Hexacoordinate phosphorus .7. Synthesis and characterization of neutral phosphorus(V) compounds containing divalent tridentate diphenol imine, azo, and thio ligands

The reactions of bis(trimethylsilyl)ated forms of the Schiff base ligands N-(2-hydroxyphenyl)salicylideneamine {(HO)C6H4N(CH)C6H4(OH)}, N-(4-tert-butyl-2-hydroxyphenyl)salicylideneamine {(HO)((t)Bu)C6H3N(CH)C6H4(OH)}, N-(2-hydroxy-4-nitrophenyl)salicylideneamine {(HO)(O2N)C6H3N(CH)C6H4(OH)} and the structurally related ligand 2,2'-azophenol with halogeno- and (trifluoromethyl)halogenophosphoranes yield a series of neutral hexacoordinate phosphorus(V) compounds by means of trimethylsilyl halide elimination. In all of these cases the ligands chelate in a meridional conformation in which bicyclic five- and six-membered chelate rings are formed through structures containing two phenolic P-O bonds and one N-P bond. The hexacoordinate nature of these compounds is evidenced by their high-field P-31 NMR chemical shifts and their characteristic J(PF) coupling patterns and is further substantiated by the crystal structures of {O((t)Bu)C6H3N(CH)C(6)H4(0)O}PCl3 and {OC6H4N=NC6H4O}PF3. Crystal data for {O((t)Bu)C6H3N(CH)C6H4O}PCl3: triclinic, space group <P(1)over bar> (No. 2), a = 11.167(1) Angstrom, b = 15.684(1) Angstrom, c = 17.047(2) Angstrom, V = 2840(1) Angstrom(3), Z = 2. Final R and R(w) values were 0.051 and 0.079, respectively. Crystal data for {OC6H4N=NC6H4O}PF3: monoclinic, space group P2(1)/c (No. 14), a 6.9393(8) Angstrom, b = 12.450(2) Angstrom, c = 13.907(2) Angstrom, V = 1190.7(6) Angstrom 3, Z = 4. Final R and R(w) values were 0.045 and 0.056, respectively. The molecular structures of {O((t)Bu)C6H3N(CH)C6H4O}PCl3 and {OC6H4N=NC6H4O}PF3 show that in both cases the Schiff base ligand chelates occupy the meridional plane about the six-coordinate phosphorus atom. In the case of {OC6H4N=NC6H4O}PF3 the equivalent nitrogen atoms in the chelate rings are disordered to form half-occupancy pairs. The silylated form of the related thiobis(phenol), 2,2'-thiobis(4,6-tert-butylphenol), reacted similarly with pentavalent halides to form the six-coordinate complex [{2-O-3,5-((t)Bu)(2)C6H2}S-2]PCl3 which was also verified by a crystal structure. Crystal data for [{2-O-3,5-((t)Bu)(2)C6H2}S-2]PCl3 : monoclinic P2(1)/n, a = 13.989(2), b = 13.594(2), c = 16.483(2) Angstrom, beta = 97.98(2)degrees, V = 3104(2) Angstrom(3), Z = 4; final R and R(w) values were 0.039 and 0.052, respectively. In contrast to the above six coordinate complexes, this compound possesses a facial structure in which two phenoxy substituents form planar chelates centered on the bridging sulfur and intersecting at the P-S axis. The P-S bond length, 2.331(1) Angstrom, is slightly shorter than has been previously observed in the example wherein the ligand possesses two tert-butyl groups and the phosphorus carries three OCH2CF3 substituents indicating stronger interaction between P and S in the present case.