Synthesis of ortho-phenyl substituted MeO-BIPHEP ligand and its application in Rh-catalyzed asymmetric hydrogenation

A new BIPHEP-type ligand with phenyl groups at the 3,3′-positions, o-Ph-MeO-BIPHEP 3 was prepared. This ligand afforded excellent enantioselectivities when used in the Rh-catalyzed asymmetric hydrogenation of α-dehydroamino acid derivatives. The strong influence of o-phenyl groups of the ligand on the enantioselectivities of the reaction has been demonstrated by a comparison with its parent ligand MeO-BIPHEP.     

Determination of absolute configuration of 2-methyl-1-(o-tolyl)naphthalene and the related axially chiral biaryls

An enantiomerically enriched sample (84.3% ee) of (aS)-2-methyl-1-[(((o-triisopropylsilyl)oxy)methyl)phenyl]naphthalene was produced via catalytic asymmetric Suzuki-Miyaura cross-coupling using an atropisomeric naphthamide-derived phosphine (A²phos) as the chiral ligand. After one recrystallization, enantiopurity of the biaryl product was improved to 98.9% ee and its absolute configuration was determined by X-ray crystal structural analysis. Through chemical transformations, the (aS)-enantiomers of 1-[(o-hydroxymethyl)phenyl]-2-methylnaphthalene, 1-[(o-chloromethyl)phenyl]-2-methylnaphthalene, and 2-methyl-1-(o-tolyl)naphthalene were obtained. Several other chiral biaryls were synthesized and stereochemically assigned.     

π-Selective stationary phases: (III) Influence of the propyl phenyl ligand density on the aromatic and methylene selectivity of aromatic compounds in reversed phase liquid chromatography

The retention characteristics of phenyl type stationary phases for reversed phase high performance liquid chromatography are still largely unknown. This paper explores the retention process of these types of stationary phases by examining the retention behaviour of linear PAHs and n-alkylbenzenes on a series of propyl phenyl stationary phases that have changes in their ligand density (1.23, 1.31, 1.97, 2.50 μmol m⁻²). The aromatic and methylene selectivities increased with increasing ligand density until a point where a plateau was observed, overall the propyl phenyl phases had a higher degree of aromatic selectivity than methylene selectivity indicating that these columns are suitable for separations involving aromatic compounds. Also, retention characteristics relating to the size of the solute molecule were observed to be influenced by the ligand density. It is likely that the changing retention characteristics are caused by the different topologies of the stationary phases at different ligand densities. At high ligand densities, the partition coefficient became constant.     

Quantum chemical modeling of the stability of reduced forms of Roussin’s red esters. Effect of the nature of the ligand

The reduced forms of Roussin’s red esters [Fe₂(μ-RS)₂(NO)₄]n? (n = 1, 2; R = Ph, Pr) and their possible decomposition products were studied by quantum chemical calculations. The energy diagram of the processes that occur in a dichloromethane solution was constructed. According to this diagram, the monoanions are much more stable than the corresponding dianions. Possible dissociation paths of the dianions in solution were proposed. The anions with the propyl ligand are more stable than the anions with the phenyl ligand.     

Effect of N1-substituted pyrazolic hybrid ligands on palladium catalysts for the Heck reaction

In this paper we have explored the influence of several linkers present on the [PdCl₂(L)] complexes, where L is 3,5-dimethylpyrazolic hybrid ligand N1-substituted by polyether chains and/or phenyl groups. These complexes have been used as pre-catalysts in the Heck reaction between phenyl halides and tert-butyl acrylate. The corresponding complexes efficiently catalyze the Heck olefination and provide good yields under phosphine-free conditions, even for aryl chlorides. Different reaction conditions were investigated and it was found that the nature of the ligand has an important influence on the effectiveness of the catalytic system. Ligand 1,8-bis(3,5-dimethyl-1H-pyrazol-1-yl)-3,6-dioxaoctane (L1), which has previously shown to be the most flexible and versatile, achieved high turnover numbers within very short reaction times and low catalyst loadings.     

