Pak-Hing Leung

Copper(II) complexes of the antitumour-related ligand salicylaldehyde acetylhydrazone (H2L) and the single-crystal X-ray structures of [{Cu(HL)H2O}2] · 2(NO3) and [{Cu(HL) (pyridine) (NO3)}2]

Binary and ternary copper(II) complexes of the ligand salicylaldehyde acetylhydrazone (H2L) have been prepared. In acid or neutral media monoanionic HL complexes separate. Addition of the Lewis bases pyridine (py) and thiourea (tu) to [{Cu(HL)H2O}2] · 2(NO3) results in the monoanionic ternary ligand adducts [{Cu(HL) (py) (NO3)}2] and [Cu(HL) (tu) (NO3)], respectively. With base, the le soluble dianionic complex [{CuL}2] was isolated. Addition of py to [{CuL}2]afforded the dianionic ternary complex [CuL(py)]·12H2O. The complexes have been characterized by a range of physicochemical techniques and the crystal and molecular structures of [{Cu(HL)H2O}2] · 2(NO3) and [{Cu(HL) (py) (NO3)}2] determined. Crystals of [{Cu(HL)H2O}2] · 2 (NO3), C18H22Cu2N6O12, are monoclinic, with space group P21/c, a=7.217(4), b=11.758(8), c=13.764(8) A, β=95.47(4)° and Z=4. [{Cu(HL)H2O}2] · 2 (NO3) is a centrosymmetric (planar) dimer, the monomeric units being bridged through the phenoxy oxygen. The copper atom has a square-pyramidal geometry with the basal donor atoms coming from the tridentate ligand (ONO) and the symmetry-related phenolate (O). The more weakly bound apical donor oxygen is supplied by a coordinated water molecule. The nitrate is not bound. Crystals of [{Cu(HL)(py) (NO3)}2], C28H28Cu2N8O10, are monoclinic, with space group P21/c, a=10.642(3), b=11.796(3), c=13.137(2) A, β=111.03(2)° and Z=4. [{Cu(HL) (py) (NO3)}2] is a weakly interacting centrosymmetric (stacked) dimer, the monomeric units being bridged axially through the phenoxy oxygen. The copper atom has a tetragonal geometry with the equatorial donor atoms coming from the tridentate ligand (ONO) and the pyridine (N). The more weakly bound nitrato anion provides the other axial donor (O). Several of the complexes exhibit interesting magnetic properties.

Direct Synthesis of Chiral Tertiary Diphosphines via Pd(II)-Catalyzed Asymmetric Hydrophosphination of Dienones

A highly diastereo- and enantioselective Pd(II)-catalyzed hydrophosphination of dienones with Ph(2)PH involving formation of double C*-P bonds has been developed, providing a series of chiral tertiary diphosphines (chiral PCP pincer ligands) in high yields. A catalytic cycle for the reaction was proposed.

Versatile chiral palladium(II) complexes for enantiomeric purities of 1,2-diamines

Abstract An efficient NMR determination of the enantiomeric excess of C 2 -symmetric 1,2-diamines can be achieved by coordination of the bidentates to the optically active forms of the diamagnetic [dimethyl(1-(2-naphthyl)ethyl)aminato- C 2 , N ]palladium(II) units.

Palladacycle-Catalyzed Asymmetric Hydrophosphination of Enones for Synthesis of C*- and P*-Chiral Tertiary Phosphines

A highly reactive and stereoselective hydrophosphination of enones catalyzed by palladacycles for the synthesis of C*- and P*-chiral tertiary phosphines has been developed. When Ph(2)PH was employed as the hydrophosphinating reagent, a series of C*-chiral tertiary phosphines were synthesized (C*-P bond formation) in high yields with excellent enantioselectivities, and a single recrystallization provides access to their enantiomerically pure forms. When racemic secondary phosphines rac-R(3)(R(4))PH were utilized, a series of tertiary phosphines containing both C*- and P*-chiral centers were generated (C*-P* bond formation) in high yields with good diastereo- and enantioselectivities. The stereoelectronic factors involved in the catalytic cycle have been revealed.

Asymmetric synthesis of P-stereogenic diarylphosphinites by palladium-catalyzed enantioselective addition of diarylphosphines to benzoquinones.

The reaction of phenyl(2,4,6-trimethylphenyl)phosphine with a substituted benzoquinone in the presence of a chiral phosphapalladacycle complex as a catalyst and triethylamine in chloroform at -45 °C proceeded in a new type of addition manner to give a high yield of a 4-hydroxyphenyl phenyl(2,4,6-trimethylphenyl)phosphinite with 98% enantioselectivity, which is a versatile intermediate readily convertible into various phosphines and their derivatives with high enantiomeric purity.

Asymmetric Synthesis of Enaminophosphines via Palladacycle-Catalyzed Addition of Ph2PH to α,β-Unsaturated Imines

A highly reactive, chemo- and enantioselective addition of diphenylphosphine to α,β-unsaturated imines catalyzed by a palladacycle has been developed, thus providing the access to a series of chiral tertiary enaminophosphines in high yields. A putative catalytic cycle has also been proposed.

