CHEMISTRY OF DIAMINO-LIGATED METHYLPALLADIUM(II) ALKOXIDE COMPLEXES - SYNTHESES, X-RAY CRYSTAL-STRUCTURES, AND HYDROGEN-BOND FORMATION

The reaction of diamino-ligated dimethylpalladium(II) complexes [Pd(Me)(2)(N similar to N)] (N similar to N = tmeda, bpy) with an equimolar amount of 1,1,1,3,3,3-hexafluoro-2-propanol or (substituted) phenols affords the new complexes [Pd(Me)(OR)(N similar to N)](N similar to N = tmeda, R = CH(CF3)(2) (1), C6H5 (3), C6H4-4-NO2 (4) C6H4-2-OH (11)); N similar to N = bpy, R = CH(CF3)(2) (2)). These methylpalladium(II) alkoxides and aryloxides are isolated in high yields as yellow-orange solids and are remarkably thermally stable. Mono- or bidentate ligands can substitute the tmeda ligand in 1 to afford a variety of methylpalladium alkoxide complexes [Pd(Me)(OCH(CF3)(2))L(2)] (L(2) = bpy (2), Ph(2)PCH(2)CH(2)-NMe(2) (12), dppe (13), 2PMe(3) (14)). Crystals of 1, 3, and 4 have been subjected to X-ray diffraction studies. Crystals of 1 are monoclinic, space group P2(1)/c, with unit-cell dimensions a = 8.2054(5) Angstrom, b = 17.2310(9) Angstrom, c = 11.1191-(12) Angstrom, beta = 105.701(7)degrees, and Z = 4. Crystals of 3 are orthorhombic, space group Pbca, with unit-cell dimensions a = 10.572(2) Angstrom, b = 16.446(2) Angstrom, 17.029(3) Angstrom, and Z = 8. Crystals of 4 are orthorhombic, space group Pbca, with unit-cell dimensions a = 11.918(5) Angstrom, b = 12.089(3) Angstrom, c = 22.684(7) Angstrom, and Z = 8. The molecular structures of these complexes show them to be square-planar species, and in 1 the C-beta-H unit of the fluorinated alkoxide is directed toward the palladium center (H ... Pd = 2.89(3) Angstrom), in what can be interpreted as the incipient stage of a beta-hydrogen elimination. The palladium alkoxide or aryloxide complexes 1-4 when treated with 1 equiv of the corresponding alcohol or (substituted) phenol afford O-H ... O hydrogen-bonded adducts [Pd(Me)(OR)(N similar to N].-HOR = (N similar to N=tmeda, R = CH(CF3)(2) (5), C6H5 (7), C6H4-4-NO2 (8); N similar to N = bpy, R = CH(CF3)(2) (6), C6H5 (9)) The X-ray molecular structures of [Pd(Me)(OC6H5)(tmeda)]. HOC6H5 (7) and [Pd(Me)(OC6H4-4-NO2)(tmeda)].- HOC(6)H(4)4-4-NO2 (8) reveal that the aromatic alcohol is associated with the oxygen atom of the aryloxide through O-H ... O hydrogen bonding. Crystals of 7 are monoclinic, space group P2(1)/c, with unit-cell dimensions a = 15.5556-(13) Angstrom, b = 11.0416(10) Angstrom, c - 12.0211(11) Angstrom, beta = 91.343(8)degrees, and Z = 4. Crystals of 8 are monoclinic, space group P2(1)/c, with unit-cell dimensions a = 8.7029(5) Angstrom, b = 15.6384(11) Angstrom, c = 16.5188(9) Angstrom, beta = 90.096(5)degrees, and Z = 4. Comparison of the solid state structures of [Pd(Me)(OC6H4-4-NO2) (tmeda)] (4) and its HOC6H4-4-NO2 adduct (8) reveal that an electron-withdrawing substituent on the aryloxide ring leads to geometric changes in the Pd-O-C unit. Proton NMR for 5-9 and the X-ray structural data of 7 and 8 indicate that the O-H ... O hydrogen bonding in these adducts is strong both in solution and in the solid state. The thermodynamic paraneterrsfor the alkoxide - alcohol exchange in the adduct [Pd(Me)(OCH(CF3)(2))(tmeda)]. HOCH(CF3)(2) (5) have been determined with NMR spin saturation transfer techniques and provide evidence for a five-coordinate species being the key intermediate in this intramolecular exchange reaction. Furthermore, the thermodynamic parameters for adduct formation, obtained by the Scatchard method, quantify the O-H ... O hydrogen bond as being strong.