Synthesis, reactivity and redox properties of dinuclear molybdenum-sulfur complexes

Abstract This paper reports the synthesis of dinuclear Mo(V) complexes containing the Mo 2 S 4 2+ core. Complexes are prepared using the starting material (NH 4 ) 2 Mo 2 (S 2 ) 6 ·2H 2 O for which a new high yield preparation is presented. Reaction of Mo 2 (S 2 ) 6 2− with eight equivalents of the monodentate thiol, PhSH, gives Mo 2 S 8 2− , i.e. ( η 2 -S 2 )MoS( μ -S) 2 Mo( η 2 -S 2 ) 2− , which has one terminal disulfido and one sulfido ligand in each molybdenum coordination sphere and has a bis(sulfido) bridge rather than the bis(disulfido) bridge of the starting material. The Mo 2 S 8 2− anion is identical to that formed by the reaction of MoS 4 2− with PhSSPh by an induced internal electron transfer process. Reaction of (NH 4 ) 2 Mo 2 (S 2 ) 6 ·2H 2 O with a large excess of PhSH yields Mo 2 S 4 (SPh) 4 2− in which the Mo 2 S 4 2+ core is bound by four monodentate thiolate ligands. The reaction of (NH 4 ) 2 Mo 2 (S 2 ) 6 ·2H 2 O with excess of a variety of S-containing bidentate ligands gives high yields of Mo 2 S 4 2+ core products with one bidentate, dithiolate on each molybdenum. The reactions involve reduction of the disulfido ligands in Mo 2 (S 2 ) 6 2− to sulfido ligands, four of which remain in the coordination spheres of the two molybdenum atoms. All reactions and interconversions involve the maintenance of molybdenum in the oxidation state V. The complexes are of the general form Mo 2 S 4 L 2 ν − ( ν = 0, L = i-Bu 2 NCS 2 , Et 2 NCS 2 , NH(CH 3 )CH 2 C(CH 3 )S, NH 2 CH 2 C(CH 3 )S, NH 2 CH 2 C(CH 3 )S, C 6 H 4 SNH 2 ; ν = 2, C 6 H 4 S 2 , CH 3 C 6 H 3 S 2 , C 6 H 4 SNH, SCH 2 CH 2 S). The X-ray crystal structures of (PPh 4 ) 2 [Mo 2 S 8 ] and (NMe 4 ) 2 [Mo 2 S 4 (SPh) 4 ] are reported. The structures are compared with other crystallographically characterized complexes containing the syn and anti Mo 2 S 4 2+ cores. Infrared and UV-visible spectroscopic and electrochemical data are given for all of the new complexes reported.