Synthesis and Reactivity of Molybdenum and Tungsten Alkyne Complexes Containing 6‐Methylpyridine‐2‐thiolate Ligands

Abstract

A series of M(II) and M(IV) (M = Mo, W) alkyne adducts employing two 6-methylpyridine-2-thiolate (6-MePyS) ligands was synthesized and investigated towards the nucleophilic attack of PMe 3 on the coordinated alkynes. For this approach, 2-butyne (C 2 Me 2 ), phenylacetylene (HC 2 Ph), and diphenylacetylene (C 2 Ph 2 ) were used. For the exploration of an intramolecular attack, but-3-yn-1-ol (HCCCH 2 CH 2 OH) was coordinated to the metal centers. A nucleophilic attack of PMe 3 was observed in [W(CO)(HC 2 Ph)(6-MePyS) 2 ] yielding an η 2 -vinyl compound. Reaction of [W(CO)(C 2 Ph 2 )(6-MePyS) 2 ] with excess PMe 3 resulted in the selective coordination of one molecule of PMe 3 concomitant with decoordination of the nitrogen atom of one 6-MePyS ligand. In contrast, the W(IV) complexes did not react with PMe 3 . While no selectivity was observed in the reaction of the Mo(II) compounds with PMe 3 , alkynes in the Mo(IV) compounds were replaced by PMe 3 . Addition of Et 3 N to the but-3-yn-1-ol complexes did not lead to the anticipated formation of 2,3-dihydrofuran.

Dioxygen Activation by a Bioinspired Tungsten(IV) Complex

“…Although the isolation of compound 4 in larger quantities proved futile, its formation delivers important information concerning the reduction process of complex 1 . Most probably, PMe 3 coordinates to the tungsten in [WO 2 (6-MePyS) 2 ] in an initial step as similar behavior was observed in related tungsten alkyne complexes . In the absence of further equivalents of phosphine, compound 4 is formed, and only with additional PMe 3 molecules OAT occurs, forming 2 .…”

“…Most probably, PMe 3 coordinates to the tungsten in [WO 2 (6-MePyS) 2 ] in an initial step as similar behavior was observed in related tungsten alkyne complexes. 49 In the absence of further equivalents of phosphine, compound 4 is formed, and only with additional PMe 3 molecules OAT occurs, forming 2 . The initial coordination of PMe 3 might be enabled by the flexibility of the 6-MePyS ligand, as observed in compound 2 ( Scheme 3 ).…”

Nucleophiles Target the Tungsten Center Over Acetylene in Biomimetic Models

“…19 In the reactions with PMe 3 , initial attack most likely occurs at the W center, as such behavior was shown with complexes bearing higher alkynes. 20 Similarly, hydride addition to cationic Mo diphenylacetylene adduct [CpMo(OPMe 3 ) 2 (PhC 2 Ph)] + led to an η 2 -vinyl complex via initial Mo−H bond formation. 21 To overcome the initial nucleophile coordination, Davidson et al employed t BuNC (isocyanide) and obtained an η 2 -vinyl complex starting from W(II) adducts of hexafluoro-2-butyne.…”

“…In the reactions with PMe 3 , initial attack most likely occurs at the W center, as such behavior was shown with complexes bearing higher alkynes . Similarly, hydride addition to cationic Mo diphenylacetylene adduct [CpMo­(OPMe 3 ) 2 (PhC 2 Ph)] + led to an η 2 -vinyl complex via initial Mo–H bond formation .…”

Synthesis and structure of two isomers of a molybdenum(II) 2-butyne complex stabilized by bioinspired S,N-bidentate ligands

“…In order to explore the interaction of Mo and W centres with acetylene (C 2 H 2 ), which is accepted as a substrate by the tungstoenzyme acetylene hydratase (Schink, 1985;Rosner & Schink, 1995), our group has focused on the synthesis of W II and Mo II complexes containing bioinspired S,N-bidentate ligands and their subsequent oxidation to the respective W IV and Mo IV complexes. Although N-donor ligands are not the closest structural mimics of the dithiolene ligands in the active site of acetylene hydratase (Seiffert et al, 2007) and other members of the dimethyl sulfoxide (DMSO) reductase enzyme family (Seelmann et al, 2020), the use of these ligands has resulted in the discovery of new reactivities at W centres (Vidovic ˇet al, 2019;Ehweiner et al, 2021c), the isolation of a so-far-elusive Mo IV C 2 H 2 complex (Ehweiner et al, 2021a) and a detailed comparison of W and Mo complexes with a variety of coordinated alkynes (Ehweiner et al, 2021b). One of the early publications of our group in this research field focused on the reversible activation of C 2 H 2 at a W IV centre coordinated by two 2-(4,4-dimethyloxazolin-2-yl)thiophenolate (S-Phoz) ligands (Peschel et al, 2015a).…”