A four-electron πT-alkyne complex as precursor for allenylidene derivatives: Preparation, structure, and reactivity of [Os(η5- C5H5)(C=C=CPh2)L(PiPr 3)]PF6 (L = CO, PHPh2)

The π-alkyne complex [Os(η5-C5H5){η2-HCCC(OH)Ph2}(PiPr3)]PF6 (1), where the alkyne acts as a four-electron donor ligand, reacts with CO to give initially the two-electron π-alkyne derivative [Os(η5-C5H5){η2-HCCC(OH)Ph2}(CO)(PiPr3)]PF6 (2). In dichloromethane, complex 2 isomerizes into the hydroxyvinylidene [Os(η5-C5H5){CCHC(OH)Ph2}(CO)(PiPr3)]PF6 (3), which dehydrates to afford the allenylidene [Os(η5-C5H5)(CCCPh2)(CO)(PiPr3)]PF6 (4). Complex 1 also reacts with PHPh2. In this case, the reaction initially gives the hydride-hydroxyalkynyl intermediate [OsH(η5-C5H5){CCC(OH)Ph2}(PHPh2)(PiPr3)]PF6 (5). Similar to 2, in dichloromethane, complex 5 isomerizes into the hydroxyvinylidene [Os(η5-C5H5){CCHC(OH)Ph2}(PHPh2)(PiPr3)]PF6 (6), which dehydrates to afford [Os(η5-C5H5)(CCCPh2)(PHPh2)(PiPr3)]PF6 (7). In the presence of HPF6, complex 4 isomerizes into [Os(η5-C5H5)(3-phenyl-1-indenylidene)(CO)(PiPr3)]PF6 (8). Under the same conditions, compound 7 affords the dicationic alkenylcarbyne derivative [Os(η5-C5H5)(C−CHCPh2)(PHPh2)(PiPr3)](PF6)2 (9). The allenylidene ligand of 4 undergoes the addition of carbodiimides to give iminiumazetidinylidenemethyl derivatives. The reaction with N,N‘-dicyclohexylcarbodiimide affords (10), whereas the reaction with N,N‘-diisopropylcarbodiimide leads to (11). Complex 4 also reacts with methanol and aniline. The addition of methanol to the allenylidene 4 gives [Os(η5-C5H5){C(OCH3)CHCPh2}(CO)(PiPr3)]PF6 (12), which undergoes deprotonation at the CHCPh2 group to afford Os(η5-C5H5){C(OCH3)CCPh2}(CO)(PiPr3) (13). The addition of aniline leads to [Os(η5-C5H5){C(CHCPh2)NHPh}(CO)(PiPr3)]PF6 (14). Treatment of 14 with NaOCH3 gives Os(η5-C5H5){C(CHCPh2)NPh}(CO)(PiPr3) (15). Complexes 4, 7, and 8 have been characterized by X-ray diffraction analysis.Financial support from the MCYT of Spain (Proyects BQU2002-00606 and PPQ2000-0488-P4-02) is acknowledged. M.L.B. thanks the Spanish MCYT and the Universidad de Zaragoza for funding through the “ Ramón y Cajal” Program.Peer Reviewe