Neutral and Anionic Monomeric Zirconium Imides Prepared via Selective C=N Bond Cleavage of a Multidentate and Sterically Demanding β‐Diketiminato Ligand

A sterically encumbering multidentate β‐diketiminato ligand, ^tBuL2 (^tBuL2=ArNC(tBu)CHC(tBu)NCH₂CH₂N(Me)CH₂CH₂NMe₂]^?, Ar=2,6‐iPr₂C₆H₃), is reported in this study along with its coordination chemistry to zirconium(IV). Using the lithio salt of this ligand, Li(^tBuL2) ( 4 ), the zirconium(IV) precursor (^tBuL2)ZrCl₃ ( 6 ) could be readily prepared in 85 % yield and structurally characterized. Reduction of 6 with 2 equiv of KC₈ resulted in formation of the terminal and mononuclear zirconium imide‐chloride C(tBu)CHC(tBu)NCH₂CH₂N(Me)CH₂CH₂NMe₂]Zr(=NAr)(Cl) ( 7 ) as the result of reductive C=N cleavage of the imino fragment in the multidentate ligand ^tBuL2 by an elusive Zr^II species (^tBuL2)ZrCl ( A ). The azabutadienyl ligand in 7 can be further reduced by 2 e^? with KC₈ to afford the anionic imide K(THF)₂]{CH(tBu)CHC(tBu)NCH₂CH₂N(Me)CH₂CH₂N(Me)CH₂]Zr=NAr} ( 8‐2THF ) in 42 % isolated yield. Complex 8‐2THF results from the oxidative addition of an amine C?H bond followed by migration to the vinylic group of the formal C(tBu)CHC(tBu)NCH₂CH₂N(Me)CH₂CH₂NMe₂]^? ligand in 7 . All halides in 6 can be replaced with azides to afford (^tBuL2)Zr(N₃)₃ ( 9 ) which was structurally characterized, and reduction with two equiv of KC₈ also results in C=N bond cleavage of ^tBuL2 to form C(tBu)CHC(tBu)NCH₂CH₂N(Me)CH₂CH₂NMe₂]Zr(=NAr)(N₃) ( 10 ), instead of the expected azide disproportionation to N^3? and N₂. Solid‐state single crystal structural studies confirm the formation of mononuclear and terminal zirconium imido groups in 7 , 8‐Et₂O , and 10 with Zr=NAr distances being 1.8776(10), 1.9505(15), and 1.881(3) Å, respectively.