Dorai Ramprasad

Hafnium(IV) and zirconium(IV) triflates as superior recyclable catalysts for the atom economic nitration of o-nitrotoluene

Abstract The hydrated group 4 metal triflates, Hf(OTf)4 and Zr(OTf)4, were found to be excellent catalysts (10 mol%) for the mononitration of o-nitrotoluene using a single equivalent of concentrated (69%) nitric acid. The only side product is water and the catalysts are readily recycled from the aqueous phase and re-used.

Lanthanide(iii) triflates as recyclable catalysts for atom economic aromatic nitration

Lanthanide(III) triflates catalyse (1–10 mol%) the nnitration of a range of simple aromatic compounds in good to excellent nyield using stoichiometric quantities of 69% nitric acid; the only nby-product is water and the catalyst can be readily recycled by simple nevaporation.

Lanthanide(III) and Group IV metal triflate catalysed electrophilic nitration: ‘nitrate capture’ and the rôle of the metal centre†

The lanthanide(III) triflate, [Ln(OH2)9](OTf)3 (Lnxa0=xa0La–Lu), catalysed nitration of a representative arene, viz. bromobenzene, is reported. The extent of nitration is found to be dependent on the charge-to-size ratio of the tripositive metal centre. A mechanistic scenario involving ‘nitrate capture’ in the auto-ionisation of nitric acid is presented where triflic acid plays a key role in the generation of the de facto nitration agent: the nitronium ion. Preparation of the putative intermediates, [(H2O)xLn(NO3)](OTf)2 (Lnxa0=xa0La–Lu), and characterisation by IR spectroscopy shows the nitrate anion is inner sphere and the triflate anions are outer sphere. Additionally, these salts show a steady increase in nitrate stretching IR frequencies as the charge-to-size ratio of the tripositive lanthanide increases, providing strong evidence for the nitrate capture model. Extrapolation to higher charge-to-size ratio predicts [Hf(OH2)x](OTf)4 to be a superior nitration catalyst. Experimental confirmation of theory is obtained by the application of [Hf(OH2)x](OTf)4 to the successful nitration of the strongly electron deficient arene o-nitrotoluene.

Solid state cyanocobaltates that reversibly bind dioxygen: synthesis, structure and reactivity relationships

New pentacyanocobaltate compositions, Li 3 Co(CN) 5 . 1.42DMF . 0.48DMAC (3) (DMF = N,N-dimethylformamide, DMAC = N,N-dimethylacetamide) and Mg 1.5 Co(CN) 5 . 2DMF (4) were prepared and as solids were found to reversibly bind dioxygen. Compound 3 was found to be more stable to repeated cycling between O 2 and N 2 atmospheres than the previously reported Li 3 Co(CN) 5 . 2DMF (2). The cyanide stretching frequencies of 3 and 4 are significantly higher than for (Et 4 N) 3 Co(CN) 5 , an irreversible O 2 sorbent. This is ascribed to a loss of electron density from cobalt due to interaction of cyanide with the cations Li(1 +) and Mg(2 +) resulting in reversible O 2 binding.

New Metal Complex Oxygen Absorbents for the Recovery of Oxygen

Emerging non-cryogenic technologies for the separation of air use zeolites and microporous “molecular sieve” carbons as moderately selective nitrogen and oxygen adsorbents, respectively.1,2 While the zeolites have a thermodynamic affinity for N2, use of carbons relies on a kinetic selectivity for the passage of oxygen into the micropores. It is well known that certain coordination compounds of cobalt and iron reversibly react with oxygen under near ambient conditions.3,4 Since this is a chemical rather than a physical interaction as is seen with zeolites and carbons, it should be possible to use such metal complexes as O2 equilibrium sorbents for air separation. We have been conducting a long term research effort to prepare such metal complex oxygen carriers for use in future generation non-cryogenic air separation devices.5 The primary interest in such complexes is in their use in pressure or temperature swing processes for the production of inert gas (N2,Ar) and oxygen.6,7 For these applications, the oxygen complex could either be used as a circulating liquid or as a solid sorbent. In order to be useful in a commercial process an oxygen complex has to satisfy several requirements. It must (a) bind O2 rapidly and reversibly, (b) have a high stability (>1 year lifetime), and (c) be accessible via simple synthetic techniques at minimal cost.