A series of spirocyclic monoorganosilicon compounds of the form RSi(OPO)2Cl [R = phenyl (1); p-tolyl (2); benzyl (3); Me (4); tBu (5); thexyl (6)] (OPO = 1-oxo-2-pyridinone) was synthesized and characterized by 1H , 13C, and 29Si NMR spectroscopy, X-ray crystallography, and elemental analysis. In the solid state, complexes 1, 2, and 3 are neutral and possess cis-OPO ligands in an octahedral arrangement, and complexes 4, 5, and 6 are cationic and possess effectively trans-OPO ligands in nearly ideal square pyramidal geometries along the Berry-pseudorotation coordinate. In 4-6, chloride dissociation is attributed to the additive effect of multiple intermolecular C—H∙∙∙Cl interactions in their crystals. In DMSO-d6 solution, compounds 1-6 form cationic hexacoordinate DMSO adducts with trans-OPO ligands, all of which undergo dynamic isomerization with energy barriers of ~18-19 kcal/mol. Compounds with better leaving groups, (p-tolyl)Si(OPO)2X [X = I (7); X = triflate (8)], exhibit identical solution NMR spectra as 2, supporting anion dissociation in each. The fluoride derivatives RSi(OPO)2F [R = benzyl (9); Me (10)] exhibit hexacoordinate geometries with cis-OPO ligands in the solid state and exhibit dynamic isomerization in solution. Overall, these studies indicate, in both the solid and solution states, that the trans-OPO ligand arrangement is favored when anions are dissociated and a cis-OPO ligand arrangement when anions are coordinated.
Koch, James; Brennessel, William W.; and Kraft, Bradley M. (2017). "Neutral and Cationic Bis-Chelate Monoorganosilicon(IV) Complexes of 1-Hydroxy-2-pyridinone." Organometallics 36.3, 594-604.
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