Synthesis, reactivity and coordination behaviour of a ferrocene phosphinostibine and intramolecular interactions in its P(v) and Sb(v) derivatives

Abstract

Compared to their P,N-analogues, compounds combining P and Sb substituents remain less common. This contribution describes the synthesis of a new ferrocene phosphinostibine, Cy₂PfcSbPh₂ (3; fc = ferrocene-1,1′-diyl, Cy = cyclohexyl), and its derivatives modified at the phosphine and stibine moieties, viz., Cy₂P(E)fcSbPh₂ (E = BH₃, O, S, AuCl), Cy₂P(E)fcSbCl₂Ph₂ (E = BH₃, S, AuCl) and stiboranes Cy₂P(E)fcSb(O₂C₆Cl₄)Ph₂ (E = void, BH₃, O, S and AuCl). The increased Lewis acidity of the Sb atom in the catecholatostiboranes Cy₂PfcSb(O₂C₆Cl₄)Ph₂ and Cy₂P(O)fcSb(O₂C₆Cl₄)Ph₂ resulted in intramolecular P → Sb and O → Sb dative interactions, which were not detected for the respective parent stibines or even in Cy₂P(S)fcSb(O₂C₆Cl₄)Ph₂. While the P → Sb interaction in Cy₂PfcSb(O₂C₆Cl₄)Ph₂ was stronger than that in the “all-phenyl” analogue Ph₂PfcSb(O₂C₆Cl₄)Ph₂ due to the electron-donating effect of the cyclohexyl groups, the bonding situations in Cy₂P(O)fcSb(O₂C₆Cl₄)Ph₂ and Ph₂P(O)fcSb(O₂C₆Cl₄)Ph₂, where the substituent effect was only indirect, remained very similar according to DFT calculations. A coordination study with 3 resulted in isolation of phosphine ([AuCl(3-κP)]), P,Sb-bridging ([(μ(P,Sb)-3)(AuCl)₂]), and P,Sb-chelate ([(arene)MCl(3-κ²P,Sb)]X, where (arene)M/X = (η⁶-p-cymene)Ru(II)/PF₆, (η⁵-C₅Me₅)Rh(III)/Cl, and (η⁵-C₅Me₅)Rh(III)/PF₆, and [MCl₂(3-κ²P,Sb)], where M = Pd and Pt) complexes. For some of these compounds, structure determination revealed structural distortions suggesting weak intramolecular Cl–Sb interactions, which were confirmed by theoretical methods.