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 ³¹P, ¹H, ¹³C NMR and IR spectroscopy. The X‐ray structures of (acetylacetonato‐κ²O,O′)(tert‐butylphosphanedicarbonitrile‐κP)carbonylrhodium(I), Rh(C₅H₇O₂)(CO)(C₈H₁₃N₂)] or Rh(acac)(CO)(^tBuP(CH₂CN)₂}] ( 2b ), (acetylacetonato‐κ²O,O′)carbonyl3‐(diphenylphosphanyl)propanenitrile‐κP]rhodium(I), Rh(C₅H₇O₂)(C₁₅H₁₄N)(CO)] or Rh(acac)(CO){Ph₂P(CH₂CH₂CN)}] ( 2h ), and (acetylacetonato‐κ²O,O′)carbonyl3‐(di‐tert‐butylphosphanyl)propanenitrile‐κP]rhodium(I), Rh(C₅H₇O₂)(C₁₁H₂₂N)(CO)] or Rh(acac)(CO){^tBu₂P(CH₂CH₂CN)}] ( 2i ), showed a square‐planar 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 π‐acceptor phosphines. The Rh—P distances displayed an inverse linear dependence with the coupling constants J_P‐Rh and the IR ν(Ctriple‐bond]O) bands, which accounts for the Rh—P electronic bonding feature (poor π‐acceptors) of these complexes. A combined study from density functional theory (DFT) calculations and an evaluation of the intramolecular H…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 three‐dimensional molecular surface contours and two‐dimensional fingerprint plots indicated that the structures are stabilized by H…H, C…H, H…O, H…N and H…Rh intermolecular interactions.