pure 6a. Salt metathesis with sodium tetraphenylborate in methanol yields the tetraphenylborate salts (2b–4b) that were used to grow X-ray quality crystals. Analysis of the M–O bond lengths confirms the larger trans-influence of the carbene donor compared with the pyridine donor. Ratios of the M–O(1)/M–O(2) bond lengths suggest that the carbene–metal bond strength follows the order 4b ≈ 3b > 2b. Protonation
吡啶鎓衍生的N-杂环卡宾络合物[[ i -BIPY)M(acac)+ [OTf] -(M = Ni(2a),Pd(3a),Pt(4a))(i -BIPY = N-(通过将
配体前体[ i -BIPY-H] + [OTf] -(OTf =三
氟甲基磺酸盐)环化为M(acac),以不溶性微晶粉末形式获得2'-
吡啶基)-
4-叔丁基吡啶-2'-亚烷基)2(acac =
乙酰丙酮)在160°C的
氯苯中。3a和4a合成中原料的消耗18 h后完成反应,完成重结晶后,以良好的收率提供(4a)和(5a)作为分析纯物质。与Ni(acac)2的反应是可逆的,并在大约75%的完成时达到平衡。通过蒸馏除去在环
金属化中产生的
乙酰丙酮,将反应驱动至完成,从而提供了良好的纯6a收率。用四苯
硼酸钠在
甲醇中进行盐置换,得到四苯
硼酸盐(2b - 4b),用于生长X射线质量的晶体。对M–O键长的分析证实了较大的反式卡宾供体与
吡啶供体的比较