NHC Moieties Research Articles

Impact of the Methylene Bridge Substitution in Chelating NHC-Phosphine Mn(I) Catalyst for Ketone Hydrogenation.

Systematic modification of the chelating NHC-phosphine ligand (NHC = N-heterocyclic carbene) in highly efficient ketone hydrogenation Mn(I) catalyst fac-[(Ph2 PCH2 NHC)Mn(CO)3 Br] has been performed and the catalytic activity of the resulting complexes was evaluated using acetophenone as a benchmark substrate. While the variation of phosphine and NHC moieties led to inferior results than for a parent system, the incorporation of a phenyl substituent into the ligand methylene bridge improved catalytic performance by ca. 3 times providing maximal TON values in the range of 15000-20000. Mechanistic investigation combining experimental and computational studies allowed to rationalize this beneficial effect as an enhanced stabilization of reaction intermediates including anionic hydride species fac-[(Ph2 PC(Ph)NHC)Mn(CO)3 H]- playing a crucial role in the hydrogenation process. These results highlight the interest of such carbon bridge substitution strategy being rarely employed in the design of chemically non-innocent ligands.

Copper-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) by Functionalized NHC-Based Polynuclear Catalysts: Scope and Mechanistic Insights.

Copper(I) [Cu2(μ-Br)2(tBuImCH2pyCH2L)]n (L = OMe, NEt2, NHtBu) compounds supported by flexible functionalized NHC-based polydentate ligands have been prepared in a one-pot procedure by reacting the corresponding imidazolium salt with an excess of copper powder and Ag2O. An X-ray diffraction analysis has revealed that [Cu2(μ-Br)2(tBuImCH2pyCH2NEt2)]n is a linear coordination polymer formed by bimetallic [Cu(μ-Br)]2 units linked by the lutidine-based NHC-py-NEt2 ligand, which acts as a heteroditopic ligand with a 1κC-2κ2N,N′ coordination mode. We propose that the polymeric compounds break down in the solution into more compact tetranuclear [Cu2(μ-Br)2(tBuImCH2pyCH2L)]2 compounds with a coordination mode identical to the functionalized NHC ligands. These compounds have been found to exhibit high catalytic activity in the Cu-catalyzed azide–alkyne cycloaddition (CuAAC) reaction. In particular, [Cu2(μ-Br)2(tBuImCH2pyCH2NEt2)]2 efficiently catalyzes the click reaction of a range of azides and alkynes, under an inert atmosphere at room temperature in neat conditions at a very low catalyst loading, to quantitatively afford the corresponding 1,4-disubstituted 1,2,3-triazole derivatives in a few minutes. The cycloaddition reaction of benzyl azide to phenylacetylene can be performed at 25–50 ppm catalyst loading by increasing the reaction time and/or temperature. Reactivity studies have shown that the activation of the polynuclear catalyst precursor involves the alkyne deprotonation by the NHC moiety of the polydentate ligand to afford a copper(I)-alkynyl species bearing a functionalized imidazolium ligand. DFT calculations support the participation of the dinuclear species [(CuBr)2(μ-tBuImCH2pyCH2NEt2)], resulting from the fragmentation of the tetranuclear compound, as the catalytically active species. The proposed reaction pathway proceeds through zwitterionic dinuclear intermediates and entails the active participation of both copper atoms, as well as the NHC moiety as an internal base, which activates the reacting alkyne via deprotonation.

Highly Ordered N-Heterocyclic Carbene Monolayers on Cu(111).

The benzannulated N-heterocyclic carbene, 1,3-dibenzylbenzimidazolylidene (NHCDBZ) forms large, highly ordered domains when adsorbed on Cu(111) under ultrahigh vacuum conditions. A combination of scanning tunnelling microscopy (STM), high-resolution electron energy loss spectroscopy (HREELS), and density functional theory (DFT) calculations reveals that the overlayer consists of vertical benzannulated NHC moieties coordinating to Cu adatoms. Long-range order results from the placement of the two benzyl substituents on opposite sides of the benzimidazole moiety, with their aromatic rings approximately parallel to the surface. The organization of three surface-bound benzyl substituents from three different NHCs into a triangular array controls the formation of a highly ordered Kagome-like surface lattice. By comparison with earlier studies of NHCs on Cu(111), we show that the binding geometry and self-assembly of NHCDBZ are influenced by intermolecular and adsorbate–substrate interactions and facilitated by the flexibility of the methylene linkage between the N-heterocycle and the aromatic wingtip substituents.

