One-step redox route to N-heterocyclic phosphenium ions

One-step reactions of the appropriate N-alkyl-, N-cycloalkyl-, and N-aryl-substituted alpha-diimines with PI3 afforded >80% yields of the triiodide salts of the following N-heterocyclic phosphenium ions, [(R1NC(R2)C(R2)NR1)P]+: 3 (R1 = t-Bu; R2 = H); 4 (R1 = 2,6-i-Pr2C6H3; R2 = H), 5 (R1 = Mes; R2 = H), 6 (R1 = 2,6-i-Pr2C6H3; R2 = H), and 7 (R1 = cyclohexyl; R2 = H). Treatment of 3 and 6 with NaB(C6H5)4 resulted in virtually quantitative yields of the corresponding [B(C6H5)4]- salts 8 and 9, respectively. The X-ray crystal structures of 3 and 5-9 were determined.     

Unsymmetrically substituted benzothiazolyl-hydrazines

New unsymmetrically substituted hydrazines containing benzothiazole residues with substituents in the 6-position were obtained by the oxidative cyclization of substituted 1,4-diphenylthiosemicarbazides with potassium ferricyanide in alkaline aqueous alcoholic media. The reaction of these new hydrazines with trichloromethyl mercaptan gave N-(6-R-2-benzothiazolyl)-N-[p-(trichloromethylthioamidosulfonyl)phenyl]hydrazines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 765–766, June, 1971.     

N-heterocyclic phosphenium cations: syntheses and cycloaddition reactions

A series of trifluoromethanesulfonate (OTf) salts of N-heterocyclic phospheniums (NHP) bearing phenyl (1a), para-methoxyphenyl (1b), 2,6-diisopropylphenyl (1c) and mesityl (1d) substituents is reported. The compounds are made by a modification to a literature procedure that improves the overall yields for and by 15 and 23%, respectively. Two unwanted side-products in the synthesis of , the diammonium salt, [(2,6-iPr-C6H3)N(H)2CH2CH2N(H)2(2,6-iPr-C6H3)]Cl2 (4) and the bisphosphine (2,6-iPr-C6H3)N(PCl2)CH2CH2N(PCl2)(2,6-iPr-C6H3) (5), are crystallographically characterized, as is the intermediate cyclic chlorophosphine, C1PN(4-OMe-C6H4)CH2CH2N(4-OMe-C6H4) (3b). The phenyl-substituted NHP is fully characterized, including by X-ray crystallography, for the first time; this compound contains a short P-O contact of 2.1850(14) A. Cycloaddition reactions of with 2,3-dimethyl-1,3-butadiene give the expected spirocyclic phospholeniums, 7,8-dimethyl-1,4-diaryl-1,4-diaza-5-phopshoniaspiro[4.4]non-7-ene, as their OTf salts (6a-d), while reactions with N,N'-dimesityl-1,4-diaza-1,3-butadiene give, except in the case of , which is too bulky to react, the aza analogues, 1,4-dimesityl-6,9-diaryl-1,4,6,9-tetraaza-5-phosphoniaspiro[4.4]non-2-ene (7a, 7b and 7d). The sterically congested is in thermal equilibrium with and free diazadiene, and undergoes a substitution reaction with 2,3-dimethyl-1,3-butadiene to give .     

N-heterocyclic phosphenium ligands as sterically and electronically-tunable isolobal analogues of nitrosyls

The coordination chemistry of an N-heterocyclic phosphenium (NHP)-containing bis(phosphine) pincer ligand has been explored with Pt(0) and Pd(0) precursors. Unlike previous compounds featuring monodentate NHP ligands, the resulting NHP Pt and Pd complexes feature pyramidal geometries about the central phosphorus atom, indicative of a stereochemically active lone pair. Structural, spectroscopic, and computational data suggest that the unusual pyramidal NHP geometry results from two-electron reduction of the phosphenium ligand to generate transition metal complexes in which the Pt or Pd centers have been formally oxidized by two electrons. Interconversion between planar and pyramidal NHP geometries can be affected by either coordination/dissociation of a two-electron donor ligand or two-electron redox processes, strongly supporting an isolobal analogy with the linear (NO(+)) and bent (NO(-)) variations of nitrosyl ligands. In contrast to nitrosyls, however, these new main group noninnocent ligands are sterically and electronically tunable and are amenable to incorporation into chelating ligands, perhaps representing a new strategy for promoting redox transformations at transition metal complexes.     

Cycloaddition of phosphenium ions to norbornadiene and quadricyclane

Bis(dimethylamino)-, bis(diethylamino)-, and chloro(diisopropylamino)phosphenium ions (1a–c, respectively) react cleanly with norbornadiene (N) to yield the homo-1,4-cycloadducts (2a–c). In addition, 1c reacts cleanly with quadricyclane (Q) to yield the same product.     

