Synthesis of C-substituted t-BuNH-8,9-R,R′-nido-7,8,9-C3B8H9 (R,R′ = H,H; MeH; Me,Me; Ph,H and Ph,Ph) tricarbollide compounds and their tautomeric conversions. Effect of substituents on tautomeric equilibria between neutral and zwitterionic forms
作者:Mario Bakardjiev、Josef Holub、Bohumil Štíbr、Ivana Císařová
DOI:10.1039/b924754h
日期:——
Treatment of C-substituted nido dicarbadecaboranes 5,6-Râ²,R-5,6-C2B8H10 (1) (where Râ²,R = H,H (1a); H,Me, (1b); Me,Me, (1c); H,Ph, (1d) and Ph,Ph, (1e) with 1,8-bis-(dimethylamino)naphthalene (proton sponge = PS) and t-BuNC in CH2Cl2, followed by acidification, generated a series of pure neutral compounds 7-t-BuNH-8,9-R,Râ²-nido-7,8,9-C3B8H9 (N2) (where R,Râ² = H,H (N2a); H,Me (N2b); Me,Me (N2c); H,Ph (N2d), and Ph,Ph (N2e)), each of which exhibits tautomerism. Dissolution of the substituted compounds (N2bâN2e) in protic solvents (PRS), such as MeCN and Me2CO, leads to tautomeric equilibrium with the zwitterionic tautomers 7-t-BuNH2-8,9-R,Râ²-nido-7,8,9-C3B8H8 (Z2) (where R,Râ²= H,H (Z2a); H,Me (Z2b); Me,Me (Z2c); H,Ph (Z2d) and Ph,Ph (Z2e)), while the unsubstituted compound N2a exhibits absolute tautomerism â a complete conversion into the zwitterionic tautomer Z2a. The tautomeric behaviour of individual compounds is therefore strongly affected by the nature of the substituent, as assessed via NMR spectroscopy in terms of tautomerisation constants KT = CZ2/CN2 (where CZ2 and CN2 are equilibrium concentrations of Z2 and N2 forms in a given solvent). Individual tautomers were characterised by 11B and 1H NMR spectroscopy and the structure of the monomethylated N2b tautomer was determined by an X-ray diffraction study.
用 1,8-双(二甲基氨基)萘(质子海绵=PS)和 t-BuNC 在 CH2 中处理 5,6-Râ²,R-5,6-C2B8H10 (1)(其中 Râ²,R=H,H (1a);H,Me, (1b);Me,Me, (1c);H,Ph, (1d) 和 Ph,Ph, (1e) 与 1,8-双(二甲基氨基)萘(质子海绵 = PS)和 t-BuNC 在 CH2Cl2 中反应,然后酸化,生成一系列纯中性化合物 7-t-BuNH-8,9-R,Râ²-nido-7,8,9-C3B8H9 (N2)(其中 R,Râ² = H,H (N2a);H,Me(N2b);Me,Me(N2c);H,Ph(N2d)和 Ph,Ph(N2e)),其中每种化合物都具有同分异构现象。将取代化合物(N2bâN2e)溶解于 MeCN 和 Me2CO 等质子溶剂(PRS)中,会导致同分异构体 7-t-BuNH2-8,9-R,Râ²-nido-7,8,9-C3B8H8 (Z2) (其中 R,Râ²= H,H (Z2a);H,Me(Z2b);Me,Me(Z2c);H,Ph(Z2d)和 Ph,Ph(Z2e)),而未取代的化合物 N2a 则表现出绝对的同分异构--完全转化成齐聚物同分异构体 Z2a。因此,单个化合物的同分异构行为受取代基性质的影响很大,这可以通过核磁共振光谱评估同分异构常数 KT = CZ2/CN2(其中 CZ2 和 CN2 是 Z2 和 N2 在给定溶剂中的平衡浓度)。通过 11B 和 1H NMR 光谱对单个同分异构体进行了表征,并通过 X 射线衍射研究确定了单甲基化 N2b 同分异构体的结构。