1,2,4-Diazaphosphole und 1,2,4-DiazaarsoIe: Ringstruktur und Struktur wasserstoffbrücken-gebundener Paare und Helices/1,2,4-Diazaphospholes and 1,2,4-Diazaarsoles: Ring Structure and Structure of Hydrogen-Bonded Pairs and Helices

Abstract

Among the large family of azaphospholes 1,2,4-diazaphospholes feature a particularly stable ring system. 3,5-Unsubstituted and 3,5-equally substituted 1,2,4-diazaphospholes and -diazaarsoles are best made from 1,3-bis(dimethylamino)-2-phospha/arsaallyl chlorides and hydrazines. This way four examples for single crystal X-ray structure investigations were prepared: The unsubstituted 1,2,4-diazaphosphole 2 and -diazaarsole 4, the N-substituted 1 -(2-pyridyl) 1.2.4-diazaphosphole 1, and the C-substituted 3,5-di-tert-butyl 1,2,4-diazaphosphole 3. They all possess planar rings with small angles at P (86°) and As (81°). The N-unsubstituted molecules are connected to each other by NH···N hydrogen bonds forming in case of the isotypic compounds 2 and 4 a helix along a crystallographic axis and in case of compound 3 for steric reasons a dimer. The structures of the aggregates found are compared to those of pyrazoles.

1,3‐Dipolarophile Character of an Extremely Bulky Phosphaalkyne Mes*C≡P (Mes* = 2,4,6‐tBu3C6H2) Leading to the Formation of 1,2,4‐Diazaphospholes with Unique Hydrogen Bonding Properties

“…Figure 4a shows one of the three independent molecules of 10 (molecule A) in the unit cell. Table 1 shows selected bond lengths and angles of 10 , indicating that the parameters are similar to the previously reported 1,2,4‐diazaphospholes 12,23–25. The parameters indicate a relatively large contribution of a 5‐substituted 1 H ‐1,2,4‐diazaphosphole structure: the P1–C1 bonds are longer than the P1–C2 distances, and correspondingly the N1–C1 lengths are shorter than the N2–C2 values.…”

13C and 15N NMR shieldings of 1,2,4‐diazaphospholes in the solid state and in solution

“…Compounds 3-5 have been described previously [1,7]. CPMAS NMR experiments: the solid state 13 C and 15 N NMR spectra were obtained at 300 K on a Bruker AC-200 spectrometer operating at 50.32 MHz ( 13 C) and 20.28 MHz ( 15 N) under cross polarization (CP) and magic angle spinning (MAS) conditions, using a 7 mm Bruker DAB 7 probehead that achieves rotational frequencies of about 3.5-4.5 kHz.…”

“…This relationship has far-reaching structural consequences. Of two 1H-1,2,4-diazaphospholes: 3 (1, R = H) and 4 (1, R = Bu t ) the structure is known from X-ray analysis: 3 crystallizes forming helical chains (catemers) and 4 forming cyclic dimers [1]. The corresponding pyrazoles, pyrazole itself 6 (2, R = H) [2][3][4] and 3,5-di-tert-butylpyrazole 7 (2, R = Bu t ) [5] crystallize using the same patterns.…”

“…The corresponding pyrazoles, pyrazole itself 6 (2, R = H) [2][3][4] and 3,5-di-tert-butylpyrazole 7 (2, R = Bu t ) [5] crystallize using the same patterns. Since 3,5-diphenylpyrazole 8 (2, R = C 6 H 5 ) crystallizes in cyclic tetramers [6] we decided to explore the structure of 3,5-diphenyl-1,2,4-diazaphosphole 5 (1, R = C 6 H 5 ) [1] in order to extend the comparison. As we could not obtain crystals of 5 suitable for X-ray analysis, we decided to investigate the structure of 1H-1,2,4-diazaphospholes 3, 4 and 5 using solid state NMR spectroscopy.…”

Molecules that we made: An essay on phosphorus chemistry

“…Because of their chemistry and structure [152], these compounds proved to be perfect analogs to pyrazoles. To conceive of another conjugated chain with a central two-coordinate phosphorus atom, we thought of a CR unit inserted in each PP bond of a triphosphenium ion.…”