Treatment of [Cp*Mo(NO)Cl mu(-Cl)](2) with magnesium (Me2Mg.dioxane, MeMgCl) or aluminum (Me3Al) methylating reagents affords the known compound [Cp*Mo(NO)Me(mu 0Cl)](2) (1). Similar treatment of the dicbloro precursor with MeLi in ethereal solvents generates an equimolar mixture of 1 and the trimethyl "ate" complex, Cp*MoMe3(NO-Li(OEt2)(n)). (2-Et2O). Reaction of 2-Et2O with a source of [Me](+) forms Cp*MoMe3(dropN-OMe) (3), a rare terminal alkoxylimido complex. Metathesis of the chloro ligands of [Cp*Mo-(NO)Cl(mu -Cl)](2) by MeLi in toluene at low temperatures produces the target dimethyl complex. Cp*Mo(NO)-Me-2 (4). in 75% isolated yield. In solution, 4 is predominantly a monomeric species, whereas in the solid state it adopts a dimeric or oligomeric structure containing isonitrosyl bridges as indicated by IR and N-15/C-13 NMR spectroscopies. Hydrolysis of 4 affords meso- and rac-[Cp*Mo(NO)Me](2)(mu -O)(5), and the reactions of 4 with a range of Lewis bases. L, to form the 18e adducts Cp*Mo(NO)(L)Me-2 (e.g., Cp*Mo(NO)(PMe3)Me-2 (7)), have established it to be the most electrophilic complex of its family. Acidolysis of the methyl groups of 4 is also facile. Most notably, 4 is thermally unstable in solution and undergoes isomerization via nitrosyl N-O bond cleavage to its oxo(imido) form, Cp*Mo(NMe)(O)Me (11), which is isolable from the final reaction mixture as the mu -oxo-bridged adduct formed by 4 and 11, i.e., Cp*Mo(NO)Me2(mu -O)Cp*Mo(NMe)Me (4 <-- 11). The rate of this isomerization is significantly faster for the tungsten dimethyl complex; hence, Cp*W(NO)- (NO)Me-2 (12) is not isolable free of a supporting donor interaction and can only be isolated as Cp*W(NO)-Me-2(mu -O)Cp*W(NMe)Me (12 <-- 13) or Cp*W(NO)Me-2(PMe3) (14) adducts.