Reactions of a dihydrogen complex with terminal alkynes: Formation of osmium-carbyne and -carbene derivatives with the hydridotris(pyrazolyl)borate ligand

The dihydrogen complex [OsTp(η2-H2) (κ1-OCMe2)(PiPr3)]BF 4 (1; Tp = hydridotris(pyrazolyl)borate) reacts with tert-butylacetylene to give the hydride-carbyne derivative [OsHTp(≡ CCH2 tBu)(PiPr3)]BF4 (2). Similarly, the treatment of 1 with (trimethylsilyl)acetylene in the presence of methanol leads to [OsHTp(≡CCH3)(PiPr 3)]BF4 (3). In chloroform at 60°C, complexes 2 and 3 evolve into the corresponding chloro derivatives [OsClTp(≡CR)(P iPr3)]BF4 (R = CH2 tBu (4), CH3 (5)), whereas in acetonitrile the carbenes [OsTPi=CHR)(NCCH3)(PiPr3)]BF4 (R = CH2 tBu (6), CH3 (7)) are formed. Complex 1 also reacts with phenylacetylene. The reaction initially gives [OsHTp(≡ CCH2Ph)(PiPr3)]BF4 (8). Subsequently, the insertion of a second molecule of alkyne into the Os-H bond of 8 and the migration of the resulting alkenyl group from the metal center to the carbyne carbon atom take place, to afford the carbene [OsTp{=C(CH 2Ph)C(Ph)=CH2}(PiPr3)]BF 4 (9). The metal center of 9 is saturated by means of a strong agostic interaction (rbp = 0.4(1)) between the osmium atom and one of the ortho-CH bonds of the phenyl substituent of the alkenyl unit of the alkenylcarbene ligand. Treatment of 1 with methylpropiolate leads to the carbene [OsTp {=CHCH2C(O)OMe} (PiPr3)]BF4 (10) in a one-pot synthesis. Complexes 2, 4, 9, and 10 have been characterized by X-ray diffraction analysis. © 2008 American Chemical Society.Financial support from the MEC of Spain (Projects CTQ2005-00656 and Consolider Ingenio 2010 CSD2007-00006) and Diputación General de Aragón (E35) is acknowledged.Peer Reviewe