Diphosphenes

Diphosphene is a type of organophosphorus compound that has a phosphorus–phosphorus double bond, denoted by R-P=P-R'. These compounds are not common, but their properties have theoretical importance.

Normally, compounds with the empirical formula RP exist as rings. However, like other multiple bonds between heavy main-group elements, P=P double bonds can be stabilized by large steric hindrance. In general, diphosphenes react like alkenes.

History

In 1877, Köhler and Michaelis claimed what would have been the first isolated diphosphene (PhP=PPh), The structure of Köhler and Michaelis' product was later revised. and X-ray crystallographic analysis proved that this "diphosphene" only had P-P single bonds and was in fact primarily a four-membered ring of the form (PPh)4. The isolation of phosphorus ylide and phosphaalkenes suggested that compounds with P=P bonds could be made.

Yoshifuji et al's isolated a sterically-hindered diphosphene in 1981. That compound's P-P bond distance is 2.034 Å, which is much shorter than the average bond length in (C6H5P)5 (2.217 Å) and (C6H5P)6 (2.237 Å) and indicates double-bond character.

Synthesis

Following Maasaka Yoshifuji and his coworkers' 1981 preparation of bis(2,4,6-tri-tert-butylphenyl)diphosphene, most disphosphene syntheses involve dehalogenation of bulkyl aryldichlorophosphine (ArPCl2). Mg is a typical dehalogenation reagent:

2 ArPCl2 + 2 Mg → ArP=PAr + 2 MgCl2

Such a synthesis works also for trisalkylsilylphosphines, or N-heterocyclic boro-phosphines.

Synthesis of diboryldiphosphene (dipp = 2,6-diisopropylphenyl)

Ylide-stabilized diphosphenes

Examples of di-vinyl-substituted diphosphenes arise via a ring opening/dimerization process from kinetically unstable 2H-phosphirenes. However, the conjugation caused the compounds to exhibit reactivity closer to a phosphinidene.

Structure

Cyclic voltammetry and UV/Vis spectra indicate that boryl-substituted diphosphenes have lower LUMO level and larger HOMO–LUMO gap than aryl-substituted diphosphenes.

Geometry

According to X-ray crystallography, the following parameters describe bis(2,4,6-tri-tert-butylphenyl)diphosphene: P-P = 2.034 (2) Å; P-C = 1.826 (2) Å; P-P-C = 102.8 (1)o; C-P-P-C = 172.2 (1)o. Compared with the length of a P-P single bond in H2PPH2 (2.238 Å), the P-P bond distance is much shorter, which reveals double bond character. The trans orientation is the thermodynamically preferred isomer.

Spectroscopic properties

Diphosphene compounds usually exhibit a symmetry-allowed () (intense) and symmetry-forbidden () (weak) electronic transitions. In the Raman spectrum, the P=P vibration is enhanced by resonance with allowed the transition than with the forbidden transition due to different geometries of excited states and enhancement mechanism. Also the observed strong Raman shifts for (CH(SiMe
3)
2)
2P
2and (CH(SiMe3)2P=PC(SiMe3)2) suggest stronger dipnictenes feature[which?] of diphosphene compared with P-P single bond.[failed verification]

Reactivity

Lithium aluminium hydride reduces diphosphene to give diphosphanes.

Color-filled map of electron density of P2H2

Carbenes add across the double bond, to give diphosphiranes, which further rearrange to 1,3-diphospha-allenes in strong bases.

Diphosphene is inert to oxygen but cycloadds to ozone to give highly unstable phosphorus-oxygen rings that tend to attack the phosphorus' organyl substituents. The reaction with ozone is much more rapid and indicates a 2:1 (ozone:diphosphene) stoichiometry.

Two oxidations of diphosphenes: a) Oxidation by triplet oxygen; b) Oxidation by ozone

When treated with strongly nucleophilic NHC's, the P=P bond cleaves giving phosphinidene compounds:

RP=PR + L → 2 RP−L

Coordination to transition metals

Coordination modes typical for diphosphenes.

Diphosphines form a variety of coordination complexes. Diphosphenes can bind to transition metal either in a η1 or in a η2 mode.

[Fe(CO)4]2[P2(CH(SiMe3)]2 is obtained by treating Na2[Fe(CO)4] with dichlorobis(trimethylsilyl)methylphosphine. The related complex [ArP=PAr]Fe(CO)4 (Ar=2,4,6-tri-tert-butylphenyl) arises by treating diphosephene with Fe2(CO)9.

