Reactivity and gelation. II. Substitution effect

The development in Paper I is extended to multifunctional condensations where the functional groups exhibit unequal reactivities induced by substitution effects in the course of the polymerization. A system R(A)₂/R′(B)₃ is examined to determine how the gel point varies with the strength and positive or negative sense of the substitution effect. As in Paper I, intramolecular interactions are not considered.     

cine‐Substitution Reactions of Metallabenzenes: An Experimental and Computational Study

Alkali‐resistant osmabenzene [(SCN)₂(PPh₃)₂Os{CHC(PPh₃)CHCICH}] ( 2 ) can undergo nucleophilic aromatic substitution with MeOH or EtOH to give cine‐substitution products [(SCN)₂(PPh₃)₂Os{CHC(PPh₃)CHCHCR}] (R=OMe ( 3 ), OEt( 4 )) in the presence of strong alkali. However, the reactions of compound 2 with various amines, such as n‐butylamine and aniline, afford five‐membered ring species, [(SCN)₂(PPh₃)₂Os{CH?C(PPh₃)CH?C(CH?NHR′)}] (R′=nBu( 8 ), Ph( 9 )), in addition to the desired cine‐substitution products, [(SCN)₂(PPh₃)₂Os{CHC(PPh₃)CHCHC(NHR′)}] (R′=nBu( 6 ), Ph( 7 )), under similar reaction conditions. The mechanisms of these reactions have been investigated in detail with the aid of isotopic labeling experiments and density functional theory (DFT) calculations. The results reveal that the cine‐substitution reactions occur through nucleophilic addition, dissociation of the leaving group, protonation, and deprotonation steps, which resemble the classical “addition‐of‐nucleophile, ring‐opening, ring‐closure” (ANRORC) mechanism. DFT calculations suggest that, in the reaction with MeOH, the formation of a five‐membered metallacycle species is both kinetically and thermodynamically less favorable, which is consistent with the experimental results that only the cine‐substitution product is observed. For the analogous reaction with n‐butylamine, the pathway for the formation of the cine‐substitution product is kinetically less favorable than the pathway for the formation of a five‐membered ring species, but is much more thermodynamically favorable, again consistent with the experimental conversion of compound 8 into compound 6 , which is observed in an in situ NMR experiment with an isolated pure sample of 8 .     

Thermal decomposition of dicyclopentadienylarylvanadium compounds

The thermolysis of compounds of the type Cp₂VR (R = aryl) in the solid state has been studied. A distinct increase in thermal stability is observed upon substitution of the ortho-position of the aryl group. Thermal decomposition occurs with formation of RH, Cp₂ V, a vanadocene homologue with the group R substituted in one of the Cp rings and, probably, a vanadocene homologue with two substituted Cp rings. It is shown that the abstraction of the hydrogen atom from the cyclopentadienyl ring, necessary for the formation of RH, is an intermolecular process, whereas the substitution of the aryl group in the Cp ring is intramolecular. A decomposition mechanism is proposed in which the group R is transferred from the vanadium atom to the C₅H₅ ring of the same molecule by interaction with an aryl group of another molecule. The thermal decomposition of Cp₂VR is compared with that of the analogous titanium compounds.     

Synthesis of peri-annelated heterocyclic systems based on 3-substituted 1-aryl-4,6-dinitro-1H-indazoles

A method for the synthesis of peri-annelated trinuclear heterocycles, including 14-electron heteroaromatic systems, namely, 1H-thiopyrano[4,3,2-cd]indazoles and 1,5-dihydropyrazolo[3,4,5-de]cinnolines, from 3-R-1-aryl-4,6-dinitro-1H-indazoles was developed. The method is based on the high mobility of the NO₂ group in position 4 and consists of either selective nucleophilic substitution of the 4-NO₂ group on treatment with the HSCH₂CO₂Me—K₂CO₃ system followed by intramolecular cyclization of the resulting sulfide (R = CHO) or the corresponding sulfone (R = CN) formed upon its oxidation or direct intramolecular substitution of the 4-NO₂ group (R = CH=NNHPh).     

