Edge‐Bridging and Face‐Capping Coordination of Alkenyl Ligands in Triruthenium Carbonyl Cluster Complexes Derived from Hydrazines: Synthetic, Structural, Theoretical, and Kinetic Studies

Abstract

The reactions of the triruthenium cluster complex [Ru3(mu-H)(mu3-eta2-HNNMe2)(CO)9] (1; H2NNMe2=1,1-dimethylhydrazine) with alkynes (PhC triple bond CPh, HC triple bond CH, MeO2CC triple bond CCO2Me, PhC triple bond CH, MeO2CC triple bond CH, HOMe2CC triple bond CH, 2-pyC triple bond CH) give trinuclear complexes containing edge-bridging and/or face-capping alkenyl ligands. Whereas the edge-bridged products are closed triangular species (three Ru-Ru bonds), the face-capped products are open derivatives (two Ru-Ru bonds). For terminal alkynes, products containing gem (RCCH2) and/or trans (RHCCH) alkenyl ligands have been identified in both edge-bridging and face-capping positions, except for the complex [Ru3(mu3-eta2-HNNMe2)(mu3-eta3-HCCH-2-py)(mu-CO)(CO)7], which has the two alkenyl H atoms in a cis arrangement. Under comparable reaction conditions (1:1 molar ratio, THF at reflux, time required for the consumption of complex 1), some reactions give a single product, but most give mixtures of isomers (not all the possible ones), which were separated. To determine the effect of the hydrazido ligand, the reactions of [Ru3(mu-H)(mu3-eta2-MeNNHMe)(CO)9] (2; HMeNNHMe=1,2-dimethylhydrazine) with PhC triple bond CPh, PhC triple bond CH, and HC triple bond CH were also studied. For edge-bridged alkenyl complexes, the Ru--Ru edge that is spanned by the alkenyl ligand depends on the position of the methyl groups on the hydrazido ligand. For face-capped alkenyl complexes, the relative orientation of the hydrazido and alkenyl ligands also depends on the position of the methyl groups on the hydrazido ligand. A kinetic analysis of the reaction of 1 with PhC[triple chemical bond]CPh revealed that the reaction follows an associative mechanism, which implies that incorporation of the alkyne in the cluster is rate-limiting and precedes the release of a CO ligand. X-ray diffraction, IR and NMR spectroscopy, and calculations of minimum-energy structures by DFT methods were used to characterize the products. A comparison of the absolute energies of isomeric compounds (obtained by DFT calculations) helped rationalize the experimental results.

Reactivity of Alkynes Containing α‐Hydrogen Atoms with a Triruthenium Hydrido Carbonyl Cluster: Alkenyl versus Allyl Cluster Derivatives

“…On the contrary, it is reasonable to propose that both the gem and trans isomers formed from 1 in short reaction times arise from a common early hydrido-alkyne intermediate that evolves through different pathways (Markonikoff and antiMarkonikoff insertions) to give the observed products. [5] Therefore, the allyl complexes do not arise from their facecapped alkenyl isomers.…”

“…In both cases, the hydrazido group caps the metal triangle in the same way as that found previously in complex 1 [8] and in most of its derivatives. [5,15] The allyl ligand spans the same Ru-Ru edge as the amido fragment of the hydrazido group and is attached to Ru1 through the carbon atoms C5 and C6 and to Ru2 through C4 and C5, the distances from the central carbon atom C5 to Ru1 and Ru2 being 0.35-0.40 longer than those from C4 and C6 to Ru2 and Ru1, respectively. The dihedral angle between the planes defined by the allyl C4, C5, and C6 atoms and the Ru 3 triangle is 63.5 (9) o in 2 and 61.9(4) o in 3.…”

“…[1][2][3][4][5] To check whether the facecapped alkenyl products could be transformed into their allyl isomers or not, compounds 8 and 9 (both arising from the reaction of compound 1 with 1-hexyne in refluxing THF, 15 min) were individually heated in refluxing THF. While compound 9 remained unaltered, a complete transformation of the gem isomer 8 into the trans isomer 9 was observed after 2 h. This long reaction time contrasts with the short reaction time required for the reaction of compound 1 with 1-hexyne, which gave compound 9 as the major product after 15 min in refluxing THF.…”

“…[5] Carrying out that study, [5] we observed that the use of some alkynes that have a-hydrogen atoms as reagents led not only to alkenyl derivatives, but also to cluster complexes with edge-bridging allyl ligands. As very few reactions of hydrido-carbonyl-triruthenium clusters with alkynes that have a-hydrogen atoms had been hitherto reported and none of them gave allyl derivatives, [3a,b] we decided to perform a thorough study on the reactivity of complex 1 with internal and terminal alkynes that have a-hydrogen atoms, such as 3-hexyne, 1-phenyl-1-propyne, 1-hexyne, propargyl alcohol, and 3-methoxy-1-propyne.…”

“…However, to date, the number of reports dealing with triruthenium-carbonyl cluster complexes containing alkenyl ligands is relatively small, [1][2][3][4][5] despite the fact that some of these clusters have been recognized as intermediates or as catalyst precursors for alkyne-alkene co-dimerization [6] and alkyne hydrogenation, [7] dimerization, [2b] polymerization, [2b] and hydroformylation [2c] processes. Without exception, these alkenyl-triruthenium cluster complexes arise from reactions of alkynes with triruthenium precursors containing hydride ligands.…”