1,5-Diaza-3,7-diphosphacyclooctanes explained

1,5-Diaza-3,7-diphosphacyclooctanes are organophosphorus compounds with the formula [R'NCH{{sub|2}}P(R)CH{{sub|2}}], often abbreviated PN. 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.^{[1] [2]}

Some metal-PN complexes catalyze the hydrogen evolution reaction as well as the oxidation of hydrogen (H). The catalytic mechanism involves the interaction of substrate with the amines in the second coordination sphere.^{[3] [4]}

Synthesis and reactions

The ligands are prepared by the condensation of a primary phosphine, formaldehyde, and a primary amine:^[5]

Diazadiphosphacyclooctanes function as chelating diphosphine ligands. Typical nickel complexes contain two such ligands are give the formula [Ni(P{{sup|R}}{{sub|2}}N{{sup|R'}}{{sub|2}}){{sub|2}}].

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

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.^[6] From the meso-isomer, typical nickel complexes contain two such ligands, i.e. [Ni(P{{sup|R}}{{sub|2}}NR'){{sub|2}}]. When bound to metals, these ligands adopt a conformation similar to that of 1,4-diazacycloheptanes. Acyclic phosphine-amine ligands have the formula (RPCH)NR'.

Notes and References

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