Synthesis and catalytic properties of palladium(II) complexes with P,π-chelating ferrocene phosphinoallyl ligands and their non-tethered analogues.

Hybrid phosphines usually combine a phosphine moiety with another heteroatom secondary donor group in their structures while compounds equipped with hydrocarbyl π-donor moieties remain uncommon. This contribution reports the synthesis and structural characterization of the first P/π-allyl-chelating complexes that were obtained using the structurally flexible and redox-active ferrocene unit as the scaffold, viz. [PdCl(R2PfcCHCHCH2-η3:κP)] (1R; R = Ph and cyclohexyl (Cy); fc = ferrocene-1,1'-diyl). These compounds were synthesized from the respective phosphinoferrocene carboxaldehydes R2PfcCHO via reaction with vinylmagnesium bromide to generate 1-(phosphinoferrocenyl)allyl alcohols, which were subsequently acetylated. The resulting allyl acetates reacted smoothly with [Pd2(dba)3]/[Et3NH]Cl (dba = dibenzylideneacetone) to produce the target compounds. Complexes 1R and their nontethered analogues [PdCl(η3-C3H5)(FcPR2-κP)] (5R; Fc = ferrocenyl) were evaluated as pre-catalysts for the Pd-catalysed allylic amination of cinnamyl acetate with aliphatic amines and Suzuki-Miyaura-type cross-coupling of 4-tolylboronic acid with benzoyl chloride. In these reactions, better results were achieved with compounds 5R (particularly with 5Ph), presumably because they form more stable LPd(0)-type catalysts.

Synthesis, Structure, Reactivity, and Intramolecular Donor-Acceptor Interactions in a Phosphinoferrocene Stibine and Its Corresponding Phosphine Chalcogenides and Stiboranes.

Ferrocene-based phosphines equipped with additional functional groups are versatile ligands for coordination chemistry and catalysis. This contribution describes a new compound of this type, combining phosphine and stibine groups at the ferrocene backbone, viz. 1-(diphenylphosphino)-1'-(diphenylstibino)ferrocene (1). Phosphinostibine 1 and the corresponding P-chalcogenide derivatives Ph2P(E)fcSbPh2 (1E, fc = ferrocene-1,1'-diyl, E = O, S, Se) were synthesized and further converted to the corresponding stiboranes Ph2P(E)fcSb(O2C6Cl4)Ph2 (6 and 6E) by oxidation with o-chloranil. All compounds were characterized by spectroscopic methods, X-ray diffraction analysis, cyclic voltammetry, and theoretical methods. Both NMR spectroscopy and DFT calculations confirmed the presence of P → Sb and P═O → Sb donor-acceptor interactions in 6 and 6O, triggered by the oxidation of the stibine moiety into Lewis acidic stiborane. The corresponding interactions in 6S and 6Se were of the same type but significantly weaker. A coordination study with AuCl as the model metal fragment revealed that the phosphine group acts as the "primary" coordination site, in line with its higher basicity. The obtained Au(I) complexes were applied as catalysts in the Au-catalyzed cyclization of N-propargylbenzamide and in the oxidative [2 + 2 + 1] cyclization of ethynylbenzene with acetonitrile and pyridine N-oxides. The catalytic results showed that the stibine complexes had worse catalytic performance than their phosphine counterparts, most likely due to the formation of weaker coordination bonds and hence poorer stabilization of the active metal species. Nevertheless, the stibine moiety could be used to fine-tune the properties of the ligated metal center by changing the oxidation state or substituents at the "remote" Sb atom.

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(SbPh2X2)2 (X = Cl, 2*; F, 6*; fc = ferrocene-1,1'-diyl) and to stibine-stiborane Ph2SbfcSbPh2F2 (5*). Compounds 2 and 6 were easily hydrolysed to produce ferrocenophanes fc[SbPh2XOSbPh2X] (X = Cl, 3*; F, 7*). Removing the halogen from 3 with silver(I) salts afforded the corresponding ferrocenophanes with O-bound oxyanions, fc[SbPh2ZOSbPh2Z] (Z = NO3, 4a*; ClO4, 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-ClO4)2{Ag(1-κ2Sb,Sb')}2] (8*), [Ag(1-κ2Sb,Sb')2]X (X = ClO4, 9a; SbF6, 9b*), [(µ(Sb,Sb')-1){(arene)MCl2}2] (10*, 11*) and [(arene)MCl(1-κ2Sb,Sb')][PF6] (12*, 13*; 10, 12: M/arene = Ru/η6-p-cymene, 11, 13; Rh/η5-C5Me5), [(η5-C5Me5)RuCl(1-κ2Sb,Sb')] (14), [MCl2(1-κ2Sb,Sb')] (M = Pd, 15*; Pt, 16*), [Pd(1-κ2Sb,Sb')2]X2 (X = BF4, 17a; SbF6, 17b*), [Pd(η2-ma)(1-κ2Sb,Sb')] (18*; ma = maleic anhydride), [(µ(Sb,Sb')-1)(AuCl)2] (19*), and [Au(1-κ2Sb,Sb')2]X (X = AuCl2, 20a*; SbF6, 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.).