Zirconium-butene complex

In this regard, zirconium-butene complex ( Cp2Zr ) [74] was widely used to promote the carbocyclization of vinyl glycosides [75], Thus, sequential treatment of 5-vinyl pyranose 91 with Cp2Zr-(n-Bu)2 (prepared in situ fromzirconocene dichloride and 2 equivalents of butyl lithium) and boron trifluoride etherate in THF afforded vinyl cyclopentanol 92 as the major product in a 75% yield (Scheme 3.36) [76]. 

The 7r-back donation stabilizes the alkene-metal 7c-bonding and therefore this is the reason why alkene complexes of the low-valent early transition metals so far isolated did not catalyze any polymerization. Some of them catalyze the oligomerization of olefins via metallocyclic mechanism [25,30,37-39]. For example, a zirconium-alkyl complex, CpZrn(CH2CH3)(7/4-butadiene)(dmpe) (dmpe = l,2-bis(dimethylphosphino)ethane) (24), catalyzed the selective dimerization of ethylene to 1-butene (Scheme I) [37, 38]. 

Heterobimetallic complexes of zirconium and molybdenum have also been prepared from zirconocene olefin complexes. Displacement of 1-butene from the phosphine-substituted zirconocene 1-butene complex, (775-C5H4PPh2)2Zr( 72-CH2=CHCH2CH3) 107, by addition of /< //-butyl isonitrile in the presence of Mo(CO)4(norbornadiene) furnishes the formal zirconium(n)-molybdenum(0) compound, 108 (Equation (4)).47... 

Certain half-sandwich phenoxides have been shown to be highly active olefin polymerization catalysts. For example, the zirconium complex (60) polymerizes ethylene with an activity of 1,220 gmmol-1 h-1 bar-1.181 A similar titanium complex (61) displays an activity of 560gmmol ll bar 1 at 60°C.182-189 Comparable activities were also recorded for the copolymerization of ethylene with 1-butene and 1-hexene. 

The use of a zirconium complex (dibutylzirconocene, — 78 °C to rt, 2 h) to induce intramolecular co-cyclization of A-methyl-5-azanona-l,8-diene to an intermediate zirconacycle was a key step in a new azepane synthetic route hydrolysis (MeOH, aq. NaHC03) of this intermediate then realized the trans- 1,4,5-trimethylazepane in 75% yield the active reagent for the initial cyclization was zirconocene (1-butene). The overall transformation represents a type d ring construction process <2006SL3439>. This synthetically versatile process is also applicable to aza eneyne and aza diyne precursors as well as benz-fused analogues. 

Cationic [ZrBz3]+ species are capable of polymerising oc-olefins such as propylene, 1-butene and 1-pentene at elevated temperature. It is worth emphasising that the non-metallocene [Zr(CH2Ph)3] + [PhCH2B(C6F5)3] catalyst, which is a cationic arene zirconium complex [189], is capable, at least partially, of isospecific a-olefin polymerisation at relatively high temperature [162,189,190],... 

Compound (CsH4SiMe2NBut)TiCl2 has been synthesized and used as pre-catalyst for ethylene polymerization. The activities and the properties of the polymers have been compared to similar zirconium and hafnium derivatives.720 The consequences of anion-cation interactions on the activity of GGG group 4 metal complexes in olefin polymerizations have been explored for a series of zirconocene derivatives as well as the cationic species [(C5Me4SiMe2NBut)TiMe]+ with the sterically congested tris(perfluorobiphenyl)fluoroaluminate as the counteranion.721 The co-polymerization of ethylene and 1-butene by (CsMe iMe Bu TiC in the presence of... 

Codimers with alkynes can also be obtained from 1,2-diphenylcyclopropene when the trimethylphosphane-stabilized metallocene complexes 20 (M = Ti, Zr) of this cyclopropene derivative are used as substrates. The titanocene complex is prepared from bis(>/ -cyclopen-tadienyl)bis(trimethylphosphane)titanium (18), while the zirconocene complex is most conveniently formed from (f7 -but-l-ene)bis(f7 -cyclopentadienyl)(trimethylphosphane)zirconium (19) via a substitution reaction of the butene ligand. When 20 (M = Ti) is reacted with but-2-yne, the titanacycle 21 can be isolated as blue crystals in 71% yield. The zirconacycle 21 (M = Zr) is obtained in 78% yield as an orange powder. ... 

Dimerization of ethylene in the presence of homogeneous titanium and zirconium complexes proceeds with mass selectivity up to 98-99 % with respect to 1-butene, but one always observes at least 0.5 - 1% mass of polymer formation which creates problems when scaling up. 

It can be seen from Table 1 that when using gel immobilized complexes of titanium and zirconium, very high selectivity with respect to 1-butene, up to 99.9 % mass practically, can be achieved without any formation of polymer. Besides, homogeneous complexes are not stable enough and loose their activity after a few hours, whereas gel immobilized complex catalysts remain active for hundred hours and more. 

Chiral zirconocene complexes have also been studied as catalysts for the hydrogenation of nonfunctionalized olefins115. Using homogeneous Ziegler Natta-type catalyst systems derived from [ethylenebis(4,5.6,7-tetrahydro-l-indenyl)]zirconium complexes and methyl aluminoxane [A1(CH3)0] , 2-phenyl-l-butene was hydrogenated in 36% optical yield (20 bar H2, benzene, 25 °C). Under the same conditions, the reaction of styrene with D2 gave optically active 1,2-dideuteroethylbenzene with 65% ee. 

Alkene and Alkyne Dimerization and Trimerization. The low-valent mono-Cp zirconium compound CpZrMe(DMPE)2 (DMPE = l,2-bis(di-methylphosphino)ethane) catalyzes the dimerization of ethylene to 1-butene at low frequency (3 t.o./d), a process wherein the 1,3-butadiene complex 64 is presumed to be the catalyst (256). The clean dimerization of olefins using the Cp2ZrCl2/MAO (Al/Zr = 1) catalyst has recently been reported (257). Recently,... 

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