Sequential coordination and oxidative addition of terminal alkynes to the Tp′PtMe fragment

Engelman, Kristi L.; White, Peter S.; Templeton, Joseph L.

doi:10.1016/j.ica.2009.06.006

Cited by 16 publications

(14 citation statements)

References 37 publications

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“…The calculated activation free energy (27.0 kcal/mol) for this reaction was much higher than that of hydroboration, suggesting that ruthenium-vinylidene is not involved. Second, the relatively weak sp C–H bond of terminal alkyne suggests that oxidative addition should be considered . Oxidative addition of the C–H bond to the metal center might overcome a barrier of 24.7 kcal/mol but is not competitive with respect to hydroboration.…”

Section: Resultsmentioning

confidence: 99%

A Combined DFT/IM-MS Study on the Reaction Mechanism of Cationic Ru(II)-Catalyzed Hydroboration of Alkynes

et al. 2017

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Recently, the Furstner group reported the first general trans-hydroboration of internal alkynes by using a cationic ruthenium(II) complex, [Cp*Ru(MeCN) 3 ]PF 6 , as the catalyst. Density functional theory (DFT) calculations have been carried out to elucidate the reaction mechanism and the origin of stereoselectivity. The reaction mechanism was suggested to initiate with the rate-determining oxidative hydrogen migration to stereoselectively form a metallacyclopropene intermediate (that determines the trans selectivity), followed by a reductive boryl migration to form the unusual trans-addition alkenyl-borane product. A combined ion-mobility mass spectrometry (IM-MS) and DFT study has also been employed to investigate the unsuccessful reaction with terminal alkynes. Key oxidative-coupling intermediates have been identified. Our results suggest that [2 + 2 + 2] cycloaddition of terminal alkynes to form a very stable arene compound could be the reason for the unsuccessful hydroboration of the terminal alkynes. Moreover, unreactive catecholborane reagent attributes the strong coordination of its arene part with the catalyst. Our proposed nonclassical mechanism also accounted for the other related Ru(II)-catalyzed reactions (such as hydrogenation and hydrogermylation). Our combined computational and experimental study provides in-depth mechanistic understanding and insights on the unusual trans-addition catalyzed by the cationic ruthenium(II) complexes and could help design the other trans-addition reactions.

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Section: Resultsmentioning

confidence: 99%

A Combined DFT/IM-MS Study on the Reaction Mechanism of Cationic Ru(II)-Catalyzed Hydroboration of Alkynes

et al. 2017

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“…The Pt−Me resonance at 0.9 ppm with 2 J Pt−H = 88 Hz is compatible with data for other Pt(II)−Me resonances. 25,48,49 The phosphine oxide resonance in the 31 P NMR spectrum moves slightly upfield from −5.7 ppm for free Tt Ph to −8.4 ppm when two scorpionate arms bind to the metal. It is noteworthy that the 1 J P−C value at the dome of the scorpionate umbrella is dependent upon the binding of the triazolyl ring, so this coupling constant serves as a convenient spectroscopic probe of the coordination mode.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Thermolysis of Tp′PtMe 2 H above 100 °C or protonation at low temperature dechelates the apical Tp′ arm, generating a reactive unsaturated species that eliminates methane . An array of reactivity patterns stemming from the resulting Tp′PtMe fragment has been documented (Scheme ). − In the presence of cyclic alkanes, Tp′PtMe activates C–H bonds and generates dehydrogenated products after β-H elimination . Trapping Tp′PtMe with carbon monoxide results in formation of the Tp′PtMe(CO) complex, which can undergo nucleophilic attack by hydroxide to generate CO 2 and a platinum dihydride species.…”

Section: Introductionmentioning

confidence: 99%

C–H and C–C Bond Formation Promoted by Facile κ³/κ² Interconversions in a Hemilabile “Click”-Triazole Scorpionate Platinum System

Frauhiger¹,

White²,

Templeton³

2011

Organometallics

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A series of platinum complexes bearing 3-fold symmetrical “Click”-triazole-based scorpionate ligands (TtR) has been prepared. Metalation of these weakly donating ligands results in neutral Pt(II) complexes that display a κ2 coordination mode. Such complexes are susceptible to oxidative addition using a variety of electrophilic alkyl and allyl reagents to generate isolable cationic κ3 Pt(IV) complexes. Protonation of the κ2 precursors results in Pt(IV) dimethyl hydride cations. Thermolysis of the dimethyl hydride species at 35 °C in the presence of a trapping π-acid ligand initiates reductive elimination of methane and formation of a Pt(II) species of the type [TtPhPtMe(L)][BF4] (L  CO, ethylene, propylene, cis-2-butene, trans-2-butene, isobutylene) in good yield. Furthermore, the κ3 σ-allyl complexes [TtRPt(Ph)2(CH2CHCH2)][I] cleanly undergo Csp2–Csp2 reductive coupling to form biphenyl at ambient temperatures. The TtR ligand serves as a homofunctional hemilabile ligand and exhibits a lower barrier κ3/κ2 interconversion to generate reactive unsaturated five-coordinate complexes than the well-studied Tp′PtMe2H complex, which requires thermolysis at temperatures above 100 °C.

