Reactions of group IV organometallic compounds : XXVII. Some reactions of [(trimethylsilyl)imino]phosphorane

The reaction of [(trimethylsilyl)imino]methyldiphenylphosphorane: Ph₂MePNSiMe₃ (I) with several acid anhydrides or alkyl isocyanates took place by the simple cleavage of silicon-nitrogen bond. In contrast the interaction of (I) with phenyl isocyanate, isothiocyanate or carbon disulphide led to addition-elimination reactions of the Wittig type. Detailed investigation in the case of phenyl isocyanate indicated the usual elimination of Ph₂MePO is suppressed by the strong affinity of the trimethylsilyl group for anionic oxygen atom.     

Versatile Organometallic Initiators for the Living Polymerization of Isocyanates

Shashoua and Sweeney first demonstrated that isocyanates could by polymerized via an anionic mechanism to form high molecular weight materials. We have sought to eliminate the problems associated with the anionic procedure by developing transition metal complexes which are capable of catalyzing the living polymerization of isocyanates. Recently, we reported the living polymerization of alkyl isocyanates using TiCl₃OCH₂CF₃, I. Using I, polyisocyanates with controlled molecular weights and narrow polydispersities can be obtained at room temperature. ε⁵-CpTiCl₂N(CH₃)₂ (Cp = cyclopentadienyl), III, is also an excellent catalyst for the polymerization of isocyanates, and in terms of ease of handling and purification and tolerance toward monomer functionality, superior to I. In order to prepare triblock copolymers containing amorphous segments sandwiched between two isocyanate segments, we have prepared bimetallic initiators comprised of titanium alkoxides con- nected by flexible linkers. These linkers may be a small molecule (1,4- dihydroxycyclohexane, V) or a polymer (polydimethylsiloxane, PDMS, VI). Complexes V and VI can be used to initiate the living polymerization of isocyanates to yield polymers possessing central cyclohexyl bends (ldquo;broken worms rdquo;) or PDMS segments (triblock copolymers), respectively. Finally, cyclopolymerizations of 1,2-diisocyanates using these or- ganometallic initiators are reported.     

Investigation of stabilizing action of mixtures of organic phosphites with trialkyl(aryl)tin isocyanates in the thermal degradation of poly(vinyl chloride)

Investigation was made on the effects of mixtures of organic phosphites (tributyl-, trioctyl-, diphenylisooctyl) with isocyanates (triethyl-, tributyl-, triphenyl-, tribenzyltin) upon the rate of dehydrochlorination and crosslinking, and on the absorption spectrum of PVC during degradation in evacuated ampoules at 180°. The effectiveness of stabilizing action of these synergistic mixtures depends on the chemical structures of both phosphite and isocyanate. The activity of isocyanates in mixtures with phosphites decreases in the order: Bz₃SnNCO, Ph₃SnNCO > Bu₃SnNCO > Et₃SnNCO. At 180°. triphenyltin isocyanate decomposes with formation of tetraphenyltin and diphenyltin diisocyanate; parallel with disproportionation, decarboxylation of triphenyltin isocyanate occurs, during which carbon dioxide and N,N′-bis(triphenyltin)carbodiimide are generated. N,N′-bis(triphenyltin)carbodiimide is a stabilizer for PVC in thermal degradation and gives synergistic mixtures with organic phosphites.     

Metal‐Mediated Production of Isocyanates,R3ENCO from Dinitrogen,Carbon Dioxide,and R3ECl

A highly efficient and versatile chemical cycle has been developed for the production of isocyanates through the molecular fixation of N₂, CO₂ and R₃ECl (E=C, Si, and Ge). Key steps include a ‘one‐pot’ photolytic N? N bond cleavage of a Group 6 dinuclear dinitrogen complex with in situ trapping by R₃ECl to provide a metal terminal imido complex that can engage in simultaneous nitrene‐group transfer and oxygen‐atom transfer to generate an intermediate metal terminal oxo complex with release of the isocyanate product. Reaction of the oxo complex with additional equivalents of R₃ECl regenerates a metal dichloride that is the precursor for dinuclear dinitrogen starting material.     

