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Four iminopyridines (N-N') differing in the nature of the substituents on the iminic carbon and on the ortho positions of the aryl ring (H or CH3) on the iminic nitrogen were used for the synthesis of neutral and monocationic palladium(ii) complexes of general formulae [Pd(CH3)Cl(N-N')] and [Pd(CH3)(NCCH3)(N-N')][PF6]. The detailed NMR characterization in solution highlighted that: (i) for both series of complexes, the Pd-CH3 signal is progressively shifted to a lower frequency on increasing the number of methyl groups on the ligand skeleton; (ii) for the neutral derivatives, the chemical shift of the (15)N NMR signals, determined through {(1)H,(15)N}-HMBC spectra, is significantly affected by the coordination to palladium; (iii) the coordination induced shift (CIS) of the nitrogen atom trans to the CH3 ligand is smaller than the other. The structure in the solid state for the neutral derivatives with all the four ligands was solved, pointing out that: (iv) the Pd-C bond distance increases with the basicity of the nitrogen-donor ligand; (v) the Pd-N bond distance correlates well with the CIS value. The combining of the solution and solid state structural features allows stating that: (vi) the Pd-CH3 singlet is a good probe for the electron donor capability of the ligand; (vii) the CIS value might be used as a probe for the strength of the Pd-N bond. All monocationic complexes generated active catalysts for the CO/vinyl arene copolymerization, leading to prevailingly syndiotactic polyketones. The catalyst performances, both in terms of catalyst productivity and polymer molecular weight, correlate well with the precatalyst structural features.

Both symmetric and non symmetric bis(aryl)acenaphthenequinonediimine ligands, featured by substituents in meta-positions of the aryl rings, have been applied for the first time as ancillary ligands for the palladium catalyzed CO/vinyl arene copolymerization. The nature and the number of substituents affect both the productivity and the molecular weight of the synthesized copolymers. Palladium complexes containing the nonsymmetric ligands are the most efficient catalysts reported so far for the synthesis of atactic polyketones.

CHIM03 Abstract: The coordination chemistry of the chiral bioxazoline ligand (4S,4'S)-2,2'-bis(4-isopropyl-4,5-dihydrooxazole) to Pd-II provides evidence that the ligand bonding can occur either through chelation of one Pd-II ion leading to a mononuclear species with the expected cis geometry, or by double bridging of two Pd-II ions giving a dinuclear complex with trans geometry. The species in solution are identified by H-1 NMR spectroscopy Both the mononuclear and the dinuclear complexes promote the CO/styrene copolymerization, yielding the corresponding polyketone with a fully or a predominantly isotactic microstructure, depending on the reaction medium. The nature of the anion present in the palladium precatalysts affects the polyketone stereochemistry. MALDI-TOF analysis of the copolymers synthesized reveals the presence of p-hydroxyphenolic end-groups, thus confirming and explaining the role of 1,4-hydroquinone as a molecular weight regulator.

The abundant and inexpensive carbon monoxide (CO) is widely exploited as a C1 source for the synthesis of both fine and bulk chemicals. In this context, photochemical carbonylation reactions have emerged as a powerful tool for the sustainable synthesis of carbonyl-containing compounds (esters, amides, ketones, etc.). This review aims at giving a general overview on visible light-promoted carbonylation reactions in the presence of metal (Palladium, Iridium, Cobalt, Ruthenium, Copper) and organocatalysts as well, highlighting the main features of the presented protocols and providing useful insights on the reaction mechanisms.

The first example of the bis-alkoxycarbonylation of acrylic esters and acrylic amides, leading to differently substituted 1,1,2-ethanetricarboxylate compounds and 2-carbamoylsuccinates respectively, is reported. The catalyst is formed in situ by mixing Pd(TFA)2 (TFA=trifluoroacetate) and the ligand bis(2,6-dimethylphenyl)butane-2,3-diimine. The reaction, that proceeds using p-benzoquinone as oxidant and p-toluenesulfonic acid as additive, has been applied to variously substituted electron-poor alkenes, employing different alcohols as nucleophiles, under very mild reaction conditions (4 bar of carbon monoxide at 20 °C). Remarkably, this catalytic system is able to promote the carbonylation of both the β- and the generally unreactive α-positions of acrylic esters and amides, allowing the formation of bis-alkoxycarbonylated products in good to excellent yields (up to 98%). The trend of reactivity, observed with the different electron-deficient olefins, has been rationalized on the basis of the proposed catalytic cycle and DFT calculations. (Figure presented.).

