‘Electronic bending’ of imido ligands and the effect on the coordination mode of a tridentate ancillary ligand

The five-coordinate mixed-imido complex [Mo(Nt-Bu)(NC6F5)(L)] (1) can be prepared in high yield via treatment of [Mo(Nt-Bu)(NC6F5)(Ot-Bu)2] with LH2, where LH2 is 2,6-bis(2-hydroxy-2,2-diphenylethyl)pyridine. Contrastingly, the reaction of [Mo(NAd)(NC6F5)(Ot-Bu)2] (Ad = adamantyl, C6H10) with LH2 gave [Mo(NAd)2(L)] (2) via an imido-exchange reaction. Complex 2 can also be synthesised via treatment of in situ generated [Mo(NAd)2(Ot-Bu)2] with LH2; the latter method also results in trace amounts of the five-coordinate complex [MoCl(NAd)2(Ldehyd)] (3) (Ldehyd = 2-(2-hydroxy-2,2-diphenylethenyl)pyridine). The structures of 1–3 have been determined by X-ray crystallographic study. In each complex, the geometry at the metal is distorted trigonal bipyramidal with the pyridinediolate ligand adopting an ‘aea’ bonding arrangement in 1 and an ‘eee’ arrangement in 2. The angle associated with the imido moiety also varies, with the greatest deviations found in 1 and 3, indeed, the pentafluoroimido ligand in 1 has one of the largest deviations from linearity for an M–N–C angle recorded to-date [135.98(16)°]. This has been rationalised on the basis of an electronic effect rather than intramolecular steric interactions or crystal packing forces.

Graphical abstractThe synthesis and structural characterisation of [Mo(Nt-Bu)(NC6F5)(L)] (1) and [Mo(NAd)2(L)] (2) are reported, which possess aea and eee coordination geometries for L, respectively, where LH2 is 2,6-bis(2-hydroxy-2,2-diphenylethyl)pyridine. Complex 1 has one of the largest deviations from linearity for an M–N–C angle recorded to-date [135.98(16)°]. The structure of the trace product [MoCl(NAd)2(Ldehyd)] (3) is also reported.Figure optionsDownload full-size imageDownload as PowerPoint slide