Metal‐Mediated Production of Isocyanates,R3ENCO from Dinitrogen,Carbon Dioxide,and R3ECl

A highly efficient and versatile chemical cycle has been developed for the production of isocyanates through the molecular fixation of N₂, CO₂ and R₃ECl (E=C, Si, and Ge). Key steps include a ‘one‐pot’ photolytic N N bond cleavage of a Group 6 dinuclear dinitrogen complex with in situ trapping by R₃ECl to provide a metal terminal imido complex that can engage in simultaneous nitrene‐group transfer and oxygen‐atom transfer to generate an intermediate metal terminal oxo complex with release of the isocyanate product. Reaction of the oxo complex with additional equivalents of R₃ECl regenerates a metal dichloride that is the precursor for dinuclear dinitrogen starting material.     

Reactions of fused dihydro-1,2,4-thiadiazoles with isocyanates and isothiocyanates to give 6aλ4-thia-1,3,4,6-tetraazapentalene derivatives

3-Methyl-6,7-dihydro-5H-1,2,4-thiadiazolo[4,5-a]pyrimidine 4a reacted with isocyanates and isothiocyanates with elimination of acetonitrile and concomitant addition of two molecules of the heterocumulene to give the 2,3-disubstituted-6,7-dihydro-5H-2aλ⁴-thia-2, 3, 4a, 7a-tetraazacyclopent[cd]indene-1 (2H), 4(3H)-diones 8a–8e and the corresponding dithiones 9a–9h , respectively. 3-Methyl-5, 10-dihydrobenzo[e]-1,2,4-thiadiazolo[4,5-a][1,3]diazepine 5a likewise reacted with isocyanates and isothiocyanates to give the 2,3-disubstituted-5,10-dihydro-2aλ⁴-thia-2,3, 4a, 10a-tetraazapentaleno[3, 3a, 4-gh]benzocyclopheptene-1, 4-diones 10a–10f and the corresponding dithiones 11a–11f . The base 4a reacted with phenyl isocyanate, methyl isothiocyanate, and phenyl isothiocyanate in toluene at room temperature to give the zwitterions 14a , 14b , and 14c , respectively, and the diazepine 5a reacted with phenyl isothiocyanate to give the zwitterion 17 .     

The effect of masked isocyanates on the moisture absorption of MY 720/DDS epoxy resin

Several masked isocyanates were prepared with variations in both the type of isocyanate and masking group. They were characterized by elemental analysis and NMR spectroscopy, and their unblocking temperatures were determined. In general, higher unblocking temperatures were obtained using acyclic and cyclic aliphatic isocyanates and fluorinated phenols. Those with unblocking temperatures in the range of 120–180°C were incorporated into MY 720/DDS epoxy resin prior to cure. Highly fluorinated variations were incompatible with the resin. IR and DSC analyses showed that residual functional groups in the epoxy resin reacted with the masked isocyanates. Reductions in moisture absorption as high as 65% were obtained depending on the masked isocyanate. DMA studies showed that the T_g of the epoxy resin is lowered by incorporation of the masked isocyanate but the elastic modulus (E′) is relatively unchanged at temperatures below T_g.     

Determination of airborne isocyanates as di-n-butylamine derivatives using liquid chromatography and tandem mass spectrometry