An efficient phosphorus-containing oxazoline ligand derived from cis-2-amino-3,3-dimethyl-1-indanol: application to the palladium-catalyzed asymmetric Heck reaction

Enantiopure 2-[2-(diphenylphosphino)phenyl]oxazoline, derived from a non-natural chiral aminoalcohol, cis-2-amino-3,3-dimethyl-1-indanol, was found to be an efficient ligand for the palladium-catalyzed asymmetric Heck reaction.     

Effect of added donor ligands on the selective oxygenation of organic sulfides by oxo(salen)chromium(V) complexes

Oxo(salen)chromium(V) complexes, [(salen)Cr^VO]⁺, oxidize organic sulfides selectively to sulfoxides in high yield. This oxygenation reaction is catalyzed by ligand oxides (LO's), pyridine N-oxide, 4-picoline N-oxide, 4-phenyl pyridine N-oxide and triphenylphosphine oxide. The rate is accelerated by 10-20 times with an increase in yield of sulfoxide in less reaction time. This catalytic activity is highly sensitive to the nature of the substituent in the phenyl ring of ArSMe and in the 3- and 5-position of the salen ligand. The reaction constant (ρ) value obtained with the ligand oxide catalyzed reaction is low compared to the value in the absence of LO. The strong binding and catalytic activity of ligand oxides on the oxo(salen)chromium(V) ion oxygenation is explained in terms of binding constants and a mechanism involving the electrophilic attack of [(salen)Cr^VO]⁺-LO adduct on the sulfur centre of phenyl methyl sulfide.     

Dialkylzinc additions with a chiral osmaimidazolidine ligand from asymmetric diamination of olefins

A new chiral ligand was prepared in a convenient two-step procedure starting from an asymmetric diamination reaction. Subsequent treatment of the resulting osmaimidazolidine with a phenyl Grignard reagent and titanium tetra(iso-propoxide) furnished a complex that catalyses asymmetric dialkylzinc additions to aromatic aldehydes.     

Reactivity of mixed manganese complexes with porphyrins and anionic ligands. Effect of modification of the organic part of the molecule

Manganese(III) complexes with octaethyl-, 5-phenyloctaethyl-, 5,10-and 5,15-diphenyloctaethyl-, 5,10,15-triphenyloctaethyl-, and 5,10,15,20-tetraphenyloctaethylporphyrins were synthesized, and the kinetics and mechanism of their dissociation in mixed AcOH-H₂SO₄ system were studied. The complete stability series of octaethylporphyrin manganese(III) complexes with increasing number of phenyl substituents at the meso positions of the porphyrin ligand was obtained.     

Study of incidence of DiPAMP ligand modification on the rhodium(I)-catalyzed asymmetric hydrogenation of α-acetamidostyrene

A series of P-stereogenic enantiopure 1,2-bis[(aryl)(phenyl)phosphino]ethane ligands was prepared through an extensive systematic incorporation of various substituents onto the P-o-anisyl rings of Knowles’ DiPAMP (DiPAMP = 1,2-bis[(o-anisyl)(phenyl)phosphino]ethane). The study of incidence of such modification on the Rh(I)-catalyzed hydrogenation of α-acetamidostyrene is reported revealing that substitution on position 3 is detrimental, while it is beneficial on position 5. Namely, a 2.5-fold increased catalyst activity coupled with a higher enantioselectivity (90% ee) was attained with the P-(2-MeO-3-naphthyl)-substituted ligand under mild conditions (1 bar H₂, rt in MeOH).     

A new pyrrolidine-derived atropisomeric amino alcohol as a highly efficient chiral ligand for the asymmetric addition of diethylzinc to aldehydes

A highly efficient pyrrolidine-derived atropisomeric amino alcohol, (S_a)-1-[2-diphenylhydroxymethyl-6-(trifluoromethyl)phenyl]-2-(1-pyrrolido)methyl-1H-pyrrole, has been synthesized as a chiral ligand for the enantioselective addition of diethylzinc to some prochiral aldehydes to afford (S)-alcohols. The conversion rates were close to quantitative with good to excellent enantiomeric excesses (up to 95% ee).     