Dinuclear silver(I)- and gold(I)-N-heterocyclic carbene complexes of N-alkyl substituted bis-benzimidazol-2-ylidenes with aliphatic spacer: Synthesis, characterizations and antibacterial studies

New series of dinuclear Ag(I)-NHC and Au(I)-NHC complexes (NHC = N-heterocyclic carbene) bearing n-alkyl homologous series with propylene spacers were synthesized. Initially, bis-benzimidazolium salts, 1-5 were synthesized via two steps n-alkylation reaction. The salts were then subsequently deprotonated with basic metal source (Ag2O) using in-situ deprotonation method to obtain the Ag(I)-NHC complexes 6-10, respectively. The Au(I)-NHC complexes,11-15were synthesized via transmetalation reaction from their respective Ag(I)-NHC complexes. All compounds were fully characterized by elemental analyses, FT-IR, 1H and 13CNMR spectroscopy. The antibacterial studies of these compounds were evaluated against E. coli and S. aureus using disc diffusion method. The Ag(I)-NHC complexes exhibit better activities with inhibition zone of11 ± 1-20 ± 1mm and 9 ± 0-16 ± 1mm against E. coli and S. aureus respectively, while Au(I)-NHC complexes show inhibition zone of 7 ± 0-14 ± 1mmfor both E. coli and S. aureus bacteria. All the respective benzimidazolium salts were found to be inactive against the bacterial strains. Herein, we found that the antibacterial activity is enhanced by the degree of bond strength due to the match between the hardness and softness of the metal centre (Lewis acid) and NHC moiety (Lewis base). In this point of view, the Ag(I)-C bond was found to be stronger bond to NHC ligand (hard acid-hard base combination) than that of Au(I)-C (soft acid-hard base combination) which resulted the slow release of silver ions for better activity. This is due to the fact that the antibacterial activities of complexes are related with delaying in releasing the metal ions (Ag+ and Au+) into the cell membrane.

Cluster Expansion versus Complex Formation: Coinage Metal Coordination to Silylated [Ge9] Cages

Deltahedral nine-atom tetrel element Zintl clusters are promising building blocks for the straightforward solution-based synthesis of intermetalloid clusters through the reaction with organometallic compounds. Herein we report on novel coordination sites of metal-N-heterocyclic carbene (NHC) complexes to [Ge9] clusters and unexpected cluster isomerization. We present the synthesis of a series of coinage metal-NHC complexes of silylated [Ge9] clusters [NHCiPrCu(η4-Ge9{Si(TMS)3}3)] (1; TMS = trimethylsilyl) and [NHCRM(η4-Ge9{Si(TMS)3}2)]- (2a, M = Cu, R = iPr; 3a, M = Cu, R = Mes; 4a, M = Cu, R = Dipp; 5a, M = Ag, R = Dipp; 6a, M = Au, R = Dipp), in which the coinage metals coordinate to open rectangular cluster faces and act as additional cluster vertex atoms. Besides representing promising intermediates on the way to larger intermetalloid clusters, the formation of compound 1 shows that Cu-NHC fragments also coordinate to the open-square Ge faces of the tris-silylated [Ge9] clusters, contrasting the typical interactions with triangular faces of tris-silylated [Ge9] clusters. In compounds 3a and 4a bearing bulky NHC moieties, an unusual silyl group substitution pattern is observed in contrast to 2a, which corresponds to the silyl group arrangement of other metal complexes of bis-silylated [Ge9] clusters. In this context, potential silyl group migration mechanisms are discussed.

Multidentate N‐Heterocyclic Carbene Complexes of Nickel and Palladium: Structural Analysis and Catalytic Application in Mizoroki–Heck Coupling Reaction

Two series of electron‐rich metal (Ni and Pd) complexes, namely a pyridine‐coordinated tridentate NHC/amidate/phenoxy metal complex and a tetradentate complex bearing an extra pyridyl group, were synthesized. Two carbene moieties, imidazole‐based and benzimidazole‐based NHCs, were also incorporated into the ligand backbones. Seven of the new complexes were structurally characterized and comparative structural analysis revealed that the tetradentate complex with a flanking pyridyl side‐arm was less distorted, leading to chelation‐assisted stronger NHC coordination and hence a shorter metal–carbene bond. The catalytic activities of the two sets of palladium complexes for the Mizoroki–Heck coupling reaction were investigated. The comparative data showed that despite the higher thermal stability and the presence of the flanking hemilabile pyridyl side‐arm which provided unsaturation to the metal center, the catalytic performance was slightly inferior to that of the tridentate palladium complex with a “throw‐away” pyridine ligand. The tridentate palladium complex with the benzimidazole‐based NHC moiety was the most effective catalyst, allowing the utilization of a range of aryl chlorides including deactivated substrates with a low 0.2 mol‐% Pd loading in molten n‐tetrabutylammonium bromide.

