The preparation of 2-iminoimidazolines - has been accomplished by the Staudinger reaction of the carbenes 1,3-di-tert-butylimidazolin-2-ylidene (), 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene (), 1,3-diisopropylimidazolin-2-ylidene (), 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (), 1,3-bis(2,6-diisopropylphenylimidazolin-2-ylidene () and 1,3,4,5-tetramethylimidazolin-2-ylidene () with trimethylsilyl azide (Me3SiN3) followed by desilylation of the resulting 2-trimethylsilyliminoimidazolines -. The X-ray crystal structures of and have been established, revealing C1-N1-Si1 angles that are more obtuse than the corresponding P-N-Si angles observed in related trimethylsilyl iminophosphoranes. Together with , the disilylated side product 1,3-diisopropyl-2-(trimethylsilylimino)-4-trimethylsilylimidazoline () has been isolated and structurally characterized. Cleavage of the N-Si bonds in and formation of is easily achieved by stirring in methanol. The molecular structures of the 2-iminoimidazolines are reported, indicating that the structural parameters are best described by non-ylidic resonance structures and that electron delocalization within the imidazole heterocycle does not play a crucial role in these imine systems. Compound forms a head-to-head dimer in the solid state via weak intermolecular N-H...N contacts, which have additionally been characterized by means of compliance constants. To further analyze the electronic structure of these imines in comparison to related guanidine ligands, the proton affinities (PAs) of the model compounds 2-imino-1,3-dimethylimidazoline (), 2-imino-1,3-dimethylimidazolidine () and tetramethylguanidine () have been calculated by means of density functional theory. Finally, the charge distribution in - and the relative contribution of relevant resonance structures have been determined using natural bond orbitals (NBO) and natural resonance theory (NRT).

A series of copper(I) complexes with a sterically hindered, bidentate ligand, BL iPr, derived from an N-heterocyclic carbene precursor have been isolated, characterized and their reactivity studied. The ethylene-bridged bis(imidazolin-2-imine) ligand (BL iPr) provides strongly donating N-donor atoms for the stabilization of a copper(I) metal center, priming it for reactivity. The complexes [(BL iPr)Cu(XyNC)]PF6 (4) and [(BL iPr)CuCl] (5) were characterized by X-ray crystallography and exhibit trigonal coordination at the copper centers. The reactivity of [(BL iPr)Cu]SbF6 toward dioxygen was studied at low temperature, indicating formation of a thermally sensitive intermediate with intense UV/Vis features and an isotope-sensitive vibration at 625 cm(-1) (599 cm(-1) with 18 O2). The intermediate is assigned as containing the bis(mu-oxo)dicopper(III) core, [2](PF6)2, and the related, stable hydroxo form was crystallized as [{(BL iPr)Cu}2(mu-OH)2](PF6)2, [3](PF6)2. The reactivity of 5 as a catalyst for the ATR polymerization of styrene was assessed in terms of reaction kinetics and polymer properties, with low PDI values achieved for polymers with molecular weights up to 30 000 g mol(-1).

The 1,2-bis(imidazolin-2-imino)ethane ligands BL Me and BL iPr were prepared, in which the ability of the imidazolium moiety to effectively stabilize a positive charge leads to highly basic ligands with a strong electron-donating capacity. This feature is illustrated by the isolation of very stable half-sandwich 16-electron ruthenium complexes of the type [(η 5 -C 5 Me 5 )Ru(BL R )] + (1, R = Me; 2, R = iPr), which even resist coordination of the chloride counterion. Their inertness towards hard, π-basic ligands does not prevent these complexes from displaying high reactivity towards soft σ-donor/

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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)

The bis(imidazolin‐2‐imine) ligand N,N′‐bis(1,3‐diisopropyl‐4,5‐dimethylimidazolin‐2‐ylidene)‐1,2‐ethanediamine (BLiPr) was used to synthesize a complete series of transition metal dichloride complexes of the type [(BLiPr)MCl2] with M = Mn, Fe, Co, Ni, Cu, Zn. The molecular structure of each complex was established by X‐ray diffraction analysis; the complexes are isomorphous and crystallize in the monoclinic space group C2/c, which allows comparison of their structural parameters in a constant packing environment. The complexes exhibit distorted tetrahedral coordination around the metal atoms with the dihedral angles between the MN2 and MCl2 planes ranging from 53.9° (M = Cu) to 75.5° (M = Zn).

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The coordination chemistry of the tridentate pincer ligand TL tBu , which contains two electron-rich imidazolin-2-imine moieties, has been explored. The reaction of TL tBu with metal dihalides gave complexes of the general formula [(TL tBu )-MX 2 ] (M = Mn, Fe, Co, Ni; X = Cl, Br). These complexes were characterized by X-ray diffraction analysis, which showed them to have different geometries in the solid state. Although [(TL tBu )MnCl 2 ] (1) is best described as distorted square-pyramidal, the complexes [(TL tBu )FeCl 2 ] (2) and [(TL tBu )CoCl 2 ] (3) show distorted tetrahedral geometries with the TL tBu ligand bound in a κ 2 fashion and one of its imidazolin-2-imine fragments not coordinated to the metal atom. [(TL tBu )NiBr]Br (4) crystallizes with a slightly distorted square-planar cation. The reaction of the triflate (OTf) salts [M(OTf) 2 ·nMeCN] (M = Mn, n = 1; M = Fe, Co, n = 2; OTf = CF 3 SO 3 ) with TL tBu resulted in [(TL tBu )M(OTf)][OTf] (M = Mn, 5; M = Fe, 6) and [(TL tBu )Co(NCMe)][OTf] 2 ( 7). Complexes 6 and 7 were characterized by X-ray diffraction analysis, and both showed distorted square-planar geometries. Magnetic measurements of 5, 6 and 7 showed them to possess a S = 5/2, 2 and 1/2 ground states, respectively. The [a] www.eurjic.org FULL PAPER plained by the pronounced ability of the imidazolium moiety to stabilize a positive charge by delocalization over the five-membered N-heterocycle. [5] For related bidentate bis-(imidazolin-2-imine) ligands (BL R ), [6] the enhanced nucleophilicity of the exocyclic N-imino groups was successfully exploited for the stabilization of unusual 16-valenceelectron half-sandwich complexes of the type [(η 5 -C 5 Me 5 )-Ru(BL R )] + , [(η 6 -C 6 H 6 )Ru(BL R )] 2+ and [(η 7 -C 7 H 7 )Mo-(BL R )] + . [7,8,9] In addition, copper(I) complexes containing the tridentate TL tBu ligand are very reactive and have a tendency to form stable, square-planar copper(II) complexes of the general type [(TL tBu -κ 3 )CuX], which have been applied successfully in aerobic CO 2 fixation (X = HCO 3 -κO), C-Cl bond activation and Cu I disproportionation reactions (X = Cl). [10] Scheme 1.As a continuation of our work, [11] we aimed to extend the coordination chemistry of the tridentate TL tBu ligand to the "earlier" first row transition metals manganese, iron, cobalt and nickel. Accordingly, the ligand was directly reacted with the corresponding divalent metal halide and trifluoromethanesulfonate (triflate, OTf) salts. [12] Owing to the specific steric and electronic characteristics of the ligand, we envisaged the formation of unusual square-planar metal complexes, which might show potentially interesting chemical reactivities and magnetic properties. In addition, these complexes could also serve as valuable starting materials for the preparation of high-valent (TL tBu )M complexes, in which the particularly strong electron-releasing capability of the coordinated pincer ligand might facilitate the isolation of new and highly reactive complexes such as metaloxo (M=O), [13,14] -imido...