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

摘要

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) NCCH _(2) )] ( 2 ), [HOs _(3) (CO) _(9) (μ _(3) -C _(5) H _(4) NCCCO _(2) )] ( 3 ), and [HOs _(3) (CO) _(10) (μ-CHCHC _(5) H _(4) N)] ( 4 ) formed through either the direct addition of the Os–H bond across the CC 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) NCCHC(C _(5) H _(4) N)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).