Nitrogen activation and cleavage by a multimetallic uranium complex

<p>Multimetallic-multielectron cooperativity plays a key role in the metal-mediated cleavage of N2&nbsp;to nitrides&nbsp;(N3-)&nbsp;In particular, low-valent uranium complexes coupled with strong alkali metal reducing agents can&nbsp;lead to N2&nbsp;cleavage, but often, it is ambiguous how many electrons are transferred from the uranium&nbsp;centers to cleave N2. Herein, we designed new dinuclear uranium nitride complexes presenting&nbsp;a combination of electronically diverse ancillary ligands to promote the multielectron transformation of&nbsp;N2. Two heteroleptic diuranium nitride complexes, [K{UIV(OSi(OtBu)3)(N(SiMe3)2)2}2(m-N)] (1) and&nbsp;[Cs{UIV(OSi(OtBu)3)2(N(SiMe3)2)}2(u-N)] (3-Cs), containing different combinations of OSi(OtBu)3&nbsp;and N(SiMe3)2&nbsp;ancillary ligands, were synthesized. We found that both complexes could be reduced to their U(III)/U(IV)&nbsp;analogues, and the complex, [K2{UIV/III(OSi(OtBu)3)2(N(SiMe3)2)}2(m-N)] (6-K), could be further reduced to&nbsp;a putative U(III)/U(III) species that is capable of promoting the 4e&nbsp;reduction of N , yielding the&nbsp;N24- complex [K3{UV(OSi(OtBu)3)2(N(SiMe3)2)}2(m-N)(m-h2:h2-N2)],&nbsp;7. Parallel N2&nbsp;reduction pathways were also identified, leading to the isolation of N2&nbsp;cleavage products, [K3{UVI(OSi(OtBu)3)2(N(SiMe3)2)(^N)}(m- N)2{UV(OSi(OtBu)3)2(N(SiMe3)2)}]2,&nbsp;8, and&nbsp;[K4{(OSi(OtBu)3)2UV)(^N)}(m-NH)(m-k2:C,N-CH2SiMe2NSiMe3)- {UV(OSi(OtBu)3)2][K(N(SiMe3)2]2,&nbsp;9. These complexes provide the&nbsp;first example of N2&nbsp;cleavage to nitride by a uranium complex in the absence of reducing alkali metals,</p>