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.

顺式-二氯二(异氰)合钯(II)配合物cis-[PdCl₂(CNR)₂]（其中R=2,6-二甲基苯基(2,6-Me₂C₆H₃)记为配合物1，2-氯-6-甲基苯基(2-Cl-6-MeC₆H₃)记为配合物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(diaminocarbene)物种cis-[PdCl₂(CNR){C(NHR)=NH(1,3-C₆H₄NH₂)}]，分别对应产物5和6。在此反应中，BDA1作为单官能团亲核试剂，通过其中一个氨基进攻RNC配体。
相比之下，配合物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，生成双核配合物[cis-PdCl₂(CNR){μ-C(NHR)=NH(1,4-C₆H₄)NH=C(NHR)}-(cis)-PdCl₂(CNR)]，对应产物6和7，该配合物包含两个1,4-双官能团二氨基卡宾配体。
当R为环己基(cyclohexyl)的顺式-二氯二(异氰)合钯(II)配合物cis-[PdCl₂(CNR)₂]（记为配合物3）与BDA1或BDA2反应时，未得到任何可分离的卡宾类衍生物。
当配合物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，可观察到最为丰富的反应化学行为。
加入上述二胺后，可生成三类产物：单卡宾阳离子配合物cis-[PdCl(CNR){C(NHR)=NHC₆H₂X₂NH₂}]Cl（X=H、Me、Cl，对应产物8~16）、楚加耶夫型(Chugaev-type)C,C-键合双卡宾配合物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）。
除产物17和18外，所有合成的配合物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）、高分辨电喷雾质谱(HRESI±-MS)、红外光谱(IR)、¹H核磁共振波谱及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)确定了其晶体结构。
配合物17和18则通过高分辨电喷雾质谱、红外光谱进行了表征，并通过X射线晶体衍射(X-ray crystallography)确定了其分子结构。