Boryl-Dihydrideborate Osmium Complexes: Preparation, Structure, and Dynamic Behavior in Solution

Abstract

The metal fragment Os(CO)(PiPr3)2 stabilizes boryl-dihydrideborate species, which can be viewed as snapshots of states of B–H oxidative addition of a R2BH molecule and frustrated B–H bond activation of a second one. Complex OsH2(η2-CH2═CHEt)(CO)(PiPr3)2 (2) shows a tendency to dissociate the olefin. The resulting dihydride OsH2(CO)(PiPr3)2 (3) rapidly coordinates catecholborane (HBcat) and pinacolborane (HBpin) to give the corresponding σ-borane derivatives OsH2(η2-HBR2)(CO)(PiPr3)2 (BR2 = Bcat (4), Bpin (5)). Complex 4 reacts with a second molecule of HBcat to release H2 and to afford the octahedral boryl dihydride borate derivative Os(Bcat)(κ2-H2Bcat)(CO)(PiPr3)2 (6), which undergoes a thermally activated Bcat site exchange process in solution. Borane displaces catecholborane from the dihydride-borate of 6 to generate the boryl-tetrahydrideborate Os(Bcat)(κ2-H2BH2)(CO)(PiPr3)2 (7). This compound and the Bpin counterpart Os(Bpin)(κ2-H2BH2)(CO)(PiPr3)2 (8) have also been prepared by reaction of the corres...