The synthesis, characterization, and ethylene polymerization behavior of a series of iron and cobalt halide complexes, LMX n (M ) Fe, X ) Cl, n ) 2, 3, X ) Br, n ) 2; M ) Co, X ) Cl, n ) 2), bearing chelating 2,6-bis(imino)pyridyl ligands L [L ) 2,6-(ArNCR 1 ) 2 C 5 H 3 N] is reported. X-ray diffraction studies show the geometry at the metal centers to be either distorted square pyramidal or distorted trigonal bipyramidal. Treatment of the complexes LMX n with methylaluminoxane (MAO) leads to highly active ethylene polymerization catalysts converting ethylene to highly linear polyethylene (PE). LFeX 2 precatalysts with ketimine ligands (R 1 ) Me) are approximately an order of magnitude more active than precatalysts with aldimine ligands (R 1 ) H). Catalyst productivities in the range 3750-20600 g/mmol‚h‚bar are observed for Fe-based ketimine catalysts, while Co ketimine systems display activities of 450-1740 g/mmol‚h‚bar. Molecular weights (M w ) of the polymers produced are in the range 14000-611000. Changing reaction conditions also affects productivity and molecular weight; in some systems, a bimodal molecular weight distribution is observed. On the basis of evidence gathered to date, the lower molecular weight fraction is a result of chain transfer to aluminum while the higher molecular weight fraction is produced by a combination of mainly -H transfer and some chain transfer to aluminum.

No abstract

-90°C). When the temperature was near -60°C. quenching of the solution in water and standard workup afforded crude reaction products in ca. 90Yo yield (GC). Purification (recrystallization or column chromatography) gave pure products.[9] Only the Markownikoff regioisomer 9 (by GC and I3C NMR analyses) was fund to be present in yields of 69%-91% after quenching in water.Academic Press, Orlando, FL, USA 1984, Chapter 5, p. 341. Chem. 88 (1976 Cyclobis(paraquat-p-phenylene). A Tetracationic Multipurpose ReceptorBy Barbara Odell, Mark V. Reddington, Alexandra M. Z . Slawin, Neil Spencer, J. Fraser Stoddart,* and David J . WilliamsRecently, we reported''] on cyclophane-like molecular receptors, such as bisparaphenylene-34-crown-10 1, which contains n-electron-rich hydroquinone units for face-to-face complexation ( Fig. 1) with paraquat 2, a n-electron-deficient dication. These observations led us to propose that it might be possible to reverse constitutionally the roles of the receptor and the substrate and so bind a n-electronrich diphenol ether, such as 1,4-dimethoxybenzene 3a, inside a tetracationic molecular receptor (Fig. 1). Such a receptor is the tetracation cyclobis(paraquat-p-phenylene) 4 which incorporates two n-electron-deficient paraquat residues connected in a phane-like manner by means of two para-phenylene groups.[21 Here, we describe (i) the synthesis of 4 as its tetrakis(hexafluorophosphate) 4 . 4 PF,, (ii) its X-ray structural characterization as the acetonitrile solvate 4 . 4 PF6.3 MeCN, (iii) the UV and 'H-NMR spectroscopic evidence for 1 : 1 complex formation (a) between 4 . 4 PF6 and 1,2-, 1,3-, and 1,4-dimethoxybenzene 3a/3b/ 3c in acetonitrile (CD,CN) and (b) between 4 . 4 C I and 1,4-dihydroxybenzene 6 in water (D20)J3' and (iv) the results of molecular and semiempirical quantum mechanical calculations on 4 and on 4 . 2 MeCN.[ Fig. 1 Schematic representation of the basis for the proposal that the cyclobis(paraquat-p-phenylene) 4 should act as a tetracationic receptor for 1,4-dimethoxybenzene 3a.The procedure (cf. Ref.[2]) employed for the preparation of 4 -4 P F 6 starting from the bis(pyridinium) salt 5 and 1,4-bis(bromomethyl)benzene is outlined in Scheme 1. (Fig. 2, top) that 4 adopts a rigid centrosymmetric rectangular box-like conformation with the two paraquat units forming the longer sides and the two para-xylylene residues, the shorter ones. There is a 19" twist angle between the two pyridinium rings of each paraquat unit: in addition, there are deformations of both the paraquat and para-xylylene components producing a bowing of the sides of the cyclophane. Thus, the strain within the molecule is relieved by out-of-plane bending of the six aromatic rings and is distributed throughout the macrocycle with the maximum deviations associated with the exocyclic C-CH2 bonds emanating from the para-phenylene residues: these bonds subtend an angle of 14" with respect to each other whilst the two Ne-CH, bonds associated with the paraquat units subtend an angle of 23 O . There is also a con...

