Normal and anomalous ring opening of 1-3-.eta.-pentaarylcyclobutenylpalladium complexes
Normal and anomalous ring opening of 1-3-.eta.-pentaarylcyclobutenylpalladium complexes
复制标题
1-3-η-五芳基环丁烯基钯配合物的正常和异常开环
DOI：
10.1021/ja00483a013
复制
发表时间：
1978
影响因子：
15
通讯作者：
P. Maitlis
中科院分区：
文献类型：
--
作者：
S. H. Taylor;P. Maitlis
将环丁二烯钯配合物[PdCl 2（C4 To 4）] 2（To=对甲苯基）芳基化（用丙酮中的NaBPfu），得到1 -3-N-环丁烯基配合物[Pd（C4 To 4Ph）Cl] 2，其中苯基立体特异性地进入金属内。在单体[Pd（C4 To 4Ph）X]（X= acac，S2 CNR 2）与配体（特别是PPhMe 2）反应时发生开环，得到-丁二烯基络合物[Pd（C4 To 4Ph）X（PPhMe 2）]，其中1 -3-？;-环丁烯基配体以预期的对旋方式立体特异性地打开。相比之下，环丁烯基二硫代氨基甲酸酯[Pd（C4 T04 Ph）（S2 CNR 2>]（17）进行自发开环（2天/20 ℃或2小时/60 ℃），得到预期的顺旋开环的β-丁二烯基[Pd（C4 To 4Ph）（S2 CNR 2）][20，C（3），C（4）上的对甲苯基E]和意外的形式上对旋异构体[21，对甲苯基Z在C（3），C（4）上]。40：60比例，如通过X射线结构测定、HPLC和NMR光谱所示。调查得出的路线，其中异构体21的形成进行了说明。反应17- 20+ 21是单分子的，似乎不涉及离子中间体或光化学引发。自由环丁烯基很容易从这些配合物中形成，一种方便的方法是通过环丁烯基配合物与Ph 2 PCH 2 PPh 2（dppm）反应;这也导致Pd（I）配合物[Pd 2Cl 2（dppm）2]。反对自由基参与开环的证据，并赞成他们的中间体分解副反应。该反应似乎也不是通过自由基链式机理进行的。提出了一种机理，该机理涉及17的顺旋开环得到预期的异构体（20），然后通过一个C（3）可以从一侧翻转到另一侧的双环戊烯中间体与意外的异构体（21）平衡。在这方面，我们中的一个人已经表明，在Pd（II）诱导的带有大体积取代基的二取代乙炔的低聚反应中，主要产物是环丁二烯络合物（例如，3），它是由中间体丁二烯络合物（例如，I）环化产生的; 1· 2推测的但迄今尚未证实的进一步中间体是氯环丁烯络合物（2）。
Arylation (with NaBPfu in acetone) of the cyclobutadienepalladium complex,[PdCl2 (C4To4)] 2 (To= p-tolyl), gives the l-3-T/-cyclobutenyl complex [Pd (C4To4Ph) Cl] 2 with the phenyl group entering stereospecificallyendo to the metal. Ring opening occurs on reaction of the monomeric [Pd (C4To4Ph) X](X= acac, S2CNR2) with ligands (in particular, PPhMe2) to give the-butadienyl complexes [Pd (C4To4Ph) X (PPhMe2)], where the l-3-?;-cyclobutenyl ligand has opened ste-reospecifically in the expected conrotatory manner. In contrast, the cyclobutenyl dithiocarbamates [Pd (C4To4Ph)(S2CNR2>](17) undergo a spontaneous ring opening (2 days/20 C or 2 h/60 C) to give a mixture of theexpected conrotatory ring-opened,-butadienyl [Pd (C4To4Ph)(S2CNR2)][20, p-tolyls E on C (3), C (4)] and the unexpected, formally disrotatory, iso-mer [21, p-tolyls Z on C (3), C (4)] in a ca. 40: 60 ratio, as shown by an x-ray structure determination, HPLC, and NMR spec-troscopy. Investigations to elicit the route by which the isomer 21 is formed are described. The reaction 17— 20+ 21 is unimo-lecular and does not appear to involve ionic intermediates or to be photochemicallyinitiated. Free cyclobutenyl radicals are easily formed from these complexes and a convenient way is by reaction of cyclobutenyl complexes with Ph2PCH2PPh2 (dppm); this also leads to the Pd (I) complex [Pd2Cl2 (dppm) 2]. Evidence is presented against free radicals participating in the ring opening, and in favor of their being intermediates in decomposition side reactions. The reaction does notappear to proceed by a radical chain mechanism either. A mechanism is proposedwhich involves the conrotatory ring opening of 17 to give the expected isomer (20) which then equilibrates with theunexpected isomer (21) via a metallocyclopentenyl intermediate in which C (3) can flip from one side to the other.Over the past few years considerable interest has developed in ring-opening and closing reactions in organometallic systems and the mechanisms by which they proceed. One of us has, in this context, shown that in the Pd (II)-induced oligomerization of disubstituted acetylenes bearingbulky substituents the chief products are cyclobutadiene complexes (eg, 3) which arise by a cyclization of intermediate-butadienyl complexes (eg, I); 1· 2 a presumed but so far unconfirmed further intermediate is a chlorocyclobutenyl complex (2).