Insertion of Substituted Alkynes into the Pd−C Bond of Methyl and Vinyl Palladium(II) Complexes Bearing Pyridylthioethers as Ancillary Ligands. The Influence of Ligand Substituents at Pyridine and Sulfur on the Rate of Insertion

The palladium(II) chloro methyl complexes bearing the bidentate 6-R-C5H3N-2-CH2SR‘
(RN-SR‘; R = H, Me, Cl; R‘ = Me, t-Bu, Ph) and the potentially terdentate 2,6-(CH2SR‘)2-C5H3N (S-N-S(R‘); R‘ = Me, t-Bu, Ph) pyridylthioethers as ancillary ligands were synthesized,
characterized, and reacted with substituted alkynes ZC⋮CZ (Z = COOMe, Z‘ = COOt-Bu,
Z‘ ‘ = COOEt). The reactions were followed under second-order conditions by 1H NMR
technique, and the reaction rates were determined. The corresponding vinyl derivatives were
synthesized, and in the case of the complexes [PdCl(ZCCZMe)(MeN-SPh)] and [PdCl(ZCCZMe)(C1N-St-Bu)] (Z = COOMe) reaction rates for alkyne insertion yielding the corresponding butadienyl complexes were also determined. The rate of insertion of the second
alkyne on the vinyl complex is more than 3 orders of magnitude lower than the first insertion
rate in both the studied complexes, thereby allowing easy separation between vinyl and
butadienyl derivatives and an easy preparation of mixed butadienyl esters. Furthermore,
the reaction rates are strongly dependent on the steric and electronic features of the ancillary
ligands. In particular, the distortion of the complex main coordination plane, induced by
the substituent in position 6 of the pyridine ring, was found to significantly influence the
substrate reactivity. The structures of the mono-inserted vinyl [PdCl(ZCCZMe)(MeN-St-Bu)] (1) and the bis-inserted butadienyl [PdCl((ZCCZ)2Me)(MeN-St-Bu)] (2) complexes were
determined by X-ray diffraction, and the persistence of a structural distortion of the complex
skeleton was observed. Moreover, the distortion may be related to facile ancillary ligand
displacement, a feature that can be exploited for the synthesis of substrates that would not
be easily obtained otherwise.

本研究合成并表征了以双齿配体6-R-吡啶-2-基甲基硫醚（RN-SR'，其中R=H、甲基、氯；R'=甲基、叔丁基、苯基）与潜在三齿配体2,6-二(硫代甲基)吡啶（S-N-S(R')，其中R'=甲基、叔丁基、苯基）这类吡啶硫醚（pyridylthioethers）作为辅助配体（ancillary ligands）的氯甲基钯(II)配合物，随后将其与取代炔烃ZC≡CZ（Z=甲氧羰基，Z'=叔丁氧羰基，Z''=乙氧羰基）进行反应。采用氢核磁共振（¹H NMR）技术追踪二级反应条件下的反应过程，并测定了各反应的速率。合成了对应的乙烯基衍生物；针对配合物[PdCl(ZC≡CZMe)(MeN-SPh)]与[PdCl(ZC≡CZMe)(ClN-St-Bu)]（Z=甲氧羰基），还测定了其经炔烃插入反应生成对应丁二烯基配合物的反应速率。在两种研究的配合物中，乙烯基配合物上第二次炔烃插入反应的速率较第一次插入速率低三个数量级以上，因此可便捷分离乙烯基与丁二烯基衍生物，并简便制备混合丁二烯基酯类化合物。此外，反应速率强烈依赖于辅助配体的空间位阻与电子效应。具体而言，吡啶环6位取代基诱导的配合物主配位平面畸变，会显著影响底物的反应活性。通过X射线衍射（X-ray diffraction）测定了单插入产物乙烯基配合物[PdCl(ZC≡CZMe)(MeN-St-Bu)]（化合物1）与双插入产物丁二烯基配合物[PdCl((ZC≡CZ)₂Me)(MeN-St-Bu)]（化合物2）的晶体结构，观察到配合物骨架存在持续性的结构性畸变。进一步而言，该畸变或与辅助配体的易解离特性相关，这一特性可用于合成常规方法难以获得的底物。