Shahid Namrah, Burrows Kay E, Pask Christopher M, Cespedes Oscar, Howard Mark J, McGowan Patrick C, Halcrow Malcolm A
School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, UK LS2 9JT.
School of Physics and Astronomy, University of Leeds, WH Bragg Building, Leeds, UK LS2 9JT.
Dalton Trans. 2022 Mar 15;51(11):4262-4274. doi: 10.1039/d2dt00393g.
Complexation of Fe[ClO]·6HO by 1 equiv. 2,6-bis((4)-4-phenyl-4,5-dihydrooxazol-2-yl)pyridine (()-LPh) and 2,6-bis((4)-4-phenyl-4,5-dihydrothiazol-2-yl)pyridine (()-LPh) cleanly affords [Fe(()-LPh)(()-LPh)][ClO]; [Fe(()-LiPr)(()-LiPr)][ClO] (LiPr = 2,6-bis(4-isopropyl-4,5-dihydrooxazol-2-yl)pyridine; LiPr = 2,6-bis(4-isopropyl-4,5-dihydrothiazol-2-yl)pyridine) was prepared by a similar route. The compounds exhibit thermal spin-crossover in solution, at temperatures midway between the corresponding [Fe(()-LR)(()-LR)][ClO] and [Fe(()-LR)(()-LR)][ClO] (R = Ph or iPr) species. The spin states of [Fe(LR)(bimpy)][ClO] and [Fe(LR)(bpp)][ClO] (LR = LR or LR; bimpy = 2,6-bis(1-benzimidazol-2-yl)pyridine; bpp = 2,6-di(pyrazol-1-yl)pyridine) are also reported, with most examples exhibiting gradual spin-crossover in solution and the solid state. Although some products undergo partial ligand exchange in solution by H NMR, their solution values appear unaffected by this and correlate well with their spin state energies from gas phase DFT calculations. The high-spin state of [Fe(LR)(bpp)] is more stabilised than expected, compared to the other [Fe(LR)L] complexes studied (L = bimpy, bpp or terpy). That is explained by an interplay between the relative σ-basicities and π-acidities of the two ligands in each molecule. The steric influence of their phenyl or isopropyl 'R' substituents stabilises the heteroleptic complexes by up to 5 kcal mol, compared to analogues lacking these groups.
1当量的2,6-双（（4）-4-苯基-4,5-二氢恶唑-2-基）吡啶（（）-LPh）和2,6-双（（4）-4-苯基-4,5-二氢噻唑-2-基）吡啶（（）-LPh）与Fe[ClO]·6H₂O络合，可直接得到[Fe（（）-LPh）（（）-LPh）][ClO]；[Fe（（）-LiPr）（（）-LiPr）][ClO]（LiPr = 2,6-双（4-异丙基-4,5-二氢恶唑-2-基）吡啶；LiPr = 2,6-双（4-异丙基-4,5-二氢噻唑-2-基）吡啶）通过类似的路线制备。这些化合物在溶液中表现出热自旋交叉现象，温度介于相应的[Fe（（）-LR）（（）-LR）][ClO]和[Fe（（）-LR）（（）-LR）][ClO]（R = Ph或iPr）物种之间。还报道了[Fe（LR）（bimpy）][ClO]和[Fe（LR）（bpp）][ClO]（LR = LR或LR；bimpy = 2,6-双（1-苯并咪唑-2-基）吡啶；bpp = 2,6-二（吡唑-1-基）吡啶）的自旋态，大多数例子在溶液和固态中表现出逐渐的自旋交叉。尽管一些产物在溶液中通过¹H NMR发生部分配体交换，但其溶液值似乎不受此影响，并且与气相DFT计算得到的自旋态能量有很好的相关性。与所研究的其他[Fe（LR）L]配合物（L = bimpy、bpp或terpy）相比，[Fe（LR）（bpp）]的高自旋态比预期更稳定。这可以通过每个分子中两个配体的相对σ-碱性和π-酸性之间的相互作用来解释。与缺乏这些基团的类似物相比，它们的苯基或异丙基“R”取代基的空间影响使杂配体配合物稳定高达5千卡/摩尔。
