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(λ(3),σ(2))-phosphapropene and 1,3-bis(2,6-diisopropylphenyl)-2-(4-methoxyphenyl)-3-aza-1(λ(3),σ(2))-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(C ≡ O) 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-P=CPh2. 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.
Highlights
Van Dijk et al have reported several additional examples of such phosphaamidines 4, all with backbone tBu and various aromatic groups on N and P, as well as some lithium and rhodium complexes.6. In parallel with these reports using conventional synthesis followed by complexation of deprotonated anions, Waterman has reported the elegant assembly of phosphaformamidinate complexes 5 from precursors coordinated to a zirconium scorpionate framework
The data show that in 10–12, the HOMO–LUMO gap is lowered by some 3400 to 3500 cm−1 in the complexes compared to the free phosphaamidines, which amounts to 13% reduction in the energy gap
Replacement of one nitrogen atom in bulky aryl N,N′-disubstituted amidines by phosphorus produces the atom-equivalent N,P-monophosphaamidines. This element-exchange has a profound effect on the coordination of these ligands as neutral molecules in LM(CO)5 complexes of Cr, Mo and W
Summary
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 -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. Detailed orbital interaction diagrams based on DFT calculations are reported for the title complexes as well as for the Cr(CO) complex of Mes–PvCPh2. 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
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