Cooperative C–H activation of pyridine by PBP complexes of Rh and Ir can lead to bridging 2-pyridyls with different connectivity to the B–M unit

Cao, Yihan; Shih, Wei‐Chun; Bhuvanesh, Nattamai; Zhou, Jia; Ozerov, Oleg V.

doi:10.1039/d1sc01850g

Cited by 6 publications

(11 citation statements)

References 40 publications

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“…For example, transition metal complexes bearing Lewis acidic ligands (based on B or Al) can activate the ortho C–H bond of pyridine substrates (Figure ). − C–H activation is believed to take place by an oxidative addition mechanism at the transition metal center, leading to products in which the pyridyl group is directly bonded to this metal. − The main group ligand plays a role in substrate coordination and determining the ortho selectivity but itself does not lead to new types of reactivities.…”

Section: Introductionmentioning

confidence: 99%

Cooperative C–H Bond Activation by a Low-Spin d⁶ Iron–Aluminum Complex

2022

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The reactions of transition metal complexes underpin numerous synthetic processes and catalytic transformations. Typically, this reactivity involves the participation of empty and filled molecular orbitals centered on the transition metal. Kinetically stabilized species, such as octahedral low-spin d 6 transition metal complexes, are not expected to participate directly in these reactions. However, novel approaches that exploit metal–ligand cooperativity offer an opportunity to challenge these preconceptions. Here, we show that inclusion of an aluminum-based ligand into the coordination sphere of neutral low-spin d 6 iron complex leads to unexpected reactivity. Complexes featuring an unsupported Fe–Al bond are capable of the intermolecular C–H bond activation of pyridines. Mechanistic analysis suggests that C–H activation proceeds through a reductive deprotonation in which the two metal centers (Fe and Al) act like a frustrated Lewis pair. The key to this behavior is a ground state destabilization of the d 6 iron complex, brought about by the inclusion of the electropositive aluminum-based ligand. These findings have immediate implications for the design of reagents and catalysts based on first-row transition metals.

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Section: Introductionmentioning

confidence: 99%

Cooperative C–H Bond Activation by a Low-Spin d⁶ Iron–Aluminum Complex

2022

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“…Pincer ligands and metal–ligand cooperativity (MLC) represent two of the most active themes in the development of transition metal and main group metal chemistry and catalysis, and there has been a substantial overlap between these areas of investigation. Numerous examples of pincer ligands engaging in novel catalytic and stoichiometric MLC-related reactions have been and continue to be reported. − Yet, despite the large number of pincer ligands for which MLC is based on a coordinating N atom, − there are very few examples involving the next congener, phosphorus. In particular, in spite of the great value that has been proven for addition of H 2 across M–N bonds, there are relatively few examples of H 2 addition across a phosphorus metal bond − and even fewer examples of the reverse elimination of H 2 . , …”

Section: Introductionmentioning

confidence: 99%

Reactivity of Iridium Complexes of a Triphosphorus-Pincer Ligand Based on a Secondary Phosphine. Catalytic Alkane Dehydrogenation and the Origin of Extremely High Activity

et al. 2022

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The selective functionalization of alkanes and alkyl groups is a major goal of chemical catalysis. Toward this end, a bulky triphosphine with a central secondary phosphino group, bis(2-di-t-butyl-phosphinophenyl)phosphine (tBuPHPP), has been synthesized. When complexed to iridium, it adopts a meridional (“pincer”) configuration. The secondary phosphino H atom can undergo migration to iridium to give an anionic phosphido-based–pincer (tBuPPP) complex. Stoichiometric reactions of the (tBuPPP)Ir complexes reflect a distribution of steric bulk around the iridium center in which the coordination site trans to the phosphido group is quite crowded; one coordination site cis to the phosphido is even more crowded; and the remaining site is particularly open. The (tBuPPP)Ir precursors are the most active catalysts reported to date for dehydrogenation of n-alkanes, by about 2 orders of magnitude. The electronic properties of the iridium center are similar to that of well-known analogous (RPCP)Ir catalysts. Accordingly, DFT calculations predict that (tBuPPP)Ir and (tBuPCP)Ir are, intrinsically, comparably active for alkane dehydrogenation. While dehydrogenation by (RPCP)Ir proceeds through an intermediate trans-(PCP)IrH2(alkene), (tBuPPP)Ir follows a pathway proceeding via cis-(PPP)IrH2(alkene), thereby circumventing unfavorable placement of the alkene at the bulky site trans to phosphorus. (tBuPPP)Ir and (tBuPCP)Ir, however, have analogous resting states: square planar (pincer)Ir(alkene). Alkene coordination at the crowded trans site is therefore unavoidable in the resting states. Thus, the resting state of the (tBuPPP)Ir catalyst is destabilized by the architecture of the ligand, and this is largely responsible for its unusually high catalytic activity.

