Synthesis and reactivity of metallacyclic manganese .alpha.-hydroxyalkyl complexes containing aliphatic bridges and phosphorus and nitrogen donor atoms; first carbonylation of an isolable .alpha.-hydroxyalkyl complex
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Reaction of (CO)5MnH with (C6H5)2PCH2CH2CHO (3) gives cis-(CO)4Mn(H)P(C6H5)2CH2CH2CHO (4, 97%), which cannot be induced to cyclize to a-hydroxyalkyl complex (CO)4MnP(C6H5)2CH2CH2CHOH (5). Two other attempted syntheses of 5—the photochemical decarbonylation of hydroxyacyl complex (CO)4MnP(C6H5)2CH2CH2CH(OH)—C=O (7) and the BH3•THF reduction of acyl complex (CO)4MnP(C6H5)2CH2CH2C=O (8)—also give 4. However, analogues of 5 in which the phosphorus is replaced by nitrogen are stable. Complexes (CO)4MnNH2CHRCHR’CHOH (10a, R = R’ = H; 10b, R = CH3, R’ = H; 10c, R = R’ = -(CH2)4-) are prepared in ≥90% yields via BH3 reduction of the corresponding acyl complexes (CO)4MnNH2CHRCHR’—C=O (9a-c). Treatment of 10c with (CH3)3SiCl/[(CH3)3Si]2NH gives α-(silyloxy)alkyl complex (CO)4MnNH2CHRCHR’CHOSi(CH3)3(12, R = R’= -(CH2)4- 52%). Under 250–360 psi of CO in CH3NO2 at -3 °C, 10c and 12 carbonylate to acyl complexes (CO)4MnNH2CHRCHR’CH(OH)—C=O (11) and (CO)4MnNH2CHRCHR’CH(OSi(CH3)3)—C=O (13), respectively. The former reaction is ca. 16 times faster. IR (vO-H, vc=o) and 13C NMR spectra show the presence of a hydrogen bond between the hydroxyl and acyl oxygen in 11. This is proposed to account, at least in part, for the faster carbonylation of 10c. The possible relevance of these data to the metal-catalyzed conversion of CO/H2 to oxygenates is discussed. © 1986, American Chemical Society. All rights reserved.
author list (cited authors)
Vaughn, G. D., & Gladysz, J. A.