Migratory insertion of a phosphorus ligand into a transition metal-alkyl bond

Article abstract of DOI:10.1021/om00010a030

Treatment of Cp(CO)(R¹)Fe{PN(Me)CH₂CH₂NMe(OR²)} (R¹ = R² = Me, 1a; R¹ = Me, R² = Et, 2a; R¹ = CH₂Ph; R² = Me, 3a) with BF₃·OEt₂ and then with PPh₃ yields [Cp(CO)(PPh₃)Fe(PN(Me)CH₂CH₂NMe(R ¹)}]⁺ (R¹ = Me, 1b; R¹ = CH₂Ph, 3b). The reaction proceeds via the formation of a cationic phosphenium complex, [Cp(CO)(R¹)Fe{PN(Me)CH₂CH₂NMe}]⁺, by the abstraction of an OR group as an anion from a phosphorus atom, and then migratory insertion of the phosphenium ligand into the iron-alkyl bond takes place to give [Cp(CO)(BF₂OR²)Fe{PN(Me)CH₂CH ₂NMe(R¹)}]⁺, which is characterized by spectroscopic data. The cationic complex readily reacts with PPh₃ to give the final product. A η⁵-C₅Me₅ derivative of 1a and a monoamino-substituted phosphite complex Cp(CO)(Me)Fe{PN(Me)CH₂CH₂O(OMe)} show the same reactivity. The reaction of silyl complexes Cp(CO)(SiMe₃)Fe{PN(Me)CH₂CH₂NMe(OR)} (R = Me, Et) with BE₃·OEt₂ affords a phosphenium complex [Cp(CO)(SiMe₃)Fe{PN(Me)CH₂CH₂NMe}]⁺, which does not show the migratory insertion into an iron-silyl bond. Iron complexes Cp(CO)(CH₂OMe)Fe{PN(Me)CH₂CH₂NMe(OR)} (R = Me, 9a; R = Et, 10a) having an alkoxy group both on a carbon and on a phosphorus react with BF₃·OEt₂ and then with PPh₃ to give [Cp(CO)(CH₂PPh₃)Fe{PN(Me)CH2CH2NMe(OR)}]⁺ (R = Me, 9e; R = Et, 10e). The results prove that the OMe in the CH₂OMe ligand is selectively abstracted to give the methylidene complex which is trapped with PPh₃ to give a phosphine ylide complex. Complexes 1b·BF₄ and 10e·BF₄ have been characterized by X-ray diffraction (crystal data for 1b·BF₄, monoclinic, P2₁/n, a = 9.099(1) A?, b = 13.727 (2) A?, c = 23.134 (5) A?, β = 91.48 (1)°, Z = 4, R = 0.063; for 10e·BF₄, orthorhombic, Pcab, a = 18.033 (6) A?, b = 24.619 (6) A?, c = 14.501 (4) A?, Z = 8, R = 0.059).