Synthesis, Structure, and Ring‐Expansion Reactions of a 3‐Ferrocenyl‐Substituted 2H‐Azaphosphirene Tungsten Complex

Abstract

Reaction of C-ferrocenyl-substituted aminocarbene tungsten complex 1 with [bis(trimethylsilyl)methylene]chlorophosphane (2) and triethylamine yielded 2H-azaphosphirene complex 3 in good yield. Reaction of complex 3 with aryl nitriles 4a-c, N-piperidinonitrile (4d), and acetonitrile (4e) in the presence of ferrocenium hexafluorophosphate yielded regioselectively 2H-1,4,2-diazaphosphole complexes 5a-e through single-electron-transfer-induced ring expansion to-

Strong Evidence for an Unprecedented Borderline Case of Dissociation and Cycloaddition in Open‐Shell 1,3‐Dipole Chemistry: Transient Nitrilium Phosphane‐Ylide Complex Radical Cations

“…The reaction of 3-ferrocenyl-substituted 2H-azaphosphirene complex 1c [12] in the presence of substoichiometric amounts of ferrocenium hexafluorophosphate but in the absence of a nitrile yielded the 3,5-diferrocenyl-substituted 2H-1,4,2-diazaphosphole complex 3c at ambient temperature (Scheme 3, i). To our surprise, difluorophosphane complex 4c [13] was formed, too, which complicated the workup.…”

“…In order to study the dependence of the unexpected reaction (i) on the nature of the pentacarbonyl metal fragment, we also reacted the chromium and molybdenum complexes 1a,b, which were easily obtained by using the synthetic protocol for complex 1c, [12] with [FcH]PF 6 under analogous conditions in the absence (i) and in the presence (ii) of cyanoferrocene (2). During reaction (i) of complex 1b, reso-nances at δ = 132.6 and 96.3 ppm were detected by 31 P{ 1 H} NMR spectroscopy, which are tentatively assigned to complex 3b and the liberated heterocyclic ligand 5, respectively.…”

“…Solvents were distilled from sodium or CaH 2 (CH 2 Cl 2 ). 2H-Azaphosphirene complexes 1a-c [12] and cyanoferrocene [45] were synthesized according to the methods described in the literature. Melting points were determined with a Büchi apparatus Type S. The values are not corrected.…”

“…[11] As part of our current research is focused on template-directed synthesis of functional heterocycles, we recently conducted oxidative SET reactions of 3-ferrocenyl-substituted 2H-azaphosphirene tungsten complexes with electron-rich nitrile derivatives by using ferrocenium hexafluorophosphate. [12] Some of these reactions showed a nitrile-dependent degree of byproduct formation, whereas the latter displayed 31 P{ 1 H} NMR spectroscopic data typical for a 2H-1,4,2-diazaphosphole complex but with an unknown substitution pattern. [12] As this ring expansion methodology offers the interesting perspective to construct extended ligand architectures with redox-active functionalities, it became a necessity to understand and thus be able to disfavor or avoid this side reaction.…”

“…[12] Some of these reactions showed a nitrile-dependent degree of byproduct formation, whereas the latter displayed 31 P{ 1 H} NMR spectroscopic data typical for a 2H-1,4,2-diazaphosphole complex but with an unknown substitution pattern. [12] As this ring expansion methodology offers the interesting perspective to construct extended ligand architectures with redox-active functionalities, it became a necessity to understand and thus be able to disfavor or avoid this side reaction. Here we present first results of transient nitrilium phosphane-ylide complex radical cation dissociation and 1,3-dipole reactions that represent an unprecedented borderline case in open-shell 1,3-dipole chemistry.…”