Tailoring the Fe → Pd interaction in cationic Pd(ii) complexes via structural variation of the ligand scaffold of sterically demanding dppf-analogs and their P,N-counterparts

Two 1,1'-azaphospha substituted dppf-analogues Fc'(NMe2)(PPh2) (Ph = C6H5, Fc' = 1,1'-ferrocenediyl, 3a) and Fc'(NMe2)(PMes(2)) (Mes = 2,4,6-Me3C6H2, 3b) have been prepared, via reductive amination, followed by salt-metathesis (of 2), starting from 1,1'-azabromoferrocene 1. Their donor properties have been explored using heteronuclear NMR spectroscopy based on their (1)(JP-Se) coupling, and the formation of PdCl2-complexes in comparison to a set of related dppf analogs with gradual steric variation, such as Fc' (PMes(2))(PPh2) (5) and Fc'(PMes(2))((PBu2)-Bu-t) (6). Chloride abstraction from these complexes, namely Fc'(PMes(2)) (PPh2)center dot PdCl2 (7), Fc'(PMes(2))((PBu2)-Bu-t)center dot PdCl2 (8), and [Fc'(NMe2)(PPh2)] 2 center dot PdCl2 (9) using AgSbF6 produced the corresponding cationic Pd(II) complexes [Fc'(PMes(2))((PBu2)-Bu-t)center dot PdCl][SbF6] (10), [Fc'(PPh2)(NMe2)center dot PdCl][SbF6] 2 (11) and [Fc'(PPh2)(NMe2)center dot Pd(PPh2C5H5)][SbF6] (2) (12) featuring Fe -> Pd interactions. Variation of the counter anion by coordination of 3a to a chloride-free Pd(II) source furnished [Fc'(PPh2)(NMe2)center dot Pd (PPh3)][BF4] (2) (13), [Fc'(PPh2)(NMe2)center dot Pd(PPh2)Fc'(NMe2)][BF4] (2) (14), and [Fc'(PPh2)(NMe2)center dot PdP( p-OMeC6H4)(3)][BF4] (2) (15) with similar Fe -> Pd interactions. Comparison with previously reported diphospha- and azaphospha- counterparts, revealed that 10 and 11 display the shortest and 15 the longest Fe-Pd bond, within their ligand scaffold congeners. DFT calculations performed on compounds 10-15 were further able to verify their intrinsic structural features and trends and shed light on the nature of the Fe double right arrow Pd bonding interactions which are furthermore consistent with CV measurements.

Automated summary

Two 1,1'-azaphospha substituted dppf-analogues Fc'(NMe2)(PPh2) and Fc'(NMe2)(PMes(2)) have been prepared via reductive amination and salt-metathesis reactions. Their donor properties have been explored using heteronuclear NMR spectroscopy, and they can form PdCl2-complexes. Comparison with related dppf analogs reveals the Fe-Pd bond lengths within their ligand scaffold congeners.