Iminophosphines: synthesis, formation of 2,3-dihydro-1H-benzo[1,3]azaphosphol-3-ium salts and N-(pyridin-2-yl)-2-diphenylphosphinoylaniline, coordination chemistry and applications in platinum group catalyzed Suzuki coupling reactions and hydrosilylations

The aprotic and protic bi- and multidentate iminophosphines 2-Ph₂PC₆H₄N=CR¹R² (R¹=H, R²=Ph=2a; R¹=Me R²=Ph=2b; R¹=H, R²=2-thienyl=2c; R¹=H, R²=C₆H₄-2-PPh₂=2d; R¹=H, R²=C₆H₄-2-OH=2e, R¹=H, R²=C₆H₄-2-OH-3-Bu^t=2f; R¹=H, R²=CH₂C(O)Me=2g) have been prepared by the acid catalyzed condensation of 2-(diphenylphosphino)aniline with the corresponding aldehyde–ketone. Iminophosphine 2d can be reduced with sodium cyanoborohydride to give the corresponding amino-diphosphine 2-Ph₂PC₆H₄N(H)CH₂C₆H₄-2-PPh₂ (2h). In the presence of a stoichiometric quantity of acid, 2-(diphenylphosphino)aniline reacts in an unexpected manner with benzaldehyde, salicylaldehyde, or acetophenone to give the corresponding 2,3-dihydro-1H-benzo[1,3]azaphosphol-3-ium salts and with pyridine-2-carboxaldehyde to give N-(pyridin-2-ylmethyl)-2-diphenylphosphinoylaniline, the latter of which has been characterized by single-crystal X-ray crystallography, as its palladium dichloride derivative. The attempted condensation of 2-(diphenylphosphino)aniline with pyridine-2-carboxaldehyde to give the corresponding pyridine-functionalized iminophosphine resulted in an unusual transformation involving the diastereoselective addition of two equivalents of aldehyde to give 1,2-dipyridin-2-yl-2-(o-diphenylphosphinoyl)phenylamino-ethanol, which has been characterized by a single-crystal X-ray structure determination. The bidentate iminophosphine 2-Ph₂PC₆H₄N=C(H)Ph reacts with [(cycloocta-1,5-diene)PdClX] X=Cl, Me) to give [Pd{2-Ph₂PC₆H₄N=C(H)Ph}ClX] and the imino-diphosphine 2-Ph₂PC₆H₄N=C(H)C₆H₄-PPh₂ reacts with [(cycloocta-1,5-diene)PdClMe] to give [Pd{2-Ph₂PC₆H₄N=C(H)C₆H₄---PPh₂}ClMe] and each has been characterized by single-crystal X-ray crystallography. The monobasic iminophosphine 2-Ph₂PC₆H₄N=C(Me)CH₂C(O)Me reacts with [Ni(PPh₃)₂Cl₂] in the presence of NaH to give the phosphino–ketoiminate complex [Ni{2-Ph₂PC₆H₄N=C(Me)CHC(O)Me}Cl], which has been structurally characterized. Mixtures of iminophosphines 2a–h and a palladium source catalyze the Suzuki cross coupling of 4-bromoacetophenone with phenyl boronic acid. The efficiency of these catalysts show a marked dependence on the palladium source, catalysts formed from [Pd₂(OAc)₆] giving consistently higher conversions than those formed from [Pd₂(dba)₃] and [PdCl₂(MeCN)₂]. Catalysts formed from neutral bi- and terdentate iminophosphines 2a–d gave significantly higher conversions than those formed from their monobasic counterparts 2e–f. Notably, under our conditions the conversions obtained with 2a–c compare favorably with those of the standards; catalysts formed from tris(2-tolyl)phosphine and tris(2,4-di-tert-butylphenyl)phosphite and a source of palladium. In addition, mixtures of [Ir(COD)Cl]₂ and 2a–h are active for the hydrosilylation of acetophenone; in this case catalysts formed from monobasic iminophosphines 2e–f giving the highest conversions.     

Synthesis of 5-aminothiazoles as building blocks for library synthesis

A convenient route to 4-phenyl-5-aminothiazoles is described, which offers control over substitution at the 2-position. 2-N-Acylglycinamides were dithionated and a subsequent TFAA-mediated cyclisation step was followed by removal of the 5-N-trifluoroacetyl group providing the free amines. Though applicable generally the method was found to be most effective when introducing aromatic substituents at the 2-position, whereupon moderate overall yields of the 5-amino compounds were obtained.     

Synthesis of stereo-defined α-trifluoromethyl (Tfm)-malic units

Aldol reactions of titanium enolates of N-acyl-1,3-oxazolidin-2-ones with ethyl trifluoropyruvate occurred with low to good stereoselectivity depending on the steric properties of the N-acyl group. Attempts to transform the resulting aldols into peptidomimetics incorporating stereo-defined α-trifluoromethyl (Tfm)-malic units are described.     

