Indenyl Rhenium Alkyne Complexes:  CO Substitution via Alkyne-Assisted Ring Slippage and CO-Catalyzed Phosphine Substitution

• Published in: Organometallics Vol. 22; no. 6; pp. 1183 - 1195
• Main Authors: Casey, Charles P, Vos, Thomas E, Brady, John T, Hayashi, Randy K
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 17.03.2003; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Physical Sciences; Science & Technology; CYCLOPENTADIENYL; MECHANISM; HETEROBIMETALLIC DIHYDRIDE; KINETICS; ENHANCEMENT
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om020884q

CO substitution of the indenyl alkyne complex (η5-C9H7)(CO)2Re(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)2Re(η2-cis-MeHCCHMe) (2) or the cyclopentadienyl alkyne complex (η5-C5H5)(CO)2Re(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)4Re(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(13CO)Re(η2-MeC⋮CMe) (B - ( 13 CO) 1 ) along with a minor amount of a second stereoisomer of B - ( 13 CO) 1 and the involvement of double-labeled η1-indenyl complex 12-( 13 CO) 2 . The reaction of 3 with PPh3 to form the phosphine complex (η5-C9H7)(CO)2Re(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.