Unsymmetrically substituted furoxans. VIII. Chloromethylfuroxans

The two isomeric chloromethylfuroxans have been prepared. Their structures, thermal equilibration and reaction toward thiophenoxide ion are discussed. Kinetics of the 4-methyl — 3-methyl isomer thermal conversion are also reported.     

Unsymmetrically substituted triazacyclohexanes and their chromium complexes

The unsymmetrically N-substituted N,N′-Ar₂-N″-R-1,3,5-triazacyclohexanes 1–4 (Ar = ortho- or para-fluorophenyl, R = n- or iso-propyl) can be obtained in good yields from a one-step condensation reaction with excess amine. Solid state structures of 1–4 resemble closely those of their triaryl-substituted analogues. The condensation reaction to 4 was looked at by detailed NMR investigations and revealed that amine/aniline exchange is occurring in solutions containing free aniline even at ambient conditions setting up an equilibrium between all possible symmetrical and unsymmetrical triazacylcohexanes. Selective crystallisation of 4 from the solution drives the reaction to high yields of 4. Complexes 1–4 react readily with CrCl₃ or CrCl₃(THF)₃ to form the corresponding CrCl₃ complexes. The complexes are insoluble in non-polar solvents and decompose under decomplexation in coordinating solvents.     

Differentiation of stereoisomeric steroids by reactions with phosphenium ions

A chemical ionization method is reported for distinction of diastereomeric hydroxysteroids by using Fourier-transform ion cyclotron mass spectrometry (FT-ICR). Certain phosphenium ions are demonstrated to react with stereoisomeric steroids to yield qualitatively different product ions. For example, 1,3,5(10)-estratriene-3,16beta,17beta-triol (cis-estriol) reacts with the dimethoxy phosphenium ion to form a diagnostic product ion (not formed for the trans-estriol) through addition followed by the loss of two molecules of methanol. In an analogous manner, the 1,3-dioxolan-2-phosphenium ion produces a diagnostic product ion through the loss of ethylene glycol from the adduct of cis-estriol only. The 1,3,5(10)-estratriene-3,16alpha,17beta-triol (trans-estriol), on the other hand, reacts with each phosphenium ion only via hydroxide abstraction-initiated pathways that indicate the presence of at least two hydroxyl groups in the molecule. These specific reactions take place for all hydroxysteroids examined, independent of their stereochemistry. Another isomer pair, cholestan-3alpha,5alpha-diol (cis-cholestandiol) and cholestan-3beta,5alpha-diol (trans-cholestandiol), is differentiated based on selective elimination of water only from the adduct of the cis-isomer. However, the method does not allow distinction between the stereoisomeric 5beta-pregnane-3alpha,17alpha,20alpha-triol and 5beta-pregnane-3alpha,17alpha,20beta-triol. The different reactivities of the three pairs of steroid isomers and of each diastereomeric compound pair are rationalized by reaction enthalpies and steric effects based on straightforward and predictable reaction mechanisms.     

Unsymmetrically substituted furoxans. Part 11. Methylfuroxancarbaldehydes

The two isomeric 3-methyl-4-furoxancarbaldehydes ( 2a ) and 4-methyl-3-furoxancarbaldehyde ( 2b ) have been prepared. Discussion of their structures, thermal equilibration and kinetic of thermal conversion from the 3-methyl to the 4-methyl isomer are also reported. (Phenylsulfonyl)hydrazones 3a and 3b have been prepared as derivatives in view of their potential antitumoral properties.     

Unsymmetrically substituted four-armed tolanes: new multichromophoric molecules

The selective synthesis of a four-armed tolane with different fluorescent chromophores that are asymmetrically distributed is described. Its optical absorption and emission properties were examined. This multichromophoric molecule exhibits a charge-transfer pathway that has a pronounced effect on the overall optical properties, together with an energy transfer process. Appropriate basic centers are present, meaning that the energy transfer processes can be stopped by the addition of acid—a process that makes this system a fluorescent pH-sensor.     

Phosphorus heterocycle synthesis using phosphenium ions and 1,4-dienes

The stabilized phosphenium ion, [Prⁱ₂NPCl]⁺, reacts readily with 1,4-dienes to afford high yields of bicyclic phosphonium salts, the structure of one of which has been determined by X-ray crystallography.     

