Inverse Aggregation Behavior of Alkali-Metal Triazenides

Abstract

Higher aggregated alkali-metal compounds are usually obtained with increasing radius of the metal. Alkali-metal salts derived from the sterically crowded triazenido ligand Tph2N3H [Tph = C6H3-2,6-(C6H2-2,4,6-iPr3)2] do not obey this principle. Interestingly, these compounds show inverse aggregation behavior in the solid state: the potassium and cesium salts crystallize as discrete monomers in which the cations interact with flanking arene rings of the diaryltriazenido ligands, whereas the lithium derivative is dimeric with a more conventional heteroatom-bridged structure.

Potassium Salts of Asymmetrically Substituted Amidinates and a Triazenide

“…[11] 19 C-tBu Dipp Dipp Anti [18] 20 C-tBu Dipp CH 2 -Fu Syn-Z [20] 21 C-tBu Dipp CH 2 -Py Syn-Z [20] 22 C-Ad Dipp C 6 H 2 -(CHPh 2 ) 2 iPr Anti [21] 23 C-NiPr 2 Dipp Dipp Anti [22] 24 C-N=CtBu 2 C 6 H 2 -(CHPh 2 ) 2 tBu C 6 H 2 -(CHPh 2 ) 2 tBu Syn-E [23] 25 C-CH 2 -NHC Dipp Dipp Anti [24] 26 N pTol pTol Syn-E [6] 27 N C 6 H 4 -4-NO 2 C 6 H 4 -4-NO 2 Syn-E [8] 28 N Mes Mes Syn-E [10] 29 N C 6 H 4 -Mes C 6 H 3 -Mes 2 Syn-E [9] 30 N C 6 H 4 -Trip C 6 H 4 -Trip Syn-E [7] 31 N C 6 H 4 -Trip C 6 H 3 -Mes 2 Syn-E [9] 32 N C 6 H 3 (C 6 H 3 Me 2 ) 2 C 6 H 3 (C 6 H 3 Me 2 ) 2 Syn-E [9] The influence of the middle moiety E can be evaluated considering similar amidinate (entries 12 and 13) and triazenide molecules (entry 32) which crystallize with (syn-E)-isomeric ligands.…”

“…[6][7][8][9][10] Amidinate ions can adopt four isomeric forms in their potassium salts as depicted in Scheme 1. [6][7][8][9][10] Amidinate ions can adopt four isomeric forms in their potassium salts as depicted in Scheme 1.…”

Hetero- and Homoleptic Magnesium Triazenides

“…For 4b, an interesting feature in the 1 H NMR spectrum at ambient temperature is a low-field shifted resonance at 7.64 ppm that moves to higher field at elevated temperatures. It has been noted before [7] that the presence of low-field shifted signals in biphenyl-substituted triazenes indicates short intermolecular C-H···N contacts at the NNN backbone of the ligands and therefore is a very sensitive probe for conformational preferences in solution. In the case of 4b, a C-H···N interaction of 2.48 Å between the central nitrogen atom N2 and a hydrogen atom of the ortho-C 6 H 3 Me 2 ring in the solid-state structure correlates with the observed low-field resonance in solution.…”

“…Much less attention has been given to the closely-related triazenides [4]. During the last decade, we reported the preparation of derivatives of diaryl-substituted, sterically-crowded triazenido ligands that are bulky enough to prevent undesirable ligand redistribution reactions [5][6][7][8][9][10][11][12]. These ligands allowed structurally characterizing the first examples of aryl compounds of the heavier alkaline earth metals Ca, Sr and Ba [5] and unsolvated pentafluorophenyl organyls of the divalent lanthanides Yb and Eu [6].…”

“…These ligands allowed structurally characterizing the first examples of aryl compounds of the heavier alkaline earth metals Ca, Sr and Ba [5] and unsolvated pentafluorophenyl organyls of the divalent lanthanides Yb and Eu [6]. The different degree of metal···π-arene interactions to pending aromatic substituents accounts for the unusual "inverse" aggregation behavior of alkali metal triazenides in their solid-state structures [7]. A series of homologous potassium and thallium triazenides crystallizes in isomorphous cells and represents the first examples of isostructural molecular species reported for these elements [8].…”