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Abstract
Trimethylphosphite ligands in about 40 different molecular environments in the solid state adopt five distinct conformations, apart from those related by chirality. The ligand symmetry is usually C 1, occasionally C 3 or C s, but never the maximum attainable C 3v. Average experimental P[sbnd]O and O[sbnd]C bond lengths in the complexes are 1.583 and 1.440 A; O[sbnd]P[sbnd]O bond angles (average 101.4°) vary considerably from conformer to conformer, whereas the mean P[sbnd]O[sbnd]C angle is 124.0°. Conformational analysis, using the MNDO method, indicates that the steric requirements of the metal rule out a C 3v, several C 3, C s and lower symmetry conformations for the ligand which are energetically favorable in case of the isolated molecule. Except for the experimentally observed C 3 symmetry conformer, none of the other ligand geometries (of C s and C 1 symmetry) is amongst the set of low energy conformations of the free molecule. This stands in relation to the steric requirement of the metal, which induces considerable torsional variations upon coordination together with changes in O[sbnd]P[sbnd]O bond angles and C[sbnd]O bond distances. The metal position is typically displaced by about 0.25 A away from the cap of the phosphorus pyramid in the P[sbnd]O[sbnd]C plane of the trans methyl group.