Complex OsH3Cl(PiPr3)2 (1) reacts with KTp (Tp ) hydridotris(pyrazolyl)borate) in tetrahydrofuran at room temperature to give OsH3( 2-Tp)(PiPr3)2 (2). In toluene at 80 °C, the 2-Tp complex 2 is transformed to the 3-Tp derivative OsH3Tp(PiPr3) (3) in quantitative yield after 7 h. Protonation of 3 with HBF4 affords the bis(dihydrogen) compound [OsTp(è2-H2)2(PiPr3)]BF4 (4). In acetone complex 4 releases the coordinated hydrogen molecules in a sequential manner. At room temperature, the dihydrogensolvate complex [OsTp(è2-H2)( 1-OCMe2)(PiPr3)]BF4 (5) is formed, while at 56 °C the loss of both hydrogen molecules gives rise to the bis-solvento derivative [OsTp( 1-OCMe2)2(PiPr3)]BF4 (6). Complexes 2-6 have been characterized by X-ray diffraction analysis, and DFT calculations support their formulation. The structures of 3-5 have been compared with those of their Cp counterparts OsH3Cp(PiPr3), [OsH2- Cp(è2-H2)(PiPr3)]BF4, and [OsH2Cp( 1-OCMe2)(PiPr3)]BF4. The results show that the Tp ligand avoids piano stool geometries, while it enforces dispositions allowing N-Os-N angles close to 90° such as octahedron and pentagonal bipyramid.

Financial support from the MEC of Spain (Projects CTQ2005-00656 and Consolider Ingenio 2010 CSD2007-00006) and Diputación General de Aragón (E35) is acknowledged.

12 pages, 1 table, 15 figures, 1 scheme.-- Supporting Information Available: http://pubs.acs.org.

Peer reviewed