Pd(II) and Rh(I) chelate complexes of the bidentate phosphino-thiourea ligand PhNHC(S)NHCH2CH2PPh2: structural properties and activity in homogeneousand hybrid catalysis

The new bifunctional ligand PhNHC(S)NHCH2CH2PPh2 (Ptu), containing the thio urea and the phosphine functions, and its Pd(II) and Rh(I) complexes were p repared. Ptu behaves as a bidentate ligand forming seven-membered chelation rings in a boat-like conformation. In the case of palladium, this was asce rtained by the X-ray determination of the structure of the complexes [Pd(Pt u)(2)]Cl-2. 6CHCl(3) (1), [Pd(Ptu)(2)Cl]Cl . EtOH (2) and [Pd(Ptu)(2)][CoCl 4]. CHCl3. 2EtOH (3). In complexes 1 and 3, the two ligands are related cen trosymmetrically, whereas in 2 they are folded by the same side in an umbre lla arrangement. The Rh(I) complexes [Rh(cod)(Ptu)]X (X = Cl or PF6; cod = 1,5-ciclooctadiene) and [Rh(cod)(Ptu)](2)[CoCl4] were characterized by P-31 -NMR and FT-IR spectroscopy. The catalytic activity in homogeneous hydrogen ation and hydroformylation reactions of the Pd(II) and Rh(I) complexes was dependent on the counter-anion, being very low in the case of Cl- and high in the case of non-coordinating anionic groups such as CoCl4- and PF6-. The related ligand (EtO)(3)Si(CH2)(3)NHC(S)NHCH2CH2PPh2 (SiPtu) was sol-gel pr ocessed giving hybrid inorganic-organic xerogels (XGPtu). Anchored Pd(II) a nd Rh(I) complexes were obtained by two procedures: by treating XGPtu with solution of precursor complexes or by sol-gel processing previously prepare d SiPtu complexes. Palladium complexes of the thiourea ligand (EtO)(3)Si(CH 2)(3)NHC(S)NHPh (Siphtu), with different S-Pd ratios, were also sol-gel pro cessed. The rhodium containing xerogel was found to be an active catalyst f or the hydroformylation of styrene, but metal leaching occurred, even if to a limited extent. In the case of Pd-containing materials, it was ascertain ed that the heterogeneous hydrogenating activity depends on the presence of colloidal metal particles, which form when the metal species are not adequ ately surrounded by the P,S- or S-ligands. (C) 2000 Elsevier Science S.A. A ll rights reserved.