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Synthesis and structure of some di-iron α-diimine complexes containing a ferracyclopentadienyl system resulting from the CC coupling of two alkynes

1989; Elsevier BV; Volume: 158; Issue: 1 Linguagem: Inglês

10.1016/s0020-1693(00)84017-7

1873-3255

Fred Muller, I. M. HAN, Gerard van Koten, Kees Vrieze, D. Heijdenrijk, Roeland L. De Jong, Martin C. Zoutberg,

Boron Compounds in Chemistry

The dinuclear α-diimine complexes Fe2(CO)6(L) [L=R-DAB (RNCHCHNR, R=i-Pr (1a), c-Hex (1b)), i-Pr-Pyca (C5H4NCHNi-Pr)(1c)] react with two equivalents of alkyne R′CCR″ [R′=H, R″= C(O)OMe, Ph, p-Tol, CMe2OH; R′=R″=H, C(O)OMe, Ph], probably via Fe2(CO)5(σ,σ-N,N′-L)[μ2,η2R′C CR″], to give various amounts of different isomers of Fe2[C4R′2R″2](CO)4(σ,σ-N,N′-L). These complexes have a ferracyclopentadienyl fragment FeC4R′2R″2 and a chelating 4e donating α-diimine coordinated to the Fe atom bonded to the FeC4 ferracycle (3) or to the Fe atom within the ferracycle (4). Fe2[HCCHCHCH](CO)4(i-Pr-DAB) (5) is formed in the thermal reaction of 1a with ethyne and also has the α=diimine bonded to the Fe within the ferracycle. The product distribution of the reactions seems to depend mainly on steric requirements of the alkyne substituents. In some of the reactions small amounts of alkyne cyclotrimerization products were formed. The X-ray crystal structures of Fe2[PhCC(H)C(H)CPh](CO)4(σ,σ-N,N′-c-Hex-DAB) (3a), Fe2[MeOC(O)CC(H)C(C(O)OMe)CH](CO)4(σ,σ-N,N′-i-Pr-DAB) (3h), Fe2[MeOC(O)CC(C(O)OMe)C(C(O)OMe)CC(O)OMe](CO)4(σ,σ-N,N′-i-Pr-DAB) (4e) and Fe2[HCC(H)C(H)CH](CO)4(σ,σ-N,N′-i-Pr-DAB) (5) were determined. (3a (Fe2C34H36N2O4): orthorhombic crystals, space group Pbca, a=17.353(3), b=22.814(6), c=15.911(4) Å, Z=8, R=0.070 for 1238 observed reflections. 3h (Fe2C20H24N2O8): monoclinic crystals, space group C2/c, a=29.609(5), b=9.969(2), c=19.611(3) Å, β=127.08(1)°, Z=8, R=0.064 for 1804 observed reflections. 4e (Fe2C24H28N2O12): monoclinic crystals, space group P21/a, a=18.287(4), b=17.966(6), c=9.002(3) Å, β=98.96(3)°, Z=4, R=0.076 for 1701 observed reflections. 5 (Fe2C16H20N2O4): triclinic crystals, space group P1, a= 9.8291(16), b=12.1898(22), c=9.0322(12) Å, α=111.269(11)°, β=115.626(19)°, γ=79.987(23)°, Z=2, R=0.046 for 3758 observed reflections.) The complexes 4 contain a bridging CO which makes them the first ferracyclopentadienyl complexes with a bridging CO. The complexes 3 and 5 contain a semi-bridging CO. This coordination behaviour is mainly due to electronic effects. The 1H NMR spectra of the type 3 complexes with two tail-to-tail coupled alkynes show a dynamic behaviour in solution involving the back and forth rocking of the Fe(CO)(α-diimine) fragment with respect to the Fe(C4R4)(CO)3 ferracyclopentadienyl fragment.