Pincer-type ligand having acridane structure and metal complex using the same

Abstract

Disclosed are a pincer-type ligand having a structurally rigid acridane structure and a metal complex consisting of the pincer-type ligand and a metal bound to each other, and exhibiting high reactivity and stability during a variety of bonding activation reactions. T-shaped complexes can be prepared from .sup.acriPNP(4,5-bis(diisopropylphosphino)-2,7,9,9-tetramethyl-9H-acridin-10-ide), which is a pincer-type PNP ligand having an acridane structure, and metal complexes, which can be structurally rigid and thus exhibit excellent reactivity and stability based on minimized structural change thereof, can be prepared by introducing an acridane structure into the backbone thereof. The PNP ligand is structurally stable and has novel chemical properties, as compared to conventional similar ligands, and thus can be utilized in a wide range of catalytic reactions and material chemistry.

Claims

1. A metal complex in which the PNP ligand having an acridane structure represented by a following Chemical Formula 1 and a metal are bound to each other: ##STR00018## wherein R, R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each independently hydrogen, a C1 to C20 alkyl group, a halogen-substituted C1 to C20 alkyl group, a C2 to C20 alkenyl group, a halogen-substituted C2 to C20 alkenyl group, a C1 to C20 alkoxy group, a halogen-substituted C1 to C20 alkoxy group, a C3 to C20 cycloalkyl group, a halogen-substituted C3 to C20 cycloalkyl group, a C6 to C40 aryl group, a C5 to C40 heteroaryl group, halogen, C1 to C20 alkylamine, C6 to C40 arylamine, C7 to C60 alkylarylamine, a C1 to C20 thioalkyl group, a C6 to C40 thioaryl group, C1 to C20 alkyl phosphine or C6 to C40 aryl phosphine, with the proviso that when each R is C6 aryl, then R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are not all hydrogen, wherein the metal is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo.

2. The metal complex of claim 1, wherein the PNP ligand is represented by a following Chemical Formula 1-1: ##STR00019##

3. The metal complex of claim 1, wherein the metal complex is represented by (PNP)MX.sub.n, wherein n=0, 1, 2 or 3, and X is ABC, wherein A, B and C are each independently represented by a monodentate ligand or bidentate ligand.

4. The metal complex of claim 1, wherein the metal complex is represented by following Chemical Formula 2 or Chemical Formula 3: ##STR00020## wherein M is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo, and X is Cl, Br, OTf, ClO.sub.4 or OAc, ##STR00021## wherein M is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo.

5. The metal complex of claim 1, wherein the metal complex is selected from the group consisting of Chemical Formulas 2-1 to 2-5 and Chemical Formula 3-1: ##STR00022## ##STR00023##

6. A method of preparing a metal complex represented by a Chemical Formula 2, comprising: (a) producing a compound of Chemical Formula 5 by reacting a compound of Chemical Formula 4 with 3 equivalents of alkyl lithium, aryl lithium or a Grignard reagent and 2 equivalents of one compound selected from the group consisting of halogen-substituted alkyl phosphine or aryl phosphine; and (b) producing a metal complex of Chemical Formula 2 by adding MX.sub.n, wherein M is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo, and X is Cl, Br, OTf, ClO.sub.4 or OAc, to the compound of Chemical Formula 5 to induce metallation: ##STR00024## wherein M is Fe, Co, Ni, Co, Pd or Pt, and X is Cl, Br, OTf or OAc. ##STR00025##

7. A method of preparing a metal complex represented by a Chemical Formula 3, comprising: (a) producing a compound of Chemical Formula 5 by reacting a compound of Chemical Formula 4 with 3 equivalents of alkyl lithium, aryl lithium or a Grignard reagent and 2 equivalents of one compound selected from the group consisting halogen-substituted alkyl phosphine or aryl phosphine; (b) producing a metal complex of Chemical Formula 2 by adding MX2, wherein M is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo, and X is Cl, Br, OTf, ClO.sub.4 or OAc, to the compound of Chemical Formula 5 to induce metallation; and (c) producing a metal complex of Chemical Formula 3 by adding a reducing agent to the metal complex of Chemical Formula 2, ##STR00026## wherein M is AI, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo, and X is Cl, Br, OTf, ClO.sub.4 or OAc; ##STR00027## wherein M is AI, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo. ##STR00028##