Macrocyclic NHC complexes of group 10 elements with enlarged aromaticity for biological studies.

Two sets of macrocyclic, bio-inspired, non-heme ligands are utilized for the synthesis of NiII, PdII and PtII complexes. The ligands consist of a 16-atom macrocycle, formed by four methylene bridged NHC moieties, with imidazole or benzimidazole as building blocks. The complexes exhibit a square planar coordination geometry and are characterized by NMR, ESI-MS, elemental analysis, SC-XRD and UV/Vis. For complexes incorporating benzimidazole, an evaluation of luminescence properties is performed, and is found that phosphorescence is present for the PdII derivative and there is fluorescence for the PtII derivative. Stability studies in cell culture medium are performed for subsequent MTT assays. Here, the NiII complexes show low to no activity, and PdII and PtII complexes exhibit remarkable low IC50 values in cisplatin resistant A2780cisR cells.

Selective catalytic 2e−-oxidation of organic substrates by an FeII complex having an N-heterocyclic carbene ligand in water

An FeII complex, 1, having a pentadentate ligand with an NHC moiety catalyzes substrate oxidation to afford 2e--oxidized products with high selectivity by suppression of overoxidation in water. A Bell-Evance-Polanyi plot for the substrate oxidation catalyzed by 1 exhibited an inflection point around 86 kcal mol-1, indicating strong C-H abstraction ability of the reactive species derived from 1.

Palladium(ii) pincer complexes of a C,C,C-NHC, diphosphonium bis(ylide) ligand.

A new family of pincer palladium(ii) complexes bearing an electron-rich C,C,C-NHC, diphosphonium bis(ylide) ligand of LX2-type was prepared through the dual N-functionalization of 1H-imidazole by (3-bromopropyl)triphenylphosphonium bromide. Selected basic conditions allowed the sequential coordination of the NHC and phosphonium ylide moieties to Pd(ii). This strategy led to an original ortho-metallated complex where the Pd center is bonded to four carbon atoms of three different natures: carbenic (sp2), arylic (sp2), and chiral ylidic (sp3). Protonation of the latter afforded NHC, diphosphonium bis(ylide) pincer Pd(ii) complexes as a mixture of meso- and dl-diastereomers (de = 50%). The selectivity of C-coordination was rationalized on the basis of DFT calculations, evidencing the quasi-degeneracy of the two diastereomeric forms.

Surface anchors target golden bullets.

Gold nanomaterials are attractive for a variety of applications, including in medicine, but need to be made stable enough to operate in biological systems. Now, gold nanorods have been stabilized for photothermal therapy by sequential surface anchoring, using a bidendate PEG-based ligand that features a thiolate moiety and an Au–NHC moiety.

Synthesis, Characterization, and Catalytic Studies of Unsymmetrical Chiral NCC Pincer Pd(II) and Ni(II) Complexes Bearing (Imidazolinyl)aryl NHC Ligands

A series of palladium(II) and nickel(II) complexes based on unsymmetrical chiral (imidazolinyl)aryl NHC ligands are reported. The new ligand presursors 3a–g were prepared from commercially available 3-bromobenzoic acid, in which the carboxyl and bromo functionalities were converted to chiral imidazoline and NHC moieties, respectively, in three steps. Treatment of 3a–g with Pd(OAc)2 in dimethylacetamide in the presence of NaOAc, followed by addition of LiCl, gave the seven palladium(II) pincer complexes 4a–g via direct aryl C–H activation. Likewise, the six nickel(II) pincer complexes 5a–f were obtained by reacting 3a–f with anhydrous NiCl2. All of the ligand precursors and pincer complexes are bench-stable and were fully characterized. The absolute configurations of palladium complexes 4a,c and 5e were further determined by X-ray diffraction. Finally, Pd pincer complex catalyzed asymmetric Friedel–Crafts alkylation and aza-Morita–Baylis–Hillman reactions were briefly assessed.

