Versatility of Iminophosphoranes and Noninnocent Behavior of the 1,5-Cyclooctadiene Ligand in Palladium(II) Complexes. Synthesis of σ-Allyl Derivatives

The treatment of PdCl2(NCPh)2 with Ph3PNPh (1) gives the expected complex trans-PdCl2[N(Ph)PPh3]2 (3). However, the reaction of PdCl2(COD) (COD = 1,5-cyclooctadiene) with 1 or Ph3PN-1-Np
(2) (Np = naphthyl) occurs through nucleophilic attack of 1 or 2 on one olefinic bond of the COD ligand
followed by proton abstraction on the adjacent methylene group, giving the η1-allyl complexes
[Ph3P(R)NH···Cl2Pd(C8H11)] (R = Ph, 4; Np, 5). The X-ray structure of 4 has been determined and
shows two interesting facts:  (i) the η1-η2-bonded cyclooctadienyl ligand, containing a η1-allyl fragment,
and (ii) the presence of a strong H bond between one of the Cl ligands and the proton of the NH group.
This H bond persists in solution, as shown by NMR and molar conductance measurements. The abstraction
of a chloride on 4 by reaction with AgClO4 cleaves the H bond and gives a mixture of the salt [Ph3PN(H)Ph](ClO4) (6) and the neutral η1-η2-cyclooctadienyl complex [Pd(μ-Cl)(C8H11)]2 (7). Complex 7 is
an adequate precursor for the synthesis of other stable η1-allyl complexes, and no η1−η3 allyl
interconversion has been observed.

将二氯二(苯甲腈)合钯(II)（PdCl₂(NCPh)₂）与N-苯基亚胺三苯基膦（Ph₃P=NPh，化合物1）反应，可得到目标配合物反式-二氯二[N-苯基亚胺三苯基膦]合钯(II)（3）。然而，二氯(1,5-环辛二烯)合钯(II)（PdCl₂(COD)，COD=1,5-环辛二烯）与化合物1或N-(1-萘基)亚胺三苯基膦（Ph₃P=N-1-Np，化合物2，Np=萘基）的反应过程则有所不同：首先由1或2对COD配体的一条烯烃双键进行亲核进攻，随后夺取相邻亚甲基上的质子，最终得到η¹-烯丙基配合物[Ph₃P(R)NH···Cl₂Pd(C₈H₁₁)]（R=Ph，4；Np，5）。已测定配合物4的X射线晶体结构，其呈现两处值得关注的特征：(i) 含有η¹-烯丙基片段的η¹-η²键合环辛二烯基配体；(ii) 其中一个氯配体与NH基团的质子之间存在强氢键相互作用。核磁共振(NMR)与摩尔电导测量结果证实，该氢键在溶液中依然存在。向配合物4中加入高氯酸银(AgClO₄)以夺取一个氯离子，可断裂该氢键，得到盐[Ph₃PN(H)Ph](ClO₄)（6）与中性η¹-η²环辛二烯基配合物[Pd(μ-Cl)(C₈H₁₁)]₂（7）的混合物。配合物7是合成其他稳定η¹-烯丙基配合物的合适前驱体，且未观察到η¹-η³烯丙基互变现象。