The Synthesis, Structure and Reactivity of B(C 6 F 5 ) 3 ‐Stabilised Amide (MNH 2 ) Complexes of the Group 4 Metals

Treatment of the homoleptic titanium amides [Ti(NR 2 ) 4 ] (R=Me or Et) with the Brønsted acidic reagent H 3 N⋅B(C 6 F 5 ) 3 results in the elimination of one molecule of amine and the formation of the four‐coordinate amidoborate complexes [Ti(NR 2 ) 3 {NH 2 B(C 6 F 5 ) 3 }], the identity of which was confirmed by X‐ray crystallography. The reaction with [Zr(NMe 2 ) 4 ] proceeds similarly but with retention of the amine ligand to give the trigonal‐bipyramidal complex [Zr(NMe 2 ) 3 {NH 2 B(C 6 F 5 ) 3 }(NMe 2 H)]. Cyclopentadienyl (Cp) amidoborate complexes, [MCp(NR 2 ) 2 {NH 2 B(C 6 F 5 ) 3 }] (M=Ti, R=Me or Et; M=Zr, R=Me) can be prepared from [MCp(NR 2 ) 3 ] and H 3 N⋅B(C 6 F 5 ) 3 , and exhibit greater thermal stability than the cyclopentadienyl‐free compounds. H 3 N⋅B(C 6 F 5 ) 3 reacts with n BuLi or LiN(SiMe 3 ) 2 to give LiNH 2 B(C 6 F 5 ) 3 , which complexes with strong Lewis acids to form ion pairs that contain weakly coordinating anions. The attempted synthesis of metallocene amidoborate complexes from dialkyl or diamide precursors and H 3 N⋅B(C 6 F 5 ) 3 was unsuccessful. However, LiNH 2 B(C 6 F 5 ) 3 does react with the highly electrophilic reagents [MCp 2 Me(μ ‐ Me)B(C 6 F 5 ) 3 ] to give [MCp 2 Me(μ ‐ NH 2 )B(C 6 F 5 ) 3 ] (M=Zr or Hf). Comparison of the molecular structures of the Group 4 amidoborate complexes reveals very similar BN, TiN and ZrN bond lengths, which are consistent with a description of the bonding as a dative interaction between an {M(L) n (NH 2 )} fragment and the Lewis acid B(C 6 F 5 ) 3 . Each of the structures has an intramolecular hydrogen‐bonding arrangement in which one of the nitrogen‐bonded hydrogen atoms participates in a bifurcated F⋅⋅⋅H⋅⋅⋅F interaction to ortho ‐F atoms.