Synthesis and Structural Investigation of <i>N,N</i>‘<i>,N</i>‘ ‘<i>-</i>Trialkylguanidinato-Supported Zirconium(IV) Complexes

The addition of 2 equiv of N,N‘,N‘ ‘-triisopropylguanidine (guanH2) to Zr(CH2Ph)4 produced the bis(guanidinato)bis(benzyl)zirconium complex {(iPrNH)C(NiPr)2}2Zr(CH2Ph)2 (1). The mono(guanidinato) complex {(iPrN)2C(NHiPr)}ZrCl3 (2) was accessible by the reaction of 2 equiv of guanH2 with ZrCl4. Guanidinium hydrochloride, {C(NHiPr)3}Cl, is a byproduct of this reaction. When crystallized from THF, complex 2 was isolated as the THF adduct {(iPrNH)C(NiPr)2}ZrCl3(THF) (2-THF). The mixed cyclopentadienyl guanidinato complex {η5-1,3-(Me3Si)2C5H3}{(iPrNH)C(NiPr)2}ZrCl2 (3) was prepared by treatment of {1,3-(Me3Si)2C5H3}ZrCl3 with the in situ generated lithium triisopropylguanidinate salt. The reaction of guanH2 with {1,3-(Me3Si)2C5H3}ZrMe3 affords the dimethyl derivative {η5-1,3-(Me3Si)2C5H3}{(iPrNH)C(NiPr)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 π delocalization within the guanidinato ligand is discussed in the context of the metrical parameters obtained from these structural studies.