A catalytic carbonylative double cyclization method for the synthesis of furo[3,4-b]benzofuran-1(3H)-ones is reported. It is based on the reaction between readily available 2-(3-hydroxy-1-yn-1-yl)phenols, CO, and oxygen carried out in the presence of catalytic amounts of PdI2 (1 mol %) in conjunction with KI (20 mol %) and 2 equiv of diisopropylethylamine at 80 degrees C for 24 h under 30 atm of a 1:4 mixture of CO-air. Interestingly, the process was not selective when carried out in classical organic non-nucleophilic solvents (such as MeCN or DME), leading to a mixture of the benzofurofuranone derivative and the benzofuran ensuing from simple cycloisomerization, whereas it turned out chemoselective toward the formation of the double cyclization compound in BmimBF(4) as the reaction medium. Moreover, the ionic liquid solvent containing the catalyst could be easily recycled several times without appreciable loss of activity.

The straightforward in situ synthesized bis(2,6-diisopropyl)acenaphthenequinonediimine palladium triflate catalyst was generally employed for both the mono-alkoxycarbonylation of terminal alkynes, and the bis-alkoxycarbonylation of 1,2-disubstituted alkynes by using mild reaction conditions [carbon monoxide pressure (PCO)=4 bar, temperature=20 °C]. Utilizing low catalyst loading (down to 0.5 mol%), a variety of propiolic esters were synthesized with good to excellent isolated yields. Most importantly the system was very efficient not only with methanol but also with a range of different alcohols, starting from the less hindered benzyl alcohol to the most hindered ones, such as isopropyl alcohol and tert-butyl alcohol. In addition, aromatic and aliphatic 1,2-disubstituted alkynes were converted into maleic acid derivatives, together with an acid-catalyzed isomerization reaction, showing modest to good selectivity and excellent combined yields. In particular 3-hexyne showed a satisfactory degree of selectivity for the maleic diesters of methanol and benzyl alcohol, obtaining the corresponding products with good isolated yields.

Two pairs of enantiomerically pure chiral bidentate nitrogen-donor ligands (N*-N) featuring one sp(3) and one sp(2) nitrogen atom have been applied to the CO/vinyl arene copolymerization reaction catalyzed by the corresponding monocationic palladium(11) complexes [Pd(CH3)(CH3CN)-(N*-N)][PF6]. The ligand frame containing the sp(2) nitrogen atom is a 2-pyridinyl or an 8-quinolinyl building block, while the chiral framework of the ligand derives from (S)-(+)-2.2'-(2-azapropane-1,3-diyl)-1,1'-binaphthalene or from trans-2.5-dimethylpyrrolidinyl. Ligands with the binaphthyl moiety generate catalysts showing a moderate activity, while ligands having the pyrrolidinyl fragment results in very low activity species. The stereochemistry of the synthesized polyketones depends of the sp(2) nitrogen-containing fragment: ligands with the 2-pyridinyl group lead to atactic copolymers, whereas those with the quinolinyl moiety give an isotactic polyketone. The effect of the nature of the quinone, added to the reaction mixture as oxidant, has been investigated MALDI-TOF analysis reveals the formation of several polymeric chains, differing in the presence of various end-groups.

Insertion of 1,2-disubstituted alkynes into (Pd(CH3)(CO)(BIOX)) + (B{3,5-(CF3)2C6H3}4) � (1), where BIOX = (4S,4'S)-(� )-4,4',5,5'-tetrahy- dro-4,4'-bis(1-methylethyl)-2,2'-biox- azole, leads to the formation of five- membered palladacycles, which, by re- action with carbon monoxide, produce a mixture of two diastereomeric forms of a palladium complex containing an h 3 -allylic g-lactone ligand. On leaving the mixture in solution, one isomer was converted into the other, reaching a di- astereomeric excess of up to 94 %. The steric and electronic factors responsible for the epimerization process were in- vestigated by theoretical methods. Cleavage of the h 3 -allylpalladium bond by nucleophiles allowed highly substituted chiral butenolides to be synthesized in good enantiomeric excess.

