Synthesis and Structures of Trans-Chelating Chiral Diphosphine Ligands Bearing Aromatic P-Substituents, (S,S)-(R,R)- and (R,R)- (S,S)-2,2″-Bis [ 1-(diarylphosphino)ethyl] -1,1″-biferrocenes (ArylTRAPs), and Their Transition Metal Complexes

The trans-chelating chiral phosphine ligand (S,S)-(R,R)-2,2'-bis[l-(diphenylphosphino)-ethyl]-1,1'-biferrocene (1a, abbreviated to PhTRAP) was synthesized from (S)-1-(N,N- dimethylamino)ethylferrocene (2) in four steps in 51% overall yield. (R,R)-(S,S)-PhTRAP and other arylTRAP derivatives (1b, AnisTRAP; 1c, Cl-PhTRAP, 1d, FurTRAP; le, Tol-PhTRAP) were synthesized in a similar manner. Through-space ³¹P-³¹P spin couplings were observed indirectly in the and ¹³C{¹H} NMR spectra of -1a-e and directly in the ³¹P{¹H} NMR spectrum of asymmetrical TRAP 1e, indicating that the two phosphorus atoms of the ligands are in close proximity. Results of NOE experiments showed that PhTRAP is a fairly rigid molecule and in a conformation favorable for trans-chelation. As square planar transition metal complexes bearing arylTRAPs as trans-chelating ligands, trans-[PdX₂{(S,S)-(R,R)-PhTRAP}] (7, X = Br; 8, X = I; 9, X = Cl), trans-[PtCl₂{(R,R(-(S,S)-PhTRAP}] (10), trans-[PtCl₂{(S,S)-(R,R)-1e}] (11), trans-[IrCl(CO){(S,S)-(R,R)-PhTRAP}] (12), trans-[RhCl-(CO){(S,S)-(R,R)-PhTRAP}] (13), and trans-[RhCl(CO){(S,S)-(R,R)-FurTRAP}] (14) were prepared and fully characterized. X-ray crystal structures were determined for the palladium complex 7 and the rhodium complex 14.