Main-group elements as transition metals

Abstract

The last quarter of the twentieth century and the beginning decade of the twenty-first witnessed spectacular discoveries in the chemistry of the heavier main-group elements. The new compounds that were synthesized highlighted the fundamental differences between their electronic properties and those of the lighter elements to a degree that was not previously apparent. This has led to new structural and bonding insights as well as a gradually increasing realization that the chemistry of the heavier main-group elements more resembles that of transition-metal complexes than that of their lighter main-group congeners. The similarity is underlined by recent work, which has shown that many of the new compounds react with small molecules such as H(2), NH(3), C(2)H(4) or CO under mild conditions and display potential for applications in catalysis.

Electrophilic Activation of Silicon–Hydrogen Bonds in Catalytic Hydrosilations

“…[31] In the field of hydrosilation catalysis, a variety of Lewis acids have been identified that operate by Si-H coordination to the catalyst, which renders the silicon center electrophilic, particularly since main group species usually cannot provide back-donation into the Si-H σ* orbital. This section highlights various main group hydrosilation catalysts that operate by variants of the ionic hydrosilation mechanism shown in Scheme 2a.…”

“…These studies include detailed mechanistic investigations that provide strong support for the ionic hydrosilation mechanism in this system. For the ether cleavage reactions, it was shown that 30 and diethyl ether exist in equilibrium with a neutral iridium dihydride (31) Mechanistic studies of ketone hydrosilations using 29 also point to the involvement of the ionic hydrosilation mechanism, though the initial report did not provide evidence as detailed as that obtained for ether substrates. [69] A follow-up study on the ketone hydrosilation mechanism using 29 was conducted by Oestreich et al, and concluded that a complex variation of the ionic mechanism occurs in this system (Scheme 34).…”

Comparing Neutral (Monometallic) and Anionic (Bimetallic) Aluminum Complexes in Hydroboration Catalysis: Influences of Lithium Cooperation and Ligand Set

“…The synthetic value of main‐group metal complexes aside from the highly reactive and versatile organolithium and organomagnesium reagents have, from a historical perspective, been overshadowed by the illustrious reputation of transition‐metal (notably precious metals) and lanthanide‐metal counterparts especially in catalysis 1. To a large extent main‐group research has been driven by fundamental curiosity and the understanding of the nature of chemical bonding and structure.…”

“…Emulating the high reactivity, selectivity and versatility of the often toxic and scarce precious metal complexes is a tantalising challenge that needs addressing. In this regard, the pioneering work of Harder, Hill, Jones, Okuda, Power, Roesky, Wright among others, are expanding the vistas of main‐group complexes in homogeneous catalysis 1, 2. Since aluminum is the most abundant metal in the earth's crust, and also benefits from low toxicity, harnessing its reactivity is given high prominence in this main group uprising with longer term sustainability being a key issue.…”

Reversible Oxidative Se−Se Coupling of Phosphine Selenides by Ph3Sb(OTf)2

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The coordination chemistry of p-blockc enters as Lewis acceptors has evolveds ignificantly in recent years, [1][2][3][4][5][6] with many analogies to the coordination chemistry of transition metal elements.I nt his context, we have recently reported complexes of Ph 3 Sb(OTf) 2 with classicalO -a nd N-donorl igands (Scheme1a).In contrast, attempts to isolate the correspondingc omplexes of Ph 3 Sb(OTf) 2 with Me 3 Pa saligand result in reduction of the antimony(V) centert oP h 3 Sb III and oxidation of the phosphine to [Me 3 PPMe 3 ][OTf] 2 (Scheme 1b), illustrating an oxidative PÀP coupling process or reductivee limination of ad iphosphonium dicationfrom antimony. [7] We have now discovered that in an analogousr eaction Ph 3 Sb(OTf) 2 effects oxidative SeÀSe coupling of trialkylphosphine selenides to give salts of 2 (Scheme1c).

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