Barbara Milani

Synthesis and characterization of new halogen-tetramethylene sulfoxide-ruthenium(II) and ruthenium(III) complexes; crystal structure of cis-dichlorotetrakis(tetramethylene sulfoxide)ruthenium(II) and hydrogen trans-bis(tetramethylene sulfoxide)tetrachlororuthenate(III)

In this paper we report the synthesis and characterization of the following ruthenium(II) and ruthenium(III) complexes with tetramethylene sulfoxide (TMSO): cis-RuCl2(TMSO)4 (1), trans- RuCl2(TMSO)4 (2), the corresponding dibromo derivatives cis- and trans-RuBr2(TMSO)4 (3 and 4, respectively), (TMSO)H[trans-Ru(TMSO)2Cl4] (5) and mer-RuCl3(TMSO)3 (6). Most of the reported complexes are described here for the first time, together with a new, easy synthetic path for the previously known complexes 1 and 3. The chemical behavior of 1 and 2 in solution of aprotic, non- coordinating solvents is described. Among the Ru(II) derivatives, the cis isomers are thermodynamically more stable and a photochemically driven cis to trans isomerization reaction is observed in tetramethylene sulfoxide solution. We also report the crystal structures of cis-RuCl2(TMSO)4 (1) and (TMSO)H[trans- Ru(TMSO)2Cl4] (5), as determined by three dimensional X-ray analyses. Crystal data: 1, a=9.104(2), b=11.317(2), c=21.867(6) A, β=90.62(2)°, monoclinic, space group P21/c, Z=4; 5, a=14.642(4), b=14.999(4), c=9.667(4) A, β=103.57(1)°, monoclinic, space group P1/c, Z=4. Least-squares refinement based on 3813 (1) and 4706 (5) reflections converged to R=0.032 and 0.033 for 1 and 5, respectively. In 1, all the TMSO ligands are S-bonded to Ru, with average RuS bond distances of 2.355(6) (trans to S) and 2.273(1) (trans to Cl) A. The TMSO ligands in 5 are both S-bonded to Ru (av. 2.33(1) A). The protonated TMSO molecule is hydrogen bonded to one of the two crystallographically independent anions.

New atropisomeric bidentate nitrogen-donor compounds as potential stereocontrollers in mild CO–styrene copolymerisation catalysed by palladium(II) salts

Two new atropisomeric bidentate nitrogen-donor chelating ligands, namely (–)-(S,S)-3,3′-(1,2-dimethylethylenedioxy)-2,2′-bipyridine L1 and (+)-(R)-3,3′-(1-methylethylenedioxy)-2,2′-bipyridine L2, have been synthesised and characterised. The crystal structure of L2 confirmed its atropisomeric nature, the dihedral angle between the planes containing the pyridine rings being 50.1(1)°. The interaction of the new compounds, with palladium(II) salts led to the corresponding monochelated palladium complexes, [PdL1(O2CCF3)2]1 and [PdL2(O2CCF3)2]2, the crystal structures of which have been determined. Both complexes crystallised with two independent molecules in the unit cell. In the two molecules of 1 the ligand L1 is in the same conformation; while for 2 the two independent molecules correspond to two different atropisomers. The co-ordination geometry around palladium is square planar in all the molecules. In the two independent molecules of 1 and 2 the dihedral angle between the pyridine rings is considerably smaller than that observed in free L2. The complexes are very active catalyst precursors in CO–styrene copolymerisation under mild reaction conditions (PCO= 1 atm, 30 °C). The inhibiting role of carbon monoxide is evidenced. A low asymmetric induction was observed together with short isotactic sequences in the copolymer chain.

Palladium‐Catalyzed Ethylene/Methyl Acrylate Cooligomerization: Effect of a New Nonsymmetric α‐Diimine

A new nonsymmetric bis(aryl‐imino)acenaphthene (Ar‐BIAN) ligand, featured by a subtle steric and electronic unbalance of the N‐donor atoms, is reported. With the new ligand and the corresponding symmetrically substituted derivatives, both neutral and monocationic PdCH3 compounds have been synthesized and characterized. The series of the monocationic complexes [Pd(CH3)(L)(Ar‐BIAN)][PF6] (L=CH3CN, dmso) has been extended to dimethyl sulfoxide derivatives. The monocationic complexes are tested as precatalysts for the ethylene/methyl acrylate cooligomerization under mild reaction conditions of temperature and ethylene pressure. The catalytic product is a mixture of ethylene/acrylate cooligomers and higher alkenes. The catalysts containing the new nonsymmetric ligand are found to be more productive than those with the symmetric Ar‐BIANs. The Pd–dmso catalysts are more productive and show a longer lifetime than their Pd–NCCH3 counterparts.

Pd(II) Complexes with Bidentate Nitrogen-Donor Chelating Ligands: Very Versatile and Active Catalyst Precursors for the CO/Olefin Co- and Terpolymerization Reactions

Abstract The perfect alternating CO/olefin copolymers constitute an important class of new materials. Their synthesis requires a catalyst; in general, the applied catalytic systems are formed by a palladium(II) salt, modified by diphosphine or dinitrogen chelating ligands, in the presence of a BrOnsted acid as cocatalyst and, frequently, an oxidant such as 1,4-benzoquinone. Alcoholic medium is generally preferred. This overview will report on the main catalytic systems based on bidentate nitrogen-donor chelating ligands; particular attention will be dedicated to the CO/styrene copolymerization. A detailed analysis of several parameters influencing the yield and the quality of CO/styrene polyketone will be presented, together with the discussion of the control of the stereochemistry of the insertion of styrene in the growing chain.

