Alkylation of Dinitrogen in [(HIPTNCH[subscript 2]CH[subscript 2])[subscript 3]N]Mo Complexes (HIPT = 3,5-(2,4,6-i-Pr[subscript 3]C[subscript 6]H[subscript 2])[subscript 2]C[subscript 6]H[subscript 3])

Abstract

In this paper we explore the ethylation of dinitrogen (employing [Et[subscript 3]O][BAr[f over 4]]; Ar[superscript f] = 3,5-(CF[subscript 3])[subscript 2]C[subscript 6]H[subscript 3]) in [HIPTN[subscript 3]N]Mo (Mo) complexes ([HIPTN[subscript 3]N][superscript 3−] = [N(CH[subscript 2]CH[subscript 2]NHIPT)[subscript 3]][superscript 3−]; HIPT = 3,5-(2,4,6-i-Pr[subscript 3]C[subscript 6]H[subscript 2])[subscript 2]C[subscript 6]H[subscript 3]) with the objective of developing a catalytic cycle for the conversion of dinitrogen into triethylamine. A number of possible intermediates in a hypothetical catalytic cycle have been isolated and characterized: MoN═NEt, [Mo═NNEt[subscript 2]][BAr[f over 4]], Mo═NNEt[subscript 2], [Mo═NEt][BAr[f over 4]], Mo═NEt, MoNEt[subscript 2], and [Mo(NEt[subscript 3])][BAr[f over 4]]. Except for MoNEt[subscript 2], all compounds were synthesized from other proposed intermediates in a hypothetical catalytic reaction. All alkylated species are significantly more stable than their protonated counterparts, especially the Mo(V) species, Mo═NNEt[subscript 2] and Mo═NEt. The tendency for both Mo═NNEt[subscript 2] and Mo═NEt to be readily oxidized by [Et[subscript 3]O][BAr[f over 4]] (as well as by [H(Et[subscript 2]O)[subscript 2]][BAr[f over 4]], [Mo═NNH[subscript 2]][BAr[f over 4]], and [Mo═NH][BAr[f over 4]]) suggests that their alkylation is unlikely to be part of a catalytic cycle. All efforts to generate NEt[subscript 3] in several stoichiometric or catalytic runs employing MoN[subscript 2] and Mo≡N as starting materials were unsuccessful, in part because of the slow speed of most alkylations relative to protonations. In related chemistry that employs a ligand containing 3,5-(4-t-BuC[subscript 6]H[subscript 4])[subscript 2]C[subscript 6]H[subscript 3] amido substituents alkylations were much faster, but a preliminary exploration revealed no evidence of catalytic formation of triethylamine.