Use of N NMR spectroscopy to probe covalency in a thorium nitride.

Reaction of the thorium metallacycle, [Th{N(R)(SiMe)CH}(NR)] (R = SiMe) with 1 equiv. of NaNH in THF, in the presence of 18-crown-6, results in formation of the bridged thorium nitride complex, [Na(18-crown-6)(EtO)][(RN)Th(μ-N)(Th(NR)] (), which can be isolated in 66% yield after work-up. Complex is the first isolable molecular thorium nitride complex. Mechanistic studies suggest that the first step of the reaction is deprotonation of [Th{N(R)(SiMe)CH}(NR)] by NaNH, which results in formation of the thorium bis(metallacycle) complex, [Na(THF) ][Th{N(R)(SiMeCH)}(NR)], and NH. NH then reacts with unreacted [Th{N(R)(SiMe)CH}(NR)], forming [Th(NR)(NH)] (), which protonates [Na(THF) ][Th{N(R)(SiMeCH)}(NR)] to give . Consistent with hypothesis, addition of excess NH to a THF solution of [Th{N(R)(SiMe)CH}(NR)] results in formation of [Th(NR)(NH)] (), which can be isolated in 51% yield after work-up. Furthermore, reaction of [K(DME)][Th{N(R)(SiMeCH)}(NR)] with , in THF- , results in clean formation of , according to H NMR spectroscopy. The electronic structures of and were investigated by N NMR spectroscopy and DFT calculations. This analysis reveals that the Th-N bond in features more covalency and a greater degree of bond multiplicity than the Th-NH bond in . Similarly, our analysis indicates a greater degree of covalency in comparable thorium imido and oxo complexes.