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

Abstract

The ligands N,N′‐bis(1,3,4,5‐tetramethylimidazolin‐2‐ylidene)‐1,2‐ethanediamine (BLMe) and N,N′‐bis(1,3‐diisopropyl‐4,5‐dimethylimidazolin‐2‐ylidene)‐1,2‐ethanediamine(BLiPr) react with [(η5‐C5Me5)RuCl]4 to afford cationic 16‐electron half‐sandwich complexes [(η5‐C5Me5)Ru(BLR)]+ (R = Me, 3; R = iPr, 4), which resist coordination of the chloride counterion because of the strong electron‐donating ability of the diimine ligands. Upon reaction with [(η6‐C6H6)RuCl2]2 or [(η6‐C10H14)RuCl2]2, these ligands stabilize dicationic 16‐electron benzene and cymene complexes of the type [(η6‐C6H6)Ru(BLR)]2+ (R = Me, 5; R = iPr, 6) and [(η6‐C10H14)Ru(BLR)]2+ (R = Me, 7; R = iPr, 8). The X‐ray crystal structure of [5]Cl2 reveals the absence of any direct Ru–Cl interaction, whereas a long Ru–Cl bond, supported by two CH···Cl hydrogen bonds, is observed for [(6)Cl]Cl in the solid state. Treatment of the dichlorides of 6 and 8 with NaBF4 affords [6](BF4)2 and [8](BF4)2, which are composed of individual dications and tetrafluoroborate ions with no direct Ru–F interaction. All complexes catalyze the transfer hydrogenation of acetophenone in boiling 2‐propanol. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

On the Electronic Structure of NiII Complexes That Feature Chelating Bisguanidine Ligands

“…For example, in the field of biomimetic coordination chemistry, peralkylated bifunctional nitrogen ligands for Cu and Fe were designed, [3,4] and in the transfer hydrogenation of acetophenone, Mo and Ru complexes of these ligands demonstrated their catalytic potential. [5] Abstract: In this work we report on the syntheses and properties of several new Ni complexes featuring the chelating bisguanidines bis(tetramethylguanidino)benzene (btmgb), bis(tetramethylguanidino)naphthalene (btmgn), and bis(tetramethylguanidino)biphenyl (btmgbp) as ligands. All complexes were structurally characterized by single-crystal X-ray diffraction and quantum chemical calculations.…”

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

“…for the ring-opening polymerization of lactides and for the atom transfer radical polymerization of styrene [15,16]. Furthermore, it was shown that bis(imidazolin-2-imine) ligands (BL R ), which exhibit pronounced electron-donor properties, are able to stabilize coordinative unsaturated 16- [19]. 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.…”

“…The II -η 6 -p-cymene-diamine complexes [22] and organo-ruthenium(III) amidinates [23]. They are also considerably longer than those for half-sandwich ruthenium(II) bis(imidazolin-2-imine) complexes [17,19] and indicate that the ligands 3a and 3b display a weaker electron-releasing capability.…”

“…Unfortunately, single crystals of 6 suitable for X-ray diffraction analysis could not be obtained but the characteristic color, the elemental analysis and the 1 H, 13 C, and 19 F NMR spectroscopic data proved the formation of a 16-electron Ru II complex. 19 F NMR spectroscopy is particularly useful for determining whether the triflate anions are coordinated to the metal atom. The resonances for uncoordinated triflate anions, as in triflic acid for example, are typically observed around -78 ppm, whereas the signals for coordinated triflate ligands are shifted downfield [25,26].…”

“…The resonances for uncoordinated triflate anions, as in triflic acid for example, are typically observed around -78 ppm, whereas the signals for coordinated triflate ligands are shifted downfield [25,26]. The 19 F NMR spectrum of 6 in [D 6 ]acetone shows a single peak at -77.74 ppm, which can be assigned to an uncoordinated triflate anion.…”