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

(2) The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

(3) FIG. 1 schematically shows an electronic structure of D.sub.3h and a T-shaped morphology structure of the d.sup.9 system (a) and SOMO of d.sup.7 Rh porphyrin species and C—H bond activation (b);

(4) FIG. 2 shows a synthesis process of Compound 3 according to the present invention (a) and crystal structures of Compound 1 (b), Compound 2 (c) and Compound 3 (d) (wherein thermal ellipsoids are set at a probability of 50%, and co-crystallized C.sub.10H.sub.8 molecules and hydrogen atoms are omitted for clarity);

(5) FIG. 3 is a cyclic voltammogram (a) of Compound 2 in THF according to the present invention, an X-band EPR spectrum (b) of Compound 3, and a Mulliken atomic spin density plot (c), wherein Ni 72.6%, P1 7.8%, P2 7.8%, N 6.8%;

(6) FIG. 4 shows various metalloradical reactivity allowing for use of Compound 3 according to the present invention;

(7) FIG. 5 shows SOMO of Compound 3 according to the present invention; SOMO of Compound 3 (a), (.sup.acriPNP)Ni and SOMO of Compound 4 (b), (.sup.acriPNP)Ni(THF) (c), and electronic structures of Compound 3, (.sup.acriPNP)Ni(THF) and Compound 4 (d);

(8) FIG. 6 shows a chemical structure and of (.sup.acriPNP)Ni(py) of Compound 5 according to the present invention, a crystal structure of (.sup.acriPNP)NiCO of Compound 6 (a) and crystal structure of (.sup.acriPNP)Ni(PMe.sub.3) of Compound 7 (wherein thermal ellipsoids are set at a probability of 50%, and C.sub.10H.sub.8 molecules and hydrogen atoms are omitted for clarity), and X-band EPR spectra collected at 113K for Compounds 5, 6 and 7 (c, d and e); and

(9) FIG. 7 shows crystal structures of Compound 8 {(.sup.acriPNP)Ni}.sub.2(μ-C.sub.2H.sub.4) (a), Compound 9 (.sup.acriPNP)Ni(CH.sub.3) (b), Compound 10 {(.sup.acriPNP)Ni}.sub.2(μ-CO.sub.2) (c) and Compound 11 (.sup.acriPNP)Ni(CN) (d) according to the present invention (wherein thermal ellipsoids are set at a probability of 50% and hydrogen atoms are omitted).

BEST MODE FOR CARRYING OUT THE INVENTION

(10) Unless defined otherwise, all technical and scientific terms used herein have the same meaning as those appreciated by those skilled in the field to which the present invention pertains. In general, nomenclature used herein is well-known in the art and is ordinarily used.

(11) As a result of intensive efforts to solve the aforementioned problems, the present inventors have found that T-shaped complexes can be prepared from .sup.acriPNP ligand (4,5-bis(diisopropylphosphino)-2,7,9,9-tetramethyl-9H-acridin-10-ide), which is a pincer-type PNP ligand having an acridane structure, and that metal complexes, which can be structurally rigid and thus exhibit excellent reactivity and stability based on minimized structural change thereof, can be prepared by introducing an acridane structure into the backbone thereof.

(12) In one aspect, the present invention provides .sup.acriPNP (4,5-bis(diisopropylphosphino)-2,7,9,9-tetramethyl-9H-acridin-10-ide), which is an acridane-based PNP ligand having the backbone into which an acridane moiety is introduced, and a metal complex including the PNP ligand and a metal bound to each other.

(13) In another aspect, the present invention is directed to a PNP ligand having an acridane structure represented by the following Chemical Formula 1:

(14) ##STR00007##

(15) wherein R, R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each independently hydrogen, a C1 to C20 alkyl group, a halogen-substituted C1 to C20 alkyl group, a C2 to C20 alkenyl group, a halogen-substituted C2 to C20 alkenyl group, a C1 to C20 alkoxy group, a halogen-substituted C1 to C20 alkoxy group, a C3 to C20 cycloalkyl group, a halogen-substituted C3 to C20 cycloalkyl group, a C6 to C40 aryl group, a C5 to C40 heteroaryl group, halogen, C1 to C20 alkylamine, C6 to C40 arylamine, C7 to C60 alkylarylamine, a C1 to C20 thioalkyl group, a C6 to C40 thioaryl group, C1 to C20 alkyl phosphine or C6 to C40 aryl phosphine.

