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

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, Cy 2 PfcSbPh 2 ( 3 ; fc = ferrocene-1,1′-diyl, Cy = cyclohexyl), and its derivatives modified at the phosphine and stibine moieties, viz. , Cy 2 P(E)fcSbPh 2 (E = BH 3 , O, S, AuCl), Cy 2 P(E)fcSbCl 2 Ph 2 (E = BH 3 , S, AuCl) and stiboranes Cy 2 P(E)fcSb(O 2 C 6 Cl 4 )Ph 2 (E = void, BH 3 , O, S and AuCl). The increased Lewis acidity of the Sb atom in the catecholatostiboranes Cy 2 PfcSb(O 2 C 6 Cl 4 )Ph 2 and Cy 2 P(O)fcSb(O 2 C 6 Cl 4 )Ph 2 resulted in intramolecular P → Sb and O → Sb dative interactions, which were not detected for the respective parent stibines or even in Cy 2 P(S)fcSb(O 2 C 6 Cl 4 )Ph 2 . While the P → Sb interaction in Cy 2 PfcSb(O 2 C 6 Cl 4 )Ph 2 was stronger than that in the "all-phenyl" analogue Ph 2 PfcSb(O 2 C 6 Cl 4 )Ph 2 due to the electron-donating effect of the cyclohexyl groups, the bonding situations in Cy 2 P(O)fcSb(O 2 C 6 Cl 4 )Ph 2 and Ph 2 P(O)fcSb(O 2 C 6 Cl 4 )Ph 2 , 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 -κ 2 P,Sb)]X, where (arene)M/X = (η 6 - p -cymene)Ru( ii )/PF 6 , (η 5 -C 5 Me 5 )Rh( iii )/Cl, and (η 5 -C 5 Me 5 )Rh( iii )/PF 6 , and [MCl 2 ( 3 -κ 2 P,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. A ferrocene phosphinostibine equipped with different substituents at the P and Sb atoms coordinates as a typical hybrid ligand. Manipulation of the pnictogen substituents in its molecule results in intramolecular P → Sb donor-acceptor interactions.