Reactivity of 1,6-enynes on the Ruthenium 1,2-Bis(diphenylphosphino)ethane Complexes
Date Issued
2010
Date
2010
Author(s)
Yang, Hsuan
Abstract
A series of ruthenium acetylide complexes Cp(dppe)Ru-C≡CCH(OMe)C(R1)(R2)CH2C(R3)=C(R4)(R5) (4a, R1 = Ph, R2 = Ph, R3 = H, R4 = H, R5 = H; 4b, R1 = Ph, R2 = CH3, R3 = H, R4 = H, R5 = H; 4d, R1 = Ph, R2 = Ph, R3 = H, R4 = CH3, R5 = CH3) containing pendant olefinic group, which has either none or with various substituted methyl groups, were prepared. Interestingly, these acetylide complexes display novel reactivity.
Treatment of the acetylide complexes 4a, 4b and 4d with HBF4 in ether/H2O at 0oC, caused surprising transformation. Protonation of 4a, 4b and 4d generated the hydroxycarbene complexes 5a, 5b and 5d [Cp(dppe)Ru=C(OH)CH=CHC(R1)(R2)CH2C(R3)=C(R4)(R5)][BF4] (5a, R1 = Ph, R2 = Ph, R3 = H, R4 = H, R5 = H; 5b, R1 = Ph, R2 = CH3, R3 = H, R4 = H, R5 = H; 5d, R1 = Ph, R2 = Ph, R3 = H, R4 = CH3, R5 = CH3), respectively. It seems that the acetylide alpha-carbon atom was attacked by a hydroxyl group. Possibly the vinylidene complex eliminates MeOH, and the presence of H2O brings about the attack of the hydroxyl group at alpha-carbon to give the hydroxycarbene complexes 5a, 5b and 5d.
Astonishingly, with the presence of two methyl groups at the terminal carbon of the tethering allyl group, the ruthenium acetylide complex 4d displays novel reactivity. Oxygen molecule readily reacts with 4d to yield the neutral acyl ruthenium complex 8 and acetone. When oxygen was gently bubbled through a CDCl3 solution of the acetylide complex 4d at room temperature, the terminal three-carbon-unit in 4d was smoothly cleaved and the acyl complex 5d was formed in almost quantitative yield. A C–C bond formation between beta-carbon and the internal carbon of the allylic group gives an intermediate A. The intermediate, then, isomerizes to give the acyl product, which is accompanied with elimination of acetone.
Previously, photo activation of oxygen to singlet state was required in most oxygen addition reactions, which were commonly followed by a thermal decomposition. However, in our enyne case, no photoexcitation of oxygen is required. This reaction of oxygen with the 1,6-enyne ligand in 4d was achieved under mild condition in less than 10 min.
Subjects
Ruthenium
Acetylide
Hydroxycarbene
Acyl
Oxidative addition
1,2-Bis(diphenylphosphino)ethane
Type
thesis
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