ic500065s_si_002.cif (203.4 kB)
K–H3C and K–Sn Interactions in Potassium Trimethylstannyl Complexes: A Structural, Mechanochemical, and NMR Study
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posted on 2014-05-05, 00:00 authored by Christian Kleeberg, Jörg Grunenberg, Xiulan XieA series of trimethylstannyl potassium
complexes [K(L)SnMe3] with different auxiliary ligands
L (L = 18-C-6, (TMEDA)2 (TMEDA = tetramethylethylenediamine),
and (12-C-4)2) were synthesized by alkoxide-induced B–Sn
bond cleavage. X-ray structure determinations were performed for all
these complexes, and the structural chemistry was studied in detail.
For L = 18-C-6 and (TMEDA)2 the solid state structures
comprise polymeric [K(L)SnMe3]n chains containing bidentate trimethylstannyl anions bridging two
[K(L)]+ ions, featuring unsymmetrical coordination of the
[K(L)]+ ion by K–Sn and K–H3C
interactions as a central structural motif. In contrast, for L = (12-C-4)2, separated [K(12-C-4)2]+ and [SnMe3]− ions are observed. Unexpectedly, in the
presence of tetrahydrofuran (THF), [K(18-C-6)SnMe3]n forms upon crystallization a new species
consisting of separated [K(18-C-6)(THF)2]+ and
[(Me2SnCH3)K(18-C-6)SnMe3]− ions. In this unsymmetrical anion two trimethylstannyl anions coordinate
a single [K(18-C-6)]+ ion; one trimethylstannyl anion coordinates
via a K–Sn interaction, and the second coordinates via a K–H3C interaction. Simulations of the mechanochemical properties
(compliance constants) applying approximated density functional theory
revealed that both interactions are very soft and are of comparable
strength. Moreover, according to our gas phase simulations the unsymmetrically
coordinated [(Me2SnCH3)K(18-C-6)SnMe3]− is indeed thermodynamically favored over both
possible symmetrical isomers with either K–Sn or K–H3C coordination. Furthermore, the existence of multiple species
due to the two coordination modes and aggregates of [K(18-C-6)SnMe3] in solution is suggested by NMR spectroscopic studies using 1H, NOESY/ROESY, and 1H pulsed field gradient diffusion
experiments.
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NMR spectroscopic studiesTHFPotassium Trimethylstannyl Complexestrimethylstannyl anion coordinatescoordinationNMR StudyA seriestrimethylstannyl potassium complexesinteractionfield gradient diffusion experimentsunsymmetricalbidentate trimethylstannyl anionsNOESY2SnCH1 HTMEDAspeciesgas phase simulations
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