Hemilabile and reversible carbon monoxide binding properties of iron(ii), cobalt(ii) and nickel(ii) complexes containing a new tridentate P-S-N ligand

摘要

Several first-row transition metal complexes of the formulation [M(1) _2](X)_2 {where 1 = Ph_2PCH_2CH _2S(2-C_6H_4NH_2); M = Fe~(II), X = BF_4~- (2); M = Co~(II), X = BF_4~- (3), Ni~(II), X = ClO_4~- (4)} have been prepared by reaction of two equivalents of the new P-S-N ligand Ph _2PCH_2CH_2S(2-C_6H_4NH _2) 1 with one equivalent of the appropriate [M(OH_2) _6](X)_2 precursor in acetonitrile. In the solid state, complexes 2-4 exist as distorted centrosymmetric octahedral structures featuring facially capping ligands in an all-trans arrangement. Reaction of 2 and 3 with a stream of carbon monoxide (1 atm.) for 5 min in acetonitrile generates iron(ii) monocarbonyl species of formulation [Fe(CO)(1)_2](BF _4)_22a, and a cobalt(ii) dicarbonyl complex, [Co(CO) _2(1)_2](BF_4)_23a, which can be isolated in the solid state. Complete removal of CO is achieved by either heating to reflux samples of 2a in acetonitrile for 5 min or by heating solid samples of 3a at 120 °C in vacuo over a period of 4 h. The binding of carbon monoxide is fully reversible for 2 and 3 and can be repeated over multiple cycles. When the same trapping reactions were carried out with very low radiochemical ~(11)CO concentrations, metal carbonyl species were no longer formed. It is likely that the kinetics of ~(11)CO adduct formation are too slow to allow for effective trapping under the applied radiochemical conditions. This journal is