Synthesis and Reactivity of a Bioinspired Molybdenum(IV) Acetylene Complex

Abstract

The isolation of a molybdenum(IV) acetylene (C 2 H 2 ) complex containing two bioinspired 6-methylpyridine-2-thiolate ligands is reported. The synthesis can be performed either by oxidation of a molybdenum(II) C 2 H 2 complex or by substitution of a coordinated PMe 3 by C 2 H 2 on a molybdenum(IV) center. Both C 2 H 2 complexes were characterized by spectroscopic means as well as by single-crystal X-ray diffraction. Furthermore, the reactivity of the coordinated C 2 H 2 was investigated with regard to acetylene hydratase, one of two enzymes that accept C 2 H 2 as a substrate. While the reaction with water resulted in the vinylation of the pyridine-2-thiolate ligands, an intermolecular nucleophilic attack on the coordinated C 2 H 2 with the soft nucleophile PMe 3 was observed to give a cationic ethenyl complex. A comparison with the tungsten analogues revealed less tightly bound C 2 H 2 in the molybdenum variant, which, however, shows a higher reactivity toward nucleophiles.

Dioxygen Activation by a Bioinspired Tungsten(IV) Complex

“… 44 Interestingly, a monophosphine molybdenum(IV) complex with 6-methylpyridine-2-thiolate ligands reacts with acetylene by substituting a phosphine ligand. 45 This behavior resembles the binding of acetylene in AH, which was suggested to take place via substitution of the O donor ligand at the sulfur-rich tungsten(IV) center according to some computational studies. 37 − 39 The analogous tungsten complex has not yet been described.…”

“…Acetylene Coordination. Since the molybdenum(IV) analogue of 3 has previously been reported to react with acetylene by substitution of PMe 3 to yield the corresponding molybdenum(IV) acetylene adduct, 45 the reactivity of the reduced W complex toward acetylene was investigated. In situ generation of tungsten(IV) was carried out starting from 1 and 10 equiv of PMe 3 in benzene.…”

Inspired by Nature—Functional Analogues of Molybdenum and Tungsten-Dependent Oxidoreductases

“…More recently, extensive functional studies were carried out by the group of Mösch-Zanetti employing the [W II (CO)(C 2 H 2 )(PyS) 2 ] complexes with different PyS derivatives (Figure 13) [147,[151][152][153]. The corresponding complex [W IV O(C 2 H 2 )(PyS) 2 ] was synthesized with oxygen donor reagent pyridine-N-oxide (PyNO) to establish a structurally more similar analogue of the reduced active site.…”

“…In the case of W II , acetylene and PMe 3 generated a P-C bond accompanied by formation of an ethylidene, whereas for the W IV complex the same P-C bond formation was observed accompanied by ethenyl generation. The reactivity study was extended to molybdenum with the [Mo IV O(C 2 H 2 )(PyS) 2 ] complex [152]. This compound reacted with excess of acetylene and traces of water yielding the N-vinylated 1-vinylpyridine-2(1H)-thione which is the protonated CHCH-PyS species formerly reported for the W II analogue.…”

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).…”