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

Abstract

The reactions of the hydrido-triruthenium cluster complex [Ru3(mu-H)(mu3-kappa(2)-HNNMe2)(CO)9] (1; H2NNMe2 = 1,1-dimethylhydrazine) with alkynes that have alpha-hydrogen atoms give trinuclear derivatives containing edge-bridging allyl or face-capping alkenyl ligands. Under mild conditions (THF, 70 degrees C) the isolated products are as follows: [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(3)-1-syn-Me-3-anti-EtC3H3)(mu-CO)2(CO)6] (2) and [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(3)-1-syn-Me-3-syn-EtC3H3)(mu-CO)2(CO)6] (3) from 3-hexyne; [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(3)-3-anti-PhC3H4)(mu-CO)2(CO)6] (4), [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(2)-MeCCHPh)(mu-CO)2(CO)6] (5) and [Ru3(mu3-kappa(2)-HNNMe2)(mu3-kappa(2)-PhCCHMe)(mu-CO)2(CO)6] (6) from 1-phenyl-1-propyne; [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(2)-3-anti-PrC3H4)(mu-CO)2(CO)6] (7), [Ru3(mu3-kappa(2)-HNNMe2)(mu3-kappa(2)-BuCCH2)(mu-CO)2(CO)6] (8), and [Ru3(mu3-kappa(2)-HNNMe2)(mu3-kappa(2)-HCCHBu)(mu-CO)2(CO)6] (9) from 1-hexyne; [Ru3(mu3-kappa(2)-HNNMe2)(mu3-kappa(2)-HOH2CCCH2)(mu-CO)2(CO)6] (10) from propargyl alcohol; and [Ru3(mu3-kappa(2)-HNNMe2)(mu3-kappa(2)-MeOCH2CCH2)(mu-CO)2(CO)6] (11) from 3-methoxy-1-propyne. The regioselectivity of these reactions depends upon the nature of the alkyne reagent, which affects considerably the kinetic barriers of important reaction steps and the stability of the final products. It has been established that the face-capped alkenyl derivatives are not precursors to the allyl products, which are formed via edge-bridged alkenyl intermediates. At higher temperature (toluene, 110 degrees C), the complexes that have allyl ligands with an anti substituent are isomerized into allyl derivatives with that substituent in the syn position, for example, 4 into [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(3)-3-syn-PhC3H4)(mu-CO)2(CO)6] (14). The diene complex [Ru3(mu-H)(mu3-kappa(2)-HNNMe2)(mu-kappa(4)-trans-EtC4H5)(CO)7] (13) has been obtained from the thermolysis of compounds 2 and 7 at 110 degrees C (3 and [Ru3(mu3-kappa(2)-HNNMe2)(mu-kappa(2)-3-syn-PrC3H4)(mu-CO)2(CO)6] (12) are also formed in these reactions). A DFT theoretical study has allowed a comparison of the thermodynamic stabilities of isomeric compounds and has helped rationalize the experimental results. Mechanistic proposals for the synthesis of the allyl complexes and their isomerization processes are also provided.

Reactions of μ3‐Alkenyl Triruthenium Carbonyl Clusters with Alkynes: Synthesis of Trinuclear μ‐//‐Alkyne, μ‐Vinylidene, and μ‐Dienoyl Derivatives

“…In the context of alkenyl triruthenium complexes, we have recently revised the studies of Hansert and Vahrenkamp4 on the reactivity of the Süss‐Fink's hydrazido‐bridged hydrido carbonyl triruthenium complex [Ru 3 (μ‐H)(μ 3 ‐ κ 2 ‐HNNMe 2 )(CO) 9 ]9 ( 1 ) with terminal and internal alkynes without α‐hydrogen atoms, showing that the products have alkenyl ligands in edge‐bridging or face‐capping positions ( A and B , respectively, in Scheme ) and that the nature of the substituents on the alkyne reagent strongly affects the stability of each product 5. We have also reported that alkynes with α‐hydrogen atoms react with complex 1 to give trinuclear derivatives that contain edge‐bridging allyl ligands ( C and D in Scheme ) 6…”

“…Alkenyl groups are important ligands in organometallic chemistry because they are invoked in many metal‐mediated transformations of alkynes and alkenes. However, to date, the number of reports dealing with triruthenium carbonyl cluster complexes containing alkenyl ligands is relatively small,1–6 despite the fact that some of these clusters have been recognized as intermediates or as catalyst precursors in alkyne–alkene co‐dimerization7 as well as alkyne hydrogenation,8 dimerization,2b polymerization,2b and hydroformylation2c processes.…”

Bridging allyl ligands upon allene insertion into electron-deficient triosmium-hydride clusters [Os3(CO)9(μ3-NSC7H3R)(μ-H)] (R = H, Me)

“…In accord with the solid-state structure the aromatic region of the 1 While (2), Os (2) binding of the bridging allyl ligands in these are very similar to those found in 3 and 4, most notably the CeCeC angle of 133.9 (17) and 127(2) in 3 and 4, respectively, are close to those found in the hexanuclear clusters [CeCeC 125.5e128.7 ]. More recently, Cabeza and co-workers have prepared a series of triruthenium clusters with bridging allyl ligands resulting from the insertion of alkynes [32] or conjugated dienes [30,31], including allenes [29] into the metalehydride moiety in [Ru 3 (CO) 9 (m 3 Àk 2 -HNNMe 2 )(m-H)].…”

Reactivity of a triruthenium alkenyl cluster complex with conjugated diynes: Coupling of two diyne molecules via a face-capping diyne intermediate

“…We have also reported that alkynes with a-hydrogen atoms react with complex A to give trinuclear derivatives that may contain edge-bridging allyl ligands (D and E in Scheme 1) [6]. In all cases, the nature of the substituents of the alkyne reagent strongly affects the stability of each product and the regioselectivity of the reactions [5,6].…”

“…However, to date, the number of reports dealing with triruthenium carbonyl cluster complexes containing alkenyl ligands is relatively small [1][2][3][4][5][6][7][8][9], despite the fact that some of these clusters have been recognized as intermediates or as catalyst precursors for alkyne-alkene codimerization [8] and alkyne hydrogenation [9], dimerization [2b], polymerization [2b] and hydroformylation [2c] processes.…”