(Invited) Endohedral Metallofullerene-Based Lewis Acid-Base Pairs

Carbon-based Lewis acids are limited merely to trityl cations and some electron-poor allenes. [1] Recently, Bazan and coworkers reported that C60 and C70 can behave as all-carbon Lewis acids to form the corresponding Lewis acid–base pairs with a normal NHC structure. [2] This work opens a new perspective on the research of carbon-based Lewis acids. Meanwhile, as a novel class of metal-carbon hybrid molecules, endohedral metallofullerenes (EMFs) feature electron transfer from the internal metallic species to the carbon cage, forming zwitterionic compounds. [3] Accordingly, it is of special interest to study whether the highly charged carbon cages of EMFs are willing to accept additional electrons to act as Lewis acids or not. In this representation, taking several kinds of EMFs as a representative, we show that EMFs also exhibit excellent Lewis acidity to form Lewis acid-base pairs with NHCs. Our unambiguous X-ray results reveal that the NHC moiety uses either its normal site or abnormal active center to react with the EMFs under study to form the corresponding adducts with different structures (Scheme 1). It is conformed theoretically the the inherent characteristic of the EMFs is responsible for the addition patterns. R eferences： [1] F. E. Ahn and M. C. Jahnke, Angew. Chem., Int. Ed., 2008, 47, 3122. [2] H. P. Li, C. Risko, J. H. Seo, C. Campbell, G. Wu, J. Bredas and G. C. Bazan, J. Am. Chem. Soc., 2011, 133, 12410. [3] X. Lu, L. Echegoyen, A. L. Balch, S. Nagase and T. Akasaka, Endohedral Metallofullerenes: Basics and Applications, CRCPress, New York, 2015. [4] M. Q. Chen, L. P. Bao, M. Ai, W. Q. Shen and X. Lu. Chem. Sci., 2016, 7, 2331-2334.

Half-Sandwich Manganese Complexes Bearing Cp Tethered N-Heterocyclic Carbene Ligands: Synthesis and Mechanistic Insights into the Catalytic Ketone Hydrosilylation

Manganese(I) complexes [(Cp(CH2)nNHCMes)Mn(CO)2] (2a, n = 1; 2b, n = 2) bearing Cp tethered NHC ligands have been prepared in good yield from [CpMn(CO)3] and N-mesitylimidazole as main components, using a novel synthetic strategy based on the anchoring of an imidazolium moiety to the coordinated Cp ligand, followed by an intramolecular photochemical CO substitution for the pendent NHC moiety generated in situ upon addition of a base. The catalytic performances of 2a–b in the hydrosilylation of 2-acetonaphthone with Ph2SiH2 were found to be essentially indifferent to the length of the linker between the Cp and the NHC moieties, and lower than the one of the nontethered [Cp(CO)2Mn(IMes)] (1) parent complex. Still, the presence of Cp tethered NHC ligands allowed isolation and full characterization of monocarbonyl η2-silane complexes [(Cp(CH2)nNHCMes)Mn(CO)(η2-H–SiHPh2)] (8a, n = 1; 8b, n = 2), which are generated upon photochemical reactions of 2a–b with diphenylsilane. Both of these silane complexes are ina...

Tethered N-heterocyclic carbene-carboranes: unique ligands that exhibit unprecedented and versatile coordination modes at rhodium.

Four brand new hybrid ligands combining an N-heterocyclic carbene tethered with two isomeric nido-dicarbaundecaborane dianions, a neutral closo-dicarbadodecaborane or a closo-dicarbadodecaborane anion are described. Versatile coordination of the ligands to Rh(I) is demonstrated, in which both NHC and carborane moieties covalently coordinate a metal centre.

NHC Versus Pyridine: How “Teeth” Change the Redox Behavior of Iron(II) Complexes

A series of octahedral iron(II) complexes with tetradentate NHC/pyridine hybrid ligands containing up to three pyridyl units was designed to study the influence of NHC and pyridine donors on the electronic structure of the metal center. Structural analysis of the iron complexes by NMR spectroscopy and single-crystal X-ray diffraction reveals different coordination modes of the ligand depending on the linkage of the different donor moieties. The oxidation potentials of all complexes correlate linearly with the number of NHC moieties coordinated to iron, as shown by cyclic voltammetry. The influence, although minor, of structural properties on the oxidation potential and (in one case) the influence of the oxidation state of the coordination geometry of the hybrid ligand are also demonstrated.

