95386-58-6Relevant academic research and scientific papers
Regioselective electrophilic substitution via lithiation and intramolecular arene exchange (haptotropic rearrangement) in (naphthalene)tricarbonylchromium
Kündig,Desobry,Grivet,Rudolph,Spichiger
, p. 1173 - 1180 (2008/10/08)
The sequential reaction of (η6-naphthalene)tricarbonylchromium (1) with (tetramethylpiperidyl)lithium (TMPLi) and electrophiles (D+, ClSiMe3, CO2, MeI, EtOSO2CF3) is highly regioselective and exclusively yields (2-substituted naphthalene)tricarbonylchromium complexes bearing the substituent in the coordinated ring. With n-BuLi, the same sequence gives mixtures of the 1- and 2-substituted naphthalene complexes in the ratio of 3:7. [1-4a,8a-η-1,3-(SiMe3)2C10H 6]Cr(CO)3 (5) is obtained in reactions with excess TMPLi and ClSiMe3. The selectively labeled complexes (1-4a,8a-η-[2-D]naphthalene)Cr(CO)3 (3a) and (1-4a,8a-η-[1,3-8-D7]naphthalene)Cr(CO)3 (3b) were used in a kinetic study of the haptotropic rearrangement of (naphthalene)tricarbonylchromium. The rate constants and activation parameters of the rearrangement in cyclohexane-d12 and in benzene were determined by 1H and 2H NMR methods. In cyclohexane, the activation parameters for the intramolecular rearrangement in 3b were found to be ΔH? = 20.4 kcal mol-1 and ΔH? = -23 cal mol-1 K-1. Haptotropic rearrangement was found to proceed by first-order kinetics and, within experimental error limits, at the same rate in benzene as in cyclohexane. Addition of THF accelerated intra- as well as intermolecular arene exchange. In benzene, at 100°C, the intramolecular ring migration of 3b is 9 times faster than arene exchange. (1-4a,8a-η-2-Methylnaphthalene)Cr(CO)3 (3e) rearranges (ΔH? = 26.2 kcal mol-1) on heating in cyclohexane to an equilibrium mixture (65:35) of the two isomers, the major isomer being the one in which the metal is coordinated to the substituted ring.
