Structure and Reactivity of Neutral and Cationic trans-N,N′-Dibenzylcyclam Zirconium Alkyl Complexes

Reactions of (Bn2Cyclam)ZrCl2 (1) (where Bn2Cyclam = trans-N,N′(PhCH2)2Cyclam) with appropriate alkylating reagents produced (Bn2Cyclam)ZrR2 (R = Me (2), CH2Ph (3), nBu (4), CCPh (5)). Activation of the ortho C−H bond of the two macrocycle benzyl substituents in complexes 2, 3, and 4 was thermally induced, leading to the formation of a bis(ortho-metalated) complex, ((C6H4CH2)2Cyclam)Zr (6). This reaction proceeds along with RH elimination and converts the original dianionic tetracoordinated cyclam in a tetraanionic hexacoordinated ligand where two new Zr−CPh bonds complete the metal sphere. Treatment of 6 with one equivalent of HC≡CPh led to ((C6H4CH2)BnCyclam)Zr(CCPh) (7) via protonation of one Zr−CPh bond by phenylacethylene. Further reaction of 7 with an excess of HC≡CPh led to 5. The reactions of 2 and 3 with B(C6F5)3 are strongly solvent dependent. Solvent-stabilized cationic species of formula [(Bn2Cyclam)ZrR(Solv)][RB(C6F5)3] were obtained from reactions of 2 in CD2Cl2 (10) or d8-THF (12) and from ...