Synthesis, characterisation and molecular structure of [Rh(COE)2(acac)] (COE=cyclooctene, η2-C8H14), an important starting material for the preparation of rhodium catalyst precursors

The compound [Rh(COE)2(acac)] (1) is a catalyst precursor in its own right, and a starting material for the preparation of other catalyst precursors for use in a variety of reactions such as hydroboration, diboration and the addition of arylboronic acids to aldehydes. Although a preparation using Tl(acac) and [Rh(COE)2(μ-Cl)]2 is in the literature, it would appear that it is not widely known and we have received several requests for our synthetic protocol for 1, which does not use any thallium salts. We present herein a synthesis of 1 from [Rh(COE)2(μ-Cl)]2 and Na(acac), along with its full spectroscopic and structural characterisation. The single crystal X-ray structure of 1 indicates approximate square-planar geometry at Rh, with the two olefinic CC bonds lying perpendicular to the square plane.