Alkylation of Dinitrogen in (HIPTNCH2CH2)3NMo Complexes (HIPT = 35-(246-i-Pr3C6H2)2C6H3)

摘要

In this paper we explore the ethylation of dinitrogen (employing [Et3O][BAr^f4]; Ar^f = 3,5-(CF3)2C6H3) in [HIPTN3N]Mo (>Mo) complexes ([HIPTN3N]^3- = [N(CH2CH2NHIPT)3]^3-; HIPT = 3,5-(2,4,6-i-Pr3C6H2)2C6H₃) 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; they are >MoN=NEt, [>Mo=NNEt₂][BAr^f₄], >Mo=NNEt₂, [>Mo=NEt][BAr^f₄], >Mo=NEt, >MoNEt₂, and [>Mo(NEt₃)][BAr^f₄]. Except for >MoNEt₂, 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=NNEt₂ and >Mo=NEt. The tendency for both >Mo=NNEt₂ and >Mo=NEt to be readily oxidized by [Et₃O][BAr^f₄] (as well as by [H(Et₂O)₂][BAr^f₄], [>Mo=NNH₂][BAr^f₄], and [>Mo=NH][BAr^f₄]) suggest that their alkylation is unlikely to be part of a catalytic cycle. All efforts to generate NEt₃ in several stoichiometric or catalytic runs employing >MoN₂ 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-BuC₆H₄)₂C₆H₃ amido substituents alkylations were much faster, but a preliminary exploration revealed no evidence of catalytic formation of triethylamine.