STRUCTURAL, FAR-IR, AND P-31 NMR-STUDIES OF 2-COORDINATE COMPLEXES OF TRIS(2,4,6-TRIMETHOXYPHENYL)PHOSPHINE WITH SILVER(I) HALIDES

Reaction of the highly basic, sterically hindered tertiary phosphine ligand tris(2,4,6-trimethoxyphenyl)phosphine [=TMPP] with silver(I) halides, AgX (X = Cl, Br), yields the 1:1 adducts [(TMPP)AgX]. The structures of these complexes have been determined by X-ray crystallography. The two compounds are isomorphous, crystallizing in the tetragonal space group P4(1). For the chloride (C27H33AgClO9P), a = 15.310 (1) angstrom, c = 12.366 (1) angstrom, Z = 4, and R = 0.03 I for 5771 "observed" (I/sigma(I) greater-than-or-equal-to 3.0) reflections, while for the bromide (C27H33AgBrO9P), a = 15.319 (4) angstrom, c = 12.441 (6) angstrom, Z = 4, and R = 0.029 for 2114 "observed" reflections. Both complexes contain mononuclear [(TMPP)AgX] molecules with approximately linear two-coordination about the silver atom. For the chloro complex, Ag-P is 2.379 (1) angstrom and Ag-Cl is 2.342 (1) angstrom, while for the bromo complex, Ag-P is 2.374 (2) angstrom and Ag-Br is 2.448 (1) angstrom. In both complexes, the silver atom is slightly displaced toward one of the o-methoxy oxygens with Ag---O = 2.818 (3) angstrom (Cl) and 2.826 (5) angstrom (Br), giving rise to slightly nonlinear P-Ag-X angles of 175.0 (1)-degrees (Cl) and 174.40 (6)-degrees (Br). This represents the first complete structural characterization of compounds with a two-coordinate P-Ag-X grouping. The far-infrared spectra of these complexes show strong-nu(Ag-Cl) and nu(Ag-Br) bands at 282 and 215 cm-1, respectively. Reaction of TMPP with AgI in a 1:1 mole ratio yields a solid which shows no band that is assignable to nu(Ag-I). The P-31 NMR spectra of these complexes in chloroform solution show a superposition of two doublets due to coupling of the phosphorus nucleus with the two magnetic isotopes of silver (Ag-107, Ag-109). The P-31 NMR parameters are delta = -67.2, -66.4, and -64.6 ppm and 1J(Ag-107P-31) = 821, 796, and 745 Hz for X = Cl, Br, and 1, respectively. Reaction of [(TMPP)AgX] with TMPP in a 1:1 mole ratio yields [(TMPP)2Ag]+X- in solution, as evidenced by the halogen-independence of the P-31 NMR parameters and the closeness of these parameters to those for [(TMPP)2Ag]+[ClO4]- (delta = -70.9 ppm; 1J(Ag-107P-31) = 665.4 Hz). The 1J(Ag-P) coupling constants for the species observed in the present study are larger in magnitude than those previously observed for corresponding complexes with other phosphine ligands, providing further evidence for the high base strength of TMPP. The P-31 CP/MAS solid-state NMR spectra of the X = Cl and Br complexes are similar to the solution spectra and provide the first examples of Ag-107/Ag-109 isotopic splitting in the solid state. Attempts to characterize the 1:1 [(TMPP)AgI] complex by X-ray crystallography have thus far been unsuccessful. The P-31 CP/MAS NMR and far- IR spectra of the solid complex obtained from the 1:1 reaction of TMPP with AgI suggest that this is an ionic complex (or a mixture of such complexes), containing [(TMPP)2Ag]+ as the cation; the solution P-31 NMR results indicate that this forms the molecular species [(TMPP)AgI] upon dissolution.