Highly distorted diiron(II,II) complexes containing four amidinate ligands. A long and a short metal-metal distance .2.

The reaction of FeCl2(HDPhF)(2) (HDPhF=N,N'-diphenylformamidine) with methyllithium in Et2O followed by extraction into solvent mixtures containing THF, toluene and hexanes produces crystals of Fe-2(mu-DPhF)(4)(I). This dinuclear compound contains four formamidinato bridges but in an arrangement that is highly distorted compared to the known paddle-wheel structures of M-2(amidinato)(4) molecules. A similar reaction using FeCl2(HDPhBz)(2) (HDPhBz=N,N'-diphenylbenzamidine) also gives a distorted molecule Fe-2(mu-DPhBz)(2)(eta(2)-DPhBz)(2) . 2THF (II), in which two amidine groups form bridges between the metal centers while the other two groups chelate to an iron atom each. The Fe-Fe distances are 2.462(2) and 3.124(1) Angstrom, respectively. Both compounds I and II have been structurally characterized by X-ray crystallography. At -60 degrees C, crystal data for I are: monoclinic, space group I2/a, a=18.001(6), b=10.019(1), c=25.422(9) Angstrom, beta=105.28(1)degrees, Z=4. For II: triclinic, space group <P(1)over bar>, a=10.7874(6), b=13.1756(7), c=13.4552(8) Angstrom, alpha=99.89(1), beta=109.405(3),gamma=100.210(7)degrees, Z=1.