Synthesis and Molecular Structure of Bis(pentamethylcyclopentadienyl) Phospholyl- and Arsolylsamarium(III) Complexes: Influence of Steric and Electronic Factors

The title complexes could be easily synthesized respectively from the following biphospholyls: 2,3,4,5,2‘,3‘,4‘,5‘-octamethylbi-1,1‘-phospholyl (1); 3,4,3‘,4‘-tetramethylbi-1,1‘-phospholyl (2); 2,5,2‘,5‘-tetra-tert-butylbi-1,1‘-phospholyl (3), and Cp*2Sm or Cp*2Sm(Et2O) (Cp* = pentamethylcyclopentadienyl). 3,4,3‘,4‘-Tetramethylbi-1,1‘-arsolyl (4), a precursor of the new 3,4-dimethylarsolyl ligand, was prepared in three steps from the known 1-chloro-2,5-di(trimethylsilyl)-3,4-dimethylarsole (5). The reaction of 4 with Cp*2Sm afforded the title complex 12. Although the unsubstituted bi-1,1‘-phospholyl could be observed by NMR, it decomposed during the isolation, and thus the title complex 13 with the unsubstituted phospholyl was prepared from Cp*2Sm(Et2O) and the new thallium phospholide 8, synthesized by metathesis of lithium phospholide with thallous ethoxide. Compounds 8−13 were characterized by X-ray crystallography. The solid state structures of complexes 9−13 vary depending on the substitution pattern on the phospholyl ligand. They can be η1- or η5-coordinated monomers (respectively 9 and 12), a μ:η1,η5- symmetrical dimer (13), or even unsymmetrical dimers where both the η1- and the μ:η1,η5-coordination modes are found (10 and 11). These structures are discussed by taking into account the electronic and steric properties of the phospholyl and arsolyl ligands.