Vinylic C−H Bond Activation and Hydrogenation Reactions of Tp‘Ir(C₂H₄)(L) Complexes

Abstract

The substitution of one of the ethylene ligands of the complexes Tp'Ir(C(2)H(4))(2) (Tp' = Tp(Me)()2, 1; Tp' = Tp, 1) by soft donors such as tertiary phosphines or carbon monoxide is a facile reaction that gives the corresponding Tp'Ir(C(2)H(4))(L) adducts. Spectroscopic studies support their formulation as five-coordinate, 18-electron species that possess a distorted trigonal bipyramidal geometry. This proposal has been confirmed by a single-crystal X-ray study carried out with the PMe(2)Ph complex Tp(Me)()2Ir(C(2)H(4))(PMe(2)Ph) (3b). Related hydride derivatives of Ir(III) can be obtained either by hydrogenation of the Ir(I) adducts (in general, this gives Tp'IrH(2)(L) compounds) or by thermal activation of one of the C-H bonds of the coordinated C(2)H(4) ligand of the Tp(Me)()2Ir(C(2)H(4))(L) compounds. All these reactions can be understood by invoking the participation of transient, 16-electron (eta(2)-Tp')Ir intermediates, but the thermodynamics of the [Ir](C(2)H(4)) to [Ir]H(CH=CH(2)) conversion does not require an overall change in the coordination mode of the Tp' ligand.

Ultrafast infrared studies of chemical reaction dynamics in room-temperature liquids

“…Furthermore, if the activation barrier of a S i-H bond is comparably small, the apparent rate determining step would be the dissociative rearrangement from D to B. Our measured rates for the formation of B are also consistent with the observation that the overall enthalpy of activation is dominated by the enthalpy of dissociating the solvent from the reaction site, and that the transition state consists of a very loosely bound R3SiH [90,100].…”

Synthesis and Properties of TpMe2IrH4and TpMe2IrH3(SiEt3): Ir(V) Polyhydride Species withC3vGeometry

“…By forcing the conditions of the reaction (2 atm, 90 °C, 6 h), complex 1* was obtained as the main product in very high yield. Other Ir(III) species can be used as starting materials for the synthesis of 1* , and thus, for example, Tp Me2 IrH(C 2 H 3 )(C 2 H 4 ) , and Tp Me2 Ir(C 6 H 5 ) 2 (N 2 ) react with H 2 at 70−90 °C with ultimate formation of 1* . While in the first case the known 14 Tp Me2 IrH 2 (C 2 H 4 ) can be detected as an active intermediate, in the hydrogenation of the bis(phenyl) derivative no intermediates are observed (NMR monitoring).…”

“…The simplest preparative route, and the only one described in the Experimental Section, however, involves the Ir(I) complex Tp Me2 Ir(C 2 H 4 ) 2 9 as the starting material, thus avoiding the preparation of the above-mentioned Ir(III) species that, after all, need be synthesized from the same bis(ethylene) derivative. In that case, the intermediates Tp Me2 IrH 2 (C 2 H 4 ) and Tp Me2 Ir(C 2 H 5 )(C 2 H 4 ) are formed under H 2 , even at room temperature, and further hydrogenation under more forcing conditions (C 6 H 12 , 2 atm, 90 °C, 3 days) is needed to transform this mixture into 1* (eq 1). Quite recently, Venanzi et al have also observed the formation of 1* in the hydrogenation of other Tp Me2 Ir substrates…”

“…Although the related TpIr(C 2 H 4 ) 2 complex can be easily hydrogenated at 25 °C to give TpIrH(C 2 H 5 )(C 2 H 4 ), further reaction with H 2 at higher temperatures gives only small yields (∼10%) of the corresponding TpIrH 4 ( 1 ), along with a mixture of uncharacterized products. This is a not a surprising result since, in general, TpIr compounds exhibit poorer thermal stability and more complex decomposition routes than the Tp Me2 analogues. , For this reason, 1 has only been characterized by high-field 1 H NMR spectroscopy without attempted purification.…”

Synthesis and Reactivity of Iridacycles Containing the TpMe2Ir Moiety

“…[14] The other mechanistic way [path (b)] was invoked to explain the reactions of Ir-dienes 1-3 with hard Lewis bases (NCMe, pyridine, etc.). The two different mechanisms shown in Scheme 4 may also account for the different types of processes in which the 2,3-dimethylbutadiene derivative 3 (the most reactive among 1-3, and hence the most studied) takes part.…”