A Comprehensive Analysis of the Metal-Nitrile Bonding in an Organo-Diiron System

Nitriles (N≡CR) are ubiquitous in coordination chemistry, yet literature studies on metal-nitrile bonding based on a multi-technique approach are rare. We selected an easily-available di-organoiron framework, containing both π-acceptor (CO, aminocarbyne) and donor (Cp = η⁵-C₅H₅) ligands, as a suitable system to provide a comprehensive description of the iron-nitrile bond. Thus, the new nitrile (2-12)CF₃SO₃ and the related imine/amine complexes (8-9)CF₃SO₃ were synthesized in 58-83% yields from the respective tris-carbonyl precursors (1a-d)CF₃SO₃, using the TMNO strategy (TMNO = trimethylamine-N-oxide). The products were fully characterized by elemental analysis, IR (solution and solid state) and multinuclear NMR spectroscopy. In addition, the structures of (2)CF₃SO₃, (3)CF₃SO₃, (5)CF₃SO₃ and (11)CF₃SO₃ were ascertained by single crystal X-ray diffraction. Salient spectroscopic data of the nitrile complexes are coherent with the scale of electron-donor power of the R substituents; otherwise, this scale does not match the degree of Fe → N π-back-donation and the Fe-N bond energies, which were elucidated in (2-7)CF₃SO₃ by DFT calculations.

From cyclic amines and acetonitrile to amidine zinc(ii) complexes

A seemingly simple combination of [Zn(quin)₂(H₂O)] (quin⁻ = quinaldinate) and a selected secondary cyclic amine, piperidine (pipe), pyrrolidine (pyro) or morpholine (morph), afforded in acetonitrile a number of products: anionic homoleptic quinaldinate, neutral heteroleptic quinaldinate/amine and quinaldinate/amidine complexes. The piperidine and pyrrolidine systems underwent reaction with acetonitrile to give amidines. The in situ formed piperidinoacetamidine (pipeam) or pyrrolidinoacetamidine (pyroam) coordinated to zinc(ii). Reactions with piperidine led to trans-[Zn(quin)₂(pipe)₂]·2CH₃CN (1), [Zn(quin)₂(pipe)]·cis-[Zn(quin)₂(pipe)₂] (2), pipeH[Zn(quin)₃]·CH₃CN (3), [Zn(quin)₂(pipeam)]·CH₃CN (4a), [Zn(quin)₂(pipeam)]·2CHCl₃ (4b), pipeamH[Zn(quin)₃] (5) and pipeamH[Zn(quin)₂(CH₃COO)]·acetamide (6) (pipeH⁺ and pipeamH⁺ denote protonated amine or amidine). By analogy, [Zn(quin)₂(pyro)₂] (7), pyroH[Zn(quin)₃]·CH₃CN (8), pyroH[Zn(quin)₂Cl] (9), [Zn(quin)₂(pyroam)]·CH₃CN·0.5pyroam·0.5H₂O (10a), [Zn(quin)₂(pyroam)]·2CHCl₃ (10b), [Zn(quin)₂(pyroam)]·CH₂Cl₂ (10c) and pyroamH[Zn(quin)₃] (11) were obtained in the pyrrolidine reactions. The morpholine system allowed isolation of only two novel products, trans-[Zn(quin)₂(morph)₂] (12) and morphH[Zn(quin)₃]·CH₃CN (13). Importantly, no amidine could be isolated. Instead, in autoclaves at 105 °C morpholine degraded to ammonia, as confirmed by mass spectrometry of the gas phase. pyroamH[Zn(quin)₃] exists in two polymorphs which differ in the binding modes of quinaldinate ligands. In 11triclinic, the metal ion of [Zn(quin)₃]⁻ features a five-coordinate environment, whereas that in 11monoclinic is surrounded by six donors. Stabilities of the [Zn(quin)₃]⁻ isomers were assessed with DFT calculations. The one with a six-coordinate zinc(ii) ion was found to be more stable than its five-coordinate counterpart. Favorable intermolecular interactions in the solid state stabilize both and reduce the energy difference between them. The calculations show the conversion of the five-coordinate [Zn(quin)₃]⁻ into its coordinatively saturated isomer to be an almost barrierless process.

Piperidine and pyrrolidine, both belonging to a group of secondary cyclic amines, reacted with acetonitrile in the presence of zinc(ii) to give the corresponding amidines that coordinated to the metal through their imine nitrogen.

Nucleophilic addition reactions to the ethylnitrilium derivative of nido-carborane 10-EtCN-7,8-C2B9H11

Stable imidates 10-EtC(OR)HN-7,8-C₂B₉H₁₁ and thioimidates 10-EtC(SR)HN-7,8-C₂B₉H₁₁ were synthesized via the reactions of a nitrilium derivative of nido-carborane 10-EtCN-7,8-C₂B₉H₁₁ with alcohols and thiols.

Zinc(ii)-mediated generation of 5-amino substituted 2,3-dihydro-1,2,4-oxadiazoles and their further ZnII-catalyzed and O2-involving transformations

Zn^II-activated cyanamides NCNR₂ react with the acyclic N-alkyl ketonitrones Ph₂CN⁺(O⁻)R′ achieving uncomplexed 2,3-dihydro-1,2,4-oxadiazoles.

Solid-phase cyclopalladation in S,C,S′-pincer systems: rising alternative for synthesis in solution

Cyclopalladation of pincer ligands can proceed efficiently in the solid state, serving as a powerful alternative for synthesis in solution.

Weak hydrogen bonds in bis(3-nitroanilinium) hexachloridostannate monohydrate. X-ray, vibrational and theoretical studies

Crystal structures of bis(3-nitroanilinium) hexachloridostannate monohydrate, (H3NA)2SnCl6·H2O, was determined by means of X-ray single crystal diffraction. Relaxed potential energy surface of the H3NA(+) ion was calculated at the B3LYP/6-31(d,p) level. The energy of the H3NA(+) ion is approximately independent upon rotation of the ammonio group. It significantly depends on relative position of the nitro group towards aromatic ring. Theoretical spectra were calculated for the [(A-H3NA)Cl5·H2O](4-) and [(B-H3NA)Cl5](4-) anions, and thus hydrogen bonds of the ammonio group with the nearest neighboring atoms were included. PED results revealed that no coupling among all of the N-H oscillators exists. They vibrate separately because each hydrogen atom of the ammonio group of A- and B-H3NA(+) ions has different surroundings of the acceptors. Overall, very good agreement between theoretical and experimental frequencies was achieved.