Reactions of 1,2-di(2-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene

Reactions of a sterically protected 1,2-di(2-thienyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene were investigated. The diphosphinidenecyclobutene reacted with elemental sulfur or transition metal reagents to form a thiaphosphirane derivative or the corresponding transition metal complexes, respectively. Reactions of the di(2-thienyl)diphosphinidenecyclobutene with butyllithium followed by treatment with electrophiles afforded functionalized di(2-thienyl)diphosphinidenecyclobutene derivatives.     

Facile [3+2] dimerization and formal dehydrogenative coupling mode of a cyanophenylphosphaallene

Due to a facile head-to-tail [3+2] dimerization, even a sterically demanding group such as the Mes^∗ (2,4,6-tri-tert-butylphenyl) group around the PCC moiety did not allow us to isolate 3-(4-cyanophenyl)-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaallene from the elimination reaction of 2-bromo-3-(4-cyanophenyl)-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaprop-1-ene with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), and the corresponding 1,4-diphosphafulvene containing cyano groups was obtained and characterized. Theoretical studies on the [3+2] dimerization of phosphaallene characterize possible intermediates affording 1,4-diphosphafulvenes and also suggest the cyano group effect to facilitate the saturation of the PC double bonds. On the other hand, 1,2-bis(4-cyanophenyl)-3,4-bis[(2,4,6-tri-tert-butylphenyl)phosphinidene]cyclobutene was obtained from 2-bromo-3-(4-cyanophenyl)-3-trimethylsiloxy-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaprop-1-ene together with the 3-(4-cyanophenyl)-1-phosphaallene.     

Synthesis and properties of air-stable 1,3-diphosphacyclobutane-2,4-diyls and the related compounds

A kinetically stabilized phosphaalkyne bearing a bulky Mes^∗ (2,4,6-tri-t-butylphenyl) group is useful compound to prepare an enormous number of highly stable 1,3-diphosphacyclobutane-2,4-diyls through reactions with a lithium reagent and an electrophile. By utilizing this synthetic protocol, we prepared several non-symmetrical 1,3-diphosphacyclobutane-2,4-diyls in which the substituents on the phosphorus are different. Furthermore, we succeeded in preparation and characterization of novel air-tolerant symmetrical 2,4-bis(2,4,6-tri-t-butylphenyl)-1,3-diphosphacyclobutane-2,4-diyls bearing the identical alkyl substituents on the phosphorus atoms. Structures and properties of the 1,3-diphosphacyclobutane-2,4-diyls indicate characters as singlet ground-state carbon centered biradicals. In addition to those biradicals, we succeeded in preparation and isolation of a novel P-heterocyclic air-stable neutral radical as well as a P-heterocyclic cation radical.     

Preparation, properties, and catalytic activity of transition-metal complexes containing a ligated 2-methyl-3,3-diphenyl-1,3-diphosphapropene skeleton

2-Methyl-3,3-diphenyl-1-(2,4,6-tri-t-butylphenyl)-1,3-diphosphapropene behaved as an unsymmetrical chelating ligand for transition metal complexes and the 1,3-diphosphapropene moiety was hydrolyzed to afford the 1,3-diphosphapropan-1-ol derivative upon coordination. The palladium complex showed catalytic activity for the Sonogashira coupling reaction.     

Cyclodehydration of cis-2-butene-1,4-diol with active methylene compounds catalyzed by a diphosphinidenecyclobutene-coordinated palladium complex

(π-Allyl)palladium triflate coordinated with 1,2-bis(4-methoxyphenyl)-3,4-bis(2,4,6-tri-t-butylphenylphosphinidene)cyclobutene (DPCB-OMe), [Pd(η³-C₃H₅)(DPCB-OMe)]OTf, efficiently catalyzes cyclodehydration of cis-2-butene-1,4-diol with active methylene compounds such as acetylacetone and ethyl acetoacetate in toluene in the presence of pyridine. The reactions can be performed in air, giving 2-vinyl-2,3-dihydrofurans in good to high yields.     

Synthesis and catalytic properties of cationic palladium(II) and rhodium(I) complexes bearing diphosphinidinecyclobutene ligands

Cationic palladium(II) and rhodium(I) complexes bearing 1,2-diaryl-3,4-bis[(2,4,6-tri-t-butylphenyl)phosphinidene]cyclobutene ligands (DPCB–Y) were prepared and their structures and catalytic activity were examined (aryl = phenyl (DPCB), 4-methoxyphenyl (DPCB–OMe), 4-(trifluoromethyl)phenyl (DPCB–CF₃)). The palladium complexes [Pd(MeCN)₂(DPCB–Y)]X₂ (X = OTf, BF₄, BAr₄ (Ar = 3,5-bis(trifluoromethyl)phenyl)) were prepared by the reactions of DPCB–Y with [Pd(MeCN)₄]X₂, which were generated from Pd(OAc)₂ and HX in MeCN. On the other hand, the rhodium complexes [Rh(MeCN)₂(DPCB–Y)]OTf were prepared by the treatment of [Rh(μ-Cl)(cyclooctene)₂]₂ with DPCB–Y in CH₂Cl₂, followed by treatment with AgOTf in the presence of MeCN. The cationic complexes catalyzed conjugate addition of benzyl carbamate to α,β-unsaturated ketones.     

