Bis(fluoromesityl) Palladium Complexes, Archetypes of Steric Crowding and Axial Protection by ortho Effect − Evidence for Dissociative Substitution Processes − Observation of 19F−19F Through‐Space Couplings

Bartolomé, Camino; Espinet, Pablo; Martín‐Alvarez, José M.; Villafañe, Fernando

doi:10.1002/ejic.200300756

Cited by 28 publications

(14 citation statements)

References 67 publications

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“…The mechanism was first proposed by Petrakis and Sederholm in 1961 and later refined by Ng and Sederholm . A few cases of through-space 19 F– 19 F coupling within organometallic complexes have been reported previously. − The most relevant example is a dinuclear Pd(II) complex bearing 3,5-(CF 3 ) 2 C 6 H 3 – (“fluoromesityl”) ligands that exhibits through-space coupling between the CF 3 groups with a coupling constant of 8 Hz . Figure depicts the results of selective decoupling of the resonances at −75.01 and −78.37 ppm.…”

Section: Resultsmentioning

confidence: 92%

Synthesis and Characterization of Group 4 Trianionic ONO^3– Pincer-Type Ligand Complexes and a Rare Case of Through-Space ¹⁹F–¹⁹F Coupling

et al. 2015

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This report describes the synthesis and characterization of a new series of group 4 complexes supported by a trianionic ONO3– pincer-type ligand. Treating TiCl4 with the proligand [CF3–ONO]H3 (1) and NEt3 in benzene afforded {[CF3–ONO]TiCl3}{HNEt3}2 (2). By means of a lithium transmetalation route, the neutral monochloride complex [CF3–ONO]TiCl(THF) (3) was synthesized in 91% yield. The analogous Hf(IV) derivative could not be obtained using this method. Instead, transmetalation with thallium(I) resulted in the formation of the seven-coordinate complex [CF3–ONHO]HfCl2(THF)2 (4-(THF) 2 ), which was characterized by combustion analysis and X-ray crystallography. Applying vacuum to 4-(THF) 2 liberated the THF ligands to provide the five-coordinate THF-free complex [CF3–ONHO]HfCl2 (4). Alkylation of complex 4 with alkyllithium or Grignard reagents resulted in a mixture of unidentifiable products. However, access to the neutral complex 3 enabled the subsequent preparation of organotitanium complexes [CF3–ONO]TiR(THF) (5-R; R = Me, Bn, Mes). Single-crystal X-ray analysis of 5-Me indicated that the organotitanium complexes are mononuclear. Single-crystal X-ray diffraction and NMR studies in solution confirmed that complex 5-Mes exhibits rare through-space 19F–19F coupling (5 Hz).

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Section: Resultsmentioning

confidence: 92%

Synthesis and Characterization of Group 4 Trianionic ONO^3– Pincer-Type Ligand Complexes and a Rare Case of Through-Space ¹⁹F–¹⁹F Coupling

et al. 2015

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“…The activation time is short for the complexes with the poorer donor ligands (AsRfPh 2 , SbPh 3 ), since they are more easily substituted by NB. For stronger ligands (AsPh 3 , AsMePh 2 , AsCyPh 2 ; the last ligand might additionally impose severe steric hindrance to associative substitution), the activation energy for L-for-NB substitution is expected to be larger, and the induction time is consistently longer. , …”

Section: Resultsmentioning

confidence: 99%

Palladium Catalysts for Norbornene Polymerization. A Study by NMR and Calorimetric Methods

2008

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Neutral trans-[Pd(C 6 F 5 )XL 2 ] (X ) Cl, Br) and cationic trans-[Pd(C 6 F 5 )L 2 (NCMe)]BF 4 (L ) SbPh 3 , AsPh 3 , As(C 6 Cl 2 F 3 )Ph 2 , AsCyPh 2 , AsMePh 2 , PPh 3 ) complexes have been studied and tested for norbornene (NB) polymerization and copolymerization with 5-norbornene-2-carboxaldehyde (NB-CHO). The neutral complexes are almost inactive and produce only small amounts of oligomers, but the cationic complexes with arsines and stibines are very good for palladium-catalyzed norbornene polymerization. External coordinating molecules (e.g., ligands or monomers with O-donor groups) compete with the olefin function for the coordination sites on Pd and inhibit the reaction. In spite of this, copolymerization of norbornene and 5-norbornene-2-carboxaldehyde could be achieved, with lower yields and higher incorporations of the functionalized norbornene as the NB:NB-CHO ratio decreases. The complex with the fluorinated arsine AsPh 2 (C 6 Cl 2 F 3 ) is the most active catalyst and allows for easy spectroscopic study of the reacting systems by 19 F NMR. Calorimetry provides straightforward monitoring and detection of activation and deactivation processes in polymerization reactions that give insoluble products and cannot be followed by NMR spectroscopy.

