“…Values of enthalpy relative to their corresponding hydrido–ethylene counterparts follow a similar trend in such a way that the three ethyl complexes in Table are more stable than the corresponding hydride–ethylene counterparts. This constitutes a quite unusual situation in rhodium chemistry, since the general trend is just the opposite (as expected for second row transition metals). Since other factors such as trans or solvent effects can be excluded, the steric pressure exerted by the phenyl groups on the PhBP 3 – ligand should be the key factor that favors the inserted products versus the hydrido–ethylene derivatives, since the former are expected to be less constrained structures than the latter.…”
Ethylene insertion into Rh−H bonds in complexes 8 bearing an anionic fac-triphosphane ligand gives hydrido 9 complexes, β-agostic species, or noninteracting ethyl derivatives 10 depending on the reaction conditions. Several chemical equilibria 11 between these species have been analyzed by NMR and DFT 12 calculations, which revealed that they are mainly controlled by the 13 entropy. Moreover, β-agostic species were found to be lower in 14 enthalpy than the corresponding hydride−ethylene complexes, 15 probably due to the steric pressure exerted by the bulky fac-16 triphosphane ligand. 17 ■ INTRODUCTION 18 Weak interactions between nonpolar C−H bonds and 19 transition metals have been proved to be of paramount 20 importance in organometallic chemistry and catalysis, con-21 tributing to major developments in the field of C−H bond 22 activation and/or functionalization processes, 1 as well as in 23 dehydrogenation reactions. 2 Both versions, intermolecular (σ-24 complexes) and intramolecular (agostic 3 complexes) are 25 known, the latter being important intermediates connecting 26 two fundamental reactions in organometallic chemistry, namely, 27 the insertion of olefins into M−H bonds and the reverse one, 28 the β-hydrogen elimination. Nowadays, the significance of 29 agostic species becomes evident from the large body of 30 literature in which the multiple roles they can play is 31 enlightened. 4 As a way of example, α-agostic interactions 32 have been proved to have a strong impact on the stereo-33 specificity and rate of olefin insertion in polymerization; 5 β-34 agostic species often lead to C−H activation reactions, 6 while 35 the γ-agostic ones have been reported to be crucial in the 36 stabilization of the propagating species in vinyl norbornene 37 polymerization. 7 Moreover, a delicate balance between 38 electronic versus steric factors can tip the stability of αversus 39 β-agostic compounds, 8 or even between βand γ-agostomers. 9 40 Furthermore, longer range interactions such as the rare δand 41 ε-agostic ones are involved in uncommon intramolecular 1,4-, 42 metal migration or 1,5-σ bond metathesis, respectively. 10 In 43 other instances, they are valuable intermediates connecting the 44 transition states that lead to C−H versus C−C activation 45 reactions, 11 and also documented is their participation in the 46 stabilization of highly unsaturated intermediatessuch as T-47 shaped d 8 -ML 3 complexes 12 requiring two agostic interac-48 tions in some cases. 13
49A key feature of these particular M−alkyl moieties can be 50 related to their lability, providing (or not) a vacant site on the 51 coordination sphere of the metal, which, in turn, significantly 52 impacts the reactivity of the complex. Consequently, the study 53 of the dynamics of such species has been the focus of much 54 attention from both experimental 14 and theoretical ap-55 proaches, 15 most of them related to the estimation of the 56 migratory insertion barriers in the context of the polymerization 57 of olefins. 16 58 The s...
