Bioinspired complexes employing the ligands 6‐tert‐butylpyridazine‐3‐thione (SPn) and pyridine‐2‐thione (SPy) were synthesized and fully characterized to mimic the tungstoenzyme acetylene hydratase (AH). The complexes [W(CO)(C2H2)(CHCH‐SPy)(SPy)] (4) and [W(CO)(C2H2)(CHCH‐SPn)(SPn)] (5) were formed by intramolecular nucleophilic attack of the nitrogen donors of the ligand on the coordinated C2H2 molecule. Labelling experiments using C2D2 with the SPy system revealed the insertion reaction proceeding via a bis‐acetylene intermediate. The starting complex [W(CO)(C2H2)(SPy)2] (6) for these studies was accessed by the new acetylene precursor mixture [W(CO)(C2H2)n(MeCN)3−nBr2] (n=1 and 2; 7). All complexes represent rare examples in the field of W−C2H2 chemistry with 4 and 5 being the first of their kind. In the ongoing debate on the enzymatic mechanism, the findings support activation of acetylene by the tungsten center.

The synthesis and structural determination of four tungsten alkyne complexes coordinated by the bio‐inspired S,N‐donor ligand 2‐(4′,4′‐dimethyloxazoline‐2′‐yl)thiophenolate (S‐Phoz) is presented. A previously established protocol that involved the reaction of the respective alkyne with the bis‐carbonyl precursor [W(CO) 2 (S‐Phoz) 2 ] was used for the complexes [W(CO)(C 2 R 2 )(S‐Phoz) 2 ] (R=H, 1 a ; Me, 1 b ; Ph, 1 c ). Oxidation with pyridine‐ N ‐oxide gave the corresponding W‐oxo species [WO(C 2 R 2 )(S‐Phoz) 2 ] (R=H, 2 a ; Me, 2 b ; Ph, 2 c ). All W‐oxo‐alkyne complexes ( 2 a , b , c ) were found to be capable of alkyne release upon light irradiation to afford five‐coordinate [WO(S‐Phoz) 2 ] ( 3 ). The photoinduced release of the alkyne ligand was studied in detail by in situ 1 H NMR measurements, which revealed correlation of the photodissociation rate constant ( 2 b>2 a>2 c ) with the elongation of the alkyne C≡C bond in the molecular structures. Oxidation of [WO(S‐Phoz) 2 ] ( 3 ) with pyridine‐ N ‐oxide yielded [WO 2 (S‐Phoz) 2 ] ( 4 ), which shows highly fluxional behavior in solution. Variable‐temperature 1 H NMR spectroscopy revealed three isomeric forms with respect to the ligand arrangement versus each other. Furthermore, compound 4 rearranges to tetranuclear oxo compound [W 4 O 4 (μ‐O) 6 (S‐Phoz) 4 ] ( 5 ) and dinuclear [{WO(μ‐O)(S‐Phoz)} 2 ] ( 6 ) over time. The latter two were identified by single‐crystal X‐ray diffraction analyses.

Poly(phenylene methylene)s (PPMs) with high molar masses were isolated by polymerization of benzyl chloride catalyzed with tungsten(II) compounds and subsequent fractionation. Four different tungsten(II) catalysts were successfully exploited for the polymerization, for which a strict temperature profile was developed. The PPMs possessed roughly a trimodal molar mass distribution. Simple fractionation by phase separation of 2-butanone solutions allowed to effectively segregate the products primarily into PPM of low molar mass (Mn = 1600 g mol−1) and high molar mass (Mn = 167,900 g mol−1); the latter can be obtained in large quantities up to 50 g. The evolution of the trimodal distribution and the monomer conversion was monitored by gel permeation chromatography (GPC) and 1H NMR spectroscopy, respectively, over the course of the polymerization. The results revealed that polymerization proceeded via a chain-growth mechanism. This study illustrates a new approach to synthesize PPM with hitherto unknown high molar masses which opens the possibility to explore new applications, e.g., for temperature-resistant coatings, fluorescent coatings, barrier materials or optical materials.

Intending to deepen our understanding of tungsten acetylene (C 2 H 2 ) chemistry, with regard to the tungstoenzyme acetylene hydratase, here we explore the structure and reactivity of a series of tungsten acetylene complexes, stabilized with pyridine-2-thiolate ligands featuring tungsten in both +II and +IV oxidation states. By varying the substitution of the pyridine-2-thiolate moiety with respect to steric and electronic properties, we examined the details and limits of the previously reported intramolecular nucleophilic attack on acetylene followed by the formation of acetylene inserted complexes. Here, we demonstrate that only the combination of high steric demand and electron-withdrawing features prevents acetylene insertion. Nevertheless, although variable synthetic approaches are necessary for their synthesis, tungsten acetylene complexes can be stabilized predictably with a variety of pyridine-2-thiolate ligands.

The synthesis and characterization of a series of novel tungsten complexes employing the bioinspired, sulfur-rich scorpionate ligand [PhTt] (phenyltris­((methylthio)­methyl)­borate) are reported. Starting from the previously published tungsten precursor [WBr2(CO)3(NCMe)2], a salt metathesis reaction with 1 equiv of Cs­[PhTt] led to the desired complex [WBr­(CO)3(PhTt)] (1), making it the first tungsten complex employing a poly­(thioether)­borate ligand. Surprisingly, the reaction of [WBr2(CO)3(NCMe)2] with an excess of the ligand gave complex [W­(CO)2(η2-CH2SMe)­(PhTt)] (2) with a bidentate (methylthio)­methanide ligand as the major product. Thereby, phenyldi­((methylthio)­methyl)­borane is formed, which was isolated and characterized by NMR spectroscopy. The bromido ligand in [WBr­(CO)3(PhTt)] was further substituted by the S,N-bidentate methimazole in order to make the first coordination sphere more sulfur-rich forming [W­(CO)2(mt)­(PhTt)] (3). Alkyne tungsten complexes employing the sulfur-rich scorpionate ligand were accessible by reaction of [WBr2(CO)­(C2R2)2(NCMe)] (R = Me, Ph) with Cs­[PhTt] forming [WBr­(CO)­(C2R2)2(PhTt-S,S′)] (R = Me 4, Ph 5), with the potentially tridentate ligand coordinated only via two sulfur atoms. In the case of 4, the higher flexibility of the bidentate coordination leads to the formation of two isomers with respect to the six-membered ring formed by the tungsten center and the two coordinated sulfur atoms of the ligand. All complexes 1–5 were characterized by single-crystal X-ray diffraction analysis.