Synthesis and Structures of Bis(dithiolene)molybdenum Complexes Related to the Active Sites of the DMSO Reductase Enzyme Family

Abstract

Structural analogues of the reduced (Mo(IV)) sites of members of the DMSO reductase family of molybdoenzymes are sought. These sites usually contain two pterin-dithiolene cofactor ligands and one protein-based ligand. Reaction of [Mo(MeCN)3(CO)3] and [Ni(S2C2R2)2] affords the trigonal prismatic complexes [Mo(CO)2(S2C2R2)2] (R = Me (1), Ph (2)), which by carbonyl substitution serve as useful precursors to a variety of bis(dithiolene)molybdenum-(IV,V) complexes. Reaction of 1 with Et4NOH yields [MoO(S2C2Me2)2]2- (3), which is readily oxidized to [MoO(S2C2Me2)2]1- (4). The hindered arene oxide ligands ArO- afford the square pyramidal complexes [Mo(OAr)(S2C2R2)2]1- (5, 6). The ligands PhQ- affordthe trigonal prismatic monocarbonyls [Mo(CO)(QPh)(S2C2Me2)2]1- (Q = S (8), Se (12)) while the bulky ligand ArS- forms square pyramidal [Mo(SAr)(S2C2R2)2]- (9, 10). In contrast, reactions with ArSe- result in [Mo(CO)(SeAr)(S2C2R2)2]1-(14, 15), which have not been successfully decarbonylated. Other compounds prepared by substitution reactions of 1 and 2 include the bridged dimers [Mo2(mu-Q)2(S2C2Me2)4]2- (Q = S (7), Se (11)) and [Mo2(mu-SePh)2(S2C2Ph2)4]2- (13). The complexes 1, 3-5, 7-10, 12-14, [Mo(S2C2Me2)3] (16), and [Mo(S2C2Me2)3]1- (17) were characterized by X-ray structure determinations. Certain complexes approach the binding arrangements in at least one DMSO reductase (5/6) and its Ser/Cys mutant, and in dissimilatory nitrate reductases (9/10). This investigation provides the initial demonstration of the new types of bis(dithiolene)molybdenum(IV) complexes available through [Mo(CO)2(S2C2R2)2] precursors, some of which will be utilized in reactivity studies. (Ar = 2,6-diisopropylphenyl or 2,4,6-triisopropylphenyl.)

Molybdenum Dithiolene Complexes as Structural Models for the Active Sites of Molybdenum(IV) Sulfide Hydrodesulfurization Catalysts

“…[22] [Mo(CO) 2 -(S 2 C 2 Me 2 ) 2 ] complexes are known and offer both the square-pyramidal MoS 4 structure as well as labile CO groups. [19,23] While CO is a labile ligand in such complexes (as we also confirmed experimentally, see below), we pro-vide here an alternative approach to the opening up of two labile sites at "S 4 Mo".…”

“…Thus, carbon monoxide and thioethers have a similar binding strength when coordination to Mo(tfd) 2 fragments is involved. Some metal bisdithiolene complexes containing carbonyls are already known, [19,23] and it may be-come useful knowledge for future syntheses that CO and thioethers can be of comparable lability in such systems.…”

The Electronic Structure and Spectroscopy of Metallo‐Dithiolene Complexes

“…2À (33,34,70,314,(391)(392)(393) and desoxo [MX(dithiolene) 2 ] nÀ (X ¼ OR, SR, or SeR) (58,327,394) complexes have also been studied, considerably less is known of their spectroscopic properties and electronic structures. Therefore, they will not be discussed further.…”

“…Therefore, they will not be discussed further. Monooxo-molybdenum(V)-bis(dithiolene) compounds possess a distinctive broad low-energy absorption feature with maxima ranging from 729 to 842 nm and a higher energy feature at 446-575 nm (31,33,58,70,106,393,395). The absorption spectrum of [MoO(bdt) 2 ] 1À is given in Fig.…”

Electronic Control of the “Bailar Twist” in Formally d0-d2 Molybdenum Tris(dithiolene) Complexes: A Sulfur K-edge X-ray Absorption Spectroscopy and Density Functional Theory Study

“…Indeed, crystallographic investigations showed that tris(dithiolene) complexes such as [Mo(mnt) 3 ] 2-(mnt = maleonitriledithiolate(2-)) and [Mo(bdt) 3 ] 1-(bdt = benzene-1,2-dithiolate(2-)) adopt a geometry between trigonal prismatic and octahedral; 6,7 however, there are some notable exceptions such as [Mo(mdt) 3 ] z (mdt = 1,2-dimethylethene-1,2-dithiolate(2-), z = 2-, 1-), where the Mo-S 6 trigonal prism is maintained throughout the series, and [Ta(bdt) 3 ] 1-, which is isoelectronic with [Mo(S 2 C 2 H 2 ) 3 ] but forms a distorted octahedron. [8][9][10] Another factor thought to stabilize the trigonal prism was interligand sulfur-sulfur bonding. However, this was refuted by comparing the S-S distances in the trigonal prismatic complexes [Mo(bdt) 3 Rotation about the C 3 axis from O h (θ = 60°) to D 3h (θ= 0°), which is the pathway used to explain the racemization of certain octahedral tris(chelate) complexes, is known as a Bailar twist (Scheme 1b, θ).…”