(16) Regarding R, R.sup.1, R.sup.2, R.sup.3 and R.sup.4, preferred examples of the C1 to C20 alkyl group include methyl, ethyl, propyl, pentyl, hexyl, isopropyl, butyl, sec-butyl, tert-butyl groups and the like, preferred examples of the C2 to C20 alkenyl group include vinyl, allyl, 1-butenyl, 2-butenyl, 3-butenyl and isobutenyl groups and the like, and preferred examples of the halogen-substituted C1 to C20 alkyl group include C1 to C4 alkyl groups substituted by at least one fluorine, chlorine, bromine or iodine atom, such as, fluoromethyl, difluoromethyl, trifluoromethyl, pentafluoroethyl, 1,1-difluoroethyl and trichloromethyl groups, but are not limited thereto.

(17) The C1 to C20 alkoxy group includes oxygen substituted by one of the aforementioned C1 to C20 alkyl groups, and the halogen includes fluorine, chlorine, bromine and iodine.

(18) The C6 to C40 arylamine includes phenyl, naphthyl, phenanthryl, anthracyl, indenyl, azulenyl, biphenyl, biphenylenyl or fluorenyl group or the like.

(19) The C1 to C20 alkylamine may be primary alkylamine, secondary alkylamine or tertiary alkylamine, the C6 to C40 arylamine may be primary arylamine, secondary arylamine or tertiary arylamine, and the C7 to C60 alkylarylamine may be secondary alkylarylamine, tertiary dialkylarylamine, or tertiary alkylarylamine.

(20) The C1-C20 thioalkyl includes methylthio, ethylthio, propylthio, 1-methylethylthio, butylthio, 1-methylpropylthio, 2-methylpropylthio, 1,1-dimethylethylthio, pentylthio, 1-methylbutylthio, 2-methylbutylthio, 3-methylbutylthio, 2,2-dimethylpropylthio, 1-ethylpropylthio, hexylthio, 1,1-dimethylpropylthio, 1,2-di-methylpropylthio, 1-methylpentylthio, 2-methylpentylthio, 3-methylpentylthio, 4-methylpentylthio, 1,1-dimethylbutylthio, 1,2-dimethylbutylthio, 1,3-dimethylbutylthio, 2,2-dimethylbutylthio, 2,3-dimethylbutylthio, 3,3-dimethylbutylthio, 1-ethylbutylthio, 2-ethylbutylthio, 1,1,2-trimethylpropylthio, 1,2,2-trimethylpropylthio, 1-ethyl-1-methylpropylthio, 1-ethyl-2-methylpropylthio, or the like, but is not limited thereto.

(21) The PNP ligand according to the present invention may be represented by the following Chemical Formula 1-1:

(22) ##STR00008##

(23) In another aspect, the present invention is directed to a metal complex including the PNP ligand and a metal bound to each other.

(24) The metal complex according to the present invention may be represented by (PNP)MX.sub.n (wherein n=0, 1, 2 or 3, and X is ABC, in which A, B and C are each independently represented by a monodentate ligand or bidentate ligand.

(25) A preferred example of the metal complex according to the present invention may be represented by Chemical Formula 2 or Chemical Formula 3:

(26) ##STR00009##

(27) wherein M is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo, and X is Cl, Br, OTf, ClO.sub.4 or OAc;

(28) ##STR00010##

(29) wherein M is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo.

