Preliminary Studies of the Mechanism of Metal-Halogen Exchange. The Kinetics of Reaction of n-Butyllithium with Substituted Bromobenzenes in Hexane Solution
Initial measurements of the rate of reaction of bromobenzene with n-butyllithium in hexane solution have shown the exchange to be first order in bromobenzene and first order in n-butyllithium, with an activation energy of 12 kcal mol-1 (52 kJ mol-1).A Hammett relationship for the reaction of substituted bromobenzenes with n-butyllithium suggests negative charge character in the transition state (ρ ca 2).The addition of a Lewis donor (p-methylanisole) to the hexane solution was found to result in an increase in the rate of exchange, but did not affect the Hammett reaction constant.Several transition-state structures are considered; available evidence suggests that the exchange may be concerted, with either a four-centered structure, or SN2-type attack of the n-butyl anion at the bromine of the aryl bromide
Copper-catalysed cross-coupling of arylzirconium reagents with aryl and heteroaryl iodides
An unprecedented CuI-catalysed cross-coupling of arylzirconium reagents with aryl and heteroaryl iodides is reported. Mechanistic studies with a Cp2ZrAr2 complex revealed that Cp2Zr(Ar)(Cl) is the reactive species that undergoes transmetalation with (PN-1)CuI. In addition, experiments with radical probes indicated that the reaction proceeds via a non-radical pathway. This journal is
Method for producing alkyl-bridged ligand systems and transition metal compounds
The invention relates to a method for producing highly substituted alkyl-bridged ligand systems on the basis of indene derivatives and transition metal compounds. Said alkyl-bridged ligand systems can be obtained in high yields using this method.
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(2008/06/13)
Arene-catalysed lithiation of fluoroarenes
The reaction of different fluoroarenes 1 with lithium and a catalytic amount (7%) of naphthalene in THF at -30°C affords the corresponding aryllithium intermediates which, by reaction with several electrophiles at temperatures ranging between -30 and 0°C, lead to the expected products 2, after hydrolysis. (C) 2000 Elsevier Science Ltd.
Guijarro, David,Yus, Miguel
p. 1135 - 1138
(2007/10/03)
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