Alkylation of nitrogen heterocycles with 1,3-bis(hydroxymethyl)ferrocene. Generation of the ferrocene dicarbocation [{1,3-(CH2)2C5H3}Fe(C5H5)]2+

Abstract

The alkylation of imidazole and 5 benzyloxycarbonyl 3,4 diethylpyrrole with 1,3 bis (hydroxymethyl)ferrocene (1) afforded bis imidazole (4) and bis pyrrole (7) derivatives of ferrocene, respectively. The reaction of diol 1 with trifluoroacetic acid gave the dicarbocationic complex [{1,3 (CH 2 ) 2 C 5 H 3 }Fe(C 5 H 5 )] 2+ (2) characterized by 1 H NMR spectroscopy.Previously, 1 we have reported on the phosphorylation of 1,3 bis(hydroxymethyl)ferrocene (1) giving ferrocene diphosphines {1,3 (R 2 PCH 2 ) 2 C 5 H 3 }Fe(C 5 H 5 ) (R = Pr i , Bu t ). The latter were used as the starting compounds for the synthesis of P,C,P pincer complexes with the ferrocene backbone. Rhodium, 1 palladium, 2,3 iridium, 4 and ruthe nium 5 bis(phosphine) pincer complexes with the ferrocene or ruthenocene backbone are presently known. These com plexes have attracted interest due to their ability to acti vate small molecules and hydrocarbon substrates and cat alyze a variety of reactions, among which of great impor tance is the homogeneous dehydrogenation. Recently, 4 it has been shown that the iridium complex IrH 2 [{2,5 (Bu t 2 CH 2 ) 2 C 5 H 2 }Fe(C 5 H 5 )] is the most active catalyst for alkane dehydrogenation among all known homogeneous systems.The chemistry of metallocene based pincer complexes is in its infancy. In the future, it is necessary to use in a greater extent the potential of these systems conditioned by the sandwich geometry of metallocenes and the ability to vary the metallocene central atom and its oxidation state in the case of the iron atom in ferrocene. It would expect that pincer complexes having the metallocene back bone would be used for the creation of new generation polymetallic catalysts and materials having useful photo physical and sensor properties. The progress in this area is related to the development of convenient methods for the synthesis of functionalized 1,3 disubstituted metal locenes, 3-9 which are nowadays much more difficult to synthesize compared to 1,1´ and 1,2 disubstituted ana logs. It is also necessary to design pincer ligands contain ing donor atoms other than phosphorus, for example, car bon atoms of N heterocyclic carbenes and nitrogen atoms of N heterocycles.In the present study, we describe the first results on the synthesis of precursors of new types of pincer ligands based on ferrocene. The alkylation of imidazole and substituted pyrrole with diol 1 afforded the diimidazole and dipyrrole derivatives of ferrocene, respectively. Results and DiscussionThe ferrocenylmethylation can be performed with the use of ferrocenylmethyl halides (rather unstable com pounds), ferrocenylcarbinols, or ferrocenylmethylammo nium salts. 10 These reactions proceed through the forma tion of α ferrocenyl carbocations, whose enhanced stabil ity is well known. 11 The ferrocene carbocations were char acterized by 1 H, 13 C, and 57 Fe NMR spectroscopy. The most stable of them, as well as their ruthenium and osmi um analogs, were isolated as crystalline salts and were studied by X ray diffraction. 11,12 Unlike fe...

Rhodium and iridium complexes of a new ferrocene-derived chelating bis(NHC) ligand

“…The most common method for the synthesis of 1,2-disubstituted ferrocenes is a stepwise introduction of substituents, mainly by the application of a selective ortho-metallation procedure. However in the present work, the synthesis of 1,2-disubstituted ferrocenes was accomplished according to Scheme 1, similar to the preparation of 1,3-disubstituted derivatives we described earlier, 10 which was based on the application of the substituted fulvenes. 15 Compound 3 was prepared by the photochemical reaction of the cationic iron naphthalene complex 1 16 with fulvene 2.…”

“…Crystals of 8a (C 28 H 34 N 4 FeRh•BF 4 •CHCl 3 , M = 791.53) are monoclinic, space group P2 1 /c, at 100 K a = 13.3083 (10), b = 17.0735 (13), c = 14.1248(11) Å, β = 90.194(2)°, V = 3209.4(4) Å 3 , Z = 4, d calc. = 1.638 g cm −3 , μ = 1.266 mm −1 .…”

“…Recently we have reported the synthesis of [(1,3-ferrocenylene)bis(methylene)]bis(1-methylimidazolium) diiodide. 10 It turned out, however, that metallation of this compound to form C,C,C pincer-type complexes is not an easy task. In this connection, we may note that Braunstein and co-workers 11 observed only the formation of non-pincer mono-and dinuclear Rh and Ir complexes under a wide variety of reaction conditions, when the central arene fragment was connected to two NHC moieties through CH 2 spacers.…”