Rhodium-Mediated Dehydrogenative Borylation–Hydroborylation of Bis(alkyl)alkynes: Intermediates and Mechanism

Curto, Sheila G.; Esteruelas, Miguel A.; Oliván, Montserrat; Oñate, Enrique

doi:10.1021/acs.organomet.9b00104

Cited by 23 publications

(14 citation statements)

References 79 publications

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“…Hydride RhH{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} ( 1 ) and pinacolboryl Rh(Bpin){κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} ( 2 ) complexes add the Rh–H and Rh–B bonds to the C–C triple bond of bis(alkyl)alkynes, in a syn -manner . The formed E -bis(alkyl)-alkenyl derivatives evolve into Z -bis(alkyl)-alkenyl counterparts, via four-coordinate rhodacyclopropene intermediates, resulting from the release of the xanthene oxygen and the coordination of the alkenyl-C β atom .…”

Section: Introductionsupporting

confidence: 67%

“…Complex 3 is unstable in benzene solution and evolves into its Z -isomer Rh{( Z )-C(Ph)CHPh}{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} ( 4 ), in agreement with that observed for bis(alkyl)alkynes . Noticeable spectroscopic features of the new species are a doublet of triplets ( 1 J C–Rh = 42.5 Hz and 2 J C–P = 11.8 Hz) at 168.6 ppm in the 13 C{ 1 H} NMR spectrum, due to the alkenyl C α atom, and a doublet ( 1 J P–Rh = 177.6 Hz) at 33.4 ppm in the 31 P{ 1 H} NMR spectrum, corresponding to the pincer.…”

Section: Resultsmentioning

confidence: 99%

“…Thus, the formation of the pincer by coordination of the oxygen atom allows xant(P i Pr 2 ) 2 to stabilize square-planar hydride, aryl, boryl, and silyl complexes of rhodium(I) without the above-mentioned protection (Chart ). This, along with the oxygen lability of the ligand, was revealed as key for developing catalysis with these compounds, including borylation reactions , that have particular interest because of the relevance of C–B bonds in organic synthesis …”

Section: Introductionmentioning

confidence: 93%

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Insertion of Diphenylacetylene into Rh–Hydride and Rh–Boryl Bonds: Influence of the Boryl on the Behavior of the β-Borylalkenyl Ligand

et al. 2019

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Reactions of complexes RhH{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (1) and Rh(Bpin){κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (2; Bpin = pinacolboryl, xant(P i Pr 2 ) 2 = 9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) with diphenylacetylene have been studied. Complex 1 reacts with the alkyne to give the E-alkenyl derivative Rh{(E)-C(Ph)=CHPh}{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (3) as a result of the synaddition of the Rh-H bond to the C-C triple bond. In benzene, at room temperature, complex 3 is unstable and slowly evolves into its Z-alkenyl isomer Rh{(Z)-C(Ph)=CHPh}{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (4), which is also unstable and undergoes an alkenyl-to-orthoalkenylaryl transformation to afford Rh{C 6 H 4 -2-(E-CH=CHPh)}{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (5). The latter adds HBpin. The resulting rhodium(III) species, RhH(Bpin){C 6 H 4 -2-(E-CH=CHPh)}{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (6), eliminates trans-4,4,5,5-tetramethyl-2-(2styrylphenyl)-1,3,2-dioxaborolane and regenerates 1, closing a cycle for the hydroboration of the alkyne to the ortho-alkenyl-aryl compound. However, this cycle is not catalytic. The direct reaction of the alkyne with the borane in presence of 1 leads to Z,Emixtures of PhCH=C(Ph)Bpin. Diphenylacetylene also undergoes syn-addition of the Rh-B bond of 2. The Bpin group accelerates the isomerization of the alkenyl ligand. Thus, the resulting E-β-borylalkenyl derivative Rh{(E)-C(Ph)=C(Bpin)Ph}{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (7) rapidly evolves into its Z-isomer Rh{(Z)-C(Ph)=C(Bpin)Ph}}{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (8), which also undergoes alkenyl-to-ortho-alkenylaryl transformation to give Rh{C 6 H 4 -2-[E-CH=C(Bpin)Ph]}{κ 3 -P,O,P-[xant(P i Pr 2 ) 2 ]} (9). However, in contrast to 5, complex 9 is less stable than its precursor 8. ASSOCIATED CONTENTSupporting Information. The Supporting Information is available free of charge on the ACS Publications web site.. General information, crystallographic data, and NMR spectra (PDF)Accession codes CCDC 1943084 and 1943085 contain the crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by e-mailing da-

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Section: Introductionsupporting

confidence: 67%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 93%

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Insertion of Diphenylacetylene into Rh–Hydride and Rh–Boryl Bonds: Influence of the Boryl on the Behavior of the β-Borylalkenyl Ligand

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“…The former can change their coordination mode from mer to fac , in addition to displaying hemilability . As a consequence, they adapt to the requirements of the different intermediates of the catalytic cycles . There are rigid ligands that cooperate with the metal undergoing reversible chemical transformations during the catalysis .…”

