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Reduction of Metal‐Stabilized α‐CF 3 ‐Carbenium Ion Complexes under Mild Conditions: Synthesis, Structures, and Reactivity
Author(s) -
Gruselle Michel,
Malézieux Bernard,
Andrés Román,
Amouri Hani,
Vaissermann Jacqueline,
Melikyan Gagik G.
Publication year - 2000
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(200002)2000:2<359::aid-ejic359>3.0.co;2-v
Subject(s) - chemistry , alkyne , adduct , medicinal chemistry , propargyl alcohol , protonation , diastereomer , propargyl , stereochemistry , reactivity (psychology) , ion , organic chemistry , catalysis , medicine , alternative medicine , pathology
Complexed α‐CF 3 propargyl alcohols of the general formula [(M 2 L 6 ){μ‐η 2 ,η 2 ‐RC≡CCH(CF 3 )(OH)}] were prepared with M 2 L 6 = Co 2 (CO) 6 , R = CH 3 (CH 2 ) 4 – ( 1 ), R = C 6 H 5 – ( 2 ); M 2 L 6 = Co 2 (CO) 5 P(C 6 H 5 ) 3 , R = CH 3 (CH 2 ) 4 – ( 3a , b ), R = C 6 H 5 – ( 4a , b ); M 2 L 6 = Co 2 (CO) 4 dppm, R = C 6 H 5 – ( 5 ); M 2 L 6 = Co(CO) 3 MoCp(CO) 2 , R = CH 3 (CH 2 ) 4 – ( 6a , b ), R = C 6 H 5 – ( 7a , b ). An X‐ray molecular structure of the propargyl‐alcohol complex [{Co 2 (CO) 4 dppm}{μ‐η 2 ,η 2 ‐C 6 H 5 C≡CCH(CF 3 )(OH)}] ( 5 ) was also determined. The related carbenium ions [(M 2 L 6 ){μ‐η 2 ,η 3 ‐RC≡CCH(CF 3 )}][BF 4 ] ( 8–12 ) were obtained from the parent propargyl alcohol complexes by direct protonation with HBF 4 · Et 2 O in diethyl ether. These carbenium ions were reduced further by Zn in CH 2 Cl 2 to give the alkyne adducts [(M 2 L 6 ){μ‐η 2 ,η 2 ‐RC≡CCH 2 (CF 3 )}] ( 13–17 ), as confirmed by the X‐ray molecular structure of [(Co 2 (CO) 4 dppm){μ‐η 2 ,η 2 ‐C 6 H 5 C≡CCH 2 (CF 3 )}] ( 17 ). Treatment of the carbenium ion complex [{Co(CO) 3 MoCp(CO) 2 }{μ‐η 2 ,η 3 ‐CH 3 (CH 2 ) 4 C≡CCH(CF 3 )}][BF 4 ] ( 8 ) with NaSMe unexpectedly afforded the reduced alkyne adduct [{Co(CO) 3 MoCp(CO) 2 }{μ‐η 2 ,η 2 ‐CH 3 (CH 2 ) 4 C≡CCH 2 (CF 3 )}] ( 13 ), along with the alkyne‐thioether diastereomers {Co(CO) 3 MoCp(CO) 2 }{μ‐η 2 ,η 2 ‐CH 3 (CH 2 ) 4 C≡CCH(CF 3 )[(SMe)}] ( 18a , b ). Presumably, all the reduction reactions proceed primarily by the formation of the transient radical species, which are subsequently transformed into the reduced alkyne complexes by hydrogen abstraction from the solvent medium. Interestingly, in the case of the complexed alcohols [{Co 2 (CO) 5 P(C 6 H 5 ) 3 }{μ‐η 2 ,η 2 ‐RC≡CCH(CF 3 )(OH)}] ( 3a , b ) and ( 4a , b ), the reduction process occurs in acidic medium in THF/CH 2 Cl 2 . An extensive study of the electronic and steric factors that influence the stability and reactivity of the carbenium ions were performed, which allowed us to explain the behavior of the related radical species in solution during the reduction process.