Spin crossover complex [](ClO4)2·H2O (L1 = 4-methyl-2,6-bis(1H-pyrazol-1-yl)pyrimidine): Synthesis and properties

Recent advances in the synthesis and applications of 2,6-dipyrazolylpyridine derivatives and their complexes

“…That has allowed lanthanide complexes of the podands L 20 -L 22 to find use in bioanalytical chemistry and fluorescent materials. Lanthanide complexes of bpp derivatives can be more emissive that their 25 terpy counterparts, reflecting an improved match between the forbital energies and the bpp -acceptor levels. 6 The importance of [Fe(bpp) 2 ] 2+ derivatives in spin-crossover research also reflects the balance of heterocyclic donor groups in the bpp framework.…”

“…A number of 1-bpp derivatives bearing simple alkyl or aryl 20 substituents have been prepared in this way, 6,7,[14][15][16][17] including chiral derivatives produced using optically pure pyrazole reagents. 6 An exception to this generalisation is where indazole reagents are used, when eq 1 yields the more hindered 2,6-di(indazol-1-yl)pyridine products (1-bip, Scheme 1) in moderate 25 yield. 18,19 That reflects the usual reactivity pattern for deprotonated indazoles, which prefer electrophilic attack at N1.…”

“…24 The methods in eq 1 and eq 3 have also been used to prepare 1-bppym derivatives (Scheme 1), starting from the appropriate 2,6-dihaloor 2,6-di(hydrazino)-pyrimidine. 25,26 Chemical modification of 1-bpp itself can be achieved by 50 halogenation (Scheme 3). Mild electrophilic chlorination, bromination or iodination reagents lead to selective dihalogenation at the pyrazole C4 positions.…”

“…7,[33][34][35][36][37][38][39][40][41][42][43][44][45][46] Recently, however, 4-bromo-2,6-difluoropyridine has been identified as an alternative starting material for 4-substituted 1-bpp derivatives. The fluoro groups of this precursor are selectively displaced in eq 1 (X = F, Y = Br), 25 yielding a 4-bromo-1-bpp product that can be further modified by Sonogashira cross-coupling or substitution reactions.…”

“…However, other classes of tris-heterocycle such as 2,6-di(benzimidazol-2-20 yl)pyridines 3,5 and the 2,6-di(pyrazolyl)pyridines [6][7][8] have certain advantages over the terpyridines for some applications and are also well-studied in their own right. The coordination chemistry of 2,6-di(pyrazol-1-yl)pyridine (1-bpp) and 2,6-di(pyrazol-3-yl)pyridine (3-bpp, Scheme 1) was first developed in two 25 particular areas: their iron(II) complexes which can show unusual, and useful, spin-crossover switching properties; and, a class of podands based on the 1-bpp skeleton which form strongly emissive lanthanide complexes. 6 While those areas have continued to expand, more recently the use of bpp derivatives in 30 other areas of research has also been explored, including catalysis, solar cell photosensitisation and soft materials.…”