of dicationic bis-chelated Pd-II complexes, [Pd(N-N)(2)][PF6](2), in the CO/ethylene/styrene terpolymerization reaction is studied in detail. The bidentate N-donor ligands were chosen among 2,2'-bipyridine (1), 1,10-phenanthroline (3), their symmetrically substituted derivatives 2,4, and 5, and 3 -alkyl-substituted 1,10-phenanthrolines 6-10. The effect of several parameters (like temperature, CO/ethylene pressure, styrene content, reaction time) was investigated and related to the productivity of the catalytic system, to the relative content of the two olefins in the polymeric chains, and to the molecular mass of the synthesized polyketones. The presence of 1,4-benzoquinone was necessary to reach productivities as high as 16 kg of terpolymer (TP) per gram of Pd. C-13-NMR spectroscopy was useful to characterize the distribution of the two repetitive units along the polymer chain. Terpolymers with prevailingly isolated CO/styrene units in CO/ethylene blocks as well as terpolymers with CO/styrene and CO/ethylene blocks were obtained by varying the reaction conditions. Detailed MALDI-TOF-MS analysis was performed on the CO/ethylene/styrene terpolymers for the first time, and it allowed us to characterize the end groups of the terpolymer chains. The presence of different chain end groups was found to be related to the initial amount of the two alkenes, thus suggesting that different reactions are involved in the initiation and termination steps of the terpolymerization catalytic cycle.

A series of cationic palladium complexes of general formula [Pd(CH3)(NCCH3)(N-N)][X] (N-N = phen 1, 3-sec-butyl-1,10-phenanthroline (3-sBu-phen) 2, bpy 3, (-)-(S,S)-3,3'-(1,2-dimethylethylenedioxy)-2,2'-bipyridine (bbpy) 4, (+)-(R)-3,3'-(1-methylethylenedioxy)-2,2'-bipyridine (pbpy) 5, N,N'-bis(2,6-diisopropylphenyl)-2,3-butanediimine (iso-DAB) 6; X = PF6- a, OTf (OTf = triflate) b) containing different nitrogen-donor ligands were prepared from the corresponding neutral chloro derivatives [Pd(CH3)(Cl)(N-N)] (1c-6c). They were characterized by H-1 NMR spectroscopy and elemental analysis. Single crystals suitable for X-ray determination were obtained for complexes [Pd(CH3)(NCCH3)(bbpy)][PF6] (4a), [Pd(CH3)(NCCH3)(iso-DAB)][PF6] (6a) and [Pd(Cl)(2)(bbpy)] (4c'). The latter is the result of an exchange reaction of the methyl group, present in complex 4c, with a chloride, that occurred after dissolution of 4c in CDCl3, for 1 week at 0 degrees C. The catalytic behavior of complexes 1a-5a and 1b-5b in the CO/styrene copolymerization was studied in CH2Cl2 and 2,2,2-trifluoroethanol (TFE) evidencing the positive effect of the fluorinated alcohol both in terms of productivity and molecular weight values of the polymers obtained. Influence of the nitrogen ligand, the anion and the reaction time in both solvents were investigated and is discussed in detail. Encouraging preliminary results were also obtained in the synthesis of polyethylene, in TFE, catalyzed by [Pd(CH3)(NCCH3)(iso-DAB)][PF6] (6a). (c) 2005 Elsevier B.V. All rights reserved.

Cationic Pd(II) complexes modified with achiral C(2v)-symmetric alpha-diimine ligands allow preparation of atactic or isotactic stereoblock CO/p-methylstyrene copolymers; both catalyst activity and polyketone microstructure depend on the choice of alpha-diimine substituents and counterion.

