CARBON-MONOXIDE REACTIONS OF THE FLUXIONAL PHOSPHINE COMPLEX (ETA-3-PR3)MO(CO)3 (R=2,4,6-TRIMETHOXYPHENYL)

The syntheses, spectral properties, and structures of complexes (eta(x )-TMPP)Mo(CO)y (TMPP = tris(2,4,6-trimethoxyphenyl)phosphine; x = y = 3, 1; x = 2, y = 4, 2; x = 1, y = 5, 3) are described. Compounds 1-3 e xhibit octahedral geometries with the TMPP ligand bound to the metal i n monodentate, bidentate and tridentate coordination modes, respective ly. These compounds constitute the first homologous series that demons trates all three possible binding modes of the TMPP ligand and the fir st such series involving group VI tri-, tetra-, and pentacarbonyl comp lexes supported by an identical ligand that changes hapticity. Compoun d 1, (eta3-TMPP)Mo(CO)3, was isolated from the reaction of (cht)Mo(CO) 3 (cht = cycloheptatriene, C7H8) with 1 equiv of TMPP. The molecule cr ystallizes as a CH2Cl2 solvate in the monoclinic space group P2(1)/a: a = 17.155(8) angstrom, b = 12.019(4) angstrom, c = 16.985(6) angstrom , beta = 95.69(3)degrees, V = 3485(2) angstrom3, and Z = 4. The struct ure was refined to least-squares residuals of R = 0.069 (R(w) = 0.084) and a goodness-of-fit index of 2.09. Compound 2, (eta2-TMPP)MO(CO)4, was isolated in high yield from solutions of 1 treated with CO and in lower yield from solutions of 1 purged with N2 or H-2 which facilitate dissociation of CO. Compound 2 crystallizes in the monoclinic space g roup P2(1)/n: a = 12.222(3) angstrom, b = 17.756(8) angstrom, c = 15.3 42(2) angstrom, beta = 97.94(2)degrees, V = 3297(2) angstrom3, and Z = 4. The structure was refined to residuals of R = 0.032 (R(w) = 0.046) and goodness-of-fit = 1.29. (eta1-TMPP)Mo(CO)5, 3, was prepared by re action of 2 with CO and by workup of CO saturated solutions of 1 under a CO atmosphere; the conversion between 2 and 3 is a reversible proce ss. Compound 3 crystallizes in the monoclinic space group P2(1)/n: a = 11.232(3) angstrom, b = 23.250(7) angstrom, c = 13.515(4) angstrom, b eta = 103.79(2)degrees, V = 3428(2) angstrom3, and Z = 4. The structur e was refined to least-squares residuals of R = 0.032 (R(w) = 0.043) a nd goodness-of-fit = 1.94. The ether interactions in 1 and 2 are fluxi onal, as confirmed by variable-temperature H-1 NMR spectroscopy wherea s 3 exhibits H-1 NMR properties in accord with a freely rotating monod entate phosphine ligand. H-1 NMR spectroscopy is a powerful tool for t he assignment of structure in these systems, with the solution behavio r correlating well with the solid-state structures. The syntheses, spe ctroscopic properties, and structural details of this series of relate d compounds will be discussed and compared to related compounds in the literature.