Arbusov Rearrangement Involving (η5-C5H5)Co(dppe)I+ and P(OCH3)3. A 1H and 31P NMR Study of the Mechanism Leading to the Formation of an Organometallic Phosphonate Complex

Article abstract of DOI:10.1021/ja00388a016

The Arbusov reaction, in which an alkyl halide converts an alkyl phosphite to a phosphonate, can also occur with a transition-metal halide complex in place of the alkyl halide.Thus, the previously unreported complex <(η⁵-C5H5)Co(dppe)I>X, (1), where X = I^- and BF4^- and dppe = 1,2-bis(diphenylphosphino)ethane, undergoes the Arbusov reaction with P(OCH3)3 to produce <(η⁵-C5H5)Co(dppe)P(O)(OCH3)2>⁺, (2).The reaction is well suited for a mechanistic study of the Arbusov rearrangement involving an organometallic complex.According to the 1H and 31P NMR spectra, the reaction progresses by the equilibration of P(OCH3)3 and 1 to produce <(η⁵-C5H5)Co(dppe)>²⁺ (3). 3 is significant intermediate complex that is unequivocally identified by its high-field 1H and 31P spectrum.The association of I^- probably with the methyl groups of the coordinated P(OCH3)3 molecule results in the actual Arbusov rearrangement to yield 2 and CH3I (k_obsd = 1.5 x 10^-2 L mol^-1 s^-1 at 16 deg C).Comparison of this transition-metal-based Arbuzov reaction with the classical reaction is given along with some possible conditions that optimize the likelihood of an Arbusov rearrangement occuring in a transition-metal halide complex.