Probing Limits of a C=C Bond Activation by N‐Coordinated Organopnictogen(I) Compounds

Abstract

The C=C bond in selected N-alkyl/aryl-maleimides RN(C(O)CH) 2 (R=Me, tBu, Ph) is activated by organopnictogen(I) compounds producing bridged bicyclic [2.2.1] products exhibiting both endo and exo orientations. This is achieved by a synergic element-ligand cooperation, thereby resembling a hetero-Diels-Alder reaction. A wide range of pnictogen(I) complexes is considered in this study including the bis(aldiminine) pincer compounds ArE (1) (Ar=2,6-(R'N=CH) 2 C 6 H 3 , R'=tBu, E=P (P-1), As (As-1), Sb (Sb-1), Bi (Bi-1) or R' = Dmp, E=P (P-1'), As (As-1'), Sb (Sb-1'), where Dmp = 2,6-Me 2 C 6 H 3 ) and the C,N-coordinated compounds Ar'E (2) (Ar'=2-(DippN = CH)C 6 H 4 , E=P (P-2), As (As-2), where Dipp = 2,6-iPr 2 C 6 H 3 ). On this set of compounds, the reversibility of C=C bond activation was examined mainly by means of the 1 H variable temperature (VT) NMR spectroscopy and this study revealed trends showing a dependence both on the E atom and on the structure of the ligand. The structure of the addition products was elucidated by multinuclear NMR and single-crystal X-ray diffraction analysis. The whole study is accompanied by a theoretical survey targeting decisive factors for the C=C bond activation and a preference for endo/exo forms by the particular pnictogen(I) compound.

Exploring Differences between Bis(aldimino)- and amino-aldimino-N,C,N-Pincer-Stabilized Pnictinidenes: Limits of Synthesis, Structure, and Reversible Tautomerization-Controlled Oxidation

“…Due to the presence of two lone pairs at the pnictogen atom, these compounds have clearly demonstrated their potential as nonconventional ligands for transition metals . In addition to their coordination capabilities, these compounds have been shown to activate carbon–carbon multiple bonds via the element–ligand cooperative (ELC) , mechanism, resembling thereby a hetero Diels–Alder reaction protocol . Related bismuthinidenes are also able to undergo an oxidative addition toward a variety of C­(sp 3 )–X bonds (X = I or OTf) .…”

Beyond simple hetero Diels–Alder cycloadditions. A new type of element–ligand cooperativity at N,C,N-coordinated arsinidene and stibinidene centres in the reaction with an electron-deficient alkyne

“…12 On the other hand, these pnictinidenes are able to activate electron-deficient alkynes 13 or reversibly bind CC double bonds, thereby serving as hidden heterodienes. 14 These reactions include formal dearomatization of heteropnictole rings, thereby exhibiting ELC-like reactivity (Scheme 1D). The back aromatization was achieved in the case of arsenic compounds leading to the formation 1-arsanaphthalenes, but this type of reactivity was not possible for heavier analogues.…”