| Abstract |
In the current investigation, the reaction of [Cr-(CO)(6)] with the ligand precursor PO(C-Br)OP-tBu (la) was investigated. When a suspension of [Cr(CO)(6)] and la in toluene was transferred into a sealed microwave glass vial and stirred for 3 h at 180 degrees C, the square-planar Cr(II) complex [Cr(POCOP-tBu)(Br)] (2a) was obtained. With PO(C-Br)OP-iPr (1b) the dibromo Cr(III) complex trans-[Cr(POCOP-iPr)(Br)(2)(THF)] (2b) was formed, after recrystallization from THF. Treatment of 2a with 1 equiv of LiBH4 in THF led to the formation of the borohydride complex [Cr(POCOP-tBu)(kappa(2)-BH4)] (3). Exposure of a toluene solution of 3 to NO gas (1 bar) at room temperature afforded the Cr(I) complex [Cr(POCOP-tBu)(NO)(kappa(2)-BH4)] (4). Alternatively, 4 was also obtained by reacting [Cr(POCOP-tBu)(NO)(Br)] (5) with LiBH4. On the basis of magnetic and EPR measurements as well as DFT calculations, compounds 4 and 5 adopt a low-spin d(5) configuration and feature a nearly linearly bound NO ligand, suggesting (CrNO+)-N-I rather than (CrNO center dot)-N-II character. The reaction of 2a with 1 equiv of Li[CH2SiMe3] in toluene afforded the square-planar alkyl complex [Cr(POCOP-tBu)(CH2SiMe3)] (6) in 57\% yield. This compound is catalytically active for the hydrosilylation of ketones at room temperature with a catalyst loading of 0.5 mol \%. X-ray structures of all complexes are presented. |