Pyrazole-tethered phosphine ligands for Pd(0): useful catalysts for Stille, Kumada and Hiyama cross-coupling reactions

Combination of 3,5-dimethyl-1-(2-(diphenylphosphino)phenyl)-1H-pyrazole, A, and 3-tert-butyl-5-methyl-1-(2-(diphenylphosphino)phenyl)-1H-pyrazole, B, with Pd₂(dba)₃ furnished excellent catalysts for Stille, Kumada and Hiyama cross-coupling reactions. Effects of solvents, bases and ligand/palladium ratio on efficiency of coupling reactions were studied. Molecular structures of palladium(II) complexes of A and B determined by single-crystal X-ray diffraction method revealed a close similarity of ligand arrangement around the metal centre.     

Antimony-Carbon bond activation in a Pt(II) complex: The crystal structure of [Pt(9S3)(SbPh3)(Ph)](PF6)·CH3NO2

The complex [Pt(9S3)(SbPh₃)(Ph)](PF₆) forms directly from [Pt(9S3)(SbPh₃)₂](PF₆)₂ during the room temperature crystallization of the latter in nitromethane. The crystal structure shows a five-coordinate Pt(II) center containing the tridentate thiacrown ligand, a Sb donor from the triphenylstibine ligand, and a σ-coordinating phenyl group. The phenyl group forms via Sb-C bond cleavage from one of the SbPh₃ ligands in the bis complex.     

New developments in the chemistry of organoaluminum and organogallium hydrides

A survey of our recent work on organoaluminum and organogallium hydrides is presented. Three types of ligand system have been employed for the stabilization of monomeric aluminum and gallium mono- and dihydrides. The “two-armed” 2,6-bis (dimethylaminomethyl) phenyl ligand is effective when intramolecular bis(base) stabilization is necessary; its use has permitted the isolation of the first examples of monomeric aluminum and gallium dihydrates. The use of the corresponding “one-armed” 2-(dimethylaminomethyl) phenyl ligand resulted in the formation of gallium mono- and dihydride monomers and an aluminum dihydride dimer. The first base-free aluminum and gallium monohydrides and gallium dihydride have been stabilized by employing the bulky 2, 4, 6, -tris(t-butyl) phenyl ligand.     

Reversible double insertion of aryl isocyanates into the Ti-O bond of titanium(IV) isopropoxide

The insertion of phenyl isocyanate into titanium isopropoxide leads to the formation of a dimeric complex [Ti(OⁱPr)₂(μ-OⁱPr){C₆H₅N(OⁱPr)CO}]₂ (1) which has been structurally characterized. Reaction of titanium isopropoxide with two and more than 2 equiv. of phenyl isocyanate is complicated by competitive, reversible insertion between the titanium carbamate and titanium isopropoxide. The ligand formed by insertion of phenyl isocyanate into the titanium carbamate has been structurally characterized in its protonated form C₆H₅N{C(OⁱPr)O}C(O)N(H)C₆H₅ (3aH). Insertion into the carbamate is kinetically favored whereas insertion into isopropoxide gives the thermodynamically favored product.     

N-Arylation of carbazole by microwave-assisted ligand-free catalytic CuI reaction

N-Arylation of carbazole has been achieved in high yields within 1 h using a microwave-assisted catalytic CuI reaction with no organic ligand. The N-arylation can be performed by various arylhalides, such as phenyl, pyridine, thiophene, and thiazole moieties. Specifically, N-arylated bromocarbazoles were converted into useful synthetic intermediates for functionalized carbazole materials.     

