White Phosphorus as a ligand for Copper, Silver and Gold

A new paper by Chris Russell's research group was published recently in Chem. Commun. (Chemical Communications). Russell's group have done some pretty cool things with phosphorus recently, for example this and this. I love phosphorus, so I was excited to see this latest research.

Phosphorus can exist in several forms, or allotropes. The two most common of these are white phosphorus and red phosphorus. White phosphorus consists of tetrahedral P₄ molecules, in which each atom is bound by single bonds to the other three atoms. White phosphorus is the least stable and the most reactive allotrope. Red phosphorus has a polymeric structure and can be thought of as a derivative of P₄ where one of the P-P bonds has been broken and two additional bonds to neighbouring tetrahedra have been formed. Other allotropes of phosphorus include violet (or Hittorf's) phosphorus and black phosphorus, however these are far less commonly encountered. 

Russell's latest research involved reacting white phosphorus with MX (M = Cu, Au: X = Cl; M = Ag: X = OTf) and GaCl₃ in dicholoromethane. Interestingly, three completely different products were formed depending on which of the three metals was used.

Cu was found to form chains of CuGaCl₄ units linked by P₄ molecules to form a polymeric framework, in which each P₄ is bound to two Cu atoms in an η²-fashion.

Part of the polymeric framework formed in the reaction between P₄, CuCl and GaCl₃.

Ag also forms a polymeric structure, however in this case each P₄ is only bound to one Ag atom.

Part of the polymeric structure formed in the reaction between P₄, AgOTf and GaCl₃.

Au, on the other hand, forms [Au(P₄)₂][GaCl₄], which consists of discrete [Au(P₄)₂]⁺ cations and [GaCl₄]^– anions. [Au(P₄)₂]⁺ consists of two P₄ molecules bonded to a Au atom in an η²-fashion. This is the first time [Au(P₄)₂]⁺ has been isolated, however both [Cu(P₄)₂]⁺ and [Ag(P₄)₂]⁺ were previously synthesised by Krossing. 

[Au(P₄)₂]⁺.

Elements in the same group of the periodic table can sometimes behave very differently, a fact that is brilliantly illustrated by this research: three metals, same group, same reaction, three very different products. I also think this paper has shown that phosphorus can be used to form some really beautiful structures, something I will say more about in a later post...