Osmium(II)–Bis(dihydrogen) Complexes Containing Caryl,CNHC–Chelate Ligands: Preparation, Bonding Situation, and Acidity

The hexahydride complex OsH6(PiPr3)2 (1) reacts with the BF4-salts of 1-phenyl-3-methyl-1-H-benzimidazolium, 1-phenyl-3-methyl-1-H-5,6-dimethyl-benzimidazolium, and 1-phenyl-3-methyl-1-H-imidazolium to give the respective trihydride-osmium(IV) derivatives OsH3(κ2-Caryl,CNHC)(PiPr3)2 (2–4). The protonation of these compounds with HBF4·OEt2 produces the reduction of the metal center and the formation of the bis(dihydrogen)-osmium(II) complexes [Os(κ2-Caryl,CNHC)(η2-H2)2(PiPr3)2]BF4 (5–7). DFT calculations using AIM and NBO methods reveal that the Os–NHC bond of the Os-chelate link tolerates a significant π-backdonation from a doubly occupied dπ(Os) atomic orbital to the pz atomic orbital of the carbene carbon atom. The π-accepting capacity of the NHC unit of the Caryl,CNHC-chelate ligand, which is higher than those of the coordinated aryl group and phosphine ligands, enhances the electrophilicity of the metal center activating one of the coordinated hydrogen molecules of 5–7 toward the heterolysis. As a result, these compounds are strong Brønsted acids with pKawater values between 2.5 and 2.8. In acetonitrile the hydrogen molecules of 5 and 6 are displaced by the solvent, the resulting bis(solvento) compounds [Os(κ2-Caryl,CNHC)(CH3CN)2(PiPr3)2]BF4 (8, 9) react with acetylacetonate (acac) and cis-1,2-bis(diphenylsphosphino)ethylene (bdppe) to give Os(κ2-Caryl,CNHC)(acac)(bdppe) (10, 11) as a mixture of the two possible isomers, namely with P trans to the aryl group or to the NHC moiety.

NHC Bis-Phenolate Aluminum Chelates: Synthesis, Structure, and Use in Lactide and Trimethylene Carbonate Polymerization

A novel family of Al(III) complexes supported by a tridentate, dianionic N-heterocyclic carbene bis-phenolate ligand ((OCO)2–) was prepared via various synthetic routes, and the derived compounds were all structurally characterized. The methane elimination reaction of the protio ligand N,N′-bis(2-hydroxy-3,5-di-tert-butylphenyl)-4,5-dihydroimidazolium chloride (1·H3Cl) with AlMe3 quantitatively led to the formation of the bis-phenolate imidazolinium Al zwitterion (1·H)Al(Me)(Cl) (2), whose formulation was established by X-ray diffraction studies. The deprotonation of species 2 with 1 equiv of lithium diisopropylamide (LDA) proceeded with the elimination of LiCl to afford the Al-NHC methyl derivative [(OCO)AlMe]2 (3), which was isolated as a dimer, as confirmed by X-ray diffraction studies. Alternatively, compound 3 may be accessed via a salt metathesis route involving the reaction of the NHC bis-phenolate Li salt 1·Li2, generated in situ via reaction of 1·H3Cl with 3 equiv of nBuLi (−40 °C, THF), with 1 equiv of MeAlCl2. The serendipitous hydrolysis of compound 3 allowed the X-ray characterization of the Al-oxo dinuclear species [(OCO)Al-O-Al-(OCO)] (3′), in which both Al(III) centers adopt a distorted-trigonal-monopyramidal geometry. The reaction of the salt 1·H3Cl with Al(OiPr)3 afforded the corresponding bis-phenolate imidazolinium Al zwitterion (1·H)Al(OiPr)(Cl) (4), which incorporates a four-coordinate tetrahedral Al center effectively κ2O,O-chelated by the two phenolate moieties of the OCO2– ligand. Compound 4 may be readily converted to the Al-NHC alkoxide derivative [(OCO)AlOiPr]2 (5) upon reaction with 1 equiv of LDA. Alternatively, the alcoholysis of the Al-NHC methyl species 3 with iPrOH also permitted access to the derived Al alkoxide 5 and proceeds via the formation of the kinetic product (1·H)Al(OiPr)(Me) (6) that may readily eliminate methane upon heating to produce species 5. The Al alkoxide species 5 was shown to efficiently polymerize rac-lactide and trimethylene carbonate in a highly controlled manner for the production of narrow disperse materials. The observed catalytic performances are in the range of the majority of those for group 13 metal based ROP catalysts developed thus far, and all data support the noninvolvement of the NHC moiety in these polymerization reactions.

