Coupling reactions of ynamines. Syntheses, structural characterization and electrochemistry of some nido and closo ferracyclopentadiene complexes

Abstract

The reaction of [Fe 2(CO) 7C(Ph)C(NEt 2)] ( 1) with ynamines RCCNEt 2 (R  Me, C 3H 5, or CH 2Ph) at 20°C yielded dinuclear ferracyclopentadiene complexes [Fe 2(CO) 6C(Ph)C(NEt 2)C-(NEt 2)C(R)] (R  Me ( 2), R  CH 2Ph ( 3), R  C 3H 5 ( 4)). Complex 5, [Fe 2(CO) 6C(C 3H 5)C(NEt 2)C-(NEt 2)C(C 3H 5)], was obtained directly from the reaction of C 3H 5CCNEt 2 with [Fe 2(CO) 9]. All complexes were characterized by a combination of microanalytical and spectroscopic techniques. The molecular structure of 4 was determined X-ray crystallographically: triclinic, P 1 , a = 8.820(2) Å, b = 9.261(2) Å, c = 18.470(2) Å, α = 89.40(1)°, β = 81.81(1)°, γ = 70.23(2)°, R w = 0.0406 for 2580 reflections. The nido complexes 4 and 5 transformed to the closo tripledecker compounds [Fe 3(CO) 8 C(Ph)C(NEt 2)C(NEt 2)C(R)] (R  Ph ( 6); R  C 3H 5 (7)) by an excess of [Fe 2(CO) 9] in refluxing hexane. Both complexes were characterized by IR, 1H NMR, mass spectra and chemical analysis. The X-ray structure of 6 was carried out: monoclinic, P2 1 / c, a = 14.900(3), b = 11.149(2), c = 18.453(4) Å, β = 91.14(2)°, R w = 0.0414 for 2304 reflections. Only one isomer could be isolated for the nido compounds. The nido-closo transformation did not modify the coupling within the butadiene moiety. Electrochemistry of the nido and closo complexes is reported. The closo compounds showed two reversible one-electron reduction waves whereas the nido species were completely irreversibly reduced.