A DFT study on proton transfers in hydrolysis reactions of phosphate dianion and sulfate monoanion

B3LYP calculations were carried out on hydrolysis reactions of monosubstituted(R) phosphate dianion and sulfate monoanion. In the reacting system, water clusters (H₂O)₂₂ and (H₂O)₃₅ are included to trace reaction paths. For both P and S substrates with R = methyl group, elementary processes were calculated. While the phosphate undergoes the substitution at the phosphorus, the sulfate does at the methyl carbon. For the S substrate with R = neopentyl group, the product tert‐amyl alcohol was found to be formed via a dyotropic rearrangement from the neopentyl alcohol intermediate. For R = aryl groups, transition‐state geometries were calculated to be similar between P and S substrates. Calculated activation energies are in good agreement with experimental values. After the rate‐determining transition state of the substitution, the hydronium ion H₃O⁺ is formed at the third water molecule. It was suggested that alkyl and aryl substrates are of the different reactivity of the hydrolysis. © 2014 Wiley Periodicals, Inc.     

Complexes carbeniques des ferroporphyrines: Preparation de complexes carbeniques comportant deux substituants electrodonneurs par alcoolyse ou thionolyse des complexes halogenocarbeniques correspondants

α-Halocarbeneporphyriniron complexes, Fe(P)(C(Cl)R) react with alcohols or thiols with substitution of the chlorine atom by OR′ or SR′ groups. This reaction has been used to obtain new carbeneporphyriniron complexes in which the carbene ligand is substituted by two electrodonating groups. The complexes Fe(P)(C(XR′)R) with XR′ = OCH₃ or OC₂H₅, R = CH₃ or (CH₃)₂CH and P = TPP (tetraphenylporphyrin) or TTP (tetratolylporphyrin) and with XR′ = SCH₂C₆H₅, R = CH₃ and P = TPP or TTP, have been isolated and fully characterized.     

Diverse Reactivity of an Electrophilic Phosphasilene towards Anionic Nucleophiles: Substitution or Metal–Amino Exchange

The reaction of MesLi (Mes=2,4,6‐trimethylphenyl) with the electrophilic phosphasilene R₂(NMe₂)Si‐RSi=PNMe₂ ( 2 , R=Tip=2,4,6‐triisopropylphenyl) cleanly affords R₂(NMe₂)Si‐RSi=PMes and thus provides the first example of a substitution reaction at an unperturbed Si=P bond. In toluene, the reaction of 2 with lithium disilenide, R₂Si=Si(R)Li ( 1 ), apparently proceeds via an initial nucleophilic substitution step as well (as suggested by DFT calculations), but affords a saturated bicyclo[1.1.0]butane analogue as the final product, which was further characterized as its Fe(CO)₄ complex. In contrast, in 1,2‐dimethoxyethane the reaction of 1 with 2 results in an unprecedented metal–amino exchange reaction.     

Substitution reactions of H2GeFBeF with RH (R = F,OH, NH2): A theoretical study

A combined density functional and ab initio quantum chemical study of the substitution reactions of the germylenoid H₂GeFBeF with RH (R = F, OH, NH₂) compounds was carried out. The geometries of all the stationary points of the reactions were optimized using the DFT B3LYP method and then the QCISD method was used to calculate the single-point energies. The theoretical calculations indicated that along the potential energy surface, there were one transition state (TS) and one intermediate (IM) which connected the reactants and the products. The three substitution reactions of H₂GeFBeF with RH are compared with the addition reactions of H₂Ge with RH. And based on the calculated results we concluded that the substitution reactions of H₂GeFBeF + RH involve two steps. One is dissociation onto H₂Ge + BeF₂, and the other is the addition reaction of H₂Ge with RH.     