η2-coordination is illustrated by (M(PhP=PPh)L2) (with M=Pt or Pd and L = (PPh3)2 or Ph2P[CH2]2PPh2).

See also

References

  1. ↑ Power, Philip P. (2010-01-14). "Main-group elements as transition metals". Nature. 463 (7278): 171–177. Bibcode:2010Natur.463..171P. doi:10.1038/nature08634. ISSN 1476-4687. PMID 20075912. S2CID 205219269.
  2. ↑ Kohler, H; Michaelis, A (1877). "Ueber Phenylphosphin und Phosphobenzol (Diphosphenyl)". Ber. Dtsch. Chem. Ges. 10: 807–814. doi:10.1002/cber.187701001222.
  3. ↑ In Horner, Leopold; Hoffmann, Hellmut; Beck, Peter (August 1958). "Phosphororganische Verbindungen, XVI. Wege zur Darstellung primärer, sekundärer und tertiärer Phosphine". Chemische Berichte (in German). 91 (8): 1583–1588. doi:10.1002/cber.19580910803. ISSN 0009-2940,
  4. ↑ Kuchen, W; Grilnewald, W (1965). "Zur Kenntnis der Organophosphorverbindungen, VIII. Über ein neues Verfahren zur Darstellung von Organooligophosphinen". Chem. Ber. 98 (2): 480–486. doi:10.1002/cber.19650980220.
  5. ↑ Daly, J; Maier, L (1964). "Molecular Structure of Phosphobenzene". Nature. 203 (4950): 1167. Bibcode:1964Natur.203.1167D. doi:10.1038/2031167b0. S2CID 4213722.
  6. 1 2 Corbridge, D. E. C. (1995) "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam. § 6.19. ISBN 0-444-89307-5.
  7. 1 2 3 Yoshifuji, M.; Shima, I.; Inamoto, N.; Hirotsu, K.; Higuchi, T. (1981-07-01). "Synthesis and structure of bis(2,4,6-tri-tert-butylphenyl)diphosphene: isolation of a true phosphobenzene". Journal of the American Chemical Society. 103 (15): 4587–4589. doi:10.1021/ja00405a054. ISSN 0002-7863.
  8. 1 2 Cowley, A. H.; Kilduff, J. E.; Newman, T. H.; Pakulski, M. (1982-10-01). "Diphosphenes (RP:PR). Synthesis and NMR characterization". Journal of the American Chemical Society. 104 (21): 5820–5821. doi:10.1021/ja00385a060. ISSN 0002-7863.
  9. 1 2 Asami, Shun-suke; Okamoto, Masafumi; Suzuki, Katsunori; Yamashita, Makoto (2016-10-04). "A Boryl-Substituted Diphosphene: Synthesis, Structure, and Reaction with n-Butyllithium To Form a Stabilized Adduct by pπ-pπ Interaction". Angewandte Chemie. 128 (41): 13019–13023. Bibcode:2016AngCh.12813019A. doi:10.1002/ange.201607995. ISSN 1521-3757.
  10. ↑ Liu, Liu Leo; Zhou, Jiliang; Cao, Levy L.; Stephan, Douglas W. (2018-11-15). "Facile Cleavage of the P=P Double Bond in Vinyl-Substituted Diphosphenes". Angewandte Chemie International Edition. 58 (1): 273–277. doi:10.1002/anie.201812592. ISSN 1521-3757. PMID 30444313. S2CID 53564701.
  11. ↑ Matus, Myrna H.; Nguyen, Minh Tho; Dixon, David A. (2007-03-01). "Heats of Formation of Diphosphene, Phosphinophosphinidene, Diphosphine, and Their Methyl Derivatives, and Mechanism of the Borane-Assisted Hydrogen Release". The Journal of Physical Chemistry A. 111 (9): 1726–1736. Bibcode:2007JPCA..111.1726M. doi:10.1021/jp067892v. ISSN 1089-5639. PMID 17298044.
  12. ↑ Caminade, Anne-Marie; Verrier, Martine; Ades, Claude; Paillous, Nicole; Koenig, Max (1984-01-01). "Laser irradiation of a diphosphene: evidence for the first cis–trans isomerization". J. Chem. Soc., Chem. Commun. (13): 875–877. doi:10.1039/c39840000875. ISSN 0022-4936.
