The reaction of co-ordinated cyclo-octatetraene with arenediazonium ions: azo-coupling vs. arylation

Abstract

Arenediazonium ions, [N₂C₆H₄R′-p][BF4], react with [Fe(CO)_3–n{P(OMe)₃}_n(η⁴-cot)](1; n= 1 or 2, cot = cyclo-octatetraene) to give the azo-coupled cyclo-octatrienyl [Fe(CO)_3–n{P(OMe)₃}_n^–(η⁵-C₈H₈N₂C₆H₄R′-p)]X (2; n= 1, R′= NO₂, X = BF₄; n= 1 or 2, R′= F, X = BPh₄) which is deprotonated to give the fluxional, arylazo-substituted cot complex [Fe(CO)_3–n{P(OMe)₃}_n(η⁴-C₈H₇N₂C₆H₄R′-p)](3). The reaction of (3; n= 2, R′= F) with NMe₃(O)·2H₂O yields the un-co-ordinated azo-compound C₈H₇N₂C₆H₄F-p(4). The tricarbonyl [Fe(CO)₃(η⁴-cot)] and [N₂C₆H₄NO₂-p][BF₄] afford the arylated bicyclo[5.1.0]octadienyl complex [Fe(CO)₃(η⁵-C₈H₈C₆H₄NO₂-p)][BF₄](5) which is deprotonated to the fluxional aryl-cot complex [Fe(CO)₃(η⁴-C₈H₇C₆H₄NO₂-p)](6). Hydride-ion addition to (5) gives the bicyclo[5.1.0]octadiene compound [Fe(CO)₃(η⁴-C₈H₉C₆H₄NO₂-p)](7), ¹H n.m.r. studies on which reveal an endo-aryl substituent. The mechanism of the reaction between (1) and [N₂C₆H₄R′-p]+ involves competitive electrophilic attack at the metal and cot ring.