d¹ Oxosulfido-Mo(V) Compounds: First Isolation and Unambiguous Characterization of an Extended Series

Abstract

Reaction of Tp(iPr)Mo(VI)OS(OAr) with cobaltocene in toluene results in the precipitation of brown, microcrystalline oxosulfido-Mo(V) compounds, [CoCp2][Tp(iPr)Mo(V)OS(OAr)] (Cp(-) = η(5)-C5H5(-), Tp(iPr)(-) = hydrotris(3-isopropylpyrazol-1-yl)borate, OAr(-) = phenolate or 2-(s)Bu, 2-(t)Bu, 3-(t)Bu, 4-(s)Bu, 4-Ph, 3,5-(s)Bu2, 2-CO2Me, 2-CO2Et or 2-CO2Ph derivative thereof). The compounds are air- and water-sensitive and display ν(Mo═O) and ν(Mo[Formula: see text]S) IR absorption bands at ca. 890 and 435 cm(-1), respectively, 20-40 cm(-1) lower in energy than the corresponding bands in Tp(iPr)MoOS(OAr). They are electrochemically active and exhibit three reversible cyclovoltammetric waves (E(Mo(VI)/Mo(V)) = -0.40 to -0.66 V, E([CoCp2](+)/CoCp2) = -0.94 V and E(CoCp2/[CoCp2](-)) = -1.88 V vs SCE). Structural characterization of [CoCp2][Tp(iPr)MoOS(OC6H4CO2Et-2)]·2CH2Cl2 revealed a distorted octahedral Mo(V) anion with Mo═O and Mo[Formula: see text]S distances of 1.761(5) and 2.215(2) Å, respectively, longer than corresponding distances in related Tp(iPr)MoOS(OAr) compounds. The observation of strong S(1s) → (S(3p) + Mo(4d)) S K-preedge transitions indicative of a d(1) sulfido-Mo(V) moiety and the presence of short Mo═O (ca. 1.72 Å) and Mo[Formula: see text]S (ca. 2.25 Å) backscattering contributions in the Mo K-edge EXAFS further support the oxosulfido-Mo(V) formulation. The compounds are EPR-active, exhibiting highly anisotropic (Δg 0.124-0.150), rhombic, frozen-glass spectra with g1 close to the value observed for the free electron (ge = 2.0023). Spectroscopic studies are consistent with the presence of a highly covalent Mo[Formula: see text]S π* singly occupied molecular orbital. The compounds are highly reactive, with reactions localized at the terminal sulfido ligand. For example, the compounds react with cyanide and PPh3 to produce thiocyanate and SPPh3, respectively, and various (depending on solvent) oxo-Mo(V) species. Reactions with copper reagents also generally lead to desulfurization and the formation of oxo-Mo(V) or -Mo(IV) complexes.

Scorpionate Complexes as Models for Molybdenum Enzymes

“…The crystal structure of [CoCp 2 ][Tp i Pr MoOS(OC 6 H 4 CO 2 Et‐2)] (Figure ) confirmed the ionic formulation and revealed an Mo anion with a distorted octahedral geometry, Mo=O and Mo=S distances of 1.760(5) Å and 2.219(2) Å, respectively, and an O=Mo=S angle of ca. 107° , . The small increase of the O=Mo=S angle compared to the value for the Mo VI analogue (103.7°) is indicative of a predominantly two‐center (MoS) π* SOMO in these Mo V compounds.…”

“…The reduction of 29 by cobaltocene in toluene results in the precipitation of [CoCp 2 ][Tp i Pr MoOS(OAr)] (OAr = phenolate derivative) 32 as kinetic products, as shown by Equation , , . Similarly, the N n Bu 4 + salts may be generated (in situ) upon reduction of 29 with N n Bu 4 SH.…”

“…(b) Frozen‐glass spectrum of N n Bu 4 [Tp i Pr MoOS(OC 6 H 4 Ph‐4)] generated in situ by reduction of [Tp i Pr MoOS(OC 6 H 4 Ph‐4)] using N n Bu 4 SH in toluene. Adapted with permission from ref . Copyright (2015) American Chemical Society.…”

“…The two higher energy band assignments are tentative and based on results from the Mo VI analogue (Figure ). Adapted with permission from ref . Copyright (2015) American Chemical Society.…”

“…The sulfido ligand is highly reactive and attacks the co‐ligand phenyl group to form κ 2 ‐ O,S ‐2‐mercaptophenolate (nb. 31 ) ligands; it also attacks specific co‐ligand substituents to form related κ 2 ‐ O,S ‐bidentate ligand complexes , . The sulfido ligand also reacts with cyanide to produce free thiocyanate and a range of oxido‐Mo IV and ‐Mo V complexes depending on the solvent used , …”