OXYGEN TRIPOD LIGANDS WITH FUNCTIONALIZED PENDANT ARMS - THE DANGLINGLIGAND CONCEPT IN HOMOGENEOUS CATALYSIS

The cobalt complex [CPCoI2(CO)] reacts with the trialkyl phosphites P( OCH3)2(OR) (R = (C2H4O)nCH2CH=CH2, (C2H4O)nC2H4CN, (C3H6)nCH=CH2, (C3H 6)nCN, C3H6C(O)CH3; n = 1, 2) and NaI in a series of Arbuzov reactions to produce anionic complexes of the type [CpCo{P(O)(OCH3)(OR)}3]- = L (OMe,OR-) in high yields. The products consist of two pairs of enantio mers, which have been characterized by H-1, C-13, and P-31 NMR and IR spectroscopy. The anions L(OMe,OR-) have been shown to behave as tris- chelating ligands toward metal ions by using the oxygen atoms of the t hree P=O groups. The functional groups (olefin, nitrile, ketone) of th e pendant side chains OR can act as additional intramolecular complexa tion sites. The rhodium complexes [(L(OMe,OR))Rh(CO)2] have been used as catalyst precursors for hydroformylation of 1-propene, hydrogenatio n of cyclohexene, and cyclotrimerization of dimethyl acetylenedicarbox ylate. They show considerably higher catalytic activities than the ana logous complexes containing ligands L- without functionalized pendant arms. The solubility of the ligands in water or hydrocarbons can be co ntrolled by choosing alkyl or polyether side chains OR.