Generation and Reactivity of Polychalcogenide Chains in Binuclear Cobalt(II) Complexes.

A series of six binuclear Co(II)-thiolate complexes, [Co 2 (BPMP)(S-C 6 H 4 - o -X) 2 ] 1+ (X = OMe, 2 ; NH 2 , 3 ), [Co 2 (BPMP)(μ-S-C 6 H 4 - o -O)] 1+ ( 4 ), and [Co 2 (BPMP)(μ-Y)] 1+ (Y = bdt, 5 ; tdt, 6 ; mnt, 7 ), has been synthesized from [Co 2 (BPMP)(MeOH) 2 (Cl) 2 ] 1+ ( 1a ) and [Co 2 (BPMP)(Cl) 2 ] 1+ ( 1b ), where BPMP 1- is the anion of 2,6-bis[[bis(2-pyridylmethyl)amino]methyl]-4-methylphenol. While 2 and 3 could allow the two-electron redox reaction of the two coordinated thiolates with elemental sulfur (S 8 ) to generate [Co 2 (BPMP)(μ-S 5 )] 1+ ( 8 ), the complexes, 4-7 , could not undergo a similar reaction. An analogous redox reaction of 2 with elemental selenium ([Se]) produced [{Co 2 (BPMP)(μ-Se 4 )}{Co 2 (BPMP)(μ-Se 3 )}] 2+ ( 9a ) and [Co 2 (BPMP)(μ-Se 4 )] 1+ ( 9b ). Further reaction of these polychalcogenido complexes, 8 and 9a / 9b , with PPh 3 allowed the isolation of [Co 2 (BPMP)(μ-S)] 1+ ( 10 ) and [Co 2 (BPMP)(μ-Se 2 )] 1+ ( 11 ), which, in turn, could be converted back to 8 and 9a upon treatment with S 8 and [Se], respectively. Interestingly, while the redox reaction of the polyselenide chains in 9a and 11 with S 8 produced 8 and [Se], the treatment of 8 with [Se] gave back only the starting material ( 8 ), thus demonstrating the different redox behavior of sulfur and selenium. Furthermore, the reaction of 8 and 9a / 9b with activated alkynes and cyanide (CN - ) allowed the isolation of the complexes, [Co 2 (BPMP)(μ-E 2 C 2 (CO 2 R) 2 )] 1+ (E = S: 12a , R = Me; 12b , R = Et; E = Se: 13a , R = Me; 13b , R = Et) and [Co 2 (BPMP)(μ-SH)(NCS) 2 ] ( 14 ), respectively. The present work, thus, provides an interesting synthetic strategy, interconversions, and detailed comparative reactivity of binuclear Co(II)-polychalcogenido complexes.