A Four-Electron π-Alkyne Complex as Precursor for Allenylidene Derivatives:  Preparation, Structure, and Reactivity of [Os(η⁵-C₅H₅)(CCCPh₂)L(PⁱPr₃)]PF₆ (L = CO, PHPh₂)

Abstract

2 (9). The allenylidene ligand of 4 undergoes the addition of carbodiimides to give iminiumazetidinylidenemethyl derivatives. The reaction with N,N′-dicyclohexylcarbodiimide affords [Os(η 5 -C 5 H 5 ){CHdCC(Ph) 2 N(Cy)+C+NdC(CH 2 ) 4 CH 2 }(CO)(P i Pr 3 )]PF 6 (10), whereas the reaction with N,N′-diisopropylcarbodiimide leads to [Os(η 5 -C 5 H 5 ){CHdCC(Ph) 2 N-( i Pr)+C+NdC(CH 3 ) 2 }(CO)(P i Pr 3 )]PF 6 (11). Complex 4 also reacts with methanol and aniline. The addition of methanol to the allenylidene 4 gives [Os(η 5 -C 5 H 5 ){C(OCH 3 )CHdCPh 2 }(CO)-(P i Pr 3 )]PF 6 (12), which undergoes deprotonation at the CHdCPh 2 group to afford Os(η 5 -C 5 H 5 ){C(OCH 3 )dCdCPh 2 }(CO)(P i Pr 3 ) (13). The addition of aniline leads to [Os(η 5 -C 5 H 5 )-{C(CHdCPh 2 )dNHPh}(CO)(P i Pr 3 )]PF 6 (14). Treatment of 14 with NaOCH 3 gives Os(η 5 -C 5 H 5 ){C(CHdCPh 2 )dNPh}(CO)(P i Pr 3 ) (15). Complexes 4, 7, and 8 have been characterized by X-ray diffraction analysis.

Repercussion of a 1,3-Hydrogen Shift in a Hydride-Osmium-Allenylidene Complex

“…The diphenylallenylidene ligand is bonded to the metal center in a nearly linear fashion (Os–C(1)–C(2) = 175.1(5)° and C(1)–C(2)–C(3) = 175.1(6)°). The Os–C(1), C(1)–C(2), and C(2)–C(3) distances of 1.858(6), 1.261(8), and 1.351(8) Å, respectively, compare well with those reported for the previously structurally characterized osmium-allenylidene complexes. ,, In agreement with them, C(1)–C(2) and C(2)–C(3) are about 0.05 Å shorter and longer, respectively, than the bond length expected for a carbon–carbon double bond (about 1.30 Å), which suggests a notable contribution of the canonical form [M] − CCC + Ph 2 to the structure of the C 3 -chain. In accordance with the presence of hydride and allenylidene ligands, the IR spectrum of the molecule contains the corresponding characteristic ν­(Os–H) and ν­(CCC) bands at 2090 and 1863 cm –1 .…”

Halide Effects on the Stability of Osmium Indenylidene Complexes: Isolation, Characterization, and Reactivities

“…The complex 6I is interesting as it represents, to the best of our knowledge, the first well-characterized mononuclear indenylidene complex synthesized from a stoichiometric reaction of a diazoindene with a transition-metal complex. Reported transition-metal indenylidene complexes are mainly those of ruthenium and osmium which were prepared by other routes. − …”

Osmium–carbon multiple bonds: Reduction and C–C coupling reactions

“…In accordance with this, the reactions of these compounds with electrophiles lead to alkenylcarbyne derivatives, which are stable with electron-rich co-ligands [16,18]. When some of the substituents of the unsaturated chain are phenyl groups and the complex containing p-acidic ligands, the reduction into the corresponding metaleindenylidene compound, an isomer of the starting allenylidene, is observed [19].…”

“…In contrast to the diphenylallenylidene complexes of the iron triad with a-electrophilic character that in alcoholic solutions afford a,b-unsaturated alkoxycarbene derivatives, as a result of the addition of the OeH bond of the alcohols to the C a eC b double bond of the C 3 -chain of the h 1 -carbon donor ligand [19,24], the hydrideeallenylidene complex 27 evolves into the hydrideealkenylcarbene derivative 33 in methanol, ethanol, n-propanol, and 2-propanol. The hydrogenation of the C a eC b double bond of the allenylidene takes place by means of hydrogen transfer from the alcohols, which undergo dehydrogenation to give the carbonyl compounds (Eq (10)).…”