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“…On a different vein, poly(pyrazolyl)-borate or -methane ligands have been widely used as auxiliary ligands in coordination, organometallic, and bioinorganic chemistry, − and they have shown an important role in a wide range of topics, such as C–H bond activation, − catalytic processes, − models for enzymatic reactions, , metal extraction, ,,,,, and biomedical applications. , However, there have been few reports on the influence of these ligands on the photophysical properties of metal complexes, − and in particular, very few studies are related to square-planar cycloplatinated complexes. , These ligands would be expected to introduce a remarkable steric hindrance above and below the square-planar coordination plane, disfavoring undesirable face-to-face intermolecular π···π and Pt···Pt interactions.…”

Section: Introductionmentioning

confidence: 99%

Luminescent Cycloplatinated Complexes Containing Poly(pyrazolyl)-borate and -methane Ligands

et al. 2011

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Cycloplatinated neutral [Pt(C ∧ N){H 2 B(pz) 2 }] (1À3) [C ∧ N = benzoquinolate (bzq), 2-phenylpyridinate (ppy), and 2-phenylquinolate (pq)] and [Pt(pq){HB(pz) 3 }] 10 and cationic [Pt(C ∧ N){H 2 C(pz) 2 }] + (4À6) and [Pt(C ∧ N){HC(pz) 3 }] + (7À9)complexes were synthesized by the reaction of the corresponding precursors [Pt(C ∧ N)(μ-Cl)] 2 with the adequate poly-(pyrazolyl)-borate or -methane ligand. However, the reactions of [Pt(C ∧ N)(μ-Cl)] 2 (C ∧ N = bzq, ppy) with [HB(pz) 3 ] À evolve with BÀN bond cleavage, yielding the binuclear systems [Pt(C ∧ N)(μ-pz)] 2 as a mixture of cis and trans isomers. Complexes were characterized in solution by multinuclear and multidimensional NMR spectroscopy. The solid-state structures of 1, 3, 6, 7À9, and [Pt(bzq)(μ-pz)] 2 were confirmed by X-ray single-crystal studies. The absorption, emission, and electrochemical properties of these complexes are mainly dominated by the nature of the cyclometalated ligand and the charge of the complex. On the basis of TD-DFT calculations (1, 7À9), the lowest-energy absorption for neutral 1 has been ascribed to a mixed 1 ILCT/ 1 MLCT transition, whereas for the cationic 7À9, it is mainly attributed to 1 ILCT combined with some CT to both ligands in 9 ( 1 MLCT/ML 0 CT 9) or to the HC(pz) 3 in 7 and 8 ( 1 ML 0 CT). These compounds are emissive in all media (except 4 and 10 in the solid state at 298 K). In the solid state at 298 K and at 77 K, these complexes display intense phosphorescence, which is typical of monomers. In deoxygenated CH 3 CN solutions at 298 K, phosphorescence is accompanied by higher-energy fluorescence in complexes 1, 4, and 8, which disappears at concentrated solutions and at 77 K. Complex 7 displays a special behavior, observing fluorescence and/or excimer fluorescence only at 298 K and excimeric emission (diluted glasses) and emission from aggregates in concentrated glasses. TD-DFT of the lowest-lying excited states responsible for the phosphorescence of 1 and 7À9 reveals a 3 ILCT origin with a mixed 3 MLCT character for 1 and, in the case of the cationic 7À9, a 3 ILCT transition mixed with 3 ML 0 CT (especially in 8) and with some 3 MLCT in 9. ' INTRODUCTIONCyclometalated square-planar platinum(II) complexes have attracted great interest in recent years due to their luminescent properties 1À12 with potential applications in optoelectronic devices, 2,3,7,10,11,13À25 photocatalysts, 26 and chemical or biochemical sensors. 27À31 Emission from these Pt(II) complexes is typically assigned to ligand-centered ( 3 LC) and/or metal-to-ligand charge-transfer ( 3 MLCT) states, although some degree of ligand-to-ligand 0 charge-transfer ( 3 LL 0 CT) states is also possible. Additionally, the square-planar nature of these complexes facilitates the formation of dimers or aggregates through noncovalent π 3 3 3 π and/or Pt 3 3 3 Pt interplanar stacking interactions, both in the solid state and in solution. 32À44 As a consequence, they exhibit rich photophysical behavior causing a marked red shift relative to the mononuclear emissio...

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Sequential coordination and oxidative addition of terminal alkynes to the Tp′PtMe fragment

Cited by 16 publications

References 37 publications

A Combined DFT/IM-MS Study on the Reaction Mechanism of Cationic Ru(II)-Catalyzed Hydroboration of Alkynes

A Combined DFT/IM-MS Study on the Reaction Mechanism of Cationic Ru(II)-Catalyzed Hydroboration of Alkynes

C–H and C–C Bond Formation Promoted by Facile κ³/κ² Interconversions in a Hemilabile “Click”-Triazole Scorpionate Platinum System

Luminescent Cycloplatinated Complexes Containing Poly(pyrazolyl)-borate and -methane Ligands

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Sequential coordination and oxidative addition of terminal alkynes to the Tp′PtMe fragment

Cited by 16 publications

References 37 publications

A Combined DFT/IM-MS Study on the Reaction Mechanism of Cationic Ru(II)-Catalyzed Hydroboration of Alkynes

A Combined DFT/IM-MS Study on the Reaction Mechanism of Cationic Ru(II)-Catalyzed Hydroboration of Alkynes

C–H and C–C Bond Formation Promoted by Facile κ3/κ2 Interconversions in a Hemilabile “Click”-Triazole Scorpionate Platinum System

Luminescent Cycloplatinated Complexes Containing Poly(pyrazolyl)-borate and -methane Ligands

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C–H and C–C Bond Formation Promoted by Facile κ³/κ² Interconversions in a Hemilabile “Click”-Triazole Scorpionate Platinum System