Syntheses and optoelectronic properties of four photochromic dithienylethenes

Four photochromic dithienylethene compounds, 1,2-bis(2-methyl-5-naphthalene-3-thienyl)perfluorocyclopentene 1a, 1,2-bis[2-methyl-5(p-fluorophenyl)-3-thienyl]perfluorocyclopentene 2a, 1,2-bis[2-methyl-5(p-ethoxyphenyl)-3-thienyl]perfluorocyclopentene 3a, and 1,2-bis[2-methyl-5(p-N,N-dimethylaminophenyl)-3-thienyl]perfluorocyclopentene 4a were synthesized, and their optoelectronic properties, such as photochromism in solution as well as in poly-methylmethacrylate (PMMA) amorphous films, fluorescences and electrochemical properties were investigated in detail. These dithienylethenes have shown good photochromic behavior both in solution and in PMMA amorphous film. All of them exhibited relatively strong fluorescence and gave a bathochromic shift upon increasing concentration in THF. The irreversible anodic oxidation of 1a, 2a and 4a was observed by performing cyclic voltammetry experiments.     

ESCA STUDIES OF A DIPHOSPHENE

Abstract

The nature of the P[dbnd]P bond in E-bis(2,4,6-tri-tert-butylphenyl)diphosphene was studied by means of ESCA, indicating that the phosphorus 2p binding energy is the lowest among those for common organophosphorus compounds.     

Silver tetrakis(hexafluoroisopropoxy)aluminate as hexafluoroisopropyl transfer reagent for the chlorine/hexafluoroisopropyl exchange in imino phosphanes

Treating 1,3-dichloro-2,4-bis[tris(trimethylsilyl)silyl]-cyclo-diphosphadiazane, [HypNPCl]₂ ((Me₃Si)₃Si = Hyp), or N-(2,4,6-tri-tert-butylphenyl)imino(chloro)phosphane, Mes^∗-NP-Cl (Mes^∗ = 2,4,6-tri-tert-butylphenyl), with Ag[Al(OCH(CF₃)₂)₄] leads to the abstraction of [OCH(CF₃)₂]⁻ from the counter ion [Al(OCH(CF₃)₂)₄]⁻ in a formal Lewis acid/Lewis base reaction. The final products Hyp₂N₂P₂(Cl)(OCH(CF₃)₂), Mes^∗-NP-OCH(CF₃)₂ and the dimeric Lewis acid [Al(OCH(CF₃)₂)₃]₂ have been characterized by means of X-ray analysis.     

Glucose ferrocenyl-oxazolines: Coordination behavior toward [Pd(η-allyl)Cl]2 studied by ESI-MS

Several new oxazolin-2-yl-substituted ferrocenes based on 2-amino-2-deoxy-α-d-glucose were synthesized via the corresponding amides followed by closing the oxazoline-ring with SnCl₄.Coordination properties of representatives of the group of mono- and bis-oxazolinyl ferrocenes, 2-ferrocenyl-4,5-(3,4,6-tri-O-acetyl-1,2-dideoxy-d-glucopyrano)-[2,1-d]-oxazoline and 1,1′-bis{4,5-(3,4,6-tri-O-acetyl-1,2-dideoxy-d-glucopyrano)-[2,1-d]-oxazolin-2-yl}ferrocene, respectively, toward [Pd(η³-allyl)Cl]₂ were investigated by electrospray ionization mass spectrometry in positive ion mode and by MS/MS technique.With the monooxazoline derivative mainly a 1:1 complex with the Pd-moiety was found in the mass spectrum while the bisoxazoline yields a stoichiometry of 2:1 (oxazoline:Pd). The latter result is attributed to steric hindrance of the coordination of a second Pd-moiety to the bulky bisoxazolinyl-ferrocene.In the case of 1,1′-bis{4,5-(3,4,6-tri-O-acetyl-1,2-dideoxy-d-glucopyrano)-[2,1-d]-oxazolin-2-yl}ferrocene 9 overlapping of two signals in the m/z range from 955-965 was found which can be assigned to the singly charged adduct [C₃₆H₄₀FeN₂O₁₆ + Pd(η³-C₃H₅)]⁺ and a doubly charged Pd-ligand cluster with the general formula Pd₂[L(9)]₂.In addition, the molecular structure of 1,1′-bis{4,5-(3,4,6-tri-O-acetyl-1,2-dideoxy-d-glucopyrano)-[2,1-d]-oxazolin-2-yl}ferrocene was determined by X-ray diffraction analysis.     

