C≡N and N≡O Bond Cleavages of Acetonitrile and Nitrosyl Ligands at a Dimolybdenum Center to Render Ethylidyne and Acetamidinate Ligands.

Extended reduction of [Mo 2 Cp 2 (μ-Cl)(μ-P t Bu 2 )(NO) 2 ] ( 1 ) with Na(Hg) in acetonitrile (MeCN) at room temperature resulted in an unprecedented full cleavage of the C≡N bond of a coordinated MeCN molecule to yield the vinylidene derivative Na[Mo 2 Cp 2 (μ-P t Bu 2 )(μ-CCH 2 )(NO) 2 ], which upon protonation with (NH 4 )PF 6 gave the ethylidyne complex [Mo 2 Cp 2 (μ-P t Bu 2 )(μ-CMe)(NO) 2 ] [Mo1-Mo2 = 2.9218(2) Å] in a selective and reversible way. Controlled reduction of 1 at 273 K yielded instead, after protonation, the 30-electron acetamidinate complex [Mo 2 Cp 2 (μ-P t Bu 2 )(μ-κ N :κ N '-HNCMeNH)(μ-NO)]PF 6 [Mo1-Mo2 = 2.603(2) Å], in a process thought to stem from the paramagnetic MeCN-bridged intermediate [Mo 2 Cp 2 (μ-P t Bu 2 )(μ-NCMe)(NO) 2 ], followed by a complex sequence of elementary steps including cleavage of the N≡O bond of a nitrosyl ligand.