Tetrathiomolybdate Complexes of Rhodium(I) with Molybdenum–Rhodium Interactions

The
synthesis and characterization of the tetrathiomolybdatorhodium­(I)
monoanionic complexes [L2Rh­(μ-S)2MoS2]− (L = CO (3), P­(OPh)3 (4), P­(O-o-Tol)3 (P­(o-CH3C6H4)3; 5), P­(OMe)3 (6), P­(OEt)3 (7), P­(O-i-Pr)3 (8); L2 = COD (1,5-cyclooctadiene; 2), cis-dppen (cis-Ph2PCHCHPPh2; 9), dppe (Ph2PCH2CH2PPh2; 10), dppb
(Ph2P­(CH2)4PPh2; 11)) is presented. The complex 2 (NEt4+ salt) was characterized by X-ray diffraction analysis.
A detailed DFT study of the electronic structures of 2–4 and 6–8 has
revealed the existence of extended electron delocalization over the
four-membered Rh­(μ-S)2Mo ring and hence the possibility
of electronic communication between the metal centers. The electronic
spectra were studied with TDDFT calculations, and the main absorption
band in the visible region was assigned to ν­(Rh→Mo) electron
transfer transition, which is actually a HOMO–LUMO transition.
The ν­(Rh→Mo) transition was found to correlate linearly
both with Tolman’s electronic parameter of the phosphite ligands
and the calculated HOMO–LUMO gap of the complexes, rendering
it a well-defined ligand electronic parameter, which describes the
net donating ability of monodentate and bidentate ligands (CO, COD,
phosphites, diphosphines). The study of the variation of Δδ­(31P) and 1J(Rh–P) of the
phosphite complexes with respect to the QALE model electronic parameters
χd, πp, and Ear has succeeded in the assessment of the σ and π
effects on these NMR spectral parameters.