Renate Schwickardi

A New Catalyst System for the Heck Reaction of Unreactive Aryl Halides

A simple solution to the age-old problem of the Heck reaction of cheap but unreactive chloro- and bromoarenes [for example, reaction (1)] has been found in the catalyst [Pd(CH3 CN)2 Cl2 ]⋅6 Ph4 PCl in the presence of N,N-dimethylglycine as additive. The reaction then proceeds with exceptionally high efficiency.

Ein neues Katalysatorsystem für die Heck-Reaktion von reaktionsträgen Arylhalogeniden

Eine einfache Losung fur ein altes Problem: Die Heck-Reaktion der billigen, aber wenig reaktiven Arylchloride [Gl. (1)] und -bromide wird mit dem Katalysator [Pd(CH3CN)2Cl2]⋅6 Ph4PCl in Gegenwart von N,N-Dimethylglycin als Additiv mit ungewohnlich hoher Effizienz moglich.

Additionen von vinyl- und allyl-titan-bindungen an ethylen

Abstract Reaction of Cp 2 TiCl ( 1 ) with the alkylmagnesium halides 2a – 2d , 2g (alkyl = Me, Et, Pr, iso-Pr, hexyl) and ethylene give bis(η 5 -cyclopentadienyl)(η 3 -1-methylallyl)titanium ( 3 ). Mechanistic investigations indicate that hydrogen transfer from ethylene either to the initially formed Cp 2 alkyltitanium or to Cp 2 ethyltitanium, formed by βH-elimination to Cp 2 -titaniumhydride and addition to ethylene, leads to liberation of alkane or alkene and ethane and formation of Cp 2 vinyltitanium F as an intermediate. Insertion of ethylene (even below 0°C) into the vinyltitanium bond of F leads to Cp 2 3-butenyltitanium, which isomerizes to 3 . Reaction of 3 at ca. 80°C with ethylene in toluene occurs in part with hydrogen transfer to give the butene isomers 4 , 5 and F and in part with addition of the allyltitanium bond to ethylene to give the 2,4-hexadiene isomers 6a – 6c by βH-elimination. The compounds 6a – 6c are also formed in the catalytic codimerization of butadiene with ethylene in the presence of 3 . This reaction has a regioselectivity of > 99%.

Bis(indenyl)titanacyclopentan und bis(indenyl)(η2-ethylen)titan

Abstract Attempts to prepare (di-η 5 -indenyl)(η 2 -ethylene)methyltitamum ( A ) from (ind) 2 TiCl, MeMgCl and ethylene led to the disproportionation products bis(η 5 -indenyl)titanacyclopentane ( 5 ) and bis(η 5 -indenyl)dimethyltitanium ( 4 ) instead of to A. 5 dissociates reversibly upon heating from −80 to −20°C giving (di-η 5 -indenyl)(η 2 -ethylene)titanium ( 6 ) and ethylene.