The Dichotomy of Mn-H Bond Cleavage and Kinetic Hydricity of Tricarbonyl Manganese Hydride Complexes

• Published in: Molecules (Basel, Switzerland) Vol. 28; no. 8; p. 3368
• Main Authors: Osipova, Elena S, Kovalenko, Sergey A, Gulyaeva, Ekaterina S, Kireev, Nikolay V, Pavlov, Alexander A, Filippov, Oleg A, Danshina, Anastasia A, Valyaev, Dmitry A, Canac, Yves, Shubina, Elena S, Belkova, Natalia V
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 11-04-2023; MDPI
• Subjects: Acidity; Chemical Sciences; Coordination chemistry; Equilibrium; hydricity; hydride transfer; hydrogen bond; Hydrogen bonds; Hydrogen ions; Hydrogenation; Lewis acid; Ligands; Manganese; manganese hydrides; Metal hydrides; NMR; non-covalent interactions; Nuclear magnetic resonance; or physical chemistry; Phosphorus; Polarity; proton transfer; Protons; Spectrum analysis; Theoretical and; Russia; proton transfer; manganese hydrides; non-covalent interactions; hydricity; hydride transfer; hydrogen bond; Hydride transfer; Non-covalent interactions; Hydricity; Manganese hydrides; Proton transfer; Hydrogen bond
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules28083368

Acid-base characteristics (acidity, p
a, and hydricity, ΔG°
or
) of metal hydride complexes could be a helpful value for forecasting their activity in various catalytic reactions. Polarity of the M-H bond may change radically at the stage of formation of a non-covalent adduct with an acidic/basic partner. This stage is responsible for subsequent hydrogen ion (hydride or proton) transfer. Here, the reaction of tricarbonyl manganese hydrides
,
-[L
Mn(CO)
H] (
; L = P(OPh)
,
; L = PPh
) and
-[(L-L')Mn(CO)
H] (
, L-L' = Ph
PCH
PPh
(dppm);
, L-L' = Ph
PCH
-NHC) with organic bases and Lewis acid (B(C
F
)
) was explored by spectroscopic (IR, NMR) methods to find the conditions for the Mn-H bond repolarization. Complex
, bearing phosphite ligands, features acidic properties (p
a 21.3) but can serve also as a hydride donor (ΔG
= 19.8 kcal/mol). Complex
with pronounced hydride character can be deprotonated with KHMDS at the CH
-bridge position in THF and at the Mn-H position in MeCN. The kinetic hydricity of manganese complexes
-
increases in the order
,
-[(P(OPh)
)
Mn(CO)
H] (
) <
,
-[(PPh
)
Mn(CO)
H] (
) ≈
-[(dppm)Mn(CO)
H] (
) <
-[(Ph
PCH
NHC)Mn(CO)
H] (
), corresponding to the gain of the phosphorus ligand electron-donor properties.