Catalyst activity or stability: the dilemma in Pd-catalyzed polyketone synthesis

A series of Pd-complexes containing nonsymmetrical bis(aryl-imino)acenaphthene (Ar-BIAN) ligands, characterized by substituents on the meta positions of the aryl rings, have been synthesized, characterized and applied in CO/vinyl arene copolymerization reactions. Crystal structures of two neutral Pd-complexes have been solved allowing comparison of the bonding properties of the ligand. Kinetic and mechanistic investigations on these complexes have been performed. The kinetic investigations indicate that in general ligands with electron-withdrawing substituents give more active, but less stable, catalytic systems, although steric effects also play a role. The good performance observed with nonsymmetrical ligands is at least in part due to a compromise between catalyst activity and lifetime, leading to a higher overall productivity with respect to catalysts based on their symmetrical counterparts. Additionally, careful analysis of the reaction profiles provided information on the catalyst deactivation pathway. The latter begins with the reduction of a Pd(II) Ar-BIAN complex to the corresponding Pd(0) species, a reaction that can be reverted by the action of benzoquinone. Then the ligand is lost, a process that appears to be facilitated by the contemporary coordination of an olefin or a CO molecule. The so formed Pd(0) complex immediately reacts with another molecule of the initial Pd(II) complex to give a Pd(I) dimeric species that irreversibly evolves to metallic palladium. Mechanistic investigations performed on the complex with a nonsymmetrical Ar-BIAN probe evidence that the detected intermediates are characterized by the Pd-C bond trans to the Pd-N bond of the aryl ring bearing electron-withdrawing substituents. In addition, the intermediate resulting from the insertion of 4-methylstyrene into the Pd-acyl bond is a five-member palladacycle and not the open-chain η(3)-allylic species observed for complexes with Ar-BIANs substituted in ortho position.

Crystal structure of a palladium metallacyclic complex: A key-intermediate in the carbonylation of nitrobenzene to isocyanates and carbamates

Abstract The metallacyclic complexes Download : Download full-size image have been obtained under mild reaction conditions with different bidentate nitrogen-donor chelating ligands, starting both from nitrobenzene and nitrosobenzene; the crystal structure of Download : Download full-size image is reported.

Dalton communications. Bow–step and twist conformations and stacking interactions in palladium bipyridine and phenanthroline complexes

Crystal structures for [Pd(L–L)2][PF6]2(L–L = bipyridine, 1,10-phenanthroline or 3,4,7,8-tetramethyl-1,10-phenanthroline) were determined: a variety of ligand distortions and stacking interactions were found.

Cationic palladium complexes with mono- and bidentate nitrogen-donor ligands: synthesis, characterization and reactivity in CO/styrene copolymerization reaction

Abstract 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.

Analogies and Differences in Palladium‐Catalyzed CO/Styrene and Ethylene/Methyl Acrylate Copolymerization Reactions

The catalytic CO/styrene and ethylene/methyl acrylate copolymerizations are compared for the first time by applying the same precatalysts. With this aim, PdII neutral, [Pd(CH3)Cl(N–N)], and monocationic, [Pd(CH3)(L)(N–N)][PF6] (L=CH3CN, DMSO), complexes with 1‐naphthyl‐ and 2‐naphthyl‐substitued α‐diimines with both an acenaphthene and a diazabutadiene skeleton as chelating nitrogen‐donor ligands (N–N) have been studied. In the case of the complexes with the 1‐naphthyl‐substituted ligands, syn and anti isomers are found both in solid state and in solution. All the monocationic complexes generate active catalysts for the CO/styrene copolymerization leading to atactic or isotactic/atactic stereoblock copolymers depending on the ligand bonded to palladium. Instead, in the case of the ethylene/methyl acrylate copolymerization only the complexes with the 1‐naphthyl‐substituted ligands generate catalysts for this reaction.

The synthesis of RuBr2(DMSO)3 revisited: a mixture of Li[fac-RuClnBr3-n(DMSO)3] isomers (n = 0-3) is the reaction product

Abstract In this paper we report the correct formulation of a ruthenium(II)-dimethyl sulfoxide complex previously reported in the literature as RuBr2(DMSO)3. By repeating the published synthetic procedure we isolated a product that has been unambiguously characterized as a mixture of Li[fac-RuClnBr3−n(DMSO)3] (n=0−3) isomers. Our proposal is supported by detailed 1H NMR spectroscopic studies, as well as by 7Li and 37Cl NMR spectra. We also report the crystal structure of [NEt4][fac-RuBr3(DMSO)3]·0.5MeOH as determined by three dimensional X-ray analysis. Crystal data: a=10.96(1), b=14.30(1), c=18.25(1) A; β=106.0(1)°, space group P21/c, Z=4. Least-squares refinement based on 1470 reflections converged to R=0.113.