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Monosubstituted nitrogen donors as ligands in cyclopentadienyliron complexes: synthesis, reactivity, ligand properties, and crystal structure of [C5H5Fe(CO)2(C5H5N)]SbF6

1991; Elsevier BV; Volume: 403; Issue: 1-2 Linguagem: Inglês

10.1016/0022-328x(91)83098-o

1872-8561

Hans Schumann, Martin Speis, W. P. Bosman, J. M. M. Smits, Paul T. Beurskens,

Organometallic Complex Synthesis and Catalysis

Cationic complexes [C5H5Fe(CO)2)]BF4, with L a monosubstituted nitrile, RCN, or a pyridine C5H4NR′ have been prepared by oxidative cleavage of [C5H5Fe(CO)2]2 with [(C5H5)2Fe]BF4 in the presence of an excess of L. The coordinated nitriles act as relatively weak donors and the donor strength dependence or R as observed by NMR and IR spectroscopy is in good agreement with Taft's inductive factor δ* for the uncoordinated ligand. These constants correlate roughly with the charge on the nitrogen atom of the uncoordinated RCN ligand as found by AM1 calculations. For the stronger donor ligands C5H4NR′ there is no overall dependence of their donor strength, but for systems with substituents in the same ring position there is a correlation of the δ13C CO shift of the complex with the pKa value of the uncoordinated pyridine ligand. The lability of the coordinated nitrile has been demonstrated by ligand replacement with anionic nucleophiles (X− = I and CN) or Group Vb donor ligands ER3 (E = P, R = C6H5, OCH3, OC6H5; E = As, Sb, R = C6H5) to give the related C5H5Fe(CO)2X and [C5H5Fe(CO)2(ER3)]BF4 complexes in high yields. Related substitutions are only found with X− in the pyridine series. When L = C5H4NR′ with R′ = 3-4-CN or 4-N(CH3)2, a nonseparable mixture of isomeric complexes involving coordination of the pyridine-nitrogen or of the pyridine substituent R′ are obtained. The observed ratio between these isomers depends on the pKa value of the uncoordinated pyridine and on the reaction conditions.