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

Abstract

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.

Reactivity of Pincer Complexes Toward Carbon Monoxide

“…However, Kaska and coworkers, in 1983 [19], retook the work carried by Shaw and coworkers and carried out similar reactions (Scheme 2.21) of the (PCP)Rh(III) pincer complex (38) with carbon monoxide in the presence of the very basic compound NaN (Si(CH 3 ) 3 ) 2 obtaining the same species (40). Later, in the study of the reactivity of the (PCP)Rh(I) complex (38), Kaska and coworkers [20] realized that the reaction of this compound with CO 2 was, in fact, a CO 2 reducing process to water and CO in what amounted to be a reversal of the water gas shift reaction.…”

“…Hence, the (PCP) rhodium derivative (38) affords complex (40), as a product of the decomposition of the unstable hydrido chloro carbonyl intermediate (39) via a hydrodechlorination process, although this compound is obtained impure. To favor the hydrodechlorination process, an alternative route was attempted employing EtONa as base.…”

“…This approach afforded exclusively compound (40) (Scheme 2.21). It is noteworthy that analogous reactions with the iridium analogous to complex (38) only afford impure samples of the carbonyl species analogous to complex (40 Scheme 2. 20 Sacco and coworkers [18] also made an important contribution to the chemistry of rhodium carbonyl pincer complexes.…”

Activation of sp3 Carbon–Hydrogen Bonds by a Ruthenium(II) Complex and Subsequent Metal‐Mediated CC and CN Bond Formation

“…Limited examples of well-defined nitromethane CÀH activation mediated by transition metals have been reported. [19] Heating [7] and a second complex, which is assigned as [TpRu(PMe 3 )(pyridine)Cl] (Scheme 3). The overall transformation from 1 and acetone is a metal-mediated aldol-type reaction between acetone and acetonitrile.…”

“…Limited examples of well-defined nitromethane CÀH activation mediated by transition metals have been reported. [19] Heating 1 Heating the reaction mixture at 60 8C results in the formation of free acetylacetonamine in 86 % yield (verified by 1 H NMR spectroscopy and GC-MS), free pyridine, [TpRu(PMe 3 )-(NCCD 3 )Cl], [7] and a second complex, which is assigned as [TpRu(PMe 3 )(pyridine)Cl] (Scheme 3). The overall transformation from 1 and acetone is a metal-mediated aldol-type reaction between acetone and acetonitrile.…”