CHIRAL TRIPOD RHODIUM COMPLEXES - LIGAND SYNTHESIS, CHEMISTRY OF COMPLEXES, CATALYSIS

The reaction of epichlorohydrine (O-CH2-CH-CH2Cl) with lithium-dipheny lphosphide (LiP(Ph)(2)) yields the alcohol (HOCH(CH2P(Ph)(2))(2)) 1 in a stereochemically controlled reaction. To prove the constitution and coordination ability of 1, the compound has been used to synthesise t he homoleptic bisdiphosphine-rhodium complexes trans/cis-[(1)(2)Rh-1]B (Ph)(4) 2a,b. The X-ray structure of 2b shows a significant tetrahedra l distortion of the planar coordination geometry theoretically favoure d for a tetracoordinate metal d(8) coordination compound, The diphosph ino alcohol 1 easily reacts with chiral phosphorchloridites X(2)PCl(X( 2) = 2R,4R-2,4-pentanedioxy(3a); (+/-)- and R-2,2'-bi-1-naphthoxy- (3b )) to yield chiral-racemic as well as enantiomerically pure mixed dono r group tripodal ligands (X(2)POCH(CH2P(Ph)(2))(2)) 5a,b containing bo th phosphite and phosphine donor groups. The identity of these compoun ds has been proven by H-1-, P-31- and C-13-NMR spectroscopy, mass-spec tra and microanalysis. The coordination capabilities of these novel tr ipod ligands are demonstrated by the synthesis and characterisation of the chiral rhodium-cyclooctadiene complexes {[(5a,b)Rh-1(COD)]PF6} 6a ,b, which show the typical hetero-bicyclooctane tripod metal cage of t his type of tripod metal template. The rhodium complexes 6a,b are cata lysts for the hydrogenation of prochiral olefines. Their activity is n ot too high and the enantioselectivity is low, The trihapto-coordinati on of the tripodal ligands is more of an impediment for this type of c atalytic transformation.