Methylstyrene insertion

Interception of the reaction sequence at the alkylcobalt carbonyl stage before carbonyl insertion, and hydrogenation of this intermediate, produces an alkane. This undesired side reaction is only minor (1-3%) in cobalt-catalyzed hydroformylation of a nonfunctional olefin, but may become predominant with phenyl- or acyl-substituted olefins. Ethylbenzene has been obtained in >50% yield from styrene (37), and even more alkane was obtained from a-methylstyrene (35). 

When the reaction of DMFL with alcohols, cyclohexane, or a-methylstyrene is initiated by triplet senitization, the outcome is virtually the same as it is for the direct irradiation. Thus ethers are formed in high yield with the alcohols, direct insertion accounts for the major product in cyclohexane, and the olefin cyclopropanation is stereospecific. 

Secondary (1,2) insertion of 4-methylstyrene into the Pd-acyl bond gave the P-chelate, which transformed into the propagating y-chelate upon CO insertion. 

Monomers were purchased from Polysciences, Inc. The liquid monomers (methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, methyl acrylate, n-butyl acrylate, methacrylic acid, acrylic acid, styrene and a-methylstyrene) were purified by vacuum distillation under nitrogen, poured into thin-walled ampules, degassed at 10 - 10 torr and subsequently frozen in liquid nitrogen. The partially filled ampules were then inserted between a pair of parallel plate electrodes connected to an International Plasma Corporation Model 3001 Radiofrequency Generator, which operates at 13.56 MHz and delivers up to 150 watts of power. In most of these experiments discussed in this work, the power input was limited to 40 - 80 watts. The ampules were allowed to warm up until droplets of liquids appeared. A glow discharge was then in-Current address Department of Chemistry, Ibaraki, University, Mito 310 Japan... 

The enantioselective copolymerization of styrenes and CO has also been achieved (Scheme 12). Using bidentate pyridine-imine ligands (26), Sen synthesized optically active styrene and 4-methylstyrene copolymers [80]. Based on a microstructural analysis, a 36% ee for olefin insertion was reported. Brookhart employed a C2-symmetrical bisoxazoline complex (27) to produce styrene-based... 

Block copolymers produced by anionic polymerization do possess a very narrow MM distribution (Chapter 2). Wilczek-Vera et al. recorded the MALDI-TOF mass spectrum of a block copolymer containing units of a-methylstyrene and units of styrene. MALDI peak intensities were inserted in the equations which define M and and the result was M = 4273, = 4411, in fair... 

Investigation of the reactivity of these borylpalladium complexes demonstrated that the electron-deficient borylpalladium 39d (Ar= 3,5-(CF3)2C,5H3) smoothly reacted with (F)- 3-methylstyrene to give (Z)-p-boryl-(3-methylstyrene 42 quantitatively whereas normal 39a (Ar = Ph) caused no reaction (Scheme 9.10) [27]. Thus, electron-withdrawing nature of the PSiP-Hgand clearly accelerates the borylpalladation step, leading to high catalytic activity of 39d. Additionally, the stereospecific formation of (Z)-alkenylboronic ester 42 from ( )-P-methylstyrene supports the proposed mechanism for borylation of alkenes via syn-insertion/syn-ehmination. 

To deepen these results, the same OA alkyl a-olefins already mentioned were also copolymerized in addition to styrene, with 1-vinyl-naphthalene or 2-methylstyrene with the same Ziegler-Natta catalyst. Fractionation by solvent extraction as well as the optical properties and X-ray spectra demonstrate the formation of an isotactic copolymer which is, at the first sight predominantly random but also block formation seems to occur, depending on the reactivity of vinyl aromatic monomers with respect to the a-olefin and on the composition of the starting co-monomer mixture. The remarkable contribution to optical rotation by aromatic units observed in their copolymers with (/ )3,7-dimethyl-l-octene is at least 10—15% larger than predictable from the corresponding model. The CD spectra relative to the formally forbiden electronic transition of lowest energy (with very low ellipticity) of aromatic nuclei show that, when inserted in OA copolymers, they assume a preferential chiral conformation [171]. (see chapter of Chiellini etd.). 

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