Hexacoordination via Sulfur Donor Action in Nitrogen and Chlorine Bonded Bicyclic Tetraoxyphosphoranes¹

Abstract

Oxidative addition reactions of a quinone with the sulfur containing cyclic chlorophosphine S[(t-Bu)MeC6H2O]2PCl (1) yielded the new bicyclic tetraoxyphosphoranes, S[(t-Bu)MeC6H2O]2PCl(O2C6Cl4) (2) and S[(t-Bu)MeC6H2O]2PCl(O2C14H8) (5). Further new derivatives of this class were prepared by chlorine displacement reactions of 2 and 5 to give S[(t-Bu)MeC6H2O]2P(NHC6H4Me)(O2C6Cl4) (3), S[(t-Bu)MeC6H2O]2P(NMe2)(O2C6Cl4) (4), S[(t-Bu)MeC6H2O]2P(NHCH2C6H5)(O2C14H8) (6), and S[(t-Bu)MeC6H2O]2P(NMe2)(O2C14H8) (7). X-ray studies of 2−6 revealed hexacoordination due to donor action by sulfur which is present as part of an eight-membered ring system. The series 2−6 formed geometries that were displaced along a coordinate from a square pyramid to an octahedron, ranging from 24% to 71%. The respective P−S distance decreased along this series from 3.04 to 2.48 Å as the octahedral character increased. Increased 31P NMR shielding accompanied the chloro derivatives 2 and 5, while increased π P−N back-bonding resulted in the least shielded members 4, 6, and 7 containing the less electronegative nitrogen atom. These changes in 31P chemical shift correlate with the extent of octahedral character where the more shielded phosphorus atom has the greater octahedral character. The analysis allows a lower limit in the phosphorus atom electrophilicity to be established that will allow hexacoordination in this series of bicyclic tetraoxyphosphoranes provided by a variation in ligand properties.

Hexacoordinate Phosphorus via Donor Interaction. Implications Regarding Enzymatic Reaction Intermediates

“…The electronegativity effect is clearly evident on going from pentaoxyphosphoranes to tetraoxyphosphoranes, where ligands of lower electronegativity replace attached oxygen atoms. This is seen in the tetraoxyphosphorane 16, 35 which has an NMe 2 group in place of a pentafluorophenyl group in the pentaoxyphosphorane 17. 48 This results in over a 0.2 Å shortening in the P-S distance in 17 relative to 16.…”

Pentacoordinated Organo and Hydrido Cyclic Silanes via Sulfur Donor Action1

“…Previous studies have shown that phosphorus compounds undergo an increase in coordination geometry with sulfur, − oxygen, ,− and nitrogen donor atoms that are present as part of flexible ring systems. As a consequence of donor interaction, oxyphosphoranes traverse a coordinate from square pyramidal to octahedral, − , while phosphates, ,, phosphines, ,, and phosphites 2,13,14 are displaced toward trigonal bipyramidal (TBP).…”

New Trends in Hexacoordinated Phosphorus Chemistry

“…The stability of the resulting P(VI) is emphasized by displacement coordinate experiment as shown in Scheme 11 [59]. If the sulfur atom is oxidized to a sulfonyl moiety, then oxygen donation occurs to the phosphorus as observed in compounds 49a-49h (Fig.…”

“…Since 1996, Holmes and coworkers have investigated further the formation of hexacoordinated phosphorus derivatives by virtue of sulfur donation [59][60][61][62][63][64].…”