Comparative study of electronic and steric properties of bulky, electron-rich bisphosphinoethane, bis-NHC and phosphino-NHC chelating ligands in analogous rhodium(I) and iridium(I) COD and carbonyl complexes

The synthesis and characterization of rhodium(I) and iridium(I) COD (1,5-cyclooctadiene) and carbonyl complexes containing small-bite angle and bulky bisphosphine (bis(di-tert-butylphosphino)ethane = dtbpe), bis-NHC (1,1′-di-tert-butyl-3,3′-methylenediimidazolin-2,2′-ylidene = BisNHC) and phosphino-functionalized NHC (3-tert-butyl-1-(di-tert-butylphosphinomethyl)-imidazolin-2-ylidene = NHCP) ligands is described. X-ray diffraction analysis of most compounds made and spectroscopic data permitted a valuable comparison of the characteristic steric and electronic properties of these related ligand classes and also of the “abnormally” bound form of the NHCP ligand (aNHCP). While the dicarbonyl complexes indicated similar overall donating abilities for the BisNHC and NHCP ligands, dtbpe and the aNHCP ligand were shown to be significantly less or more electron donating, respectively. These complexes also allowed the evaluation of the different σ-donating influences of the NHC moiety in comparison to the phosphine moiety within the hybrid NHC–P systems.

Synthesis, Characterization and Luminescence of Gold Complexes Bearing an NHC Ligand Based on the Imidazo[1,5‐a]quinolinol Scaffold

AbstractWe report on the synthesis and characterization of an NHC ligand based on the imidazo[1,5‐a]quinolinol scaffold. The benzyl‐protected NHC precursor was used for the preparation of the corresponding AgI, AuI and AuIII complexes. The molecular structures of the AuI and AuIII halide complexes determined by single‐crystal X‐ray diffraction reveal considerable distortion of the rigid NHC moiety due to steric repulsion between the gold and oxygen atoms. At ambient temperature, the complexes are weakly fluorescent from an intraligand excited state, whereas at 77 K the emission spectra are dominated by intraligand phosphorescence.

Synthesis and Characterization of Novel Iron(II) Complexes with Tetradentate Bis(N-heterocyclic carbene)–Bis(pyridine) (NCCN) Ligands

Three novel iron(II) complexes bearing tetradentate ligands of the type pyridine–bis(N-heterocyclic carbene)–pyridine (NCCN) have been synthesized. The compounds trans-diacetonitrile[bis(o-imidazol-2-ylidenepyridine)alkane]iron(II) hexafluorophosphate (alkane = methane (2a), ethane (2b)) and cis-diacetonitrile[1,3-bis(o-imidazol-2-ylidenepyridine)propane]iron(II) hexafluorophosphate (2c) have been characterized by single-crystal X-ray diffraction (XRD), nuclear magnetic resonance spectroscopy (NMR), and infrared spectroscopy (IR). Cyclic voltammetry (CV) measurements show reversible oxidation of Fe(II) to Fe(III). The rotational barrier of the bridge has been determined via variable-temperature NMR (VT-NMR) studies of 2b. In all complexes, the Fe centers coordinate—in addition to the NCCN ligands—two acetonitrile ligands in the solid state as well as in solution. The alkylene bridge connecting the two NHCs has an influence on the coordination mode of the NCCN ligands. Whereas the methylene- and ethylene-bridged NHC moieties lead to a nearly planar geometry of the NCCN ligand and two trans-positioned acetonitrile ligands, the propylene-bridged complex 2c exhibits a sawhorse-type coordination mode, with two cis-oriented acetonitrile ligands. The reactivity of the synthesized complexes toward substitution of the solvent ligands was investigated, showing that acetonitrile is readily substituted by benzonitrile. Upon addition of carbon monoxide, one acetonitrile ligand is replaced by CO to yield complexes 3a–c, as shown by NMR and IR spectroscopy, as well as by XRD in the case of compound 3c.