(30) A more preferred example of the metal complex according to the present invention may be selected from the group consisting of Chemical Formulas 2-1 to 2-5 and Chemical Formula 3-1:

(31) ##STR00011## ##STR00012##

(32) In another aspect, the present invention is directed to a method of preparing a metal complex represented by the following Chemical Formula 2, including:

(33) (a) producing a compound of Chemical Formula 5 by reacting a compound of Chemical Formula 4 with 3 equivalents of alkyl lithium, aryl lithium or a Grignard reagent and 2 equivalents of one compound selected from the group consisting of halogen-substituted alkyl phosphine or aryl phosphine and linear ether, cyclic ether, alkyl amine, aryl amine and a sulfur compound; and

(34) (b) producing a metal complex of Chemical Formula 2 by adding MX.sub.2, wherein M is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo, and X is Cl, Br, OTf, ClO.sub.4 or OAc, to the compound of Chemical Formula 5 to induce metalation:

(35) ##STR00013##

(36) wherein M is Fe, Co, Ni, Co, Pd or Pt, and X is Cl, Br, OTf, ClO.sub.4 or OAc.

(37) ##STR00014##

(38) In a preferred embodiment, the method may include: (a) reacting the compound of Chemical Formula 4 with 3 equivalents of n-BuLi and 2 equivalents of i-Pr.sub.2PCl and THF to produce a compound of Chemical Formula 5; and (b) adding MX.sub.2 (wherein M is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo, and X is Cl, Br, OTf, ClO.sub.4 or OAc) to the compound of Chemical Formula 5 to induce metalation and thereby produce a metal complex of Chemical Formula 2.

(39) In another aspect, the present invention is directed to a method of preparing a metal complex represented by the following Chemical Formula 3, including:

(40) (a) producing a compound of Chemical Formula 5 by reacting a compound of Chemical Formula 4 with 3 equivalents of alkyl lithium, aryl lithium or a Grignard reagent and 2 equivalents of one compound selected from the group consisting halogen-substituted alkyl phosphine or aryl phosphine and linear ether, cyclic ether, alkyl amine, aryl amine and a sulfur compound;

(41) (b) producing a metal complex of Chemical Formula 2 by adding MX.sub.2, wherein M is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo, and X is C1, Br, OTf or OAc, to the compound of Chemical Formula 5 to induce metalation; and

(42) (c) producing a metal complex of Chemical Formula 3 by adding a reducing agent to the metal complex of Chemical Formula 2,

(43) ##STR00015##

(44) wherein M is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo, and X is Cl, Br, OTf, ClO.sub.4 or OAc;

(45) ##STR00016##

(46) wherein M is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo.

(47) ##STR00017##

(48) In a preferred embodiment, the method may include: (a) reacting the compound of Chemical Formula 4 with 3 equivalents of n-BuLi and 2 equivalents of i-Pr2PCl and THF to produce a compound of Chemical Formula 5; (b) adding MX.sub.2 (wherein M is Al, Cr, Fe, Co, Ti, W, Si, Ir, Rh, Pt, Pd, Ru, Th, Ni, Cu, V, Au, Re, Zr or Mo, and X is Cl, Br, OTf, ClO.sub.4 or OAc) to the compound of Chemical Formula 5 to induce metalation and thereby produce a metal complex of Chemical Formula 2; and (c) a reducing agent including NaC.sub.10H.sub.8 as well as LiC.sub.10H.sub.8, KC.sub.10H.sub.8, Li(Hg), Na(Hg), K(Hg), Li(anthracene), Na(anthracene), K(anthracene), Li, Na, K, Li(benzophenone), Na(benzophenone), K(benzophenone), Li(acenaphthalene), Na(acenaphthalene), K(acenaphthalene), LiC.sub.8, NaC.sub.8 or KC.sub.8 to the metal complex of Chemical Formula 2 to produce a metal complex of Chemical Formula 3.

(49) Hereinafter, the present invention will be described in more detail with reference to examples. However, it is obvious to those skilled in the art that these examples are provided only for illustration of the present invention and should not be construed as limiting the scope of the present invention.

EXAMPLE

Example 1: Preparation of Ligand and Metal Complex

(50) For ligand synthesis, 4,5-dibromo-2,7,9,9-tetramethyl-9,10-dihydroacridine) was prepared (H. Liu et al., Lett. Org. Chem. 2010, 7, 114). The phosphine arm was installed by lithiation with PiPr.sub.2Cl and subsequent phosphorylation. The .sup.acriPNP ligand was isolated as a lithium adduct with the THF molecule, (.sup.acriPNP)Li(THF) (Compound 1 of FIG. 2) in an appropriate yield (55%). In the .sup.31P NMR spectrum, Compound 1 shows a quartet peak at 3.3 ppm (.sup.1J.sub.PLi=55 Hz), which indicates that two phosphorus donors are coordinated symmetrically to the lithium ion. X-ray diffraction studies show that the .sup.acriPNP ligand is prone to planarity (FIG. 2(b) and Table 1).

