Stoichiometric Alkyne Metathesis at Metal Cluster Compounds: Interconversion of Os3W Alkyne-Alkylidyne and Dimetalloallyl Clusters

Abstract

Treatment of O S~( C O )~O ( C J~~Z ) with C p W -(CO)z(=CTol) produced the alkylidyne-alkyne cluster C~WOS~(CO)IO(~~~-CM~)(CM~CTO~) (2) and the dimeta 1 loa 1 ly 1 complex C p WOs3(CO),[C(Me) C(Me) C( To01 (3) in sequence. Thermolysis of 3 induced the selective scission of one C-C bond t o give a second alkylidynealkyne cluster, Cp WOS~(CO)B(~~-CTO~)(CJ~~Z) (4, providing a model of alkyne metathesis through a dimetalloallyl intermediate.We have recently prepared and examined the reactivity of Os3W clusters with ligated Cq hydrocarbons by addition of tungsten acetylide complexes to Os3 alkyne complexes.' Our work has been motivated by attempts to develop a generalized strategy to mixed-metal clusters2 and to learn about the reaction pathway of chemisorbed hydrocarbon intermediates on metal surface^.^ This investigation is now extended to tetranuclear Os3W cluster compounds with the asymmetric C3 dimetalloallyl ligand p3-q3-C(Tol)C(Me)C(Me). Before our investigation of these tetranuclear dimetalloallyl clusters, others have also studied syntheses and reactivities of dinuclear and trinuclear derivative^.^ Among the various chemical reactions probed, that of forming and breaking the C-C bond is important because it provides valuable mechanistic insight into alkyne metathe~is.~ In this paper, we report a novel example of transformation of ligand pairs [p3-CMe + MeCzTol] to [p&Tol+ MeC2Mel through the ~ t National Tsing Hua University. ligand ~13-q3-[C(Tol)C(Me)C(Me)l. This experimental result substantiates an earlier report by Stone and coworkers, who demonstrated that two ligated CS allyl fragments, differing in the arrangement of substituents, were produced via cleavage and formation of a C-C bond, providing compelling evidence for scrambling of [CR + R'CzR'] and [CR' + R'CzRl fragments? Such rearrangement on metal complexes is noteworthy because it could in theory allow a dimetalloallyl species to be considered a possible intermediate of catalytic alkyne metathesis.The alkyne cluster Os3(CO)&2Mez) (1) reacts with approximately 3 equiv of CpW (C0)2(=CTol) in refluxing toluene solution (30 min) to afford the red-orange alkylidyne-alkyne complex CpWOs3(CO)&&Me)(CMeC-Tol) (2) and dark green dimetalloallyl complex CpWOs3-(CO)s[C(Me)C(Me)C(Tol)l (3) in 27 and 38% yields, respectively. These two cluster compounds were fully characterized by spectroscopic7 and X-ray measuremenh8The X-ray analysis of 2 indicated that it consists of a OSSW butterfly arrangement with the W atom located at the hinge position ( Figure 1). The alkylidyne group, which connects to both wingtip Os atoms with two long bonds (2.23(2) and 2.13(2) A) and to the W atom with a short interaction (2.01(2) A), carries a methyl substituent but not a tolyl substituent. This information suggests that the alkylidyne ligand is derived from the 2-butyne ligand but not from the CTol unit of CpW(C0)2(=CTol). In addition, the ligated alkyne [C(Me)C(Tol)l, generated from coupling of the second CMe unit and the incoming CTol fragment, lies on the W-Os(l)-Os(2) face o...

Reactivity of the Tetrametallic Carbido Cluster (C5Me5)WOs3(μ4-C)(μ-H)(CO)11 with Alkyne: Isomerization of an Allyl Fragment on a Tetrametallic Cluster Framework and Ring-Methyl Activation in the C5Me5 Ligand

“…Their formation can be visualized by, first, generation of an unsaturated, tetrahedral allyl intermediate complex ( 8 ) through removal of one CO ligand from the W atom. This hypothesis is further supported by the isolation of a structurally characterized, highly reactive Cp compound, CpWOs 3 (C 3 Me 2 Tol)CO) 9 ( 9 ) Chart , which contains only 58 cluster valence electrons . We believe that the unsaturated nature of 8 would induce the C−H activation at a methyl group of the nearby C 5 Me 5 ligand, giving the formation of tetramethylfulvene and a bridging hydride, as observed in 5 .…”