Chemistry of transition-metal complexes containing functionalized phosphines: synthesis and structural analysis of rhodium(I) complexes containing allyl and cyanoalkylphosphines

A series of related acetylacetonate-carbonyl-rhodium compounds substituted by functionalized phosphines has been prepared in good to excellent yields by the reaction of [Rh(acac)(CO)(2)] (acac is acetylacetonate) with the corresponding allyl-, cyanomethyl- or cyanoethyl-substituted phosphines. All compounds were fully characterized by P-31, H-1, C-13 NMR and IR spectroscopy. The X-ray structures of (acetylacetonato-kappa O-2,O')(tert-butylphosphanedicarbonitrile-P)carbonylrhodium(I), [Rh(C5H7O2)(CO)(C8H13N2)] or [Rh(acac)(CO)(tBuP(CH2CN)2}] (2b), (acetylacetonato-kappa O-2,O'())carbonyl[3-( diphenylphosphanyl)propanenitrile-P]rhodium(I), [Rh(C5H7O2)(C15H14N)(CO)] or [Rh(acac)(CO){Ph2P(CH2CH2CN)}] (2h), and (acetylacetonato-kappa O-2,O')carbonyl[3-(di-tert-butylphosphanyl)propanenitrile-P]rhodium(I), [Rh(C5H7O2)(C11H22N)(CO)] or [Rh(acac)(CO){(Bu2P)-Bu-t(CH2CH2CN)}] (2i), showed a squareplanar geometry around the Rh atom with a significant trans influence over the acetylacetonate moiety, evidenced by long Rh-O bond lengths as expected for poor pi-acceptor phosphines. The Rh-P distances displayed an inverse linear dependence with the coupling constants JP- Rh and the IR nu(C = O) bands, which accounts for the Rh-P electronic bonding feature (poor pi-acceptors) of these complexes. A combined study from density functional theory (DFT) calculations and an evaluation of the intramolecular H center dot center dot center dot Rh contacts from X-ray diffraction data allowed a comparison of the conformational preferences of these complexes in the solid state versus the isolated compounds in the gas phase. For 2b, 2h and 2i, an energy-framework study evidenced that the crystal structures are mainly governed by dispersive energy. In fact, strong pairwise molecular dispersive interactions are responsible for the columnar arrangement observed in these complexes. A Hirshfeld surface analysis employing threedimensional molecular surface contours and two-dimensional fingerprint plots indicated that the structures are stabilized by H center dot center dot center dot H, C center dot center dot center dot H, H center dot center dot center dot O, H center dot center dot center dot N and H center dot center dot center dot Rh intermolecular interactions.