POCOP

POCOP is a type of pincer ligand. Pincer type ligands are tridentate ligands that bind three sites on one plane of a metal complex. POCOP forms complexes with one M-C(aryl) bond and two phosphinite ligands.[1] The term POCOP is used both for the ligand, with formula C6H4(OPPh2)2, and its complexes, with formula C6H3(OPPh2)2]− (Ph = C6H5)

POCOP
Names
IUPAC name
1,3-Bis[(diphenylphosphino)oxy]benzene
Preferred IUPAC name
1,3-Phenylene bis(diphenylphosphinite)
Other names
Resorcinolbisphosphinite; 1,3-Bis(diphenylphosphinooxy)benzene
Identifiers
3D model (JSmol)
ChemSpider
UNII
  • InChI=1S/C30H24O2P2/c1-5-16-27(17-6-1)33(28-18-7-2-8-19-28)31-25-14-13-15-26(24-25)32-34(29-20-9-3-10-21-29)30-22-11-4-12-23-30/h1-24H
    Key: PFCIJALLGNUKRS-UHFFFAOYSA-N
  • O(c3cccc(OP(c1ccccc1)c2ccccc2)c3)P(c4ccccc4)c5ccccc5
Properties
C30H24O2P2
Molar mass 478.468 g·mol−1
Appearance Yellow solid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Synthesis and structure

Interest in POCOP arises from its easy synthesis, which accommodates many substituents on phosphorus and results in higher yields than other PCP analogues.[2] The parent POCOP ligand is prepared by treating resorcinol with chlorodiphenylphosphine:[3]

C6H4(OH)2 + 2 ClPPh2 → C6H4(OPPh2)2 + 2 HCl

Related ligands can be prepared from chlorodiisopropylphosphine.

Structure of a Ni(POCOP)X complex.

Representative complexes are of the type Ni(POCOP)X (X = halide, alkyl, thiolate). The halides arise by direct reaction of the ligand and a nickel halide and offer a relatively cheap, nontoxic and readily available option of the ligand for various applications.[4] There can also be variable conformations of POCOP pertaining to the various R groups branching off of the donor atoms.

Thermal ellipsoid plot of Ni(POCOP)Cl compound

In most cases the MPOCOP center features a planar MC3O2P2 core. The rigid conformation and square planar geometry of the POCOP ligand allow for systematic changes over the steric and electronic environment at the metal center.[2] The geometry of metal compounds formed with POCOP ligands can be seen through the P-Ni-P (164.01 Å ) and C-Ni-Cl (178.31Å) bond angles found for (POCOP)NiCl. The bond angles of this compound are representative of angles found for several other pocop metal compounds.[4] Because of relatively small P-Ni-P bond angle the otherwise Ni complexes exhibit a slight tetrahedral distortion.

Catalytic reaction

Pincer ligands participate in a variety of organic transformation, such as the hydrosilylation, and ethylene oligomerizations, and homocoupling of benzyl halides.[5] Ni PCP pincer complexes promote sulfur-carbon forming reactions.[2]

References
  1. Morales-Morales, David; Jensen, Craig (2007), The Chemistry of Pincer Compounds, Elsevier, ISBN 978-0-444-53138-4
  2. Morales-Morales, D. (2004). "Pincer Complexes. Applications in Catalysis". Rev. Soc. Quím. Méx. 48 (4): 338–346.
  3. Bedford, Robin B.; Draper, Sylvia M.; Noelle Scully, P.; Welch, Samantha L. (2000). "Palladium bis(phosphinite) 'PCP'-pincer complexes and their application as catalysts in the Suzuki reaction". New Journal of Chemistry. 24 (10): 745–747. doi:10.1039/B004793G.
  4. Pandarus, V; Zargarian, D (2007), "New Pincer-Type Diphosphinito (POCOP) Complexes of Nickel", Organometallics, 26 (17): 4321–4334, doi:10.1021/om700400x
  5. Chen, Tao; Yang, Limin; Li, Liang; Huang, Kuo-Wei (2012). "Homocoupling of benzyl halides catalyzed by POCOP–nickel pincer complexes". Tetrahedron. 68 (31): 6152–6157. doi:10.1016/j.tet.2012.05.075.
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