Tertiary phosphine complexes of chromium(III)

Abstract
Anhydrous Chromium(III) chloride has been treated with the tertiary phosphines Me3P, Et3P, Bun 3P, 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 Bun 3P 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.
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