Synthesis of monodentate bis(N-heterocyclic carbene) complexes of iridium: Mixed complexes of abnormal NHCs, normal NHCs, and triazole NHCs
TL;DR: In this article, a stepwise synthesis of mixed monodentate bis-NHC complexes of Ir(I), employing Ag(I) NHC complexes as transfer agents, yields complexes with two NHCs having different steric and electronic characteristics.
About: This article is published in Journal of Organometallic Chemistry.The article was published on 2008-08-01. It has received 27 citations till now. The article focuses on the topics: Denticity.
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2,594 citations
TL;DR: 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.
Abstract: 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
939 citations
TL;DR: This work presents a meta-analysis of multi-NHCs Linked by Spacers and its applications in Catalysis and Nanomaterials, which shows clear trends in both the number and complexity of the components and their applications.
Abstract: 2.3.5. Multi-NHCs Linked by Spacers 3568 2.4. The Ag2O Route 3570 2.4.1. Feasibility 3570 2.4.2. Complications 3571 2.4.3. Theoretical Consideration 3572 2.5. Applications 3572 2.5.1. Ag(I)-NHCs in NHC Transfer 3572 2.5.2. Ag(I)-NHCs in Catalysis 3572 2.5.3. Ag(I)-NHCs in Medicine 3572 2.5.4. Ag(I)-NHCs in Nanomaterials 3573 3. Au(I)and Au(III)-NHCs 3573 3.1. Historical Background 3573 3.2. General Synthetic Methods 3573 3.3. Formation of Au(I)and Au(III)-NHCs 3574 3.3.1. Neutral [Au(NHC)L] 3574 3.3.2. Ionic [Au(NHC)L][Anion] 3576 3.3.3. Multinuclear Au(I)-NHCs 3578 3.3.4. Other Classes of Au(I)-NHCs 3578 3.3.5. Au(III)-NHC Complexes 3579 3.4. Applications 3579 3.4.1. Au(I)and Au(III)-NHCs in Catalysis 3579 3.4.2. Au(I)-NHCs in Medicine 3580 4. Cu(I)and Cu(II)-NHCs 3581 4.1. Historical Background 3581 4.2. General Synthetic Methods 3582 4.3. Formation of Cu(I)and Cu(II)-NHCs 3583 4.3.1. Complexes Containing the Cu(NHC)2 Core 3583 4.3.2. [Cu(NHC)(Halide)] 3583 4.3.3. [Cu(NHC)(Ligand)] 3584 4.3.4. Multinuclear Cu(I)and Cu(II)-NHCs 3589 4.4. Catalysis 3591 4.4.1. Past Events 3591 4.4.2. Recent Advancements 3591 5. Photoluminescence 3592 6. Conclusions 3594 7. Abbreviations 3594 8. Acknowledgments 3595 9. References 3595
906 citations
TL;DR: During the last five years, new types of stable cyclic carbenes, as well as related carbon-based ligands (which are not NHCs), and which feature even stronger σ-donor properties have been developed.
Abstract: The success of homogeneous catalysis can be attributed largely to the development of a diverse range of ligand frameworks that have been used to tune the behavior of various systems. Spectacular results in this area have been achieved using cyclic diaminocarbenes (NHCs) as a result of their strong σ-donor properties. Although it is possible to cursorily tune the structure of NHCs, any diversity is still far from matching their phosphorus-based counterparts, which is one of the great strengths of the latter. A variety of stable acyclic carbenes are known, but they are either reluctant to bind metals or they give rise to fragile metal complexes. During the last five years, new types of stable cyclic carbenes, as well as related carbon-based ligands (which are not NHCs), and which feature even stronger σ-donor properties have been developed. Their synthesis and characterization as well as the stability, electronic properties, coordination behavior, and catalytic activity of the ensuing complexes are discussed, and comparisons with their NHC cousins are made.
881 citations
TL;DR: In this paper, three structural classes of NHC ligands can be distinguished: normal (nNHC), abnormal (aNHC) and mesoionic (MIC), and remote (rNHC).
470 citations
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TL;DR: In this paper, the crystal structure of compound 1 revealed that linear [Ag(Et2-Bimy)2]+ and [AgBr2]- groups were associated through a short AgI−AgI contact (2.956 A).
1,033 citations
TL;DR: N-Heterocyclic carbenes bind to both hard and soft metals making it a very versatile ligand system, and has been shown to equal, if not exceed, phosphines in their ability to bind to a variety of metals.
Abstract: Öfele and Wanzlick first pioneered the metalation of imidazol-2-ylidenes, better known as N-heterocyclic carbenes (NHCs), from imidazolium salts in 1968.1,2 Lappert and co-workers followed this work with the investigation of N-heterocyclic carbene complexes synthesized from electron-rich olefins.3,4 However, it was not until the isolation of the first free carbene by Arduengo, in 1991, that significant interest was given to the area.5 Since then the complexation chemistry of these new ligands has become a major area of research.6-10 This new class of ligand has shown to equal, if not exceed, phosphines in their ability to bind to a variety of metals. Complexes of N-heterocyclic carbenes with virtually every transition metal and many main group elements have been reported.1-10 N-Heterocyclic carbenes bind to both hard and soft metals making it a very versatile ligand system. NHCs bond to metals primarily through σ donation of the carbene lone pair to the metal. The bonding of the carbene was believed to have been purely σ donation in nature; however, recent evidence suggests that some degree of backdonation may occur.11,12 The bond strength of Nheterocyclic carbenes, as mentioned earlier, has been shown to rival phosphines. Due to this bonding * To whom correspondence should be addressed. Phone: (330)972-5362. E-mail: youngs@uakron.edu. 3978 Chem. Rev. 2005, 105, 3978−4008
950 citations
TL;DR: The use of N-heterocyclic carbenes as ligands for transition metals has increased dramatically in the last few years, spurred on by their remarkable successes in the areas of metathesis chemistry and coupling reactions as discussed by the authors.
901 citations
TL;DR: A comprehensive overview of the progress in this area can be found in this paper, where the N-heterocyclic carbene-based organometallic chemistry has drawn increasing attention to this class of ancillary ligands.
763 citations
TL;DR: In this article, the authors provide an updated and comprehensive review on the subject of Ag(I)-NHCs, which may further accelerate work on this topic, focusing on the ease and limitations in the synthesis of AgI-NHC, and the parameters influencing the solid state structures.
585 citations