First Structure Analysis and Photoelectron Spectroscopic Investigation of an Azete and an Azete‐Cobalt Complex

Abstract

Fig. 1). For vinylcyclopropanes, 1 has an energetically high-lying "Walsh orbital" in the three-membered ring, which, together with the 71-system of the double bond has suitable symmetry for interaction with the LUMO of Z.1141 The endo-addition is preferred over the exo-addition, presumably on steric grounds (hindrance by the methoxycar-bony1 group in 1).

Thermochemistry of Tetrazete and Tetraazatetrahedrane: A High-Level Computational Study

“…Our calculations show that the azetes have planar structures with a well-pronounced bond-length alternation, which are minima both at the HF/6-31G(d) and MP2/6-31G(d,p) levels. This agrees with the experimental findings for 17 and 18 , which showed planar distorted rectangular structures of the four-membered rings . The CC (1.337 Å) and CC (1.537 Å) bond lengths in azete 9 calculated at the MP2/6-31G(d,p) level are close to those (1.35 and 1.59 Å, respectively) 15b found by the X-ray study of 18 .…”

“…The CC (1.337 Å) and CC (1.537 Å) bond lengths in azete 9 calculated at the MP2/6-31G(d,p) level are close to those (1.35 and 1.59 Å, respectively) 15b found by the X-ray study of 18 . A similar agreement is observed for the calculated CN (1.296 Å) and CN (1.567 Å) bond lengths in 9 and the X-ray values of 1.28 and 1.58 Å, respectively 15b. The CC and CC bond lengths in 9 are slightly shortened when compared to the corresponding bond lengths in cyclobutadiene (1.344 and 1.564 Å at the MP2/6-31G(d,p) level)…”

“…Although tetrazete is still unknown experimentally, and the detection and/or synthesis of its stabilized derivatives remains a challenge for the chemistry of reactive molecules, a lot of effort − has been directed to the solution of “the azacyclobutadiene problem” 54a. This has resulted in the syntheses of kinetically stabilized azetes, e.g., tri- tert -butylazete ( 17 ), and in X-ray, 1 H NMR, and 13 C NMR spectrometry and photoelectron spectroscopic studies of their structures 15,16 and reactivities . Our calculations show that the azetes have planar structures with a well-pronounced bond-length alternation, which are minima both at the HF/6-31G(d) and MP2/6-31G(d,p) levels.…”

“…Tetrazete ( 1 ) and tetraazatetrahedrane ( 2 ) are of particular interest as possible high-energy-density materials − like the N 6 , N 8 , N 10 , N 12 , and N 20 molecules. − The isoelectronic and structural relationships of 1 and 2 with cyclobutadiene ( 3 , D 2 h ) and its valence isomer, tetrahedrane ( 4 ), which play key roles in the development of the antiaromaticity and strain theories, respectively, fascinate chemists. ,− Although 3 is 108.9 kJ mol -1 lower in energy than 4 at the G2 level, the computational data on the relative stabilities of 1 and 2 indicate a much smaller difference in their energies. , Thus, correspondingly, the prediction of either 1 or 2 as the lower energy valence isomer is controversial and depends strongly upon the level of the calculation used. ,, Earlier estimates of the stability of tetraazatetrahedrane, which were based on the energies of isodesmic bond-separation reactions, showed that the destabilization energy is half that of tetrahedrane . These calculations, however, were performed at the HF/3-21G level and ignored the effects of polarization functions (including f functions) and electron correlation although their importance in the description of strained systems has been well established …”

Ligand Behavior of a (Z)-Phosphazide (a 1,2,3,4λ5-Triazaphosphinine) and of the Corresponding Phosphazene (a 1,2λ5-Azaphosphete)

“…The results observed with Schwartz's reagent demonstrate that the chemistry of ( Z )-phosphazides is not restricted to dinitrogen elimination, giving the corresponding phosphazenes. It can also be noted that, not surprisingly, in contrast to its organic analogues, especially the azetes, 1,2λ 5 -azaphosphete 2 acts as an η 1 -ligand, giving stable complexes.…”