Deep Green

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    Crystal structure of rac-(6R,1'R)-6-(1',2'-diacetoxyethyl)-2-phenyl-5,6-dihydro-4H-1,3-oxazine, (C6H5)C4H5NO[C2H3(OCOCH3)2]
    (2014) Peters, K.; Peters, E.-M.; Kugler, Rolf; Jäger, Volker
    C16H19NO5, triclinic, P‾1 (No. 2), a = 9.211(1) Å, b = 9.259(2) Å, c = 9.796(2) Å, α = 84.36(1)°, β = 85.26(1)°, γ = 69.21(1)°, V = 776.2 Å3, Ζ = 2, Rgt(F) = 0.069, Rw(F) = 0.069, Τ = 293 Κ.
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    ItemOpen Access
    The role of spacer length in macrocyclization reactions under confinement
    (2024) Nandeshwar, Muneshwar; Weisser, Kilian; Ziegler, Felix; Frey, Wolfgang; Buchmeiser, Michael R.
    We studied the influence of the distance of olefin metathesis catalysts from the inner surface of a mesoporous support on macrocyclization and Z‐selectivity under confinement. For these purposes, the cationic molybdenum imido alkylidene N‐heterocyclic carbene (NHC) catalysts [Mo(N‐(2‐tBu‐C6H4)(1‐mesityl‐3‐(3‐trimethoxysilylprop‐1‐yl)‐imidazol‐2‐ylidene)(CHCMe2Ph)(MeCN)Br+ B(ArF)4-] Mo2, [Mo(N‐(2‐tBu‐C6H4)(1‐mesityl‐3‐(3‐trimethoxysilylprop‐1‐yl)‐imidazol‐2‐ylidene)(CHCMe2Ph)(MeCN)OTf+ B(ArF)4-] Mo3, [Mo(N‐(2,6‐Me2‐C6H3)(1‐mesityl‐3‐(3‐trimethoxysilylprop‐1‐yl)‐imidazol‐2‐ylidene)(CHCMe2Ph)(MeCN)Br+ B(ArF)4-] Mo5, and [Mo(N‐(2,6‐iPr2‐C6H3)(1‐mesityl‐3‐(3‐trimethoxysilylprop‐1‐yl)‐imidazol‐2‐ylidene)(CHCMe2Ph)(MeCN)+Br B(ArF)4-] Mo7 (B(ArF)4 = tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate), all containing a trimethoxysilylpropyl tether, were selectively immobilized inside the mesopores of SBA‐15. Under confinement, both macro(mono)cyclization (MMC) and Z‐selectivity were higher than in solution but lower than with catalysts directly bound to the surface of the mesoporous supports. These findings are in agreement with existing theoretical models on substrate and product distribution in mesopores, which suggest that the highest substrate concentration is found at the pore wall and that it increases with decreasing pore diameter.
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    ItemOpen Access
    What makes a branched aromatic compound a crystallization chaperone? Insights from a comparison of three organic scaffolds
    (2025) Hartenfels, Jan; Berking, Tim; Rebelo, Ruben Pereira; Tsimopoulou, Katerina; Schiele, Stefanie; Stark, Leon; Frey, Wolfgang; Richert, Clemens
    Some tetraaryladamantane (TAA) octa‐ and tetraethers have the ability to crystallize into well‐ordered lattices without full desolvation. In many cases, the solvates then yield high‐resolution X‐ray crystal structures of the encapsulated liquids. To shed light on this unusual effect of TAAs as crystallization chaperones, we have synthesized a series of spirobiflourene and porphyrin derivatives with four phenyl arms also found in TAA chaperones. Despite the structural similarity, neither of the non‐TAA compounds showed promising crystallization properties. Six new X‐ray crystal structures were obtained, but neither gave a high‐resolution structure of an encapsulated guest. Quantum chemical computations suggest that conformational changes have low activation barriers for the TAAs, which may help to adapt to the structures of guest molecules in tightly packed arrangements. These findings on supramolecular chemistry in the crystalline state may help to design new chaperones with improved properties.