Ruthenium-Induced Decomposition of Hexamethylenetetramine as a Tool for the Acid-Free Sommelet Reaction in Aqueous Medium.

Hexamethylenetetramine (HMTA) is one of the most versatile and most utilized nitrogen-containing heterocyclic compounds in academia and industry. Most of the reactions involving HMTA employ stoichiometric or excess amounts of acid, which hamper the sustainability of the reactions. Herein, we report the first example of the ruthenium-mediated decomposition of HMTA at room temperature, supported by a detailed mechanistic study using thermogravimetric analysis/differential thermal analysis, variable-temperature NMR, UV-vis spectroscopy, and density functional theory techniques. The mechanism study also involves a comparison of the decomposition of HMTA, protonated HMTA, [RuCl3(HMTA)], and [FeCl3(HMTA)], which revealed that [RuCl3(HMTA)] decomposes at the lowest temperature and has the lowest HOMO-LUMO band gap of 2.66 eV. The ruthenium-induced decomposition of HMTA is successfully used as a tool to increase the sustainability of the Sommelet reaction as it employs simple RuCl3·nH2O as a catalyst in as low as 0.5 mol % concentration in aqueous medium. The developed methodology is found to be very selective and efficient even for the very challenging substrates, namely, aliphatic aldehydes and substrates with electron-withdrawing substituents. The findings of this work are the first of its kind in which ruthenium is employed in the Sommelet reaction and also provide a possible platform to improve the sustainability of all reactions involving HMTA as a reactant/reagent.

Extending the chemistry of carbones: P-N bond cleavage via an S(N)2'-like mechanism.

The reactivity of nucleophilic carbodiphosphorane (C(PPh3)2, 1) and carbodicarbene (C(C(NMe)2C6H4)2, 2) towards various dichlorophosphines has been explored. In most cases the expected carbone-for-chloride ligand exchange was observed. However, the use of MeN(PCl2)2 resulted in a unique P-N bond cleavage that, according to computational studies, occurred via an SN2'-like mechanism.

C-F bond activation by transient phosphenium dications.

C-F bond cleavage by transient phosphorus(III)-based dications [RP(C(PPh3)2)](2+) (4a(2+), R = Ph; 4b(2+), R = 4-F-Ph) is reported. These dications were generated by reaction of the corresponding monocationic precursors with excess Na[BAr4(Cl)]. Evidence for the existence of transient dicationic species was obtained by trapping the dication 4a(2+) with PMe3. According to theoretical analysis, the low-lying lowest unoccupied molecular orbitals of these species were responsible for the observed activation of C-F bonds.

Direct amide synthesis from either alcohols or aldehydes with amines: activity of Ru(II) hydride and Ru(0) complexes.

An in situ generated catalyst from readily available RuH(2)(PPh(3))(4), an N-heterocyclic carbene (NHC) precursor, NaH, and acetonitrile was developed. The catalyst showed high activity for the amide synthesis directly from either alcohols or aldehydes with amines. When a mixture of an alcohol and an aldehyde was reacted with an amine, both of the corresponding amides were obtained with good yields. Homogeneous Ru(0) complexes such as (eta(4)-1,5-cyclooctadiene)(eta(6)-1,3,5-cyclooctatriene)ruthenium [Ru(cod)(cot)] and Ru(3)(CO)(12) were also active in the amidation of an alcohol or an aldehyde with the help of an in situ generated NHC ligand.