New σ-bonded rhodium(I) complexes containing a metal—carbon bond. I

Keim, W.

doi:10.1016/s0022-328x(00)92654-8

Cited by 117 publications

(31 citation statements)

References 8 publications

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“…9 Bennet and Milner observed that ortho -C–H bonds of triphenylphospine ligands underwent oxidative addition to give [Ir(III)–H] species 22 , 10 and other metals were found to exhibit analogous reactivity with both phosphines and phosphonites ( 23 and 24 ). 11, 12 …”

Section: Historical Perspective On Cyclometallationmentioning

confidence: 99%

Weak Coordination as a Powerful Means for Developing Broadly Useful C–H Functionalization Reactions

et al. 2011

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Conspectus Reactions that convert carbon–hydrogen (C–H) bonds into carbon–carbon (C–C) or carbon–heteroatom (C–Y) bonds are attractive tools for organic chemists, potentially expediting the synthesis of target molecules through new disconnections in retrosynthetic analysis. Despite extensive inorganic and organometallic study of the insertion of homogeneous metal species into unactivated C–H bonds, practical applications of this technology in organic chemistry are still rare. Only in the past decade have metal-catalyzed C–H functionalization reactions become more widely utilized in organic synthesis. Research in the area of homogeneous transition metal–catalyzed C–H functionalization can be broadly grouped into two subfields. They reflect different approaches and goals and thus have different challenges and opportunities. One approach involves reactions of completely unfunctionalized aromatic and aliphatic hydrocarbons, which we refer to as “first functionalization.” Here the substrates are nonpolar and hydrophobic and thus interact very weakly with polar metal species. To overcome this weak affinity and drive metal-mediated C–H cleavage, chemists often use hydrocarbon substrates in large excess (for example, as solvent). Because highly reactive metal species are needed in first functionalization, controlling the chemoselectivity to avoid over-functionalization is often difficult. Additionally, because both substrates and products are comparatively low-value chemicals, developing cost-effective catalysts with exceptionally high turnover numbers that are competitive with alternatives (including heterogeneous catalysts) is challenging. Although an exciting field, first functionalization is beyond the scope of this Account. The second subfield of C–H functionalization involves substrates containing one or more pre-existing functional groups, termed “further functionalization.” One advantage of this approach is that the existing functional group (or groups) can be used to chelate the metal catalyst and position it for selective C–H cleavage. Precoordination can overcome the paraffin nature of C–H bonds by increasing the effective concentration of the substrate so that it needn't be used as solvent. From a synthetic perspective, it is desirable to use a functional group that is an intrinsic part of the substrate so that extra steps for installation and removal of an external directing group can be avoided. In this way, dramatic increases in molecular complexity can be accomplished in a single stroke through stereo- and site-selective introduction of a new functional group. Although reactivity is a major challenge (as with first functionalization), the philosophy in further functionalization differs—the major challenge is developing reactions that work with predictable selectivity in intricately functionalized contexts on commonly occurring structural motifs. In this Account, we focus on an emergent theme within the further functionalization literature: the use of commonly occurring functional groups to direct C–H cle...

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Section: Historical Perspective On Cyclometallationmentioning

confidence: 99%

Weak Coordination as a Powerful Means for Developing Broadly Useful C–H Functionalization Reactions

et al. 2011

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“…The latter (like its σ-Me analogue) 15 was found to be unstable under the reaction conditions (80°C), rapidly decomposing to 5.…”

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confidence: 99%

The Fluoro Analogue of Wilkinson's Catalyst and Unexpected Ph−Cl Activation

2004

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The fluoro analogue of Wilkinson's catalyst, [(Ph3P)3RhF] (1), was synthesized and fully characterized. Both solution behavior and solid-state geometry parameters of 1 were found to be surprisingly similar to those of Wilkinson's catalyst. Unlike Wilkinson's catalyst however, 1 exhibited most unusual reactivity toward the notoriously inert C-Cl bond of nonactivated chloroarenes. The novel Ph-Cl activation with 1 includes fluorine transfer from the metal to a phosphine ligand and evidently phenyl transfer from the phosphine to Rh to produce an electron-rich sigma-phenylrhodium intermediate.

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“…The far-IR spectra of the complexes displayed peaks corresponding to rhodium-halogen stretches and are indicative of the presence of only terminal halides. [20] The spectra also displayed a peak due to ν Rh -C in the range 300-360 cm −1 ; the result pointing to cyclometallation [21] of the tris/tetrakis-benzimidazole derivatives. Cyclometallation is further supported by the 1 H and 13 C NMR spectra of the complexes.…”

Section: Resultsmentioning

confidence: 95%

Synthesis of rhodium(III) complexes with tris/tetrakis‐benzimidazoles and benzothiazoles—quick identification of cyclometallation by nuclear magnetic resonance spectroscopy

Chandrashekhar

Gayathri

Gowda

2009

Magnetic Reson in Chemistry

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] (X = Cl, Br, I). Elemental analysis, IR and 1 H nuclear magnetic resonance (NMR) chemical shifts supported the binuclear nature of the complexes. Cyclometallation was detected by conventional 13 C NMR spectra that showed a doublet around ∼190 ppm. Cyclometallation was also detected by gradient-enhanced heteronuclear multiple bond correlation (g-HMBC) experiment that showed cross-peaks between the cyclometallated carbon and the central benzene ring protons of 1-3. Cyclometallation was substantiated by two-dimensional 1 H-1 H correlated experiments (gradiant-correlation spectroscopy and rotating frame Overhauser effect spectroscopy) and 1 H-13 C single bond correlated two-dimensional NMR experiments (gradient-enhanced heteronuclear single quantum coherence). The 1 H-15 N g-HMBC experiment suggested the coordination of the heterocycles to the metal ion via tertiary nitrogen.

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New σ-bonded rhodium(I) complexes containing a metal—carbon bond. I

Cited by 117 publications

References 8 publications

Weak Coordination as a Powerful Means for Developing Broadly Useful C–H Functionalization Reactions

Weak Coordination as a Powerful Means for Developing Broadly Useful C–H Functionalization Reactions

The Fluoro Analogue of Wilkinson's Catalyst and Unexpected Ph−Cl Activation

Synthesis of rhodium(III) complexes with tris/tetrakis‐benzimidazoles and benzothiazoles—quick identification of cyclometallation by nuclear magnetic resonance spectroscopy

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