Cationic polymerization by aromatic initiating systems. IV. Synthesis and characterization of α-ω-diphenylpolyisobutylene

The polymerization of isobutylene using ø₃Al coinitiator and the tertiary chlorides tert.-butyl chloride (t-BuCl) and 2,6-dichloro-2,6-dimethylheptane (Cl^t-R-Cl^t) initiators has been studied. Polymerization rates with the t-BuCl/ø₃Al and Cl^t-R-Cl^t/ø₃Al initiating systems were high in the ?20 to ?70°C range. Yields and molecular weights increased with decreasing temperature. As predicted by model experiments the extent of phenylation increases with decreasing temperatures. According to spectroscopic evidence the polyisobutylenes carry phenyl end groups.     

Thermally reversible polymer systems by cyclopentadienylation. II. The synthesis of cyclopentadiene-containing polymers

The synthesis of polymers containing either terminal or pendant cyclopentadiene (CPD) groups has been studied. Using information obtained from model studies, the synthesis of polyisobutylenes containing a CPD terminus was accomplished by the use of the tert-butylchloride–dimethylcyclopentadienylaluminum initiator system. Isobutylene polymerization by this system under carefully chosen conditions is essentially transfer free, and termination occurs by cyciopentadienylation. The presence of CPD end group has been established by UV spectroscopy and reaction with maleic anhydride. Selectivity toward termination by cyclopentadienylation increases with decreasing temperatures; at ?41°C and low conversion (<10%) ca. 72% of the polymer chains terminate in this manner. The synthesis of polymers containing randomly distributed pendant CPD groups along the chain has been accomplished by cyclopentadienylating with dimethylcyclopentadienylaluminum chlorobutyl rubber and chlorinated poly(ethylene-co-propylene) (Cl-EPM). Pendant CPD groups undergo Diels-Alder/retro-Diels-Alder condensations yielding thermally reversible networks; e.g., a cyclopentadienylated Cl-EPM was remolded three times to elastic sheets.     

N,N,N′,N′-Tetramethylethylendiamin-di(tert-butyl)aluminium-Kationen — Molekülstruktur des [(Me3C)2Al · TMEDA]⊕[(Me3C)2AlBr2]⊖

(N,N,N′,N′ -tetramethylethylendiamine) di(tert-butyl)aluminium Cations — Molecular Structure of [(Me₃C)₂Al(TMEDA)]^⊕[(Me₃C)₂AlBr₂]^? Dimeric di(tert-butyl)aluminium halides (Me₃C)₂AlX (X = Cl, Br) react with N,N,N′,N′ -tetramethylethylendiamine (TMEDA) to give three compounds: the salt-like [(Me₃C)₂Al(TMEDA)]^⊕[(Me₃C)₂AlX₂]^? 1 , characterized by crystal structure determination, and [(Me₃C)₂Al(TMEDA)]^⊕X^? 3 both with chelating amine, and the more covalent, pentane soluble (Me₃C)₂AlX(TMEDA) 2 with TMEDA bound by only one nitrogen atom. The reaction resembles the symmetrical and unsymmetrical cleavage of diborane(6). 3 (X = Cl) is also formed by treatment of 1 with boiling n-hexane in the presence of TMEDA over a period of 24 hours, while for X = Br the more covalent 2 is the main product under similar conditions. In solution 2 decomposes slowly yielding different products in dependency of the solvent: in benzene 3 and in n-pentane 1 are formed.     

Beiträge zur Chemie des Arsens. 5. Zur Existenz von Penta-tert-butyl-cyclopentaarsan, (t-BuAs)5

Contributions to the Chemistry of Arsenic. 5. On the Existence of Penta-tert-butyl-cyclo-pentaarsane, (t-BuAs)₅ The reaction of tert-butyldichlorarsane with magnesium in tetrahydrofurane or diethylether yields the hitherto unknown penta-tert-butyl-cyclopentaarsane, (t-BuAs)₅ ( 1 ), in addition to the cycloarsanes (t-BuAs)₄ and t-Bu₆As₈. Compound 1 was preparatively concentrated to ? 80 mole-% and characterized by its ¹H-NMR and mass spectrum. The thermodynamic stability of the tert-butyl substituted monocyclic arsanes decreases in the order (t-BuAs)₄ > (t-BuAs)₅ > (t-BuAs)₃. By thermolysis of 1 t-Bu₆As₈ and other polycyclic arsanes are formed.     