A method for the determination of isocyanates as di-n-butyl amine (DBA) derivatives using tandem mass spectrometry (MS/MS) and electrospray ionisation (ESI) is presented. Multiple-reaction monitoring (MRM) of the protonated molecular ions and corresponding deuterium-labelled d₉-DBA derivatives resulted in selective quantifications with correlation coefficients >0.998 for the DBA derivatives of isocyanic acid (ICA), methyl isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC), phenyl isocyanate (PhI), 1,6-hexamethylene diisocyanate (HDI), 2,4-, 2,6-toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), 4,4′-methylenediphenyl diisocyanate (MDI), 3-ring MDI, 4-ring MDI, HDI-isocyanurate, HDI-diisocyanurate, HDI-biuret and HDI-dibiuret. The instrumental precision for 10 repeated injections of a solution containing 0.1 μg ml⁻¹ of the studied derivatives was <2%. Performing MRM of the product ion [DBA + H]⁺ (m/z = 130) from the protonated molecular ion resulted in the lowest detection limits, down to 10 amol (for TDI). Quantification of concentrations below 10⁻⁶ of the occupational exposure limit (OEL) for TDI during 10 min of air sampling was made possible. In an effort to control the formation of alkali adducts, addition of lithium acetate to the mobile phase and monitoring of lithium adducts was evaluated. Having lithium present in the mobile phase resulted in complete domination of [M + Li]⁺ adducts, but detection limits for the studied compounds were not improved. Different deuterium-labelled derivatives as internal standards were evaluated. (1) DBA derivatives of deuterium-labelled isocyanates (d₄-HDI, d₃-2,4-TDI, d₃-2,6-TDI and d₂-MDI), (2) d₉-DBA derivatives of the corresponding isocyanates and (3) d₁₈-DBA derivatives of the corresponding isocyanates. An increase in number of deuterium in the molecule of the internal standard resulted in an increase in instrumental precision and a decrease in correlation within calibration series.     

The heI photoelectron spectra of the halogen azides,XN3(X = Cl and Br) and the halogen isocyanates,XNCO(X = Cl,Br and I)

High yield routes to the unstable halogen azides and isocyanates have permitted vacuum ultraviolet photoelectron spectra to be obtained for the chlorine and bromine azides, and the chlorine, bromine and iodine isocyanates. The results are compared with ab initio and semi-empirical calculations, leading to a reassignment of the photoelectron spectra of the parent acids, HN₃ and HNCO in the high energy region. The halogen azide and isocyanate photoelectron spectra provide an interesting investigation into how the orbitals of a linear pseudohalide grouping are perturbed by an off-azis halogen atom. A photoelectron spectrum for the unknown molecule FNCO is predicted.     

簇合物(p-H2)N-HCCCN的结构和能量

采用两体作用势模型和遗传算法对簇合物（p-H₂）_N-HCCCN的极小能量结构和能量进行了理论研究.结果表明,20 个para-H₂分子形成HCCCN周围的第一个溶剂层,第一个溶剂层包含三个溶剂环,每个溶剂环都有6 个para-H₂分子,第19和20个para-H₂分子分别聚集在HCCCN分子的N、H原子末端. 进一步计算了（p-H₂）_N-HCCCN的化学势,发现化学势随para-H₂分子个数的增加呈震荡变化.     

Structural elucidation of isocyanate-peptide adducts using tandem mass spectrometry

Diisocyanates are highly reactive chemical compounds widely used in the manufacture of polyurethanes. Although diisocyanates have been identified as causative agents of allergic respiratory diseases, the specific mechanism by which these diseases occur is largely unknown. To better understand the chemical species produced when isocyanates are reacted with model peptides, tandem mass spectrometry was employed to unambiguously identify the binding site of four commercially-relevant isocyanates on model peptides. In each case, the isocyanates react preferentially with the N-terminus of the peptide. No evidence of side-chain/isocyanate adduct formation exclusive of the N-terminus was observed. However, significant intra-molecular diisocyanate crosslinking was observed between the N-terminal amine and a side-chain amine of arginine, when Arg was located within two residues of the N-terminus. Addition of multiple isocyanates to the peptide occurs via polymerization of the isocyanate at the N-terminus, rather than via addition of multiple isocyanate molecules to varied residues within the peptide. The direct observation of isocyanate binding to the N-terminus of peptides under these experimental conditions is in good agreement with previous studies on the relative reaction rate of isocyanate with amino acid functional groups.     

Lanthanoid isopropoxide as a novel initiator for anionic polymerization of isocyanates

Lanthanum isopropoxide was found to serve as a novel anionic initiator for the polymerization of hexyl isocyanate affording poly(hexyl isocyanate) with very high molecular weight (M _n > 10⁶) under appropriate conditions. Other lanthanoid alkoxides, such as samarium, ytterbium and yttrium isopropoxides, also brought about the polymerization of hexyl isocyanate. Butyl, isobutyl, octyl and m-tolyl isocyanates also underwent the polymerization reaction to form the corresponding polymers by using lanthanum isopropoxide as initiator, while polymerizations of tert-butyl and cyclohexyl isocyanates with lanthanum isopropoxide did not occur under identical conditions.     

