Synthesis, coordination and catalytic use of phosphinoferrocene ligands bearing 6-phospha-2,4,6-trioxaadamantane P-donor moieties
Abstract
1,1'-Bis(diphenylphosphino)ferrocene (dppf) and structurally related ferrocene bis-phosphines are indispensable ligands for coordination chemistry and catalysis. This contribution focuses on the coordination behaviour and catalytic properties of two dppf congeners bearing 1,3,5,7-tetramethy1-2,4,6-trioxa8-phosphatricyclo[3.3.1.1 (3,7)]decane-8-yl groups (CgP) as the P-donor moieties, viz.
Ph(2)PfcCgP (1) and its semi-homologous counterpart Ph(2)PfcCH(2)CgP (2; fc = ferrocene-1,1'-diyl). In reactions with a PdCl2 source, compound 1 produced exclusively the cis-chelate complex [PdCl2 (1-κ(2) P,P')], while the homologated ligand 2 afforded a complex mixture of compounds which equilibrated upon heating in methanol in favour of the symmetrical dimeric complex trans-[(µ-2)PdCl2](2) as a mixture of racemic and meso isomers.
Notably, in aqueous Pd-catalysed cyanation of aryl bromides and Suzuki-Miyaura-type cross-coupling of benzoyl chlorides with boronic acids producing benzophenones, catalysts generated in situ from bis-phosphine 1 and Pd(II) sources were often more active than their counterparts resulting from dppf and 2.