Organometallic nucleophiles. A mechanistic study of halide displacement at saturated carbon by 2- and 4-pyridyl complexes of palladium(II) and platinum(II)

Canovese, Luciano; Visentin, Fabiano; Uguagliati, Paolo; Bianca, F. Di; Fontana, Alberta; Crociani, B.

doi:10.1016/s0022-328x(96)06490-x

Cited by 15 publications

(17 citation statements)

References 17 publications

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“…In the early 1980s, the groups of Isobe 88,89 and Crociani [90][91][92][93][94][95] successfully prepared nickel, palladium, and platinum py- These early studies focused on the effect of the metal fragment on the reactivity of the pyridine, rather than on the carbene-type bonding of the ligand. Titration experiments showed that the Brønsted basicity of pyridine in the palladium complex 123a is ∼4 orders of magnitude higher than that of unsubstituted pyridine.…”

Section: Nitrogen Functionalization Of Metallated Pyridyl Ligandsmentioning

confidence: 99%

“…C4 > C3, and it is larger for the platinum complexes 125 than for the corresponding palladium complexes 123. 89,95 Contribution of a carbene resonance structure in the protonated species 124a was inferred from 13 C NMR spectroscopy. The resonance frequency of the metal-bound carbene (δ C ) 184.9) indicated a downfield shift, compared to the precursor pyridyl system 123a (Δδ ≈ 5).…”

Section: Nitrogen Functionalization Of Metallated Pyridyl Ligandsmentioning

confidence: 99%

“…94 Replacing the trans-coordinated phosphine spectator ligands by bidentate cis-chelating ligands such as1,2-bis(diphenylphosphino)ethane (dppe) or dimethyldithiocarbamate (dmtc) does not influence this reactivity pattern. 93,[95][96][97] Because the 2-and 4-metallated congeners differ considerably in their reactivity, the contribution of a zwitterionic pyridinylium-type resonance structure (130′; see Scheme 43) has been suggested to be more relevant than the neutral pyridylidene structure 130′′. 95,96 Comparison of the Pt-C bond distances in 100, its protonated form 130a, and 130b is not conclusive for establishing metal-carbon π-interactions (see Table 3).…”

Section: Nitrogen Functionalization Of Metallated Pyridyl Ligandsmentioning

confidence: 99%

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Beyond ConventionalN-Heterocyclic Carbenes: Abnormal, Remote, and Other Classes of NHC Ligands with Reduced Heteroatom Stabilization

et al. 2009

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theme are found via the replacement or displacement of one N atom, thus providing carbenes derived from pyrazolium, isothiazolium, and even quinolinium salts that contain a stabilizing heteroatom in a remote position (G-J in Figure 1). Recently, carbenes such as K, which are comprised of only one heteroatom and lack delocalization through the heterocycle, have been discovered as versatile ligands, thus constituting another important class of carbenes with low heteroatom stabilization. Both the synthesis of the organometallic complexes of these ligands as well as the (catalytic) properties of the coordinated metal centers generally show distinct differences, compared to the more classical NHC complexes, such as C2-metallated imidazolylidenes. This review intends to describe such differences and highlights the chemical peculiarities of these types of N-heterocyclic carbene complexes. It introduces, in a qualitative manner, the synthetic routes that have been established for the preparation of such complexes, covering the literature from the very beginning of activities in this area up to 2008. While specialized reviews on some aspects of the present topic have recently appeared, 7 a comprehensive overview of the subject has not been available thus far. Rather than just being descriptive, the present account is mainly directed toward the impact of these still unusual metal-carbene bonding modes on the electronic properties and on the new catalytic applications that have been realized by employing such new carbene complexes. As a consequence of our focus on complexes with less-stabilized heterocyclic ligands, systems comprising acyclic carbenes have not been included, and the interested reader is, instead, referred to the pioneering and

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Section: Nitrogen Functionalization Of Metallated Pyridyl Ligandsmentioning

confidence: 99%

Section: Nitrogen Functionalization Of Metallated Pyridyl Ligandsmentioning

confidence: 99%

Section: Nitrogen Functionalization Of Metallated Pyridyl Ligandsmentioning

confidence: 99%

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Beyond ConventionalN-Heterocyclic Carbenes: Abnormal, Remote, and Other Classes of NHC Ligands with Reduced Heteroatom Stabilization

et al. 2009

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“…24 This result also provides an explanation for the increased basicity of the nitrogen in pyridyl metal complexes which can even lead to the activation of dichloromethane. [50][51][52][53][54][55] …”

