Synthesis, Properties, and Structure of Tethered Molybdenum Alkylidenes

A new class of molybdenum alkylidenes has been prepared where the alkylidene is tethered to an imido ancillary ligand. The amine required for the synthesis is accessible in 38% yield in five steps from 1,3-diisopropylbenzene. The amine is then installed to generate the tethered alkylidene bis(triflate) complex, which was structurally characterized as its DME adduct. The triflates are replaced by hexafluoro-tert-butoxide groups using the thallium salt of the alkoxide, and the bis(alkoxide) was characterized as its quinuclidine adduct. For comparison, an alkylidene bis(alkoxide) was prepared without the tether and having a formula similar to that of the tethered system. The structures from X-ray diffraction and NMR spectroscopy of the two complexes with and without the tether but with similar formulas are compared. The tether has the apparent effect, judging from JCH couplings in the alkylidene and angles in the solid-state structure, of reducing the strength of the α-agostic interaction. Four complexes were structurally characterized during this study: Mo[═N-2,4-Pri2C6H2-2-CH2CH2CMe2CH═](DME)(OTf)2, Mo(OButF6)2(quin)[═N-2,4-Pri2C6H2-2-CH2CH2CMe2CH═], Mo[N(2,4-Pri2-6-MeC6H2)]2(neopentyl)2, and Mo(OButF6)2(quin)[N(2,4-Pri2-6-MeC6H2)][═C(H)But].