Title of article :
Synthesis, X-ray crystallographic, and reactivity studies of rhenium(V) alkyne complexes
Author/Authors :
June-Ho Jung، نويسنده , , David M. Hoffman، نويسنده , , T. Randall Lee، نويسنده ,
Issue Information :
دوفصلنامه با شماره پیاپی سال 2000
Abstract :
[ReOMe2(bipy)(CH3CN)][PF6], prepared in situ, reacted with alkynes (ethyne, propyne, 2-butyne, 3-hexyne, phenylacetylene, and diphenylacetylene) to give the cationic alkyne complexes trans-[ReOMe2(bipy)(alkyne)][PF6] (trans-MeReMe). 1H-NMR studies indicated that a cis isomer was formed initially. Kinetics studies showed that the isomerizations were first order in the alkyne complex. The observed rate constants depended on the steric bulk of the alkyne with bulkier alkynes producing smaller kobs values. An Eyring plot for the isomerization of [ReOMe2(bipy)(2-butyne)][PF6] yielded ΔH‡=21(1) kcal mol−1 and ΔS‡=6(3) eu. The isomerization mechanism was proposed to involve the rearrangement of a five-coordinate intermediate formed by dissociation of a ReN bond. Treatment of [ReOMe2(bipy)(CH3CN)][PF6] with dimethyl acetylenedicarboxylate afforded the metallacycle [)(OMe)}(O)Me(bipy)][PF6] via insertion of the alkyne into a ReCH3 bond. Trans-[ReOMe2(RCCH)(bipy)][PF6] reacted with PMe3 or PPh3 to form the ylide complexes cis-[ReOMe2(bipy){C(R)CH(PR′3)}][PF6] (R=H, R′=Me or Ph; R=Ph, R′=Me). In each case, a trans isomer (trans-MeReMe) of the ylide complex was formed initially, which isomerized to the cis isomer. Spectroscopic and X-ray crystallographic studies suggest that the ylide complexes can be described as organometallic analogs of resonance-stabilized phosphonium ylides. The structures of trans-[ReOMe2(bipy)(PhCCPh)][PF6], [)(OMe)}(O)Me(bipy)][PF6], cis-[ReOMe2(bipy){C(H)CH(PPh3)}][PF6] and cis-[ReOMe2(bipy){C(Ph)CH(PMe3)}][PF6] were determined by X-ray crystallography.
Keywords :
insertion reaction , Alkyl complexes , Alkyne complexes , Ylide complexes , Rhenium
Journal title :
Journal of Organometallic Chemistry
Journal title :
Journal of Organometallic Chemistry