Ligand-Dominated Activation of CO2 and CS2 by the Putative Nickel Phosphiniminato Intermediates.

Room-temperature photoactivation of the first- and second-generation PN3P-pincer nickel azido complexes 1a and 1b in the presence of CO2 or CS2 afforded N-bound carbamates, dithiocarbamates, and isothiocyanates, providing insights into CO2 and CS2 activation and demonstrating how a seemingly small difference in the ligand structure significantly influences the reactivity. Theoretical calculations disclosed that the charge of the phosphorus atom plays a critical role in determining the nitrogen atom transfer to form a plausible nickel phosphiniminato intermediate.

Selective benzylic Csp3-H bond activations mediated by a phosphorus-nitrogen PN3P-nickel complex.

In contrast to the typical Csp2-H activation, a PN3P-Nickel complex chemoselectively cleaved the benzylic Csp3-H bond of toluene in the presence of KHMDS, presumably via an in situ generated potassium benzyl intermediate. Under similar conditions, CO underwent deoxygenation to afford the corresponding nickel cyano complex, and ethylbenzene was dehydrogenated to give styrene and a nickel hydride compound. 2,6-Xylyl isocyanide was transformed into an unprecedented indolyl complex, likely by trapping the activated benzyl species with an isocyanide moiety.

Interrogating the steric outcome during H2 heterolysis: in-plane steric effects in the regioselective protonation of the PN3P-pincer ligand.

H2 heterolysis to generate well-defined nickel hydride-proton complexes was achieved by the 2nd generation PN3P-pincer nickel platform. The regioselective protonation in the ligand framework was demonstrated for the first time to highlight the importance of in-plane hindrance during the H2 splitting process.

Monomeric nickel hydroxide stabilized by a sterically demanding phosphorus-nitrogen PN3P-pincer ligand: synthesis, reactivity and catalysis.

A terminal nickel hydroxide complex (PN3P)Ni(OH) (3) bearing the 2nd generation phosphorus-nitrogen PN3P-pincer ligand has been synthesized and structurally characterized. As a nucleophile, 3 reacts with CO to afford the hydroxycarbonyl complex 4, (PN3P)Ni(COOH). 3 can also activate CO2 and CS2 to produce nickel bicarbonate (PN3P)Ni(OCOOH) (5) and bimetallic dithiocarbonate [(PN3P)NiS]2CO (6) respectively, as well as to promote aryl isocyanate and isothiocyanate insertion into the Ni-OH bond to give the corresponding (PN3P)NiEC(O)NHAr complexes (E = O, 7; E = S, 8). In addition, 3 catalyzes the nitrile hydration to various amides with well-defined intermediates (PN3P)Ni-NHC(O)R (R = Me, 9; R = Ph, 10).

Nitrogen atom transfer mediated by a new PN3P-pincer nickel core via a putative nitrido nickel intermediate.

A 2nd generation PN3P-pincer azido nickel complex (PN3P)Ni(N3) reacts with isocyanides to afford monosubstituted carbodiimides under irradiation, presumably via a transient nitrido intermediate. The resulting species can further generate unsymmetrical carboddimides and the PN3P nickel halide complex, accomplishing a synthetic cycle for a complete nitrogen atom transfer reaction.

Highly cis-1,4 Selective Living Polymerization of Unmasked Polar 2-(2-Methylidenebut-3-enyl)Furan and Diels-Alder Addition.

The polymerization of a new polar diene-based monomer 2-(2-methylidenebut-3-enyl)furan (MBEF) without masking is achieved by using the bis(phosphino)carbazoleide-ligated yttrium (Y) alkyl complex upon the activation of [Ph3 C][B(C6 F5 )4 ]. Under mild conditions, the polymerizations under the monomer-to-Y ratios ranging from 100:1 to 500:1 perform fluently in high yields. The afforded polydienes bearing pendant terminal furan groups have high cis-1,4-regularity up to 98.6% and molecular weights close to the theoretic values and narrow polymer dispersity index(PDI) (1.13-1.17) suggesting a livingness polymerization mode. In addition, this novel polydiene is an excellent building block for preparing functional rubber materials. For example, via Diels-Alder addition of furan groups under mild conditions, hydroxyl groups are successfully introduced on the side chains efficiently in a 75% conversion. Furthermore, the copolymerization of polar MBEF and nonpolar isoprene is also successfully realized by the bis(phosphino) carbazoleide-ligated scandium analog to access furan-modified cis-1,4 (>97%) polyisoprene with different MBEF contents (5.3%, 8.7%).

