Molecular Structures of Three-, Four-, and Five-Coordinate Phosphorus Compounds Containing Salicylate Ligands(1)

The new cyclic compound 2,2'-sulfurylbis(4-methyl-6-tert-butylphenyl) methyl 2-benzoate phosphite, O(2)S[(t-Bu)MeC(6)H(4)O](2)(OC(6)H(4)CO(2)Me)P (3), containing a salicylate ligand was synthesized from 2,2'-sulfurylbis(4-methyl-6-tert-butylphenyl) chlorophosphite and methyl salicylate in the presence of triethylamine in ether solution. X-ray analyses of bis(methyl salicylate-O)phenylphosphine, (OC(6)H(4)CO(2)Me)(2)PPh (1), and bis(methylsalicylato-O)phenyl(tetrachlorophenylene-1,2-dioxy)phosphorane, (O(2)C(6)Cl(4))(OC(6)H(4)CO(2)Me)(2)PPh (2), as well as that for 3 were obtained. The phosphane 1 has a pseudo trigonal bipyramidal (TBP) structure due to coordination of a carbonyl oxygen atom at an axial site. The cyclic phosphorane 2 and the phosphite 3 lack any coordination from salicylate ligands. This results in a TBP geometry and a pyramidal geometry respectively for 2 and 3. Comparisons with X-ray structures for carboxylate-containing phosphorus compounds exhibiting oxygen coordination show the formation of four- and five-membered cyclic systems. Thus, 1 appears to be the first example of formation of a six-membered ring via carbonyl oxygen coordination. Reference is made to the tyrosyl-tRNA synthetase system where it is proposed that carbonyl oxygen atom coordination is a likely occurrence in the transition state on the basis of the analysis presented in this work.