氮異環碳烯銥與鈀錯合物之合成及催化研究

Iridium and Palladium Complexes with N-Heterocyclic Carbene Ligands and Their Catalytic Applications

傅勁逢(Ching-Feng Fu)

指導教授 ： 劉緒宗

國立臺灣大學/理學院/化學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.01530

摘要

氮異環碳烯具有很強的電子予體特性，
可以穩定過渡金屬中心，並且具有良好的
空氣、熱穩定性，因此近年來被廣泛使用
在各式催化反應中。本論文利用羰基-鎢金
屬錯合物可將其上的碳烯配體轉移至其他
過渡金屬之特性，成功合成出一系列具有
不同側鏈的飽和氮異環碳烯銥、鈀錯合物。
在銥錯合物〔(L)Ir(CO)2Cl〕方面，藉由羰
基的紅外線光譜伸縮訊號分析可反映出配
位基(L)電子予體的強弱，證明碳烯比膦為
強的配基。若以膦對此類銥錯合物進行取
代測試，或以13CO對〔(L)Ir(CO)2Cl〕進行交
換速率的量測，亦可得到相同結論。若碳
烯側鏈上具有可配位的吡啶基團，則會阻
礙13CO與銥的配位，使羰基交換速率大幅
減緩。
碳烯銥錯合物在催化分子內還原胺化反
應、acetylenic carboxylic acid環化反應及
2-(o-aminophenyl)ethanol的氧化合環反應，
都有優異的效果。在催化酮類的氫轉移反
應中，以具有拉電子基的苯酮類化合物反
應性最佳，催化劑的選擇則以〔(NHC)Ir(CO)2Cl〕
效果最好，若於催化劑結構中增加吡啶或膦的
配位，反而會使活性下降。
於碳烯上取代兩個吡啶基團鎢錯合物，經
transmetalation後可得三配位的碳烯鈀錯合物，
由單晶結構得知，吡啶的配位會使氮異環與鈀
金屬配位平面的交角大幅偏離直角，僅35.07度。
而對位的雙碳烯鈀錯合物與銀鹽反應可使配位氯
離去，在乙腈中能形成穩定的陽離子，根據
trans-influence，順式的雙碳烯鈀錯合物在熱
力學上較為穩定，因此將配位氯補回可單離
出全部順式的碳烯鈀錯合物。氯橋鍵鈀碳烯
錯合物與三苯基膦的反應亦有類似的情形，
會生成順式的碳烯-膦鈀錯合物。
氯橋鍵鈀碳烯錯合物亦可與其他的碳烯前驅
物反應，使飽和碳烯與不飽和碳烯配位於同
一鈀中心，形成非對稱的雙碳烯鈀錯合物，
研究這些非對稱碳烯錯合物與碘、三氟醋酸
或銀鹽反應的結果，顯示飽和碳烯與鈀的鍵
結強於不飽和碳烯與鈀的鍵結。
碳烯鈀錯合物對於芳香氯的Suzuki-Miyaura耦
合反應有良好的活性，尤以鈀中心的電子密
度較高的雙飽和碳烯錯合物最佳，因反應中
形成的零價鈀有利於氧化加成；但在碳-硫耦
合反應中，芳香溴的加成並非速率決定步驟
，鈀中心電子密度較低的碳烯-膦錯合物反而
有較高的效率。值得一提的是，碳烯-鈀錯合
物與銀鹽反應後形成的陽離子除了具有路易
士酸性，對於2-(phenylethynyl)aniline經還原胺
化反應，形成吲哚後再與苯甲醛反應生成雙
吲哚化合物，以及吲哚與硝化苯乙烯的共軛
加成反應都有優異的轉換率。

關鍵字

氮異環碳烯 ； 銥 ； 鈀 ； 催化

並列摘要

Recently, the use of N-heterocyclic carbenes
(denoted as NHC) as ligands for transition
metal ions in catalysis has been increased
significantly due to their strong sigma-donor
nature. In this work, we have synthesized a
series of iridium and palladium complexes
with the saturated NHCs bearing different
side chains by transmetalation from
(NHC)W(CO)n to the metal precursors.
It was demonstrated that NHCs were better
sigma-donors than phosphines via
comparison of IR stretching of the
carbonyl groups in (NHC)Ir(CO)2Cl
versus the phosphine analogs.
This trend was also consistent with
the rate determination of the CO
exchanging in (NHC)Ir(CO)2Cl and
(Cy3P)Ir(CO)2Cl. However,
the 13CO exchanging was slower in
the case of N-pyridinyl substituted
iridium complex due to the block
of pyridinyl group at the axial position.
Chelation of bis-pyridinyl NHC ligand
toward the Pd center resulted
in the formation of a pincer complex,
which was confirmed by single crystal
X-ray diffraction. Treatment of
trans-(NHC)2PdCl2 with silver salt
in CD3CN scavenges chlorides
could generate stable cationic species.
Due to the trans-influence,
the cationic species transformed
to the thermodynamically stable
cis-biscarbene complex.
Upon coordination of chloride,
cis-(NHC)2PdCl2 could be isolated.
For the same reason,
cis-(NHC)(PPh3)PdCl2 would be
formed from the reaction between
bridge-Pd carbene complexes
and triphenylphosphine.
Reactions between bridge-Pd
carbene complexes and other
carbene precursors could form
unsymmetry bis-NHC Pd complexes,
which contained saturated and
unsrturated-NHCs on the same
Pd center.
Treatment of those unsymmetry
carbene complexes with I2 , CF3COOH,
or AgBF4 to investigate the stability
of carbene-Pd bonds, it was found that
unsaturated-NHC Pd bonds were
more easily to break.
Iridium complexes were able
to catalyze intramolecular
hydroamination of alkynes,
cyclization of acetylenic
carboxylic acid, and oxidative
cyclization of 2-(o-aminophenyl)ethanol
with excellent activities.
In addition, (NHC)Ir(CO)2Cl could act
as catalysts for the hydrogen-transfer
reduction of ketones,
especially for acetophenones with
electron-withdrawing groups.
Due to the higher electron density
on the Pd center, the saturated
bis-carbene palladium complexes
exhibited good activities on the
catalysis of the Suzuki-Miyaura
coupling of chloroarenes with
phenylbonoric acid. In contrast,
the carbene-phosphine complex
with lower electron density performed
better activity for C-S coupling.
The reason was that transmetalation
of thiolates were slower than oxidative
addition of aryl bromides during
the catalytic cycle.
The stable cationic species
generated from the abstraction
of NHC-Pd-Cl with silver salt actively
catalyzed the tandem reaction of
2-(phenylethynyl)anilines with
benzaldehydes to give bisindoles
and the conjugate addition between
indoles and nitrostyrenes.

並列關鍵字

Iridium ； Palladium ； N-Heterocyclic ； Carbene ； Catalytic

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