SULFONYL-CONTAINING 8-MEMBERED RINGS VARYING IN RING CONFORMATION IN OXYPHOSPHORANES - HEXACOORDINATION VS PENTACOORDINATION

The new cyclic phosphine O2S[(t-Bu)MeC6H2O](2)PPh (1) was used to prep are the new cyclic tetraoxyphosphoranes O2S[(t-BU)MeC6H2O](2)PPh(O2C6C l4) (2) and O2S[(t-BU)MeC6H2O](2)PPh(O2C6H4) (3) by oxidative addition reactions. In similar reactions, the new cyclic pentaoxyphosphoranes O2S[(t-Bu)MeC6H2O](2)P(OCH2CCl3)(3) (4), O2S[Me2C6H2O](2)P(OPh)(3) (5) , and O2S[(t-BU)MeC6H2O](2)P(OC6F5)(3) (6) were formed from acyclic ph osphites and the appropriate diol. Yields ranged from 51% to 66%, X-ra y studies revealed hexacoorinated representations for 2 and 6 while 3- 5 are pentacoordinate in trigonal bipyramidal geometries, For 3 and 4, the eight-membered rings are positioned diequatorially in anti chair conformations, whereas for 5, this ring occupies axial-equatorial site s in a syn twist-boat form. Tetraoxyphosphorane 3 is unique in locatin g the least electronegative ligand, the phenyl group, in an axial posi tion. Oxygen donor action from the sulfone Oz group led to a displacem ent from a square pyramid to an octahedron to the extent of 82.2% for the highly fluorinated member 6 in comparison with 27.9% for the tetra chlorocatecholate derivative 2. These two pentaoxyphosphoranes provide the longest and shortest P-O distance thus far from a sulfone donor g roup, 2.646 (5) Angstrom for 2 and 1.936 (7) Angstrom for 6. In compar ison with oxyphosphoranes having bridging sulfur atoms in the eight-me mbered ring, it is apparent that sulfur atom coordination is greater t han oxygen atom coordination from the sulfone group as measured by the tendencies toward hexacoordination. P-31 and H-1 NMR data indicate th e presence of two isomeric forms for each of the phosphoranes 2-4. Str uctural comparisons are made with related cyclic phosphoranes containi ng sulfur atoms and sulfone groups relative to steric and electronic f actors that influence the formation of hexacoordination.