Polymerization of Phenylacetylenes Using Rhodium Catalysts Coordinated by Norbornadiene Linked to a Phosphino or Amino Group

The novel rhodium (Rh) catalysts [{nbd-(CH₂)₄-X}­RhR] (<b>1</b>, X = PPh₂, R = Cl; <b>2</b>, X = NPh₂, R = Cl; <b>3</b>, X = PPh₂, R = triphenylvinyl; nbd = 2,5-norbornadiene) were synthesized, and their catalytic activities were examined for the polymerization of phenylacetylene (PA) and its derivatives. Rh-103 NMR spectroscopy together with DFT calculations (B3LYP/6-31G*-LANL2DZ) indicated that catalyst <b>1</b> exists in a mononuclear 16-electron state, while <b>2</b> exists in dinuclear states. Catalyst <b>1</b> converted PA less than 1% in the absence of triethylamine (Et₃N). Addition of Et₃N and extension of the polymerization time enhanced the monomer conversion. On the other hand, catalysts <b>2</b> and <b>3</b> quantitatively converted PA in the absence of Et₃N to afford the polymer in good yields. Catalyst <b>3</b> achieved two-stage polymerization of PA

Polymerization of Phenylacetylenes Using Rhodium Catalysts Coordinated by Norbornadiene Linked to a Phosphino or Amino Group

The novel rhodium (Rh) catalysts [{nbd-(CH₂)₄-X}­RhR] (<b>1</b>, X = PPh₂, R = Cl; <b>2</b>, X = NPh₂, R = Cl; <b>3</b>, X = PPh₂, R = triphenylvinyl; nbd = 2,5-norbornadiene) were synthesized, and their catalytic activities were examined for the polymerization of phenylacetylene (PA) and its derivatives. Rh-103 NMR spectroscopy together with DFT calculations (B3LYP/6-31G*-LANL2DZ) indicated that catalyst <b>1</b> exists in a mononuclear 16-electron state, while <b>2</b> exists in dinuclear states. Catalyst <b>1</b> converted PA less than 1% in the absence of triethylamine (Et₃N). Addition of Et₃N and extension of the polymerization time enhanced the monomer conversion. On the other hand, catalysts <b>2</b> and <b>3</b> quantitatively converted PA in the absence of Et₃N to afford the polymer in good yields. Catalyst <b>3</b> achieved two-stage polymerization of PA

Characterization of the Polymerization Catalyst [(2,5-norbornadiene)Rh{C(Ph)CPh₂}(PPh₃)] and Identification of the End Structures of Poly(phenylacetylenes) Obtained by Polymerization Using This Catalyst

The structures of [(2,5-norbornadiene)­Rh­{C­(Ph)CPh₂}­(PPh₃)] (<b>1</b>) and its reaction product with CH₃CO₂H were elucidated by ¹H, ¹³C, and ³¹P NMR spectroscopy, mass spectrometry, and single-crystal X-ray analysis. The presence of two conformational isomers of <b>1</b> was verified by NMR spectroscopy, which was well-supported by DFT calculations. Phenylacetylene was polymerized using <b>1</b> as a catalyst with [M]₀/[Rh] = 10 and quenched with CH₃CO₂H and CH₃CO₂D. The incorporation of H and D at the polymer ends was confirmed by MALDI-TOF mass spectrometry and ¹H and ¹H–¹³C HSQC NMR spectroscopy. The polymerization degree was calculated to be 11 by ¹H NMR spectroscopy, which agreed well with the theoretical value

Characterization of the Polymerization Catalyst [(2,5-norbornadiene)Rh{C(Ph)CPh₂}(PPh₃)] and Identification of the End Structures of Poly(phenylacetylenes) Obtained by Polymerization Using This Catalyst

The structures of [(2,5-norbornadiene)­Rh­{C­(Ph)CPh₂}­(PPh₃)] (<b>1</b>) and its reaction product with CH₃CO₂H were elucidated by ¹H, ¹³C, and ³¹P NMR spectroscopy, mass spectrometry, and single-crystal X-ray analysis. The presence of two conformational isomers of <b>1</b> was verified by NMR spectroscopy, which was well-supported by DFT calculations. Phenylacetylene was polymerized using <b>1</b> as a catalyst with [M]₀/[Rh] = 10 and quenched with CH₃CO₂H and CH₃CO₂D. The incorporation of H and D at the polymer ends was confirmed by MALDI-TOF mass spectrometry and ¹H and ¹H–¹³C HSQC NMR spectroscopy. The polymerization degree was calculated to be 11 by ¹H NMR spectroscopy, which agreed well with the theoretical value

Characterization of the Polymerization Catalyst [(2,5-norbornadiene)Rh{C(Ph)CPh₂}(PPh₃)] and Identification of the End Structures of Poly(phenylacetylenes) Obtained by Polymerization Using This Catalyst

The structures of [(2,5-norbornadiene)­Rh­{C­(Ph)CPh₂}­(PPh₃)] (<b>1</b>) and its reaction product with CH₃CO₂H were elucidated by ¹H, ¹³C, and ³¹P NMR spectroscopy, mass spectrometry, and single-crystal X-ray analysis. The presence of two conformational isomers of <b>1</b> was verified by NMR spectroscopy, which was well-supported by DFT calculations. Phenylacetylene was polymerized using <b>1</b> as a catalyst with [M]₀/[Rh] = 10 and quenched with CH₃CO₂H and CH₃CO₂D. The incorporation of H and D at the polymer ends was confirmed by MALDI-TOF mass spectrometry and ¹H and ¹H–¹³C HSQC NMR spectroscopy. The polymerization degree was calculated to be 11 by ¹H NMR spectroscopy, which agreed well with the theoretical value

CO₂ Hydrogenation Catalysts with Deprotonated Picolinamide Ligands

In an effort to design concepts for highly active catalysts for the hydrogenation of CO₂ to formate in basic water, we have prepared several catalysts with picolinic acid, picolinamide, and its derivatives, and we investigated their catalytic activity. The CO₂ hydrogenation catalyst having a 4-hydroxy-<i>N</i>-methylpicolinamidate ligand exhibited excellent activity even under ambient conditions (0.1 MPa, 25 °C) in basic water, exhibiting a TON of 14700, a TOF of 167 h^–1, and producing a 0.64 M formate concentration. Its high catalytic activity originates from strong electron donation by the anionic amide moiety in addition to the phenolic O^– functionality

Highly Robust Hydrogen Generation by Bioinspired Ir Complexes for Dehydrogenation of Formic Acid in Water: Experimental and Theoretical Mechanistic Investigations at Different pH

Hydrogen generation from formic acid (FA), one of the most promising hydrogen storage materials, has attracted much attention due to the demand for the development of renewable energy carriers. Catalytic dehydrogenation of FA in an efficient and green manner remains challenging. Here, we report a series of bioinspired Ir complexes for highly robust and selective hydrogen production from FA in aqueous solutions without organic solvents or additives. One of these complexes bearing an imidazoline moiety (complex <b>6</b>) achieved a turnover frequency (TOF) of 322 000 h^–1 at 100 °C, which is higher than ever reported. The novel catalysts are very stable and applicable in highly concentrated FA. For instance, complex <b>3</b> (1 μmol) affords an unprecedented turnover number (TON) of 2 050 000 at 60 °C. Deuterium kinetic isotope effect experiments and density functional theory (DFT) calculations employing a “speciation” approach demonstrated a change in the rate-determining step with increasing solution pH. This study provides not only more insight into the mechanism of dehydrogenation of FA but also offers a new principle for the design of effective homogeneous organometallic catalysts for H₂ generation from FA