505066-50-2Relevant academic research and scientific papers
Indenyl rhenium alkyne complexes: CO substitution via alkyne-assisted ring slippage and CO-catalyzed phosphine substitution
Casey, Charles P.,Vos, Thomas E.,Brady, John T.,Hayashi, Randy K.
, p. 1183 - 1195 (2008/10/08)
CO substitution of the indenyl alkyne complex (η5-C9H7)(CO)2 Re(η2-MeC≡CMe) (3) to form (η5-C9H7)Re(CO)3 (8) is much faster than that of either the indenyl alkene complex (η5-C9H7)(CO)2 Re(η2-cis-MeHC=CHMe) (2) or the cyclopentadienyl alkyne complex (η5-C5H5)(CO)2 Re(η2-MeC≡CMe) (5). The acceleration of the reaction of 3 with CO is proposed to involve cooperativity between slippage of the indenyl ring from an η5 6e-donor to an η3 4e-donor and shifting of the alkyne ligand from a 2e- to a 4e-donor as CO associates with the rhenium complex. The rate of reaction of 3 with CO showed a linear dependence on CO pressure between 1 and 10 atm, consistent with CO-promoted indenyl ring slippage. At very high CO pressure, 3 is rapidly converted to (η1-C9H7)(CO)4 Re(η2-MeC≡CMe) (12). Upon release of CO pressure, 12 reverts to a 12:1 mixture of starting material 3 and CO substitution product 8 at a rate that is inversely dependent on CO pressure. When the reaction of 13CO with 3 was carried to about 50% conversion, extensive labeling of starting material 3 and product 8 was observed. The distribution of label in 3 and 8 requires largely stereospecific 13CO addition to form mainly one isomer of an η3-indenyl intermediate (η3-C9H7)(CO)2(13-CO) Re(η2-MeC≡CMe) (B-(13CO)1) along with a minor amount of a second stereoisomer of B-(13CO)1 and the involvement of double-labeled η1-indenyl complex 12-(13CO)2. The reaction of 3 with PPh3 to form the phosphine complex (η5-C9H7)(CO)2 Re(PPh3) (9) is catalyzed by 13CO. The observation of 13CO in 9 is consistent with the proposal that 9 is formed by trapping a reactive intermediate in the CO substitution reaction of 3.