Substituted 2-methylene-1,3-oxazolidines, -1,3-thiazolidines, -1,3-benzothiazines, -1,3-oxazines, and substituted imidazopyrimidinediones from Cl(CH2)nNCO and Cl(CH2)nNCS and active methylene compounds

The reaction of omega-chloroalkyl isocyanates Cl(CH2)nNCO (n = 2 (2), 3 (4)) and isothiocyanate Cl(CH2)2NCS (3) with active methylene compounds CH2YY' 1 in the presence of Et3N or Na give 2-YY'-methylene-1,3-oxazolidines, (E,Z)-1,3-thiazolidines, and 1,3-oxazines from 2, 3, and 4, respectively. 2-(Chloromethyl)phenyl isocyanate 8 gives with 1 the corresponding benzo-oxazines. Ethyl 2-isothiocyanatobenzoate 10 gives the corresponding benzothiazolinone, whereas the analogous isocyanate 12 gives noncyclic enols. Ethoxycarbonyl isothiocyanate 14 gives an open-chain thioenol or an enol-thioamide. The cyanoamides CH2(CN)CONHR, R = H, Me, CHPh2, give with Et3N and 2 the bicyclic imidazopyrimidinediones 16, derived from two molecules of 2, but with their preformed Na salt they give the 1,3-oxazolidines. Reaction of cyanoacetamide with 3 in the presence of Na gave a tricyclic triaza(thia)indacene, derived from two molecules of 3. A reaction mechanism involving an initial attack of the anion 1- on the N=C=X (X = O, S) moiety gives an anion 18, which cyclizes intramolecularly and after tautomerization gives the mono-ring heterocycle. With the cyanoamides, the N- site of the ambident ion 18 attacks another molecule of 2 giving the anion 20, which by intramolecular attack on the CN, followed by expulsion of the Cl- gives the bicyclic 16 after tautomerization.     

Generation of sulfonylureas under photoredox catalysis and their biological evaluations

Traditional synthesis of sulfonylureas largely depends on nucleophilic addition of arylsulfonamides to presynthesized isocyanates.Now we report a new access to alkylsulfonylureas with good yields and broad substrate scope.With the insertion of commercialized chlorosulfonyl isocyanate under photoredox catalysis,alkylsulfonylureas are synthesized in one-pot from the corresponding anilines and silyl enolates.A reaction mechanism is proposed showing the transformation undergoes a radical process,and...     

A facile and rapid route for the synthesis of novel 1,5-substituted tetrazole hydantoins and thiohydantoins via a TMSN3-Ugi/RNCX cyclization

This Letter describes novel methodology for the rapid assembly of new and biologically appealing 1,5-substituted tetrazole-hydantoins and thiohydantoins. The product of a TMSN₃-Ugi multi-component reaction is treated with an excess of isocyanate or isothiocyanate to generate the final scaffold in moderate to good yields. The applicability of this solution phase methodology to the preparation of a small collection of compounds is discussed.     

6,12-二乙炔基茚并[1,2-b]芴系列衍生物的非线性光学性质

采用密度泛函理论(DFT) CAM-B3LYP方法对6,12-二乙炔基茚并[1,2-b]芴系列衍生物的极化率(α_s)和第二超极化率(γ_s)进行研究. 结果表明, 此类分子具有较大的γ_s值. 用乙炔基硅烷基和氧原子取代茚并[1,2-b]芴分子6,12位的氢原子后, 分子的几何构型发生改变, 进而影响其非线性光学(NLO)性质. 连接乙炔基硅烷基的分子α_s值和γ_s值均增大, 而连接氧原子的分子α_s值和γ_s值均减小. 茚并[1,2-b]芴环2,8位取代基R(R=H, F, CH₃)的不同, 对分子的γ_s值也有一定的影响, R为CH₃时分子的α_s值和γ_s值均较大. 由含时密度泛函理论(TD-DFT)方法计算的吸收光谱分析可知, 与茚并[1,2-b]芴系列分子相比, 引入乙炔基硅烷基的分子共轭性增强, 最大吸收波长红移; 引入氧原子的分子几何结构扭曲, 共轭性降低, 最大吸收波长蓝移.     

