Zirconium derivatives

Question. From the ground electron configuration of zirconium derive the ground state (i.e. the values of L, S and J) explaining which rules enable you to do this. Then derive the states arising from the excited configuration... 

D. Seebach, B. Weidmann, L. Widler in Titanium and Zirconium Derivatives in Organic Synthesis in Modern Synthetic Methods, R. Scheffold, Ed., pp 217-353, Salle und Sauerlander, Frankfurt 1983. 

Zeijden [112] used chiral M-functionalized cyclopentadiene ligands to prepare a series of transition metal complexes. The zirconium derivative (82 in Scheme 46), as a moderate Lewis acid, catalyzed the Diels-Alder reaction between methacroleine and cyclopentadiene, with 72% de but no measurable enantiomeric excess. Nakagawa [113] reported l,T-(2,2 -bis-acylamino)binaphthalene (83 in Scheme 46) to be effective in the ytterbium-catalyzed asymmetric Diels-Alder reaction between cyclopentadiene and crotonyl-l,3-oxazolidin-2-one. The adduct was obtained with high yield and enantioselectivity (97% yield, endo/exo = 91/9, > 98% ee for the endo adduct). The addition of diisopropylethylamine was necessary to afford high enantioselectivities, since without this additive, the product was essentially... 

As the second protonation of zirconacydes with weak acids such as methanol is much slower than the first, selective reactions can easily be performed (e. g. protonation with methanol, followed by iodination of the corresponding vinyl zirconium derivative with complete control of the selectivity see Eq. 2.12) [22]. 

Zirconocene and Half-Sandwich Zirconium Derivatives The development of a single-site heterogeneous catalyst for metallocene-based polymerization catalysis has also been explored extensively with zirconocene and half-sandwich zirconium derivatives [32, 75, 91, 92]. 

Exceptions are cycloalkenes, which do form secondary zirconium derivatives,460 as well as arylalkenes461 [Eq. (6.76)] and conjugated dienes 462,463... 

The disproportionation activity in the supported species is parallel to the increased activity of ethylene polymerization on supported catalysts. Many of the steps in the reaction may be identical for example, the initial coordination of olefin to the metal center will be common to both systems. Indeed, some of these catalysts are also ethylene polymerization catalysts (see Table IV) although their activities are much less than the corresponding zirconium derivatives. A possible intermediate common to both disproportionation and polymerization could be the hydrocarbyl-olefin species (Structure I). Olefin disproportionation would result if the metal favored /3-hydrogen elimination to give the diolefin intermediate (Structure II) which is thought to be necessary for olefin disproportionation. Thus, the similarity between the mechanism and activation of olefin disproportionation and polymerization is suggested. 

Alkenyl-aluminum and -zirconium derivatives have been found to couple with allyl halides in the presence of Pd° catalysts (equation 38), although simple alkyl-aluminum and -zirconium reagents fail in the reaction.154 The 1,4-dienes thus generated are important intermediates in organic synthesis. 

The X-ray crystal structure of the silyl-hydrido zirconium derivative Cp2Zr(H)(SiPh3) (PMe3) showed that the silyl and phosphine ligands are in the outward position in the CpZr wedge, with the hydride ligand in between14. 

A l,3-diphosphabicyclo[1.1.0]butanediyl ligand chelating a zirconium or hafnium center results from the reaction of MCl2Cp2 (M = Zr, Hf) with two molar equivalents of n-butyllithium at —78°C, and treatment of intermediate M(n-Bu)2Cp2 with two molecules of phosphaalkyne. The formation of the yellow to red crystalline zirconium derivatives 136a-c is accomplished at room temperature,703 whereas heating in toluene at 110°C is needed to... 

For the preparation of enantiomerically pure ebthi zirconium derivatives, an efficient procedure using optically pure binol can be used starting from racemic mixture. ... 

In modern organic chemistry, silyl enol ethers, as well as the corresponding titanium, tin, boron, or zirconium derivatives, are widely employed as nucleophilic components in enolate alkylation reactions. Their usefulness prompted the elaboration of numerous methods for the selective production of isomeri-cally pure enol ethers from almost any type of carbonyl compounds. 

The. reaction of various monosubstituted alkenes containing hydrocarbon substituents, as well as those containing heteroatom substituents, with Me3Al and a catalytic amount of a chiral dichlorobis(l-neomenthylindenyl)zirconium derivative provides, after oxidation with O7, 2-methylalkan-l-ols in high yields with up to 85% ee [126] (Scheme 7-106). 

Alkenyl and dienyl groups can be present in Ti and Zr complexes as well. Vinyltitanium compounds cannot be exploited for nucleophilic additions, however, due to their propensity to undergo oxidative coupling reactions,likewise transition metal derivatives. Vinylzirconium compounds (20) can be prepared from alkynes (hydrozirconation equation 12) by action of zirconium derivatives like (19). ... 

---