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)] (1), 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 1 and catecholatostiborane [Fe(η5-1-Ph2(Cl4C6O2)Sb-2-Cy2PC5H3)(η5-C5H5)] as P-donors. As shown by experiments in Au-mediated
cyclization of N-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(1-κ2P,Sb)], which in turn suggested that the structural influence exerted
by ligands of this type needs to be assessed with care.