Geminal Dianions Stabilized by Main Group Elements

This review is dedicated to the chemistry of stable and isolable species that bear two lone pairs at the same C center, i.e., geminal dianions, stabilized by main group elements. Three cases can thus be considered: the geminal-dilithio derivative, for which the two substituents at C are neutral, the yldiide derivatives, for which one substituent is neutral while the other is charged, and finally the geminal bisylides, for which the two substituents are positively charged. In this review, the syntheses and electronic structures of the geminal dianions are presented, followed by the studies dedicated to their reactivity toward organic substrates and finally to their coordination chemistry and applications.

Synthesis, characterization and reactivity of potassium and barium complexes containing phosphane-borane stabilized methanides

The polymeric potassium complex [K{CH(PPh2BH3)2}]∞ (1) was prepared and used as a starting material for the syntheses of related N,N,N',N'-tetramethylethylenediamine (tmeda) and N,N,N',N',N''-pentamethyldiethylenetriamine (pmdta) ligated potassium derivatives [K{CH(PPh2BH3)2}(tmeda)2]∞ (2) and [K{CH(PPh2BH3)2}(pmdta)]2 (3). Salt metathesis reactions with [BaI2(thf)5] allowed the synthesis of the barium derivatives [BaI{CH(PPh2BH3)2}(thf)5] (5) and [Ba{CH(PPh2BH3)2}2(solv)2}] (solv = Et2O, thf) (6), which are more prone to subsequent reactions than the potassium derivatives. One of the resulting products, [Ba4O{CH(PPh2BH3)2}3{Ph2PCH(BH3)PPh2BH3}3] (7), which contains two different isomeric forms of the bis(borane) adduct of Ph2PCHPPh2, was isolated. The complexes were characterized by NMR techniques and single crystal X-ray diffraction measurements.

Formation of a Ph2PCH(BH3)P(BH3)Ph2 ligand via formal 1,2-borane migration

The transfer of the anionic Ph(2)P(BH(3))-CH-P(BH(3))Ph(2) ligand from potassium to barium results in the subsequent formation of a tetranuclear barium cluster which contains the hitherto unknown isomeric form Ph(2)P-CH(BH(3))-P(BH(3))Ph(2) of the ligand.

Early metal bis(phosphorus-stabilised)carbene chemistry

Since the discovery of covalently-bound mid- and late-transition metal carbenes there has been a spectacular explosion of interest in their chemistry, but their early metal counterparts have lagged behind. In recent years, bis(phosphorus-stabilised)carbenes have emerged as valuable ligands for metals across the periodic table, and their use has in particular greatly expanded covalently-bound early metal carbene chemistry. In this tutorial review we introduce the reader to bis(phosphorus-stabilised)carbenes, and cover general preparative methods, structure and bonding features, and emerging reactivity studies of early metal derivatives (groups 1-4 and the f-elements).