Synthesis and structures of bis(dithiolene)molybdenum complexes related tothe active sites of the DMSO reductase enzyme family

Structural analogues of the reduced (Mo(TV)) sites of members of the DMSO r eductase family of molybdoenzymes are sought. These sites usually contain t wo pterin--dithiolene cofactor ligands and one protein-based ligand. Reacti on of [Mo(MeCN)(3)(CO)(3)] and [Ni(S2C2R2)(2)] affords the trigonal prismat ic 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)mol ybdenum(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 hinde red arene oxide ligands ArO- afford the square pyramidal complexes [Mo(OAr) (S2C2R2)(2)](1-) (5, 6). The ligands PhQ(-) afford the trigonal prismatic m onocarbonyls [Mo(CO)(QPh)(S2C2Me2)(2)](1-)(Q = S (8), Se (12)) while the bu lky ligand ArS- forms square pyramidal [Mo(SAr)(S2C2R2)(2)](1-) (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 pre pared by substitution reactions of 1 and 2 include the bridged dimers [Mo-2 - (mu-Q)(2)(S2C2Me2)(4)](2-) (Q = S (7), Se (11)) and [Mo-2(mu-SePh)(2)(S2C 2Ph2)(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 deter minations. Certain complexes approach the binding arrangements in at least one DMSO reductase (5/6) and its Ser/Cys mutant, and in dissimilatory nitra te reductases (9/10). This investigation provides the initial demonstration of the new types of bis(dithiolene)molybdenum(IV) complexes available thro ugh [Mo(CO)(2)(S2C2R2)(2)] precursors, some of which will be utilized in re activity studies. (Ar = 2,6-diisopropylphenyl or 2,4,6-triisopropylphenyl.) .