Indenyl Compounds with Constrained Hapticity: The Effect of Strong Intramolecular Coordination

Abstract

A series of cyclopentadienyl and indenyl molybdenum(II) compounds with intramolecularly coordinated pyridine arm, including scorpionate-like species bearing two irreversibly coordinated arms on indenyl core, was synthesized and characterized. All presented structural types were confirmed by X-ray diffraction analysis. Due to π-basicity of pyridine, the intramolecular interaction is considerably stronger than in case of analogous species bearing tertiary amines in the side chain. Although the starting compounds for syntheses are isostructural, the reaction outcomes differ considerably. The cyclopentadienyl precursor gives a pentacoordinated η 5 :κN-compound while the indenyl analogue produces a hexacoordinated species with unprecedented η 3 :κN-coordination mode of the indenyl ligand representing an unusual example of so-called indenyl effect. The unusually high stability of η 3 :κN-coordination compounds toward η 3 to η 5 haptotropic rearrangement was clarified by theoretical calculations. As the strong intramolecular interaction prevents rotation of indenyl, it cannot reach a conformation suitable for η 3 to η 5 rearrangement. As a result, the low hapticity is effectively locked.

Cyclopentadienyl Molybdenum(II) Compounds Bearing Ether and Thioether Functions in the Side Chain: Synthesis, Characterization, and Cytotoxic/Cytostatic Studies

“…The expected triplets are split probably due to hindered rotation of the side arm. Nevertheless, coordination of the side arm to the molybdenum atom is not consistent with observed pattern, as it should cause considerably stronger splitting of the methylene signals [33] …”

“…Nevertheless, coordination of the side arm to the molybdenum atom is not consistent with observed pattern, as it should cause considerably stronger splitting of the methylene signals. [33] Indenyl compounds 13-19 show a lover molecular symmetry than their cyclopentadienyl analogues due to substitution out of mirror plane. As a result, symmetrically substituted ligands of 13-18 give a more complex pattern in 1 H NMR spectra.…”

Benz[e]indenyl and benz[f]indenyl molybdenum compounds: evidence of the η3-coordination mode

“…Labeling of 1 with deuterium in 1- and 3-positions was done following the standard H/D exchange protocol using the repeated lithiation/deuterolysis protocol (Scheme 2). 8,42…”

“…, the number of contiguous carbon atoms involved in bonding to the central metal, gives rise to processes known as “haptotropic shifts”. These rearrangements have been investigated on Cp and few congeners with annulated benzene rings (Cp′), mainly on indenyl (Ind = C 9 H 7 ) 4–12 and fluorenyl (Flu = C 13 H 9 ). 12–14 Electronically saturated transition metal complexes with η 5 -bonded extended aromatic systems exhibit a substantial increase in the reaction rates of substitution reactions, when compared to their η 5 -Cp counterpart that has given rise to the term “indenyl effect”.…”