Section: Introductionmentioning

confidence: 99%

Influence of the Bite Angle of Dianionic C,N,C-Pincer Ligands on the Chemical and Photophysical Properties of Iridium(III) and Osmium(IV) Hydride Complexes

et al. 2019

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The study of the reactions of IrH 5 (P i Pr 3) 2 (1) with 2,6-diphenylpyridine and 2-phenoxy-6-phenylpyridine and the photophysical characterization of some of the resulting compounds, as well as their osmium-counterparts, reveal that the bite angle of dianionic C,N,C-pincer ligands has a marked influence on the chemical and photophysical properties of iridium(III)-and osmium(IV)-hydride complexes. Complex 1 promotes a double o-CH bond activation of both disubstituted pyridines. The reaction with 2,6-diphenylpyridine directly leads to IrH{κ 3-C,N,C-(C 6 H 4-py-C 6 H 4)}(P i Pr 3) 2 (2), whereas the activation of 2-phenoxy-6phenylpyridine is sequential and slower. Initially, the phenyl activation gives IrH 2 {κ 2-C,N-(C 6 H 4-py-OPh)}(P i Pr 3) 2 (3), which subsequently evolves to IrH{κ 3-C,N,C-(C 6 H 4-py-OC 6 H 4)}(P i Pr 3) 2 (4). Complexes 2 and 4 are Brønsted bases, which react with HBF 4 •OEt 2. The protonation of the hydride position is elusive; the proton of the acid is selectively added to one of the metalated substituents. Thus, the reaction with 2 affords [IrH{κ 3-C,N,(C-H)-(C 6 H 4-py-Ph)}(P i Pr 3) 2 ]BF 4 (5), in which the formed C-H bond remains coordinated. The protonation of 4 selectively occurs at the phenoxy substituent to give the five-coordinate cationic complex [IrH{κ 2-C,N-(C 6 H 4-py-OPh)}(P i Pr 3) 2 ]BF 4 (6) bearing a free OPh group. In contrast to 5, complex 6 inserts acetylene and phenylacetylene into the Ir-H bond to yield [Ir{(E)-CH=CHR}{κ 2-C,N-(C 6 H 4-py-OPh)}(P i Pr 3) 2 ]BF 4 (R = H (7), Ph (8)). Complexes 2 and 4 and their osmium(IV)-counterparts OsH 2 {κ 3-C,N,C-(C 6 H 4-py-C 6 H 4)}(P i Pr 3) 2 (A) and OsH 2 {κ 3-C,N,C-(C 6 H 4-py-OC 6 H 4)}(P i Pr 3) 2 (B) are phosphorescent emitters, which display emission wavelengths between 473 nm and 619 nm and quantum yields between 0.03 and 0.96 depending upon the metal center and the presence or absence of the oxygen atom in the pincer ligand. RESULTS AND DISCUSSION C-H Bond Activation Reactions. Pentahydride IrH 5 (P i Pr 3) 2 (1) promotes the o-CH bond activation of both substituents of 2,6-diphenylpyridine and 2-phenoxy-6-phenylpyridine. Interestingly, the rate of the C-H rupture depends upon the substituent. Thus, the phenyl activation is much faster than that of the phenoxide group. The reaction of 1 with 2,6-diphenylpyridine in toluene under reflux leads to the monohydride-iridium(III) derivative IrH{κ 3-C,N,C-(C 6 H 4-py-C 6 H 4)}(P i Pr 3) 2 (2), which was isolated as a yellow solid in 52%, after 14 h (Scheme 3), and characterized by X-ray diffraction analysis. Figure 1 shows a view of the structure, which proves the formation of the C,N,C-pincer

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“…22 Furthermore, it participates in the catalytic cycle of dehydrogenative borylation-hydroborylation of bis(alkyl)alkynes. 23 So far, a handicap for its use was the preparation procedure, which afforded moderated yield. In order to solve this issue and to give it a more general use, we have significantly improved its preparation.…”

Section: Scheme 1 Reactions With Deuteriummentioning

confidence: 99%

A General Rhodium Catalyst for the Deuteration of Boranes and Hydrides of the Group 14 Elements

et al. 2020

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Rhodium-Mediated Dehydrogenative Borylation–Hydroborylation of Bis(alkyl)alkynes: Intermediates and Mechanism

Cited by 23 publications

References 79 publications

Insertion of Diphenylacetylene into Rh–Hydride and Rh–Boryl Bonds: Influence of the Boryl on the Behavior of the β-Borylalkenyl Ligand

Insertion of Diphenylacetylene into Rh–Hydride and Rh–Boryl Bonds: Influence of the Boryl on the Behavior of the β-Borylalkenyl Ligand

Influence of the Bite Angle of Dianionic C,N,C-Pincer Ligands on the Chemical and Photophysical Properties of Iridium(III) and Osmium(IV) Hydride Complexes

A General Rhodium Catalyst for the Deuteration of Boranes and Hydrides of the Group 14 Elements

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