Rhodium(III) Acyl Hydrido, Acyl Hydroxyalkyl, Diacyl, Acyl Hydrido Aldehyde, and Acyl Hydrido Alcohol Complexes. Reduction of Aldehyde to Alcohol through Rhodium Hydroxyalkyl Complexes
详细信息 查看全文
- 作者：Marí ; a A. Garralda ; Ricardo Herná ; ndez ; Lourdes Ibarlucea ; Elena Pinilla ; M. Rosario Torres ; Malkoa Zarandona
- 刊名：Organometallics
- 出版年：2007
- 出版时间：February 12, 2007
- 年：2007
- 卷：26
- 期：4
- 页码：1031 - 1038
- 全文大小：163K
- 年卷期：v.26,no.4(February 12, 2007)
- ISSN：1520-6041
文摘
[RhCl(COD)]2 (COD = 1,5-cyclooctadiene) reacts with o-(diphenylphosphino)benzaldehyde (PPh2(o-C6H4CHO)) (Rh/P = 1:1) in the presence of pyridine to give an acyl hydrido species, [RhHCl(PPh2(o-C6H4CO))(py)2] (1). In chlorinated solvents exchange of hydride by chloride gives [RhCl2(PPh2(o-C6H4CO))(py)2] (2). The reactions of 1 with PPh3 and of 2 with biacetyl dihydrazone (bdh) gives thepyridine substitution products [RhHCl(PPh2(o-C6H4CO))(PPh3)(py)] (4) and [RhCl2(PPh2(o-C6H4CO))(bdh)] (3), respectively. By using a 1:2 ratio of Rh to PPh2(o-C6H4CHO) [RhHCl(PPh2(o-C6H4CO))(
1-PPh2(o-C6H4CHO))(py)] (5) with trans phosphorus atoms is formed. The aldehyde group may undergotwo different reactions. In benzene 5 affords the acyl hydroxyalkyl species [RhCl(PPh2(o-C6H4CO))(PPh2(o-C6H4CHOH))(py)] (6) with cis phosphorus atoms, via a pyridine dissociation path. 6 undergoesdehydrogenation, with H2 evolution, to afford the diacyl derivative [RhCl(PPh2(o-C6H4CO))2(py)] (8),which shows fluxional behavior in solution, with the values 
H
= 8.8 ± 0.4 kcal mol-1 and S =-16.7 ± 1 eu. Opening of the acylphosphine chelate appears to be responsible for the fluxionality. Inmethanol 5 undergoes displacement of chloride by the aldehyde to afford the cationic acyl hydrido aldehyde[RhH(PPh2(o-C6H4CO))(2-PPh2(o-C6H4CHO))(py)]+ (10), which can be isolated if precipitated immediately with an appropriate counterion. Longer reaction periods of 5 in methanol solution lead to amixture of the diacyl 8 and the cationic acyl hydrido alcohol [RhH(PPh2(o-C6H4CO))(2-PPh2(o-C6H4CH2OH))(py)]+ (11). The spectroscopic characterization of some intermediates in this reaction evidencea bimolecular ionic mechanism as being responsible for the hydrogenation of the aldehyde with thehydroxyalkyl 6 being the source of both proton and hydride. Complex 11 can also be obtained by thereaction of 5 with NaBH4 in methanol solution.
1-PPh2(o-C6H4CHO))(py)] (5) with trans phosphorus atoms is formed. The aldehyde group may undergotwo different reactions. In benzene 5 affords the acyl hydroxyalkyl species [RhCl(PPh2(o-C6H4CO))(PPh2(o-C6H4CHOH))(py)] (6) with cis phosphorus atoms, via a pyridine dissociation path. 6 undergoesdehydrogenation, with H2 evolution, to afford the diacyl derivative [RhCl(PPh2(o-C6H4CO))2(py)] (8),which shows fluxional behavior in solution, with the values H = 8.8 ± 0.4 kcal mol-1 and S =-16.7 ± 1 eu. Opening of the acylphosphine chelate appears to be responsible for the fluxionality. Inmethanol 5 undergoes displacement of chloride by the aldehyde to afford the cationic acyl hydrido aldehyde[RhH(PPh2(o-C6H4CO))(2-PPh2(o-C6H4CHO))(py)]+ (10), which can be isolated if precipitated immediately with an appropriate counterion. Longer reaction periods of 5 in methanol solution lead to amixture of the diacyl 8 and the cationic acyl hydrido alcohol [RhH(PPh2(o-C6H4CO))(2-PPh2(o-C6H4CH2OH))(py)]+ (11). The spectroscopic characterization of some intermediates in this reaction evidencea bimolecular ionic mechanism as being responsible for the hydrogenation of the aldehyde with thehydroxyalkyl 6 being the source of both proton and hydride. Complex 11 can also be obtained by thereaction of 5 with NaBH4 in methanol solution.