Complexes [Pd(eta(1), eta(2)-5-OMe-(CH12)-H-8)(N,O)]BF4 (N,O = 2,6-(i-Pr)(2)(C6H3)N=C(Ph)-C(Ph)=O, 1; 2,6-(i-Pr)(2)(C6H3)N=C(Me)C(Ph)=O, 2; 2-benzoylpyridine, 3) were synthesized by the reactions of [Pd(eta(1),eta(2)-5-OMe-C8H12)Cl]2 with the suitable N,O-ligand. They were tested as catalysts for olefin or alkyne polymerizations. During such reactions 1-3 quantitatively transformed into their eta(1),eta(2)-1-OMe-C8H12 isomers (1a-3a). The same isomerization occurred in methylene chloride, even in the absence of olefins or alkynes, with a much slower rate. All complexes were fully characterized in solution by multinuclear and multidimensional low temperature NMR spectroscopy. The solid state structures of complexes 1 and la were investigated by X-ray single crystal studies. F-19,H-1-HOESY NMR experiments carried out in methylene chloride-d(2) at 217 K indicated that the anion prefers to locate on the side of N,O-ligand shifted toward the O-arm in 1-1a and 2-2a while it approaches the N-arm in 3 and 3a compounds. (C) 2003 Elsevier B.V. All rights reserved.

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTMALDI−TOF Mass Spectrometry in the Study of CO/Aromatic Olefins TerpolymersBarbara Milani, Alessandro Scarel, Jérôme Durand, Giovanni Mestroni, Roberta Seraglia, Carla Carfagna, and Barbara BinottiView Author Information Dipartimento di Scienze Chimiche, Università di Trieste, Via Licio Giorgieri 1, 34127 Trieste, Italy CNR, Istituto di Scienze e Tecnologie Molecolari Sez. di Padova, Via Marzolo 1, 35020 Padova, Italy Istituto di Scienze Chimiche, Università di Urbino, P.zza Rinascimento 6, 61029 Urbino, Italy Cite this: Macromolecules 2003, 36, 17, 6295–6297Publication Date (Web):July 29, 2003Publication History Received11 June 2003Revised8 July 2003Published online29 July 2003Published inissue 1 August 2003https://pubs.acs.org/doi/10.1021/ma0347969https://doi.org/10.1021/ma0347969rapid-communicationACS PublicationsCopyright © 2003 American Chemical SocietyRequest reuse permissionsArticle Views260Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Copolymers,Hydrocarbons,Mass spectrometry,Palladium,Styrenes Get e-Alerts

Catalytic systems of the type [Pd(CH3)(NCCH3)(N-N)](+)[B{3,5-(CF3)(2)C6H3}(4)](-), where N-N = (4S,4'S)-(-)-4,4',5,5'-tetrahydro-4,4'-bis(1-methylethyl)-2,2'-bioxazole (BIOX) or N-N = (4S,4'S)-(-)-2,2'-(1-methylethyhdene)bis[4,5-dihydro-4-(phenylmethyl)oxazole]) (BISOX), afford highly isotactic CO/styrene or p-methylstyrene copolymers. The reactivity of the catalyst with the BIOX ligand toward carbon monoxide was studied and the corresponding methyl carbonyl Pd complex was isolated and identified as the real catalytic species. Starting from this compound the first steps of the copolymerization process were investigated and particular attention was paid to the stereochemistry of the intermediates. Specifically, NOE experiments carried out on the five-membered palladacycle, obtained from the first insertion of p-methylstyrene, indicated that regiochemistry is of the 2,1 type and that one diastereo-isomeric species is exclusively generated, with an R configuration of the new -CHAr-stereogenic center. Moreover, the investigation of the intermediate resulting after the second sequence of p-methylstyrene and CO insertion showed the presence of only one diastereoisomer. This evidence indicates that the stereocontrol of the isospecific catalyst is already very efficient at the first stages of copolymerization.

Two series of cationic palladium(II) complexes, [Pd(phen)(L)2][PF6]2 (L=pyridine (1a), 2-picoline (2-pic) (1b), 3-picoline (3-pic) (1c), 4-picoline (4-pic) (1d)) and [Pd(CH3)(L)(phen)][OTf] (L=2-pic (2b), 3-pic (2c) and 4-pic (2d)), with mono and bidentate nitrogen-donor ligands bound to the same metal center have been synthesized and characterized. For the dicationic derivatives the study of the chemical behavior in solution evidences the presence of restricted rotations around the PdN bond of the monodentate ligand, generating syn and anti isomers. Depending on the nature of L the rate of this dynamic process is different on the NMR time scale. On the other hand, only the syn isomer was found by the X-ray analysis in solid state of one of these complexes. The dicationic complexes have been tested as precatalysts in the CO/styrene copolymerization, in comparison with [Pd(phen)2][PF6]2. The main difference between the two kinds of precatalysts is related to the stability of the corresponding active species, being lower for the complexes [Pd(phen)(L)2][PF6]2 than for the bischelated derivative. The insertion reaction of carbon monoxide in the Pdmethyl bond was studied on the monocationic complexes, [Pd(CH3)(L)(phen)][OTf]. In all cases the corresponding Pdacyl species [Pd(COCH3)(L)(phen)][OTf] was formed with no dissociation of the monodentate L ligand. No effect of the nature of L on the rate of the insertion reaction was evidenced.

