π-Complexes of Tropolone and Its N-Derivatives: Ambidentate [O,O]/[N,O]/[N,N]-Cycloheptatrienyl Pentamethylcyclopentadienyl Ruthenium Sandwich Complexes

Abstract

Tropolone and its N-derivatives isopropylaminotropone and diisopropylaminotroponimine react with [Cp*Ru(CH 3 CN) 3 ]PF 6 as the source of the electron-rich Cp*Ru + synthon in a simple "capping reaction" to the first cyclopentadienyl/cycloheptatrienyl sandwich complexes containing two vicinal oxo or amino substituents. These heteroleptic, cationic C 5 /C 7 π-complexes, [Cp*Ru-(C 7 H 5 )O 2 H] + (4), [Cp*Ru(C 7 H 5 )O(N i Pr)H] + (5), and [Cp*Ru(C 7 H 5 )(N i Pr) 2 H] + (6), are air-stable 18-electron metallocenes without precedence. In solution, NMR spectroscopy proves the principal π-coordination of the substituted η 7 -cycloheptatrienyl ligands, whereas in the solid state a η 5 -cycloheptatrienyl coordination mode with bent oxo/imino moieties prevails, as shown by X-ray single-crystal structure analyses. Chemically, these compounds are the conjugate Brønsted acids of neutral [O,O]-, [N,O]-, or [N,N]metalloligands. Reaction with metal acetates or acetylacetonates by in situ deprotonation and complex formation gives access to trimetallic (M = Cu 2+ , 10−12) or tetrametallic (M = Fe 3+ , 13) complex cations. Their single-crystal structure analyses show square-planar or square-pyramidal (M = Cu 2+ ) or octahedral (M = Fe 3+ ) coordination motifs with peripheral, η 5 -coordinated Cp*Ru moieties. Electrochemical studies on the trorucenes 4−6 showed a likely metal-based chemically reversible (4) or irreversible one-electron reduction (5, 6) as well as an irreversible one-electron oxidation for the N-substituted compounds 5 and 6. The behavior of the heterotri-and tetrametallic complexes 10, 11, and 13 was rationalized by a combination of cyclic and square-wave voltammetry as well as the combination of chronocoulometry and linear-sweep voltammetry and by comparison with the mononuclear copper or iron tropolone and topolonimine precursors 14−16. These studies indicate that in 10 and 11 the trorucene moieties are reduced first in two coincident or slightly separated one-electron reductions with the Cu 2+ reduction at very negative potential, whereas in 13 the central Fe(III)-tris(troponolato) moiety is reduced prior to the trorucene appendices. An in vitro anticancer screening in MDA-MB-231 breast adenocarcinoma and HT-29 colon carcinoma cell lines showed enhanced antiproliferative activity for the [O,O]-coordinated iron and copper complexes.

New Perspectives for Aminotroponiminates: Coordination Chemistry, Redox Behavior, Cooperativity, and Catalysis

“…This deformation may be quantified using the angle between the mean planes defined by the atoms [C3–C7] on the one hand and [C1–3,C7] on the other hand (Scheme a, c). This bending mode of the ATI ligand is rare, but has been observed for the previously mentioned complex [Ru(C 5 Me 5 )(H‐ATI i Pr/ i Pr )] + , which shows a type D bonding mode . The bending angle of the H‐ATI ligand in this compound amounts to 28.2°.…”

“…More recently, the C 7 backbone of ATI ligands has been a focus of considerable research efforts with respect to its role in coordination chemistry. For neutral ATI ligands (H‐ATI) that bear a proton in the N , N ‐binding pocket, coordination mode D with M–C ATI–backbone bonding interactions has been realized (Scheme ) . The arenophilic [Ru(C 5 Me 5 )] + group could be coordinated to the ligand backbone of H‐ATI i Pr/ i Pr to give the cationic species [Ru(C 5 Me 5 )(H‐ATI i Pr/ i Pr )] + (Figure ).…”

“…Conformations of ATI ligands in which the C 7 N 2 motif deviates significantly from planarity. (a) general labeling scheme; (b) puckering of ATI ligand {structural data taken from [Ge(ATI t Bu/ t Bu )F]}; (c) bending of ATI ligand {structural data taken from [Ru(C 5 Me 5 )(H‐ATI i Pr/ i Pr )][PF 6 ]}.…”

“…The ruthenium compound [Ru(C 5 Me 5 )(H‐ATI i Pr/ i Pr )][PF 6 ] shows an irreversible oxidation and reduction wave with peak potentials of +0.9 V and –1.8 V, respectively , . The analogous aminotropone and tropolone complexes show a similar electrochemical behavior.…”

Monofunctionalized Cobaltocenium Compounds by Dediazoniation Reactions of Cobaltoceniumdiazonium Bis(hexafluorophosphate)

“…Standard methods and procedures of organic/organometallic synthesis, spectroscopic characterization, electrochemistry, and single-crystal structure analysis were performed as described recently. 33 Ball-milling reactions were performed in a Fritsch Pulverizette 7 ball mill. Chemicals were obtained commercially and used as received.…”