Intramolecular Interactions between the Pnictogen Groups in a Rigid Ferrocene Phosphinostibine and the Corresponding Phosphine Chalcogenides, Stiboranes, and Their Complexes

Differences in the chemical properties of phosphorus and antimony enable the synthesis of heteroditopic derivatives whose properties can be modified by altering the pnictogen substituents. In this work, 1-(diphenylstibino)-2-(dicyclohexylphosphino)ferrocene, [Fe(η⁵-1-Ph₂Sb-2-Cy₂PC₅H₃)(η⁵-C₅H₅)] (<b>1</b>), and the corresponding phosphine chalcogenides [Fe(η⁵-1-Ph₂Sb-2-Cy₂P(E)C₅H₃)(η⁵-C₅H₅)] (E = O, S, Se) and catecholatostiboranes [Fe(η⁵-1-Ph₂(Cl₄C₆O₂)Sb-2-Cy₂P(E)C₅H₃)(η⁵-C₅H₅)] (E = void, O, S, Se) were examined, with a focus on the intramolecular donor-acceptor interactions between the antimony and the phosphorus substituents. Experimental data and theoretical analysis consistently indicated that these interactions can be described as pnictogen bonding between the Lewis acidic antimony and the lone pair at the phosphorus substituent (either at the phosphorus or at the chalcogen atom) and that they are significantly stronger in the stiboranes due to the increased Lewis acidity of the Sb atom. Noncovalent interactions were also observed in the chlorogold(I) complexes obtained from <b>1</b> and catecholatostiborane [Fe(η⁵-1-Ph₂(Cl₄C₆O₂)Sb-2-Cy₂PC₅H₃)(η⁵-C₅H₅)] as P-donors. As shown by experiments in Au-mediated cyclization of <i>N</i>-propargylbenzamide, the noncoordinated antimony group influenced the catalytic properties of the Au(I) complexes. Notably, an intramolecular Cl → Sb pnictogen bond affected the molecular geometry of the Pd(II) complex [PdCl₂(<b>1</b>-κ²<i>P</i>,<i>Sb</i>)], which in turn suggested that the structural influence exerted by ligands of this type needs to be assessed with care.