Dehydrogenation of Formic Acid Catalyzed by a Ruthenium Complex with an N,N'-Diimine Ligand.

We report a ruthenium complex containing an N,N'-diimine ligand for the selective decomposition of formic acid to H2 and CO2 in water in the absence of any organic additives. A turnover frequency of 12 000 h-1 and a turnover number of 350 000 at 90 °C were achieved in the HCOOH/HCOONa aqueous solution. Efficient production of high-pressure H2 and CO2 (24.0 MPa (3480 psi)) was achieved through the decomposition of formic acid with no formation of CO. Mechanistic studies by NMR and DFT calculations indicate that there may be two competitive pathways for the key hydride transfer rate-determining step in the catalytic process.

Immortal Ring-Opening Polymerization of rac-Lactide Using Polymeric Alcohol as Initiator to Prepare Graft Copolymer.

In the presence of a small molecular protic initiator, immortal ring-opening polymerization (ROP) of lactide (LA) is a highly efficient strategy to synthesize polylactide in a controllable manner, while using polymeric alcohol as an initiator has been less investigated. A series of polymeric alcohols (PS⁻OH) composed of styrene and 4.3%⁻18% hydroxyl functional styrene (diethyl(hydroxy(4-vinylphenyl)methyl)phosphonate, St⁻OH) were synthesized through reversible addition-fragmentation transfer (RAFT) polymerization. Using PS⁻OH as an initiator, the immortal ROP of rac-LA was catalyzed by dibutylmagnesium (MgnBu2) under various ratios of monomer to hydroxyl group within PS⁻OH to generate polystyrene-g-polylactide (PS⁻g⁻PLA) copolymers with different graft lengths. After thermal annealing at 115 °C, the PLA domain aggregated to nanospheres among the PS continuum. The size of the nanospheres, varying from 130.1 to 224.2 nm, was related to the graft density and length of PS⁻g⁻PLA. Nanoporous films were afforded through chemical etching of the PLA component.

Highly isoselective coordination polymerization of ortho-methoxystyrene with ß-diketiminato rare-earth-metal precursors.

Stereoselective coordination/insertion polymerization of the polar ortho-methoxystyrene has been achieved for the first time by using the cationic ß-diketiminato rare-earth-metal species. High activity and excellent isoselectivity (mmmm>99 %) were acheived. The unmasked Lewis-basic methoxy group does not poison the Lewis-acidic metal center, but instead activates the polymerization through σ-π chelation to the active species together with the vinyl group, thus lower the coordination and activation energies as compared with those of styrene derivatives lacking the methoxy group.

Syndioselective coordination polymerization of unmasked polar methoxystyrenes using a pyridenylmethylene fluorenyl yttrium precursor.

Unprecedented coordination-insertion polymerizations of polar methoxyl substituted styrene derivatives, in despite of the position of the substituent, have been achieved using a pyridyl methylene fluorenyl yttrium bis(alkyl) precursor with high activity to give polar polystyrenes of high molecular weight and perfect syndiotacticity.

Neutral binuclear rare-earth metal complexes with four µ2-bridging hydrides.

The first neutral rare-earth metal dinuclear dihydrido complexes [(NPNPN)LnH2]2 (2-Ln; Ln = Y, Lu; NPNPN: N[Ph2PNC6H3((i)Pr)2]2) bearing µ2-bridging hydride ligands have been synthesized. In the presence of THF, 2-Y undergoes intramolecular activation of the sp(2) C-H bond to form dinuclear aryl-hydride complex 3-Y containing three µ2-bridging hydride ligands.