Derivatization of Niobium Complexes Bearing Imido and Acetophenone Imine Ligands

Abstract

The successful isolation and characterization of derivatization reaction products of the niobium imido complex L 2 NbCl(NAr) (L = ortho-metalated acetophenone imine, Ar = 2,6-i Pr 2 C 6 H 3 ) with carbon and oxygen donor ligands such as Me, Me 3 SiCH 2 , PhCC, Me 3 SiCC, CF 3 SO 3 , and MeO are described. These more reactive σ-donor ligands were readily installed in place of the chloride ligand through salt metathesis reactions. The (trimethylsilyl)methyl complex showed significant R-agostic interactions between the methylene group and the niobium center. Similar strategies to derivatize the chloride complex utilizing lithiated amides (LiNMe 2 , LiNEt 2 , LiN i Pr 2 , and LiNC 5 H 10 ) resulted in the production of a niobium hydride species due to β-hydrogen elimination processes. All of the resulting C 1 -symmetric complexes were formed as predominantly a single isomer and were fully characterized using a combination of 1 H and 13 C NMR spectroscopy, elemental analyses, and X-ray crystallography, when possible.

CH Bond Activation of Unsaturated Hydrocarbons by a Niobium Methyl Cyclopropyl Precursor. Cyclopropyl Ring Opening and Alkyne Coupling Reaction

“…For 4 , an almost linear (Nb1–C8–C9, 172.5(3)°; C8–C9–C10, 179.0(4)°) phenyl alkynyl (C8–C9, 1.206(5) Å) is η 1 -bound to the niobium (Nb1–C8, 2.197(4) Å). Similar data have been obtained for two other structurally characterized niobium complexes with the phenylalkynyl ligand . Remarkably the niobium–cyclopropyl bond is even shorter than the Nb–alkynyl bond.…”

A niobium pentafulvene ethylene complex: synthesis, properties and reaction pathways

“…45,46 The Nb-H bond length (1.75(4) Å) lies in the range of reported niobium hydrides. 8,[47][48][49] Similar to the formation of 4, reacting 2 with three equivalents of N-methylaniline in toluene at 60 °C for four days yields niobaaziridine hydride 5 (Scheme 4, bottom). Complex 5 tends to oil out of solution rather than crystallize, impeding full purification and structure elucidation by X-ray diffraction.…”

Isolation and characterization of main group and late transition metal complexes using orthometallated imine ligands

“…52 The reactions of Li-L 1 and Li-L 4 with ZnCl 2 resulted in good yields of the corresponding zinc complexes: Zn(L 1 ) 2 (4) and Zn(L 4 ) 2 (5) (Scheme 4). Crystals suitable for X-ray crystallography were grown from concentrated solutions of pentane (4) and diethyl ether (5). Both complexes exhibited a distorted tetrahedral arrangement of the ligands around the zinc centers (Fig.…”

“…The residue was dissolved in diethyl ether and cooled to -25 • C. 4 was isolated as a white crystalline solid (240 mg, 47%). 1 Zn(L 4 ) 2 (5). A Schlenk flask was charged with Li-L 4 (0.25 g, 1.1 mmol) and toluene (25 ml) was added via cannula.…”

“…1 The coordination chemistry of these ortholithiated imines was also investigated with a number of early transition metals including titanium, zirconium, tantalum, and niobium. [2][3][4][5] With the exception of compounds incorporating imido ligands, most of the metal complexes studied exhibited very low solubility in ethereal, aromatic or hydrocarbon solvents. Furthermore, in the course of our studies, it has become apparent that lithium reagents may not be the best way to access the chemistry supported by orthometallated imines.…”