Cp. Casey et al., Protonation of rhenium alkyne complexes produces eta(3)-allyl rhenium complexes via observable 1-metallacyclopropene intermediates, J AM CHEM S, 120(48), 1998, pp. 12500-12511
Protonation of the rhenium eta(2)-alkyne complex C5Me5(CO)(2)Re(eta(2)-MeC
equivalent to CMe) (4) with HBF4 at room temperature produced the eta(3)-al
lyl complex C5Me5(CO)(2)Re(eta(3)-exo,anti-MeHC-CH-CH2)+BF4- (5). The proto
nation of 4 at -78 degrees C occurred at rhenium to give the rhenium alkyne
hydride complex C5Me5(CO)(2)ReH(eta(2)-MeC equivalent to CMe)+BF4- (6). At
-16 degrees C, net proton migration from rhenium to the alkyne ligand of 6
occurred to produce the 1-metallacyclopropene complex C5Me5(CO)(2)Re(eta(2
)-CMeCHMe)+BF4- (7), which then rearranged to form the eta(3)-allyl complex
5. The degenerate rearrangement of 7 by hydride migration between the two
metallacyclopropene carbons was demonstrated by deuterium labeling. Protona
tion of the rhenium eta(2)-alkyne complex C5Me5(CO)(2)Re(eta(2)-PhC equival
ent to CPh) (10) with HBF4 at -78 degrees C initially produced the rhenium
alkyne hydride complex C5Me5(CO)(2)ReH(eta(2)-PhC equivalent to CPh)+BF4- (
11), which was observed spectroscopically. Upon warming to room temperature
, 11 was converted to the stable 1-metallacyclopropene complex C5Me5(CO)(2)
Re(eta(2)-CPhCHPh)+BF4- (12), which was characterized by X-ray crystallogra
phy, Hybrid density functional theory calculations and natural bond orbital
analysis were performed on the 1-metallacyclopropene cation [C5H5(CO)(2)Re
(eta(2)-MeCCHMe)](+) to compare eta(2)-vinyl vs 1-metallacyclopropene formu
lations.