A rational protocol for the synthesis of arylated bipyridine ligands via a cycloaddition pathway
A rational protocol for the synthesis of arylated bipyridine ligands via a cycloaddition pathway
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DOI：
10.1021/jo7019866
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发表时间：
2007-12-21
影响因子：
3.6
通讯作者：
Ziessel, Raymond
中科院分区：
文献类型：
--
作者：
Diring, Stephane;Retailleau, Pascal;Ziessel, Raymond
一个通用的设计原则，用于制备各种取代的苯基多吡啶配体的描述。这些配体容易通过缺电子二烯如2，6-二取代-1，3，4-三嗪与乙炔基芳烃或乙炔基烷烃之间的区域选择性[4+2]环加成反应制备。异常的反应性被发现与富含电子的亲双烯体轴承乙炔基没食子酸酯或乙炔基苯基二丁基氨基。形成两种区域异构体，由于过渡态中有利的π-π相互作用，Meta是优选的，而帕拉异构体在大多数情况下以低收率形成。然而，使用叔丁基乙炔或N，N-二甲基氨基-2-丙炔将反应排他地驱动为帕拉异构体。二-N，N-二丁基氨基苯基或异喹啉配体也可以通过逆Diels -桤木反应在单一步骤中制备。碘取代配体或其铂（II）配合物在Pd（0）催化下的交叉偶联反应产生带有链烷烃链、电子给体或电子受体基团的支化配体和配合物。碘官能化配体的氯-Pt（II）络合物的使用允许通过使用不同的催化剂将两个卤素都替换为乙炔基。这种方法很容易容纳各种官能团，并已成功地扩展到含有各种供体/受体框架的系统。所有配体在近紫外区有很强的吸收，室温下在溶液中发光，量子产率为0 ~ 66%。激发态寿命在纳秒范围内，溶剂效应与单重激发态混合电荷转移特性保持一致。从光谱和电化学研究中推断，二正丁基氨基衍生物在激发态下是强还原剂。
A generic design principle for the preparation of a variety of substituted phenyl-polypyridine ligands is described. These ligands are readily prepared by a regioselective [4+2] cycloaddition between electron-deficient dienes, such as 2,6-disubstituted-1,3,4-triazines, and ethynyl-arenes or ethynyl-alkanes.. Exceptional reactivity is found with electron-rich dienophiles bearing ethynylgallate or ethynylphe-nyldibutylamino groups. Two regioisomers are formed, the meta being preferred due to favorable pi-pi interactions in the transition state, while the para isomers are formed in low yields in most cases. The use of tert-butylacetylene or N,N-dimethylamino-2-propyne, however, drives the reaction exclusively to the para isomer. Di-N,N-dibutylaminophenyl or isoquinoline ligands can also be produced in a single step by reverse Diels - Alder reactions. Cross-coupling reactions of iodo-substituted ligands or their platinum(II) complexes under Pd(0) catalysis gives branched ligands and complexes bearing paraffin chains, electron-donor or electron-acceptor groups. The use of a chloro-Pt(II) complex of an iodo-functionalized ligand allows both halogens to be replaced by ethynyl groups by using different catalysts. This methodology readily accommodates various functional groups and has been successfully extended to systems containing a variety of donor/acceptor frameworks. All ligands strongly absorb in the near-UV and luminesce in solution at rt with quantum yields ranging from 0 to 66%. Excited state lifetimes are in the nanosecond range and the solvent effects are in keeping with singlet excited states mixed with charge-transfer character. As deduced from spectroscopic and electrochemical studies, the di-n-butylamino derivatives are strong reductants in the excited state.