A New Family of Chiral Chelating Diamines with Transition-Metal Stereocenters: Synthesis, Structure, and Reactivity of the Enantiomerically Pure Dirhenium-Substituted 1,2-Diamine (η⁵-C₅H₅)Re(NO)- (PPh₃)(CH₂N(CH₃)CH₂CH₂(H₃C)NCH₂)(Ph₃P)(ON)Re(η⁵-C₅H₅)

Abstract

Reaction of enantiopure (S)-(η5-C5H5)Re(NO)(PPh3)(CH3) ((S)-1) with Ph3C+BF4- (1 equiv) and then the N,N‘-dimethyl 1,2-diamine HN(CH3)CH2CH2(H3C)NH (0.5 equiv) gives the diammonium salt (SReSRe)-[(η5-C5H5)Re(NO)(PPh3)(CH2NH(CH3)CH2CH2(H3C)HNCH2)(Ph3P)(ON)Re(η5-C5H5)]2+(BF4-)2 (94%) as a mixture of Re/N configurational diastereomers. Reaction with t-BuOK yields the title compound (SReSRe)-4 (66%) as an air-stable orange powder. Reaction with (PhCN)2PdCl2 gives a single diastereomer of a chelate complex, (80%), the configuration and approximate C2 symmetry of which has been established crystallographically. Racemic 1, Ph3C+BF4- (1 equiv), and the N,N‘-dimethyl 1,2-diamine HN(CH2CH3)CH2CH2(H3CCH2)NH (1 equiv) give [(η5-C5H5)Re(NO)(PPh3)(CH2NH(CH2CH3)CH2CH2NH(CH2CH3))]+BF4-, and the crystal structure of the SReSN,RReRN diastereomer is determined. The ReCH2N conformations of the preceding compounds, and their influence upon the diastereoselectivities, are analyzed in detail.