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, t Bu L2 ( t Bu L2=[ArNC( t Bu)CHC( t Bu)NCH 2 CH 2 N(Me)CH 2 CH 2 NMe 2 ] − , Ar=2,6‐ i Pr 2 C 6 H 3 ), is reported in this study along with its coordination chemistry to zirconium(IV). Using the lithio salt of this ligand, Li( t Bu L2) ( 4 ), the zirconium(IV) precursor ( t Bu L2)ZrCl 3 ( 6 ) could be readily prepared in 85 % yield and structurally characterized. Reduction of 6 with 2 equiv of KC 8 resulted in formation of the terminal and mononuclear zirconium imide‐chloride [C( t Bu)CHC( t Bu)NCH 2 CH 2 N(Me)CH 2 CH 2 NMe 2 ]Zr(=NAr)(Cl) ( 7 ) as the result of reductive C=N cleavage of the imino fragment in the multidentate ligand t Bu L2 by an elusive Zr II species ( t Bu L2)ZrCl ( A ). The azabutadienyl ligand in 7 can be further reduced by 2 e − with KC 8 to afford the anionic imide [K(THF) 2 ]{[CH( t Bu)CHC( t Bu)NCH 2 CH 2 N(Me)CH 2 CH 2 N(Me)CH 2 ]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( t Bu)CHC( t Bu)NCH 2 CH 2 N(Me)CH 2 CH 2 NMe 2 ] − ligand in 7 . All halides in 6 can be replaced with azides to afford ( t Bu L2)Zr(N 3 ) 3 ( 9 ) which was structurally characterized, and reduction with two equiv of KC 8 also results in C=N bond cleavage of t Bu L2 to form [C( t Bu)CHC( t Bu)NCH 2 CH 2 N(Me)CH 2 CH 2 NMe 2 ]Zr(=NAr)(N 3 ) ( 10 ), instead of the expected azide disproportionation to N 3− and N 2 . Solid‐state single crystal structural studies confirm the formation of mononuclear and terminal zirconium imido groups in 7 , 8‐Et 2 O , and 10 with Zr=NAr distances being 1.8776(10), 1.9505(15), and 1.881(3) Å, respectively.