Reaction of [V(X)(OR)3] (X=O, Np-tolyl; R=Et, nPr or tBu) with p-tert-butylhexahomotrioxacalix[3]areneH3, LH3, affords the air-stable complexes [{V(X)L}n] (X=O, n=1 (1); X=Np-tolyl, n=2 (2)). Alternatively, 1 is readily available either from interaction of [V(mes)3THF] with LH3, and subsequent oxidation with O2 or upon reaction of LLi3 with [VOCl3]. Reaction of [V(Np-tolyl)(OtBu)3] with 1,3-dimethylether-p-tert-butylcalix[4]areneH2, Cax(OMe)2(OH)2, afforded [{VO(OtBu)}2(mu-O)Cax(OMe)2(O)2].2 MeCN (42 MeCN), in which two vanadium atoms are bound to just one calix[4]arene ligand; the n-propoxide analogue of 4, namely [{VO(OnPr)}2(mu-O)Cax(OMe)2(O)2].1.5 MeCN (51.5 MeCN), has also been isolated from a similar reaction using [V(O)(OnPr)3]. Reaction of [VOCl3], LiOtBu, (Me3Si)2O and Cax(OMe)2(OH)2 gave [{VO(OtBu)Cax(OMe)2(O)2}2Li4O2].8 MeCN (68 MeCN), in which an Li4O4 cube (two of the oxygen atoms are derived from the calixarene ligands) is sandwiched between two Cax(OMe)2(O)2. The reaction between [V(Np-tolyl)(OtBu)3] and Cax(OMe)2(OH)2, afforded [V(Np-tolyl)(OtBu)2Cax(OMe)2(O)(OH)]5 MeCN (75 MeCN), in which two tert-butoxide groups remain bound to the tetrahedral vanadium atom, which itself is bound to the calix[4]arene through only one phenolic oxygen atom. Reaction of p-tert-butylcalix[4]areneH4, Cax(OH)4 and [V(Np-tolyl)(OnPr)3] led to loss of the imido group and formation of the dimeric complex [{VCax(O)4(NCMe)}2].6 MeCN (86 MeCN). Monomeric vanadyl oxo- and imidocalix[4]arene complexes [V(X)Cax(O)3(OMe)(NCMe)] (X=O (11), Np-tolyl (12)) were obtained by the reaction of the methylether-p-tert-butylcalix[4]areneH3, Cax(OMe)(OH)3, and [V(X)(OR)3] (R=Et or nPr). Vanadyl calix[4]arene fragments can be linked by the reaction of 2,6-bis(bromomethyl)pyridine with Cax(OH)4 and subsequent treatment with [VOCl3] to afford the complex [{VOCax(O)4}2(mu-2,6-(CH2)2C5H3N)].4 MeCN (134 MeCN). The compounds 1-13 have been structurally characterised by single-crystal X-ray diffraction. Upon activation with methylaluminoxane, these complexes displayed poor activities, however, the use of dimethylaluminium chloride and the reactivator ethyltrichloroacetate generates highly active, thermally stable catalysts for the conversion of ethylene to, at 25 degrees C, ultra-high-molecular-weight (>5, 500,000), linear polyethylene, whilst at higher temperature (80 degrees C), the molecular weight of the polyethylene drops to about 450,000. Using 1 and 2 at 25 degrees C for ethylene/propylene co-polymerisation (50:50 feed) leads to ultra-high-molecular-weight (>2,900,000) polymer with about 14.5 mol% propylene incorporation. The catalytic systems employing the methyleneoxa-bridged complexes 1 and 2 are an order of magnitude more active than the bimetallic complexes 5 and 13, which, in turn, are an order of magnitude more active than pro-catalysts 8, 11 and 12. These differences in activity are discussed in terms of the structures of each class of complex.
