SYNTHESIS AND REACTIVITY OF A HETEROMETALLIC CO2 COMPLEX

Reduction of CO2 by (COD)RhH3OsP3 (COD = 1,5-cyclooctadiene; P = PMe2Ph) proceeds at 1 atm and 25 °C in benzene or THF to give H2Os(CO)P3, [(COD)Rh]2OsH2CO2P3 (I), and H2O. The metal-containing products are characterized by NMR and vibrational spectroscopy (including products from 13CO2), as well as an X-ray structure determination of compound I. Crystal data (−155 °C): a = 10.338 (4) Å, b = 23.184 (11) Å, c = 19.943 (8) Å, β = 123.20 (1)°, with Z = 4 in space group P21/c. Space-filling models of I show that only the oxygens of the coordinated CO2 are accessible to external reagents, and Na+ (as the BPh4− salt) is shown to bind in THF with a large formation constant but to exchange raidly on the NMR time scale with free I. Reaction of I with ZnBr2 in THF also gives a 1:1 adduct, which has been characterized by NMR and vibrational spectroscopy, as well as X-ray diffraction. Crystal data (at −150 °C): a = 19.677 (11) Å, b = 11.267 (5) Å, c = 22.376 (15) Å, β = 103.59 (3)°, with Z = 4 in space group P21/a. Zinc achieves a tetrahedral geometry by binding to both oxygens of CO2. The major structural change in I upon binding the ZnBr2 electrophile is a shortening of the Os–C distance by 0.048 Å. Small changes of the identity of the metal or ligands in (COD)RhH3OsP3 are shown to quench its reactivity toward CO2. © 1990, American Chemical Society. All rights reserved.