Beyond phosphorus: synthesis, reactivity, coordination behaviour and catalytic properties of 1,1'-bis(diphenylstibino)ferrocene.

Compared to their widely studied phosphine counterparts, ferrocene stibines have received only marginal attention thus far. This paper describes the synthesis of 1,1'-bis(diphenylstibino)ferrocene (1*), which is an antimony analogue of the ubiquitous dppf, and our investigations into the reactivity and coordination behaviour of this compound. Thus, distibine 1 was oxidised to stiboranes fc(SbPh 2 X 2 ) 2 (X = Cl, 2*; F, 6*; fc = ferrocene-1,1'-diyl) and to stibine-stiborane Ph 2 SbfcSbPh 2 F 2 (5*). Compounds 2 and 6 were easily hydrolysed to produce ferrocenophanes fc[SbPh 2 XOSbPh 2 X] (X = Cl, 3*; F, 7*). Removing the halogen from 3 with silver(I) salts afforded the corresponding ferrocenophanes with O-bound oxyanions, fc[SbPh 2 ZOSbPh 2 Z] (Z = NO 3 , 4a*; ClO 4 , 4b*), which were alternatively prepared from 2 and also converted back to 2 by adding a chloride source. Through investigations into the coordination behaviour of distibine 1, the following compounds were isolated and characterised: [(μ-ClO 4 ) 2 {Ag(1-κ 2 Sb , Sb ')} 2 ] (8*), [Ag(1-κ 2 Sb , Sb ') 2 ]X (X = ClO 4 , 9a; SbF 6 , 9b*), [(μ(Sb,Sb')-1){(arene)MCl 2 } 2 ] (10*, 11*) and [(arene)MCl(1-κ 2 Sb , Sb ')][PF 6 ] (12*, 13*; 10, 12: M/arene = Ru/η 6 - p -cymene, 11, 13; Rh/η 5 -C 5 Me 5 ), [(η 5 -C 5 Me 5 )RuCl(1-κ 2 Sb , Sb ')] (14), [MCl 2 (1-κ 2 Sb , Sb ')] (M = Pd, 15*; Pt, 16*), [Pd(1-κ 2 Sb , Sb ') 2 ]X 2 (X = BF 4 , 17a; SbF 6 , 17b*), [Pd(η 2 -ma)(1-κ 2 Sb , Sb ')] (18*; ma = maleic anhydride), [(μ(Sb,Sb')-1)(AuCl) 2 ] (19*), and [Au(1-κ 2 Sb , Sb ') 2 ]X (X = AuCl 2 , 20a*; SbF 6 , 20b*). Inspection of the structural parameters suggested that complexes featuring 1 exhibit less sterically strained structures than their dppf analogues due to longer M-Sb and Sb-C bonds, which reduce crowding around the ligated metal centre. Cyclic voltammetry and DFT calculations revealed that the primary electrochemical oxidation of 1 is reversible and occurs at the ferrocene unit. Based on preliminary catalytic tests in Suzuki-Miyaura biaryl coupling, Pd-1 complexes exhibited a lower efficiency than their respective Pd-dppf analogues. (An asterisk indicates that the crystal structure has been determined.).