Catalytic Ambient Temperature Dinitrogen Conversion to a Bis(silyl)amine by Mononuclear Group 4 Aryloxide Complexes

The homogeneous conversion of ambient dinitrogen to amine products via the N 2 reduction reaction (N 2 RR) remains a prized yet challenging feat for d-block complexes and is scarcely reported for f-block complexes. New, mononuclear Ti IV and Zr IV aryloxide complexes Ti(DP) 2 ( 1Ti ), Zr(DP) 2 ( 1Zr ), and DP = [2-(OC 6 H 2 -2- t Bu,4-Me) 2 CHPh] produce up to 51 eq. and up to 7.0 eq. of HN(SiMe 3 ) 2 per Ti/Zr, from N 2, K 0, weak acid, and chlorotrimethylsilane. Complex 1Ti exhibits more than double the activity toward N 2 -silylation of any previously reported Ti N 2 RR catalyst and can also catalyze the formation of up to 19 eq. of NH 3, a new feature in early metal N 2 RR chemistry. The mononuclear 1Zr is the most active Zr catalyst for N 2 -silylation to date. [KSm(DP) 2 (THF) 3 ] ( 1Sm ), the mononuclear analogue of our previously reported dinuclear A-Sm complex, displays only stoichiometric N 2 -silylation due to its vulnerability to deleterious side reactions. DFT calculations confirm the catalysis can proceed via a monomeric Ti complex with a terminally bound, activated N 2, agreeing with experimental 1 H DOSY NMR measurements; the N–H bond is formed first, directing the catalyst selectivity. The isolable reduction product [K 3 (THF)Ti(DP)(DP – )(N 2 )] is also an active catalyst, and an intermediate in the calculated cycle.