Metal carbonyl complexes of phosphaamidines. Coordinative integrity detected in C-amino(λ3,σ2)-phosphaalkene isomers coordinated through n(P) HOMO−1 donor orbitals

Abstract

Metal(0) complexes L(Cr,Mo,W)(CO)₅ have been prepared from 1,3-bis(2,6-diisopropylphenyl)-2-(4-methylphenyl)-3-aza-1(λ³,σ²)-phosphapropene and 1,3-bis(2,6-diisopropylphenyl)-2-(4-methoxyphenyl)-3-aza-1(λ³,σ²)-phosphapropene using standard methods. Full characterization of four products and crystal structures of these complexes as well as the methoxyphenyl-phosphapropene are reported. The ligands coordinate κP, common for simple phosphaalkenes, despite the strongly-perturbing amino substitution at the double bond C atoms. Analyses of the NMR and vibrational spectroscopic data reveal that the complexes have very similar character to similarly-coordinated phosphaalkenes, with strong σ-donor character. The presence of some net π-interactions (acceptor or donor) is indicated by structures in which the ligands coordinate fully eclipsed with the M–CO groups. The synthetic and structural results have been augmented by B3PW91/LANL2DZ calculations that reproduce the structures of the Cr complexes accurately. The calculated vibrational spectra are used to confirm the assignment of the ν(CO) vibrational data. Detailed orbital interaction diagrams based on DFT calculations are reported for the title complexes as well as for the Cr(CO)₅ complex of Mes–PCPh₂. The electronic absorption spectra of the title complexes have intense low-energy absorptions ranging from 24 500 to 25 300 cm⁻¹, which can be interpreted qualitatively using the DFT results.