Coordination Properties of Bridging Diazene Ligands in Unusual Diiron Complexes

Combined Electron-Diffraction, Spectroscopic, and Theoretical Determination of the Structure of N-Deuterio- trans-Methyldiazene, CH3N═ND. Conformational Effects of the N═N Double Bond

Gas phase electron-diffraction (GED) data obtained at a nozzle-tip temperature of 273 K have been combined with spectroscopic vibrational-rotational constants to determine the structure of trans-methyldiazene, an important prototype for the N═N double bond. The N-deuterio form CH₃N═ND was used in the study since it is appreciably more stable than CH₃N═NH. Both the theoretical and experimental results are consistent with a planar C _s trans-CNND framework. The experimental results ( r_α⁰/ r_g²⁷³) are 1.465(2)/1.467(2) Å for the CN bond, 1.248(1)/1.251(1) Å for the N═N double bond, and 1.037(17)/1.048(17) Å for the ND bond. The NND angle is 105.9(20)/105.6(20)° and the CNN angle is 112.4(5)/112.2(5)°, where the uncertainties in parentheses are twice the standard deviation from a simultaneous least-squares fit of the GED and microwave data. For the methyl group, both theory and experiment indicate that two CH bonds are symmetrically arranged out of the molecular plane while the third CH' lies in the plane in an eclipsed (not staggered) cis-H'CNN arrangement. Theoretical calculations (B3LYP/cc-PVnZ and CCSD(T)/cc-PVnZ) suggest a slight distortion of the methyl group, with a tilt of the methyl top axis about 5° away from the N═N bond. The experimental data are consistent with this picture but are equally consistent with an undistorted methyl group. Inclusion of distortions predicted by theory in a complete basis set limit (CBS) lead to a preferred analysis with average values of 1.086(5)/1.106(5) Å for the CH bond length and an average HCH angle of 108.3(8)/107.8(8)°. Features of the structure of methyldiazene and related compounds are discussed. It is found that the short N═N bond length in the diazenes produces much greater steric repulsion than in analogous ethylene compounds and this effect leads to some interesting conformational and distortion differences for attached CH₃ groups.

Inducing chemical reactivity on specific sites of a molecule using the Coulomb interaction exerted by a low energy electron

Remarkable site-specificity in the resonant attachment of low energy electrons (LEEs) to molecular targets is proposed as an efficient method for inducing chemical reactivity on specific sites of molecules. The Coulomb interaction between the attached electron and the most polarizable molecular electrons localized on the attached site is the reason for site-specific chemical reactivity. The Coulombically induced site-specific chemical reactivity is best illustrated by the LEE induced chemical transformation of a weakly bound molecular complex into a strong covalent adduct. The chemical transformation occurs due to the Coulombically induced nucleophilicity on a specific molecular moiety in the complex. A simple strategy for inducing site-specific chemical reactivity using a LEE may find new avenues in chemical synthesis.

The Mechanism of N-N Double Bond Cleavage by an Iron(II) Hydride Complex

The use of hydride species for substrate reductions avoids strong reductants, and may enable nitrogenase to reduce multiple bonds without unreasonably low redox potentials. In this work, we explore the N═N bond cleaving ability of a high-spin iron(II) hydride dimer with concomitant release of H2. Specifically, this diiron(II) complex reacts with azobenzene (PhN═NPh) to perform a four-electron reduction, where two electrons come from H2 reductive elimination and the other two come from iron oxidation. The rate law of the H2 releasing reaction indicates that diazene binding occurs prior to H2 elimination, and the negative entropy of activation and inverse kinetic isotope effect indicate that H-H bond formation is the rate-limiting step. Thus, substrate binding causes reductive elimination of H2 that formally reduces the metals, and the metals use the additional two electrons to cleave the N-N multiple bond.