Boryl-dihydrideborate osmium complexes: Preparation, structure, and dynamic behavior in solution

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 corresponding Os(BR2)Cl(CO)(PiPr3)2 with Na[BH4].Financial support from the Spanish MINECO (Projects CTQ2011-23459 and CTQ2014-51912-REDC), the DGA (E35), and the European Social Fund (FSE) is acknowledged. M.M. thanks the Spanish MEC for her FPU grant.Peer reviewe