Monodentate phosphine substitution in [Pd(κ³-dppf)(PR₃)][BF₄]₂(dppf = 1,1′-bis(diphenylphosphino)ferrocene) compounds

Abstract

The ligand 1,1'-bis(diphenylphosphino)ferrocene (dppf) is commonly employed in a variety of catalytic systems. There are a variety of coordination modes known for dppf, the least studied being the κ coordination mode, in which both phosphorus atoms and the iron atom of dppf interact with another metal center. One such compound is the previously reported [Pd(κ-dppf)(PPh)]. A series of related compounds, [Pd(κ-dppf)(P(p-CHR))] (R = OCH, CH, F and CF), has been synthesized and characterized. The X-ray crystal structure of [Pd(dppf)(P(p-CHF))][BF] was determined. Electrochemical and computational studies indicate that the electron donor ability of the P(p-CHR) ligands influences the properties of these compounds. Substitution reactions of the P(p-CHR) ligands have been examined, and, in general, the more electron donating P(p-CHR) ligands completely replace the less electron donating ones. The kinetics of the reaction of [Pd(κ-dppf)(P(p-CHF))] with P(p-CHOCH) indicate that the reaction proceeds through a dissociative mechanism, contrary to the associative substitutions prevalent in square planar palladium(ii) chemistry.

Beyond Common Metal–Metal Bonds, κ3‐Bis(donor)ferrocenyl→Transition‐Metal Interactions

“…The decrease in anisotropy of the ferrocenyl moiety in [ 7 ] 2+ and the red shift in the UV/Vis was due to the weakening of the Fe→Pd bond . A similar study was done on [Pd(dppf)(P( p ‐C 6 H 4 R′) 3 )] 2+ (R=‐CF 3 [ 7 d] 2+ , ‐F [ 7 e] 2+ , ‐CH 3 [ 7 f] 2+ , and ‐OCH 3 [ 7 g] 2+ ) (Scheme ) where the ligands have the same cone angle but different electronic parameters . The acceptor ligand had a shorter d Fe−Pd =2.98 Å in [ 7 d] 2+ , while the donor lengthened the d Fe−Pd =3.04 Å in [ 7 e] 2+ .…”

“…The influence of the ligand trans to the Fe→Pd bond in [ 7 a,d–g] 2+ was further studied by means of CV measurements and DFT calculations (Scheme ) . The weakly donating PR 3 ligands were readily substituted by stronger donating PR ′ 3 ligands.…”

“…This ligation of MeCN breaks the Fe→Pd bond and PR 3 substitution did not occur (Scheme ). The stability of the 14 VE intermediate proposed in the dissociative mechanism was due to how the κ 3 ‐bis(donor)ferrocenyl ligand‐binding mode buries the Pd center in the Fc pocket provided by the dppf ligand (Scheme ) …”

“…The redox process of the Fe(II/III) follows a similar anodic shift based on the donor/acceptor ability of the phosphine ligand. The potentials at which redox of the complexes [ 7 a,d–g] 2+ occurred was sensitive to the electronic character of the P( p ‐C 6 H 4 R) 3 ligand, showing that the P( p ‐C 6 H 4 R) 3 ligand had a significant impact on the electronic character of the Fe−Pd interaction …”

“…[21] As imilar study wasd one on [Pd(dppf)(P(p-C 6 H 4 R') 3 3 [7f] 2 + , and -OCH 3 [7g] 2 + )( Scheme 6) where the ligands have the same cone angle but different electronic parameters. [22] The acceptor ligand had as horter d FeÀPd = 2.98 in [7d] 2 + ,w hile the donor lengthened the d FeÀPd = 3.04 in [7e] 2 + .…”