(51) TABLE-US-00001 TABLE 1 Selected bond lengths and angles of 1, 2, and 3. Parameter 1 2 3 d.sub.M-N [Å] 1.952(4) 1.894(2) 1.943(1) d.sub.M-P [Å] 2.495(4) 2.1821(6) 2.1980(5) 2.499(4) 2.1797(6) d.sub.M-L [Å] 1.919(4).sup.[a] 2.1767(6).sup.[b] —  N-M-L [°] 117.6(2).sup.[a] 178.88(6).sup.[b] —  P-M-P [°] 130.8(2) 171.61(2) 171.39(2)  N-M-P [°] 81.4(2) 86.78(5) 87.06(9) 82.2(2) 86.67(5) .sup.[a]L = O. .sup.[b]L = Cl.

(52) The reaction of Compound 1 with NiCl.sub.2 in THF results in generation of (.sup.acriPNP)NiCl (Compound 2 of FIG. 2) as a green powder with a yield of 81%. The .sup.31P NMR spectrum showed a single peak at 41.0 ppm and the solid state structure of Compound 2 showed that the .sup.acriPNP ligand had a square planar structure (τ.sub.4=0.07, FIG. 2(c)). One reversible wave at 0.13V and two irreversible waves at −2.28 and −2.80V, were shown, as compared with Fc/Fc.sup.+(Fc=[(η−C.sub.5H.sub.5).sub.2Fe]).

(53) The Mindiola group reported a similar (PNP)NiCl complex (PNP.sup.−=.sup.−N[2-P.sup.iPr.sub.2-4-Me-C.sub.6H.sub.3].sub.2) which shows an irreversible Ni.sup.II/I couple at 2.48V, producing a dimeric Ni.sup.I species, {(μ.sub.2-PNP)Ni}.sub.2 (D. Adhikari et al., Inorg. Chem. 2008, 47, 10479; D. Adhikari et al., J. Am. Chem. Soc. 2008, 130, 3676; b) V. Vreeken et al., Angew. Chem. Int. Ed. 2015, 54, 7055; Angew. Chem. 2015, 127, 7161). In contrast, Compound 2 does not produce any dimeric species after chemical reduction. The new brown species was immediately produced upon addition of one equivalent of NaC.sub.10H.sub.8 and exhibited a semi-permanently shifted .sup.1H NMR spectrum. The nickel (I) species, (.sup.acriPNP)Ni (Compound 3) with neutral naphthalene molecules co-crystallized during recrystallization of a pentane solution was obtained in a yield of 72%. The solid state structure showed that the nickel center had a T-shaped geometry (FIG. 2(d)). Dimer formation of Compound 3 was completely inhibited. As a result, the acridane skeleton of the present invention is supported. Since the .sup.acriPNP ligand is pre-organized, Compound 3 has an almost perfect T-type structure with L-M-L angles of 87.06 (9), 87.06 (9) and 171.39 (2)° (Table 1). A similar 3-coordinate nickel complex supported by the pincer-type ligand, (.sup.SiPNP)Ni(.sup.SiPNP)═(R.sub.2PCH.sub.3SiMe.sub.2).sub.2N.sup.− was reported by Caulton (M. J. Ingleson et al., Inorg. Chem. 2008, 47, 407). In this case, because the bite angle of two phosphines is greater than about 190° and the silicon atoms of the ligand backbone are large, the nickel is surrounded and protected by the ligand. Surprisingly, there is no intramolecular or intermolecular interaction at the coordination sites available for the nitrogen donors, although the 3-coordinate nickel ion of Compound 3 is considerably exposed. The closest H atom of the co-crystallized naphthalene in the crystal lattice is 2.926 Å from Ni.