Synthesis of several cyclopalladated biacetylmonoxime arylhydrazones

Palladium(II) complexes of biacetylmonoxime arylhydrazones (HL, aryl = phenyl, o-, m-, and p-tolyl, p-chloro- and p-nitrophenyl) and biacetylmonoxime N′-methyl-phenylhydrazone (HL′) have been prepared and characterized. The hydrazomines, HL and HL′, are coordinated through oxime- and hydrazone-nitrogen atoms as a bidentate ligand in the complexes [PdX₂(HL or HL′)] (X = halogen atom) formed under neutral conditions. Under basic conditions the deprotonated complexes [PdX(L or L′)] are obtained. Deprotonation occurs at the oxime group of HL′ and the ligand remains coordinated through oxime- and hydrazone-nitrogen atoms. The other hydrazoximes (HL) are cyclopalladated at the ortho position of the benzene rings and act as an NNC terdentate ligand in the deprotonated complexes [PdXL].     

Malonate-type bis(oxazoline) ligands with sp hybridized bridge carbon: synthesis and application in Friedel-Crafts alkylation and allylic alkylation

A series of simple and new C₂-symmetric diphenylmethylidene malonate-type bis(oxazoline) ligands were synthesized and applied to the Friedel-Crafts reaction and allylic alkylation. The Cu(II) complex of ligand 4b bearing the benzyl group afforded good to excellent enantioselectivity for the F-C adducts (up to >99% ee) between indole and alkylidene malonate, and the palladium complex of ligand 4c bearing the phenyl group afforded excellent enantioselectivity (up to 94% ee) for the allylic alkylation product.     

The effect of phenyl group on the electronic and phosphorescent properties of cyclometalated analogues of platinum(II) terpyridine complexes: a theoretical study

In this work, we theoretically investigate the effect of phenyl group on the electronic and phosphorescent properties of cyclometalated platinum(II) complexes, thereby designing an efficient blue emitting material. Three platinum(II) complexes Pt(N^N^N)Cl (N^N^N = terpyridine), Pt(N^C^N)Cl (N^C^N = 1,3-di(2-pyridyl)-benzene) and Pt(N^N^C)Cl (N^N^C = 6-phenyl-2,2′-bipyridines) are chosen as the models. Their electronic and phosphorescent properties are investigated utilizing quantum theoretical calculations. The results reveal that the phenyl group significantly affects the molecular and electronic structures, charge distribution and phosphorescent properties. The coordination bond length trans to phenyl group is the longest among the same type of bonds owing to the trans influence of phenyl group. Moreover, the phenyl group largely restricts the geometry relaxation of cyclometalated ligand. The strong σ-donor ability of Pt–C bond makes more electrons center at Pt atom and the fragments trans to phenyl group. In comparison with Pt(N^N^N)Cl and Pt(N^N^C)Cl, the complex Pt(N^C^N)Cl has the smallest excited-state geometry relaxation and the biggest emission energy and spatial overlap between the transition orbitals in the emission process. As a result, Pt(N^C^N)Cl has the largest emission efficiency, which well agrees with the experimental observation. Based on these calculation results, a potentially efficient blue-emitting material is designed via replacing pyridine groups in Pt(N^C^N)Cl by 3-methylimidazolin-2-ylidene.     

Synthesis of Re(I) complexes bearing tridentate 2,6-bis(7-azaindolyl)phenyl ligand with green emission properties

The Re(I) complexes bearing 2,6-bis(7^′-azaindolyl)phenyl ligand as a tridentate ligand were synthesized by treatment with Re₂(CO)₁₀. The structures of the complexes were confirmed by X-ray crystallography. Both 7-azaindolyl ligands of Re(I) complexes are present in butterfly forms. The Re-C_ipso bonds showed a partial double bond character by π back-donation between the phenyl moiety and Re atom. In THF solution at room temperature, these complexes exhibited green emission (λ_em=510 nm), which is considered to be attributable to MLCT (dz²(Re) →π^* (7^′-azaindolyl group)) transition containing π→π^* (7^′-azaindolyl group) transition.