BNN-1,3-dipoles: isolation and intramolecular cycloaddition with unactivated arenes

The mono-base-stabilized 1,2-diboranylidenehydrazine derivatives featuring a 1,3-dipolar BNN skeleton are obtained by dehydrobromination of [ArB(Br)NH]₂ (Ar = 2,6-diphenylphenyl (Dpp), Ar = 2,6-bis(2,4,6-trimethylphenyl)phenyl (Dmp) or Ar = 2,4,6-tri-tert-butylphenyl (Mes*)) with N-heterocyclic carbenes (NHCs). Depending on the Ar substituents, such species can be isolated as a crystalline solid (Ar = Mes*) or generated as reactive intermediates undergoing spontaneous intramolecular aminoboration of the proximal arene rings via [3 + 2] cycloaddition (Ar = Dpp or Dmp). The latter reactions showcase the 1,3-dipolar reactivity toward unactivated arenes at ambient temperature. In addition, double cycloaddition of the isolable BNN species with two CO₂ molecules affords a bicyclic species consisting of two fused five-membered BN₂CO rings. The electronic structures of these BNN species and the mechanisms of these cascade reactions are interrogated through density functional theory (DFT) calculations.

The mono-base-coordinated 1,2-diboranylidenehydrazine derivatives exhibiting the BNN-1,3-dipolar reactivity toward unactivated arenes and CO₂ are reported.     

X-Ray structure analyses of diphosphinidenecyclobutene and its chelate type tetracarbonylmolybdenum(O) complex

The structure of [(E,E)-3,4-bis(2,4,6-tri-t-butylphenylphosphinidene)-1,2-bis(trimethylsilyl)cyclobutene]tetracarbonylmolybdenum(O) has been analyzed by X-ray crystallography. The structure of the free ligand, diphosphinidenecyclobutene, has also been analyzed and compared with that of the metal carbonyl complex.     

Acid-catalyzed disproportionation of N,N-bis(4-tert-butylphenyl)hydroxylamine. Synthesis and structure of 10-[5-tert-butyl-2-(4-tert-butylphenylamino)phenyl]-3,7-di-tert-butylphenoxazine

New method of synthesis was developed for N,N-bis(4-tert-butylphenyl)hydroxylamine by reduction of the corresponding aminoxyl with hydrazine hydrate. At the treatment with strong acids this hydroxylamine derivative is converted in bis(4-tert-butylphenyl)amine and 10-[5-tert-butyl-2-(4-tert-butylphenylamino) phenyl]-3,7-di-tert-butylphenoxazine. The structure of the latter was established by X-ray diffraction analysis. The mechanism was suggested of the acid-catalyzed disproportionation of N,N-bis(4-tert-butylphenyl) hydroxylamine.     

Ligand effect of bulky 2,2-dialkyl-1-phosphaethenes on Au-catalyzed cycloisomerization of 1,6-enynes and lactonization of pent-4-ynoic acids

2,2-Dimethyl- and 2-benzyl-2-methyl-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaethenes were employed as ligand of mononuclear chlorogold(I) complexes, which catalyzed cycloisomerization of 1,6-enyne affording vinylcyclopentene exclusively in the absence of silver co-catalyst. The reaction mechanisms are discussed based on DFT calculations. In addition to the cycloisomerization, the phosphaalkene-chlorogold(I) complexes catalyzed cyclization of pent-4-ynoic acids providing γ-methylene-γ-lactones under basic conditions.     

Electronic properties of thienylene vinylene oligomers: synthesis and theoretical study

(E)-1,2-bis(2-thienyl)vinylene (TV), (E)-1,2-bis(3-octyl-2-thienyl)vinylene (TOV), (E)-1,2-bis(3-(2-ethylhexyl)-2-thienyl)vinylene (T2EHV), and (E)-1,2-bis-[2,2??-bithienyl] vinylene (BTV) have been synthesized by a combination of formylation reaction and Mc Murry dimerization. UV?CVis spectra of BTV showed the longest wavelength absorption, TOV and T2EHV showed a bathochromic shift to the red compared with TV, due to an increment of delocalization of the conjugated ??-system as the result of the weakening of the carbon?Ccarbon double bonds of the thienyl rings due to the substitution of one hydrogen by the alkyl group. Based on optical data, the effect of linear and branched alkyl chain and extension of conjugation length on the electronic properties is discussed. ¹H, ¹³C-NMR, UV?CVisible, Fluorescence data are discussed and theoretical DFT and TD-DFT calculations of ground state and excited states have been also considered in the analysis and explanation of results.     

