Syntheses and structural analyses of chiral rhenium containing amines of the formula (η5-C5H5)Re(NO)(PPh3)((CH2)nNRR′) (n = 0, 1)

The reaction of the racemic chiral methyl complex (η5-C5H5)Re(NO)(PPh3)(CH3) (1) with CF3SO3H and then NH2CH2C6H5 gives [(η5-C5H5)Re(NO)(PPh3)(NH2CH2C6H5)]+CF3SO3- ([4a-H]+CF3SO3-; 73%), and deprotonation with t-BuOK affords the amido complex (η5-C5H5)Re(NO)(PPh3)(NHCH2C6H5) (76%). Reactions of 1 with Ph3C+ X− and then primary or secondary amines give [(η5-C5H5)Re(NO)(PPh3)(CH2NHRR′)]+ X− ([6-H]+ X−; R/R′/X = a, H/NH2CH2C6H5/BF4; a′, H/NH2CH2C6H5/PF6; b, H/NH2CH2(CH2)2CH3/PF6; c, H/(S)-NH2CH(CH3)C6H5/BF4); d, CH2CH3/CH2CH3/PF6; e, CH2(CH2)2CH3/CH2(CH2)2CH3/PF6; f, CH2C6H5/CH2C6H5/PF6; g, -CH2(CH2)2CH2-/PF6; h, –CH2(CH2)3CH2–/PF6; i, CH3/CH2CH2OH/PF6 (62–99%). Deprotonations with t-BuOK afford the amines (η5-C5H5)Re(NO)(PPh3)(CH2NRR′) (6a–i; 99–40%), which are more stable and isolated in analytically pure form when R ≠ H. Enantiopure 1 is used to prepare (RReSC)-[6c-H]+BF4-, (RReSC)-6c, (S)-[6g-H]+PF6-, and (S)-6g. The crystal structures of [4a-H]+CF3SO3-, a previously prepared NH2CH2Si(CH3)3 analog, [6a′,d,f,h-H]+PF6-, (RReSC)-6c, and 6f are determined and analyzed in detail, particularly with respect to cation/anion hydrogen bonding and conformation. In contrast to analogous rhenium containing phosphines, 6a–i show poor activities in reactions that are catalyzed by organic amines.

Graphical abstractThe racemic and enantiopure title compounds are prepared from the methyl complex (η5-C5H5)Re(NO)(PPh3)(CH3) via the corresponding conjugate acids. Crystal structures of the “organometallic amines” and their conjugate acids are analyzed in detail.Figure optionsDownload full-size imageDownload as PowerPoint slide