The synthesis and reactivity of multiply -bonded dirhenium complexes containing nitrogen donor ligands

James Chantler, Purdue University

Abstract

The reactions of the halogens X2 (X = Cl or Br) with the diamagnetic, electron-rich triply bonded dirhenium(II) complexes Re2X4 μ-dppm)2(L), where L = XylNC, t-BuNC or CO, and with salts of the edge-sharing bioctahedral species [Re2(μ-Cl)(μ-CO) Cl2(μ-dppm)2(NCMe)2]+ provide convenient routes to the dirhenium (III) species [Re2Cl5(μ-dppm) 2(L)]+. These cations, which have been isolated as their halide (Cl− or Br3−), PF6−, and O3SCF3 − salts, are the first multiply bonded Re2 6+ compounds that contain these π-acceptor ligands. A crystal structure determination of the complex [Re2Cl5(μ-dppm) 2(CO)]PF6 confirms that the cation has the edge-sharing bioctahedral structure [Re2(μ-Cl)2(μ-dppm)2Cl 3(CO)]+. 31P NMR spectroscopy indicates that these salts are weakly paramagnetic, with their P resonances exhibiting unusually large upfield shifts. The complex Re2Cl4(μ-dppm) 2(CO) reacts with acetonitrile in the presence of KPF6 or TlO3SCF3 to yield salts of the cations [Re2Cl 3(μ-dppm)2(CO)(NCMe)]+ and [Re2Cl 3(μ-dppm)2(CO)(NCMe)2]+ which have been structurally characterized. The [Re2(μ-Cl)(μ-CO)Cl 2(μ-dppm)2(NCMe)2]+ cation has an all-cis edge-sharing bioctahedral structure. The nitrile ligands are labile as demonstrated by the conversion of salts of [Re 2Cl3(μ-dppm)2(μ-CO)(NCMe)2] + to the starting complex Re2Cl4(μ-dppm) 2(CO) when they are reacted with one equivalent of Cl− ion. The dirhenium(II) complex Re2Cl4(μ-dppa) 2 has been used as a template for the reductive coupling of nitrile ligands. This is demonstrated by the formation of the [Re2Cl 3(μ-HN2C2Et2)(μ-dppa)2(NCEt)] + cation in which the (μ-HN2C2Et2) moiety results from the reductive coupling of two propionitrile ligands mediated by the electron-rich triply bonded dirhenium unit. The complex [Re2Cl 3(μ-HN2C2Et2)(μ-dppa)2(NCEt)]Cl and complexes of the type [Re2X3(μ-dppa)2(NCR) 2]PF6 (X = Cl or Br) are the first examples of compounds produced by the direct reaction of Re2Cl4(μ-dppa) 2 with organic ligands.

Degree

Ph.D.

Advisors

Walton, Purdue University.

Subject Area

Chemistry

COinS