Inorganic chemistry of the p-block elements

The elements of the p-block have been of interest to chemists since the beginning of the field of chemistry. By 1869, more than half of the 30 p-block elements had been discovered. Of the 63 known elements by then, about one third were p-block elements.¹ Since about two thirds of the elements of the p-block had been discovered by the mid-19th century, they played a large part in the development of the periodic table. When Mendeleev unveiled his periodic table in 1869,² its usefulness came from two critical decisions regarding its layout, and both were related to the p-block elements. His first critical decision was to leave gaps in the table where it seemed that a corresponding element had not yet been discovered (Fig. 1, highlighted with blue circles). These missing elements, three in total, were named eka-silicon (germanium, discovered in 1885), eka-aluminium (gallium, discovered in 1875), and eka-boron (scandium, discovered in 1879).¹ The second critical decision was to occasionally ignore the order suggested by the atomic weights and switch adjacent elements, such as tellurium and iodine, to better classify them into chemical families (Fig. 1, highlighted with a green rounded rectangle). Mendeleev had discovered that the elements, if arranged according to their atomic mass, exhibit an apparent periodicity of properties.

Fig. 1 Mendeleev's first periodic table in 1869, highlighting the 20 known and three unknown p-block elements at the time in red, also the three predicted elements in blue, and the two elements where their position was switched to describe chemical families as opposed to mass in green.

The importance of the chemistry of p-block elements did not stop with the design of the periodic table. Some of the biggest results in chemistry have origins in p-block elements. For example, Fritz Haber,³ William Lipscomb,⁴ H. C. Brown,⁵ Georg Wittig,⁶ Ei-ichi Negishi,⁷ and Akira Suzuki⁸ have received the Nobel Prize in Chemistry for their work on p-block elements. These are just a few of the many advances in p-block chemistry^9,10 that have shaped the way we think about chemistry today.

Although the chemistry of the p-block elements has been at the forefront of past chemical research, as early as the 1970's, it seemed that the p-block elements had already given up all their secrets, leaving future generations of researchers with little new chemistry to find. This assumption was soon learned to be incorrect, as the incorporation of steric bulk into p-block complexes allowed for the ability to explore new reactivity of the p-block elements.^11–14 A remarkable aspect of the p-block is the diversity in the properties and reactivity of these elements, as can be seen in the manuscripts that are included as part of this special collection on the chemistry of the p-block elements.

For the triels (Group 13), there are reports on the design of chiral frustrated Lewis pairs (Stephan et al., DOI: 10.1039/C8DT04070B), 1,1-carboborations with halogen-B(C₆F₅)₂ reagents (Erker et al., DOI: 10.1039/C9DT00413K), the insertion of carbenes into 9-phenyl-9-borafluorene (Martin et al., DOI: 10.1039/C9DT01032G), the generation of a hydrogen-bridging tetraborane (Yamashita et al., DOI: 10.1039/C9DT01117J), the metal-free borylation of heteroarenes (Fontaine et al., DOI: 10.1039/C9DT00484J), and the synthesis of 9,10 boron-doped anthracenes (Wagner et al., DOI: 10.1039/C8DT04820G). There are also reports that describe the generation of triarylborane functionalized Ir complexes (Thilagar et al., DOI: 10.1039/C9DT00590K), the incorporation of ligand-centered borenium ions into Mo complexes (Daly et al., DOI: 10.1039/C9DT00733D), the use of a Ni catalyst for the hydroboration of olefins (Mandal et al., DOI: 10.1039/C9DT00468H), the reduction of CO₂ with aluminum borohydrides stabilized by β-diketiminates (Aldridge et al., DOI: 10.1039/C9DT00535H), and the fixation of CO₂ to aluminum formates (Moya-Cabrera et al., DOI: 10.1039/C9DT00515C), and as cyclic carbonates (Otero et al., DOI: 10.1039/C9DT00323A). This collection also includes a description of Al and Ga adducts of the phosphaethynolate anion (Grützmacher et al., DOI: 10.1039/C9DT00485H), aluminium dihydropyridinates whose dimerization leads to a new type of ditopic pincer ligands (Rodríguez-Delgado et al., DOI: 10.1039/C9DT00847K), heterobimetallic aluminates for the catalytic generation of crosslinked polymers (Mosquera et al., DOI: 10.1039/C9DT00761J), an investigation on the modification of methyaluminoxane (MAO) (McIndoe et al., DOI: 10.1039/C8DT04242J), the post-functionalization of an aluminate anion (García-Rodríguez et al., DOI: 10.1039/C9DT00869A), and the use of 2D indium metal–organic frameworks for catalyzed multicomponent reactions (Monge et al., DOI: 10.1039/C8DT04977G).

This theme issue also contains contributions from the tetrels (Group 14). Reports include: a description of the reactivity of both a substituted silane, HSiMe₂Ph, for the reduction of formamides (Fernandez-Alvarez et al., DOI: 10.1039/C8DT05070H), and a NHC stabilized hydrosilylene with electrophilic boron sources (Inoue et al., DOI: 10.1039/C9DT00608G), in addition to the synthesis of germylone bridged bimetallic complexes of Ir and Rh (Kinjo et al., DOI: 10.1039/C9DT00145J), the generation tetrastannoles and distannadiazanes (Schulz et al., DOI: 10.1039/C8DT04295K), the preparation of monomeric organo-main group halides (Beckmann et al., DOI: 10.1039/C9DT00827F), and the description of a phosphorescent sensor for Pb²⁺ in water (Ceroni et al., DOI: 10.1039/C9DT00251K).