Dimerization of cyclopentadienyl ligands in the synthesis of transition metal complexes. 1,4,5,6,7,10,11,12-Octamethyltricyclo[7.3.0.03,7]-dodeca-3,5,9,11-tetraene and the complex of 1,1′,3,3′-tetrakis-(tert-butyl)-1,1′-dihydrofulvalene with I3 −

1,4,5,6,7,10,11,12-Octamethyltricyclo[7.3.0.0^3,7]dodeca-3,5,9,11-tetraene was obtained as a by-product in the synthesis of (C₅Me₅)₂CeCl from CeCl₃ and NaC₅Me₅. The complex of 1,1′,3,3′-tetrakis(tert-butyl)-1,1′-dihydrofulvalene with I₃ ⁻ was obtained as the major product in the reaction of YbI₃ with 1,3-Bu^t ₂C₅H₃Na. The structures of the title compounds were established by X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2310–2314, December, 1999.     

Rate constants for the decarboxylation of the t-butoxicarbonyl radical and concurring radical terminations directly obtained by kinetic ESR

Rate constants of various simultaneous reactions of t-butoxicarbonyl and t-butyl radicals generated by photolysis of t-butylpivalate in n-heptane are directly determined by kinetic electron spin resonance. The temperature dependence of the decarboxylation reaction t-BuO?O → t-Bu^. + CO₂ obeys log )K/S^?1( = 13.8?49.0/θ where θ = 2.303 RT/kJ ^. mol^?1. The self- and cross-termination of the radicals are diffusion limited.     

Olefin Polymerization and Copolymerization with Alkylaluminum-lnitiator Systems. VII. Initiation by Electrophilic Halogens

Abstract

The discovery of initiation of cat ionic polymerization of isobutylene and styrene by electrophilic chlorine generated by the reaction of chlorine and trimethylaluminum in the temperature range -40 to -100° is reported. Bromine and trimethylaluminum is a very poor initiating system, and iodine and trimethylaluminum does not initiate the polymerization of either isobutylene or styrene. Polymerization of isobutylene initiated by chlorine and trimethylaluminum shows a linear plot of log M_v vs 1/T with an overall E_DPof ～1.9 kcal, mole. The molecular weights (M_w) of polystyrene obtained with the Cl₂/Me₃Al system appear to be the highest ever reported for cationic polymerization of this monomer under comparable conditions. The mechanism of initiation has been investigated by model experiments: The reaction between Cl₂/ Me₃Al and 2,2,4-trimethyl-l-pentene gave three chlorinated products (2-chloromechyl-4,4-dimethyl-l-pentene, 1-chloro-2,4,4-trimethyl-1-pentene, and 2-chioromethyl-2,4,4-trimethyl-pentane). The position of chlorine in these compounds indicate initiation by electrophilic chlorine, Cl. Some preliminary results obtained using diethylaluminum chloride-halogens as coinitiator-initiator systems are also described.     

Cationic polymerizations by aromatic initiating systems. III. Model reactions for initiation and termination using the t-BuCl/ϕ3Al and Clt-R-Clt/ϕ3Al systems

Preparatory for the synthesis of terminally functional polyisobutylenes carrying one or two phenyl end groups, model experiments have been carried out using novel tert-butyl chloride/triphenylaluminum and 2,6-dichloro-2,6-dimethylheptane/triphenylaluminum initiating systems. As anticipated, t-BuCl was phenylated by ø₃Al and the product is tert-butylbenzene. The reaction is extremely rapid and temperature has little effect on it in the 0 to ?60°C range. The interaction between the 2,6-dichloro-2,6-dimethylheptane and ø₃Al was found to be complicated by a proximity effect which leads to proton elimination in addition to phenylation. The formation of the desired diterminally phenylated product is not quanititative even at ?60°C.     

Synthesen und Kristallstrukturen von [(t-Bu4Sb4)Fe(CO)4], [(t-Bu4Sb4)Mo(CO)5] und [(t-Bu3Sb4)Mo(η5-C5Me5)(CO)3]

Syntheses and Crystal Structures of [( t -Bu₄Sb₄)Fe(CO)₄], [( t -Bu₄Sb₄)Mo(CO)₅], and [( t -Bu₃Sb₄)Mo(η⁵-C₅Me₅)(CO)₃] t-Bu₄Sb₄ reacts with Fe₂(CO)₉ to form [(t-Bu₄Sb₄)Fe(CO)₄] ( 1 ). [(t-Bu₄Sb₄)Mo(CO)₅] ( 2 ) is formed from (thf)Mo(CO)₅ and t-Bu₄Sb₄. [(t-Bu₃Sb₄)Mo(η⁵-C₅Me₅)(CO)₃] ( 3 ) is a product of the reaction of t-Bu₄Sb₄ with [(η⁵-C₅Me₅)Mo(CO)₃]₂. The crystal structures of 1–3 are reported.     

