Tertiary phosphine complexes of chromium(III)

Abstract

Anhydrous Chromium(III) chloride has been treated with the tertiary phosphines Me₃P, Et₃P, Buⁿ₃P, PhPEt₂, and Ph₂PEt by heating under reflux in benzene or toluene at 60°. Only in the first three cases did reaction take place and only for Et₃P and Buⁿ₃P could the green complexes [CrCl₃(PR₃)₂]₂ be isolated. These complexes lose one mole of trialkylphosphine on gentle warming in 1:1 CCl₄–CH₂Cl₂ to form insoluble purple complexes [CrCl₃(PR₃)]_n, which are probably polymeric, with halogen bridging. Treatment of the green complexes [CrCl₃(PR₃)₂]₂ with Ph₄PCI (or in some cases with Ph₄AsCl) results in the formation of green salts of the type Ph₄P[CrCl₄(PR₃)₂] which are unstable in solution. Their i.r. and electronic spectra (together with spectra of the neutral dimers) show that the anions have trans-octahedral stereochemistry. Assignments for the Cr–Cl and Cr–P stretching frequencies in these complexes are given, together with values for various ligand-field parameters.