The reaction of [Pd(η 1 ,η 2 -C 8 H 12 OMe)Cl] 2 with α-iminoketone ligands affords cationic η 1 ,η 2 -5-methoxycyclooctenyl Pd(II) complexes, the intramolecular and interionic structures of which were investigated in both solution and solid state; such complexes undergo unprecedented isomerisation to η 1 ,η 2 -1-methoxycyclooctenyl complexes assisted by weak nucleophiles such as olefins or alkynes.

Complexes [M(eta(1),eta(2)-C8H12OMe)(pz(2)-YH2)]((+)) (M = Pd, Y = C, 1; M = Pt, Y = C, 2; M = Pt, Y = B, 3) and [M(eta(1),eta(2)-C8H12OMe)(pz(3)-YH)]((+)) (M = Pd, Y = C, 4; M = Pd, Y = B, 5; M = Pt, Y = C, 6; M = Pt, Y = B, 7) were synthesized by the reaction of the dimers [M(eta(1),eta(2)-C8H12OMe)Cl](2) with the poly(pyrazol-1-yl)borate and -methane ligands. Complexes 1-7 were characterized in solution by multinuclear and multidimensional low-temperature NMR spectroscopy. The solid-state structures of olefinic five-coordinate Pd complexes 4 and 5 were investigated by X-ray single-crystal studies. The relative cation-anion position (interionic structure) was investigated in solution, for all cationic complexes at room and low temperature by (IF)-I-19, H-1-HOESY NMR spectroscopy, and in the solid state for 4. A remarkable specifity of the interionic contacts is observed in solution: the counterion is placed close to the peripheral protons of the pyrazolyl ligands probably due to the partial protection of the apical positions introduced by the nonplanar ligands and the delocalization of the positive charge on the pyrazolyl rings. In the case of complex 4 there is an excellent agreement between the solid state and solution results: the anion selectively interacts with the CH and five protons of the pz(3)-CH ligand via an assembly of hydrogen bonds.

Complexes [M(η1,η2-C8H12OMe)((2,6-(R)2C6H3)NC(R′)C(R′)N((2,6-(R)2C6H3))]PF6 (where M=Pd, R=H and R′2=Me2 (1), M=Pd, R=Me and R′2=Me2 (2), M=Pd, R=Et and R′2=Me2 (3), M=Pd, R=iPr and R′2=Me2 (4), M=Pd, R=iPr and R′2=An (5), M=Pt, R=iPr and R′2=An (6)) were synthesized by the reaction of [M(η1,η2-C8H12OMe)Cl]2 with the appropriate α-diimine ligand in the presence of NH4PF6. Their ion pair structure in solution was investigated by detecting dipolar interactions between protons belonging to the cation and fluorine nuclei of the anion (interionic contacts) in the 19F, 1H-HOESY NMR spectra. In complexes 1–4, the anion in solution is located close to the peripheral protons of the α-diimine ligand and it interacts with the R′ protons and with the R protons that point toward the R′ groups. The steric protection of apical position exerted by the R substituents is clearly illustrated by the absence of interionic contacts between any protons of the cycloctenylmethoxy-moiety and the anion for R≥Me in 1–4. In complexes 5 and 6 the interactions between the anion and the peripheral N,N protons also predominate but other anion–cation orientations are significantly present and, consequently, the interionic structure is less specific.

NOE and PGSE NMR experiments provide crucial information for the structural characterization of non-covalent intimate adducts in solution. The possible presence and the favorite relative orientation of the interacting units can be deduced from NOE results, while the size of the non-covalent adducts can be estimated through PGSE measurements. The complementarity of the two methodologies has been successfully used to investigate transition metal complex ion pairs and, to a lesser extent, intermolecular adducts. The main results concerning the solution structures of non-covalent inorganic adducts are reported and compared with those in the solid state and those from theoretical calculations.