Synthesis, Spectroscopic Characterization, and Reactivity of the Unusual Five-Coordinate Hydrido−Vinylidene Complex OsHCl(CCHPh)(PiPr₃)₂:  Precursor for Dioxygen Activation

Abstract

The hydrido−carbyne complex OsHCl2(CCH2Ph)(PiPr3)2 (1) reacts with sodium methoxide in 1:1 molar ratio to give the five-coordinate hydrido−vinylidene OsHCl(CCHPh)(PiPr3)2 (2), which affords [OsHCl(CCH2Ph)(H2O)(PiPr3)2]BF4 (3) by reaction with HBF4·H2O. The spectroscopic data obtained for 2 indicate that in solution, it is a mixture of two conformers in equilibrium. The thermodynamic magnitudes involved in the equilibrium as well as the activation parameters for the conversion between them were determined by 1H NMR spectroscopy in toluene-d 8 . The values obtained were ΔH° = −0.7 (±0.1) kcal mol-1, ΔS° = −2.3 (±0.6) cal K-1 mol-1 , ΔH ⧧ = 11.0 (±0.2) kcal mol-1 and ΔS ⧧ = 3.2 (±0.6) cal K-1 mol-1. At room temperature under argon, complex 2 is stable in the solid state and in solution. However in the presence of air, it activates molecular oxygen to give the dioxo−styryl compound OsCl{(E)-CHCHPh}(O)2(PiPr3)2 (4), which has been characterized by X-ray diffraction analysis. The geometry around of the osmium atom can be described as a distorted octahedron with the two oxygen atoms occupying two relative trans positions (O(1)−Os−O(2) = 179.5(5)°). Complex 2 also reacts with trimethylphosphite, sodium acetylacetonato (acetylacetonato = acac), and sodium acetato to give the six-coordinate hydrido−vinylidene derivatives OsHCl(CCHPh){(P(OMe)3}(PiPr3)2 (8), OsH(acac)(CCHPh)(PiPr3)2 (9), and OsH(η2-O2CCH3)(CCHPh)(PiPr3)2 (10), respectively. Complex 10 can also be prepared by treatment of OsH3(η2-O2CCH3)(PiPr3)2 (11) with phenylacetylene. Similarly, the reactions of 11 with 1,1-diphenyl-2-propyn-1-ol and 1-ethynyl-1-cyclohexanol lead to OsH (η2-O2CCH3){CCHC(OH)Ph2}(PiPr3)2 (12) and OsH(η2-O2CCH3){CCHCCH (CH2)3CH2}(PiPr3)2 (13), respectively.

Backward synthesis of rhenium(I) γ-hydroxyvinylidene and γ-methoxyvinylidene complexes and their conversion to the allenylidene [Re{CCCPh2}(CO)2(MeC(CH2PPh2)3)](OSO2CF3)

“…Indeed, α,β-unsaturated hydroxy-and alkoxy-carbenes are inherently unstable and very few examples of such compounds have been isolated. [10][11][12][13][14][15][16] Accordingly, the apparent stability of 1 in the presence of water and alcohols might be determined predominantly by electronic factors, which is consistent with our observation that both thiols and amines smoothly react with 1 to give isolable α,β-unsaturated thio-and amino-carbene derivatives. 17 On the other hand, the six phenyl substituents at the phosphorus atoms provide remarkable steric congestion at C α and therefore one cannot rule out a steric contribution to the stability of 1.…”

Amide-Directed Formation of Five-Coordinate Osmium Alkylidenes from Alkynes

“…In agreement with this, it has been observed that, in the presence of a base, the six-coordinate hydride alkylidyne complexes afford five-coordinate hydride vinylidene species. 19 In the current case, the distal amide group prevents the tautomerization of the triple bond as a consequence of the weak coordination of its oxygen atom, which also exerts a directing effect for the hydride migration (path b in Scheme 3 ). Thus, there is an insertion of the triple bond into the Os–H bond of the generated monohydrides, followed by the addition of the proton of the eliminated HCl to the C β atom of the resulting α-substituted alkenyl group, along with the displacement of the coordinated carbonyl group by chloride to give the alkylidene derivatives.…”

Sigma-bond activation reactions induced by unsaturated Os(IV)-hydride complexes

“…In contrast to the latter, compound 82 eliminates ROH to afford OsHCl(=C=CH 2 )(P i Pr 3 ) 2 (84), which is one of the few five-coordinate hydride-vinylidenes known. 54,55 There is a ring constraint against intramolecular migration to make an alkylidyne when the vinyl ether is cyclic. Thus, the reaction of 10 with 2,3-dihydrofuran gives tetrahydrofuran and the hydride-cyclic carbene derivative 31 (Scheme 31), which is stable in contrast to 81 and 82.…”