Bimetallic reactivity: unusual change in the coordination mode of the bridging ligands arising from an oxidative addition process

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The reactions of the dinuclear complex [{Rh(μ-C 7H 4NS 2)(CO)(PPh 3)}2] ( 1) (C 7H 4NS 2 = benzothiazole-2-thiolate) with electrophilic agents have been studied. Iodomethane reacts with 1 to give the diacetyl complex [{Rh(μ-C 7H 4NS 2)(COCH 3) (I)(PPh 3)}2] ( 2) as the result of the addition of one MeI molecule to each metal atom followed by the insertion of the carbonyl groups into the RhMe bonds. Monitoring this reaction by 31P{ 1H} NMR and IR shows that it goes through a dinuelear pathway. The crystal structure analysis of 2 shows a significant change in the coordination mode of the bridging benzothiazol-2-thiolates relative to the parent compound 1. In 2 each bridging ligand bonds through the exocyclic sulphur atom to both rhodium atoms, and the azolate nitrogen maintains a weak bonding interaction with one metal as shown by the long RhN distance, 2.588(3) Å. A further rearrangement is observed in solution, since spectroscopic studies show that 2 is in equilibrium with an acyl-mononuclear complex arising from the fragmentation of the dinuclear unit. Iodine also reacts with 1 to give the insoluble rhodium(III) complex [{Rh(C 7H 4NS 2)I 2(CO)(PPh3)} n ] whereas HgI 2 and methyl triflate react with 1 to give the heterotrinuclear and homotrinuclear aggregates [(PPh 3) 2(CO) 2Rh 2(μ 3-C 7H 4NS 2) 2HgI] [HgI 3]( 4) and [Rh 3(μ 3-C 7H 4NS 2) 2(CO) 3(PPh 3) 3] + respectively, as a result of the attack of the electrophiles on the exocyclic sulphur atoms of the benzothiazole-2-thiolates.