Synthesis and Reactivity of [(silox)2MoNR]2Hg (R = tBu, tAmyl; silox = OSitBu3): Unusual Thermal Stability and Ready Nucleophilic Cleavage Rationalized by Electronic Factors

Treatment of (DME)Cl2Mo(NR)2 (R = tBu, (1-tBu), tAmyl (1-tAmyl)) with 2 equiv of tBu3SiOH (siloxH) and 1 equiv of HCl produced (silox)2Cl2MoNR (R = tBu, (3-tBu), tAmyl (3-tAmyl)); subsequent reduction by Na/Hg afforded the Mo(V) chloride, (silox)2ClMoNtBu (4-tBu), and the Mo(IV) mercury derivatives, [(silox)2MoNR]2Hg (R = tBu ((5-tBu)2Hg), tAmyl ((5-tAmyl)2Hg)). Reductions of 3-tBu and 3-tAmyl in the presence of L (L = PMe3, pyridine, 4-picoline) led to the isolation of adducts (silox)2(Me3P)MoNR (R = tBu (6-tBu), tAmyl (6-tAmyl)) and (silox)2L2MoNtBu (L = py (7-py), 4-pic (7-4-pic)). Single-crystal X-ray structural investigations of pseudo-tetrahedral 4-tBu, Hg-capped, pseudo-trigonal planar (5-tBu)2Hg, pseudo-tetrahedral 6-tBu, and trigonal bipyramidal 7-4-pic reveal that all possess a closed O−Mo−O angle when compared to the NMo−O angles. A molecular orbital rationale and supporting calculations suggest that this is a manifestation of the greater π-donating ability of the imido relative to that of the ...