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 J CH 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-Pr i 2 C 6 H 2 -2-CH 2 CH 2 CMe 2 CH═](DME)(OTf) 2, Mo(OBu t F6 ) 2 (quin)[═N-2,4-Pr i 2 C 6 H 2 -2-CH 2 CH 2 CMe 2 CH═], Mo[N(2,4-Pr i 2 -6-MeC 6 H 2 )] 2 (neopentyl) 2, and Mo(OBu t F6 ) 2 (quin)[N(2,4-Pr i 2 -6-MeC 6 H 2 )][═C(H)Bu t ].