Bimolecular Homolytic Substitutions at Nitrogen: An Experimental and Theoretical Study on the Gas‐Phase Reactions of Alkyl Radicals with NF3

The X‐ray irradiation of binary mixtures of alkyl iodides R?I (R=CH₃, C₂H₅, or i‐C₃H₇ radicals) and NF₃ produces R?NF₂ and R?F. Based on calculations performed at the CCSD(T), MRCI(SD+Q), G3B3, and G3 levels of theory, the former product arises from a bimolecular homolytic substitution reaction (S_H2) by the alkyl radicals R, which attack the N atom of NF₃. This mechanism is consistent with the suppression of R?NF₂ by addition of O₂ (an efficient alkyl radical scavenger) to the reaction mixture. The R?F product arises from the attack of R to the F atom of NF₃, but additional contributing channels are conceivably involved. The F‐atom abstraction is, indeed, considerably more exothermic than the S_H2 reaction, but the involved energy barriers are comparable, and the two processes are comparably fast.     

Étude radiocristallographique des solutions solides KAuCl3,69Br0,31, KAuCl1,94Br2,06et KAuCl1,82Br2,18,2H2O

The structures of anhydrous solid solutions KAuCl_3.69Br_0.31 (a=8.687(2) b=6.420(1) c=12.290(1)Å β=95.568(3)° R=0.046) and KAuCl_1.94Br_2.06 (a=8.789(2) b=6.578(1) c=12;562(2)Å β=96.147(3)° R=0.074) have been determined by X-ray diffraction to be in the P2₁/c centrosymmetric group. The structure of the hydrous solid solution KAuCl_1.82Br_2.18,2H₂O (a=9.414(1) b=11.842(1) c=8.399(2)Å β=94.459(2)° R=0.068) corresponds to the P2₁/n group. The statistical substitution coefficient observed in the anhydrous or hydrous solid solutions with a bromine/chlorine ratio near 50% gives proof of a trans substitution. In the anhydrous solid solution KAuCl_1.94Br_2.06 the length between gold and halides (Hal) is equal to 2.330(14)Å for Au(2)-Hal(3) and 2.400(5)Å for Au(2)-Hal(4), close to the corresponding lengths Au-Cl (2.288Å) in KAuCl₄,2H₂O and Au-Br (2.427Å) in KAuBr₄,2H₂O. These results are in agreement with the existence of an intermediate trans entity [AuCl₂Br₂]⁻.     

Preparation of polymer-anchored dinuclear rhodium(I) catalysts attached by the bridging groups

We describe a method to anchor dinuclear rhodium(I) complexes by substitution of the chlorine bridge in Rh₂(μ-Cl)₂L₄ with LiSR where R represents a polymeric chain. The catalytic activity of such complexes compares well with that observed in homogeneous phase.     

Synthesis of β‐monosubstituted α,β‐unsaturated amides with Z‐selectivity using diphenylphosphonoacetamides

The utility of diphenylphosphonoacetamides [(PhO)₂P(O)CH₂CONRR′] as Horner–Wadsworth–Emmons reagents was examined with five different patterns of substitution upon the amide nitrogen atom ( 2a : R, R′ = CH₂Ph; 2b : R = CH₂Ph, R′ = H; 2c : R = Me, R′ = OMe; 2d : R, R′ = Ph; 2e : R, R′ = (CH₂)₄). The reaction of 2a was found to be Z‐selective for aromatic aldehydes with selectivities up to 95:5. Reagent 2b led to reasonable selectivity for both benzaldehyde (85:15) and 3‐phenylpropionaldehyde (87:13), while 2c was somewhat effective for only the latter alkyl aldehyde (83:17). Compounds 2d and 2e exhibited slightly lower selectivities compared with 2a . © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:515–523, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20054     

Molecular parameters of sodium cellulose xanthate in dilute solution

Molecular parameters of sodium cellulose xanthate in NaOH solution have been determined by means of light scattering and viscometry. The effect of the degree of substitution on the molecular configuration of sodium cellulose xanthate has been studied for three series of samples of varying degree of substitution. The expansion factor has been determined from the expression due to Orofino and Flory. The effective bond length b and the ratio of the unperturbed dimension to the dimension assuming free rotation of the chain units (R?_o²/R?_f²)^1/2, have also been determined. It is concluded that sodium cellulose xanthate in dilute solution is a loosely coiled molecule, comparable to other cellulose derivatives in chain stiffness.     

