Base-catalyzed dinitrogen cleavage by molybdenum amides

Abstract

The amides Mo(NRAr) 3 (R=CMe 3 or C(CD 3) 2CH 3, Ar=3,5-C 6H 3Me 2) and HMo(η 2-Me 2CNAr)(NRAr) 2 (R=CHMe 2 or CH(CD 3) 2, Ar=3,5-C 6H 3Me 2) are known to effect the six-electron reductive cleavage of dinitrogen in the absence of added reagents to provide terminal nitrido molybdenum complexes of formula NMo(NRAr) 3. However, this reaction typically has required a lengthy incubation period at −35 °C during which N 2 uptake takes place. This work reports on the catalytic effect of addition of stoichiometric amounts of N-heterocyclic bases such as 2,6-dimethylpyrazine, 1-methylimidazole, 4-dimethylaminopyridine (DMAP), and pyridine itself. Certain combinations of molybdenum amide and base lead to complete conversion to NMo(NRAr) 3 within minutes at 25 °C, 1 atm of N 2, in ether or n-pentane solution. Monitoring of reaction progress and probing for possible intermediates has been carried out using 2H NMR spectroscopy, while taking advantage of samples labeled with CD 3 groups. In some cases the 2H NMR data are in accord with intermediate base adduct formation, while in other cases adducts are not observed. The effect of potassium hydride in THF as the added base similarly has been investigated.