Reports describing the chemistry of the pnictogens (Group 15) are also included in this collection. A discussion of the chemistry of the heavier pnictogens for opto-electronic materials (Orthaber et al., DOI: 10.1039/C9DT00574A), the use of organophosphorous compounds for organic light-emitting diodes (Romero-Nieto et al., DOI: 10.1039/C9DT00380K), the utilization of steric bulk to stabilize primary phosphines (Schulz et al., DOI: 10.1039/C9DT00399A), the generation of polyphosphorus complexes (Scheer et al., DOI: 10.1039/C8DT03723J), phosphazenes (Balakrishna et al., DOI: 10.1039/C8DT04819C), and N-heterocyclic phosphido ligands (Thomas et al., DOI: 10.1039/C8DT05052J), in addition to two reports describing the chemistry of pnictogens in lanthanide complexes with interesting magnetic properties (Chandrasekhar, Colacio et al., DOI: 10.1039/C9DT00592G and DOI: 10.1039/C9DT00504H). There are also reports describing hydroxyl-pyridine anion-based ionic liquids for the capture of CO₂ (Luo et al., DOI: 10.1039/C8DT04680H), and the influence of ligands adjacent to pendant amines on the stabilization of the resulting iron complexes (Wiedner et al., DOI: 10.1039/C9DT00708C).

The chemistry of the chalcogens (Group 16), is represented with reports such as: the use of sulfur containing ligands to generate trimetallic clusters (Ghosh et al., DOI: 10.1039/C8DT05061A), the generation of biologically active Mn complexes with chalcogenide-based ligands (Braga et al., DOI: 10.1039/C9DT00616H), the synthesis of unsymmetrical hexasubstituted benzenes (Singh et al., DOI: 10.1039/C9DT00465C), vanadium(III) halcogenidoantimonates (Zhou et al., DOI: 10.1039/C9DT00268E), telluraporphyrinoids (Ravikanth et al., DOI: 10.1039/C9DT00079H) and even organogermanium chalcogenide complexes (Dehnen et al., DOI: 10.1039/C9DT00310J). Furthermore, a discussion on the redox chemistry of the first stable anionic dithiolene radical is also included (Robinson et al., DOI: 10.1039/C8DT04989K). As well, this collection contains several reports describing the use of iso-tellurazole N-oxides in Pt(II) and Rh(III) complexes (Vargas-Baca et al., DOI: 10.1039/C9DT00500E), and tellurorhodamine for the photocatalyzed aerobic oxidation of organo-silanes and phosphines (McCormick et al., DOI: 10.1039/C9DT00487D).

Although this collection does not contain a contribution on the noble gases (Group 18), the chemistry of the halogens (Group 17) is encompassed with reports on iodine chemistry, the bonding and activation modes of hypercoordinate iodine(III) compounds are reviewed (Sreenithya and Sunoj, DOI: 10.1039/C9DT00472F) and the influence of the pore size on the catalytic activity of iodine supported on MOFs is described (Cozzolino et al., DOI: 10.1039/C9DT00368A).

This fine selection of more than 40 reports on the chemistry of p-block elements, encompassing five of the six p-block families and 18 of the 31 p-block elements, is evidence of an increasing interest in this field, not to mention, the impact these reports will have on the future growth of the chemistry of p-block elements. Given the many breakthroughs in the last decades, the future of p-block chemistry is bright. We'd like to finish by thanking the contributors to this collection, the diligent reviewers who evaluated the manuscripts, and hope that all those readers working in this exciting area will be intrigued by the contributions included in this special issue on the chemistry of the p-block elements.

References

1. J. Emsley, Nature's Building Blocks: An A-Z Guide to the Elements, Oxford University Press Inc., New York, 2011.
2. D. Mendelejeff, Z. Chem., 1869, 12, 405–406.
3. F. Haber, Naturwissenschaften, 1922, 10, 1041–1049.
4. W. N. Lipscomb, Angew. Chem., 1977, 89, 685–696.
5. H. C. Brown, Angew. Chem., 1980, 92, 675–683.
6. G. Wittig, Angew. Chem., 1980, 92, 671–675.
7. E.-i. Negishi, Angew. Chem., Int. Ed., 2011, 50, 6738–6764.
8. A. Suzuki, Angew. Chem., Int. Ed., 2011, 50, 6722–6737.
9. J. A. McCleverty, Annu. Rep. Prog. Chem., Sect. A, 2004, 100, 3–13.
10. T. Chivers and J. Konu, Comments Inorg. Chem., 2009, 30, 131–176.
11. J. M. Crow, Main Group Renaissance, Chemistry World [Online], 2013. https://www.chemistryworld.com/features/main-group-renaissance/6230.article.
12. P. P. Power, Nature, 2010, 463, 171–177.
13. A. R. Jupp and D. W. Stephan, Trends in Chemistry, 2019.
14. F.-G. Fontaine and D. W. Stephan, Philos. Trans. R. Soc., A, 2017, 375.

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