The reaction of bis(triethylaluminum), A12(C2H5)6, with a variety of tetradentate Schiff-base ligands in benzene/acetonitrile solution yields ethane and the monoethylaluminum Schiff-base complexes. The ligands used include the 2:1 condensation products of salicylaldehyde with ethylenediamine, o-phenylenediamine, and propylenediamine (SALEN, SALOPHEN, and SALPN, respectively) and of acetylacetone with ethylenediamine (ACEN). These complexes are stable in the solid state in the absence of moisture but react with moisture and anhydrous HC1 in solution to yield ethane and the corresponding hydroxoaluminum and chloroaluminum complexes, respectively. The susceptibility of these complexes to moisture in solution is dependent to a remarkable degree on the flexibility of the ligand. It is proposed that the remarkable resistance to hydrolysis, as compared with nonchelated aluminum alkyl species, is related to the high energy state of the square-planar four-coordinate Al3+ species remaining on loss of the alkyl group. The X-ray crystal structure of C18H19N202A1 (A1(SALEN)C2H5, orthorhombic, P2¡2l2u a = 6.930 (3) Á, b = 10.186 (4) A, c = 23.092 (8) Á, Z = 4) reveals a 5-coordinate, square-pyramidal aluminum complex with an Al-C bond distance of 1.966 (7) Á. The average Al-O distance, 1.815 (15) Á, is much shorter than the Al-N distance, 2.020 (7) A. The aluminum is displaced 0.540 A from the least-squares plane of the ligating nitrogen and oxygen atoms, toward the ethyl group.The SALEN moiety adopts the usual "inverted umbrella" structure observed for monomeric transition-metal species.

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Szsmmary Several monocarbon monoxide complexes of iron(I1) with a macrocyclic ligand have been prepared, and a crystal structure of one of these complexes shows that the Fe-C=O angle is linear, 178", with an Fe-C distance of 1.75A and an unusually long axial Fe-N distance of 2-12 A.AN understanding of the binding of small molecules such as O,, CO, NO, and H,S to iron in biological heme systems is important. The study of synthetic macrocyclic complexes of iron@) has established the role of many structural parameters of the ligands in influencing iron reactivity.l We report on the synthesis and structural characterization of some monocarbon monoxide complexes of iron@) of the completely conjugated dianionic 14-membered macrocyclic ligand (I). The ligand was first prepared by the template condensation of o-phenylenediamine with pentane-2,P

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