(54) Compound 3 exhibits an S=1/2 ground state according to Evans' method (μ.sub.eff=1.78 μB at C.sub.6D.sub.6) and X-band electron paramagnetic resonance (EPR) spectroscopic data (g=1.99, 2.22, 2.33, FIG. 3(b)). DFT calculations using the Mulliken population analysis performed on Compound 3 suggest that about 73% of unpaired spins are positioned on the Ni phase (FIG. 3(c)). Accordingly, the T-shaped Ni.sup.I center has a d.sub.x.sub.2.sub.-y.sub.2 orbital that is half-filled with a singly occupied molecular orbital (SOMO) (M. J. Ingleson et al., Inorg. Chem. 2008, 47, 407; C. Yoo et al., Chem. Sci. 2014, 5, 3853). This is because the addition of the fourth ligand is difficult in consideration of energy due to the σ-antibonding property of SOMO. Possible binding of σ-donors such as THF, NMe.sub.3 and NEt.sub.3 was tested, but the formation of adducts could not be detected (FIG. 4). The geometric optimization of (.sup.acriPNP)Ni(THF) could not stabilize the Ni—O bond through DFT calculations and the THF molecules remained unbound. The optimized structure of (.sup.acriPNP)Ni(THF) obtained by freezing Ni—O bonds showed a significant increase in SOMO energy level, as compared to Compound 3 (FIG. 5).

(55) π-accepting ligands such as pyridine bind to Compound 3, possibly using stabilization associated with π-backdonation. Addition of one equivalent of pyridine to a solution of 3.C.sub.10H.sub.8 in C.sub.6D.sub.6 resulted in a new paramagnetic shift resonance with the absence of free pyridine signals in the .sup.1H NMR spectrum. Formation of (.sup.acriPNP)Ni(py) was confirmed from the frozen solution X-band EPR data representing the new axial signals (g=2.00, 2.09, FIG. 6(c)). Bonding of pyridine is reversible, while stronger pi-accepting ligands such as CO and PMe.sub.3 are irreversibly adjusted, so (.sup.acriPNP)Ni(CO) (Compound 6) and (.sup.acriPNP)Ni(PMe.sub.3) (Compound 7), which are stable 4-coordinate species, are produced, respectively (FIG. 6). The CO vibration of Compound 4 at 1,936 cm.sup.−1 indicates an important π-back donation phenomenon for CO of Compound 4. The X-ray structures for Compounds 6 and 7 showed that two nickel centers had pyramidal geometries (τ4=0.50 and 0.37, respectively, L. Yang et al., Dalton Trans. 2007, 955). The average angles between planes of the two aryl rings are 9.08° (4) and 37.25° (5), and the distances between the nickel ions and the .sup.acriPNP plane thereof are 0.699 Å (4) and 0.609 Å (5). This geometric change reduces the M-L anti-bonding interaction in the SOMO identified in the DFT analysis (FIG. 5).

(56) T-shaped metal radical Ni.sup.I complexes were used to evaluate reactivity to the substrate. Because Compound 3 has a considerably exposed center of nickel with half-filled d.sub.x.sub.2.sub.-y.sub.2 orbital, one electron oxidation of the metal readily occurs with formation of the nickel-ligand bond. Substrates containing double bonds such as C.sub.2H.sub.4 and CO.sub.2 easily produced dinuclear Ni.sup.II species {(.sup.acriPNP)Ni}.sub.2(μ-C.sub.2H.sub.4)) (Compound 8) and {(.sup.acriPNP)Ni}.sub.2(μ-CO.sub.2) (Compound 10), respectively. The XRD structure clearly shows that the C.sub.2H.sub.4 moiety is reduced by two electrons; C.sub.sp3-C.sub.sp3 exhibits a single bond property (dc−c=1.538 (6), FIG. 7(a)). This process is reversible and Compound 6 loses ethylene at room temperature under vacuum. Binuclear reduction of C.sub.2H.sub.4 and CO.sub.2 by transition metal complexes occurs infrequently (B. de Bruin et al., Organometallics 2002, 21, 4312; M. Devillard et al., J. Am. Chem. Soc. 2016, 138, 4917). Although C.sub.2H.sub.4 activation was previously reported by Ir and Os complexes (B. de Bruin et al., Organometallics 2002, 21, 4312), this is the first example of C.sub.2H.sub.4 reduction performed by the transition metal of the first row. Previous dinuclear CO.sub.2 activation was performed by a two-electron process in a single metal center, while other metal centers acted as Lewis acids (M. Devillard et al., J. Am. Chem. Soc. 2016, 138, 4917).

