Synthesis, structure, and reactivity of chiral rhenium alkyne complexes of the formula [(.eta.5-C5H5)Re(NO)(PPh3)(RC.tplbond.CR')]+BF4- Academic Article uri icon

abstract

  • Reactions of [(η6-C5H6)Re(NO)(PPh3)(ClC6H6)]+BF4− and RC≡CR′ (R = R′ = H (a), CH3 (b), CH2CH3 (c), C6H5 (d); R/R′ = C(CH3)3/H (e)) give alkyne complexes [(η6-C5H5)Re(NO)(PPh3)(RC≡CR′)]+BF4− (4a-e; 73–97%). A crystal structure of 4c-ClCH2CH2Cl (orthorhombic, Pbca; a = 15.724 (1) Å, b = 18.593 (2) Å, c = 22.128 (2) Å, Z = 8) shows a 3-hexyne ligand conformation that directs the ethyl substituents syn and anti to the PPh3 ligand. The C≡C bond is only slightly longer (1.24 (1) Å) than in free alkynes, but the propargylic carbons are bent back from the C≡C axis (∠C≡C-C = 143.4 (8), 147 (1)°). NMR data show high barriers to alkyne ligand rotation (4b,c: ΔG‡(180 °C) ≥ 22 kcal/mol). Difference 1H NOE and decoupling experiments enable detailed assignments of NMR resonances. Reactions of 4a,e and t-BuO−K+ give acetylide complexes (η5-C5Hs)Re(NO)(PPh3)(C≡CR′) (5a,e; 74–97%). Complex 4e rearranges (80 °C, C6H6C1,1 h) to vinylidene complex [(η5-C5H5)Re(NO)(PPh3)(=C=CHC(CH3)3)]+BF4−, a sample of which can be independently prepared from 5e and HBF4•O(CH2CH3)2 (92%). The physical and chemical properties of 4a-e are compared to those of other alkyne complexes. © 1991, American Chemical Society. All rights reserved.

author list (cited authors)

  • Kowalczyk, J. J., Arif, A. M., & Gladysz, J. A.

citation count

  • 27

publication date

  • April 1991