Bis(phenoxyimine)Zr complexes 1 − 8 containing a series of cycloalkyl groups on the imine-N's were synthesized (1: cyclopropyl; 2, 3: cyclobutyl; 4: cyclopentyl; 5, 7: cyclohexyl; 6, 8: 2-methylcyclohexyl). X-ray crystallographic analyses suggested that complexes 3, 5, and 8 assume an octahedral coordination geometry with a trans-phenoxy-O, cis-imine-N, and cis-Cl disposition and that the cycloalkyl groups on the imine-N's influence steric environments around the chlorine bound sites (i.e., potential polymerization sites). Upon activation with MAO at 25 °C, these complexes produced low-to-high molecular weight polyethylenes (PEs) (M w 1900−960000, M w/M n 1.6−4.9) with very high efficiency (22−290 kg of PE/(mmol of cat. h)), which is comparable to or exceeds that seen with Cp2ZrCl2/MAO (28 kg of PE/(mmol of cat. h)). The cycloalkyl group has a profound effect on both catalytic activity and product molecular weight, indicating the critical importance of the substituent on the imine-N for polymerization catalysis. The catalytic activity increased with an increase in the steric bulk of the cycloalkyl substituent, albeit too much steric bulk reduced the activity. The product molecular weight was also related to the steric bulk of the cycloalkyl group, in that increased steric bulk normally resulted in higher molecular weight PEs. The PEs produced with complexes 1 − 5/MAO (Al/Zr molar ratio = 1250) possess a high degree of vinyl unsaturation at one of the two polymer chain ends (M w 2000−14000, vinyl selectivity, 90−96 mol %). Polymerizations performed at a much higher Al/Zr molar ratio of 12500 confirmed the marked preference of these complexes for β-H transfer as the chain termination mechanism (M w 1900−14000, vinyl selectivity, 90−95 mol %). The vinyl-terminated PEs were readily transformed to the corresponding epoxy- and diol-terminated PEs, which are valuable materials for PE- and polar polymer-based block and graft copolymers. Ethylene pressure studies on complexes 1, 2, 4, and 5 revealed a first-order dependence on ethylene for both the rate of chain propagation and the rate of chain transfer. On the basis of this polymerization behavior together with X-ray analyses and DFT calculation studies, we concluded that β-H transfer to an incoming monomer is responsible for the formation of vinyl-terminated PEs. The calculations revealed that the complexes disfavor β-H transfer to the Zr metal due to the extreme instability of a metal hydride species that is produced in such a chain transfer process. Therefore, the unique polymerization catalysis and distinctive polymer formation with phenoxycycloalkylimine ligated Zr complexes were demonstrated.
Multinuclear alkylene zinc (MAZ) compounds of the type EtZn-(R″-Zn)n-Et (R″ = ethyl and propyl branched alkylene groups) were synthesized by a simple one-step procedure in nonpolar hydrocarbon solvents from α,ω-dienes (e.g., 1,7-octadiene or 1,9-decadiene) and diethylzinc using a bis(salicylaldiminato)Zr(IV) complex, [(2-methylcyclohexyl)N═CH(2-O-C6H3-3,5-di-tert-butyl)]2ZrMe2, as a catalyst. The MAZ serves as a divalent reversible chain-transfer agent for olefin polymerization, resulting in telechelic Zn-metalated polyolefins whose molecular weights are controllable over a wide range. The Zn-terminated telechelics serve as a polymer precursor for further reactions and can be converted into a variety of telechelic functionalized polyolefins in high yield.
Vanadyl complexes of C or N-capped tripodal ligands, possessing distorted tetrahedral geometry at vanadium, serve as extremely active, thermally robust pro-catalysts for ethylene homo- and ethylene/propylene copolymerisation, whereas pseudo-octahedral pro-catalysts produce far lower activities.
The ovarian structure and batch fecundity of anglerfish Lophiomus setigerus were examined from specimens collected in the East China Sea during March 1991 to September 1995. The right and left ovarian lobes were connected at their posterior ends. Stalk-like ovigerous lamellae protruded from the ovarian wall. During the spawning season, gelatinous material was secreted from the epithelia of both the ovigerous lamellae and ovarian wall, and these epithelia showed morphological changes accompanying the ovarian maturation cycle. Tertiary yolk, migratory nucleus, and mature stage oocytes occurred in the ovaries between May and November, when females with postovulatory follicles and developing vitellogenic oocytes were collected also. These results suggested an extended spawning season during which females undergo repeated spawnings. When the most advanced oocytes attained the secondary yolk stage, they formed a batch that separated from the adjacent group of smaller oocytes. Batch fecundity (F) in 20 females with secondary yolk stage ovaries was related to total length (L T , mm) as F=556·2 L T 1·157 (300cL T c396).1998 The Fisheries Society of the British Isles
A major spawning of the seagrass rabbitfish Siganus canaliculatus occurred 4 days after the new moon in both May and June 1993, and 7 days after the new moon in 1994. The gonadosomatic index (I G ) and serum vitellogenin (VTG) levels fluctuated according to the lunar cycle; I G and VTG levels showed peaks at around the new moon and the waning moon, respectively, suggesting that spawning of this species is synchronized with the lunar cycle. Vitellogenic oocytes appeared on day 2 after the first spawning and were fully mature on day 30. When a greater percentage of the most advanced oocytes attained the tertiary yolk stage, they formed a batch and separated from the adjacent group of smaller pre-vitellogenic oocytes, indicating that S. canaliculatus is a multiple spawner with an ovary belonging to the group-synchronous type of oocyte development. Batch fecundity, assessed using batches of oocytes at and after the tertiary yolk stage, ranged from c. 0·52 to 2·56 million eggs. The relationship between batch fecundity (F) and fork length (L) can be represented as F=0·0536854L 5·07292 . 1999 The Fisheries Society of the British Isles
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