POCOP is a type of

pincer ligand In chemistry, a transition metal pincer complex is a type of coordination complex with a pincer ligand. Pincer ligands are chelating agents that binds tightly to three adjacent coplanar sites in a meridional configuration. The inflexibility of t ...

. 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 In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used ...

) bond and two

phosphinite In organic chemistry, phosphinites are organophosphorus compounds with the formula . They are used as ligands in homogeneous catalysis and coordination chemistry. Preparation Phosphinites are prepared by alcoholysis of organophosphinous chlori ...

ligands. The term POCOP is used both for the ligand, with formula C₆H₄(OPPh₂)₂, and its complexes, with formula C₆H₃(OPPh₂)₂]⁻ (Ph = phenyl, C₆H₅)

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. The parent POCOP ligand is prepared by treating

resorcinol Resorcinol (or resorcin) is a phenolic compound. It is an organic compound with the formula C6H4(OH)2. It is one of three isomeric benzenediols, the 1,3-isomer (or ''meta- (chemistry), meta''-isomer). Resorcinol crystallizes from benzene as co ...

with

chlorodiphenylphosphine Chlorodiphenylphosphine is an organophosphorus compound with the formula (C6H5)2PCl, abbreviated Ph2PCl. It is a colourless oily liquid with a pungent odor that is often described as being garlic-like and detectable even in the ppb range. It is ...

: :C₆H₄(OH)₂ + 2 ClPPh₂ → C₆H₄(OPPh₂)₂ + 2 HCl Related ligands can be prepared from chlorodiisopropylphosphine. 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. There can also be variable conformations of POCOP pertaining to the various R groups branching off of the donor atoms. 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. 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. Because of relatively small P-Ni-P bond angle the otherwise Ni complexes exhibit a slight tetrahedral distortion.

Catalytic reaction

Pincer ligand In chemistry, a transition metal pincer complex is a type of coordination complex with a pincer ligand. Pincer ligands are chelating agents that binds tightly to three adjacent coplanar sites in a meridional configuration. The inflexibility of t ...

s participate in a variety of organic transformation, such as the

hydrosilylation Hydrosilylation, also called catalytic hydrosilation, describes the addition of Si-H bonds across unsaturated bonds."Hydrosilylation A Comprehensive Review on Recent Advances" B. Marciniec (ed.), Advances in Silicon Science, Springer Science, 200 ...

, and

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...

oligomer In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relativ ...

izations, and homocoupling of benzyl halides.{{cite journal , doi = 10.1016/j.tet.2012.05.075 , title = Homocoupling of benzyl halides catalyzed by POCOP–nickel pincer complexes , journal = Tetrahedron , volume = 68 , issue = 31 , pages = 6152–6157 , year = 2012 , last1 = Chen , first1 = Tao , last2 = Yang , first2 = Limin , last3 = Li , first3 = Liang , last4 = Huang , first4 = Kuo-Wei Ni PCP pincer complexes promote sulfur-carbon forming reactions.

References

Phosphinites