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
CAS Number	279214-81-2
3D model (JSmol)	Interactive image
ChemSpider	9345060
PubChem CID	11169966
UNII	RV3YH2Y6FP Y
CompTox Dashboard (EPA)	DTXSID301241325
InChI 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
SMILES O(c3cccc(OP(c1ccccc1)c2ccccc2)c3)P(c4ccccc4)c5ccccc5
Properties
Chemical formula	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]