Reduction Pathway of End-On Terminally Coordinated Dinitrogen. IV. Geometric, Electronic, and Vibrational Structure of a W(IV) Dialkylhydrazido Complex and Its Two-Electron-Reduced Derivative Undergoing N−N Cleavage upon Protonation

Abstract

The molybdenum and tungsten dialkylhydrazido complexes [M(dppe)2 (NNC5H10)]2+ (M = Mo, W; compounds A(Mo) and A(W)) and their two-electron-reduced counterparts [M(dppe)2 (NNC5H10)] (compounds B(Mo) and B(W)) are characterized structurally and spectroscopically. The crystal structure of B(W) indicates a geometry between square pyramidal and trigonal bipyramidal with the NNC5H10 group in the apical position and in the trigonal plane of the complex, respectively. Temperature-dependent 31P NMR spectra of B(Mo) show that this geometry is present in solution as well. At room temperature, rapid Berry pseudorotation between the "axial" and "equatorial" ligand positions gives rise to a singlet in the 31P NMR spectrum. This exchange process is slowed at low temperature, leading to a doublet. The N-N distance of B(W) is 1.388 A, and the W-N distance is 1.781 A. Infrared and Raman spectroscopy applied to A(W), B(W), and their 15N isotopomers reveals extensive mixing between the N-N and W-N vibrations of the metal-N-N core with the modes of the piperidine ring. The N-N force constant of A(W) is determined to be 6.95 mdyn/A, which is close to the values of the Mo and W NNH2 complexes. In B(W), the N-N force constant decreases to 6.4 mdyn/A, which is between the values found for the Mo/W NNH3 and NNH2 complexes. This allows us to attribute N-N double bond character to A(W) and intermediate character between the double and single bonds for the N-N bond of B(W). These findings are supported by DFT calculations. More importantly, the HOMO of B(W) corresponds to a linear combination of the metal d(sigma) orbital with a ligand orbital having N-N sigma* character, inducing a weakening of the N-N bond. This contributes to the cleavage of the N-N bond taking place upon protonation of B(W) at the Nbeta atom of the NNC5H10 group.

Theoretical and spectroscopic studies of lanthanum (III) complex of 5-aminoorotic acid

“…In the IR spectra they can be seen at 1234 and 1237 cm À1 , while in the Raman spectra they are blue (8 cm À1 ) and red (7 cm À1 ) shifted, respectively ( Table 3). The N-C stretching mode [44,85] appears as a shoulder at 1140 cm À1 in the IR spectrum of the HAOA and as a weak peak at 1122 cm À1 in the IR spectra of its La(III) complex.…”

“…The assignment of the C-H and N-H bands is quite difficult because they appear overlapped in the same spectral region, and the involvement of these groups in hydrogen bonds affects their wavenumbers and produces a relevant band broadening [48,[91][92][93][94][95]. In the IR spectra, the strong band at 3457 cm À1 (HAOA) and the medium bands at 3479 and 3448 cm À1 (La(III) complex) were assigned to the N-H stretching modes from the pyrimidine rings (Table 3) [81,85,100], while the bands at 3333 cm À1 and 3044 cm À1 in the IR spectrum of HAOA as well as the bands at 3339 cm À1 , 3263 cm À1 , and 3038 cm À1 (IR spectrum of La(III) complex) were attributed to the C-H stretching modes [44,85,101] (Fig. 5, Table 3).…”

Theoretical and spectroscopic studies of 5‐aminoorotic acid and its new lanthanide(III) complexes

“…The assignment of the C-H and N-H bands is quite difficult because they appear overlapped in the same spectral region and the involvement of these groups in hydrogen bonds affects their wavenumbers and produces a relevant band-broadening. 48,62 -66 In the IR spectra, the strong band at 3457 cm 1 complex of H 4 L) were assigned to the N-H stretching modes of the pyrimidine rings (Table 3), 59,67,68 while the bands at 3333 cm 1 (strong) and 3044 cm 1 (weak/medium) in the IR spectrum of H 4 L, as well as the bands at 3340 cm 1 (medium), 3258 cm 1 (medium) and 3035 cm 1 (weak/medium) of the IR spectrum of the Ce(III) complex, and the bands at 3339 cm 1 (medium), 3251 cm 1 (medium), 3038 cm 1 (weak/medium) of the IR spectrum of the Nd(III) complex, were attributed to the C-H stretching modes 44,67,69 (Fig. 4, Table 3).…”

(Dinitrogen)molybdenum Complexes Supported by Asymmetric Silicon‐Centered Tripod Ligands: Steric and Electronic Influences on the Coordination of Mono‐ and Diphosphine Coligands

“…So far, a large number of N 2 complexes have been synthesized, only a few of which, however, allow the reduction of N 2 to NH 3 in a cyclic or even catalytic fashion. [11][12][13][14][15][16][17][18] More recently we focused our attention on the design of new ligand environments. On the basis of the latter systems, the first complete mechanistic scenario of N 2 reduction has been established by Chatt and co-workers.…”