Section: Figurementioning

confidence: 99%

Pyridine-Derived N-Heterocyclic Carbenes: An Experimental and Theoretical Evaluation of the Bonding in and Reactivity of Selected Normal and Abnormal Complexes of Nickel(II) and Palladium(II)

et al. 2010

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“…Iridium biscarbene dihalides have been demonstrated as robust catalysts for the ketone transfer hydrogenation, 19 and Ir(III) monohydrates was also proposed as the active species, a structure related to complexes 5 and 8a-c. We reason that they should also be active in this catalysis. Transfer hydrogenation between acetophenone and i PrOH proceeded smoothly in the presence of 0.1 mol% of complexes 8a-b-(PF 6 ) and 10 mol% NaOH (eq 2.2).…”

Section: Catalysis Resultsmentioning

confidence: 99%

Ir and Rh complexes of under-explored n-heterocyclic carbenes : synthesis, mechanism, dynamics and catalysis

Song¹

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In this dissertation, my aim is to study different type of under-explored N-Heterocyclic Carbenes (NHC) complexes of Ir and Rh. These complexes have been synthesized, and the reaction mechanism, solution dynamics, and catalytic activity studies are presented in this dissertation. In Chapter 2 shows that phosphine-tethered imidazolium ions can undergo C-H oxidative addition when treated with [Ir(COD)Cl] 2 to give abnormal iridium(III) NHC hydrides. The effects of the length of the linker, the kinetic studies of C-H activation and catalytic application of these complexes are systematically studied. Chapter 3 describes the synthesis of iridium and rhodium complexes stabilized by 2-methyleneimidazoline ligands via highly selective intramolecular activation of 2-methyl C-H vs C4/5-H bonds of the imidazolium moieties with the chelation assistance of phosphine ligands. The selectivity of C(sp 3)-H vs C(sp 2)-H activation, the conversion of methyleneimidazoline to abnormal complex and the electronic properties of ligands are also presented. Chapter 4 shows that the preparation of rhodium and iridium complexes of a new type of abnormal NHCs derived from imidazol[1,2-a]pyridiniums via silver transmetalation. The donating and π-back donation abilities of these new NHC ligands are systematically studied by VT NMR and CO stretching frequency. Chapter 5 shows that a series of iridium(III) hydride complexes of chelating pyridine-based N-heterocyclic carbenes (py-NHCs) and remote N-heterocyclic carbenes (remote py-NHCs) could be synthesized as from the C-H oxidative addition reactions of i ATTENTION: The Singapore Copyright Act applies to the use of this document. Nanyang Technological University Library pyridine-tethered pyridinium halides and [Ir(COD) 2 ] +. X-ray crystal studies, catalytic application in transfer hydrogenation of ketone and enones and Computational studies of the donor capacity of those ligands are also described in this chapter. In chapter 6, we discuss rather rare Ir(I)-induced tautomerization of a pyridine moiety in 2,3-bipyridyls to a carbene. The experimental data indicate that the H-bondings play crucial roles in not only stabilizing the NH tautomers but also accelerating the hydrogen migration process.

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Organometallic nucleophiles. A mechanistic study of halide displacement at saturated carbon by 2- and 4-pyridyl complexes of palladium(II) and platinum(II)

Cited by 15 publications

References 17 publications

Beyond ConventionalN-Heterocyclic Carbenes: Abnormal, Remote, and Other Classes of NHC Ligands with Reduced Heteroatom Stabilization

Beyond ConventionalN-Heterocyclic Carbenes: Abnormal, Remote, and Other Classes of NHC Ligands with Reduced Heteroatom Stabilization

Pyridine-Derived N-Heterocyclic Carbenes: An Experimental and Theoretical Evaluation of the Bonding in and Reactivity of Selected Normal and Abnormal Complexes of Nickel(II) and Palladium(II)

Ir and Rh complexes of under-explored n-heterocyclic carbenes : synthesis, mechanism, dynamics and catalysis

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