Zirconium intermolecular

Zirconium Intermolecular hydroamination of both terminal and internal alkynes R C=CR with primary amines R NH2 to produce (after subsequent reduction) saturated secondary amines RiCH2-CH(NHR )R can be attained with the in situ generated zirconium catalysts (Me2N)4Zr (5 mol%) and sulfonamide (10 mol%). " Zirconium-catalysed intramolecular hydroamination (225) (226) has been studied theoretically " as for the analogous iridium-catalysed cyclization of (177) discussed (g) earlier " and similar conclusions have been reached regarding the hydrogen bonding, and so on. 

In 1992, Bergman et al. reported that zirconium bisamides Cp2Zr(NHR)2 catalyze the intermolecular hydroamination of alkynes with sterically hindered primary amines to give enamines or their tautomeric imines (e.g., Eq. 4.77) [126]. 

Various zirconium compounds are used as delayed crosslinkers, (see Table 17-12). The initially formed complexes with low-molecular-weight compounds are exchanged with intermolecular polysaccharide complexes, which cause delayed crosslinking. 

A mechanism involving the generation of a cationic alk(en)ylzirconocene (I X = R ) through chloride abstraction by silver(I) has been postulated (Scheme 8.22). This cationic intermediate is capable of activating the carbonyl group towards addition (II). Irrespective of whether an alk(en)yl group is added intra- or intermolecularly, a new cationic species is generated (either by R -transfer or Cl-abstraction from III) and the reaction thus proceeds in a zirconium-catalyzed manner [50]. 

Only one example of electrophilic behavior of silicon-stabilized lithiooxiranes is reported. Intermolecular C—Li insertion followed by Li20 elimination occurs by raising the temperature, and ( ) vinylsilanes are obtained stereoselectively (Scheme 80). Reaction of lithiooxiranes with aluminum , zirconium and silicon reagents leads to the corresponding ate complexes, which undergo 1,2-metallate rearrangements. 

Zirconium and hafnium complexes are highly fluxional. NMR studies indicate stereochemical nonrigidity, facile exchange of terminal and bridging ligands, and rapid intermolecular ligand exchange. 

Cyclic amino-carbenes, in molybdenum carbonyls, 5, 457 Cyclic bis(phosphine) dichlorides, with iron carbonyls, 6, 48 Cyclic carbenes, as gold atom ligands, 2, 289 Cyclic carbometallation, zirconium complexes, 10, 276 Cyclic carbozirconation characteristics, 10, 276 intermolecular reactions, 10, 278 intramolecular reactions, 10, 278 Cyclic dinuclear ylides, and gold , 2, 276 Cyclic 1,2-diols, intramolecular coupling to, 11, 51 Cyclic enones, diastereoselective cuprate additions, 9, 515 Cyclic esters, ring-opening polymerization, via lanthanide catalysis, 4, 145 Cyclic ethers... 

The analogous reaction using tetramethyltitanium 14 results in a 42 58 product ratio, whereas CH3MgI is non-selective (1 1 mixture) 83). It is possible that in case of 14 the transfer of the second methyl group occurs to some extent intramolecularly via a bicyclo[l,l,4] transition state. Indeed, sixfold dilution (which should reduce the amount of intermolecularity) reverses diastereoseleetivity, 166 167 being 52 48 83). Clearly, systematic studies are required before final conclusions regarding the use of titanium or zirconium mediated intramolecular addition reactions can be reached. 

Some other intermolecular C-H activations involving the NHC ligand have been observed during the synthesis of particular NHC-containing pincer -type complexes also called CCC-NHC complexes. In addition to zirconium- and rhodium-based complexes (210) and (211)/ several examples involving palladium of general structure (271) have been synthesized. Whereas Faller... 

M(OCMc3)4 and f-butanol evidence rapid intermolecular exchange of f-butoxide ligands. IR spectra of zirconium and hafnium tetraalkoxides exhibit a strong v(C—O) band near 1000 cm and one or more v(M—O) bands in the region 520-590 Calorimetric measurements... 

The first hydroaminations by this mechanism were reported by Bergman with zircono-cene complexes and by Livinghouse with monocyclopentadienyl titanium and zirconium complexes. Bergman reported the intermolecular addition of a hindered aniline to an alkyne. The hindrance of the aniline was important to prevent formation of stable dimeric complexes containing bridging imido groups. Livinghouse reported intramolecular reactions that occurred at lower temperatures over shorter times. The intramolecularity of this process allows the [2+2] cycloaddition of the imido complex with the alkyne to be faster than the dimerization. 

On the basis of the comparative volatilities of titanium, zirconium, and hafnium tertiary alkoxides measured at various pressures, the following order of volatility may be deduced Per > Pzr > Pti- The anomalous order cannot be explained in terms of intermolecular forces between tertiary alkoxides as the heats of vaporization are quite close to each other for these alkoxides. Bradley et however, concluded that... 

Zirconium- and Silicon-Containing Intermediates with Three Fused Rings in a Zirconocene-Mediated Intermolecular Coupling Reaction. 

Zhang WX, Zhang S, Sun X et al (2009) Zirconium- and silicon-containing intermediates with three fused rings in a zirconocene-mediated intermolecular coupling reaction. Angew Chem Int Ed 121 7363-7367... 

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