Zirconium complexes reactions

Alkenyl zirconium complexes derived from alkynes form C—C bonds when added to aHyUc palladium complexes. The stereochemistry differs from that found in reactions of corresponding carbanions with aHyl—Pd in a way that suggests the Cp2ZrRCl alkylates first at Pd, rather than by direct attack on the aUyl group (259). 

Thermolysis of the t]-coordinated zirconium complex of thiophene Cp2Zr(SiMc3) (C4H3S) is a thienyl ring cleavage reaction (920M1646). 

Thus, a novel chiral zirconium complex for asymmetric aza Diels-Alder reactions has been developed by efficient catalyst optimization using both solid-phase and liquid-phase approaches. High yields, high selectivity, and low loading of the catalyst have been achieved, and the effectiveness of chiral catalyst optimization using a combination of solid-phase and liquid-phase methods has been demonstrated. 

Zirconium complexes, 3, 363-440 acetylacetone, 2,372,377 ligand exchange reactions, 2, 381 rearrangement, 2, 383 alkyl... 

In this method, one alkyne is treated with Schwartz s reagent (see 15-17) to produce a vinylic zirconium intermediate. Addition of MeLi or MeMgBr, followed by the second alkyne, gives another intermediate, which, when treated with aqueous acid, gives the diene in moderate-to-good yields. The stereoisomer shown is the one formed in usually close to 100% purity. If the second intermediate is treated with I2 instead of aqueous acid, the 1,4-diiodo-1,3-diene is obtained instead, in comparable yield and isomeric purity. This reaction can also be done intramolecularly Diynes 56 can be cyclized to ( , E) exocychc dienes 57 by treatment with a zirconium complex. 

Similar reactions, in which two alkyl groups are added to a triple bond, have been carried out with trialkylalanes R3AI, with zirconium complexes as catalysts. ... 

Titanium-acetylene complexes 29 generated in situ from acetylenes, Ti(0-i-Pr)4 and /-PrMgX react with imines to form azatitanacyclopentenes 30 which then react with carbon monoxide under atmospheric pressure to provide pyrroles 31 <96TL7787>. This reaction, which utilizes commercially available reagents is an improvement over a related procedure via the corresponding zirconium complexes under 1500 psi CO <89JA776>. 

The first organometallic zirconium complexes to be prepared all contained Zr( 1V) and were reported almost contemporaneously. The reaction of Zr(TPP)-(OAc)2 with RLi or RMgBr produced the dialkyl complexes Zr(TPP)R2 (R = Me, Et, n-Bu or Ph), characterized by. spectroscopy. The development of the chlorozirconium complexes opened up the chemistry further, with... 

The tendency to form ate complexes observed for yttrium is also seen in the preparation of a novel zirconium alkynyl complex. Reaction of Zr(Por)Cl2 (Por = OEP or TPP) with either two or three equivalents of LiC=CR (R = Ph or SiMe ) gives the trisalkynyl complexes Zr(Por)(C=CR)3Li(TFIF). An X-ray crystal structure of Zr(OEP)(C=CPh)2Li(THF) shows that all three alkynyl ligands are on... 

As mentioned already, new methylidene-group IV metal complexes have been prepared and were subsequently used in nucleophilic additions to carbonyl electrophiles (Scheme 43).53 In contrast to titanium and zirconium, the reaction of methylidene hafnium dichloride 97 benzophenone stopped at the first stage (i.e., addition). The tertiary alcohol was obtained in 73% yield, while the corresponding alkene was formed only as minor product. 

The bis(trimethylphosphino)zirconium complex 92 undergoes unusual reactions with alkynes.114 With diynes, metallocyclic products 93 are formed, whereas acetylene affords 94 whose nonplanar boratanaphthalene ligand is... 

The interesting feature of 20 is that the Si-H interaction occurs for the set of electron-donating ancillary ligands Cp2/PMe3. Thus, the only factor that can, in principle, account for the different behavior of titanium and its heavier analogs in these reactions is the contracted nature of the titanium d-orbitals and hence the less effective backdonation from metal as discussed in Section II.B. The nonclassical nature of the zirconium complex 19 compared with neutral 18 can be then attributed to the presence of a positive charge. 

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