Effect of polar aprotic solvents and organometallic catalysts on the reaction of alcohols with isocyanates

DMF and DMSO catalyse the reaction of butanol with PhNCO but inhibit that with aliphatic isocyanates, due to formation of an active 1:1 charge transfer complex with the aromatic isocyanate. Similarity was found in the mode of catalysis of the urethane reaction with these solvents to that with tert, amines. Various organometallic compounds were tested as catalysts for urethane formation with aliphatic isocyanates. Those that gave fast addition to the NCO group, such as tributyltin oxide, Zr(OBu)₄ and Zr(acac)₄, were the strongest catalysts. In the presence of organometallic catalysts, urethane formation was the sole reaction and trimerization of the isocyanate was suppressed.     

Anionic copolymerization of isocyanates with ketenes

Diphenyl-, phenylethyl, and phenylmethylketene have been copolymerized with phenyl isocyanate by use of sodium naphthalene in dimethylformamide (DMF) at ?45°C. Reactivity ratios of phenyl isocyanate (r₂) with diphenylketene (r₁) were r₁ = 0.10, r₂ = 0.29; with phenylethylketene (r₁) were r₁ = 1.6, r₂ = 0.10; and with phenyl methyl ketene (r₁) were r₁ = 4.8, r₂ = 0.02. The same initiator and solvent system were used for homopolymerization of phenylethylketene and copolymerization with m-chloro-, p-chloro-, p-methoxy-, and m-methoxyphenyl isocyanate as well as with phenyl isocyanate. Molecular weights ranged from 1740 to 4000. The effect of substituents on the order of isocyanate incorporation into the copolymer was m-Cl = p-Cl > m-MeO > H > p-MeO. Phenylethylketene was also copolymerized with m-methoxyphenyl, p-methoxyphenyl, and p-tolyl isocyanate in tetrahydrofuran (THF) at ?78°C. Molecular weights ranged from 2800 to 10,500. The least reactive isocyanate was incorporated into the copolymer to a greater extent in this solvent than in the more polar DMF. DTA showed the presence of crystallinity only in polymers of high isocyanate content. The ketenes copolymerized less readily with alkyl isocyanates, such as ethyl, n-butyl, n-hexyl, and cyclohexyl isocyanate, than with the aromatic isocyanates when sodium naphthalene was used in either DMF or THF.     

The stability and structure of (N<Subscript>2</Subscript>)<Subscript>j</Subscript>(H<Subscript>2</Subscript>O)<Subscript>i</Subscript> and (Ar)<Subscript>j</Subscript>(H<Subscript>2</Subscript>O)<Subscript>i</Subscript> clusters

The stability and structure of water clusters absorbing nitrogen molecules or argon atoms was analyzed by molecular dynamics simulation at 233 K. The (?μ/?i)_{V, T} derivative of the chemical potential, a value characterizing the stability of a cluster with respect to its size, depends linearly on the number of molecules i. According to this criterion, the clusters under study become stable near i = 40. The average length of H-bonds increases monotonically in the growing cluster of pure water and exhibits oscillatory behavior if the growing cluster contains N₂ molecules or Ar atoms. The number of H-bonds per molecule oscillates between one and six as the cluster size changes. These oscillations are damped in pure water and sustained for clusters containing impurities, especially argon.     

Organosilicon synthesis of isocyanates: I. Synthesis of isocyanates of the furan, thiophene, and mono-and polyfluorophenyl series

A convenient synthesis of known and unknown isocyanates of the furan, thiophene, and mono-and polyfluorophenyl series, involving silylation of starting amines with hexamethyldisilazane or chlorotrimethylsilane, followed by phosgenation of the resulting N-silyl-substituted amines. An unusual high-temperature rearrangement of 3-(methoxycarbonyl)-4,5-dimethylthiophene-2-yl isocyanate into its 5-ethyl isomer. ortho-Fluorine substituent in anilines decreases the yield of isocyanates, whereas 2,3,5,6-tetrafluorophenyl isocyanate exists for only a short time as a 5% toluene solution.