Reactions of 1,3,5-trinitrobenzene with primary aliphatic alcohols

Analysis of reactions of 1,3,5-trinitrobenzene (TNB) with alcoholates of primary aliphatic alcohols (substitution of the nitro group or generation of σ^H-complexes at the unsubstituted position of TNB) leads to the conclusion that high basicity of alcoholates (MeONa, EtONa) of unsubstituted primary alcohols promotes formation of σ^H-complexes, thus preventing nucleophilic substitution of a nitro group. Introduction of electron-withdrawing substitutes (R = HC≡C, H₂C = CH, pyridyl) into the alcohol molecule (RCH₂OH) reduces the basicity of their alcoholates which makes substitution of nitro groups possible aff ording the corresponding 1-alkoxy-3,5-dinitrobenzenes in the presence of K₂CO₃ in N-methylpyrrolidone at 80 °C.     

Platinum thiosemicarbazide and thiourea complexes: the crystal structure of [PtCl(dppe){SC(NHMe)NHNMe2-S}](PF6) and the influence of intramolecular hydrogen bonding on ligand co-ordination mode

The reaction of [PtCl₂(dppe)] [dppe=1,2-bis(diphenylphosphino)ethane] with two equivalents of the thioureas NHRC(S)NHR (R=H, Me, Et) in the presence of NH₄PF₆ led to substitution of both chlorides and formation of the complexes [Pt(dppe){SC(NHR)₂}₂](PF₆)₂ (1a, R=H; 1b, R=Me; 1c, R=Et). In contrast, the reaction of [PtCl₂(dppe)] with one equivalent of the potentially bidentate thiosemicarbazides NHRC(S)NHNR′₂ (R=Me, R′=H; R=Et, R′=H; R=Ph, R′=H; R=Me, R′=Me) in the presence of NH₄PF₆ led to substitution of only one chloride and formation of the complexes [PtCl(dppe){SC(NHR)NHNR₂′-S}](PF₆) (2a, R=Me, R′=H; 2b, R=Et, R′=H; 2c, R=Ph, R′=H; 2d, R=Me, R′=Me). An X-ray analysis of complex 2d revealed that an intramolecular N–H⋯Cl hydrogen bond [N(2)⋯Cl(1)=3.29(2) Å] helps to stabilise the monodentate co-ordination mode. The chloride ligand can be abstracted from complex 2d by treatment with TlPF₆, and this reaction led to formation of [Pt(dppe){SC(NHMe)NHNMe₂-S,N}](PF₆)₂ 3d. Reaction of [PtCl₂(dppe)] with unsubstituted thiosemicarbazide NH₂C(S)NHNH₂ in the presence of NH₄PF₆ resulted in a mixture of products containing mono- and bidentate co-ordinated ligands, [PtCl(dppe){SC(NH₂)NHNH₂-S}](PF₆) 2e and [Pt(dppe){SC(NH₂)NHNH₂-S,N}](PF₆)₂ 3e. [PtCl₂(dppe)] also reacts with two equivalents of NHMeC(S)NHNMe₂ in the presence of NH₄PF₆ to yield [Pt(dppe){SC(NHMe)NHNMe₂-S}₂](PF₆)₂ 1d, in which the thiosemicarbazide is acting as an S-donor, directly analogous to the thiourea ligands in complexes 1a–c.     

The reaction of carbanions with 2-substituted-2-nitropropanes : Substitution and dimerization occurring by radical chain processes involving electron transfer

The reaction of mono-enolate anions with O₂NCMe₂X where X = Cl, NO₂, p-MePhSO₂ yield coupling (RCOCH(R′)(CMe₂NO₂) and enolate dimerization products (RCOCH(R′)CH(R′)COR) by free radical chain mechanisms involving bimolecular substitution or electron transfer reactions between the enolate anion and the intermediate nitro alkane radical anion (XCMe₂NO₂^?).     

