Reaction of Nitromethane with an Iridium Pincer Complex. Multiple Binding Modes of the Nitromethanate Anion

The reaction of nitromethane with (PCP)Ir (PCP = κ3-2,6-( t Bu2PCH2)2C6H3) yields the bidentate O,O-ligated nitromethanate complex (PCP)Ir(H)(κ2-O,O-NO2CH2) (1). Reaction of 1 with CO affords a CO adduct with a mono-oxygen-ligated nitromethanate, 2, which represents the first characterized transition metal mono-oxygen-ligated nitromethanate complex. At elevated temperature, complex 2 isomerizes to give the carbon-bound nitromethyl complex 3. Complex 1 also undergoes addition of cyclohexylisocyanide (analogous to the reaction with CO) to form the mono-oxygen-ligated nitromethanate complex 4, which also isomerizes to form the corresponding nitromethyl complex, 5. The (PCP)Ir-(CH3NO2) system is the first species known to display three binding modes with a nitromethanate anion. Results from density functional calculations illustrate the structures and energies of the minima and transition states on the potential energy surfaces. The calculations suggest that 1 is the thermodynamic product of (PCP)Ir reacting with nitromethane; a kinetic product, formed via oxidative addition of a nitromethane C−H bond, should readily rearrange to form 1.