Dendrimer ferrocenyl ligands

The research group of Van Leeuwen has focused on catalysis at the core of a carbosilane dendrimer in an effort to be able to control stereoselectivity [10]. To this end, a ferrocenyl diphosphine backbone was functionalized with different generations of carbosilane dendrons producing a series of dendrimer phosphine ligands with an increasing steric demand (see 7 for an example, Scheme 6). In situ... 

Togni et al.169 synthesized dendrimers using a cyclophosphazene core and 16 peripheral chiral ferrocenyl ligands (Figure 10.13). The periphery of these ferrocenyldiphosphine metallo-dendrimers was decorated with [Rh(COD)2][BF4] to instill the desired catalytic properties necessary to reduce dimethyl itaconate. These metalloconstructs showed 98% ee, which compared well with the 99% ee obtained with monomeric Rh-based josiphos catalyst. 

Recently Togni et al. [19] focussed on the preparation of asymmetric dendrimer catalysts derived from ferrocenyl diphosphine ligands anchored to dendritic backbones constructed from benzene-1,3,5-tricarboxylic acid trichloride and adamantane-l,3,5,7-tetracarboxylic acid tetrachloride (e.g. 11, Scheme 11). In situ catalyst preparation by treatment of the dendritic ligands with [Rh(COD)2]BF4 afforded the cationic Rh-dendrimer, which was then used as a homogeneous catalyst in the hydrogenation reaction of, for example, dimethyl itaconate in MeOH. In all cases the measured enantioselectivity (98.0-98.7%) was nearly the same as observed for the ferrocenyl diphosphine (Josiphos) model compound (see Scheme 11). 

When the catalyst is located in the core of a dendrimer, its stability can also be increased by site-isolation effects. Core-functionalized dendritic catalysts supported on a carbosilane backbone were reported by Oosterom et al. 19). A novel route was developed to synthesize dendritic wedges with arylbromide as the focal point. These wedges were divergently coupled to a ferrocenyl diphosphine core to form dppf-like ligands (5). Other core-functionalized phosphine dendritic ligands have also been prepared by the same strategy 20). 

Ferrocenyl diphosphine core-functionalized carbosilane dendrimers have been prepared as ligands for homogeneous catalytic reactions applied in a CFMR by Van Leeuwen et al. [20,21,67,68]. The syntheses of these dppf-like ligands (Go-G2)-17 were performed using carbosilane dendritic wedges with an aryl bromide as focal point. These wedges were coupled to the core via quenching of the lithiated species with ferrocenyl phosphonites (Scheme 11). 

Figure 5. Structures of some functional dendrimers A. Dendrimer with lanthanide ion as the central core with dendrons as ligands B. Dendrimer based on metal complex C. Silicon-based ferrocenyl dendrimer and D. Dendrimer with zinc-porphyrin core...

Electrodes modified by ferrocenyl polymers have been known for a long time.54,61,62 More recently, the Madrid group has extensively studied the derivatization of silylferrocenyl dendrimers.63 Nishihara s group has reported the first example of modified electrodes with AuNPs containing ferrocenyl thiol ligands, in which the stabilization of the modified electrodes is... 

Complexes of different dendrimers with rhodium that contained ferrocenyl phosphine ligands on the surface, 52-53, were also active in hydrogenation. They catalyzed dimethylacetone hydrogenation at an optical selectivity of 98%, which is comparable to the selectivity of a low molecular weight analogue [113, 123, 124]. 

It is also possible to design mixed inorganic-organometallic systems by appropriate decoration of such clusters, as in the case of MogBri4 " below. The 6 apical Br ligands can be substituted by triflates, then by functional pyridines to synthesize dicationic cluster-cored ferrocenyl dendrimers ... 

Dendrimers Containing Triazole Ligands and Ferrocenyl Termini as Useful Templates for Transition-Metal Ions and Transition-Metal Nanoparticles... 

Scheme 8.10 Coordination of the triazole ligand by Pd(OAc>2 monitored by ferrocenyl redox sensing followed by Pd(II) reduction to dendrimer-encapsulated Pd (0) nanoparticles used further in catalysis. The variety of nanoparticle sizes obtained with this strategy is ciudal for catalyst optimization and mechanistic investigation...

Routaboul L, Vincendeau S, Turrin C-O, Caminade A-M, Majoral J-P, Daran J-C, Manoury E (2007) New phosphorus dendrimers with chiral ferrocenyl phosphine-thioether ligands on the periphery for asymmetric catalysis. J Organomet Chem 692 1064—1073... 

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