Isolation of an Arsenic Diradicaloid with a Cyclic C₂As₂‐Core

Abstract

Herein, we report on the synthesis, characterization, and reactivity studies of the first cyclic C2As2‐diradicaloid {(IPr)CAs}2 (6) (IPr = C{N(Dipp)CH}2; Dipp = 2,6‐iPr2C6H3). Treatment of (IPr)CH2 (1) with AsCl3 affords the Lewis adduct {(IPr)CH2}AsCl3 (2). Compound 2 undergoes stepwise dehydrochlorination to yield {(IPr)CH}AsCl2 (3) and {(IPr)CAsCl}2 (5 a) or [{(IPr)CAs}2Cl]OTf (5 b). Reduction of 5 a (or 5 b) with magnesium turnings gives 6 as a red crystalline solid in 90% yield. Compound 6 featuring a planar C2As2 ring is diamagnetic and exhibits well resolved NMR signals. DFT calculations reveal a singlet ground state for 6 with a small singlet‐triplet energy gap of 8.7 kcal mol−1. The diradical character of 6 amounts to 20% (CASSCF, complete active space self consistent field) and 28% (DFT). Treatments of 6 with (PhSe)2 and Fe2(CO)9 give rise to {(IPr)CAs(SePh)}2 (7) and {(IPr)CAs}2Fe(CO)4 (8), respectively.

A comparative study of biradicaloids as ligands in iron tetracarbonyl complexes

“…1 Only recently, an Fe(CO)4 complex of the biradicaloid [As(μ-C-IPr)]2 (X) was published by the Ghadwal group. 9 Considering these findings, the further investigation of the coordination chemistry of biradicaloids 1 and 2 towards iron carbonyl fragments seemed worthwhile. The coordination of Fe(CO)4 fragments is especially interesting since they are expected to bind to the phosphorus atoms in 1 and 2 in a mono-dentate fashion.…”

“…8 Fe(CO)4 complex of the biradicaloid [As(μ-C-IPr)]2 (X). 9 Further examples of biradicaloids were presented by Bertrand, 10 Power, 11 Schulz (1), 12 Grützmacher (2) 13 and others. 6 Reactivities of 1 and 2 towards small molecules, 13,14 alkenes, 14 alkines, 1 oxidizing agents 13,15 Lewis acids 7 and Lewis bases 7 were studied in detail.…”

Concerted addition of aldehydes to the singlet biradical [P(μ-NTer)]2

“…The stability of these compounds mostly depends on two key factors: (i) the localization of the radical centres at (heavier) main group elements and (ii) kinetic stabilization by sterically demanding substituents. 9 In particular, research in the field of cyclic biradicals that can formally be derived from cyclobutanediyl 11,12 (Chart 1) has produced a variety of derivatives that are stable for long periods of time under inert conditions [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] or even when exposed to air. 31 These formal hetero-cyclobutanediyls are known to readily activate small molecules in formal 1,1-or 1,3-addition reactions.…”

“…For comparison, the mechanisms of the literature-known cycloadditions of H 2 , alkenes, and alkynes were also studied, indicating a similar reaction profile for all unsaturated reactants.Chart 1 Transient cyclobutanediyl (A) and examples of symmetrical singlet hetero-cyclobutanediyls (B-G, R = sterically demanding substituents). [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]…”

“…Chart 1 Transient cyclobutanediyl (A) and examples of symmetrical singlet hetero-cyclobutanediyls (B-G, R = sterically demanding substituents). [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]…”