Experimental and Computational Insights into the Stabilization of Low-Valent Main Group Elements Using Crown Ethers and Related Ligands

Abstract

A series of tin(II) triflate and chloride salts in which the cations are complexed by either cyclic or acyclic polyether ligands and which have well-characterized single-crystal X-ray structures are investigated using a variety of experimental and computational techniques. Mössbauer spectroscopy illustrates that the triflate salts tend to have valence electrons with higher s-character, and solid-state NMR spectroscopy reveals marked differences between superficially similar triflate and chloride salts. Cyclic voltammetry investigations of the triflate salts corroborate the results of the Mössbauer and NMR spectroscopy and reveal substantial steric and electronic effects for the different polyether ligands. MP2 and DFT calculations provide insight into the effects of ligands and substituents on the stability and reactivity of the low-valent metal atom. Overall, the investigations reveal the existence of more substantial binding between tin and chlorine in comparison to the triflate substituent and provide a rationale for the considerably increased reactivity of the chloride salts.

Non‐Innocent Ligand Effects on Low‐Oxidation‐State Indium Complexes

“…This potential is considerably smaller than the E pc1 of Mes DAB H and the result suggests that destabilization of the non-bonding electrons on In I by the donor is important in this system. [49] Such destabilization is apparently sufficient to drive the first reduction of the Mes DAB H ligand but not that of the methyl derivative. Notably, after addition of a stoichiometric amount of InOTf to the electrochemical cell, the first reduction wave for Mes DAB H rapidly diminishes in intensity but that of the second reduction wave remains un-changed, suggesting that 2 has a very similar reduction potential to [ Mes DAB H ]C À .…”

“…[74] More strongly interacting anions and donors have been demonstrated to destabilize the lone pair of electrons on low-valent main-group metals and to render them more reactive. [49] In this vein, it is perhaps not surprising that the pentamethylcyclopentadienyl substituents in Cp*E actually promote transfer of two electrons from the metal to DAB ligands. [15][16] Conversely, univalent triel salts with anions that are non-interacting appear to be even more amenable to the formation of stable donor-acceptor adducts without decomposition.…”

Synthesis and structural characterization of new polyether complexes of germanium(II) and tin(II)

“…An overwhelming majority of these cationic crown or glyme complexes are paired with triflate counter anions or anions derived from chloride, with the heavier halides being present in only a handful examples. 7,11 As a part of our group's long-standing interest in the synthesis and reactivity of polyether complexes of group 13 and 14 elements, 12,13 we sought to fill this gap by examining in detail the reactions between germanium(II) and tin(II) bromide with various cyclic and acyclic polyethers.…”

“…As with the previously described germanium examples, we sought to also examine the ligand redistribution of SnBr 2 using glymes. Though our group had reported tetraglyme and triglyme complexes of tin(II) triflates, 13 there have only been two other structurally authenticated example of such complexes since then, and recently such complexes have received attention as metal-containing ionic liquid precursors for high-speed metal electrodeposition. 24,25 [SnBr] + fragments of 3.2552(7) Å.…”

Water and Ammonia Complexes of Germanium(II) Dications

“…The uncrowned system favors the Ge II over Ge IV to a greater extent and illustrates the effect of crown ether ligation. [44,45] Finally, the relatively small energy difference between 2' and 6' suggests that variants of the ligated Ge IV tautomer might be accessible experimentally.…”