Chiral [Iminophosphoranyl]ferrocenes: Synthesis,Coordination Chemistry,and Catalytic Application

摘要

A series of new chiral [iminophosphoranyl]ferrocenes,{eta~5-C_5H_4-(PPh_2=N-2,6-R_2-C_6H_3)}Fe{eta~5-C_5H_3-l-PPh_2-2-CH(Me)NMe_2} (1: R = Me,~iPr),{eta~5-C_5H_4-(PPh_2=N-2,6-R_2~1-C_6H_3)}Fe{eta~5-C_5H_3-l-(PPh_2=N-2,6-R_2-C_6H_3)-2-CH(Me)R~2} (2: R~1 = Me,~iPr;R~2 = NMe_2,OMe),and (eta~5-C_5H_5)Fe{eta~5-C_5H_4-l-PR_2-2-CH(Me)N=PPh_3} (3: R = Ph,C_6H_(11)) have been prepared from the reaction of [l,l'-diphenylphosphino-2-(N,N-dimethyl-amino)ethyl]ferrocene with arylazides (1 & 2) and the reaction of phosphine dichlorides (R_3PCl_2) with [1,1'-diphenylphosphino-2-aminoethyl]ferrocene (3),respectively.They form palladium complexes of the type [Pd(C_3H_5)(L)]BF_4 (4-6: L = 1-3),where the ligand (L) adopts an eta~2-N,N (2) or eta~2-P,N (3) as expected.In the case of 1,a potential terdentate,an eta~2-P,N mode is realized with the exclusion of the -P=NAr group from the coordination sphere.Complexes 4-6 were employed as catalysts for allylic alkylation of 1,3-diphenylallyl acetate leading to an almost stoichiometric product yield with modest enantiomeric excess (up to 74% ee).Rh(I)-complexes incorporating 1-3 were also prepared in situ for allylic alkylation of cinnamyl acetate as a probe for both regio- and enantioselectivities of the reaction.The reaction exhibited high regiocontrol in favor of a linear achiral isomer regardless of the ligand employed.