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The steric tuning of a tridentate acridane‐derived NNN pincer ligand allows for the isolation of a strictly T‐shaped phosphine that exhibits ambiphilic reactivity. Well‐defined phosphorus‐centered reactivity towards nucleophiles and electrophiles is reported, contrasting with prior reports on this class of compounds. Reactions towards oxidants are also described. The latter result in the two‐electron oxidation of the phosphorus atom from +III to +V and are accompanied by a strong geometric distortion of the NNN pincer ligand. By contrast, cooperative activation of E−H (HCl, HBcat, HOMe) bonds proceeds with retention of the phosphorus redox state. When using H2O as a substrate, the reaction results in the full disassembly of H2O to its constituent atoms, highlighting the potential of this platform for small molecule activation reactions. [ABSTRACT FROM AUTHOR]

The reaction of [V(PS3")]− (1) (PS3"=[P(C6H3‐3‐Me3Si‐2‐S)3]3−) with H2O led to the formation of [VIV(PS3")(PS2"SH)]− (2) (PS2"SH=[P(C6H3‐3‐Me3Si‐2‐S)2(C6H3‐3‐Me3Si‐2‐SH)]2−), indicating a hydrogen atom transfer from H2O to a bound thiolate in 1. Furthermore, the reaction of 1 with CH3OH gave the generation of complexes 2 and 3, [VIV(PS3")(PS2"SCH3)]− (PS2"SCH3=[P(C6H3‐3‐Me3Si‐2‐S)2(C6H3‐3‐Me3Si‐2‐SCH3)]2−), implying that C−O and O−H bonds are cleaved by 1. Quantum mechanical calculations were performed to provide the mechanistic understanding for the reactivity of 1 with water. A key transition state with a lower kinetic barrier is identified. It involves an O−H bond cleavage by a dissociated thiyl radical with an interaction between an OH group and a neighboring bound sulfur donor. To our knowledge, the reactivity of 1 represents a new mode for water activation conducted through cooperation between a metal‐stabilized thiyl radical and a neighboring thiolato donor. A metal‐bound thiyl radical is capable of activating H2O and CH3OH through the homolytic cleavage of O−H and C−O bonds, leading to the formation of thiol and methyl thioether. The system also represents a new type of transformation for water activation conducted through cooperation between a metal‐stabilized thiyl radical and a neighboring thiolato donor. [ABSTRACT FROM AUTHOR]

The NiII complex 1 containing pyridyl- and hydroxy-functionalized N-heterocyclic carbenes (NHCs) is synthesized and its catalytic utility for the selective nitrile hydration to the corresponding amide under base-free conditions is evaluated. The title compound exploits a hemilabile pyridyl unit to interact with a catalytically relevant water molecule through hydrogen-bonding and promotes a nucleophilic water attack to the nitrile. A wide variety of nitriles is hydrated to the corresponding amides including the pharmaceutical drugs rufinamide, Rifater, and piracetam. Synthetically challenging α-hydroxyamides are accessed from cyanohydrins under neutral conditions. Related catalysts that lack the pyridyl unit (i.e., compounds 2 and 4) are not active whereas those containing both the pyridyl and the hydroxy or only the pyridyl pendant (i.e., compounds 1 and 3) show substantial activity. The linkage isomer 1′ where the hydroxy group is bound to the metal instead of the pyridyl group was isolated under different crystallization conditions insinuating a ligand hemilabile behavior. Additional p Ka measurements reveal an accessible pyridyl unit under the catalytic conditions. Kinetic studies support a ligand-promoted nucleophilic water addition to a metal-bound nitrile group. This work reports a Ni-based catalyst that exhibits functional hemilability for hydration chemistry. [ABSTRACT FROM AUTHOR]

Our recently synthesised phosphorus dication is observed to activate water (and methanol) under reactions conditions atypical for other systems containing a non-metal centre. This particular activation described as oxidative addition is quite rare and has been reserved exclusively for a couple of metal-based compounds. [ABSTRACT FROM AUTHOR]

A detailed mechanism of hydrogen production by reduction of water with decamethyltitanocene triflate [Cp*2TiIII(OTf)] has been derived for the first time, based on a comprehensive in situ spectroscopic study including EPR and ATR-FTIR spectroscopy supported by DFT calculations. It is demonstrated that two H2O molecules coordinate to [Cp*2TiIII(OTf)] subsequently forming [Cp2*TiIII(H2O)(OTf)] and [Cp*TiIII(H2O)2(OTf)]. Triflate stabilizes the water ligands by hydrogen bonding. Liberation of hydrogen proceeds only from the diaqua complex [Cp*TiIII(H2O)2(OTf)] and involves, most probably, abstraction and recombination of two H atoms from two molecules of [Cp*TiIII(H2O)2(OTf)] in close vicinity, which is driven by the formation of a strong covalent TiOH bond in the resulting final product [Cp*2TiIV(OTf)(OH)]. [ABSTRACT FROM AUTHOR]