Abstract
Electrochemical oxidation of fundamentally and practically important half-sandwich compound CoCp(CO)(2), 1, has been undertaken in benign solvent/electrolyte media, comprising CH2Cl2/[NBu4][B(C6F5)(4)], in the presence of strong PR3 nucleophiles (PR3 = PPh3 or P(OMe)(3)). In the absence of PR3, the electro-generated 17-electron cation [CoCp(CO)(2)](+), 1(+) is known to undergo fast coupling with neutral 1 to produce metal-metal bonded dimer cation, [Co2Cp2(CO)(4)](+), 2(+) via an unprecedented radical-substrate (R-S) dimerization process. However, generation of 1(+) in the presence of 1 or 2 equiv of PPh3 or P(OMe)(3) resulted in complete elimination of the R-S coupling and promoted CO-substitution reactions that afforded the corresponding mono-and di-substituted products. Thus, in the presence of PPh3 and via implementation of the "electrochemical switch" approach both [CoCp(CO)(PPh3)](+) and [CoCp(PPh3)(2)](+) have been successfully generated on synthetically useful timescale, with the former species being the major product. In a marked contrast, reaction of 1(+) with 1 equiv P(OMe)(3) ligand surprisingly yielded the tri-substituted dication, [CoCp{P(OMe)(3)} 3](2+) as a major product, along with small amount of the mono-substituted congener, [CoCp{P(OMe)(3)}(CO)](+). The outcomes of this study clearly show the importance of medium effects and the degree of metal-metal interactions in manipulating the properties and reactivity of the generated cation radicals towards nucleophilic attack and redox reactions.