Room temperature olefination of methane with titanium–carbon multiple bonds

Abstract

C–H activation of methane followed by dehydrocoupling at room temperature led ultimately to the formation of the olefin H2CCHtBu via the addition of redox-active ligands (L) such as thioxanthone or 2,2′-bipyridine (bipy) to (PNP)TiCHtBu(CH3) (1).

Terminal Mo Carbide and Carbyne Reactivity: H2 Cleavage, B–C Bond Activation, and C–C Coupling

“…Improved understanding can lead to rationally tuned catalysts, greater selectivity toward desired products, and, importantly, reduced cost . Toward this end, discrete organometallic model systems have been investigated as a means of parsing the elementary steps of C–O bond cleavage, C–C coupling, and hydrogenation. − Of these, complexes with multiply bonded ligands including terminal carbides, alkylidynes, and alkylidenes remain of interest, as these have been invoked as intermediates of hydrogenation and oligomerization to catenated products. , While the C–C coupling of alkylidyne and alkylidene complexes has been extensively studied, ,− the reactivity of carbides remains much more poorly understood, likely owing to the rarity of these structures, particularly the more reactive terminal examples. − Still, terminal carbides have strong potential for the development of new catalytic methodologies owing to their steric accessibility and reactivity.…”

“…Direct hydrogenation with H 2 is well-known for other types of multiply bonded transition-metal complexes, including terminal nitrides, − oxides, − carbenes, − and carbynes. − More recently, methane C–H insertion into a Ti carbyne was reported for a system that also subsequently underwent dehydrogenative C–C coupling to olefins. , While for carbide 1 hydrogenation occurs under relatively mild conditions, attempts toward productive C–C coupling from any formed methylidene species were hampered by an undesired conversion to 4 , even at reduced temperatures. Alternatively, we considered that heterolytic H 2 activation via a frustrated Lewis pair (FLP)-type mechanism could potentially be promoted by addition of a suitable Lewis acid to support the hydride as a counterpart to the methylidyne. − However, we found that BPh 3 (computed Δ G H – = 36 kcal/mol in MeCN) reacted directly with the carbide, while the bulkier but less Lewis acidic mesityl derivative BMes 3 (Δ G H – = 22 kcal/mol in MeCN) did not produce any measurable effect, even though both of these boranes satisfy the hydricity requirements for productive H 2 cleavage with carbide 1 (see the Supporting Information for details).…”

“…33−35 More recently, methane C−H insertion into a Ti carbyne was reported for a system that also subsequently underwent dehydrogenative C−C coupling to olefins. 9,36 While for carbide 1 hydrogenation occurs under relatively mild conditions, attempts toward productive C−C coupling from any formed methylidene species were hampered by an undesired conversion to 4, even at reduced temperatures. Alternatively, we considered that heterolytic H 2 activation via a frustrated Lewis pair (FLP)-type mechanism could potentially be promoted by addition of a suitable Lewis acid to support the hydride as a counterpart to the methylidyne.…”

Pioneers and Influencers in Organometallic Chemistry: Dr. Patricia Watson and the Molecular Dance of M–C and C–H Bonds

“…Tricia conducted fundamental organometallic chemistry and explored the reactivity of M–H and M–R bonds with small molecules. Her efforts have inspired many others, including my research work on 1,2-CH bond addition of methane across titanium alkylidynes, dehydrocoupling of methane with carbenes and ylides, and methane borylation catalysis. − Tricia’s discovery of an organometallic complex that could activate CH 4 and detailed mechanistic studies surrounding this reaction are the epitome of synthetic elegance and mechanistic work. Time will only tell how many other organometallic complexes having metal–carbon bonds have been overlooked in methane activation due to similar degenerate exchange or other equilibrium phenomena.…”

Asymmetric bis-PNP pincer complexes of zirconium and hafnium – a measure of hemilability

“…However recent work has shown rich chemistry within early transition metal pincer complexes which are capable of facilitating extremely challenging transformations, for example the activation of methane. 16 With the pyrrolide-based [PNP R ] ligand (where R represents the substituents on the phosphines), the formally anionic pyrrolide should bind strongly, however the phosphorus centres will form comparatively weaker interactions with early transition metals versus later transition metals. This provides the tantalising prospect of hemilability.…”