Sequential Protonation and Methylation of a Hydride−Osmium Complex Containing a Cyclopentadienyl Ligand with a Pendant Amine Group

Complex OsH{η5-C5H4(CH2)2NMe2}(PiPr3)2 (1) reacts with 1 equiv of trifluoromethanesulfonic acid (HOTf) and trifluoromethanesulfonic acid-d1 (DOTf) to produce the dihydride and hydride−deuteride complexes, [OsHE{η5-C5H4(CH2)2NMe2}(PiPr3)2]OTf (E = H (2), D (2-d1)), respectively. Treatment of 2 and 2-d1 with a second equivalent of HOTf gives [OsHE{η5-C5H4(CH2)2NHMe2}(PiPr3)2][OTf]2 (E = H (3), D (3-d1)) as a result of the protonation of the nitrogen atom. While the hydride and deuteride ligands of 2, 2-d1,3, and 3-d1 do not undergo any H/D exchange process with the solvent, in acetone-d6, the NH proton of 3 and 3-d1 changes places with a deuterium atom of the solvent to yield [OsHE{η5-C5H4(CH2)2NDMe2}(PiPr3)2][OTf]2 (E = H (3-Nd1), D (3-d2)). Complex 3-Nd1 can also be obtained from the treatment of complex 2 with DOTf in dichloromethane. No exchange process between the hydride and the ND positions in 3-Nd1 or between the deuteride and NH positions in 3-d1 has been observed. Treatment of 3-Nd1 and 3-d1 with sodium methoxide results in a selective reaction of the base with the ammonium group to regenerate 2 and 2-d1, respectively. Complex 1 also reacts with methyl and methyl-d3 trifluoromethanesulfonate (CH3OTf and CD3OTf, respectively) to give [OsH{η5-C5H4(CH2)2NMe2CE3}(PiPr3)2]OTf (E = H (4), D (4-d3)) as a result of the addition of the CE3 (E = H, D) group to the nitrogen atom. Complex 4 has been characterized by an X-ray diffraction analysis. It reacts with a second molecule of CH3OTf or CD3OTf to produce [ (5). Similarly, complex 4-d3 reacts with a second molecule of CH3OTf or CD3OTf to yield (5-d3). In acetonitrile, complex 5 evolves to an equilibrium mixture of the acetonitrile adducts [Os{η5-C5H4(CH2)2NMe3}(NCCH3)(PiPr3)2][OTf]2 (7) and [Os{η5-C5H4(CH2)2NMe3}(NCCH3)2(PiPr3)][OTf]2 (8). In methanol or methanol-d4, complex 4 is not stable and loses trimethylamine to give the vinylcyclopentadienyl derivatives [OsHE(η5-C5H4CHCH2)(PiPr3)2]OTf (E = H (9), D (9-d1)) as a result of the protonation or deuteration of the metallic center and a subsequent Hofmann elimination. Protonation of 4 with HOTf gives the dihydride−trimethylammonium derivative [OsH25-C5H4(CH2)2NMe3}(PiPr3)2][OTf]2 (10). Treatment of 9 with sodium methoxide produces OsH(η5-C5H4CHCH2)(PiPr3)2 (11).