Reactions of triosmium and triruthenium clusters with 2-ethynylpyridine: new modes for alkyne C-C bond coupling and C-H bond activation

• Published in: RSC advances 2020-08, Vol.1 (51), p.3671-3682
• Main Authors: Joy, Md. Tuhinur R, Roknuzzaman, Hossain, Md. Emdad, Ghosh, Shishir, Tocher, Derek A, Richmond, Michael G, Kabir, Shariff E
• Format: Article
• Language: English
• Subjects: Activation; Alkynes; Carbon monoxide; Chemistry; Clusters; Coupling (molecular); Covalent bonds; Crystallography; Crystals; Hydrides; Hydrogen bonds; Ligands; NMR; Nuclear magnetic resonance; Ruthenium; Single crystals; Substitutes; Substrates
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d0ra05393g

The reaction of the trimetallic clusters [H 2 Os 3 (CO) 10 ] and [Ru 3 (CO) 10 L 2 ] (L = CO, MeCN) with 2-ethynylpyridine has been investigated. Treatment of [H 2 Os 3 (CO) 10 ] with excess 2-ethynylpyridine affords [HOs 3 (CO) 10 (μ-C 5 H 4 NCH=CH)] ( 1 ), [HOs 3 (CO) 9 (μ 3 -C 5 H 4 NC&z.dbd;CH 2 )] ( 2 ), [HOs 3 (CO) 9 (μ 3 -C 5 H 4 NC&z.dbd;CCO 2 )] ( 3 ), and [HOs 3 (CO) 10 (μ-CH&z.dbd;CHC 5 H 4 N)] ( 4 ) formed through either the direct addition of the Os-H bond across the C&z.tbd;C bond or acetylenic C-H bond activation of the 2-ethynylpyridine substrate. In contrast, the dominant pathway for the reaction between [Ru 3 (CO) 12 ] and 2-ethynylpyridine is C-C bond coupling of the alkyne moiety to furnish the triruthenium clusters [Ru 3 (CO) 7 (μ-CO){μ 3 -C 5 H 4 NC&z.dbd;CHC(C 5 H 4 N)&z.dbd;CH}] ( 5 ) and [Ru 3 (CO) 7 (μ-CO){μ 3 -C 5 H 4 NCCHC(C 5 H 4 N)CHCHC(C 5 H 4 N)}] ( 6 ). Cluster 5 contains a metalated 2-pyridyl-substituted diene while 6 exhibits a metalated 2-pyridyl-substituted triene moiety. The functionalized pyridyl ligands in 5 and 6 derive via the formal C-C bond coupling of two and three 2-ethynylpyridine molecules, respectively, and 5 and 6 provide evidence for facile alkyne insertion at ruthenium clusters. The solid-state structures of 1-3 , 5 , and 6 have been determined by single-crystal X-ray diffraction analyses, and the bonding in the product clusters has been investigated by DFT. In the case of 1 , the computational results reveal a rare thermodynamic preference for a terminal hydride ligand as opposed to a hydride-bridged Os-Os bond (3c,2e Os-Os-H bond). The reactivity of 2-ethynylpyridine at low-valent triosmium and triruthenium centers has been investigated.