Synthesis and structural investigation of N,N′,N"-trialkylguanidinato-supported zirconium(IV) complexes

The addition of 2 equiv of N,N',N"-triisopropylguanidine (guanH(2)) to Zr(CH2Ph)(4) produced the bis(guanidinato)-bis(benzyl)zirconium complex {((PrNH)-Pr-i)C((NPr)-Pr-i)(2)}(2)Zr(CH2Ph)(2) (1). The mono(guanidinato) complex {((PrN)-Pr-i)(2)C((NHPr)-Pr-i)}ZrCl3 (2) was accessible by the reaction of 2 equiv of guanH(2) with ZrCl4. Guanidinium hydrochloride, {C((NHPr)-Pr-i)(3)}Cl, is a byproduct of this reaction. When crystallized from THF, complex 2 was isolated as the THF adduct {((PrNH)-Pr-i)C((NPr)-Pr-i)(2)}ZrCl3(THF) (2-THF). The mixed cyclopentadienyl guanidinato complex {eta(5)-1,3-(Me3Si)(2)C5H3}{((PrNH)-Pr-i)C((NPr)-Pr-i)(2)}ZrCl2 (3) was prepared by treatment of {1,3-(Me3Si)(2)C5H3}ZrCl3 with the in situ generated lithium triisopropylguanidinate salt. The reaction of guanH(2) with {1,3-(Me3Si)(2)C5H3}ZrMe3 affords the dimethyl derivative {eta(5)-1,3-(Me3Si)(2)C5H3}{((PrNH)-Pr-i)C((NPr)-Pr-i)(2)}ZrMe2 (4). Definitive evidence for the molecular structures of these products is provided through single-crystal X-ray characterization of 1, 2-THF, and 3, which are presented. The extent of pi delocalization within the guanidinato ligand is discussed in the context of the metrical parameters obtained from these structural studies.