Cis Labilization of Ligand Dissociation. 7. Substitution Reactions of Acetonitrilepentacarbonylmanganese(I). Cis Labilization via Nucleophilic Attack at Metal-Bound Co

Article abstract of DOI:10.1021/ja00539a008

Reaction of acetonitrilepentacarbonylmanganese(I) tetrafluoroborate, BF4, with pyridine in CH3NO2 solvent yields Mn(CO)3(NC5H5)3⁺ and CO2 as products.Reduction of 1 mol of solvent is shown occur.Reaction is inhibited by added pyridinium tetrafluoroborate.Pentacarbonylpyridinemanganese(I) tetrafluoroborate, BF4, reacts with pyridine in CH3NO2 solvent to afford the same products, but at a somewhat slower rate.These and other evidences suggest that reaction proceeds via a rate-determining attack of the aci anion of solvent, CH2NO2^-, at the carbon of metal-bound CO.In acetonitrile, reaction of BF4 with pyridine affords BF4 as principal product.The reaction rate is much faster than for reaction of BF4 with triphenylphosphine.A nucleophilic attack of pyridine at metal-bound CO to produce a cis-labilizing adduct ligand appears to precede the rate-determining loss of CH3CN.Reactions of BF4 with triphenylphosphine in acetonitrile, to yield principally Mn(CO)5PPh3⁺, with CD3CN to yield Mn(CO)5CD3CN⁺ + Mn(CO)3(CD3CN)3⁺, or with CH3CN to yield Mn(CO)3(CH3CN)3⁺ all proceed at comparable rates.Dissociative loss of CO (k(35 deg C) = 1.2 +/- 0.6 * 10^-6 s^-1) is slower than loss of CH3CN (k(35 deg C) = 4.2 +/- 1.0 * 10^-6 s^-1).The rate of substitution of BF4 by PPh3 in acetic anhydride proceeds via dissociative loss of CO (k(35 deg C) = 5.2 +/- 0.6 * 10^-7 s^-1).These comparative rates suggest than CH3CN is only slightly labilizing in Mn(CO)5CH3CN⁺.Reaction of BF4 with pyridine in wet acetonitrile leads to formation of additional products such as Mn(CO)5^- and dinuclear manganese species, that can be related to nucleophilic attack of OH^- at metal-bound CO.