929101-35-9Relevant academic research and scientific papers
Rhodium(III) acyl hydrido, acyl hydroxyalkyl, diacyl, acyl hydrido aldehyde, and acyl hydrido alcohol complexes. Reduction of aldehyde to alcohol through rhodium hydroxyalkyl complexes
Garralda, Maria A.,Hernandez, Ricardo,Ibarlucea, Lourdes,Pinilla, Elena,Rosario Torres,Zarandona, Malkoa
, p. 1031 - 1038 (2007)
[RhCl(COD)]2 (COD = 1,5-cyclooctadiene) reacts with o-(diphenylphosphino)benzaldehyde (PPh2-(o-C6H 4CHO)) (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 the pyridine 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-C 6H4CHO) [RhHCl(PPh2(o-C6H 4CO))(κ1-PPh2(o-C6H 4CHO))(py)] (5) with trans phosphorus atoms is formed. The aldehyde group may undergo two 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 undergoes dehydrogenation, with H2 evolution, to afford the diacyl derivative [RhCl(PPh 2(o-C6H4CO))2(py)] (8), which shows fluxional behavior in solution, with the values ΔH? = 8.8 ± 0.4 kcal mol-1 and ΔS? = - 16.7 ± 1 eu. Opening of the acylphosphine chelate appears to be responsible for the fluxionality. In methanol 5 undergoes displacement of chloride by the aldehyde to afford the cationic acyl hydrido aldehyde [RhH(PPh 2(o-C6H4CO))(κ2-PPh 2(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 a mixture of the diacyl 8 and the cationic acyl hydrido alcohol [RhH(PPh2(o-C6H 4CO))(κ2-PPh2(o-C6H 4-CH2OH))(py)]+ (11). The spectroscopic characterization of some intermediates in this reaction evidence a bimolecular ionic mechanism as being responsible for the hydrogenation of the aldehyde with the hydroxyalkyl 6 being the source of both proton and hydride. Complex 11 can also be obtained by the reaction of 5 with NaBH4 in methanol solution.
