SYNTHESIS, STRUCTURE, AND REACTIVITY OF THE FORMALDEHYDE COMPLEX [(ETA-5-C5H5)RE(NO)(PPH3)(ETA-2-H2C=O)]+PF6-
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Reaction of [(5-C5H5)Re(NO)(PPh3)(=CH2)]+PF6- with C6H5I+-O- gives formaldehyde complex [(5-C5H5)Re(NO)(PPh3 )(2-H2C=O)] +PF6- (1, 83%), which is characterized by X-ray crystallography. The 2-H2C=O ligand adopts a conformation such that overlap of its * orbital with the rhenium fragment HOMO is maximized, and its oxygen terminus is syn to the PPh3. Extended Huckel MO calculations on model compound [(5-C5H5)Re(NO)(PH3)(2-H2C=O)]+ predict a similar conformational energy minimum. Complex 1 slowly reacts with CD3CN (18 days, 25 C) to give [(5-C5H5)Re(NO)(PPh3)(CI)3CN)]+PF6- (2-d3, 67-92%) and rapidly reacts with Nal (acetone, 25 C) to precipitate [(5-C5H5)Re(NO)(PPh3)(2-H2C=O)]+I- (3, 68%). Addition of 3 to CH3OH rapidly gives (5-C5H5)Re(NO)(PPh3)(I) (4, 65%). Unlike previously synthesized (neutral) 2-H2C=O complexes, 1 undergoes nucleophilic additions but not well-defined electrophilic additions. Thus, addition of PR3 to 1 gives [(5-C5H5)Re(NO)(PPh3)(OCH2PR3)]+PF6- (5, R = Ph, 89%; 6, R = Me, 85%). Reaction of 1 with formyl complex (5-C5H5)Re(NO)(PPh3)(CHO) gives methoxide complex (5-C5H5)Re(NO)(PPh3)(OCH3) (7, 52%) and [(5-C5H5)Re(NO)(PPh3)(CO)]+PF6-. Attempted addition of (5-C5H5)Co(CO)(PMe3) to 1 in acetone-d6 gives [(5-C5H5)Re(NO)(PPh3)(1-(CD3)2C-O)]+PF6- (8-d6). The relationship of this chemistry to metal-catalyzed reactions involving formaldehyde is discussed. 1986, American Chemical Society. All rights reserved.
