Poly(vinyl chloride) Dechlorination Catalyzed by Zirconium.

Poly(vinyl chloride) undergoes dechlorination in the presence of triethylsilane (Et3SiH) and a catalytic amount of [Cp2Zr(NPh2)][CH3B(C6F5)3] (1 b) at 40-80 °C, with up to 91 % efficiency. Stoichiometric reactivity studies conducted on cyclohexyl chloride as a model suggest that 1 b dechlorinates PVC by initial chloride abstraction, followed by hydride transfer to the cationic PVC chain from Et3SiH. Consumer items such as pipe fitting, vinyl disc or electric cable insulation undergo either dechlorination or hydrosilylation of the carbonyl-containing copolymer (polyvinyl acetate) or plasticizer (phthalate).

Bis(salicylamidine) Ligands (FAlen): A Variant of Salen with "à la Carte" Denticity.

Ethylene- and phenylene-bridged bis(salicylamidine) ligands have been readily prepared from ethylene or phenylenediamine and iminium chloride derivatives generated in situ from N,N-dialkylsalicylamides. The former, in its diprotonated form (FAlenH2), reacts with AlMe3 to afford a zwitterionic dimethyldiphenoxyaluminate complex with the FAlen ligand monoprotonated and in a bidentate κ2O,O' fashion. A phenylene-bridged proligand behaves differently, yielding a neutral methylaluminum complex bearing a κ3O,N,O'-coordinated FAlen ligand. From these complexes, methyl anion abstraction with B(C6F5)3 or a reaction with Schrock's alcohol leads to the corresponding aluminum cationic or alkoxy complexes in which a κ4O,N,N',O'-coordination mode of the FAlen ligand is observed. X-ray diffraction studies of the proligands and of the complexes show that the amidine functions feature a trans configuration when the N-amidine atom is not coordinated to the metal and conversely a cis configuration when it is. Density functional theory calculations show that trans-cis isomerization of the amidine functions occurs upon coordination with the metal ion with very low energy barriers. They also confirm the intuition that the denticity of the FAlen ligands in the complexes is directly related to the electron richness of the metal ion. At last, FAlen Al complexes are used as initiators for the controlled ring-opening polymerization of rac-lactide to afford poly(lactic acid) with slight isotactic bias.

Template Synthesis of NPN' Pincer-type Ligands at Titanium Using an Ambiphilic Phosphide Scaffold.

Ti-imido complex [TiCl(NtBu)(BIPP)] [1; BIPP = bis(iminophosphoranyl)phosphide ligand] reacts with terminal alkynes R-C≡CH (R = phenyl, isopropenyl, cyclopropyl, and 2-pyridyl) via P-P bond cleavage of the BIPP ligand. The resulting complexes [TiCl(NPN')(NPhPPh2)] (2a-d) contain a pincer-type NPN' phosphide ligand that incorporates the terminal alkyne and the imido ligand from complex 1. Complexes 2a-d feature two chiral centers (Ti and P) with interdependent absolute configurations; thus, they are formed stereoselectively. Complex 2a (R = phenyl) undergoes chloride abstraction with [Et3SiHSiEt3][B(C6F5)4], yielding [Ti(NPN')(NPhPPh2)][B(C6F5)4] (3). Complex 3 is a moderately active and stereoselective initiator for the ring-opening polymerization of rac-lactide. Complex 3 activates the C═O bond of 4-iodobenzaldehyde to give complex 4 as a single diastereomer despite the presence of three chiral centers. Complex 3 undergoes transmetallation with SbCl3, yielding [Sb(NPN')][B(C6F5)4] (5) and [TiCl3(NPhPPh2)] (6) selectively. The bonding situation in 3 and 5 was analyzed using Bader's atoms in molecules and the electron localization function, showing that the nitrogen atoms of the NPN' ligand are electronically similar, and that the metal-phosphide interaction is more polar in the case of titanium.

Al and Zn phenoxy-amidine complexes for lactide ROP catalysis.

We report the synthesis of a new generation of phenoxy-amidine ligands based on an aryloxy moiety possessing an ortho-N-linked trisubstituted amidine. The reaction of the phenol-amidine proligands with aluminum and zinc alkyls gave mono- or bis-ligated complexes depending on the metal/ligand ratio used. The solid-state structure of four proligands and thirteen Zn and Al complexes has been determined by X-Ray diffraction analysis. The mono-ligated complexes present an aryloxy-bridged dimeric structure, which is retained in solution in the case of Zn complexes but not with aluminum according to DOSY NMR experiments. Bis(ligated) Al and Zn complexes exhibit fluxional behaviour in solution attributed to coordination-decoordination of the amidine moiety and the rotation around the amidine C-NR'2 and C-Ar bonds. These complexes were tested for the ROP of rac-lactide in solution and under bulk conditions. In both cases, the most performant catalysts are Zn complexes featuring a phenoxy-amidine ligand with a pendant additional dimethylamino arm.