C−H Bond Activation and C−C Bond Formation in the Reactions of the Methyl Complex [Ir₂(CH₃)(CO)₂(Ph₂PCH₂PPh₂)₂][CF₃SO₃] with Alkynes

Abstract

The methyl complex [Ir 2 (CH 3 )(CO)(µ-CO)(dppm) 2 ][CF 3 SO 3 ] (1) reacts readily with a variety of alkyne molecules. With alkynes containing electron-withdrawing substituents (RCtCR′; R ) R′ ) CO 2 Me, CF 3 ; R ) CO 2 Me, R′ ) H), the alkyne-bridged products, [Ir 2 (CH 3 )(CO) 2 -(µ-alkyne)(dppm) 2 ][CF 3 SO 3 ], result. With other 1-alkynes (HCtCR, R ) Me, Ph) reaction at -80 °C results in oxidative addition to give acetylide hydrides [Ir 2 H(CH 3 )(CO) 2 (µ-C 2 R)-(dppm) 2 ][CF 3 SO 3 ], which upon warming undergo transfer of the hydride ligand to the β-carbon of the acetylide to give the vinylidene-bridged products. At ambient temperature methane elimination occurs, yielding the acetylide-bridged "A-frames", [Ir 2 (CO) Reaction of 1 with 1 equiv of acetylene proceeds through analogous acetylide and vinylidene intermediates; however under carbon monoxide exchange of a vinylidene hydrogen and the methyl ligand occurs to give a methylvinylidene-bridged hydride [Ir 2 (H)(CO) 3 (µ-CCHMe)(dppm) 2 ][CF 3 SO 3 ]. Reaction of 1 with an excess of acetylene results in the incorporation of two acetylene molecules, giving [Ir 2 (CH 3 , containing terminal methyl and acetylide ligands and bridging hydride and vinylidene groups. Reaction of 1 with a number of internal, nonactivated alkynes results first in the formation of the alkyne-bridged products, which slowly rearrange to the unusual species [Ir 2 H(CO) 2 (µ-CHCRC(H)R)(dppm) 2 ][CF 3 SO 3 ], in which cleavage of two C-H bonds of the methyl group has occurred accompanied by condensation of the resulting methyne group at one end of alkyne linkage and transfer of a hydrogen to the other end. The resulting hydrocarbyl moiety can be viewed as a vinylcarbene. The X-ray structures of three representative products are reported, including one of these vinylcarbenes (R ) C 2 H 5 ).

Alkyne/Methylene Coupling Reactions at Adjacent Rh/Os Centers: Stepwise Transformations from C1- through C4-Bridged Species

“…These data clearly indicate that the added methylene group is bound to Rh, while the original CH 2 group of compound 5 has undergone C−H activation to yield the alkylidene-bridged group and the bridging hydride. The chemical shift for this alkylidene carbon and the C−H coupling constant are consistent with previous determinations. , Although the top/bottom asymmetry of 11 , by virtue of the unsymmetrical bridging alkylidene group, should give rise to a complex pattern in the 31 P{ 1 H} NMR spectrum of an ABCDX (X = 103 Rh) spin system, this spectrum at ambient temperature is deceptively simple, appearing as an AA‘BB‘X spin system. Upon cooling to −80 °C the spectrum becomes more complex as new peaks appear, but the chemical shifts for the pair of Rh-bound phosphorus nuclei are superimposed, as are those for the Os-bound ends.…”

Successive Activation of C–H and C–O Bonds of Vinyl Ethers by a Diphosphine and Hydrido-Bridged Diiridium Complex

“…In the 13 C{ 1 H} NMR spectrum, the signals due to the αand β-carbon of the vinylidene moiety were observed at δ 192.5 and 121.8, respectively. These signal patterns are very similar to those of the vinylidene-bridged diiridium complexes, which have been previously reported by Cowie et al [67,68]. The structure of 4 was unequivocally confirmed by X-ray diffraction study ( Figure 3, details are indicated in the Supplementary Materials).…”

Double Activation of the Geminal Carbon−Hydrogen Bonds in 1,3-Butadiene by a Diiridium Complex

“…At ambient temperature, over a 48 h period compound 1 reacts with a butadiene-saturated CH 2 Cl 2 solution to give the dihydrido vinylvinylidene-bridged product [Ir 2 (CH 3 )(H)(CO) 2 (μ-H)(μ-CC(H)C(H)CH 2 )(dppm) 2 ][CF 3 SO 3 ] ( 2 ), as shown in Scheme . In the 13 C{ 1 H} NMR spectrum three resonances are observed for the vinylvinylidene fragment; the two at δ 145.8 and 112.0 are typical of olefinic moieties, and the resonance at δ 196.0 shows the usual downfield shift characteristic of the α-carbon of a bridging vinylidene group . The signal for the β-carbon is not observed and is presumably obscured by the phenyl resonances.…”

“…Our previous studies have shown that the reaction of [Ir 2 (CH 3 )(CO) 2 (dppm) 2 ][CF 3 SO 3 ] ( 1 ; dppm = Ph 2 PCH 2 PPh 2 ) with a variety of substrates resulted in C−H bond cleavage of the methyl ligand by the adjacent metal, yielding the methylene-bridged hydride products [Ir 2 H(L)(CO) 2 (μ-CH 2 )(dppm) 2 ][CF 3 SO 3 ] (L = CO, SO 2 , PR 3 , CNR) . In addition, reaction with unsaturated organic substrates yielded vinyl carbenes, and these have also been proposed to proceed via methylene-bridged intermediates . The present study was initiated as part of a continuation of the reactivity studies of 1 , in which olefins were investigated as the substrates.…”