Phosphorus bidentate ligand interaction at platinum group metals: A catalytic and solid state study

[摘要] English: Hydroformylation of alkenes (olefins) is one of the world's leading aldehyde producing process. The resulting aldehydes can easily be converted to secondary products such as alcohols for production of plasticizers and detergents. Recent studies are directed towards the production of highly selective catalysts as linear aldehydes are the most desired products. A number of phosphine ligands have been investigated regarding this process, showing that fine tuning of the ligands electronic and steric properties significantly affects the activity and selectivity of a catalyst.A range of diphosphinoamine (PNP) ligands with various substituents on the nitrogen atom were synthesized and characterized, namely (1) N,N-Bis(diphenylphosphino)-p-toluidine [CH3-Ph-PNP],(2) N,N-Bis(diphenylphosphino)-4-chloroaniline [Cl-Ph-PNP], (3) N,N-Bis(diphenylphosphino)-4-fluoroaniline [F-Ph-PNP], (4) N,N-Bis(di-p-tolylphosphino)-p-toluidine [5-p-tolyl-PNP], (5) N,N-Bis(di-p-tolylphosphino)-o-toluidine [4-p-tolyl-o-tol], (6) N,N-Bis(di-p-tolylphosphino)cyclohexylamine [Chzyl-4-p-tolyl] and (7) N,N-Bis(di-p-tolylphosphino)cyclobutylamine [Cbutyl-4-p-tolyl] (see Figure 1). These ligands were systematically synthesized to induce different steric and electronic properties on the nitrogen atom. All the ligands were coordinated to Pt(II) and Pd(II) metals to serve as models for Rh(I) pre-catalysts systems to be used in hydroformylation of 1-octene. Metal complexes which produced crystals suitable for X-ray data analysis were (A) Dichloro-[N,N-Bis(di-p-tolylphosphino)-p-toluidine-k2P,P']platinum(II) [Pt(5-p-tolyl-PNP)Cl2], (B) Dichloro-[N,N-Bis(di-p-tolylphosphino)-o-toluidine-k2P,P']platinum(II) [Pt(4-p-tolyl-o-tol)Cl2], (C) Dichloro-[N,N-Bis(diphenylphosphino)-4-chloroaniline-k2P,P']palladium(II) [Pd(Cl-Ph-PNP)Cl2], (D) Dichloro-[N,N-Bis(diphenylphosphino)-p-toluidine-k2P,P']palladium(II) [Pd(5-p-tolyl-PNP)Cl2], (E) Dichloro-[N,N-Bis(di-p-tolylphosphino)cyclobutylamine-k2P,P']platinum(II) [Pt(Cbutyl-4-p-tolyl)Cl2] and (F) Dichloro-[N,N-Bis(di-p-tolylphosphino)cyclohexylamine-k2P,P']palladium(II) [Pd(Chzyl-4-p-tolyl)Cl2] (see Figure 2). This data provided information regarding the coordination modes of the ligands. To evaluate the electronic properties of ligand 1, 2 and 3, the first order coupling constants J(Pt-P) were determined and correlated.Hydroformylation of 1-octene was performed using a Rh(I)-PNP catalyst. An increase in linear product yield was observed when the ligand electron withdrawing ability and the steric bulk on the nitrogen were systematically increased. The highest recorded linear product yield was 35.1 % with Ligand 3 and the lowest was 20.3 % with ligand 4 in the first three hours of the sampling period. The highest calculated θN-sub was 80.6 ° for ligand 6 and gave a linear product of 28.5%. The lowest recorded θN-sub was 33.7 ° for ligand 4. These results showed that both the electronic and the steric properties have a significant influence on the catalysts selectivity.

[发布机构] University of the Free State