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 = PF 6 - 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 1H 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 °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).

A polyether, moisture curable, polyurethane resin was used as an adhesive on plastic and aluminium substrates, in order to investigate the influence of the surface properties on adhesion. The curing kinetics of the adhesive, in controlled temperature and humidity conditions, was evaluated and an elastomeric product was obtained after curing. The surface properties of the cured resin and of the different substrates (PPO/PA6 blend, polypropylene and aluminium) were evaluated and compared by using a contact angle technique. Adhesion measurements were performed using single-lap joints; the strength values obtained were correlated to the structure of the adhesive and to the surface treatments performed on the substrates.

The coordination chemistry of a series of 3-alkyl-substituted-1,10-phenanthrolines (3-R-phen) to palladium as well as the catalytic behavior of the corresponding bischelated derivatives, [Pd(3-R-phen)2][PF6]2, in the CO/vinyl arenes copolymerization reaction has been investigated in detail. The alkyl substituents differ in length and steric hindrance. The crystal structure characterization reveals that the two molecules of 3-R-phen are bound to palladium in a syn arrangement with the alkyl groups on the same side of the square planar geometry. In solution a dynamic process involving the equilibrium between syn and anti isomers is evidenced by NMR spectroscopic analysis. This is in agreement with the results of DFT calculations, which indicate similar stabilities for the two isomers. The severe distortions from the ideal square planar coordination geometry observed in the solid state are rationalized, through the DFT analysis, in terms of the HOMO orbitals responsible for the Pd−N bonds. The [Pd(3-R-phen)2][PF6]2 complexes efficiently promote the CO/styrene and CO/p-Me-styrene copolymerizations to the corresponding syndiotactic polyketones. Yields and molecular weights show an increasing trend on increasing the steric demand of the R substituent, and the values recorded are the best ones ever reported for copolymerization reactions of this kind in the absence of the oxidant. From the TON numbers this result seems related to an increase of the olefin insertion rate, which proceeds faster when 3-R-phen are used as ligands. A change of the physical nature of the active species, from homogeneous to heterogeneous, occurs during the polymerization process, and the time at which this variation takes place depends on the nature of the olefin. The positive effect of the alkyl substitution is less evident in the CO/ethylene copolymerization.

New atropisomeric bidentate bipyridine-based ligands (3,3’-(ethylenedioxy)-2,2’-bipyridine 3;3,3’-(propylenedioxy)-2,2’-bipyridine 4; 3,3’-(butylenedioxy)-2,2’-bipyridine 5) containing a bridge between the 3,3’ positions of the aromatic rings have been prepared. Together with the previously reported analogous ligands ((R)-3,3’-(1-methylethylenedioxy)-2,2’-bipyridine) 1 and ((S,S)-3,3’-(1,2-dimethylethylenedioxy)-2,2’-bipyridine) 2, they were used to synthesize the corresponding bis-chelated dicationic complexes [Pd(N–N)2][PF6] 2. Crystal structures and comparison of the data obtained by X-ray analysis on four of these complexes is reported. These palladium compounds were used as precatalysts in the CO/styrene and CO/4-Me-styrene copolymerization reactions, where they showed that small variations in the ligand backbone remarkably affects the productivity of the catalytic system.

The catalytic activity and ste- reoselectivity of complexes (Pd(h 1 ,h 2 - C8H12OMe)AN=C(R')� C(R')=N� Ar))X in the copolymerization of CO and p-methylstyrene have been corre- lated with their interionic structure in solution and in the solid state, as deter- mined by 19 F, 1 H-HOESY NMR spec- troscopy and X-ray diffraction studies, respectively. The highest productivity is obtained with unhindered diimine li- gands bearing electron-donating sub- stituents and with the least coordinat- ing counterion. Copolymers with a mi- crostructure ranging from atactic to predominantly isotactic are obtained. The degree of isotacticity increases as the steric hindrance in the apical posi- tions and the coordinating ability of the counterion increase. The counter- ion 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 conse- quently 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 produc- tivity. However, it contributes to in- creasing the stereoregularity of the co- polymer by making the aryl moieties more rigid. With R' = Me and Ar = o- Me2C6H3 an ll of 81 % and 72 % was obtained with X � = CF3SO3 � or BArF � , respectively. The isotacticity of the co- polymers produced by ortho-monosub- stituted catalysts depends greatly on the counterion and ranges from 30 % to 59 % with X � = BArFand X � = CF3SO3 � , respectively, with Ar = o- EtC6H4 and R' = Me. Based on the in- terionic structural results, this effect can be explained by a greater reduction of the copolymerization rate of Cs-sym- metric isomers with respect to their C2- symmetric counterparts.

