Titanium <i>tert</i>-Butoxyimido Compounds

Abstract

The synthesis and molecular and electronic structures of the first tert-butoxyimido complexes of titanium (TiNOtBu functional group) are reported, featuring a variety of mono- or poly-dentate, neutral or anionic N-donor ligands. Reaction of Ti­(NMe2)2Cl2 with tBuONH2 gave good yields of Ti­(NOtBu)­Cl2(NHMe2)2 (1). Compound 1 serves as an excellent entry point into new tert-butoxyimido complexes by reaction with a variety of fac-N3 donor ligands, namely, Me3[9]­aneN3 (trimethyl-1,4,7-triazacyclononane), HC­(Me2pz)3 (tris­(3,5-dimethylpyrazolyl)­methane), or Me3[6]­aneN3 (trimethyl-1,3,5-triazacyclohexane) to give Ti­(NOtBu)­(Me3[9]­aneN3)­Cl2 (2), Ti­(NOtBu)­{HC­(Me2pz)3}­Cl2 (3), or Ti­(NOtBu)­(Me3[6]­aneN3)­Cl2 (4) in good yield. It was found that 4 could be converted into Ti­(NOtBu)­Cl2(py)3 (5) in very good yield by reaction with an excess of pyridine. Compound 5 is effective in a range of salt metathesis reactions with lithiated amide or pyrrolide ligands, and reacts with Li2N2Npy, Li2N2NMe, LiNpyrNMe2, or Li2N2pyrNMe to give Ti­(N2Npy)­(NOtBu)­(py) (6), Ti­(N2NMe)­(NOtBu)­(py) (7), Ti­(NpyrNMe2)­(NOtBu)­Cl­(py)2 (9), or Ti­(N2pyrNMe)­(NOtBu)­(py)2 (10) in moderate to good yields (N2Npy = (2-NC5H4)­C­(Me)­(CH2NSiMe3)2; N2NMe = MeN­(CH2CH2NSiMe3)2; NpyrNMe2 = Me2NCH2(2-NC4H3); N2pyrNMe = MeN­{CH2(2-NC4H3)}2). Compounds 7, 9, and 10 reacted with 2,2′-bipyridyl by pyridine exchange reactions forming Ti­(N2NMe)­(NOtBu)­(bipy) (8), Ti­(NpyrNMe2)­(NOtBu)­Cl­(bipy) (11), and Ti­(N2pyrNMe)­(NOtBu)­(bipy) (12). Ten tert-butoxyimido compounds, namely, 1–6, 11, and 12, have been structurally characterized revealing approximately linear Ti–N–OtBu linkages with Ti–N distances [range 1.686(2)–1.734(2) Å] that are generally intermediate between those in the homologous alkylimido and phenylimido analogues, and shorter than in the diphenylhydrazido counterparts. Density functional theory (DFT) studies on the model compounds Ti­(NR)­Cl2(NHMe2)2 (1_R; R = OMe, Me, Ph, NMe2) confirmed this trend and found that the destabilizing effect of the −OMe oxygen 2pπ lone pair on one of the Ti–N π-bonds in 1_OMe is comparable to that of the occupied phenyl ring π orbitals in the phenylimido homologue 1_Ph but much less than for the −NMe2 nitrogen lone pair in 1_NMe2