ReviewBH activation of carboranes induced by late transition metals☆
Graphical abstract
Introduction
Dicarba-closo-dodecaboranes are a class of icosahadral clusters containing ten BH vertices and two CH units [1]. Due to their rigidity and robustness, they constitute a series of structurally unique skeletons with excellent thermal and chemical stabilities and the ability to tolerate various substituents [1]. Using these physical and chemical properties, a range of promising applications have been successfully explored in supramolecular design, medicine, catalysts and materials [2], [3]. Recently, Weller and Mirkin reported separately that carboranes have two faces: one is the electron-rich motif of the B atoms, while the C atoms represent a strongly electron-poor motif [4], [5]. These persuasive reports have indicated why these compounds have the above-mentioned exceptional chemical behaviors and can further accommodate distinct organic groups to substitute the BH or CH vertices. The group of Xie has published numerous papers on the inclusion of small organic groups to carboranes and radicals through activation of BH or CH bonds (Chart 1) [1]. A wide range of organometallic frameworks prepared by BH bond activation induced by half-sandwich metal (Co, Rh, Ir, Ru and Os) fragments have emerged recently [6], [7].
Moreover, half-sandwich metal fragments (i.e. containing ruthenium, osmium, rhodium, iridium, etc.), due to their accessibility, robustness, air-stability and water-solubility, have been logically used in the construction of versatile organometallic compounds [8], [9], [10], [11], [12], [13], which can be applied in various fields such as synthesis and catalysis, or as building blocks in supramolecular chemistry [14], [15], [16], [17], [18]. More recently, half-sandwich complexes based on Co, Rh, Ru, and Ir, for example, have been explored as promising anticancer drugs due to their biological behavior and have shown structure–activity relationships, guiding new design concepts [19], [20], [21], [22], [23]. Over the past few decades, chemists have successively constructed many organometallic macrocycles based on half-sandwich motifs. In particular, our research group has successfully assembled multinuclear macrocycles through activation of BH bonds of o-/m-/p-carboranes triggered by half-sandwich Ir fragments [6]. Meanwhile, Yan and co-workers have also utilized half-sandwich Co motifs to activate BH bonds of o-carboranes to afford diverse functionalizations of organometallic compounds, which underwent insertion of small organic molecules [7].
A wide range of methodologies for the BH activation of carboranes have been developed in the past several years for the construction of fascinating organometallic compounds based on half-sandwich motifs [6], [7]. Rational design of carborane-based ligands and suitable half-sandwich metal fragments constitute the two main requirements for constructing organometallic complexes based on BH activation of carboranes. Compared with organometallic frameworks constructed via BH activation by naked metal motifs, these complexes based on half-sandwich metal fragments have attractive molecular architectures and extraordinary properties in terms of their solubility, spatial effects, and reactivity [6], [7]. In this review, we present an update of developments in the controllable syntheses of organometallic complexes based on BH activation of carboranes induced by transition metals and half-sandwich metal motifs, and concisely summarize more recent works on the functionalization of such BH bonds of carboranes.
This review is not intended to cover all domains of BH activation in carboranes, but rather focuses on a few recent impressive examples of BH activation of carboranes induced by late transition metals to effect transformations of 16e− half-sandwich compounds into 18e− half-sandwich compounds, and form CB bonds, metal–metal bonds and various organometallic frameworks, which have interesting structures as well as reactivity.
Section snippets
Functionalization of BH bonds of carboranes
The BH functionalization of closo-dodecaboranes (Scheme 1) has impressively emerged since Hawthorne’s [24] first observation of intramolecular oxidative addition of a BH bond of an o-carboranyl phosphine to an iridium center. However, selective boron-vertex substitution in carboranes is still a major challenge compared with the traditional organic chemistry of aromatic systems. Many of the reported carborane BH functionalizations still rely on strong electrophiles or cross-coupling starting
Conclusion and outlook
Considerable progress has been made in the activation of BH bonds of carboranes over the past decade, which makes it an indispensable approach to the rational design and synthesis of organic carborane-based derivatives and organometallic complexes. This review summarizes briefly the approaches to functionalization of BH bonds in the presence of transition metal catalysts and the construction of frameworks based on half-sandwich transition metal fragments bearing carborane-based ligands. Naked
Acknowledgments
We are indebted to the National Science Foundation of China (21531002, 21374019), the Program for Changjiang Scholars and Innovative Research Team in University (IRT-15R12), the National Basic Research Program of China (2015CB856600) and the Shanghai Science Technology Committee (13JC1400600) for continued financial support over the years of our studies in supramolecular chemistry.
References (84)
- et al.
Acc. Chem. Res.
(2014) - et al.
Chem. Soc. Rev.
(2009) - et al.
Chem. Soc. Rev.
(2012) - et al.
J. Am. Chem. Soc.
(2010) - et al.
J. Am. Chem. Soc.
(2014) - et al.
Inorg. Chem.
(2016) - et al.
Chem. Eur. J.
(2002) - et al.
Chem. Eur. J.
(2000) - et al.
J. Am. Chem. Soc.
(2012) - et al.
J. Organomet. Chem.
(2007)
Coord. Chem. Rev.
Inorg. Chem. Commun.
Dalton Trans.
Dalton Trans.
Organometallics
J. Organomet. Chem.
Chem. Commun.
J. Am. Chem. Soc.
Acc. Chem. Res.
Chem. Rev.
Dalton Trans.
Carboranes
Boron Science: New Technologies and Applications
Nat. Chem.
Nat. Chem.
Coord. Chem. Rev.
J. Organomet. Chem.
Chem. Soc. Rev.
Coord. Chem. Rev.
Coord. Chem. Rev.
Eur. J. Inorg. Chem.
Eur. J. Inorg. Chem.
Organometallics
Angew. Chem. Int. Ed.
Dalton Trans.
J. Med. Chem.
Dalton Trans.
Chimia
Inorg. Chem.
J. Am. Chem. Soc.
Angew. Chem. Int. Ed.
Inorg. Chem.
Allg. Chem.
J. Am. Chem. Soc.
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Dedicated to Professor Pierre Braunstein on the occasion of his 70th birthday.