Divergent kinetic and thermodynamic acidity in organotransition-metal hydride complexes: synthesis, structure, and reactivity of the rhenium anion of Li+ [(.eta.-C5H5)Re(NO)(PPh3)]-.
Additional Document Info
Reaction of hydride complex (5-C5H5)Re(NO)(PPh3)(H) (1) and n-BuLi/TMEDA (THF, -78 C) gives (5-C5H4Li)Re(NO)(PPh3)(H) (Li+ -8), as shown by 31P NMR monitoring, deuterium labeling, and methylation (CH3OSO2CF3, -78 C) to (5-C5H4CH3)Re(NO)(PPh3)(H) (9, 52%). Complex Li+-8 rearranges to the rhenium anion of Li+[(5-C5H5)-Re(NO)(PPh3)](Li+-3; -32 C, 0.5 h) with H = 11.3 0.5 kcal/mol, S = -26.2 1.4 eu, and kH/kD(-22.4 C) = 1.16 0.08. Crossover experiments show hydrogen migration to be intramolecular, and K+-8 rearranges ca. 104 faster than Li+-8 at -91.6 C. Equilibration experiments show the 5-C5H5 and ReH proton pKa's (THF) in 1 to be ca. 36 and 2630, respectively. Thus, the less acidic proton is abstracted kinetically, and a rationale is proposed. Reactions of Li+-3 with alkylating agents (CH3I, n-C4H9I, ClCH2CH=CH2, ClCH2COPh), benzoic anhydride, and D2O give the corresponding alkyl, acyl, and deuteride complexes (56-90%). IR data show Li+-3 to be a mixture of three ion pairs in THF. Pentamethyl analogue (5-C5Me5)Re(NO)(PPh3)(H) (13) is prepared from methyl complex (5-C5Me5)Re(NO)(PPh3)(CH3) (11; HCOOH, then 110 C; 43%). Reaction of 13 and n-BuLi/K+-t-BuO gives principally K+[(5-C5Me5)Re(NO)(PPh3)], as assayed by 31P NMR and methylation (CH3I) to 11. 1988, American Chemical Society. All rights reserved.