Soft Scorpionate Hydridotris(2‐mercapto‐1‐methylimidazolyl) borate) Tungsten‐Oxido and ‐Sulfido Complexes as Acetylene Hydratase Models

Abstract

As eries of W IV alkyne complexes with the sulfurrich ligand hydridotris(2-mercapto-1-methylimidazolyl) borate)(Tm Me)a re presented as bio-inspired modelst oe lucidate the mechanism of the tungstoenzyme acetylene hydratase (AH). The mono-a nd/or bis-alkyne precursors were reacted with NaTm Me and the resulting complexes [W(CO)(C 2 R 2)(Tm Me)Br] (R = H 1,M e2)o xidizedt ot he target [WE(C 2 R 2)(Tm Me)Br] (E = O, R = H 4,M e5;E= S, R = H 6,M e7) using pyridine-N-oxidea nd methylthiirane. Halide abstraction with TlOTf in MeCN gave the cationic complexes [WE(C 2 R 2)(MeCN)(Tm Me)](OTf) (E = CO, R = H 10,M e11;E= O, R = H 12,M e13;E= S, R = H 14,M e15). Without MeCN, dinuclearc omplexes [W 2 O(m-O)(C 2 Me 2) 2 (Tm Me) 2 ](OTf) 2 (8)a nd [W 2 (m-S) 2 (C 2 Me 2)(Tm Me) 2 ](OTf) 2 (9)c ould be isolated showing distinct differences between the oxido and sulfido system with the latter exhibiting only one molecule of C 2 Me 2 .T his provides evidencet hat af ine balanceo ft he softnessa tWis important for acetylene coordination.U pon dissolving complex 8 in acetonitrile complex 13 is reconstituted in contrast to 9.All complexes exhibit the desired stability toward water and the observed effective coordination of the scorpionate liganda voidsd ecomposition to disulfide, an often-occurring reactioni ns ulfur ligand chemistry.H ence, the data presented here point towardamechanism with ad irect coordination of acetylene in the active site and provide the basis for further model chemistry for acetyleneh ydratase.

Bioinspired Nucleophilic Attack on a Tungsten-Bound Acetylene: Formation of Cationic Carbyne and Alkenyl Complexes

“…IR spectra show one strong band indicative of ν(W=O) at 924 cm –1 . 14 , 26 − 28 The 1 H NMR spectrum of 3 in CD 2 Cl 2 shows two equally sharp singlets flanked with 183 W satellites for the C 2 H 2 protons at 11.23 and 10.99 ppm. Thus, they are shifted upfield compared to 1 .…”

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

“…Values for the stretching frequency of the metalÀ oxygen bond are in accordance with the literature and do not vary significantly among themselves (914-927 cm À 1 ). [19,30,45] NMR spectra recorded in CD 2 Cl 2 show again the presence of only one isomer for the C 2 Me 2 and C 2 Ph 2 complexes 6a, 6b, 8a, and 8b, while two isomers with respect to the orientation of the coordinated HC 2 Ph are observed of both 7a and 7b. In 1 H-NMR spectra of 6a and 6b, the protons of the two C 2 Me 2 methyl groups appear as broad quadruplets, and hence they couple with each other with J = 1.0 Hz, while no coupling of the C 2 Me 2 protons is observed in the respective carbonyl complexes 1a and 1b.…”

“…[29,30] Due to the strong trans effect of the oxido ligand, the opposite metalÀ sulfur bond (2.6218(6) -2.6690(5) Å) is considerably longer than the other (2.4097(6) -2.4194(6) Å) in all presented complexes as already observed in [MoO (PMe 3 )(6-MePyS) 2 ]. [53] While W(IV) oxido C 2 R 2 complexes are already quite established, [19,21,45,54] the structures of complexes 6b, 7b, and 8b represent the first examples of Mo(IV) oxido C 2 R 2 complexes.…”

The Effect of Pyridine-2-thiolate Ligands on the Reactivity of Tungsten Complexes toward Oxidation and Acetylene Insertion

“…The first tungsten­(II) acetylene species bearing dithiocarbamate ligands was reported in 1978; thereafter, only a few other W–C 2 H 2 adducts have been synthesized. − For example, Templeton et al reported a tungsten­(IV) oxo acetylene complex containing an N-donor boron-based scorpionate ligand . In our group, the use of bioinspired S,N-bidentate ligands, such as SPhoz (2-(4′4′-dimethyloxazoline-2′-yl)­thiophenolate), PyS (pyridine-2-thiolate), and 6-MePyS (6-methylpyridine-2-thiolate), allows the preparation of W­(II) and W­(IV) complexes and ensures a sulfur-rich environment, more closely resembling the one in the native enzyme.…”