The migratory insertions of cis or trans olefins CH(X)=CH(Me) (X=Ph, Br, or Et) into the metal–acyl bond of the complex [Pd(Me)(CO)( iPr2dab)] + [B{3,5-(CF3)2C6H3}4]- (1) ( iPr2dab=1,4-diisopropyl-1,4-diazabuta-1,3-diene=N,N’-(ethane-1,2-diylidene)bis[1-methylethanamine]) are described (Scheme1). The resulting five-membered palladacycles were characterized by NMR spectroscopy and X-ray analysis. Experimental data reveal some important aspects concerning the regio- and stereochemistry of the insertion process. In particular, the presence of a Ph or Br substituent at the alkene leads to the formationof highly regiospecific products. Moreover, in all cases, the geometry of the substituents in the formed palladacycle was the same as in the starting olefin, as a consequence of a cisaddition of the Pd–acyl fragment to the C=C bond. Reaction with CO and MeOH of the five-membered complex derived from trans b-methylstyrene (=[(1E)-prop-1-enyl]benzene) insertion, yielded the 2,3-substitutedg-keto ester 9 with an (2RS,3SR)-configuration (Scheme 3)

The catalytic behavior of dicationic bis-chelated PdII 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. 13C-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.

The bis (homoleptic) palladium (II) complexes of the extended aromatic ligands eilatin ([Pd(eil) 2][BF4] 2) and dipyridophenazine ([Pd (dppz) 2][BF4] 2,[Pd (dppz) 2][PF6] 2) were synthesized and employed in the copolymerization of carbon monoxide and styrene, their activity found to exceed that of the parent complex [Pd (phen) 2][BF4] 2.

Palladium−azabis(oxazoline) complexes proved to be highly selective and efficient in the asymmetric copolymerization of styrene and CO at ambient pressure.

Two series of cationic palladium(II) complexes, [Pd(phen)(L) 2 ][PF 6 ] 2 (L=pyridine ( 1a ), 2-picoline (2-pic) ( 1b ), 3-picoline (3-pic) ( 1c ), 4-picoline (4-pic) ( 1d )) and [Pd(CH 3 )(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 ][PF 6 ] 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 ][PF 6 ] 2 than for the bischelated derivative. The insertion reaction of carbon monoxide in the Pdmethyl bond was studied on the monocationic complexes, [Pd(CH 3 )(L)(phen)][OTf]. In all cases the corresponding Pdacyl species [Pd(COCH 3 )(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.

Complexes [Pd(η1,η2-C8H12OMe)bipy]+X- (2a−f) (where X = BPh4- (a), CF3SO3- (b), BF4- (c), PF6- (d), SbF6- (e), and B(3,5-(CF3)2C6H3)4- (f); bipy = 2,2‘-bipyridine; C8H12OMe = cyclooctenylmethoxy group) were synthesized by the reaction of the dimer [Pd(η1,η2-C8H12OMe)Cl]2 (1) with the bipy ligand in methanol containing Y+X- salts. They were characterized in solution by multinuclear and multidimensional NMR spectroscopy. The solid-state structure of complex 2d was obtained by X-ray single-crystal investigation. The catalytic activity of complexes 2 toward CO/styrene copolymerization in methylene chloride was tested and related to the type of counterion. The order of the catalytic activity of complexes 2a−f is the following: BPh4- ≪ CF3SO3- < BF4- < PF6- < SbF6- < B(3,5-(CF3)2C6H3)4-. If the copolymerization reactions are carried out in the presence of an excess of the bipy ligand, the anion effect is less important and the order is the following: BPh4- ≪ CF3SO3- < BF4- ≈ B(3,5-(CF3)2C6H3)4- ≈ PF6- ≈ SbF6-...