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1,5-Diaza-3,7-diphosphacyclooctanes

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P2N2 ligand structure

1,5-Diaza-3,7-diphosphacyclooctanes are organophosphorus compounds with the formula 2, often abbreviated P2N2. They are air-sensitive white solids that are soluble in organic solvents. The ligands exist as meso and d,l-diastereomers, but only the meso forms function as bidentate ligands.

Some metal-P2N2 complexes catalyze the hydrogen evolution reaction as well as the oxidation of hydrogen (H2). The catalytic mechanism involves the interaction of substrate with the amines in the second coordination sphere.

Synthesis and reactions

The ligands are prepared by the condensation of a primary phosphine, formaldehyde, and a primary amine:

2 RPH2 + 4 CH2O + 2 RNH2 → [RNCH2P(R')CH2]2 + 4 H2O

Diazadiphosphacyclooctanes function as chelating diphosphine ligands. Typical nickel complexes contain two such ligands are give the formula .

Cationic complexes of these P2N2 and related ligands often exhibit enhanced reactivity toward H2. These complexes serve as electrocatalysts for H2 evolution.

Conformation of chelate rings in P2N2-M and P2N-M complexes

Related ligands

Azadiphosphacycloheptanes are a related family of diphosphines, but containing only one amine. They are prepared by condensation of 1,2-bis(phenylphosphino)ethane, formaldehyde, and a primary amine. From the meso-isomer, typical nickel complexes contain two such ligands, i.e. . When bound to metals, these ligands adopt a conformation similar to that of 1,4-diazacycloheptanes. Acyclic phosphine-amine ligands have the formula (R2PCH2)NR'.

References

  1. Erika Bálint; Adám Tajti; Anna Tripolszky; György Keglevich (2018). "Synthesis of platinum, palladium and rhodium complexes of α-aminophosphine ligands". Dalton Trans. 47 (14): 4755–4778. doi:10.1039/C8DT00178B. PMID 29565437.
  2. Wiedner, Eric S.; Appel, Aaron M.; Raugei, Simone; Shaw, Wendy J.; Bullock, R. Morris (2022). "Molecular Catalysts with Diphosphine Ligands Containing Pendant Amines". Chemical Reviews. 122 (14): 12427–12474. doi:10.1021/acs.chemrev.1c01001. PMID 35640056. S2CID 249237539.
  3. Yang, J. Y.; Chen, S.; Dougherty, W. G.; Kassel, W. S.; Bullock, R. M.; DuBois, D. L.; Raugei, S.; Rousseau, R.; Dupuis, M.; Rakowski DuBois, M. (2010). "Hydrogen oxidation catalysis by a nickel diphosphine complex with pendant tert-butyl amines". Chem. Commun. 46 (45): 8618–8620. doi:10.1039/c0cc03246h. PMID 20938535. S2CID 34168725.
  4. Bullock, R. M.; Helm, M. L. (2015). "Molecular Electrocatalysts for Oxidation of Hydrogen Using Earth-Abundant Metals: Shoving Protons Around with Proton Relays". Acc. Chem. Res. 48 (7): 2017–2026. doi:10.1021/acs.accounts.5b00069. OSTI 1582563. PMID 26079983.
  5. t. Thomas, Gilian; Isbrandt, Eric S.; Newman, Stephen G. (2024). "Synthesis of Secondary Benzylic Alcohols by Reductive Arylation of Aldehydes: α-Phenyl-6-quinolinemethanol". Organic Syntheses. 101: 1–20. doi:10.15227/orgsyn.101.0001.
  6. Karasik, A. A.; Balueva, A. S.; Moussina, E. I.; Naumov, R. N.; Dobrynin, A. B.; Krivolapov, D. B.; Litvinov, I. A.; Sinyashin, O. G. (2008). "1,3,6-azadiphosphacycloheptanes: a novel type of heterocyclic diphosphines". Heteroatom Chemistry. 19 (2): 125–132. doi:10.1002/hc.20397.
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