| The complex (tBuPOCOP)IrH2 ( tBuPOCOP = kappa3-C6H3-1,3-[OP( tBu)2]2) has been shown previously to be a useful catalyst for the dehydrogenation of ammonia borane (AB). In the course of catalytic turnovers, a new species, (tBuPOCOP)Ir(H) 2(BH3), was observed. This complex has been independently synthesized and characterized as a unique a borane complex of Ir. Reaction of (tBuPOCOP)IrH2 with pinacolborane (HBpin) at low temperature produced (tBuPOCOP)IrH3Bpin, wherein the HBpin molecule is bound to the Ir. Upon increasing the temperature, H 2 was released to give the sigma complex (tBuPOCOP)IrHBpin. Complex (tBuPOCOP)IrH2 exists in equilibrium with 9-boro-bicyclononane (9-BBN) to form (tBuPOCOP)IrH3 -9-BBN.;The dominant organometallic species during AB dehydrogenation is ( tBuPOCOP)IrH4. The arrangement of hydrogen atoms in the coordination sphere of Ir was previously undetermined. This complex and the related (tBuPCP)IrH4 (tBuPCP = kappa3-C6H3-1,3-[CH2P( tBu)2]2) were investigated using 1H NMR spectroscopy. Computational data for (tBuPOCOP)IrH 4 and (tBuPCP)IrH4 and solid state data for (tBuPCP)IrH4 obtained in a collaboration suggests the complexes are best described as containing only hydride ligands. Interpretation of the HD coupling in isotopically labeled compounds (tBuPOCOP)IrD 3H and (tBuPCP)IrD3H suggests that these complexes are best described as containing two hydride ligands and one elongated dihydrogen ligand with rHH = 0.97 +/- 0.09 and 1.06 +/- 0.11 A, respectively.;Extending the ligand (tBuPOCOP) to cobalt required use of a new ligand precursor, (tBuPOCOP)I. Activation of ( tBuPOCOP)I allowed for isolation of the complex (tBuPOCOP)CoI in excellent yield. Reduction of (tBuPOCOP)CoI in the presence of N2, H2, or Ar led to the complexes (tBuPOCOP)CoN 2, (tBuPOCOP)CoH, and (tBuPOCOP)Co, respectively. Addition of H2 to a solution of (tBuPOCOP)Co at low temperature allowed for observation of the new complexes ( tBuPOCOP)Co(H2) and (tBuPOCOP)CoH 4. The presence of a dihydrogen ligand in complex (tBuPOCOP)Co(H 2) was confirmed by the observation of JHD = 28 Hz in complex (tBuPOCOP)Co(HD) corresponding to rHH = 0.95 A for the dihydrogen ligand. Addition of substoichiometric amounts of N2 to complex (tBuPOCOP)Co allowed observation of a dinuclear bridging complex ((tBuPOCOP)Co) 2(N2), which exists in equilibrium with complexes ( tBuPOCOP)Co and (tBuPOCOP)CoN2. Complexes (tBuPOCOP)CoI, (tBuPOCOP)CoN2, and (tBuPOCOP)Co were tested for their ability to release hydrogen from AB, but none of these were found to be effective catalysts. |
