Synthesis, Structure, Spectroscopy, and Reactivity of Thiapentadienyl-Cobalt-Phosphine Complexes

The first examples of thiapentadienyl-cobalt complexes have been synthesized and structurally characterized. Treatment of (Cl)Co(PMe3)3 with potassium thiapentadienide yields a dimetallic product, 1, which is held together by two bridging thiapentadienyl ligands, one of which possesses a cis internal double bond and the other a trans internal double bond. Treatment of 1 with carbon monoxide breaks apart the cluster, producing a mixture of (5-η1-cis-5-thiapentadienyl)Co(PMe3)2(CO)2 (cis-2) and its trans isomer (trans-2). cis-2 can be made independently by reacting (Cl)Co(PMe3)2(CO)2 with potassium thiapentadienide. In contrast, treatment of (Cl)Co(PMe3)3 with lithium 2,3-dimethyl-5-thiapentadienide generates a trimetallic product, 3. This species is held together by four bridging thiapentadienyl ligands, all possessing trans internal double bonds. In compound 3, the central cobalt is a Co(II) center, produced through a disproportionation reaction, while the two terminal cobalts are Co(I) centers. Treatment of 3 with carbon monoxide again breaks apart the cluster, producing (5-η1-trans-2,3-dimethyl-5-thiapentadienyl)Co(PMe3)2(CO)2 (trans-4). The cis isomer, cis-4, can be produced by treating (Cl)Co(PMe3)2(CO)2 with lithium 2,3-dimethyl-5-thiapentadienide. Compounds 1, cis-2, 3, and trans-4 have been characterized by single-crystal X-ray diffraction.