Reversible binding of acetylene by oxobis(diethyldithiocarbamate)molybdenum

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

“… 17 , 18 As Mo-dependent nitrogenase is known to accept C 2 H 2 as a substrate, the coordination of C 2 H 2 to a molybdenum(IV) center was investigated already in the late 1970s. 8 , 19 − 22 However, the coordination of C 2 H 2 to the bioinspired Mo(IV) complex [MoO(S 2 CNR 2 ) 2 ] (R = Me, Et) was reported to be reversible, and the formed adduct [MoO(C 2 H 2 )(S 2 CNR 2 ) 2 ] was found to decompose almost immediately to [Mo 2 O 4 (S 2 CNR 2 ) 2 ] after exposure to air. Thus, the isolation and characterization by single-crystal X-ray diffraction could not be achieved for the C 2 H 2 complex, but only for a complex containing a more activated substituted alkyne.…”

“…Acetylene (C 2 H 2 ) is known to be accepted as a substrate by only two enzymes: while the tungstoenzyme acetylene hydratase (AH) catalyzes the hydration of acetylene to acetaldehyde, − nitrogenase is capable of reducing acetylene to ethylene (C 2 H 4 ). − The crystal structure of AH revealed that the octahedral coordination sphere of the tungsten­(IV) center in the active site consists of four sulfur atoms from two molybdopterin cofactors, a thiolate from cysteine, and a water molecule . The mechanism of AH is still under debate, with different suggested mechanisms where H 2 O either stays coordinated to tungsten or is replaced by C 2 H 2 . − The molybdenum variant of AH was reported to be 10 times less active in C 2 H 2 hydration than the tungsten analogue despite exhibiting the same active site architecture as well as a similar protein fold. − In contrast to experimental findings, a recent theoretical study suggests the utilization of molybdenum instead of tungsten in bioinspired complexes to be energetically more favorable when a mechanism is considered where C 2 H 2 is bound to the metal center and subsequently attacked by a hydroxide. , As Mo-dependent nitrogenase is known to accept C 2 H 2 as a substrate, the coordination of C 2 H 2 to a molybdenum­(IV) center was investigated already in the late 1970s. ,− However, the coordination of C 2 H 2 to the bioinspired Mo­(IV) complex [MoO­(S 2 CNR 2 ) 2 ] (R = Me, Et) was reported to be reversible, and the formed adduct [MoO­(C 2 H 2 )­(S 2 CNR 2 ) 2 ] was found to decompose almost immediately to [Mo 2 O 4 (S 2 CNR 2 ) 2 ] after exposure to air. Thus, the isolation and characterization by single-crystal X-ray diffraction could not be achieved for the C 2 H 2 complex, but only for a complex containing a more activated substituted alkyne. , Until now, also complexes with C 2 H 2 coordinated to molybdenum in any other oxidation state remain scarce, − with only two mononuclear examples that were characterized by single-crystal X-ray diffraction. , …”

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

“…[18,19] Similar behavior was found in Mo(IV) oxido alkyne adducts. [20] Upon reaction with nucleophiles, fourelectron-donor alkynes usually give η 2 -vinyl (or metallacyclopropene) complexes, while two-electron-donor alkynes mostly yield trans-η 1 -vinyl complexes. [21,22] Examples for this reactivity are the nucleophilic attack of a phosphine on a bis(hexafluorobut-2-yne) tungsten complex to produce the respective η 2 -vinyl compound [23] or the hydride reduction of a twoelectron-donor alkyne to form an η 1 -vinyl complex [24] (Scheme 1).…”