SYNTHESIS, STRUCTURE, AND ALKYLATION OF CHIRAL VINYLRHENIUM COMPLEXES (ETA-5-C5H5)RE(NO)(PPH3)(CX=CHR) (X = H, OCH3) - A MECHANISTIC STUDY OF 1,3-ASYMMETRIC INDUCTION FROM RHENIUM TO CARBON
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Reaction of alkylidene complexes [(775-C5H5)Re(NO)(PPh3)(=CHCH2R)]+PF6(1-PF6_; a, R = H; b, R = CH3; c, R = CH2CH2CH3; d, R = CH2C6H5) with DBU or f-BuO~K+gives vinyl complexes (')-(r?5-C5H5)Re(NO)(PPh3)(CH=CHR) (()-2a-d ; 72-86%). Complexes ()-2b-d equilibrate to 8492:168 E/Z mixtures in solution. Complex ()-2b reacts with CF3SO3H and CH30S02F to give ethylidene complex lb-CF3SOf and isobutylidene complex [(r?5-C5H5)Re(NO)(PPh3)-(=CHCH(CH3)2)]+FS03-(3-FSOf; ca. 65%) and with CF3S03D and CD30S02F to give mainly (SR,RS)-\\\\-^d-CF3SOf and (SS,#/?H(775-C5H5)Re(N0)(PPh3)(=CHCH(CH3)(CD3))]+FS03 However, experimental problems hinder quantification of the 1,3-asymmetric induction. Reaction of 3-FS03-and ?-BuOK+gives isobutenyl complex (775-C5H5)Re(NO)(PPh3)-(CH=C(CH3)2) (4, 60% from 2b), which in turn reacts with CH30S02F to give neopentylidene complex [(775-C5H5)Re-(N0)(PPh3)(=CH(CH3)3)]+FS03 (90%). Complex 2a and Ph3C+PF6 react to give alkylidene complex [(i75-C5H5)Re-(NO)(PPh3)(CHCH2CPh3)]+PF6 (81%), which in turn reacts with r-BuO~K+to give vinyl complex ()-(ij5-C5H5)Re-(NO)(PPh3)(CHCHCPh3) (74%). Reactions of methoxycarbene complexes [(7j5-C5H5)Re(NO)(PPh3)(=C(OCH3)-CH2R)]+PF6 with NaH or DBU give a-methoxyvinyl complexes (2)-(7?5-C5H5)Re(NO)(PPh3)(C(OCH3)=CHR) ((Z)-10a,b,d,e (R = C6H5)) in high yields. These are more nucleophilic than (')-2a-d and react with alkyl iodides RT to give methoxycarbene complexes [(7j5-C5H5)Re(NO)(PPh3)(=C(OCH3)CHRR')]+I-that readily demethylate to acyl complexes (775-C5H5)Re-(NO)(PPh3)(COCHRR0. Thus, (Z)-10b and C6H5CH2Br react to give (5^,^5)-(7?s-C5H5)Re(NO)(PPh3)(COCH-(CH3)(CH2C6H5)) ((SR,RS)-13; 71%), and (Z)-10d and CH31 react to give (SS,RR)A3 (88%; both diastereomers of >98% purity). Crystal structures of ()-2d and (Z)-10d and extended Hiickel MO calculations on Re-Carotamers of (77s-C5H5)Re(NO)(PH3)(CX=CH2) (X = H, OH) are also described. Data are consistent with the following model for 1,3-asymmetric induction: electrophiles attack a Re-Carotamer with the ON-Re-C^-C^ torsion angle (6) close to 0 and on the C=C face opposite the bulky PPh3ligand. 1987, American Chemical Society. All rights reserved.
