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 84—92:16—8 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 ?-BuO“K+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)(CH—CHCPh3) (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.
author list (cited authors)
Bodner, G. S., Smith, D. E., Hatton, W. G., Heah, P. C., Georgiou, S., Rheingold, A. L., ... Gladysz, J. A.