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

The preparation, characterisation and structural analysis of a series of zirconium(IV) complexes that incorporate the diamido/diamine macrocyclic ligand Bn(2)Cyclam (Bn(2)Cyclam = 1,8-dibenzyl-1,4,8,11-tetraazacyclotetradecane) are described. The reaction of one or two equivalents of the appropriate LiNHR reagents with [(Bn(2)Cyclam)ZrCl2] give the corresponding amido-chloride [(Bn(2)Cyclam)ZrCl(NHR)] (R = Bu-t, Ph-2,Ph-6-iPr) or bis(amido) [(Bn(2)Cyclam) Zr(NHR)(2)] (R = Pr-i, Bu-t, Ph-2,Ph-6-Me) complexes, respectively. Treatment of [(Bn(2)Cyclam)ZrCl(NH2,6- iPrPh)] with one equiv. of MgClMe gives the base-free, monomeric imido complex [(Bn(2)Cyclam)Zr(N2,6-iPrPh)]. The reaction of the tBu analog with MgClMe generates a dimeric bridging imido species [{(Bn(2)Cyclam)Zr}(2)(mu-NR)(2)], which can also be obtained by thermal decomposition of [(Bn(2)Cyclam)Zr(NHtBu)(2)] in toluene. The bis(hydrazido) complex [(Bn(2)Cyclam)Zr(NHNPh2)(2)] was obtained by reaction of [(Bn(2)Cyclam)ZrCl2] and two equiv. of LiNHNPh2. A hydrazido-chloride compound [(Bn(2)Cyclam)ZrCl(N(Ph)NBu(Ph))] was generated in a one-pot reaction between [(Bn(2)Cyclam)ZrCl2], LiBu and azobenzene. DFT calculations on [(Bn(2)Cyclam)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.