.beta.-Electrophilic Additions of Pentaammineosmium(II) .eta.2-Pyrrole Complexes

Nitrilium ions – synthesis and applications

“…A study on the reactivity of pentaamineosmium(II)-η 2 -pyrrole complex 32 revealed that the pyrrole group changes from the α to the β-position on addition of a nitrilium ion to give 33 (Scheme 4d). 52 A similar β-addition to nitrilium ions was shown for the analogue η 2 -furan complexes. 53 C-Phenyl nitrilium salts 1-BF 4 reportedly react in high yield with imino-imidazoles 34 to bis-imino-imidazolium salt 35 (Scheme 4e) that are precursors for bis-imino N-heterocyclic carbenes, but the parent imidoyl chloride shows no reactivity.…”

The Activation of Aromatic Molecules with Pentaammineosmium(II)

“…Alternatively, Zn°/Hg° amalgam may be used as the reducing agent if the reaction is carried out in methanol. Using this simple procedure, pentaammineosmium(II) complexes have been prepared with a diverse array of η 2 -bound aromatic ligands (Figure ) including benzenes, − anisoles, , anilines, − phenols, ,− naphthalenes, and other polyaromatic hydrocarbons, pyridines, , pyrroles, − furans, ,, and thiophenes, , with yields typically >90%. Where convenient, the ligand is used in approximately a 10-fold excess to minimize the formation of binuclear impurities.…”

“…The 4,5-η 2 - N -methylpyrrole complex readily adds electrophiles at C(3) to give 3 H -pyrrolium complexes (Figure ). , Electrophiles include nitrilium salts (A), acetic anhydride (B), aldehydes, ketones and acetals (C), Michael acceptors (D), and alkyl triflates (E). For cases in which the corresponding 3 H -pyrrolium product has a withdrawing group adjacent to the β carbon (e.g., an acyl or iminium group) deprotonation is facile, and the isolated product is usually a β-substituted pyrrole.…”

Synthesis ofC-vinylpyrroles

“…185 The addition of the complex 397 to activated acetylenes also afforded 3-vinylpyrrole complexes 407. 184,185 R 1 = Me, Pr n , Bu n , Ph; R 2 = H, Me, Et, Pr n ; R 1 ± R 2 = (CH2)4; R 3 = Me, Et, Bu n , All; X = CN, CONH2, CO2Et. The reactions in Et 2 O at 0 8C gave rise to the E isomers, whereas the reactions in THF afforded the Z isomers of compounds 409 ± 411.…”