RHODIUM COD COMPLEXES OF MIXED-DONOR SET TRIPOD LIGANDS - COORDINATION CHEMISTRY AND CATALYSIS

The reaction of the novel mixed tripod ligands RCH2C(CH2X)(CH2Y)(CH(2) Z) 1-6 (X, Y, Z = PPh2, NR2, pyrazol-1-yl; R = H, OH) with [Rh-I(COD)C l](2) is investigated. The resulting rhodium COD complexes [(1-6)Rh(CO D)]PF6, 7 are characterized by NMR spectroscopy, mass spectra and elem ental analysis. In addition, X-ray structure analysis is performed on several compounds 7, where in contrast to the behavior of the parent c ompound triphos [MeC(CH2PPh2)(3)], the potential tripod ligands 2-6 ar e found to coordinate in a bidentate mode. (2)-P,O-[HOCH2C(CH2PPh2)(CH 2NEt2)(2)]Rh(COD)]}PF6, 7i exhibits the first structurally characteriz ed example of an intramolecular hydrogen bond between a non-coordinate d and a coordinated donor atom. The activities of the complexes 7 as c atalyst precursors in the homogeneous hydrogenation of diphenylacetyle ne and (Z)-alpha-N-acetamidocinnamic acid are tested and rationalized with respect to a proposed reaction mechanism. (C) 1998 Elsevier Scien ce S.A. All rights reserved.