Papendick M, Gudat D. Reversible Binding of Hydrogen and Styrene Coordination on a Manganese Phosphenium Complex.
Chemistry 2023;
29:e202302525. [PMID:
37650872 DOI:
10.1002/chem.202302525]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Revised: 08/30/2023] [Accepted: 08/31/2023] [Indexed: 09/01/2023]
Abstract
The reactions of two complexes [(R NHP)Mn(CO)4 ] (R NHP=N-arylated N-heterocyclic phosphenium) with H2 at elevated pressure (≈4 bar) were studied by NMR spectroscopy. Irradiation with UV light initialized in one case (5 a, R=Dipp) the unselective formation of (R NHP-H)MnH(CO)4 ] (6 a) via cooperative addition of H2 across the Mn=P double bond. In the other case (5 b, R=Mes), addition of H2 was unobservable and the reaction proceeded via decarbonylation to a dimeric species [(R NHP)2 Mn2 (CO)7 ] (7 b) that was isolated and identified spectroscopically. Taking into account the outcome of further reaction studies under various conditions in the absence and presence of H2 , both transformations can be explained in the context of a common mechanism involving decarbonylation to 7 a,b as the first step, and the different outcome is attributable to the fact that 7 b is unreactive towards both H2 and CO while 7 a is not. DFT studies relate this divergence to deviations in the molecular constitution and stability arising from a different level of steric congestion. Preliminary studies suggest further that 5 a/H2 as well as 6 a enable the photo-induced hydrogenation of styrene to ethyl benzene, even if the mechanism and possibly catalytic nature of this process remain yet unknown.
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