Palladium(II)-Mediated Addition of Benzenediamines to Isocyanides: Generation of Three Types of Diaminocarbene Ligands Depending on the Isomeric Structure of the Nucleophile

Coupling
of the palladium-bis­(isocyanide) complexes cis-[PdCl2(CNR)2] (R = 2,6-Me2C6H3 1, 2-Cl-6-MeC6H3 2) with benzene-1,3-diamine (BDA1) leads to the
diaminocarbene species cis-[PdCl2(CNR)­{C­(NHR)NH­(1,3-C6H4NH2)}] (5 and 6, respectively). In this reaction, BDA1 behaves as a
monofunctional nucleophile that adds to one of the RNC ligands by
one amino group. By contrast, the reaction of 1 and 2 with benzene-1,4-diamine (BDA2) involves both
amino functionalities of the diamine and leads to the binuclear species
[cis-PdCl2(CNR)­{μ-C­(NHR)NH­(1,4-C6H4)­NHC­(NHR)}-(cis)-PdCl2(CNR)] (6 and 7) featuring two 1,4-bifunctional
diaminocarbene ligands. The reaction of cis-[PdCl2(CNR)2] (R = cyclohexyl 3) with either BDA1 or BDA2 does not afford any isolable carbene
derivatives. The most versatile chemistry was observed when 1–3 were treated with benzene-1,2-diamine
(BDA3) and the relevant substituted 1,2-diamines, viz.,
4,5-dimethylbenzene-1,2-diamine (BDA4) and 4,5-dichlorobenzene-1,2-diamine
(BDA5). The addition of these diamines brings about the
formation of the monocarbene cationic complexes cis-[PdCl­(CNR)­{C­(NHR)NHC6H2X2NH2}]Cl (X
= H, Me, Cl) (8–16), the Chugaev-type C,C-bound bis-carbenes cis-[PdCl2{C­(NHR)NHC6H2X2NHC­(NHR)}] (17, 18), and the bis­(C,N-chelated)­carbene
complexes cis-[Pd­{C­(NHR)NHC6H2X2NH2}2]­Cl2 (19–24). All prepared complexes (with the exception of 17 and 18) were isolated as colorless or pale yellow solids and characterized
by elemental analyses (C, H, N), HRESI±-MS, IR, 1H and 13C­{1H} NMR spectroscopies, and 4, 7, 13, 16, and 24 by X-ray diffraction. Complexes 17 and 18 were characterized by HRESI±-MS and IR
spectroscopy, and their structures were established by X-ray crystallography.

钯-双(异氰)配合物（palladium-bis(isocyanide) complexes）cis-[PdCl₂(CNR)₂]（R=2,6-二甲基苯基1、2-氯-6-甲基苯基2）与苯-1,3-二胺（benzene-1,3-diamine, BDA1）发生偶联反应，生成二氨基卡宾类物种cis-[PdCl₂(CNR){C(NHR)=NH(1,3-C₆H₄NH₂)}]（分别对应5和6）。该反应中，BDA1作为单官能团亲核试剂，通过其中一个氨基进攻其中一个RNC配体。与之相反，1、2与苯-1,4-二胺（benzene-1,4-diamine, BDA2）的反应则利用了二胺的两个氨基官能团，生成双核物种[cis-PdCl₂(CNR){μ-C(NHR)=NH(1,4-C₆H₄)NH=C(NHR)}-(cis)-PdCl₂(CNR)]（对应6和7），该物种包含两个1,4-双官能团二氨基卡宾配体。顺式-[PdCl₂(CNR)₂]（R=环己基3）与BDA1或BDA2的反应均未得到可分离的卡宾衍生物。当1~3与苯-1,2-二胺（benzene-1,2-diamine, BDA3）以及相关取代1,2-二胺，即4,5-二甲基苯-1,2-二胺（4,5-dimethylbenzene-1,2-diamine, BDA4）和4,5-二氯苯-1,2-二胺（4,5-dichlorobenzene-1,2-diamine, BDA5）反应时，观察到了最具多样性的化学行为。这些二胺的加入会生成单卡宾阳离子配合物cis-[PdCl(CNR){C(NHR)=NHC₆H₂X₂NH₂}]Cl（X=H、Me、Cl）（8~16）、楚加耶夫型C,C-配位双卡宾配合物cis-[PdCl₂{C(NHR)=NHC₆H₂X₂NH=C(NHR)}]（17、18），以及双(C,N-螯合)卡宾配合物cis-[Pd{C(NHR)=NHC₆H₂X₂NH₂}₂]Cl₂（19~24）。所有制备得到的配合物（17和18除外）均以无色或淡黄色固体形式分离得到，并通过元素分析（C、H、N）、高分辨电喷雾电离质谱（HRESI±-MS）、红外光谱（IR）、¹H及¹³C{¹H}核磁共振波谱进行了表征；其中配合物4、7、13、16和24还通过X射线衍射（X-ray diffraction）进行了结构确证。配合物17和18则通过HRESI±-MS和IR光谱进行了表征，其结构通过X射线晶体学（X-ray crystallography）得以确定。