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“…for C 37 H 48 NOP 2 Rh: C,64.63;H,7.04;N,2.04. Found;C,64.89;H,7.32;N,2.18. HRMS (electrospray,m/z) (200 mg, 0.37 mmol) in n-octane (3 mL) was treated with 6methylquinoline (49 μL, 0.37 mmol), and the resulting mixture was stirred at 80 °C for 48 h. After this time, the solution was evaporated to dryness to afford a brown residue.…”

Section: ■ Concluding Remarksmentioning

confidence: 98%

“…for C 37 H 48 NOP 2 Rh: C,64.63;H,7.04;N,2.04. Found: C,64.31;H,6.88;N,2.30 (200 mg, 0.37 mmol) in n-octane (3 mL) was treated with 7methylquinoline (49 μL, 0.37 mmol), and the resulting mixture was stirred at 80 °C for 48 h. After this time, the solution was evaporated to dryness to afford a brown residue. Addition of pentane (4 mL) afforded a yellow solid that was washed with pentane (2 × 2 mL) and dried in vacuo.…”

Section: ■ Concluding Remarksmentioning

confidence: 98%

Rhodium-Promoted C–H Bond Activation of Quinoline, Methylquinolines, and Related Mono-Substituted Quinolines

et al. 2022

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The C−H bond activation of methylquinolines, quinoline, 3-methoxyquinoline, and 3-(trifluoromethyl)quinoline promoted by the square-planar rhodium(I) complex RhH{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} [1; xant(P i Pr 2 ) 2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene] has been systematically studied. Results reveal that the activation of the heteroring is preferred over the activation of the carbocycle, and the activated position depends upon the position of the substituent in the substrate. Thus, 3-, 4-, and 5-methylquinoline reacts with 1 to quantitatively form square-planar rhodium(I)-(2-quinolinyl) derivatives, whereas 2-, 6-, and 7-methylquinoline quantitatively leads to rhodium(I)-(4-quinolinyl) species. By contrast, quinoline and 8-methylquinoline afford mixtures of the respective rhodium(I)-(2-quinolinyl) and -(4-quinolinyl) complexes. 3-Methoxyquinoline displays the same behavior as that of 3-methylquinoline, while 3-(trifluoromethyl)quinoline yields a mixture of rhodium(I)-(2-quinolinyl), -(4-quinolinyl), -(6-quinolinyl), and -(7-quinolinyl) isomers.

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Cooperative C–H activation of pyridine by PBP complexes of Rh and Ir can lead to bridging 2-pyridyls with different connectivity to the B–M unit

Abstract: Pyridine and quinoline undergo selective C-H activation in the 2-position with Rh and Ir complexes of a boryl/bis(phosphine) PBP pincer ligand, resulting in a 2-pyridyl bridging the transition metal and...

Cited by 6 publications

References 40 publications

Cooperative C–H Bond Activation by a Low-Spin d⁶ Iron–Aluminum Complex

Cooperative C–H Bond Activation by a Low-Spin d⁶ Iron–Aluminum Complex

Reactivity of Iridium Complexes of a Triphosphorus-Pincer Ligand Based on a Secondary Phosphine. Catalytic Alkane Dehydrogenation and the Origin of Extremely High Activity

Rhodium-Promoted C–H Bond Activation of Quinoline, Methylquinolines, and Related Mono-Substituted Quinolines

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Cooperative C–H activation of pyridine by PBP complexes of Rh and Ir can lead to bridging 2-pyridyls with different connectivity to the B–M unit

Abstract: Pyridine and quinoline undergo selective C-H activation in the 2-position with Rh and Ir complexes of a boryl/bis(phosphine) PBP pincer ligand, resulting in a 2-pyridyl bridging the transition metal and...

Cited by 6 publications

References 40 publications

Cooperative C–H Bond Activation by a Low-Spin d6 Iron–Aluminum Complex

Cooperative C–H Bond Activation by a Low-Spin d6 Iron–Aluminum Complex

Reactivity of Iridium Complexes of a Triphosphorus-Pincer Ligand Based on a Secondary Phosphine. Catalytic Alkane Dehydrogenation and the Origin of Extremely High Activity

Rhodium-Promoted C–H Bond Activation of Quinoline, Methylquinolines, and Related Mono-Substituted Quinolines

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Cooperative C–H Bond Activation by a Low-Spin d⁶ Iron–Aluminum Complex

Cooperative C–H Bond Activation by a Low-Spin d⁶ Iron–Aluminum Complex