Synthesis and Reactivity of 16-Electron Cycloheptatrienyl-Molybdenum(0) Complexes with Bis(imidazolin-2-imine) Ligands

Abstract

The reaction of the ligands 1,2-bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-imino)ethane (BL iPr ) and 1,2-bis(1,3,4,5-tetramethylimidazolin-2-imino)ethane (BL Me ) with the cycloheptatrienyl-molybdenum complex [(η 7 -C 7 H 7 )Mo(CH 3 CN) 3 ]X (X ) BF 4 , PF 6 ) leads to acetonitrile substitution and formation of stable 16-electron half-sandwich complexes (η 7 -C 7 H 7 )Mo(BL iPr )]BF 4 , [1]BF 4 , and [(η 7 -C 7 H 7 )Mo(BL Me )]X, [2]X (X ) BF 4 , PF 6 ), two of which could be crystallographically characterized to reveal undistorted two-legged piano stool geometries. Cyclovoltammetric studies exhibit very negative redox potentials of E°) -1.095 V and E°) -1.138 V versus the ferrocene/ferrocenium couple (0 V), indicative of very electron-rich metal complexes. Oxidation of [2]X with (η 7 -C 7 H 7 )BF 4 or [Fe(η 5 -C 5 H 5 ) 2 ]PF 6 furnished the Mo(I) complexes of general formula [(η 7 -C 7 H 7 )Mo(BL Me )(CH 3 CN)]X 2 , [3]X 2 (X ) BF 4 , PF 6 ), which display a three-legged piano stool geometry in the solid state by coordination of one additional acetonitrile molecule to molybdenum. The same geometry is observed upon reaction of [1]BF 4 and [2]PF 6 with 2,6dimethylphenyl isocyanide (XyNC) to afford the isocyanide complexes [1(CNXy)]BF 4 and [2(CNXy)]PF 6 . Their CN stretching vibrations are observed at 2041 and 2030 cm -1 , confirming the electron richness and strong π-electron-releasing capability of the molybdenum-imine moiety.

Quinine‐Derived Imidazolidin‐2‐imine Ligands: Synthesis, Coordination Chemistry, and Application in Catalytic Transfer Hydrogenation

“…All solvents were purified by standard methods and distilled prior to use. [18,21,36]. 1a and 1b were obtained from InnoChemTech; their preparation was previously published [5].…”

“…In accord with the presence of 16-electron species in solution, reasonable activity was observed upon using these complexes as catalysts in the transfer hydrogenation of ketones. Inspired by Sundermeyer, who reported the synthesis of the proton sponge 1,8-bis(dimethylethylene-guanidino)naphthalene (DMEGN) by treating 1,8-diaminonaphthalene with 2-chloro-1,3-dimethyl-imidazolinium chloride (2, DMC) [18], we envisaged the synthesis of the new optically active amino-imino ligands DMIQCI (3a) and DMIQCD (3b) using the 1,2-diamines 1a and 1b (Scheme 2). Compounds 3a and 3b are among the first N,N-bidentate ligands bearing a configurationally stable N*-stereogenic center in the uncoordinated form.…”

16‐Electron (Arene)ruthenium Complexes with Superbasic Bis(imidazolin‐2‐imine) Ligands and Their Use in Catalytic Transfer Hydrogenation

“…Upon metal coordination, the contribution of the ylidic form B can be expected to increase considerably, and thus these ligands exhibit a particularly strong electron-donating capacity toward transition metal atoms. [10][11][12][13][14] [a] Institut für Anorganische und Analytische Chemie, Technische Universität Carolo-Wilhelmina, Hagenring 30, 38106 Braunschweig, Germany Fax: +49-251-391-5309 E-mail: m.tamm@tu-bs.de The bidentate ligands BL iPr and BL Me can be conveniently synthesized by introducing a CH 2 CH 2 bridge between two imidazolin-2-imines, which have proved to be valuable ligands in their own right [11] and can be obtained from the reaction of trimethylsilyl azide (Me 3 SiN 3 ) with Nheterocyclic carbenes of the imidazolin-2-ylidene type. [9] The pronounced electron-donor properties of these bis-(imidazolin-2-imines) were documented by the preparation of highly reactive copper(I) complexes, allowing effective O=O and C-Cl bond activation, CO 2 fixation and Cu I disproportionation.…”

Synthese und Koordinationseigenschaften von Stickstoff(I)‐ Liganden

“…des Chlorcyclopropeniumsalzes [9] 9 mit Mesitylamin und anschließende Deprotonierung mit KH oder KHMDS hergestellt. Diese Route ist komplementär zu der von Tamm et al entwickelten Synthese von Imidazolin-2-iminen, [10,11] vermeidet die Verwendung von freien Carbenen und ermöglicht vielfältigere Strukturmodifizierungen von Verbindungen des Typs Cc als zuvor berichtet. [12] Die Donoreigenschaften dieser Liganden wurden anhand der CO-Streckschwingungen in Komplexen des Typs [RhCl(CO) 2 C] untersucht.…”

“…[19] Bis(imidazolin-2-imin)-Liganden erreicht werden. [21] Zusammengefasst haben wir die Synthese, Bindungsverhältnisse und Koordinationseigenschaften von sehr elektronenreichen Iminen untersucht, insbesondere von Cyclopropenylylideniminen. In diesen Verbindungen zeigt der zentrale Stickstoff alle Eigenschaften eines Stickstoff(I)-Atoms, nämlich die Verfügbarkeit von zwei freien Elektronenpaaren, die hauptsächlich am Stickstoff lokalisiert sind …”