ABSTRACT
Ruthenium(II) PNN complexes depolymerize many polyesters into diols and polycarbonates into glycols plus methanol via hydrogenation. Notably, polyesters with two methylene units between ester linkages depolymerize to carboxylic acids rather than diols. This methodology represents a new approach for producing useful chemicals from waste plastics.
ABSTRACT
This report describes the synthesis and characterization of metal halide complexes (M = Mn, Fe, Co) supported by a new family of pendant donor-modified alpha-diimine ligands. The donor (N, O, P, S) substituent is linked to the alpha-diimine by a short hydrocarbon spacer forming a tridentate, mer-coordinating ligand structure. The tridentate ligands are assembled from monoimine precursors, the latter being synthesized by selective reaction with one carbonyl group of the alpha-dione. While attempts to separately isolate tridentate ligands in pure form were unsuccessful, metal complexes supported by the tridentate ligand are readily synthesized in-situ, by forming the ligand in the presence of the metal halide, resulting in a metal complex which subsequently crystallizes out of the reaction mixture. Metal complexes with NNN, NNO, NNP and NNS donor sets have been prepared and examples supported by NNN, NNP and NNS ligands have been structurally characterized. In the solid state, NNN and NNP ligands coordinate in a mer fashion and the metal complexes possess distorted square pyramidal structures and high spin (S = 2) electronic configurations. Compounds with NNS coordination environments display a variety of solid state structures, ranging from those with unbound sulfur atoms, including chloride bridged and solvent ligated species, to those with sulfur weakly bound to the metal center. The extent of sulfur ligation depends on the donor ability of the crystallization solvent and the substitution pattern of the arylthioether substituent.
ABSTRACT
This report describes the synthesis, structural characterization, and polymerization behavior of a series of chromium(II) and chromium(III) complexes ligated by tris(2-pyridylmethyl)amine (TPA), including chromium(III) organometallic derivatives. For instance, the combination of TPA with CrCl(2) yields monomeric (TPA)CrCl(2) (1). A similar reaction of CrCl(2) with TPA, followed by chloride abstraction with NaBPh(4) or NaBAr(F)(4) (Ar(F) = 3,5-(CF(3))(2)C(6)H(3)), provides the weakly associated cationic dimers [(TPA)CrCl](2)[BPh(4)](2) (2A) and [(TPA)CrCl](2)[BAr(F)(4)](2) (2B), respectively. X-ray crystallographic analysis reveals that each chromium(II) center in 1, 2A, and 2B is a tetragonally elongated octahedron; such Jahn-Teller distortions are consistent with the observed high spin (S = 2) electronic configurations for these chromium(II) complexes. Likewise, reaction of CrCl(3)(THF)(3) with TPA, followed by anion metathesis with NaBPh(4) or NaBAr(F)(4), yields the monomeric, cationic chromium(III) complexes [(TPA)CrCl(2)][BPh(4)] (4A) and [(TPA)CrCl(2)][BAr(F)(4)] (4B), respectively. Treatment of 4A with methyl and phenyl Grignard reagents produces the cationic chromium(III) organometallic derivatives [(TPA)Cr(CH(3))(2)][BPh(4)] (5) and [(TPA)CrPh(2)][BPh(4)] (6), respectively. Similar reactions of 4A with organolithium reagents leads to intractable solids, presumably due to overreduction of the chromium(III) center. X-ray crystallographic analysis of 4A, 5, and 6 confirms that each possesses a largely undistorted octahedral chromium center, consistent with the observed S = (3)/(2) electronic ground states. Compounds 1, 2A, 2B, 4A, 4B, 5, and 6 are all active polymerization catalysts in the presence of methylalumoxane, producing low to moderate molecular weight high-density polyethylene.