NMR assignment of absolute configuration of a P-chiral diphosphine and mechanics of its stereoselective formation

Abstract Two-dimensional rotating-frame nuclear Overhauser enhancement (ROESY) NMR spectra are used to determine the absolute configuration of (+)-diphenyl-phosphine-2,3-dimethyl-7-phenyl-7-phosphabicyclo[2.2.1]hept-2-ene. This diphosphine ligand is obtained from the palladium complex-promoted Diels-Alder reaction between diphenylvinylphosphine and 1-phenyl-3,3-dimethylphosphole in the presence of ( R )-dimethyl(1-(α-naphthyl)ethylamine as the chiral auxiliary. The origin of the stereoselectivity in this asymmetric reaction is also revealed by solution NMR studies.

Facile interconversions between diastereomers of chloro-bridged palladium(II) dimers of orthometallated (±)-dimethyl[1-(1-naphthyl)ethyl]amine

Abstract The important chloro-bridged dipalladium(II) resolving agents (R,R)- and (S,S)-cis-di-μ-chlorobis[1-[1-(dimethylamino)-ethyl]-2-naphthalenyl-C,N]dipalladium, (R,R)- and (S,S)-cis-1, undergo facile rearrangements into unequal mixtures of cis and trans diastereomers upon dissolution in chloroform or dichloromethane, although concentration of the solution in each case affords in high yield the pure cis diastereomer of the dinuclear metal complex as the corresponding mono-solvate in a typical second-order asymmetric transformation. When equimolar solutions of (R,R)-cis- and (S,S)-cis-1 CH2Cl2 in dichloromethane are mixed together, however, an equilibrium is rapidly established between the cis and trans diastereomers of the (R ∗ ,R ∗ )-(±) and ( R ∗ ,S ∗ ) forms of 1 and from which solution configurationally homogeneous (R ∗ ,S ∗ )-trans- 1 · CH 2 Cl 2 crystallizes in high yield by second-order asymmetric transformation. The crystal and molecular structures of (R,R)-cis- 1 · CH 2 Cl 2 and (R ∗ ,S ∗ )-trans- 1 · CH 2 Cl 2 have been determined. The optical purities of the individual enantiomers of (R ∗ ,R ∗ )-(±)- 1 · CH 2 Cl 2 have been determined by reaction with (1R,2S,5R)-menthyldiphenylphosphine or (1S, 2S, 5R)-neomenthyldiphenylphosphine in chloroform-d1 and analysis of the 31P1H NMR spectra of the resulting solutions of the corresponding bridge-split palladium(II)-phosphine epimers.

Chiral Metal Complex-Promoted Asymmetric Hydrophosphinations

This chapter provides an account of the synthesis of a series of chiral tertiary phosphines via the metal complex-assisted asymmetric hydrophosphination methodology which involves secondary phosphines as the nucleophiles. Chiral aza- and phosphapalladacycles are found to function as highly efficient templates or catalysts for the asymmetric P–H addition reaction. The versatile protocol allows for the asymmetric hydrophosphination of olefinic C=C bonds of monophosphines thus yielding a family of tertiary C*-diphosphines as well as C*P*-diphosphines, depending on the nucleophile employed. The addition of two equivalents of HPPh2 to symmetrical bifunctionalized alkynes leading to generation of two new C* centers is also supported. The air-sensitive nucleophiles and the unsaturated substrates containing unprotected functionalities such as aldehyde, keto, ester, cyano, and alcohol can be utilized directly under this mild and facile reaction conditions. The methodology is equally efficient when applied to the generation of P–N ligand systems via hydrophosphination of unsaturated pyridyl-based substrates as well as systems with C=N moieties. The protocol has also the added advantage of allowing the selective formation of 1,1-, 1,2-, and 1,3-diphosphines simply by judicious control of reaction conditions. This reaction can also be extended to the synthesis of chiral triphosphine systems. This synthetic strategy therefore promises to be a versatile approach for the generation of a wide range of chiral tertiary phosphine ligands with potential applications in catalysis.

Asymmetric Synthesis of Diphosphine Ligands Containing Phosphorus and Carbon Stereogenic Centers by Means of a Chiral Palladium Complex Promoted Hydrophosphination Reaction

An organopalladium complex containing ortho-metalated (R)-(1-(dimethylamino) ethyl)naphthalene as the chiral auxiliary has been used to promote the asymmetric hydrophosphination reaction between diphenylphosphine and phenyldi[(Z)-prop-1-enyl]phosphine in high regio- and stereoselectivity under mild conditions. The hydrophosphination reaction generated only two diastereomers in a ratio of 1:1. The two hydrophosphination products contained both phosphorus and carbon stereogenic centers and were subsequently isolated by fractional crystallization. Their absolute stereochemistries were analyzed by X-ray crystallography. The naphthylamine auxiliary could be removed chemoselectively from the template products by treatment with concentrated hydrochloric acid to form the corresponding optically pure neutral dichloro complexes. Subsequently, the dichloro complexes underwent ligand displacement with aqueous cyanide to generate the optically pure diphosphine ligands in high yields.