Primary alkyl radicals: Can they be persistent?

The structure of t-Bu₃Si?H₂, (I), suggested that it might be a persistent primary alkyl radical since it has (i) a bulky group to protect the radical center; (ii) no β-hydrogens, so that a radical-radical disproportionation reaction is impossible; (iii) a β-silicon atom, which should prevent β-scission of tert-butyl as a unimolecular decomposition pathway. However, the self-reaction of (I) in isooctane was found to be a diffusion controlled process with log(A/M^?1 sec^?1) = 10.7 ± 0.3 and E = 2.5 ± 0.2 kcal mole^?1. Hence (I) is not persistent and it is concluded that a persistent primary alkyl will only be observed when the—?H₂ moiety is deeply buried among sterically protecting groups.     

Potassium and sodium 2,6-di-tert-butylphenoxides and their properties

The crucial factor of the reaction of 2,6-di-tert-butylphenol with alkali hydroxides is temperature, depending on which two types of potassium or sodium 2,6-di-tert-butylphenoxides are formed. These types exhibit different catalytic activity in the alkylation of 2,6-di-tert-butylphenol with methyl acrylate. More active forms of 2,6-Bu^t ₂C₆H₃OK or 2,6-Bu^t ₂C₆H₃ONa are synthesized at temperatures higher than 160 °C and are predominantly the monomers, which dimerize on cooling. The data of ¹H NMR, electronic, and IR spectra for the corresponding forms of 2,6-Bu^t ₂C₆H₃OK and 2,6-Bu^t ₂C₆H₃ONa isolated in the individual state are in agreement with cyclohexadienone structure. In DMSO or DMF, the dimeric forms of 2,6-di-tert-butylphenoxides react with methyl acrylate to form methyl 3-(4-hydroxy-3,5-di-tert-butylphenyl)propionate in 64–92% yield. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2138–2143, December, 2006.     

Beiträge zur Chemie des Phosphors. 122. 1,2,3,4-Tetra-tert-butyl-tetraphosphan,H(PBut)–(PBut)2–(PBut)H – ein stabiles kettenförmiges Tetraphosphan

Contributions to the Chemistry of Phosphorus. 122. 1,2,3,4-Tetra-tert-butyltetraphosphane, H(PBu^t)—(PBu^t)₂—(PBu^t)H — a Stable Chain-type Tetraphosphane The alcoholysis of 1,2,3,4-tetra-tert-butyl-1,4-bis(trimethylsilyl)-tetraphosphane, (Me₃Si)₂(PBu^t)₄, yields the hitherto unknown title compound 1 , which is the first stable partially substituted derivative of n-tetraphosphane(6), n-P₄H₆. 1 can also be obtained in the reaction of 1,4-dipotassium-1,2,3,4-tetra-tert-butyl-tetraphosphide, K₂(PBu^t)₄, with tert-butylchloride. In solution 1 forms the three diastereomers 1d (threo/d,l/threo), 1f (erythro/threo/threo), and 1b (erythro/d,l/erythro) in a ratio of about 10:5:1. Their correlation to the ³¹P-NMR spectroscopically observed spin systems results from the preferred trans arrangement of neighbouring tert-butyl groups as well as from the dependence of the ¹J(PP) coupling constant on dihedral angles and from the ³J(PP) long range coupling constant. The configuration and conformation of the existent isomers is determined by the all-trans arrangement of the tert-butyl groups and by the tendency of vicinal free electron pairs to assume a gauche conformation.     

