A new family of chiral chelating diamines with transition-metal stereocenters: Synthesis, structure, and reactivity of the enantiomerically pure dirhenium-substituted 1,2-diamine (eta(5)-C5H5)Re(NO)(PPh3) (CH2N(CH3)CH2CH2(H3C)NCH2)(Ph3P)(ON)Re(eta(5)-C5H5)
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abstract
Reaction of enantiopure (S)-(5-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)-[(5-C5H5)Re (NO)(PPh3) (CH2NH(CH3)CH2CH2(H3C)HNC H2)(Ph3P)(ON)Re (5-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, (SReRNRNSRe)-[(5- C5H5)Re(NO)(PPh3) (CH2N(CH3)CH2CH2(H3C) NCH2)(Ph3P)(ON)Re(5- C5H5)]PdCl2 (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(H3 CCH2)NH (1 equiv) give [(5-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.
