SULFURANES WITH OXIMATE AXIAL LIGANDS

New sulfuranes having one or two axial oximate (R(2)C=NO) ligands were synthesized. An improved sulfurane-forming step, involving a rapidly stirred suspension of NaHCO3, is described. The failure of sulfide oximes in which sulfur bears one or two tertiary carbons to form sulfuranes is explained by a C-S bond cleavage leading to tertiary carbocations. This represents a hitherto unanticipated limitation to the standard method of sulfurane synthesis. The X-ray crystal structure of one of the new sulfuranes, namely 2,2'-spirobi(4-phenyl-3H-1,2,5-oxathiazo is reported (R = 0.0368). An unusual feature was the quite compressed equatorial(C-S-C) angle, 102.6(1)degrees. The S-O bond length, 1.846(2) Angstrom, was similar to S-O bond lengths of sulfuranes having two axial carboxylate ligands. Since the oximate ligand has not been used previously in a 10-S-4 species, an assessment of its apicophilicity relative to other more common axial ligands was made by considering X-ray structural data, IR data, and ab initio calculations. These suggest that the R(2)C=NO ligand is as apicophilic as the hexafluorocumyloxy (ArC(CF3)(2)O) ligand.