Reductive Catenation of Phosphine Antimony Complexes

Hydrostibination of Alkynes: A Radical Mechanism*

The addition of Sb-H bonds to alkynes was reported recently as a new hydroelementation reaction that exclusively yields anti-Markovnikov Z-olefins from terminal acetylenes. We examine four possible mechanisms that are consistent with the observed stereochemical and regiochemical outcomes. A comprehensive analysis of solvent, substituent, isotope, additive, and temperature effects on hydrostibination reaction rates definitively refutes three ionic mechanisms involving closed-shell charged intermediates. Instead the data support a fourth pathway featuring open-shell neutral intermediates. Density-functional theory (DFT) calculations are consistent with this model, predicting an activation barrier that is in agreement with the experimental value (Eyring analysis) and a rate limiting step that is congruent with the experimental kinetic isotope effect. We therefore conclude that hydrostibination of arylacetylenes is initiated by the generation of stibinyl radicals, which then participate in a cycle featuring Sb^II and Sb^III intermediates to yield the observed Z-olefins as products. This mechanistic understanding will enable rational evolution of hydrostibination as a synthetic methodology.

Heavy Metals Make a Chain: A Catenated Bismuth Compound

Catenation is common for the light main-group elements whereas it is rare for the heavy elements. Herein, we report the first example of a neutral molecule containing a Bi₄ chain. It is prepared in a one-step reaction between bismuth trichloride and bis(diisopropylphosphino)amine in methanol suspension. The same reaction carried out in dichloromethane gives quite different products. All products have been characterized spectroscopically and using single-crystal X-ray analysis.

Reduction of [Cp*Sb]4 with Subvalent Main-Group Metal Reductants: Syntheses and Structures of [(L1 Mg)4 (Sb4 )] and [(L2 Ga)2 (Sb4 )] Containing Edge-Missing Sb4 Units

[Cp*Sb]₄ (Cp*=C₅ Me₅ ) reacts with [L¹ Mg]₂ and L² Ga with formation of [(L¹ Mg)₄ (μ₄ ,η^1:2:2:2 -Sb₄ )] (L¹ =iPr₂ NC[N(2,6-iPr₂ C₆ H₃ )]₂ , 1) and [(L² Ga)₂ (μ,η^2:2 -Sb₄ )] (L² =HC[C(Me)N(2,6-iPr₂ C₆ H₃ )]₂ , 2). The cleavage of the Sb-Sb and Sb-C bonds in [Cp*Sb]₄ are the crucial steps in both reactions. The formation of 1 occurred by elimination of the Cp* anion and formation of Cp*MgL¹ , while 2 was formed by reductive elimination of Cp*₂ and oxidative addition of L² Ga to the Sb₄ unit. 1 and 2 were characterized by heteronuclear NMR spectroscopy and single-crystal X-ray diffraction, and their bonding situation was studied by quantum chemical calculations.

Recent highlights in mixed-coordinate oligophosphorus chemistry

This review aims to highlight and comprehensively summarize recent developments in the field of mixed-coordinate phosphorus chemistry. Particular attention is focused on the synthetic approaches to compounds containing at least two directly bonded phosphorus atoms in different coordination environments and their unexpected properties that are derived from spectroscopic and crystallographic data. Novel substance classes are discussed in order to supplement previous reviews about mixed-coordinate phosphorus compounds.