A new family of aluminum complexes bearing tetradentate bis(aminophenoxide) ligands is reported and shown to initiate the living ring-opening polymerization of rac-lactide. The microstructures of the polylactide products are found to be highly dependent upon the ancillary ligand substituents, ranging from highly isotactic (Pm = 0.79) to very highly heterotactic (Pr = 0.96).

tided as ca. 99% unreacted 'H NMR (vide supra). The components of the aqueous phase were identified by 'H NMR as paraquat (S 4.35 (s, 3 H), 8.37 (d, J = 1,2 H), 8.90 (d, J = 1,2 H)) and 2-(ethylamino)-2-methylpropanol hydrochloride (spectrum identical to that described above). Integrals of the NMR signals for paraquat and the amino alcohol indicated a 2.5% conversion of DEM-3 dimer to the amino alcohol.B. Buffered Methanol Medium. The reaction was performed in pH 7, Tris-buffered methanol. This time the reaction mixture turned dark blue. Again, the residue from solvent evaporation was extracted into 1 mL of D20 and 1 mL of CDC13. The components of the organic phase were identified by 'H NMR as DEM-3 dimer and 2-(ethylamino)-2methylpropanol (6 1.06 (s, 6 H), 1.07 (t, J = 7.2, 3 H), 2.44 (q, J = 1.2, 2 H), 3.33 (s, 2 H)). The components of the aqueous phase were identified as paraquat and a small amount of 2-(ethylamino)-2-methylpropanol hydrochloride, also from the 'H NMR spectrum. Integrals of the NMR signals indicated a 41% conversion of DEM-3 dimer to amino alcohol.Attempted Reduction of Daunomycin with DEM-3 Dimer. The reaction vessel was a 9 mm X 20 cm Pyrex tube equipped with a 2.5-cm side arm. The side arm was charged with 2.65 X 10"* mol of DEM-3 dimer dissolved in methylene chloride, and the methylene chloride was evaporated with a stream of nitrogen. The main tube was charged with 2 mL of 2 X 10~3 M 1:1 Tris/Tris-HCl buffered methanol containing 2.66 X 10"6 mol of daunomycin. The methanol solution was freeze-thaw-degassed, and the tube was sealed with a torch. After mixing the reagents, the solution was heated at 36 °C for 18 h. C-18 reverse-phase HPLC analysis as described earlier35 showed no formation of 7-deoxydaunomycinone.

A very simple self-assembling system, which produces inclusion complexes with pseudorotaxane geometries, is described. The self-assembly of eight pseudorotaxanes with a range of stoichiometries-I : I , 1 :2, 2:1, and 2:2 (host:guest)-has been Keywords achieved. These pseudorotaxanes self-assemble from readily available componentscrown ethers -dialkylammonium well-known crown ethers, such as dibenzo [24]crown-8 and bis-p-phenylene[34lcrown-salts 9 hydrogen bonding -molecular 10, and secondary dialkylammonium hexafluorophosphate salts, such as (PhCH,),-recognition -pseudorotaxanes * NHiPF; and (nBu),NHlPF;-and have been characterized not only in the solid state, self-assembly but also in solution and in the "gas phase". The pseudorotaxanes are stabilized largely by hydrogen-bonding interactions and, in some instances, by aryl-aryl interactions.

An unprecedented intramolecular B-H activation of a hydrotris(2-sulfanyl-1-methylimidazolyl)borate ligand coordinated to ruthenium has provided the first example of metallaboratranes. The remarkable ease with which the ruthenaboratrane 1 forms relative to the case with a hydrotris(pyrazolyl)borate ligand is a consequence of the lability of the chelation and the increased ring size of the chelates.

Nonlinear optical properties are a sensitive probe of the electronic and solid-state structure of organic compounds and as a consequence find various applications in many areas of optoelectronics including optical communications, laser scanning and control functions, and integrated optics technology. Because of their strongly delocalized n electronic systems, polymeric and non-polymeric aromatic compounds show highly nonlinear optical effects. Nowadays, polymer chemists are able to tailor specific materials properties for various applications. Some organic substances with n electronic systems exhibit the largest known nonlinear coefficients, often considerably larger than those of the more conventional inorganic dielectrics and semiconductors, and thus show promise for thin-film fabrication, allowing the enormous function and cost advantages of integrated electronic circuitry. The electronic origins of nonlinear optical effects in organic n electronic systems are reviewed, with special emphasis being given to second-order nonlinear optical effects. Methods for measuring nonlinear optical responses are outlined, and the critical relationships of the propagation characteristics of light to observed nonlinear optical effects and to solid-state structure are discussed. Finally, the synthesis and characterization of organic crystals and polymer films with large second-order optical nonlinearities are summarized.