Remarkable reactivity enhancement with Sb?N inter-coordination of ethynyl-1,5-azastibocines in Pd-catalyzed cross-coupling reactions with organic halides

The reaction of 12-arylethynyl-6-methyl-5,6,7,12-tetrahydrodibenzo[c,f][1,5]-azastibocines with organic halides such as acyl halides and aryl halides in the presence of PdCl₂(PPh₃)₂ as a catalyst led to the formation of cross-coupling products, alkynyl ketones and diaryl acetylenes, in good yields. The reactivity of the ethynyl group on the 1,5-azastibocines was far superior to that on diphenyl(phenylethynyl)stibane, which brought about marked improvement in the reaction conditions (lower temperature and shorter reaction time) and in the yields of the cross-coupling products. Single-crystal X-ray analysis of the ethynyl-1,5-azastibocine showed the presence of intramolecular Sb?N interaction which should be responsible for the remarkable reactivity enhancement of the 1,5-azastibocines for this type of reaction.     

Transition metal carbene chemistry 2: kinetic studies on the nucleophilic substitution reactions of (CO)5MC(SCH3)CH3 (M = Cr and W) with morpholine in aqueous acetonitrile

Kinetic studies of the aminolysis of [methyl(thiomethyl)carbene]pentacarbonyl chromium(0),(CO)₅CrC(CH₃)(SCH₃) (1-Cr(S)) and [methyl(thiomethyl)carbene]pentacarbonyltungsten(0), (CO)₅WC(CH₃)(SCH₃) (1-W(S)), with morpholine, a secondary amine, in 50% acetonitrile-50% H₂O (v/v at 25 °C) is reported. The second-order rate constant (k_A in m⁻¹ s⁻¹) increases with amine concentration, giving a linear dependence with an intercept on the rate axis and a tendency towards leveling off at higher amine concentration. The reaction was found to undergo general base catalysis. The mechanism proposed is very similar to those for ester reactions, involving a nucleophilic addition of amine to the substrate to yield a zwitterionic tetrahedral intermediate in the first step, followed by deprotonation to form in the second step, which, in the third step, converted to product by H₂O and/or conjugate acid of the base (BH⁺), assisted MeS⁻ expulsion. The reactivity (k₁) of 1-W(S) was found to be higher than that of 1-Cr(S), whereas, comparable , water catalyzed and , BH⁺ catalyzed, leaving group departure were found for both the carbenes complexes. All these observations have been explained successfully.     

Synthesis and photoluminescence of single crystals europium ion-doped BaF2 cubic nanorods

In this work, we used the hydrothermal method to synthesize Eu³⁺ ion-doped cubic BaF₂ nanorods, which is a luminescent material. The clubbed structures were well crystallized and exhibited face-centred cubic structures, as indicated by powder X-ray diffraction, scanning electron microscopy, electron diffraction, and transmission electron microscopy. The luminescent properties were studied, and local symmetry surrounding Eu³⁺ ions and electronic transition processes included. The results indicated that Eu³⁺ occupied only one C_4ν site in nanorods.     

Oxidation of theexo- andendo-phenylcyclohexadienyl iron complexes Fe(η5-6-PhC6H6) (η5- C5H5)

The roe of oxidatively induced homolyhc scission a the C(sp³)-H bonds in the iron phenykychhexadienyl complexes Fe(⁵-6-PhC₆H₆)(⁵-C₅H₅) (1) depends on the spatial orientation of the Ph substitutent. In the case of the (1 _endo ⁺) radical cation this process, resulting in the cationic biphenyl complex (Fe(⁶ -C₆H₅C₆H₅)(⁵-C₅H₅)]⁺ (2 ⁺), is fast and proceeds for several minutes. In the case of the more stable radical cation (1 _exo ⁺) the formation of 2⁺ is slow and takes tens minutes to complete.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1698–1700, July, 1996.     

A novel class of amide-derived air-stable P,O-ligands for Suzuki cross-coupling at low catalyst loading

The benzamide-derived P,O-ligands efficiently promoted the Pd-catalyzed Suzuki cross-coupling reactions of aryl bromides with phenylboronic acid at 0.01 mol % of Pd loading at 60-80 °C to form biaryls in excellent yields. A sterically hindered arylboronic acid gave a quantitative yield of the coupling product at 110 °C with 1 mol % Pd.     

Additions- und SubstitutionsReaktionen an Tetrafluor- und Tetrachlordiboran(4)

Addition and Substitution Reactions at Tetrafluoro- and Tetrachlorodiborane(4) From equimolar mixtures of B₂F₄ and Me_nN(SiMe₃)_3-n (n = 0–3) the mono-addition products 1–4 are formed at low temperatures. By elimination of Me₃SiF the adduct 2 gives the dimeric monosubstituted diborane 8 , which slowly decomposes at room temperature to the aminoborane 6 and (BF)_n. The course of the reactions was studied by means of ¹¹B and ¹⁹F NMR spectroscopy and by measuring the vapor pressures. According to the ¹¹B and ³¹P NMR spectra the reaction of B₂Cl₄ with PCl₅ or [Me₄N]Cl in liquid hydrogen chloride at 0°C does not yield [PCl₄]₂⁺[B₂Cl₆]^2? or [Me₄N]₂⁺[B₂Cl₆]^2? but gives [PCl₄]⁺[BCl₄]^?, PCl₃ and BCl₃ or [Me₄N]⁺[BCl₄]^? and BCl₃ besides (BCl)_n.