Zirconium complexes alkyl

The case of butane is noteworthy since the selectivity at low conversions indicates that there is no selectivity in the overall hydrogenolysis step between n- and sec-butyl zirconium surface intermediates, while earUer studies had shown that the -alkyl zirconium complexes were more stable than sec-alkyl derivatives (Table 3 and Scheme 23) [94]. 

Alkyl zirconium complexes such as 67 react with CO to give an unstable 18e complex 82 that transfers the alkyl group from the metal to the CO n orbital to give the metal acyl complex 83. This is a Zr(IV) complex of an acyl anion 83a and can be protonated to give the aldehyde 84 in excellent yield. These zirconium complexes are usually made from alkenes so that any hexene or mixture of hexenes gives 85 again in excellent yield.26... 

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). 

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

As shown in Scheme 94, the fj -styrene zirconium complex Cp Zr (f/ -PhCHCH2)[MeC(NPr )2] also served as starting material in the synthesis of alkyl-substituted 1,3-diene complexes of (pentamethylcyclopentadienyl)zirco-nium amidinates. NMR spectroscopy as well as single-crystal X-ray analyses of these complexes revealed that they are best described by the Zr(lV) a, n-metallacyclopent-3-ene limiting resonance form rather than as Zr(ll) f/ -diene complexes. ... 

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. ... 

All of the reactions described above use anionic alkyl metal complexes as stoichiometric reductants. Cationic zirconium catalyst 58 was shown to re-ductively cyclize a variety of 1,5-dienes to give both mono- and bicyclic silane products when H3SiPh was employed as the stoichiometric reductant (Scheme 10) [32]. Poor yields due to competing polymerization processes were observed when less substituted dienes were employed. It is likely that... 

Although the surface zirconium complex has a lower thermal stability than the hafnium one, the nature of the gases released during thermolysis is similar, except for isobutene (hardly observed for zirconium) and isopentene (observed only for hafnium). These results suggest that isobutene resulting from ji-alkyl transfer of hafnium (Scheme 11.1) is inserted in the Hf-CHs bond. 

Both enolate species 2a and 2b are readily alkylated by iodomethane to provide the corresponding acyl complexes 3a and 3b, respectively (yield of 3b is not reported)91. No examples of the generation of zirconium-acyl enolates from chiral biscyclopentadienyl zirconium complexes has yet been reported. The reported preparation of the enantiomerically pure complex 4 indicates that chiral zirconium-acyl enolate species may be accessible92. 

HEXAHALOGENO SALTS AND ALKYL NITRILE COMPLEXES OF TITANIUM(IV), ZIRCONIUM(IV), NIOBIUM(V), TANTALUM(V), PROTACTINIUM (IV) AND -(V), THORIUM(IV), AND URANIUM(IV)... 

Friedel-Crafts alkylation has been used in an important synthesis of aryl C-glycosides, which are potent anti-tumor agents, from glycosyl fluorides (equation 99)65 661. The reaction takes place rapidly in dichloromethane, at room temperature using a novel zirconium complex and silver perchlorate combination catalyst. A similar alkylation has been performed by replacing the aromatic compound with either a silyl enol ether or an allylic compound using silver triflate as the catalyst662,663. 

Specific examples of alkene insertions are the reactions of cationic hydrides [Cp2ZrH(L)]+ to give metal alkyls which may either be stabilized by agostic interactions, as in (21-XLII), or free of such interactions (21-XLIII), depending on L.180 The insertion of isobutene into M—C bonds of electron-deficient zirconium complexes was found to be reversible.109... 

The pincer like diamino functionalised carbene ligand stabilises the group 4 metal sufficiently to perform a few very interesting insertion reactions with the M-Me bond. The reactions were performed with the hafnium rather than the zirconium complexes [113]. Small molecules used for these insertion reactions include isonitriles (aryl and alkyl) and CO (see Figure 4.36). Reaction of the hafnium carbene dimethyl complex with xylyl-isonitrile results in addition of this excellent donor ligand and subsequent insertion into the Hf-Me... 

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). 

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). ... 

Halogenative cleavage likewise appears completely general for both alkyl- and alkenyl-zirconium complexes (Scheme 10), and proceeds with complete retention of configuration at carbon. For the hydrozirconation products of 3-methyl-1,3-dienes, such as (40), cyclization competes (equation 43). Analogs without the 3-methyl subsitutent, or with more remote double bonds, give only the uncyclized products in good yields. " ... 

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