Investigation of Rational Syntheses of Heteroleptic Porphyrinic Lanthanide (Europium, Cerium) Triple-Decker Sandwich Complexes

Abstract

The use of lanthanide triple-decker sandwich molecules containing porphyrins and phthalocyanines in molecular information storage applications requires the ability to attach monomeric triple deckers or arrays of triple deckers to electroactive surfaces. Such applications are limited by existing methods for preparing triple deckers. The reaction of a lanthanide porphyrin half-sandwich complex ((Por)M(acac)) with a dilithium phthalocyanine (PcLi2) in refluxing 1,2,4-trichlorobenzene (bp 214 degrees C) affords a mixture of triple deckers of composition (Pc)M(Pc)M(Por), (Por)M(Pc)M(Por), and (Pc)M(Por)M(Pc). We have investigated more directed methods for preparing triple deckers of a given type with distinct metals in each layer. Application of the method of Weiss, which employs reaction of a (Por)M(acac) species with a lanthanide double decker in refluxing 1,2,4-trichlorobenzene, afforded the desired triple decker in some cases but a mixture of triple deckers in others. The approach we developed employs in situ formation of the lanthanide reagent EuCl[N(SiMe3)2]2 or CeI[N(SiMe3)2]2, which upon reaction with a porphyrin affords the half-sandwich complex (Por)EuX or (Por)CeX' (X = Cl, N(SiMe3)2; X' = I, N(SiMe3)2). Subsequent reaction with PcLi2 gives the double decker (Por)M(Pc). The (Por(1))EuX half-sandwich complex gave the desired triple decker upon reaction with (Pc)Eu(Pc) but little of the desired product upon reaction with (Por(2))Eu(Pc). The (Por(1))CeX' half-sandwich complex reacted with europium double deckers (e.g., (tBPc)Eu(Por(2)), (tBPc)2Eu) to give the triple deckers (Por(1))Ce(tBPc)Eu(Por(2)) and (Por(1))Ce(tBPc)Eu(tBPc) in a rational manner (tB = tetra-tert-butyl). The reactions yielding the half-sandwich, double-decker, and triple-decker complexes were performed in refluxing bis(2-methoxyethyl) ether (bp 162 degrees C). The porphyrins incorporated in the various triple deckers include meso-tetrapentylporphyrin, meso-tetra-p-tolylporphyrin, octaethylporphyrin, and meso-tetraarylporphyrins bearing iodo, ethynyl, or iodo and ethynyl substituents. The triple deckers bearing iodo and/or ethynyl substituents constitute useful building blocks for information storage applications.

Sandwich complexes of naphthalocyanine with the rare earth metals

“…It is worth noting that the yield of these double-deckers decreases gradually with contraction in size of the central metal ion, for example from 69% for M = La to 35% for M = Er [14]. This is in line with the M(Por) 2 series [2,4], but in contrast with the trend observed for M(Pc) 2 [22]. It should be stressed that a number of papers on the unsubstituted bis(naphthalocyaninato) rare earth complexes have been published, but virtually all of them are confined to lutetium complexes [11][12][13] and the one dealing with Eu(Nc) 2 could not be corroborated due to the lack of synthesis, purification and characterization data [29].…”

“…Although naphthalocyanine-containing sandwich complexes have been known for some time, most studies have been limited to the homoleptic and heteroleptic naphthalocyanine-containing lutetium complexes [5][6][7][8][9][10][11][12][13]. Sandwich-type naphthalocyanine complexes of rare earth metals other than lutetium have appeared only recently [14][15][16][17][18][19][20][21][22][23][24][25][26][27].…”

Multistate molecular information storage using S-acetylthio-derivatized dyads of triple-decker sandwich coordination compounds

“…(1) the synthesis of type-c triple deckers proceeds in good yield by reaction of a europium phthalocyanine double-decker complex with a europium porphyrin half-sandwich complex [27,29]; and (2) synthetic handles in the triple deckers (for attachment to the tether as well as for joining to other triple deckers) can be more easily introduced via a suitably functionalized porphyrin rather than with a phthalocyanine, given the state of the art of synthetic methodology in the two classes of compounds. The intact triple-decker bulding blocks bearing synthetic handles on the porphyrins can be joined to give covalent arrays of two or more triple decker monomers following established methods [17,18].…”

“…One approach to realize this objective is to utilize two different triple deckers with well resolved, interleaved redox potentials. Toward this goal, we prepared a library of > 30 triple-decker sandwich complexes to elucidate how different combinations of porphyrin and phthalocyanine macrocycles, substituents at the perimeter of the macrocycles, and lanthanides (Eu, Ce) between the macrocycles influence the redox potentials of the complexes in solution [15,16,18,27]. Another set of 14 triple deckers bearing tethers was prepared for attachment to electroactive surfaces [6,7,[15][16][17][18].…”

Dibenzotetraazamacroheterocycles: Synthesis and properties. (Review)

“…Such an approach is currently being pursued in the above-mentioned work by Chinese investigators and also in [147][148][149][150][151][152][153] and other papers.…”