Novel access to azaphosphiridine complexes and first applications using Brønsted acid-induced ring expansion reactions

Abstract

Synthesis of azaphosphiridine complexes 3a-e was achieved via thermal group transfer reaction using 2H-azaphosphirene complex 1 and N-methyl C-aryl imines 2a-e (i) or via reaction of transient Li/Cl phosphinidenoid complex 5 (prepared from dichloro(organo)phosphane complex 4) using 2a-c (ii), respectively. Reaction of complexes 3a,d and trifluoromethane sulfonic acid in the presence of dimethyl cyanamide led to a highly bond- and regioselective ring expansion yielding 1,3,4sigma3lambda3-diazaphosphol-2-ene complexes 8a,d after deprotonation with NEt3. 31P NMR reaction monitoring revealed that protonation of complex 3a yields the azaphosphiridinium complex 6a, unambiguously identified by NMR spectroscopy at low temperature. All isolated products were characterized by multinuclear NMR spectroscopy, IR and UV/Vis (for 3a,d, 6a, 8a,d), MS and single-crystal X-ray crystallography in the cases of complexes 3b-d, 8a and 8d. DFT studies on the reaction mechanism and compliance constants of the model complex of 6a are presented.

Synthesis and Reactivity of an Unusual Ferrocenophane Bis(carbene complex)

“…[5] More recently, we developed new synthetic methodologies based on 2H-azaphosphirene complexes that provide facile access to four- [6] and five-membered [7,8] heterocycles under mild oxidative [7] or protic [8] conditions, thus introducing the "clickchemistry" concept to the field of phosphorus heterocyclic chemistry. We demonstrated that this new synthetic concept can be easily extended to oxaphosphirane [9] and azaphosphiridine [10] complex chemistry. In addition, di-and polymetallic transition metal complexes have attracted considerable interest in recent years.…”

Computational Studies on Azaphosphiridines, or How to Effect Ring‐Opening Processes through Selective Bond Activation

“…This also stimulated studies on the acid-catalyzed ring opening of azaphosphiridine complexes and, here, the effect of N-protonation upon PÀN bond activation was briefly addressed [11] using the compliance constant methodology.…”

“…ROR pathways in N-protonated azaphosphiridine P-oxide 6·H + . [11] To learn about the effect of Lewis acid bonding to the nitrogen center of 5-9 and its influence on ROR processes (Scheme 7), we evaluated the change in the bond strength parameters in comparison with the free ligand, and plotted them ( Figure 4) together with the values for the N-protonated and N-alkylated derivatives described above (Scheme 9). Therefore, a series of chlorides of mono-, di-, tri-, and tetravalent metals (or metaloids) was examined.…”

“…Keywords: ab initio calculations · heterocycles · nitrogen · phosphorus · ring expansion [ plex [10] and imine derivatives; [11] the quest for a transient electrophilic terminal phosphinidene complex [12] remained open. This also stimulated studies on the acid-catalyzed ring opening of azaphosphiridine complexes and, here, the effect of N-protonation upon PÀN bond activation was briefly addressed [11] using the compliance constant methodology.…”

“…Accessible data through direct experimental or theoretical vibrational spectroscopy are not intrinsic as such, as vibrations in polyatomic molecules are coupled to varying degrees. The compliance matrix [41, 42, 13a, d] approach offers a unique numerically stable (transferable) description of bond strength, and subsequently of bond orders, [43] and it has been used to analyze multiple bonding, for example, between C and Si [44] and/or S, [40c] several types of bonding at P, [11,45] and in other interesting bonding situations. [46, 13c] The compliance constants C ii , diagonal elements of the compliance matrix, measure the flexibility (or compliance) of a specific bond.…”