Isolation of Carbene-Stabilized Arsenic Monophosphide [AsP] and its Radical Cation [AsP]+. and Dication [AsP]2

Abstract

Arsenic monophosphide (AsP) species supported by two different N-heterocyclic carbenes were prepared by reaction of (IDipp)PSiMe₃ (1) (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with (IMes)AsCl₃ (2) (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) to afford the dichloride [(IMes)As(Cl)P(IDipp)]Cl (3), which upon reduction with KC₈ furnished heteroleptic [(IMes)AsP(IDipp)] (4). The corresponding mono- and dications [(IMes)AsP(IDipp)][PF₆ ], [5]PF₆ , and [(IMes)AsP(IDipp)][GaCl₄ ]_2, [6][GaCl₄ ]₂ , respectively, were prepared by one-electron oxidation of 4 with ferrocenium hexafluorophosphate, [Fc]PF_6, or by chloride abstraction from 3 with two equivalents of GaCl₃ , respectively. Compounds 4-6 represent rare examples of heterodiatiomic interpnictogen compounds, and X-ray crystal structure determinations together with density functional theory (DFT) calculations reveal a consecutive shortening of the As-P bond lengths and increasing bond order, in agreement with the presence of an arsenic-phosphorus single bond in 4 and a double bond in 6²⁺ . The EPR signal of the cationic radical [5]^+. indicates a symmetric spin distribution on the AsP moiety through strong hyperfine coupling with the ⁷⁵ As and ³¹ P nuclei.

Keywords: N-heterocyclic carbenes; arsenic; arsenic monophosphide; main group elements; phosphorus.