  13. ↑ Sasamori, Takahiro; Tokitoh, Norihiro (2008-03-05). "Doubly bonded systems between heavier Group 15 elements". Dalton Trans. (11): 1395–1408. doi:10.1039/b715033d. ISSN 1477-9234. PMID 18322615. S2CID 6269387.
  14. ↑ Copeland, Tiffany; Shea, Michael P.; Milliken, Matt C.; Smith, Rhett C.; Protasiewicz, John D.; Simpson, M.Cather (2003). "Raman excitation profile of a sterically protected diphosphene [ArP=PAr]". Analytica Chimica Acta. 496 (1–2): 155–163. Bibcode:2003AcAC..496..155C. doi:10.1016/s0003-2670(03)00996-6.
  15. ↑ Yoshifuji, Masaaki (2017-03-01). "Sterically protected organophosphorus compounds of unusual structures". Pure and Applied Chemistry. 89 (3): 281–286. doi:10.1515/pac-2016-1029. ISSN 1365-3075.
  16. ↑ Yoshifuji, Masaaki; Shibayama, Katsuhiro; Inamoto, Naoki; Watanabe, Tokuko (1983-04-05). "Reduction of Diphosphene: Formation of dl- and meso-Diphosphanes". Chemistry Letters. 12 (4): 585–588. doi:10.1246/cl.1983.585. ISSN 0366-7022.
  17. ↑ Yoshifuji, Masaaki; Sasaki, Shigeru; Niitsu, Takashi; Inamoto, Naoki (1989). "A convenient new route from diphosphene to 1,3-diphospha-allene and dynamic NMR studies of the 2,4,6-tri-t-butylphenyl derivative". Tetrahedron Letters. 30 (2): 187–188. doi:10.1016/s0040-4039(00)95155-4.
  18. ↑ Caminade, A. M.; Khatib, F. E.; Ades, C.; Verrier, M.; Paillous, N.; Koenig, M. (1987-04-14). "ChemInform Abstract: Oxidation and Isomerization of Diphosphene". ChemInform. 18 (15): no. doi:10.1002/chin.198715272. ISSN 1522-2667.
  19. 1 2 Caminade, Anne-Marie; Couret, Claude; Escudie, Jean; Koenig, Max (1984-01-01). "Ozonolysis of bis[tris(trimethylsilyl)methyl]diphosphene". Journal of the Chemical Society, Chemical Communications (24): 1622. doi:10.1039/c39840001622. ISSN 0022-4936.
  20. ↑ Hayakawa, Naoki; Sadamori, Kazuya; Tsujimoto, Shota; Hatanaka, Miho; Wakabayashi, Tomonari; Matsuo, Tsukasa (2017-05-15). "Cleavage of a P=P Double Bond Mediated by N-Heterocyclic Carbenes". Angewandte Chemie International Edition. 56 (21): 5765–5769. doi:10.1002/anie.201701201. ISSN 1521-3773. PMID 28429503.
  21. ↑ Flynn, Kathy M.; Olmstead, Marilyn M.; Power, Philip P. (1983-04-01). "Simple one-step route to a transition-metal complex containing a phosphorus–phosphorus double bond. Synthesis and x-ray crystal structure of {trans-bis[bis(trimethylsilyl)methyl]diphosphene}bis[tetracarbonyliron(0)]". Journal of the American Chemical Society. 105 (7): 2085–2086. doi:10.1021/ja00345a080. ISSN 0002-7863.
  22. ↑ Cowley, A. H.; Kilduff, J. E.; Lasch, J. G.; Norman, N. C.; Pakulski, M.; Ando, F.; Wright, T. C. (1983-12-01). "Reactivity of diphosphenes and phosphaarsenes toward metal carbonyls". Journal of the American Chemical Society. 105 (26): 7751–7752. doi:10.1021/ja00364a051. ISSN 0002-7863.
  23. ↑ Chatt, Joseph; Hitchcock, Petter B.; Pidcock, Alan; Warrens, Christopher P.; Dixon, Keith R. (1982-01-01). "Synthesis and31P n.m.r. spectroscopy of platinum and palladium complexes containing side-bonded diphenyldiphosphene. The X-ray crystal and molecular structure of [Pd(PhP=pph){bis(diphenyl-phosphino)ethane}]". J. Chem. Soc., Chem. Commun. (16): 932–933. doi:10.1039/c39820000932. ISSN 0022-4936.