Preparation and X-ray analyses of siloxane-bridged acyclic and 8-membered cyclic phosphaethenes

Two Mes¹PC (Mes¹ = 2,4,6-tri-t-butylphenyl) parts were successfully combined with one or two disiloxane chain(s) by the reaction of 2-silyl-1-phosphaethenyllithium with dichlorotetramethyldisiloxane, and the structures of bis(1-bromo-2-phosphaethenyl)disiloxane and 3,7-diphosphinidene-2,2,4,4,6,6,8,8-octamethyl-1,5-dioxa-2,4,6,8-tetrasilacyclooctane were characterized by spectroscopic analyses and X-ray crystallography.     

Reaction of a diphosphene with various halogens

Bis(2,4,6-tri-$\text{tert}$-butylphenyl) diphosphene reacts with various halogens to give the corresponding phosphoric dihalides, haloarene, and arene depending upon the halogen and solvent used.     

Synthesis and characterization of new air stable primary amido substituted diborane(4) derivatives

Three new diborane(4) derivatives, 1,2-bis(2,4,6-trimethylanilide)-1,2-bis(dimethyamido)diborane(4) (1), 1,2-bis(2,4,6-trimethylanilide)-1,2-bis(duryl)diborane(4) (2) and 1,2-bis(anilide)-1,2-bis(duryl)diborane(4) (3), have been synthesized and characterized by means of elemental analysis, IR, ¹H, ¹³C and ¹¹B NMR spectroscopy. Additionally, the structures of compounds 1 and 2 have been determined by the single crystal X-ray diffraction technique. The compounds 1 and 2 crystallize in the monoclinic P21/c space group. All of the compounds were found to be air stable.     

Synthesis and polymerization of 1-(2,4,6-tricyanophenylthio)-3-[3,5-bis(n,n-dimethylamino)phenoxy]-2-propyl methacrylate; polymer effect on intramolecular charge–transfer interaction

1-[3,5-Bis(N,N-dimethylamino)phenoxy]-ω-(2,4,6-tricyanophenylthio)alkanes ( 1a–c ), where an electron-accepting 2,4,6-tricyanophenylthio group and an electron-donating 3,5-bis(N,N-dimethylamino)phenoxy one are linked with a spacer such as ethylene, trimethylene, and tetramethylene, were prepared in order to examine an effect of the spacer chain length on intramolecular charge–transfer interaction between the 2,4,6-tricyanophenylthio and 3,5-bis(N,N-dimethylamino)phenoxy groups. From the UV-vis spectra measurements of 1a–c , 1-[3,5-bis(N,N-dimethylamino)phenoxy]-3-(2,4,6-tricyanophenylthio)Propane ( 1b ) carrying the trimethylene chain as a spacer was found to have the strongest intramolecular charge–transfer interaction. A new methacrylate-type monomer carrying the 1b unit as a side chain, 1-(2,4,6-tricyanophenylthio)-3-[3,5-bis(N,N-dimethylamino)phenoxy]-2-propyl methacrylate ( 2 ), was prepared successfully in 9.2% total yield in seven steps. The monomer 2 homopolymerized in benzene, tetrahydrofuran, acetone, and dimethyl sulfoxide in the presence of 2,2′-azobis(isobutyronitrile) at 60°C to give polymers [poly( 2 )] with molecular weights of 6,000 to 98,000. An intramolecular charge–transfer interaction in the poly( 2 ) was found to be larger than that in the monomer 2 and to increase with an increase in the degree of polymerization of the poly( 2 ), suggesting that there is an existence of polymer effect other than the polymer effect due to the high local concentration of the donor-acceptor pair. © 1995 John Wiley & Sons, Inc.     

Synthesis of optically active polymers using P-chiral bisphosphines as anionic initiators

Anionic polymerization of triphenylmethyl methacrylate was performed by using P-chiral bisphosphine initiators. According to the optical rotation analysis and circular dichroism measurements, the polymer obtained by using the initiator (S,S)-1,2-bis(boranato(tert-butyl)methylphosphino) ethane exhibited one-handed helical conformation induced by the chirality of phosphorus atoms in the polymer terminal. The enantiomer (R,R)-1,2-bis(boranato(tert-butyl)methylphosphino) ethane gave the opposite one-handed helical polymer. Optically active bisphosphine (S,S)-1,2-bis(boranatomethylphenylphosphino) ethane was employed for the helix-sense-selective polymerization of triphenylmethyl methacrylate in order to obtain the polymer with the same helix sense as the polymer obtained from the initiator (S,S)-1,2-ethane bis(t-butylm-ethylphosphineborane). Further, removal of the coordinated boranes and complexation with platinum(II) on the chiral phosphorus atoms were carried out in order to yield the corresponding polymer-platinum(II) complex without loss of its chiral higher-ordered structure.