(57) This binuclear 2-electron process can be carried out by using more challenging sigma-bonds for hemolytic cleavage (FIG. 4). Interestingly, Compound 3 reacts with H.sub.2 (1 atm) at room temperature to produce (.sup.acriPNP)NiH (Compound 12), which is a characteristic hydride resonance at −17.22 ppm (t, J.sub.PH=62.4 Hz) of the .sup.1H NMR spectrum. The reaction is believed to involve the interaction between two metal radicals having one H.sub.2 molecule through four central transition states (BB Wayland et al., J. Am. Chem. Soc. 1991, 113, 5305; BB Wayland et al., Inorg. Chem., 1992, 31, 148). Since one meridional site transfer to the nitrogen donor of the PNP ligand is empty, the transient interaction between the SOMO (d.sub.x.sub.2.sub.-y.sub.2) of Compound 3 and the σ* orbital of the H—H bond should be easy. Thus, the geometrical and electronic structures of Compound 3 depend on homolytic degradation of sigma-bonds. The weak O—H, S—S, and C—I bonds were easily cleaved to produce the corresponding Ni.sup.II complexes (FIG. 4), which was confirmed by comparing the .sup.1H and .sup.31P NMR spectra with the corresponding independently prepared complexes. Surprisingly, (PNP)NiNH.sub.2 is produced immediately after the addition of hydrazine. N—N σ-bond of N.sub.2H.sub.4 decomposition by protonation, deprotonation or disproportionation has been previously reported, but direct homogeneous decomposition is not known.

(58) In fact, the addition of acetonitrile to Compound 3 causes unexpected results shown in FIG. 7 through C—C bond cleavage to form (.sup.acriPNP)NiMe (compound 9) and (.sup.acriPNP)NiCN (compound 10). C—C bond activation of acetonitrile is a difficult issue due to strong bond dissociation energy (133 kcalmol.sup.−1) thereof. To date, various metal complexes have been known to activate the C—C bond of CH.sub.3CN, but high temperature, irradiation or the addition of Lewis acid is required. C—C bond activation using Compound 3 occurs immediately under ambient conditions mediated by an open-shell d.sup.9 T-shaped nickel center.

(59) In conclusion, a certain three-coordinate Ni.sup.I complex (Compound 3) was synthesized using .sup.acriPNP.sup.−, a strong pincer-type ligand. Stable T-shaped Ni.sup.I species can be produced due to rigidity of .sup.acriPNP.sup.−. Despite the vacancy site of Compound 3, the coordination of the sigma-donor is invisible due to the σ-anti-bonding property of SOMO (d.sub.x.sub.2.sub.-y.sub.2) of the d.sup.9 center. Coordination of the π-acidic ligands is possible, but results in a structural change to a more stable pyramidal form. When having a sterically-exposed half-filled, d.sub.x.sub.2.sub.-y.sub.2 orbital, formation of the bond between the substrate and Compound 3 is combined with the oxidation process of the metal, which reduces unsaturated molecules (C.sub.2H.sub.4 and CO.sub.2). Finally, metal radicals can be more effectively utilized due to homogeneous decomposition of σ-bonds in the substrate such as H.sub.2N—NH.sub.2 and H.sub.3C—CN.

INDUSTRIAL APPLICABILITY

(60) The acridane-based PNP ligand according to the present invention is structurally stable and has novel chemical properties, as compared to conventional similar ligands, and thus can be utilized in a wide range of catalytic reactions and material chemistry. Therefore, metal complexes containing the acridane-based PNP ligand can be utilized in a variety of applications including organic and inorganic catalysis, polymer reactions, and material chemical industries. When new reactions replacing conventional catalysts can be developed and industrialized, based on this, considerably high economic and industrial value can be obtained.

(61) Although specific configurations of the present invention have been described in detail, those skilled in the art will appreciate that this description is provided as preferred embodiments for illustrative purposes and should not be construed as limiting the scope of the present invention. Therefore, the substantial scope of the present invention is defined by the accompanying claims and equivalents thereto.