Mercury- and Cadmium-Assisted [2 + 2] Cyclodimerization of tert-Butylselenium Diimide

Abstract

The complexes [MCl2{N,N'-(t)BuNSe(μ-N(t)Bu)2SeN(t)Bu}] [M = Cd (1), Hg (2)] were obtained in high yields by the reaction of tert-butylselenium diimide Se(IV)(N(t)Bu)2 with CdCl2 or HgCl2 in tetrahydrofuran. Recrystallization of 1 and 2 from acetonitrile (MeCN) afforded yellow crystals of 1·MeCN and 2·MeCN, respectively. Isomorphic 1·MeCN and 2·MeCN contain an unprecedented dimeric selenium diimide ligand, which is N,N'-chelated to the metal through exocyclic imido groups. In addition to the complexes 1 and 2, the (77)Se NMR spectra of acetonitrile solutions of 1·MeCN and 2·MeCN indicated the presence of the dimeric (t)BuNSe(μ-N(t)Bu)2SeN(t)Bu, monomeric Se(IV)(N(t)Bu)2, and cyclic selenium imides. Density functional theory calculations at the PBE0/def2-TZVPP level of theory were used to assign the (77)Se resonances of the dimer. A comparison of Gibbs energies of formation of some metal dichloride complexes [MCl2{N,N'-Se(IV)(N(t)Bu)2}] and [MCl2{N,N'-(t)BuNSe(μ-N(t)Bu)2SeN(t)Bu}] (M = Zn, Cd, Hg) indicated that the formation of complexes containing a dimeric selenium diimide ligand is favored over those containing a monomeric ligand for the group 12 metals. In the case of the group 10 metal halogenides (M = Ni, Pd, Pt), the Gibbs energies of the complexes with monomeric Se(IV)(N(t)Bu)2 ligands are close to those containing dimeric (t)BuNSe(μ-N(t)Bu)2SeN(t)Bu ligands. A plausible reaction pathway with a low activation energy involves the initial formation of [MCl2{N,N'-Se(IV)(N(t)Bu)2}] (M = Zn, Cd, Hg), which then reacts with another molecule of Se(N(t)Bu)2, leading to the final [MCl2{N,N'-(t)BuNSe(μ-N(t)Bu)2SeN(t)Bu}] complex. Without the presence of group 12 metal halogenides, the [2 + 2] cyclodimerization of Se(IV)(N(t)Bu)2 is virtually thermoneutral, but the activation energy is relatively high, which accounts for the kinetic stability of (t)BuNSe(μ-N(t)Bu)2SeN(t)Bu in solution. A minor byproduct, [Cd7Cl14{N,N'-Se(II)(NH(t)Bu)2}6]·4CH2Cl2, was identified by X-ray crystallography as a heptanuclear cluster with selenium(II) diamide ligands N,N'-chelated to the cadmium centers.

Selenium– and tellurium–nitrogen reagents

“…The calculated dimerization energy for the [2 + 2] cycloaddition of two E(NR)2 (E = Se, Te; R = t Bu, SiMe3) molecules is strongly exothermic for tellurium(IV) diimides, but approximately thermoneutral for selenium(IV) diimides, consistent with the experimental observations [75,76]. However, the dimerization of selenium(IV) diimides is promoted by group 12 metal dihalides MCl2 (M = Cd, Hg) to give N,N'-chelated complexes of t BuNSe(µ-N t Bu)2SeN t Bu [77], which are structurally analogous to the HgCl2 complex of the tellurium(IV) diimide dimer t BuNTe(µ-N t Bu)2TeN t Bu [78].…”

Insights into the formation of inorganic heterocycles via cyclocondensation of primary amines with group 15 and 16 halides

“…43 While the [2 + 2] cyclodimerisation has been deduced to be slightly endergonic in solution, a combination of experimental and computational studies have demonstrated that the cyclodimerisation of the tert-butyl derivative t BuN=Se=N t Bu is facilitated by group 12 metal dihalides MCl2 (M = Cd, Hg). 44 The cyclic, dimeric ligand in the MCl2 complexes formed in this way is structurally analogous to the known structure of the corresponding tellurium(IV) imide, t BuNTe(μ-N t Bu)TeN t Bu, which is dimeric in the solid state, as the free ligand. 45 t BuNSe(μ-N t Bu)SeN t Bu once formed is kinetically inert in solution, as can be deduced from the reaction energetics shown in Fig.…”

Theoretical Investigation of the Newly Designed Benzimidazole Based Metal Mediated DNA Base Couples with DFT Method

“…The methods used in the calculation of the organometallic compounds with mercury in the literature have been chosen [19] [20] [21]. It is especially known, M06 is one of the best functional for the study of organometallic and inorganomatellic thermochemistry and noncovalent interactions.…”