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“…[3,27] This is consistent with the scarcity of tricoordinated compared to pentacoordinated Pd II complexes. Dissociative mechanisms have been experimentally supported in a few cases [28,29] and some involving bulky ligands, [30,31] which should render dissociative reaction mechanisms more accessible.…”

Section: Introductionmentioning

confidence: 99%

When Are Tricoordinated Pd^IISpecies Accessible? Stability Trends and Mechanistic Consequences

Moncho

Ujaque

Lledós

et al. 2008

Chemistry A European J

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The ease of access to Pd(II) tricoordinated species (whether intermediates or transition states) in organometallic and catalytic reactions has been assessed with DFT methods to analyze the relative stability of tricoordinated [PdArXL] complexes versus their tetracoordinated derivatives formed by two most common processes of filling the fourth coordination site: solvent coordination (with tetrahydrofuran), or dimerization to give [Pd2Ar2(micro-X)2L2]. The effect of each ligand (L=PH3, PMe3, PPh3, PtBu3, 1-AdPtBu2; Ar=C6F5, C6H5, C6H4OH, C6H4OCH3, C6H4NH2, C6H2(NH2)3; X=F, Cl, Br, I, OH, SH, NH2, PH2, CH3) on these two processes has been systematically considered, and the results have been compared with the experimental information available. The trends observed, match the experimental results and suggest that: 1) the formation of bridged dimeric complexes is strongly preferred; 2) electronic effects are in general less important compared to steric effects; 3) when steric effects prevent formation of bridges and coordination of a fourth external ligand, intramolecular agostic interactions are established with C--H groups of one ligand; 4) as an exception, for X=NR2 true tricoordinated complexes, not showing agostic interactions, become stable. In the later case NR2 seems to act as pi-donor with its lone pair to the empty orbital at the fourth coordination site of palladium, thus avoiding a true 14e configuration for the tricoordinated PdII complex.

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Bis(fluoromesityl) Palladium Complexes, Archetypes of Steric Crowding and Axial Protection by ortho Effect − Evidence for Dissociative Substitution Processes − Observation of ¹⁹F−¹⁹F Through‐Space Couplings

Cited by 28 publications

References 67 publications

Synthesis and Characterization of Group 4 Trianionic ONO^3– Pincer-Type Ligand Complexes and a Rare Case of Through-Space ¹⁹F–¹⁹F Coupling

Synthesis and Characterization of Group 4 Trianionic ONO^3– Pincer-Type Ligand Complexes and a Rare Case of Through-Space ¹⁹F–¹⁹F Coupling

Palladium Catalysts for Norbornene Polymerization. A Study by NMR and Calorimetric Methods

When Are Tricoordinated Pd^IISpecies Accessible? Stability Trends and Mechanistic Consequences

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Bis(fluoromesityl) Palladium Complexes, Archetypes of Steric Crowding and Axial Protection by ortho Effect − Evidence for Dissociative Substitution Processes − Observation of 19F−19F Through‐Space Couplings

Cited by 28 publications

References 67 publications

Synthesis and Characterization of Group 4 Trianionic ONO3– Pincer-Type Ligand Complexes and a Rare Case of Through-Space 19F–19F Coupling

Synthesis and Characterization of Group 4 Trianionic ONO3– Pincer-Type Ligand Complexes and a Rare Case of Through-Space 19F–19F Coupling

Palladium Catalysts for Norbornene Polymerization. A Study by NMR and Calorimetric Methods

When Are Tricoordinated PdIISpecies Accessible? Stability Trends and Mechanistic Consequences

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Bis(fluoromesityl) Palladium Complexes, Archetypes of Steric Crowding and Axial Protection by ortho Effect − Evidence for Dissociative Substitution Processes − Observation of ¹⁹F−¹⁹F Through‐Space Couplings

Synthesis and Characterization of Group 4 Trianionic ONO^3– Pincer-Type Ligand Complexes and a Rare Case of Through-Space ¹⁹F–¹⁹F Coupling

Synthesis and Characterization of Group 4 Trianionic ONO^3– Pincer-Type Ligand Complexes and a Rare Case of Through-Space ¹⁹F–¹⁹F Coupling

When Are Tricoordinated Pd^IISpecies Accessible? Stability Trends and Mechanistic Consequences