SYNTHESIS, STRUCTURE, AND REACTIVITY OF ALLENE COMPLEXES OF THE CHIRAL RHENIUM FRAGMENT [(ETA-5-C5H5)RE(NO)(PPH3)]+
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Reactions of the chlorobenzene complex [(5-C5H5)Re(NO)(PPh3)(ClC6H5)]+BF4 and excess (a) allene, (b) methylallene, and (c) 1,1-dimethylallene give the adducts [(5-C5H5)Re(NO)(PPh3) (PPh3) (2-H2C=C= CRR')]+BF4 (1a-c) in 90-91% yields. The crystal structure of 1a (monodinic, P21/n, a = 10.327 (1) , b = 10.401 (1) , c = 23.919 (2) , = 99.233 (2), Z = 4) shows the coordinated =CH2 group to be syn to the PPh3 ligand, with a 23.7 angle between the ReP bond and the ReC=C plane. NMR data show that the methyl groups in 1b,c occupy the less hindered positions on the free C=C linkages. Analogous reactions of chiral 1,3-dialkylallenes give mixtures of diastereomeric adducts with modest selectivities. Reaction of 1a and t-BuOK+ in THF (80 to +25 C) gives the methylacetylide complex (5-C5H5)Re-(NO)(PPh3)(CCCH3) (3, 92%). A similar reaction of 1a and CH3Li gives the allenyl complex (5-C5H5)Re(NO)(PPh3)(CH=C=CH2) (4, 70%), which upon treatment with HBF4OEt2 gives mainly the propyne complex [(5-C5H5)Re(NO)(PPh3)(HCCCH3)]+BF4 (5). Reaction of Li+[(5-C5H5)Re(NO)(PPh3)] and HCCCH2OTs gives the propargyl complex (5-C5H5)Re(NO)(PPh3)(CH2CCH), which isomerizes to 4 at 67-80 C. Thus, the conversion of 1a to 3 is proposed to involve 4 and 5 as intermediates. 1992, American Chemical Society. All rights reserved.