“…Values of enthalpy relative to their corresponding hydrido–ethylene counterparts follow a similar trend in such a way that the three ethyl complexes in Table are more stable than the corresponding hydride–ethylene counterparts. This constitutes a quite unusual situation in rhodium chemistry, since the general trend is just the opposite (as expected for second row transition metals). Since other factors such as trans or solvent effects can be excluded, the steric pressure exerted by the phenyl groups on the PhBP 3 – ligand should be the key factor that favors the inserted products versus the hydrido–ethylene derivatives, since the former are expected to be less constrained structures than the latter.…”
Ethylene insertion into Rh−H bonds in complexes 8 bearing an anionic fac-triphosphane ligand gives hydrido 9 complexes, β-agostic species, or noninteracting ethyl derivatives 10 depending on the reaction conditions. Several chemical equilibria 11 between these species have been analyzed by NMR and DFT 12 calculations, which revealed that they are mainly controlled by the 13 entropy. Moreover, β-agostic species were found to be lower in 14 enthalpy than the corresponding hydride−ethylene complexes, 15 probably due to the steric pressure exerted by the bulky fac-16 triphosphane ligand. 17 ■ INTRODUCTION 18 Weak interactions between nonpolar C−H bonds and 19 transition metals have been proved to be of paramount 20 importance in organometallic chemistry and catalysis, con-21 tributing to major developments in the field of C−H bond 22 activation and/or functionalization processes, 1 as well as in 23 dehydrogenation reactions. 2 Both versions, intermolecular (σ-24 complexes) and intramolecular (agostic 3 complexes) are 25 known, the latter being important intermediates connecting 26 two fundamental reactions in organometallic chemistry, namely, 27 the insertion of olefins into M−H bonds and the reverse one, 28 the β-hydrogen elimination. Nowadays, the significance of 29 agostic species becomes evident from the large body of 30 literature in which the multiple roles they can play is 31 enlightened. 4 As a way of example, α-agostic interactions 32 have been proved to have a strong impact on the stereo-33 specificity and rate of olefin insertion in polymerization; 5 β-34 agostic species often lead to C−H activation reactions, 6 while 35 the γ-agostic ones have been reported to be crucial in the 36 stabilization of the propagating species in vinyl norbornene 37 polymerization. 7 Moreover, a delicate balance between 38 electronic versus steric factors can tip the stability of αversus 39 β-agostic compounds, 8 or even between βand γ-agostomers. 9 40 Furthermore, longer range interactions such as the rare δand 41 ε-agostic ones are involved in uncommon intramolecular 1,4-, 42 metal migration or 1,5-σ bond metathesis, respectively. 10 In 43 other instances, they are valuable intermediates connecting the 44 transition states that lead to C−H versus C−C activation 45 reactions, 11 and also documented is their participation in the 46 stabilization of highly unsaturated intermediatessuch as T-47 shaped d 8 -ML 3 complexes 12 requiring two agostic interac-48 tions in some cases. 13
49A key feature of these particular M−alkyl moieties can be 50 related to their lability, providing (or not) a vacant site on the 51 coordination sphere of the metal, which, in turn, significantly 52 impacts the reactivity of the complex. Consequently, the study 53 of the dynamics of such species has been the focus of much 54 attention from both experimental 14 and theoretical ap-55 proaches, 15 most of them related to the estimation of the 56 migratory insertion barriers in the context of the polymerization 57 of olefins. 16 58 The s...
“…The nitrile-assisted reaction of [Ru(h 6 -C 10 [23], h 6 -arenes [19,22], h 5 -cyclopentadienyl and substituted cyclopentadienyl [36e39], h 4 -tetraphenylcyclobutadiene [29], and acetylacetonate [40]. The complexes described here differ from these in the presence of an auxiliary ligand (the nitrile) that can be readily replaced even at room temperature, thus enabling oxidative coupling between the 1,3-diene and an entering unsaturated ligand.…”
“…(iv) In both the 1 H and 13 C spectra one observes four relatively low frequency absorptions, due to the four CH types in the η 6 -arene moiety. For 3a these four carbon signals, C3−C6, appear at 78.6, 95.4, 101.7, and 76.0 ppm, respectively, exactly where one expects 13 C resonances of arenes complexed to Ru(II). − 1 …”
Reaction of Ru(OAc)2(MeO-Biphep) (MeO-Biphep = 6,6‘-dimethoxybiphenyl-2,2‘-diylbis(diarylphosphine)) with 2 equiv of HBF4 in CH2Cl2 cleaves the MeO-Biphep. Products contain the exotic chelate ligand
(aryl)2POB(OH)F2 (aryl = phenyl, p-tolyl, 3,5-di-tert-butylphenyl) together with an (aryl)2P−η6-arene, 8e
donor chelate. The reaction involves a fluorophosphine
intermediate.
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