Benzylic zirconocene

Styrene hydrozirconation led to a ratio for terminal and benzylic zirconocene products of around 85 15 [97]. Experimental evidence on alkyl-substituted styrene suggested that both electronic [98,99] and steric effects [41,86] are important for the formation of the benzyhc and terminal zirconium isomers. Migration of the metal fragment during the reaction of the zirconocene moiety might occur, perturbing the terminal/benzyl regioisomer ratio of the isolated products (Scheme 8-11) [67, 83, 98-102]. 

Preparation of (l,4-diphenyl-l,3-butadiene)ZrCp2 (33) may be accomplished by photolysis of (/l-styryl)(benzyl)zirconocene (34)67 or by displacement of isoprene from (isoprene)ZrCp2 (35) at elevated temperature (Scheme 6)17. For complex 33, the s-trans/s-cis equilibrium lies far toward the s-trans isomer (95 5). 

Scheme 4.60. Ni(0)-catalyzed couplings of vinyl zirconocenes with benzylic chlorides.

In addition, Wipf and co-workers104 have used silver(i)-catalyzed addition of zirconocenes to 3,4,6-tri-O-benzyl-D-glucal epoxide 93 for the stereoselective synthesis of a-C-glucosyl compounds 95 and 96 following a similar mechanism as in the reaction with organoaluminium and organoboron reagents (Scheme 32). 

Arylations. A rather unusual reaction for the synthesis of triarylmethanes is that which involves benzylic arylation of 4-nitrotoluene and homologs catalyzed by Pd(OAc)2-PhjP in the presence of CS2CO3. One or two aryl groups can be introduced by this method. Arylation of amines by ArX employs the Pd(OAc)2-f-BuONa and a phosphine as catalyst. Pentaarylcyclopentadienes are readily formed in a reaction of metallocenes (nickelocene, titanocene dichloride, zirconocene dichloride) with ArBr in... 

Other ligand variations have resulted in a large number of metallocene dichloride complexes these include cc-phenylalkyl-substituted Cp zirconocenes,417 mixed zirconocenes of the type (L)(Ind)ZrCl2 (L = o -phenylalkyl-substituted Cp, 1-phenylsilyl-substituted Ind) and (L)(Flu)ZrCl2 (L = 1 -benzyl-substituted Ind or 2-benzyl... 

Indole synthesis. A novel route to 4-iodoindoles involves reaction of N-allyl-N-benzyl-2-bromoaniline (1) with this zirconocene to form the zirconacycle 2, which is converted into 3 by iodination and elimination. This product undergoes ene reactions... 

Nonanoylzirconocene chloride (1), readily prepared by the reaction of 1-octene and zirconocene hydrochloride (Schwartz reagent) followed by exposure to 1 atm of CO, serves as an umnasked acyl anion and provides ketones or a-diketones in moderate to good yields by the reaction with electrophiles (aryl iodide, benzyl bromide, acyl chloride, allyl chloride, aUyl acetate) in the presence of 5% of PdCl2(PPh3)2 (Scheme 47). ... 

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