Cationic polymerization with boron halides. IV. Elucidation and control of initiation and termination by the help of model experiments

The proposition that BCl₃-coinitiated olefin (isobutylene, styrene) polymerizations terminate by chlorination has been corroborated by model experiments. Key experiments showed that under simulated polymerization conditions neither tert-butyl chloride nor 2-chloro-2,4,4-trimethylpentane reacts with BCl₃; that H₂O/BCl₃ + 2,4,4-trimethyl-1-pentene (TMP) produce 2-chloro-2,4,4-trimethylpentane; and that H₂O/BCl₃ + isobutylene gives rise to tert-butyl chloride. Extended model studies demonstrated that certain alkyl and benzyl chlorides produce carbenium ions in the presence of BCl₃ and that TMP can readily be alkenylated by using 1-substituted allyl chlorides in conjunction with BCl₃. These experiments led to the discovery that olefin polymerizations may be initiated by suitable allyl or benzyl chlorides and BCl₃. Accordingly, polymerizations of isobutylene have been carried out with RCl/BCl₃, where R is allyl or benzyl. These experiments suggest that both controlled initiation and termination, i.e., initiation by alkenylation and termination by chlorination, can be achieved with the allyl chloride/BCl₃ initiator system opening new avenues toward the synthesis of asymmetric telechelic polymers.     

Polymerization of acrylonitrile by catalytic systems consisting of triphenylphosphine and a lewis acid

Polymerization of acrylonitrile in the presence of systems that consisted of triphenylphosphine (PPh₃) and a Lewis acid R_mMX_n (ZnCl₂, Me₃Al, Et₃Al, Et₂AlCl, EtAlCl₂, AlCl₃) was studied. The systems that contained Me₃Al and Et₃Al (i.e., Lewis acid of moderate acidity) were the most efficient catalysts. Conductometric measurements carried out in the polymerization systems showed the presence of ions. The presence of phosphonium cation in the polyacrylonitrile chain formed by the PPh₃–R_mMX_n catalytic systems was determined by IR, ¹H-NMR, and ³¹P-NMR spectroscopy. The average molecular weight measurements and kinetic chain lengths of polyacrylonitrile formed within the reaction time in the presence of PPh₃–Et₃Al showed that transfer reactions occur. According to the results obtained, the polymerization reaction of acrylonitrile by PPh₃–R_mMX_n involved a zwitterion formed by the attack of PPh₃ on acrylonitrile complexed by Lewis acid [Ph₃P^⊕? CH₂? C^?H? C?N → MR_mX_n] and the anion [CH₂?C^?? C?N] formed by the proton abstraction from the monomer.     

Radiochemical study of gas-phase reactions of diethylstannilium cations Et2SnT+ with oxygen-containing compounds: I. Interaction of diethylstannilium cations with methyl tert-butyl ether

Radiochemical method was applied to study the gas-phase interaction between the nucleogenic diethylstannyl cations Et₂SnT⁺ and methyl tert-butyl ether. The possible reaction mechanisms are considered. Diethylstannylium cations are found to isomerize during the reaction to tertiary cation Me₂EtSn⁺, as well as undergo a rearrangement accompanied by elimination of ethane rater than ethylene, in contrast to the cases of silicon and germilium analogs.     

Electrophilic substitution of organosilicon compounds. II. Synthesis of allyl-terminated polyisobutylenes by quantitative allylation of tert-chloro-polyisobutylenes with allyltrimethylsilane

Essentially quantitative allylation of linear and three-arm star tert-chloro capped polyisobutylenes [^tCl–PIB–Cl^t and PIB(Cl^t)₃] has been achieved by the use of allyltrimethylsilane (AllylSiMe₃) and Friedel–Crafts acids. Quantitative allylation occurs under suitable conditions, e.g., slight molar excess of TiCl₄ and AllySiMe₃ polar media, ?70°C. These conditions have been developed from quantitative model allylation experiments using 2,4,4-trimethyl-2-chloropentane. Essentially quantitative allylation occurs with long-chain or “once fired” tert-chloro-end groups. Complete allylation can also be effected in a “one-pot two-step” synthesis, i.e., by first preparing the tert-chloro-ended PIB by the inifer method and without isolating the product, completing the synthesis by allylation in the same reactor. Extensive but not quantitative allylation can also be obtained in situ, i. e., during polymerization, by the use of the AllylSiMe₃/cumyl chloride/BCI₃/isobutylene combination. While allylation proceeds with great ease under the mildest conditions, e.g., ?70°C, vinylation with vinyltrimethylsilane could not be achieved even under more forcing conditions.     

