Trianionic Carbocyclic NCN Pincer Ligand: Coordination Chemistry and Reactivity Studies.

(BCHT-NCN)H 3 ( 1 ) [1,6-bis(methylene(bis-2,6-di iso propylaniline)(benzo)cycloheptatriene)] was synthesized by nucleophilic substitution treating 1,6-bis(methylenebromide)(benzo)cycloheptatriene with 2 equiv of Li[2,6- i Pr 2 C 6 H 3 NH], Li[Dipp-NH]. Triple deprotonation of (BCHT-NCN)H 3 ( 1 ) using n -BuLi yields the deprotonation product [(BCHT-NCN)Li 3 ] ( 2 ), which crystallizes as a dimer [{[BCHT-NCN]Li 3 (Et 2 O) 2 } 2 ] ( 2 ) 2 . Coordination compounds of the trianionic pincer ligand were obtained with SnCl 2 , YCl 3 (THF) 3.5 , and HfCl 4 (THF) 2 : [(BCHT-NCN)SnLi] ( 3 ), [(BCHT-NCN)Y(THF) 2 ] ( 4 ), [(BCHT-NCN)HfCl 2 ][Li(THF) 4 ] ( 5 ), respectively. A hafnium hydride complex [(BCHT-NCN)HfH(HBEt 3 )][K(Et 2 O) 2 ] ( 6 ) was isolated after reaction of 5 with K[HBEt 3 ]. A Me NHC substitution product [(BCHT-NCN)HfCl( Me NHC)] ( 7 ) was synthesized treating compound 5 with Me NHC at rt. Following an n -BuLi reaction of 7 gives an alkyl complex [(BCHT-NCN)Hf( n -Bu)( Me NHC)] ( 8 ). Thermolysis of 7 yields the isomerization product [(BCHT-NCN # )HfCl( Me NHC)] ( 9 ), which was transferred into a methyl complex [(BCHT-NCN # )HfMe( Me NHC)] ( 10 ) upon treatment with MeMgBr. Hydride abstraction from complex 9 leads to a cationic complex [(BCHT-NCN + )HfCl( Me NHC)][Al(O t Bu F ) 4 ] ( 11 ).