Enhanced Reactivities toward Amines by Introducing an Imine Arm to the Pincer Ligand: Direct Coupling of Two Amines To Form an Imine Without Oxidant

Dehydrogenative homocoupling of primary alcohols to form esters and coupling of amines to form imines was accomplished using a class of novel pincer ruthenium complexes. The reactivities of the ruthenium pincer complexes for the direct coupling of amines to form imines were enhanced by introducing an imine arm to the pincer ligand. Selective oxidation of benzylamines to imines was achieved using aniline derivatives as the substrate and solvent

Polymerization of Isoprene Promoted by Aminophosphine(ory)-Fused Bipyridine Cobalt Complexes: Precise Control of Molecular Weight and <i>cis</i>-1,4-<i>alt</i>-3,4 Sequence

Ligands <i>N</i>-(dialkyl or arylphosphino)-(2,2′-bipyridin)-6-amine (<b>L1</b>, aryl = Ph; <b>L2</b>, alkyl = ^<i>t</i>Bu; <b>L3</b>, alkyl = adamantyl (Ad)) as well as the corresponding oxidized <i>N</i>-(2,2′-bipyridin-6-yl)-<i>P</i>,<i>P</i>-dialkyl or aryl phosphinic amide (<b>L4</b>, aryl = Ph; <b>L5</b>, alkyl = ^<i>t</i>Bu; <b>L6</b>, alkyl = Ad) congeners were designed and coordinated to cobalt dichloride. The structures of formed complexes were characterized by IR and elemental analyses, as well as characterizations of the X-ray diffractions for complexes <b>C</b><b>o</b><b>4</b> and <b>C</b><b>o</b><b>6</b>, which revealed the cobalt center is expectedly pentacoordinated in a distorted trigonal bipyramidal configuration with a prolonged CoO­(P) bond<i>.</i> In combination with MMAO, complex <b>Co2</b> was highly active in <i>cis</i>-1,4-<i>alt</i>-3,4 enchained polymerization. The hemilabile nature of OP is possible for the alternating η⁴-<i>cis</i>-1,4 and η²-3,4 coordination, and insertion at the metal–carbon bond ensued. In combination with AlEt₂Cl, each of complexes <b>Co4</b>, <b>Co5</b>, and <b>Co6</b> was capable of converting isoprene to polyisoprene in a control mode with observed polymerization rate constants (<i>k</i>_obs = 0.1531 L mol^–1 min^–1 (<b>Co4</b>), 0.1382 L mol^–1 min^–1 (<b>Co5</b>), and 0.0902 L mol^–1 min^–1 (<b>Co6</b>)). The activation energy of the polymerization by <b>Co4</b> falls in the range of 27–31 kJ/mol by determining <i>k</i>_obs values at 0, 30, and 50 °C. The ¹³C NMR analyses of the obtained polyisoprene revealed that complexes <b>Co4</b>, <b>Co5</b>, and <b>Co6</b> have a <i>cis</i>-1,4 selectivity of 86.6–93.4% with a 3,4 selectivity of 6.6–13.4%. This catalyst system can also be applied to block copolymerization of isoprene and myrcene in a living <i>cis</i>-1,4 fashion; therefore, a new biosourced monomer-based elastomer has been achieved

Influence of Polyhedral Oligomeric Silsesquioxane Structure on the Disentangled State of Ultrahigh Molecular Weight Polyethylene Nanocomposites during Ethylene in Situ Polymerization

Three kinds of polyhedral oligomeric silsesquioxane (methyl-POSS, cyclohexyl-POSS, and phenyl-POSS) were chosen to adsorb [3-<i>tert</i>-Bu-2-O-C₆H₃CHN­(C₆F₅)]₂TiCl₂ catalyst (FI catalyst) in order to synthesize ultrahigh molecular weight polyethylene (UHMWPE)/POSS nanocomposites according ethylene in situ polymerization. It was shown that the characteristic of “living’’ polymerization of the FI catalyst would be maintained when alkyl-POSS was incorporated. However, the presence of alkyl-POSS could decay the catalyst activity. The incorporation of alkyl-POSS led to an increase of the crystallinity and the lamellar thickness of nascent UHMWPE, as observed by differential scanning calorimetry. This indicated that the alkyl-POSS would be used as a nucleating agent during the chain growth procedure. Interestingly, all the nanocomposites exhibited low starting storage modulus values which was a reflection of disentangled structure in the nascent UHMWPE nanocomposites. However, polymer chains were prior to entanglement with the incorporation of alkyl-POSS. Rheology and crystallization studies were used to discuss the formation mechanism of entangled structure in the synthesized UHMWPE/POSS nanocomposites