Heterolytic addition of E-H bonds across Pt-P bonds in Pt N-heterocyclic phosphenium/phosphido complexes

The reactivity of E-H bonds (E = S, O, Cl) with Pt(II) complexes ligated by an N-heterocyclic phosphido-containing diphosphine ligand have been investigated. Addition of PhSH to [(PPP)Pt(PPh(3))][PF(6)] (1) results in clean formation of [(PP(H)P)Pt(SPh)][PF(6)] (3), in which the substrate has added across the Pt-P(NHP) bond. Similar reactivity occurs when 1 is treated with ROH (R = Ph, Me), but in this case the O-H bond adds across the Pt-P bond in the opposite direction producing [(PP(OR)P)Pt(H)(PPh(3))][PF(6)] (R = Ph (4), Me (5)). HCl addition to 1 cleanly generates [(PP(H)P)PtCl][PF(6)] (6(PF6)). The neutral Pt-NHP complex (PPP)PtCl (2) exhibits similar reactivity; however, in the presence of the nucleophilic Cl(-) anion, the (PP(OR)P)Pt(H)Cl species presumably generated via addition of ROH (R = Me, Et) undergoes an Arbuzov-like dealkylation reaction to exclusively form the N-heterocylic phosphinito species (PP(O)P)Pt(H) (7).     

Formation of N-heterocyclic, donor-stabilized borenium ions

Cationic and zwitterionic boryl bromide species and a borenium-boryl bromide cation have been synthesised which represent new N-donor stabilised cationic boron compounds with β-diketiminate ligands. The unexpected borenium-boryl bromide results from a head-to-tail dimerisation of the corresponding zwitterionic boryl bromide accompanied by proton migration. The electronic nature of these new species was studied by DFT calculations.     

Unsymmetrically substituted furoxans. Part 16 . Reaction of benzenesulfonyl substituted furoxans with ethanol and ethanethiol in basic medium

The use of benzenesulfonyl substituted furoxans as flexible intermediates for the synthesis of new functionalized furoxans interesting for their potential biological properties is discussed. Reaction of benzenesul-fonylphenylsulfonylfuroxan isomers 7a and 7b with ethanol and ethanethiol in basic medium affords the expected ethers and sulphides respectively. Reaction of bis(benzenesulfonyl)furoxan ( 1 ) with ethanol in basic medium gives 3-benzenesulfonyl-4-ethoxyfuroxan ( 2 ) or diethoxyfuroxan (3), according to the experimental procedure. In contrast the reaction of 1 with ethanethiol gives a mixture of substitution compounds and the 4-benzenesulfonyl-3-ethylthiofurazan ( 11 ). The structure of the compounds has been assigned by nmr spectroscopy and, in the case of 3-benzenesulfonyl-4-ethylthiofuroxan ( 9b ), confirmed by X-ray analysis.     

Mechanistic study of stereoselective gas-phase reactions of phosphenium ions with cis- and trans-1,2-diaminocyclohexanes

The 1,3-dioxolane-2-phosphenium ion, 1,3-benzodioxole-2-phosphenium ion, and o-biphenylenephosphenium ion are reported to react in a stereoselective manner with cis- and trans-1,2-diaminocyclohexanes in the gas phase in a Fourier transform ion cyclotron resonance mass spectrometer. Elimination of NH3 from an addition product was observed only for the trans isomer. Several reaction mechanisms were experimentally and computationally examined (B3LYP/6-31G(d)//HF/6-31G(d) + ZPVE level of theory). The most plausible mechanism is initiated by addition of one of the amino groups to the electrophilic phosphorus atom followed by proton transfer between the amino groups. A change to a diaxial conformation for the trans isomer facilitates anchimeric assistance by the now nucleophilic phosphorus atom as the C-N bond breaks to release NH3. Intramolecular proton transfer competes with the conformational change and ultimately leads to ethylene glycol elimination. The transition states for the critical steps of these two reactions are calculated to be nearly equal in magnitude, which rationalizes the observation of both reactions for the trans-diamine. In contrast, the adduct of the cis isomer can eliminate NH3 via a concerted 1,2-hydride shift without a need for a conformational change. However, the barrier associated with this reaction was found to be substantially greater than for proton transfer between the N- and O-atoms. The latter reaction dominates and ultimately leads to ethylene glycol elimination.     

Unsymmetrically substituted furoxans. IIII. Methylnitrofuroxan: Its structure and behavior toward nucleophilie substitution

A series of unsymmetrically substituted furoxans have been prepared from methyinitro-furoxan and a variety of nucleophilic reagents. The nmr study of these compounds and of their parent furazans suggested the structure of 3-methyl derivatives for all the furoxans synthesized: on this ground the 3-methyl structure for methylnitrofuroxan was proposed. On heating some 3-methylfuroxan derivatives, a partial isomerization into the corresponding 4-methyl isomers occurred.