Zirconium complexes reactivity

Zirconium hydride reactivity with carbon monoxide demonstrates the strong driving force toward products with a Zr-O bond. Indeed, the facility of the CO migratory insertion into Zr-C and especially Zr-H bonds may be from a carbonyl oxygen-zirconium interaction that stabilizes the transition state to the acyl and formyl complexes. 

The reactivity of a silyl-zirconium complex is interesting because an unsaturated bond would be inserted into the silyl-zirconium bond to provide an alternative zirconium complex. It has zirconium-carbon and silyl-carbon... 

Little is known about the reactivities of complexes having zirconium-silicon bonds. Reaction of lb with hydrogen chloride afforded triphenylsilane (Scheme 3) [16a]. The insertion of carbon monoxide or isocyanide into a zirconium-silicon bond of lc gave silaacylzirconium complex 4 or iminosilyl-zirconium complex 6 [17b,c]. As for carbon-carbon multiple bonds, ethylene can be inserted into a zirconium-silicon bond of lh [17g],but other multiple... 

In this multi-authored monograph, several experts and leaders in the field bring the reader up to date in these various areas of research (synthesis and reactivity of zirconaaziridine derivatives, zirconocene-silene complexes, ste-reodefined dienyl zirconocenes complexes, octahedral allylic and heteroallylic zirconium complexes as catalysts for the polymerization of olefins and finally the use of zirconocene complexes for the preparation of cyclopropane derivatives). It is their expertise that will familiarize the reader with the essence of the topic. 

A variety of ani a-bridged complexes such as (143) resembling those of ans a-zirconocenes have also been reported. Moreover, reduction of the zirconium complexes with n-BuLi in the presence of PMes provides an entry point to Zr(II) complexes (144) their reactivity toward aUcynes has been studied in detail. ... 

These important compounds with regards to their reactivity are obtained by transmetalation see Transmetalation) between the appropriate metallocene dichloride (see Metallocene Complexes) and an alkyl- or aryl-lithium reagent. Dialkyl and diaryl zirconium complexes are very moisture-sensitive, degrading to form /r-oxo species (see Section 5). 

Terminal chalcogenido zirconium complexes (23) are conveniently synthesized by the reactions of dicarbonylzir-conocene with either N2O or the elemental chalcogens (S, Se, Te) see Chalcogens) in the presence of pyridine. The Zr=E bond in these complexes is highly reactive and leads to a variety of 1,2-addition and cycloaddition reactions (Scheme 8). ... 

Cationic P compounds exhibit several modes of reactivity, including coordination to Lewis acids oxidation by acids, water, and alkyl chlorides and substitution of the stabilizing phosphine ligands by stronger donors (Scheme 17). Some of these P and As cations have also been shown to be useful sources of P and As ions that provide zirconium complexes (12) containing unique square-planar Pn environments (equation 22). ... 

Aryne complexes of late transition metals are very reactive towards both nucleophiles (amines, alcohols, water) and electrophiles (iodine). They also undergo insertion reactions with CO, alkenes and alkynes,but while the behaviour of ruthenium complexes is somewhat similar to that of titanium or zirconium complexes, the reactivity of nickel complexes is rather different [6,8]. Examples of these reactions that are particularly interesting for the purposes of this chapter are shown in Schemes 8 and 9. Ruthenium complex 33 undergoes insertion of a molecule of benzonitrile,benzaldehyde or di(p-tolyl)acetylene to yield met-allacycles 40,41 and 42, respectively (Scheme 8). Further insertion of a second unsaturated molecule into these metallacycles has not been observed [25,27]. 

The novel 7 -disilenide zirconium complex 44 is highly reactive and undergoes ready rearrangement via addition of a methyl C-H bond to the Si=Si bond to give the silyl zirconium complex 45, as a mixture of diastereoisomers, shown in Equation (5) <2005JA10174>. 

A variety of chiral, non-racemic zirconium complexes were explored in attempts to develop an enantioselective variant of this reaction (Scheme 3) [7-9]. Eor example, when allyUc amines lla,b were treated with EtMgCl and 10% of C2-symmetric BINOL-zirconium bis(tetrahydroindenyl)ethane (12, Brintzinger s catalyst [10], BINOL is l,l -binaphthalene 2,2 -dioate), chiral ethylated products 13a,b were obtained in 34-39% yield with enantiomeric excesses (ee) of ca. 26% [8]. Use of a (neomenthylindene)ZrCpCl2 catalyst 14, designed to improve the steric differentiation of the diastereomeric transition states, improved the chemical yields of amines at lower catalyst loadings (2-4%) and increased the ees of the reactions by a factor of three in the case of 11a [8,9]. Similar reactivity is observed in zirconocene dichloride-catalyzed cyclization of 1,6- and 1,7-enynes with 12.5% Cp2ZrCl2 using EtsAl as the stoichiometric reductant. For these substrates, the alkyne coordinates... 

Chem. Descrip. Zirconium complex in reactive diluent Uses Coating catalyst for two-component plural gun or inline mixing applies. 

Tshuva, E. Y Goldberg, L Kol, M. Weitman, H. Goldschmidt, Z. Novel zirconium complexes of amine bis(phenolate) ligands. Remarkable reactivity in polymerization of 1-hexene due to an extra donor arm. Chem. Commun. 2000, 379-380. 

Transmetallation of the organic group from zirconium to another metal opens up possibilities. The palladium-catalysed coupling reactions can be found in Section 2.4. Addition of dimethyl cuprate results In transmetallation to copper. The resulting cuprate then displays typical cuprate reactivity, such as addition to enones. More economically, small amounts of copper can catalytically activate the zirconium complex towards this kind of chemistry, although the precise mechanism is unclear. Additions to enones can also be achieved directly using nickel catalysis (Scheme 5.64). Transmetallation to zinc has also been demonstrated. ... 

Our own investigations into the chemistry of the heavier group 4 analogs have primarily focused on the hydrazinediido-zirconium complex [Zr(N2 NpP (NNPh2)(py)l (Figure 13.1) [17]. The latter has displayed similar stoichiometric and catalytic reactivity toward unsaturated substrates as found for titanium. However, its reactivity toward alkynes appears to be characterized by the absence of a hydrohydrazination step in favor of N-N bond cleavage before the formation of a hydrazone and a reaction pathway similar to that depicted in Scheme 13.8 [24]. 

In particular, 1,7-annulated indole derivatives, such as the prototypical Cilansetron A, display high activity as 5-HT3 receptor antagonists and are being clinically tested for the treatment of symptoms in the gastrointestinal system such as the irritable bowel syndrome (IBS) [26]. To extend our previous synthetic strategy based on the reactivity of hydrazinediido zirconium complexes to annulated polycyclic indole derivatives, we aimed to prepare such hydrazides derived from cyclic hydrazines (B). 

The reactivity of the side-on bound N2 ligand in the zirconium complex 19-Zr was further probed by addition of water. This leads to the rapid protonation of the [N2]" ligand to form hydrazine and a zirconocene bis (hydroxide) [(r] -C5Me4H)2Zr(OH)2] (Scheme 10). However, any attempts to observe intermediates along this reaction pathway by adding substoichiometric quantities of H2O failed. Addition of EtOH affords N2H4 and [(Ti -C5Me4H)2Zr(OEt)2] (Scheme 10). 

Scheme 15 Reactivity of mixed indenyl-cyclopentadienyl zirconium complexes toward...

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