Syntheses and structures of mono‐cyclopentadienyl di‐iodide complexes of the lanthanides: X‐ray crystal structures of Cp‴LaI 2 py 3 (Cp‴ = [η 5 ‐C 5 H 2 (SiMe 3 ) 3 ‐1,2,4] − ; py = pyridine) and Cp‴LaI 2 (bipy)py (bipy = 2, 2′‐bipyridine)

[η 5 ‐C 5 H 2 (SiMe 3 ) 3 ‐1,2,4]K reacts with LaI 3 (THF) 4 in tetrahydrofuran (THF) to form the mono‐ring complex [η 5 ‐C 5 H 2 (SiMe 3 ) 3 ‐1,2,4]LaI 2 (THF) x ( 1 ). Elemental analysis and 1 H NMR spectroscopy indicate that the coordinated THF molecules are labile and are easily removed under vacuum. The THF adduct 1 is readily converted to the more stable pyridine complex [η 5 ‐C 5 H 2 (SiMe 3 ) 3 ‐1,2,4]LaI 2 py 3 ( 2 ) by the addition of excess pyridine to a toluene solution of 1 . Although solid samples of 2 lose pyridine less readily, the pyridine molecules exchange with solvent molecules, and in the presence of a large excess of THF, 1 is re‐formed. Complex 2 may be crystallized from toluene, and an X‐ray diffraction study revealed a monomeric species with the two iodide ligands trans to each other, and three pyridines arranged in a meridional fashion. The addition of one equivalent of 2,2′‐bipyridine to a toluene solution of 1 yields the bipyridine adduct, [η 5 ‐C 5 H 2 (SiMe 3 ) 3 ‐1,2,4]LaI 2 (bipy) ( 3 ). In contrast to 1 and 2 , the bipyridine molecule in 3 remains ligated to the lanthanum center in all solvents. Complex 3·py may be crystallized from THF–pyridine; in this case, the presence of bipyridine forces a cis orientation of the two iodide ligands. Copyright © 2003 John Wiley & Sons, Ltd.