Living carbocationic polymerization of isobutyl vinyl ether and the synthesis of poly[isobutylene-b-(isobutyl vinyl ether)]

The MeCH(O-i-Bu)Cl/TiCl₄/MeCONMe₂ initiating system was found to induce the rapid living carbocationic polymerization (LC^⊕Pzn) of isobutyl vinyl ether (IBuVE) at ?100°C. Degradation by dealcoholation which usually accompanies the polymerization of alkyl vinyl ethers by strong Lewis acids is “frozen out” at this low temperature and poly(isobutyl vinyl ether)s (PIBuVEs) with theoretical molecular weights up to ca. 40,000 g/mol (calculated from the initiator/monomer input) and narrow molecular weight distributions (M?_w/M?_n ≤ 1.2) are readily obtained. According to ¹³C-NMR spectroscopy, PIBuVEs prepared by living polymerization at ?100°C are not stereoregular. The MeCH(O-i-Bu)Cl/TiCl₄ combination induces the rapid LC^⊕Pzn of IBuVE even in the absence of N,N-dimethylacetamide (DMA). The addition of the common ion salt, n-Bu₄NCl to the latter system retards the polymerization and meaningful kinetic information can be obtained. The kinetic findings have been explained in terms of TiCl₄. IBuVE and TiCl₄ · IBuVE and TiCl₄ · PIBuVE complexes. The HCl (formal initiator)/TiCl₄/DMA combination is the first initiating system that can be regarded to induce the LC^⊕Pzn of both isobutylene (IB) and IBuVE. Polyisobutylene (PIB)–PIBuVE diblocks were prepared by sequential monomer addition in “one pot” by the 2-chloro-2,4,4-trimethylpentane (TMP-Cl)/TiCl₄/DMA initiating system. Crossover efficiencies are, however, below 35% because the PIB^⊕ + IBuVE → PIB-b-PIBuVE^⊕ crossover is slow. © 1993 John Wiley & Sons, Inc.     

Alkyl(aryl)oxy derivatives of thulium(III)

The reactions of Tml₂(DME)₃ with phenol andtert-butyl alcohol afforded thulium(III)-alkoxyiodides ROTmI₂(DME)₂ (R=Ph and Bu^t, respectively). Their structures were determined by X-ray analysis. Monoiodides (RO)₂ TmI(THF)₂ were synthesized from TmI₃ (THF)₂ and ROH (taken in a ratio of 1∶2). Triphenoxides (RO)₃Tm (R=Ph or 2,4,6-Bu^t ₃C₆H₂) were prepared by the reactions of the naphthalene thulium complex [C₁₀H₈Tm(DME)]₂C₁₀H₈, with an excess of the corresponding phenol. The iodide catechoxide complex 3,6-Bu^t ₂C₆H₂O₂TmI(DME)₂ was prepared by the reaction of TmI₂(DME)₃ with 3,6-di-tert-butylbenzoquinone-1,2 or 3,6-di-tert-butylpyrocatechol. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1804–1807, September, 1999.     

Electron Impact Mass Spectra of Some Substituted C-Phenyl N-tert-Butyl Nitrones (PBN's)

Abstract

The electron impact mass spectra of fifteen 4-substituted PBN's and PBN itself have been obtained using the probe method. Strong molecular ion peaks were observed in most cases. Fragmentation follows two major pathways depending on the polarity of the substitutent: the tert-butyl bond breaks to produce either the tert-butyl cation or isobutylene. The latter route is analogous to the well known McLafferty rearrangement. Fragmentation to produce the tert-butyl radical is a minor route. Electron-donating polar substituents appear to enhance fragmentation to isobutylene.     

Vinylation and polymerization with trivinylaluminum. II. Synthesis of α,ω-diene-polyisobutylene

The polymerization of isobutylene by 3-chloro-1-butene/trivinylaluminum (V₃Al) and t-butyl chloride/V₃Al initiator systems with methyl chloride and methylene chloride as solvents has been investigated in the range from ?30 to ?72?C. The rate of polymerization increases with decreasing temperatures from ?30 to ?50°C and then decreases when the temperature is further lowered, for example, to ?72°C. Mayo plots and a determination of the number of polymer molecules n? formed per molecule of initiator employed suggests a transfer-less, i.e., termination-dominated system. A critical analysis shows that for systems containing both free ions and ion pairs, the Mayo equation is meaningful only when the degree of dissociation α remains constant over the whole [M] range investigated. This condition is achieved in RCl/V₃Al-initiated systems by using an initiator (t-BuCl) for which the rate of catalyst destruction is insignificant compared to rate of initiation, R_i, i.e., initiation efficiency, f ≈ 1 and R_i independent of [M]. Polyisobutylene, containing, 1.8 ± 0.1 terminal unsaturation, has been synthesized by the use of 3-chloro-1-butene initiator in conjunction with V₃Al coinitiator, and avenues for further efficient synthesis of α,ω-diene-polyisobutylenes have been outlined.