SYNTHESIS OF ETA(3)-PROPARGYL RHENIUM COMPLEXES

Hybride abstraction from eta(2)-alkyne rhenium complexes C(5)Me(5)(CO) (2)Re(RC=CR') (2) with Ph(3)C(+)PF(6)(-) produces eta(3)-propargyl com plexes C(5)Me(5)(CO)(2)Re(eta(3)-CHR ''-C=CR)(PF6-)-P-+ (3). Successfu l hydride abstraction to produce eta(3)-propargyl complexes was observ ed only for internal acetylenes with a methyl or primary alkyl substit uent. an unusual regioselectivity for hydride abstraction was observed : CH3CH2>CH3 much greater than CH(CH3)(2). Hydride abstraction from di ethylacetylene complex C(5)Me(5)(CO)(2)Re(eta(2)-CH3CH2C=CCH2CH3) (2c) produced a single stereoisomer of eta(3)-propargyl complex 5)Me(5)(CO )(2)Re(eta(3)-CH3CH-C=CCH2CH3)(PF6-)-P-+ (3c) in which it is suggested that the methyl group is located in the less crowded position anti to the Cp group. the regio- and stereoselectivity of hydride abstractio n can be explained in terms of transition stat A in which the carbon h ydrogen bond being cleaved is antiperiplanar with respect to rhenium a nd the syn propargylic substituent comes into close contact with the C p ligand. Protonation of C(5)Me(5)(CO)(2)Re(eta(2)-HC=CCH2OH) (6h) wi th HBF4-Et(2)O gave CO)(2)Re(eta(3)-CH2-Me(5)(CO)(2)Re(eta(2)-HC=CCH3) (2h). Protonation of propargyl alcohol complexes provides a regiospec ific synthesis of pi-propargyl complexes: protonation of C(5)Me(5)(CO) (2)Re(eta(2)-CH3CH2C=CCH2OH) (6e) gave C(5)Me(5)(CO)(2)Re(eta(3)-CH2-C =CCH2CH3)(BF4-)-B-+ (3c-BF4), while protonation of C(5)Me(5)(CO)(2)Re[ eta(2)-CH3C=CCH(CH3)OH] (6d) gave C-5-Me(5)(CO)(2)Re(eta(3)-CH3CH-C=CC H3)(BF4-)-B-+ (anti-ed-BF4).