Synthesis and structural studies of amido, hydrazido and imido zirconium(iv) complexes incorporating a diamido/diamine cyclam-based ligand

Abstract

The preparation, characterisation and structural analysis of a series of zirconium(IV) complexes that incorporate the diamido/diamine macrocyclic ligand Bn₂Cyclam (Bn₂Cyclam = 1,8-dibenzyl-1,4,8,11-tetraazacyclotetradecane) are described. The reaction of one or two equivalents of the appropriate LiNHR reagents with [(Bn₂Cyclam)ZrCl₂] give the corresponding amido–chloride [(Bn₂Cyclam)ZrCl(NHR)] (R = ^tBu, ^2,6-iPrPh) or bis(amido) [(Bn₂Cyclam)Zr(NHR)₂] (R = ⁱPr, ^tBu, ^2,6-MePh) complexes, respectively. Treatment of [(Bn₂Cyclam)ZrCl(NH^2,6-iPrPh)] with one equiv. of MgClMe gives the base-free, monomeric imido complex [(Bn₂Cyclam)Zr(N^2,6-iPrPh)]. The reaction of the ^tBu analog with MgClMe generates a dimeric bridging imido species [{(Bn₂Cyclam)Zr}₂(μ-NR)₂], which can also be obtained by thermal decomposition of [(Bn₂Cyclam)Zr(NH^tBu)₂] in toluene. The bis(hydrazido) complex [(Bn₂Cyclam)Zr(NHNPh₂)₂] was obtained by reaction of [(Bn₂Cyclam)ZrCl₂] and two equiv. of LiNHNPh₂. A hydrazido–chloride compound [(Bn₂Cyclam)ZrCl(N(Ph)NBu(Ph))] was generated in a one-pot reaction between [(Bn₂Cyclam)ZrCl₂], LiBu and azobenzene. DFT calculations on [(Bn₂Cyclam)ZrXY] complexes indicate that the coordination geometry adopted by these species is dictated by the steric bulk of the ligands X and Y, varying between six-coordinate prismatic and four-coordinate tetrahedral.