No abstract

A series of densely substituted hydroquinoid phenanthrene tricarbonyl chromium complexes prepared via benzannulation of naphthyl carbene complexes have been subjected to haptotropic metal migration. The rearrangements were monitored by IR and NMR spectrometry using dibutyl ether, hexafluorobenzene, and/or octafluorotoluene as solvents, respectively. In mildly coordinating dibutyl ether the phenanthrene complexes 8-14 were reacted in preparative scale at 90 and 120 °C, affording the haptotropic migration products 15-21 in up to 90% yield. All rearrangements led to thermodynamically stable phenanthrene chromium tricarbonyl complexes in which the organometallic fragment is attached to the less substituted terminal ring. The transformation of phenanthrene complex 11 at 90 °C also afforded bis-tricarbonyl chromium complex 22 as a low-yield byproduct. Kinetic studies of the rearrangement of complexes 8, 9, and 11-13 performed in either hexafluorobenzene or octafluorotoluene afforded the rate constants k and the free activation enthalpies ∆G q for the metal migration. Reaction of bromo-and fluorophenanthrene complexes 10 and 14 under the standard conditions resulted in decomposition of the starting material. The studies reveal that the haptotropic migration of the Cr(CO) 3 fragment along the phenanthrene π-face obeys first-order kinetics and is faster than in analogous naphthalene complexes. Quantum chemical first-principles calculations of the haptotropic rearrangement of chromium tricarbonyl naphthalene and phenanthrene model complexes support these findings.

The benzannulation of readily accessible aryl-or vinylcarbene chromium complexes by alkynes provides a straightforward synthesis of densely functionalized benzenoid and fused arenes selectively labeled with a Cr(CO) 3 fragment. The reaction occurs under mild conditions, is regioselective, and tolerates a variety of functional groups both on the alkyne and on the carbene ligand. The chromium fragment undergoes a haptotropic metal migration controlled by the substitution pattern of the arene; moreover, it activates the coordinated benzene ring towards selective nucleophilic addition and aromatic substitution. Final decomplexation occurs upon ligand exchange or oxidation reactions. Chiral information imposed on either the carbene ligand or the alkyne allows for a diastereoselective benzannulation providing optically active arene-Cr(CO) 3 complexes. 8.1

Organic chemistryOrganic chemistry Z 0200The Chromium-Templated Carbene Benzannulation Approach to Densely Functionalized Arenes (Doetz Reaction) -[225 refs.]. -(DOETZ, K. H.; STENDEL, J. J.; Modern Arene Chem. 2002, 250-296; Kekule-Inst. Org. Chem. Biochem., Rhein. Friedrich-Wilhelms-Univ., D-53121 Bonn, Germany; Eng.) -Lindner 30-271