OXIDATION OF AN O-AMINOPHENOL-DERIVED SCHIFF-BASE COMPONENT OF A BINUCLEATING LIGAND TO A BENZOXAZOLE AND THE CRYSTAL-STRUCTURES OF A MONONUCLEAR PALLADIUM DERIVATIVE AND A TETRANUCLEAR PD2AG2 DERIVATIVE WITH AN UNUSUALLY SHORT AG-AG DISTANCE

A convenient source of the di-Schiff-base binucleating ligand, L3-, derived formally from the condensation of 2 equiv of 2-amino-4,6-di-tert-butylphenol with 1 equiv of 2-mercapto-5-methylisophthalaldehyde is provided by the S-protected ligand precursor, III, which with Pd(CH3CO2)2 gave LPd2(CH3CO2) in a one-pot reaction (L3- = C37H47N2O2S3-). Reaction of triphenylphosphine with LPd2(CH3CO2) in refluxing toluene led to the oxidation of one Schiff base side arm to a benzoxazole, as in complex IV, represented as L(b)Pd(PPh3) (in which L(b)2- = C37H46N2O2S2-), whose structure was determined by single-crystal X-ray diffraction. The crystals of C55H61N2O2PSPd were rhombohedral, space group R3BAR, with a = 27.540 (4) angstrom, alpha = 117.38-degrees, and Z = 6. The structure was refined to R = 0.059 and R(w) = 0.071 by using 6496 (I greater-than-or-equal-to 3-sigma(I)) unique reflections. The X-ray study revealed the previously unsuspected benzoxazole residue. L(b)Pd(PPh3) was made deliberately by oxidation with lead tetraacetate of (LH)-Pd(PPh3) (V) (LH2- = C37H48N2O2S2-), which was obtained by reaction of the ligand precursor, III, with 1 equiv each of Pd(CH3CO2)2 and triphenylphosphine. Reaction of AgClO4 either with (LH)Pd(PPh3) (Ag in excess) or with L(b)Pd(PPh3) gave [L(b)PdAg(PPh3)]2(ClO4)2, characterized by single-crystal X-ray diffraction: C110H122Ag2Cl2N4O12P2Pd2S2. approximately 12.5H2O, monoclinic, space group P2(1)/n, a = 13.416 (3) angstrom, b = 25.397 (5) angstrom, c = 16.940 (3) angstrom, beta = 96.82 (2)-degrees, Z = 2. The structure was refined to R = 0.067 and R(w) = 0.065 by using 2584 (I greater-than-or-equal-to 2-sigma(I)) unique reflections. The structure contains centrosymmetric dimeric cations in which monomeric [LPdAg(PPh3)]+ units are linked together by bonds from the sulfur of one to the silver of the other. The Ag-S-Ag angle of 61.9 (1)-degrees is unusually acute and the Ag-Ag distance of 2.779 (3) angstrom is unusually short.