Boronic ferrocene-substituted

Naturally, it is possible to synthesise a similar ligand system without central chirality and in fact without the unnecessary methylene linker unit. A suitable synthesis starts with planar chiral ferrocenyl aldehyde acetal (see Figure 5.30). Hydrolysis and oxidation of the acetal yields the corresponding carboxylic acid that is transformed into the azide and subsequently turned into the respective primary amine functionalised planar chiral ferrocene. A rather complex reaction sequence involving 5-triazine, bromoacetal-dehyde diethylacetal and boron trifluoride etherate eventually yields the desired doubly ferrocenyl substituted imidazolium salt that can be deprotonated with the usual potassium tert-butylate to the free carbene. The ligand was used to form a variety of palladium(II) carbene complexes with pyridine or a phosphane as coligand. 

Many other electrophiles are able to react with metalated ferrocenylalkyl amines, e.g., trimethyl borate (Fig. 4-27 a), which gives, after hydrolytic workup, compounds like (S,S)-l-(iV,iV-dimethyl-l-aminoethyl)ferrocene-2-boronic acid [106]. Important intermediates for further derivatization are the halogens. For the lithiation technique, I2 (Fig. 4-27b) [151] and BrCN [106] lead to the desired compounds, but when BrCN is used, partial substitution of the dimethylamino group by cyanide occurs (see Sect. 4.3.3.2 and Fig. 4-17). For palladated amines, Brj is applicable [152]. (i ,S)-l-Iodo-2-(iV,iV-dimethyl-l-aminoethyl)ferrocene is the starting material for catalytically active zinc compounds for the enantioselective addition of zinc alkyls to carbonyl compounds [151] (see Chapter 3 for this topic). 

Metalation of sulfinylferrocene (338) to give the lithiated species, followed by transmetalation to give either the isolable boron analog (348) or the nonisolable zinc analog (349), is an approach used to access yet another class of ferrocene derivatives (equation 79)Palladium-catalyzed coupling of (348) or (349) with aryl iodides affords planar chiral aryl ferrocenes that are converted by standard transformations into planar chiral monophosphine aryl ferrocenes (350) that are also useful ligands in asymmetric catalysis. With appropriate ort/ o-substitution on the aryl ring, ferrocenes that possess axial chirality as well as planar chirality are prepared if the orfAo-substitutent is a second phosphine unit, access to a bisphosphine aryl ferrocene is achieved. ... 

As we will see, the choice of electron donors associated with porphyrins has not evolved much over the years. In previous review articles, electron donors such as carotenes, aryl amines, and ferrocene derivatives have been examined. Concerning the class of energy donors, over the past decade, boron dipyrylmethanes (BODIPY) are probably the most widely used series of compounds. A very detailed study of their association and their excitation energy transfer to porphyrins has been carried out by LindseyIt should be noted that condensed aromatics such as anthracene, and especially perylene derivatives, may be good substitutes for BODIPYs. 

The resonance between 55 and 56 (R = H, alkyl, aryl, ferrocenyl) in ferrocenyl-methyl cations including the diferrocenylmethyl cation has been used by Cais to explain the similar bending of the exocyclic C,C bonds toward the iron atom (Scheme 10.20) [65].Thefieldhas recently been reviewedbyGleiteref a/. [62],who included related isoelectronic boryl substituted systems. Wagner et al. [66] have prepared compounds of this type, and the authors proposed attractive interactions between the iron and boron atoms, because the C-B bonds are bent toward the iron atom. The analogy does not only apply to ferrocenes but also to isoelectronic (cyclobutadiene)(cyclopentadienyl)cobalt complexes and other related compounds [62]. 

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