Barbara Binotti

Application of NOE and PGSE NMR Methodologies to Investigate Non-Covalent Intimate Inorganic Adducts in Solution

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.

Solution structure investigations of olefin Pd(II) and Pt(II) complex ion pairs bearing α-diimine ligands by 19F, 1H-HOESY NMR

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.

From atactic to isotactic CO/p-methylstyrene copolymer by proper modification of Pd(II) catalysts bearing achiral α-diimines

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.

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.

Cationic olefin Pd(II) complexes bearing α -iminoketone N,O-ligands: unprecedented isomerisation of the methoxycyclooctenyl ligand

Abstract The reaction of [Pd(η1,η2-C8H12OMe)Cl]2 with α-iminoketone ligands affords cationic η1,η2-5-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 η1,η2-1-methoxycyclooctenyl complexes assisted by weak nucleophiles such as olefins or alkynes.