Trans-Chelating Chiral Peralkyldiphosphine Ligands (R,R)-(S,S)-2,2″-Bis[1-(dialkylphosphino)ethyl]-1,1″-biferrocenes (AlkylTRAPs) and Their Transition Metal Complexes

New chiral peralkyldiphosphines (S,S)-2,2″-bis[(R)-1-(dialkylphosphino)ethyl]-1,1″-biferrocenes ((R,R)-(S,S)-alkylTRAPs) were synthesized from (R)-N,N-dimethyl-1-ferrocenylethylamine in four steps in 38—68% overall yields (MeTRAP: 38%, EtTRAP: 68%, PrTRAP: 53%, BuTRAP: 56%, i-BuTRAP: 51%, i-PrTRAP: 42%). The reactions of alkylTRAP (Et-, Bu-, i-Bu, and i-PrTRAP) with 1 molar amount of PdBr2 gave trans-[PdBr2(alkylTRAP)] in good yields. The X-ray crystal structures of these palladium complexes revealed that alkylTRAPs coordinated to a palladium atom in a trans-chelating manner regardless of the P-alkyl substituents. The structures of palladium complexes of Et-, Bu-, and i-PrTRAP had nearly C2-symmetry, but that of i-BuTRAP was deviated from C2-symmetry significantly. AlkylTRAPs also reacted with [PtCl2(MeCN)2] and [RhCl(CO)2]2, giving the corresponding trans-chelate platinum and rhodium complexes. The crystal structure of trans-[RhCl(CO)(BuTRAP)] revealed that the conformation of the BuTRAP ligand in the complex was almost the same as that in the palladium complex trans-[PdBr2(BuTRAP)].