The chemistry of chromium nitrile complexes of 1,2-bis(dimethylphosphino)-ethane. X-Ray crystal structures of trans-[CrIVCl(NEt)(dmpe)2]CF3SO3, trans-[CrIV(NCHMe)2(dmpe)2][BPh4]2, and trans-[Co0(H·NCMe)2(dmpe)2][BPh4]2

Abstract

The interaction of CrCl₂(dmpe)₂ with NaBPh₄ in MeCN at room temperature gives the partially substituted complex trans-[Cr^IICl(NCMe)(dmpe)₂] BPh₄; when the reaction is carried out in refluxing MeCN the product is the previously characterised trans-[Cr^II(NCMe)₂(dmpe)₂][BPh₄]₂. The interaction of both nitrile complexes with methanol has been studied, and the X-ray structures of the products, trans-[Cr^IVCl(NEt)(dmpe)₂]CF₃SO₃ and trans-[Cr^IV(NCHMe)₂(dmpe)₂][BPh₄]₂ respectively, have been determined. These are the first octahedral Cr^IV complexes. The interaction of trans-[Cr(NCMe)₂(dmpe)₂][BPh₄]₂ with H₂ leads to a complex of stoicheiometry trans-[Cr(H·NCMe)₂(dmpe)₂][BPh₄]₂, whose structure has been confirmed by X-ray crystallography. Although hydrogens bound to acetonitrile were not detected either crystallographically or spectroscopically, the diamagnetism together with the values of the Cr–P distances eliminate the possibility of a Cr^II species and confirm the presence of Cr⁰. Two weakly acidic protons have been shown to be present chemically, and its is proposed that H⁺ is located on the electron density in the CN bond. The chromium(III) complex trans,trans-[{Cr(NCMe)(dmpe)₂}₂(µ-O)]⁴⁺ is also described.