Synthesis and Some Chemical Properties of 2,2-Dimethyl-4-R-1-oxa-4-aza-2-sila-5-benzocycloheptanones

One-pot synthesis of 2,2-dimethyl-4-R-1-oxa-4-aza-2-sila-5-benzocycloheptanones (R = Me, CH₂SiMe₂Cl) from the N-methylamide of salicylic acid and salicylamide, respectively, by treatment of these amides with a mixture of hexamethyldisilazane and dimethylchloromethylchlorosilane was developed. The hydrolysis and other nucleophilic substitution reactions of the resultant seven-membered silacyclanes were studied. In the case of the silacyclane with R = Me, hydrolysis leads to the corresponding disiloxane, while the silacyclane with R = CH₂SiMe₂Cl gives either 2,2,6,6-tetramethyl-4-(2-hydroxybenzoyl)-2,6-disilamorpholine or its hydrochloride, depending on the reaction conditions. The chlorine atom was replaced by fluorine in the silacyclane with R = CH₂SiMe₂Cl. The structures of 2,2,6,6-tetramethyl-4-(2-hydroxybenzoyl)-2,6-disilamorpholine and its hydrochloride as well as 2,2-dimethyl-4-R-1-oxa-4-az! a-2-sila-5-benzocycloheptanones (R = CH₂SiMe₂Cl, CH₂SiMe₂F) were confirmed by X-ray diffraction.     

Comparison of triel bonds with different chalcogen electron donors: Its dependence on triel donor and methyl substitution

The complexes between R₃Tr (Tr = B, Al, and Ga; R = H, F, Cl, and Br) and H₂X (X = O, S, and Se) were theoretically studied. The interaction energies of R₃Al⋯H₂X and R₃Ga⋯H₂X are consistent with the electronegativity of the halogen atom R (R ≠ H), but an opposite dependence is found for R₃B⋯H₂X. The triel bond of R₃Tr⋯H₂X is weaker for the heavier chalcogen donor. The dependence of triel bonding strength on the triel atom is complicated, depending on the nature of R and X. The methyl substitution of H₂X causes a substantial increase in the interaction energy from −5.74 kcal/mol to −22.88 kcal/mol, and its effect is relevant to the nature of Tr, X, and R groups. For the S and Se donors, the increased percentage of interaction energy is almost the same due to the methyl substitution, which is larger than that of the O analogue. In most triel-bonded complexes, electrostatic dominates and polarization has comparable contribution. However, polarization plays a dominant role in R₃B⋯ and R₃B⋯ (R = Cl and Br; R′ = H and Me).     

Beiträge zur Chemie des Brompentafluorids. 4. Arylbrom(V)-dioxide und -fluoridoxide

Contributions to the Chemistry of Brominepentafluoride. 4. Arylbromine(V) Dioxides and Fluorideoxides . Arylbromine(V) tetrafluorides RBrF₄ (R=C₆F₅, p- and m-CF₃C₆H₄, o-FC₆H₄) react in aimed hydrolysis reactions or with (Me₃Si)₂O to the corresponding arylbrominedioxides RBrO₂. However with CsNO₃ as reagent for fluorine-oxygen substitution arylbrominedifluorideoxides RBrOF₂ are formed. Fluorine-oxygen substitution reactions on BrF₅ with (Me₃Si)₂O and [F₃CC(O)]₂O in organic solvents proceed via polysubstitution and end under formation of BrO₂F whereas with C₆F₅C(O)OSiMe₃ via monosubstitution BrOF₃ is obtained. In organic solvents bromine(V) fluorideoxides are — similar to BrF₅ — principally accessible to fluorine-aryl substitution what is demonstrated by the formation of C₆F₅BrO₂ from BrO₂F.     

Structure–property relationships of ring-containing nylon 66 copolyamides

Several series of nylon 66 copolyamides were prepared with up to 30 mole-% substitution of ringed comonomers of the type X-(CH₂)_n-R-(CH₂)_n-X, where n = 0, 1, or 2; X = ?NH₂ or ? CO₂H; and R = phenylene, cyclohexylene, or naphthyle. The ring structure was correlated with glass transition temperature and melting point. The important features of ring structure fall into the following categories: ring isomerism, aromaticity, diamine vs. diacid substitution, chain length, and ring substitution. Proper “fit” (isomorphism) of the comonomer into the nylon 66 chain appears to be the main criterion for ringed copolymers of high T_g and high melting point.