RADICAL CAGE EFFECTS IN ADOCOBINAMIDE (AXIAL-BASE-OFF COENZYME-B12) - A SIMPLE METHOD FOR TRAPPING [ADO..COII] RADICAL PAIRS, A NEW BETA-H ELIMINATION PRODUCT FROM THE RADICAL PAIR AND MEASUREMENT OF AN UNPRECEDENTEDLY LARGE CAGE-RECOMBINATION EFFICIENCY FACTOR, F(C) GREATER-THAN-OR-EQUAL-TO 0.94
RADICAL CAGE EFFECTS IN ADOCOBINAMIDE (AXIAL-BASE-OFF COENZYME-B12) - A SIMPLE METHOD FOR TRAPPING [ADO..COII] RADICAL PAIRS, A NEW BETA-H ELIMINATION PRODUCT FROM THE RADICAL PAIR AND MEASUREMENT OF AN UNPRECEDENTEDLY LARGE CAGE-RECOMBINATION EFFICIENCY FACTOR, F(C) GREATER-THAN-OR-EQUAL-TO 0.94
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DOI：
10.1021/ja00052a045
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发表时间：
1992-12-16
影响因子：
15
通讯作者：
FINKE, RG
中科院分区：
文献类型：
--
作者：
GARR, CD;FINKE, RG
报道了一种简单的方法，使用高约 100 ℃ 的热解法捕获 adocobinamide（轴向脱碱基辅酶 B-12）Co-C 键热解中的有机金属笼状自由基对。 1 M，稳定硝基氧自由基 TEMPO（2,2,6,6-四甲基哌啶基-1-氧基）的浓度。作为 [TEMPO] 函数的产品研究解决了文献争议，表明 β-H 消除不是协调一致的，而是通过 [Ado...Co(II)] 笼中对进行。该方法允许首次测量 adocobinamide 的热分数笼效率因子 (F(c))，0.94 小于或等于 F(c) 小于或等于 1.0。该结果是有机金属络合物中金属-碳均裂的少数精确 F(c) 值之一，也是生物有机金属辅助因子的罕见 F(c) 值之一，与所有文献中具有相当粘度的溶剂中键均裂 F(c) 值相比，其值是前所未有的大。因此，它证实了文献中对大型有机金属自由基中相当大（大于或等于 0.5）的 F(c) 值的预测。
A simple method is reported for trapping organometallic caged radical pairs in adocobinamide (axial-base-off coenzyme B-12) Co-C bond thermolysis using high, ca. 1 M, concentrations of the stable nitroxide free radical TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy). The product studies as a function of [TEMPO] resolve a literature controversy by showing that beta-H elimination is not concerted, but rather proceeds through an [Ado...Co(II)] caged pair. The method permits the first measurement of the thermal fractional cage-efficiency factor (F(c)) for adocobinamide, 0.94 less-than-or-equal-to F(c) less-than-or-equal-to 1.0. This result, one of the few precise F(c) values for metal-carbon homolysis in an organometallic complex and a rare F(c) value for a bioorganometallic cofactor, is unprecedentedly large in comparison to all literature bond homolysis F(c) values in solvents of comparable viscosity. It thereby serves to confirm the literature's prediction of sizable (greater-than-or-equal-to 0.5) F(c) values in large, massive organometallic radicals.