Neutral and Cationic Bis-Chelate Monoorganosilicon(IV) Complexes of 1‑Hydroxy-2-pyridinone

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 1–3 are neutral and possess cis-OPO ligands in an octahedral arrangement and complexes 4–6 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 solution NMR spectra identical with those
of 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.