DPPF ligand

The structure of [Ir(cod)(dppf)]PF6 shows approximately square-planar geometry at Ir, and the cp rings of the dppf ligand are close to parallel and staggered.592 The systems [Ir(cod)(LL)]C104, where LL = dppf, l-diphenylphosphino-2-(7V,7V-dimethylamino)methyl ferrocene and 1,6-diferrocene-2,5-diazahexane, catalytically trimerize PC=CH to 1,3,5-triphenylbenzene.593 The electrochemistry of [Ir(dppf)2]BPh4 shows two one-electron reductions at —1.560 V and -1.755 V vs. ferrocenium/ ferrocene.753... 

Phosphine ligands based on the ferrocene backbone are very efficient in many palladium-catalyzed reactions, e.g., cross-coupling reactions,248 Heck reaction,249 amination reaction,250 and enantioselective synthesis.251 A particularly interesting example of an unusual coordination mode of the l,l -bis(diphenylphosphino)ferrocene (dppf) ligand has been reported. Dicationic palladium(II) complexes, such as [(dppf)Pd(PPh3)]2+[BF4 ]2, were shown to contain a palladium-iron bond.252,253 Palladium-iron bonds occur also in monocationic methyl and acylpalladium(II) complexes.254 A palladium-iron interaction is favored by bulky alkyl substituents on phosphorus and a lower electron density at palladium. 

PdCl2(dppf) was prepared acxxwding to the published procedure from PdCl2(NCPh)2 and dppf ligand purchased from Aldrich Chemical Company, Inc. The commercially available PdCl2(dppf) catalyst was also used, but the freshly prepared catalyst proved superior. 

The luminescence behavior of a binuclear gold(I) alkynyl complex with a bridging dppf ligand, [(dppf)Au2 C=CC(Me)=CH2)2], was also reported... 

Dppf is commonly seen in its chelating or bridging state. Of special interest is the quasi-closed bridging system of dppf complexes, Re2(/r-OMe)2(CO)6(/r-dppf) [33] and Rh2(yU-S-tBu)2(CO)2(/r-dppf), 2 [34], in which the sterically demanding dppf ligand coexists with two bridging ligands of much smaller size. Comparison of the... 

Fig. 1-22. Rocking motion of the dppf ligand with respect to the Re. ..Re axis in Re2( -OMe)2(CO)6(/i-dppf) (adapted from [74]).

One major advantage offered by the dppf ligand in Rh-catalyzed olefin hydroformylation is exemplified in its higher linear aldehyde selectivity when present in a dppf Rh ratio of 1.5 or higher [37,242]. This result leads to the proposed key intermediate of a Rh dimer with both chelating and bridging phosphine in the catalytic cycle. It also confirms the significance of the tris (phosphine) moieties at the point when the aldehyde selectivity is determined, i.e., the step in which the hydride is inserted into the M-olefin bond. This involvement of a dinuclear or tris (phosphine) intermediate appears to differ from the intermediate RhH(CO)(PR 3)z (olefin) (which is converted into the square planar Rh(R)(CO)(PR 3)2 by hydride insertion) commonly accepted for hydroformylation catalyzed by monophosphine complexes. P NMR studies also established the existence of the equilibrium in which the disphosphine can be... 

The electrochemistry of ferrocene-type ligands and their complexes is reviewed in detail by Zanello in Chapter 7. Hence the present description discusses only briefly some unique features of dppf complexes. These complexes are generally expected to exhibit a ferrocene-centered oxidation process. The general interest lies in the modification of the redox potential of the ferrocene/ferrocenium couple on phos-phination of the Cp rings, complexation of the resultant dppf ligand, and variations among the various known coordination modes of the ligand. 

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