Copper(I)-Facilitated Methylation and Cyclic Alkylation of 1,2-Phenylenebis(phosphine)

Abstract

The phosphorus centers in [Cu{l,2-C₆H₄(PH₂)₂}₂]CF₃SO₃ are readily methylated by methyl iodide in the presence of 4 or 8 equiv potassium tert-butoxide to give 1,2-phenylenebis (methylphosphine) or 1,2-phenylenebis(dimethylphosphine), respectively, after displacement from the metal with cyanide. Under similar conditions with 8 equiv of base, 1,4-dibromobutane and 1,5-dibromopentane react to give respectively 1,2-phenylenebis (phospholane) and 1,2-phenylenebis (phosphorinane). 1,3-Dibromopropane, however, reacts with the complex under the basic conditions to give a variety of phosphines after displacement from the metal, including (R^*, R^*)-(±)/(R^*, S^*)-2,3,4,5-tetrahydro-lH-l,5-benzodiphosphepine, (R^*, S^*)-2,3,4,5-tetrahydro-l,5-bis (prop-l-enyl)-lH-l,5-benzodiphosphepine, (R^*, S^*)-2,3,4,5-tetrahydro-l, 5-bis (prop-2-enyl)-lH-l, 5-benzodiphosphepine, and the putative cage and macrocyclic dimers of 1,2-phenylenebis (phosphetane). The crystal structure of anti-[Ni {(R^*, S^*)-2,3,4,5-tetrahydro-l, 5 bis (prop-l-enyl)-lH-l,5-benzodiphosphepine}₂] (ClO₄)₂·CH₂CI₂ has been determined. Crystal data: monoclinic, C2/c, a = 27.119(3)Å, b = 10.908(1) Å, c = 15.590 (2) Å, β =123.81(1)°, Z = 4, and R=0.047. The coordination geometry around the nickel is square-planar in the centrosymmetrical cation of the complex.