Self-Activation of a Cluster-Bound Alkyne toward Carbon−Carbon Bond Forming Reactions

Abstract

The methanol-catalyzed elimination of Cl- from the “activated” anionic species [PPN][Ru3(μ-Cl)(μ-PhCCPh)(CO)9] (1) in the presence of bis(diphenylphosphino)methane (dppm) constitutes a rational high-yield route (>90%) to either the unique unsaturated 46-e (alkyne)triruthenium cluster, Ru3(μ-PhCCPh)(CO)7(dppm) (2), or its 48-e CO adduct, Ru3(μ-PhCCPh)(CO)8(dppm) (3). Whereas the CO-induced conversion of 2 into 3 is complete within few seconds at 25 °C under 1 atm of CO, the reverse transformation takes 1 h at 80 °C. The X-ray structure analysis of 2 is reported, revealing a perpendicular conformation of the alkyne relative to the metal triangle. The high reactivity of 2 is substantiated by a high chemical reactivity toward 2-e donors. Its reaction with 1 equiv of dppm (25 °C, 3 h) leads to the bis-dppm-substituted complex, Ru3(μ-PhCCPh)(CO)6(dppm)2 (4) (53% yield). Reaction of 2 with hydrogen gas (1 atm, 25 °C, 10 min) yields the dihydrido species, Ru3(μ-H)2(μ-PhCCPh)(CO)7(dppm) (5) (89% yield) existing as a mixture of two isomers differing in the orientation of the alkyne relative to the edge-bridging dppm ligand. Complex 2 reacts with a terminal alkyne like phenylacetylene under mild conditions to afford a mixture of the “fly-over” type compound Ru3{μ-HCC(Ph)C(O)(Ph)CCPh}(dppm)(CO)6 (6) (57% yield) and the diruthenacyclopentadiene derivative Ru2{μ-HCC(Ph)(Ph)CCPh}(μ-dppm)(CO)4 (7) (20% yield). The structure of 6 reveals the occurrence of a disymmetric edge-bridging dialkenyl ketone ligand HCC(Ph)C(O)(Ph)CCPh, resulting from regioselective coupling between the two alkynes and a carbonyl group. The formal unsaturation of 6 is masked by a weak interaction between the terminal C−Ph bond of the organic chain and one of the metal centers. Facile loss of this interaction is induced by mild thermolysis of 6. As a consequence, free rotation of the organic moiety around the metal−metal edge brings the opposite end of the organic chain (i.e., the C−H bond) close to the opposite face, thereby favoring CH activation to convert the alkenyl end into a vinylidene. This leads to quantitative formation of the vinylidene alkenyl ketone derivative, Ru3(μ-H){μ-CC(Ph)C(O)(Ph)CCPh}(dppm)(CO)6 (8) (94% yield). The X-ray structure of 8 is reported. Unsuccessful attempts to release the organic moiety from the cluster core are described. The reaction of a THF solution of 6 with CO in a reactor [P(CO) = 10 atm, T = 80 °C] leads to the new binuclear “fly-over” species Ru2{μ-HCC(Ph)C(O)(Ph)CCPh}(CO)6 (9a), thereby indicating that elimination of the edge-bridging dppm and cluster fragmentation are more favorable than elimination of a free ketone from the intact cluster. The X-ray structure of Ru2{μ-HCC(C3H7)C(O)(Ph)CCPh}(CO)6 (9b) (resulting from the coupling between diphenylacetylene and 1-pentyne) is reported.

Electronic interactions in [Ru3(mu3-R² CCC6H4-4-R¹)(mu -dppm)(mu-CO) (CO)7] (R¹ = NO2 and R² = Fc; R¹ = NO2, CN and R² = Ph)

“…This suggests that these compounds are isostructural with the symmetrical derivative 3 11 whose dppm phosphorus atoms are equivalent and whose structure is proposed here to contain a CO and a dppm ligands bridging the same edge which is also parallel to the µ 3 -η 2 -alkyne 14 (see Scheme), although the X-ray molecular structure of the closely related cluster [Ru 3 (µ 3 -η 2 -PhC 2 CCPh)(µ-dppm)(µ-CO)(CO) 7 ] has been reported to be slightly different 15 with the bridging CO bonded to a different metal edge. Contrary to the analogous clusters 3, 4 and 5 and other clusters of the series containing a dppm instead of two CO ligands, 11,16 it was impossible to decarbonylate 2 to yield the unsaturated cluster [Ru 3 (µ 3 -η 2 -FcCCC 6 H 4 -4-NO 2 )(µ-dppm)(CO) 7 ] with the alkyne bonded in the perpendicular mode. Compound 2 was stable when heated in toluene, at 80 °C, for 4 h, but upon increasing the temperature it underwent decomposition.…”

Skeletal isomerism in mixed transition-metal/main-group closo clusters

“…f Fe 3 (CO) 9 (C 2 Et 2 ) [11]. g Ru 3 (CO) 7 (dppm)(C 2 Ph 2 ) [14]. h Fe 3 (CO) 9 [SiFe(CO) 2 Cp] 2 [20].…”

Effects of Halides and Related Ligands on Reactions of Carbonylruthenium Complexes (Ru0–RuII)

“…Hence, if a biphasic hexane/ methanol solvent mixture is used, the neutral complex Ru 3 (µ-RCCR)(µ-CO)(CO) 9 transfers itself to the hexane HCϭCPhϪC(O)ϪPhCϭCPh appeared as the result of an intramolecular alkyne/CO/alkyne coupling. [41] Bearing in phase, from which it can be recovered pure without chromatographic workup.…”

“…This is illustrated in Scheme 7. [41] We first made the encouraging observation that the cluster-I.2.3 Activation of Olefins bound alkyne ligand in the triruthenium complex Ru 3 (µ-PhCCPh)(µ-dppm)(CO) 7 could be readily engaged in CϪC In 1986, Gladfelter and co-workers reported that olefins can be readily hydrogenated at ambient temperature in the bond formation with an incoming phenylacetylene molecule within minutes at 0°C, giving the coordinatively unsatu-presence of the isocyanatotriruthenium cluster complex [Ru 3 (NCO)(CO) 10 ] Ϫ , [43] another member of the growing rated "fly-over"-type complex Ru 3 [µ-PhCCPhϪC(O)ϪPh-CCH](µ-dppm)(CO) 6 where the dialkenyl ketone fragment family of "anion-promoted" triruthenium clusters.…”