Propylene/propene complexes

Complex formation between olefins and Lewis acids has been demonstrated in a number of cases, e.g., isobutene and titanium tetrachloride (66), butene-2 and boron trifluoride (67—69), propylene and aluminum bromide (70), stflbene and various Lewis acids (71), styrene and stannic chloride (72), and in similar systems (73). Monomer-catalyst Ji-complex formation occurs during the polymerization of styrene or a-methyl styrene with chloroacetic acids (74,75). All these complexes are usually very weak and only stable at low temperatures. Evans contends (76) that isobutene and boron trifluoride do not interact because no polymerization occurs in the absence of moisture and therefore he postulates that BF3 HaO is the primary species. This does not rule out the possibility of a weak interaction between isobutene and the Lewis acid. Indeed, Nakana et al. (77) found direct evidence for the existence of boron trifluoride-propene complexes at low temperatures. 

The stability of olefin complexes is also sensitive to steric effects. The binding of ethylene is stronger than that of a-olefins in nearly all cases. However, the magnitude of the steric effect on the binding of an olefin depends on the other ligands. For example, the ethylene complex of bis(amine)PdMe in Equation 2.11b is 10-fold more stable than the propylene or hexene complex, while flie ethylene complex of PtClj" is ortiy two-fold more stable than the corresponding propene complex. ... 

The iridium(III)-complex, [Ir(p-acac-0,0,C )(acac-0,0)(acac-C )]2, mediates the activation of unactivated aromatic C—H bond with unactivated alkenes to form anti-Markovnikov products [57]. The reaction of benzene 131 with propene 132 (0.78 MPa of propylene, 1.96 MPa of N2) leads to the formation of n-propylbenzene 133 in 61% selectivities (turnover number (TON) = 13 turnover frequency (TOE) = 0.0110 s ) (Equation 10.34). The reaction of benzene with ethane at 180 °C for 3h gave ethylbenzene (TON = 455 TOE = 0.0421s ). The anti-Markovnikov selectivity was also proven for the reaction with 1-hexane and isobutene, giving 1-phenyUiexane (69% selectivity) and isobutylbenzene (82% selectivity), respectively. 

The cationic nickel complex [ /3-allylNi(PR3)]+, already described by Wilke etal. [21], as an efficient catalyst precursor for alkene dimerization when dissolved in chlorinated organic solvents. It proved to be very active in acidic chloroaluminate ionic liquids. In spite of the strong potential Lewis acidity of the medium, a similar phosphine effect is observed. Biphasic regioselective dimerization of propylene into 2,3-dimethylbutenes can then be achieved in chloroaluminates. However, there is a competition for the phosphine between the soft nickel complex and the hard aluminum chloride coming from the dissociation of polynuclear chloroaluminate anions. Aromatic hydrocarbons, when added to the system, can act as competitive bases thus preventing the de-coordination of phosphine ligand from the nickel complex [22 b]. Performed in a continuous way, in IFP pilot plant facilities, dimerization of propene and/or butenes with this biphasic system (Difasol process) compares... 

Certain low-valent early transition metal complexes catalyze the dimerization of ethylene and propylene selectively to 1-butene and 2,3-dimethyl-l-butene. The regioselec-tivity of this dimerization of propene signals a different mechanism than the insertion and elimination mechanism presented in the previous section. The formation of 1-butene occurs selectively because of the absence of a persistent metal hydride complex that isomerizes this olefin to the more stable 2-butene. 

Alt, H. G. Zenk, R. C2-symmetric bis(fluorenyl) complexes Four complex models as potential catalysts for the isospecific polymerization of propylene. J. Organomet. Chem. 1996, 512, 51-60. Chen, Y.-X. Rausch, M. D. Chien, J. C. W. C2y- and C2-Symmetric an5a-bis(fluorenyl)zirconocene catalysts Synthesis and a-olefin polymerization catalysis. Macromolecules 1995, 28, 5399-5404. Rieger, B. Stereospecific propene polymerization with rac-[l,2-bis(ti -(9-fluorenyl))-l-phenylethane] zirconium dichloride/methylalumoxane. Polym. Bull. (Berlin) 1994,32,41 6. 

For some leading reviews see (a) Resconi, L. Cavallo, L. Fait, A. Piemontesi, F. Selectivity in propene polymerization with metallocene catalysts. Chem. Rev. 2000,100, 1253-1345. (b) Alt, H. G Koppl, A. Effect of the nature of metallocene complexes of Group IV metals on their performance in catalytic ethylene and propylene polymerization. Chem. Rev. 2000, 100, 1205-1221. (c) Halterman, R. L. Synthesis and applications of chiral cyclopentadienyhnetal complexes. Chem. Rev. 1992, 92, 965-994. (d) Halterman, R. L. Synthesis of chiral titanocene and zirconocene dichlorides. In Metallocenes ... 

The lead(IV) alkyls and aryls are stable at ordinary temperatures, but release organic free radicals on heating. Subsequent reactions are complex and among the pyrolysis products of tetramethyl-lead are 2-methyl-2-propene, propylene, ethylene, hydrogen, methane and ethane. 

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