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Isonitriles are useful reagents that participate in many cycloaddition or multicomponent reactions of interest in organic synthesis, which are often catalyzed by transition metal complexes. Being good electron donors, RN=C bonds become activated and prone to the nuclephilic attack upon coordination to electrophilic (Lewis acidic) metal centers. Herein we explore the complexation of tBuNC to a series of iridium hydrido chlorides supported by benzene-based pincer ligands, ()IrH(Cl) ( = κ3‑C6H3–2,6-(ZPtBu2)2, where R = H (I–III), EtCO2–(IV), and Z = CH2 (I), CH2, O (II), O (III, IV)), that occurs instantaneously and quantitatively in solution yielding one of possible isomers Ia–IVa. Single crystal X-ray diffraction studies for Ia–IIIa confirmed the apical coordination of isonitrile ligand trans to hydride ligand suggested by NMR studies. Perusal of the structural data suggests stronger binding of tBuNC to PCP-supported iridium center in complex Ia in comparison to PCOP/POCOP species IIa–IIIa. Structural data also reveal a distortion in the P–Ir–P arrangement caused by tBuNC docking in apical position that is the most noticeable for asymmetric PCOP version IIa. The computational analysis of vibrational frequencies unveils an essential coupling νIr-H and νN=С modes that produce two strong bands of similar intensity in the νN=C region for Ia. Weaker isonitrile binding in IIa–IVa with shorter N=С and longer N– /Ir–CCN bonds and a plethora of intramolecular interactions result in a different degree of vibrational mixing for Ir‒H and N=C stretches as well as lead to an intense bands due to a Fermi resonance of low frequency modes involving vibrations of N–C–tBu fragment. Thus, the raw experimental IR data should be taken with care as an indicator of RN=С activation, paying attention to the vibrational coupling. An estimation of band position for the "true" (uncoupled) νNC vibration gives a small high frequency shift for Ia (+16 cm–1) but low frequency shifts for other complexes becoming less negative in the order IIa–IIa–IVa (PCOP–POCOP– EtCO2-POCOP). Overall the results obtained show the influence of the pincer ligand on the complex picture of isonitrile complexes structure and spectra, and suggest that strong binding does not always mean a strong activation. [ABSTRACT FROM AUTHOR]

The hydride ion transfer and proton transfer are the key steps in the reactions of (de)hydrogenation, dehydrocoupling, production of H2, and reduction of CO2 with the participation of transition metal hydrides; complexes with bifunctional ligands often act as catalysts for these transformations. The aim of this work was to study the hydride-donating properties of pincer palladium(II) hydride (PNP)PdH (1; PNP is bis(2-diisopropylphosphino-4-methylphenyl)amide). For this purpose, its reaction with Lewis acids (BF3·Et2O, B(C6F5)3) was studied using IR and NMR spectroscopies combined with quantum chemical calculations (DFT/M06/def2-TZVP). Correlations between electrochemical reduction potentials of the corresponding cations and thermodynamic hydridity of the metal hydrides proposed in the literature were also applied. [(PNP)Pd(MeCN)][BF4] undergoes an irreversible two-electron reduction in acetonitrile ( = –1.82 V). The use of the obtained potential in correlations gives an overestimated value of the hydride donating ability It was found that the reaction of 1 with boron-containing Lewis acids unexpectedly leads to the protonation of the nitrogen atom of the pincer ligand with an impurity of water, rather than the reaction with the hydride ligand. According to DFT calculations, the proton affinity of the nitrogen atom is much higher than that of PdH, which determines its higher activity in protonation processes. [ABSTRACT FROM AUTHOR]

Fixation of atmospheric nitrogen and N2 reduction to NH3 under mild conditions form an important and, at the same time, challenging area of modern fundamental science. This review considers studies of the reactivity of dinitrogen complexes of group 6 metals (mainly molybdenum and tungsten) with relatively simple phosphine ligands, which made it possible to identify the main stages of N2 reduction in the coordination sphere of a transition metal and factors affecting the reaction efficiency. The attention is focused on the studies of the protonation of the coordinated N2 molecule, which is a key step in the catalytic cycle of nitrogen reduction, proceeding as alternating proton and electron transfer steps. [ABSTRACT FROM AUTHOR]

A new complex of trinuclear silver(I) pyrazolate macrocycle [AgPz]3 (Pz = (CF3)2Pz) with 4,4′-dibromobiphenyl (L) was synthesized and characterized. As shown by NMR spectroscopy, X-ray diffraction (CCDC no. 2169289), and quantum chemical calculations, the π-electron density of the aromatic ligand serves as the coordination site both in solution and in the solid state. The bromine atom is not coordinated to the metal. The complexation gives rise to infinite columns composed of alternating macrocycle and biphenyl molecules {[AgPz]3·L}∞. The neighboring columns are linked by shortened Br–FCF3 contacts. In the solid state, the biphenyl geometry is flattened (the dihedral angles are 0.68° and 0.51°), which has the crucial effect on the photophysical behavior of the complex and demonstrates the possibility of controlling photoluminescence properties of oligophenylene systems. [ABSTRACT FROM AUTHOR]

The mechanism of the halogenation of decahydro-closo-decaborate dianion [B10H10]2− by HCl via the electrophile-induced nucleophilic substitution (EINS) was explored at M06/6-311++G(d,p) level of DFT theory in acetonitrile (MeCN) taking into account non-specific solvent effect (SMD model). The dihydrogen-bonded (DHB) complexes are the first and important reaction intermediates of the EINS process since they determine the principal direction of HCl attack and lead to the proton transfer to the most reactive and elongated B–H bond. Upon the successive replacement of H− with Cl− in the closo-borane structure, a gradual increase in the electron deficiency of closo-borane and the electrophilicity of boron atoms are observed. The lack of stabilization of the η2-H2 complexes for the subsequent stages of the reaction is associated with an increased electrophilicity of boron atoms in substituted closo-boranes. An increased electrophilicity of boron atoms in substituted closo-boranes and higher activation energy of each subsequent stage during the EINS process hamper the reaction and completely stop the chlorination on 3rd or 4th reactions steps. Thus, the data obtained indicate that for the selective synthesis of halogenated products [B10H(10 –x)Clx]2− (x = 5–7) it is necessary to use an approach alternative to the simple acid-initiated nucleophilic substitution. This could be the activation of the bond by Lewis superacids or transition metal catalysis. [ABSTRACT FROM AUTHOR]