Optically Active Bimetallic Complexes with a Tantalum Atom as a Chiral Center. Synthesis, Characterization, and X-ray Structures of Two Diastereoisomers: Cp‘CpTa*(CO)(μ-PMe2)W(CO)4L* (Cp‘ = 1-tBu-3,4-Me2-C5H2; L* = (R)-(+)-Phenyl(o-anisyl)methylphosphine (PAMP))

Reaction of the racemic metallophosphine Cp‘CpTa(CO)(PMe2) (1; Cp‘ = 1-tBu-3,4-Me2-C5H2) with the tungsten fragment [W(CO)5] affords the corresponding μ-bimetallic phosphido complex 2, which in a photochemical transformation gives the dibridged derivative Cp‘CpTa(μ-CO)(μ-PMe2)W(CO)4 (3). Addition of an optically active phosphine (PAMP) to 3 leads to a pair of optically active diastereoisomers (4a and 4b) which can be separated by fractionnal crystallization. Both diastereoisomers 4a and 4b crystallize in the orthorhombic noncentrosymmetric space group P212121. X-ray structure determinations of 4a and 4b allowed the assignment of absolute configurations of the tantalum chiral centers (S for 4a and R for 4b). The absolute configuration of the phosphorus atom of the PAMP ligand is the same (S) in both structures.