Heterobimetallic Cr−Mn Complexes of Fused Arenes: Chromium-Templated Benzannulation of a Cymanthrene-Type Metal Carbene and Haptotropic Metal Migration along a Dibenzo[c,e]indene Platform

Abstract

The chromium-templated benzannulation of the chromium cymanthrene-type carbene 3 with 3-hexyne affords the heterobimetallic chromium−manganese hydroquinoid dibenzo[c,e]indene complexes anti-4 and syn-5, in which the chromium entities are coordinated regioselectively to the hydroquinoid ring. Both diastereomers undergo a thermoinduced haptotropic migration of the chromium moiety to give their haptotropomers anti-6 and syn-7 in comparable yields, independent of the relative configuration of both metal centers, while the manganese fragment remains coordinated to the cyclopentadienyl ring. The molecular structures of all heterobimetallic complex structures were established by X-ray analysis. A kinetic NMR study of the chromium migration revealed first-order kinetics for the anti complex 4, supporting the intramolecular nature of the metal rearrangement.

Hydroquinoid Chromium Complexes Bearing an Acyclic Conjugated Bridge: Chromium-Templated Synthesis, Molecular Structure, and Haptotropic Metal Migration

“…This process in which the metal center remains permanently coordinated to the ligand during the metal relocation is referred to as haptotropic metal migration . Since the first report of a reversible shift of a Cr(CO) 3 fragment along the platform of 2,3-dimethylnaphthalene, the rearrangement of chromium fragments along arene platforms has attracted increasing interest. , Experimental and theoretical investigations have been undertaken to elucidate the mechanism of this process. Theoretical studies on naphthalene tricarbonyl chromium complexes suggested a metal shift along the periphery of the π-system via a η 4 -coordinated trimethylene methane-like transition state .…”

The Reduction Chemistry of Ferrocenylborole

“…[22] Although the redox-induced hapticity changes in transition-metal complexes featuring polyaromatic ring systems or tub-to-chair isomerizations in cyclooctatetraene (COT) complexes have been well studied, [18a, 23] the intramolecular migration of a metal fragment between ring systems is rare. [24] ). Remarkably, the intermolecular exchange process was not observed in the reaction between equimolar amounts of ferrocene and [C 4 Ph 4 BPh]K 2 in THF, which suggests that the ligation of the borole moiety prior to reduction is essential.…”

“…[22] Although the redox-induced hapticity changes in transition-metal complexes featuring polyaromatic ring systems or tub-to-chair isomerizations in cyclooctatetraene (COT) complexes have been well studied, [18a, 23] the intramolecular migration of a metal fragment between ring systems is rare. [24] It appears that the electron-richer [C 4 Ph 4 BR] 2À entity is a better p donor than Cp À , consequently forming a stronger bond with the iron center. Thus, two-electron reduction of 1 gives rise to the formation of the putative [CpFe(h 5 -C 5 H 4 -BC 4 Ph 4 )] 2À species, which then undergoes an intramolecular [CpFe] migration to form [CpFe(h 5 -Ph 4 C 4 B-C 5 H 4 )] 2À ([1] 2À ).…”

Dibenzo[f,h]quinoline Cr(CO)3 Complexes: Synthesis by Chromium-Templated Benzannulation, Cyclomanganation, and Haptotropic Chromium Migration

“…With the aim of exploiting metal−metal interactions, heterobimetallic complexes have become a prominent field of organometallic research. , We became interested in whether the chromium migration can be controlled by another metal moiety coordinated to an extended π-platform. Recently, we reported on a chromium shift in binuclear (Cr, Mn) dibenzo[ c , e ]indene complexes . In this paper, we focus on dibenzoquinoline manganese chromium complexes bearing a terminal pyridine ring, which is well-suited for σ-coordination of low-valent transition metals.…”