Synthesis of Phosphonito,N and Phosphito,N ligands based on quinolines and (R)-binaphthol or substituted biphenol and of their rhodium(I), palladium(II) and platinum(II) complexes

The new Phosphonito,N ligands 8-(4,8-di-tert-butyl-1,11-dimethoxy-5,7-dioxa-6-phospha-dibenzo[a,c]cyclohepten-6-yl)-quinoline (2a), and (R)-8-(3,5-dioxa-4-phospha-cyclohepta-[2,1-a;3,4-a′]dinaphthalen-4-yl)-quinoline ((R)-2b), were readily prepared starting from 8-(bis-diethylamino-phosphine)-quinoline (1), as a key intermediate, and 2,2′-dihydroxy-5,5′-dimethoxy-3,3′-di-tert-butylbiphenyl or (R)-binaphthol, respectively. The Phosphito,N ligand, 8-(4,8-di-tert-butyl-1,11-dimethoxy-5,7-dioxa-6-phospha-dibenzo[a,c]cyclohepten-6-yloxy)-quinoline (3a), was obtained by reacting equimolar amounts of 8-hydroxyquinoline and the phosphorochloridite derived from 3,3′-di-tert-butyl-2,2′-dihydroxy-5,5′-dimethoxybiphenyl, in toluene in the presence of NEt3. The corresponding Phosphito,N-ligand, 8-(3,5-dioxa-4-phospha-cyclohepta[2,1-a;3,4-a′]dinaphthalen-4-yloxy)-quinoline (R)-(3b), was obtained similarly using the phosphorochloridite derived from (R)-binaphthol. A systematic study of the coordination abilities of 2–3 to rhodium(I), palladium(II) and platinum(II) precursors has been carried out. Crystal structures of the complexes [Pt(3a)I2] (7a), and [Pd(2a)Cl2] (8a), are reported. The reactions of the chiral ligands (R)-2b and (R)-3b with [Rh(acac)(CO)2] lead to [Rh(acac)(R-2b)] (10), and [Rh(acac)(R-3b)] (11), respectively. Under hydroformylation conditions, displacement of the chiral ligands in both complexes 10 and 11 takes place, even in the presence of an excess of free ligand, leading to achiral hydrido-carbonyl rhodium complexes.