Treatment of (DME)Cl2Mo(=NR)(2) (R = Bu-t, (1-Bu-t), (t)Amyl (1-(t)Amyl)) with 2 equiv of (Bu3SiOH)-Bu-t (siloxH) and 1 equiv of HCl produced (silox)(2)Cl2Mo=NR (R = Bu-t, (3-Bu-t), (t)Amyl (3-(t)Amyl)); subsequent reduction by Na/Hg afforded the Mo(V) chloride, (silox)(2)CIMo=NtBu (4-Bu-t), and the Mo(IV) mercury derivatives, [(silox)(2)Mo=NR](2)Hg (R = Bu-t ((5-Bu-t)(2)Hg), (t)Amyl ((5-(t)Amyl)(2)Hg)). Reductions of 3-Bu-t and 3-(t)Amyl in the presence of L (L = PMe3, pyridine, 4-picoline) led to the isolation of adducts (silox)(2)(Me3P)Mo=NR (R = Bu-t (6-Bu-t), (t)Amyl (6-(t)Amyl)) and (silox)(2)L2Mo=(NBu)-Bu-t (L = py (7-py), 4-pic (7-4-pic)). Single-crystal X-ray structural investigations of pseudo-tetrahedral 4-Bu-t, Hg-capped, pseudo-trigonal planar (5-Bu-t)(2)Hg, pseudo-tetrahedral 6-Bu-t, and trigonal bipyramidal 7-4-pic reveal that all possess a closed O-Mo-O angle when compared to the N=Mo-O angles. A molecular orbital rationale and supporting calculations suggest that this is a manifestation of the greater pi-donating ability of the imido relative to that of the siloxides. While the D(Mo-Hg) of [(HO)(2)Mo=NH](2)Hg ((5 ')(2)Hg) was calculated to be 22.4 kcal/mol, (5-R)(2)Hg (R =Bu-t, (t)Amyl) are remarkably stable; (5-Bu-t)(2)Hg degraded in a first-order fashion with Delta G(double dagger) = 31.9(1) kcal/mol. In the presence of strong (L = PMe, pyridine, S-8) or weak (L = 2-butyne, ethylene, N2O, 1,4,7,10-tetrathiacyclododecane, 1,4,7,10,13,16-hexathiacyclooctadecane) nucleophiles, an enhanced rate of Mo-Hg bond cleavage was noted, with some of the former group generating adducts in <5 min; the products were 6-Bu-t, 7-py, (silox)(2)(S)Mo=(NBu)-Bu-t (10-Bu-t), (silox)(2)Mo=(NBu)-Bu-t(C2Me2) (8-Bu-t), (silox)(2)(C2H4)Mo=(NBu)-Bu-t (11-Bu-t), (silox)(2)(O)Mo=(NBu)-Bu-t (9-Bu-t), and a mixture of 10-Bu-t and 11-Bu-t, respectively. Some of these were independently prepared via substitution of 6-Bu-t. According to calculations and a molecular orbital rationale, dissociation of the Mo-Hg bond in (5-R)(2)Hg (R = Bu-t, (t)Amyl) is orbitally forbidden, and the addition of a nucleophile to the terminus of the Mo-Hg-Mo linkage mitigates the symmetry requirements. The mechanism of thermal degradation was studied with mixed success. NMR spectroscopy revealed imido exchange between (5-Bu-t)(2)Hg and (5-(t)Amyl)(2)Hg during an initial induction period and a subsequent rapid exchange period that implicated free 5-R (R = Bu-t, (t)Amyl). Further crossover studies revealed siloxide exchange as an additional complication.