London Dispersion Interactions in Pnictogen Cations [ECl₂]⁺ and [E=E]²⁺ (E=P, As, Sb) Supported by Anionic N‐Heterocyclic Carbenes

Abstract

Several pnictogen dihalide complexes of the type (WCA‐IDipp)EX2 (E=P, As, Sb; X=Cl, Br) that bear an anionic N‐heterocyclic carbene ligand with a weakly coordinating borate moiety (WCA‐IDipp, WCA=B(C6F5)3, IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) were prepared by salt metathesis reactions between the respective pnictogen trihalides EX3 and the lithium salt (WCA‐IDipp)Li⋅toluene. Two‐electron reduction of the dihalides (WCA‐IDipp)EX2 with 1,3‐bis(trimethylsilyl)‐1,4‐dihydropyrazine or elemental magnesium afforded the dipnictenes (WCA‐IDipp)2E2, which display typical element‐element double bonds as observed in diaryldiphosphenes, ‐arsenes and ‐stibenes. To provide an insight into the factors contributing to the structural stability of the pnictogen dihalide and dipnictene compounds, quantum chemical calculations were performed at the domain‐based local pair natural orbital coupled‐cluster (DLPNO‐CCSD(T)) level. A local energy decomposition (LED) analysis of the interaction between the carbene and the pnictogen dihalide or dipnictene moiety demonstrates that London dispersion is an essential factor for the stabilization of these compounds.

Finding chemical concepts in the Hilbert space: Coupled cluster analyses of noncovalent interactions

“…They observed that, if functionals like BLYP or B3LYP are used, the magnitude of the D3 correction is close to the LED estimate of the dispersion energy in a large variety of cases. These findings are consistent with previous results from our group . However, the agreement between D3 and LED dispersion is of course not universally valid and there are notable exceptions …”

“…For instance, this partitioning can be used to discuss intramolecular interactions or, more generally, any interaction for which single point energies on the isolated fragments are not feasible. Above all, the LED scheme has found widespread applications in the analysis of strong and weak intermolecular interactions within a supermolecular approach …”

Formation of an imidazoliumyl-substituted [(LC)4P4]4+tetracation and transition metal mediated fragmentation and insertion reaction (LC= NHC)

“…S3†). Notably, Tamm and co-workers recently reported on the isolation of a diphosphene derivative obtained by the reduction of related dichlorophosphane with compound 6 21. The 31 P NMR spectrum of the reaction mixture shows only one major prominent intermediate with a singlet resonance at δ (P) = –29.1 ppm, which is in the range for diphosphanes 22.…”

The key role of R–NHC coupling (R = C, H, heteroatom) and M–NHC bond cleavage in the evolution of M/NHC complexes and formation of catalytically active species

“…Facile reactions of PCl 3 , PBr 3 , SbCl 3 and AsCl 3 with Li/NHC adducts 44 afford the corresponding P–NHC, Sb–NHC and As–NHC products 45 ( Scheme 9 ). 110 …”