Fundamental Studies of Tungsten Alkylidene Imido Monoalkoxidepyrrolide Complexes
Fundamental Studies of Tungsten Alkylidene Imido Monoalkoxidepyrrolide Complexes
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DOI：
10.1021/ja9012694
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发表时间：
2009-06-10
影响因子：
15
通讯作者：
Schrock, Richard R.
中科院分区：
文献类型：
--
作者：
Jiang, Annie J.;Simpson, Jeffrey H.;Schrock, Richard R.
在W(NaR)(CH2)(Me(2)Pyr)(2)(2)中加入R*OH生成了两个单烷氧基吡咯烷基(MAP)物种的非对映异构体W(NaR)(CH2)(Me(2)Pyr)(OR*)(1；Ar=2，6-二异丙基苯基，Me(2)Pyr=2，5-二甲基吡咯烷酮，OR*=(R)-3，3‘-dibromo-2’-(tert-butyldimethylsilyloxy)-5，5‘，6，6’，7，7‘，8，8’-octahydro-1，1‘-binaphthyl-2-olate)，)。通过处理1的非对映异构体与乙烯的混合物，分离出未取代的钨环丁烷物种W(NaR)(C3H6)(Me(2)PYR)(OR*)(2)。X-射线研究表明，2具有三方双锥结构，其中亚胺和苯氧基配体处于轴向位置。在1和2上进行了各种核磁共振实验，主要结果如下：(1)1的两个非对映异构体中的亚甲基配体在22℃时容易围绕W=C键旋转(k=2-7 S(-1))，(Ii)核磁共振研究与2裂解得到中间体(R)-和(S)-W(CH_2)(C_2H_4)相一致；(3)(R)-W(CH2)(C2H4)中间体中的乙烯可以以大致相同的速度绕W-乙烯键轴旋转，或者乙烯失去生成1。化合物1与三甲基膦反应生成(R)-1(PMe3)。观察到两个中间体PMe3加合物以分子内方式转化为(R)-1(PMe3)，在5℃时的平均速率常数类似于1.4×10(-4)S(-1)。还制备了含2，3，5，6-四苯基苯氧配体的新亚叶烯(4)和亚甲基(5)MAP物种。化合物5可以加热到80摄氏度，亚甲基围绕W=C键的旋转很容易，并且可以在变温H-1核磁共振谱中观察到。20℃下苯-d(6)中5的H-1-H-1EXSY谱表明，亚甲基质子在k=90的S(-1)处发生交换。5(四氢呋喃)的结构表明它是一个四方金字塔，亚甲基配体在顶端，四氢呋喃配位到亚胺配体上。5与乙烯反应生成W(NAR)(C3H6)(Me(2)PYR)(OR)(6)，其结构类似于2。用PMe3处理5得到黄色5(PMe3)。X-射线分析表明，它是一个方形金字塔，亚甲基配体位于顶端，膦反式连接到吡咯内酯上。这些研究表明，在与MAP物种的歧化反应中，金属环丁烷中间体可能含有轴向的亚胺和苯氧基配体，当MAP物种中的烯烃接近金属时形成金属环，金属环丁烷的构型因每一正向歧化步骤而反转。
Two diastereomers of the monoalkoxidepyrrolide (MAP) species, W(NAr)(CH2)(Me(2)Pyr)(OR*) (1; Ar = 2,6-diisopropylphenyl, Me(2)Pyr = 2,5-dimethylpyrrolide, OR* = (R)-3,3'-dibromo-2'-(tert-butyldimethylsilyloxy)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl-2-olate), were generated through addition of R*OH to W(NAr)(CH2)(Me(2)Pyr)(2). The unsubstituted tungstacyclobutane species, W(NAr)(C3H6)(Me(2)Pyr)(OR*) (2), was isolated by treating the mixture of diastereomers of 1 with ethylene. An X-ray study revealed 2 to have a trigonal bipyramidal structure in which the imido and phenoxide ligands are in axial positions. A variety of NMR experiments were carried out on 1 and 2. The major findings are the following: (i) the methylidene ligands in the two diastereomers of 1 rotate readily about the W=C bond (k = 2-7 s(-1) at 22 degrees C); (ii) NMR studies are consistent with 2 breaking up to give an intermediate alkylidene/ethylene complex, (R)- and (S)-W(CH2)(C2H4); and (iii) the ethylene in the (R)-W(CH2)(C2H4) intermediate can rotate about the W-ethylene bond axis at approximately the same rate as 2 re-forms or ethylene is lost to give 1. Compound 1 reacts with trimethylphosphine to yield (R)-1 (PMe3). Two intermediate PMe3 adducts were observed and found to convert to (R)-1 (PMe3) in an intramolecular fashion with an average rate constant at 5 degrees C of similar to 1.4 x 10(-4) s(-1). Both neophylidene (4) and methylidene (5) MAP species containing 2,3,5,6-tetraphenylphenoxide ligand also were prepared. Compound 5 can be heated to 80 degrees C, where methylidene rotation about the W=C bond is facile and observable in a variable-temperature H-1 NMR spectrum. A H-1-H-1 EXSY spectrum of 5 in benzene-d(6) at 20 degrees C showed that the methylidene protons are exchanging with k = 90 s(-1). A structure of 5(THF) showed it to be a square pyramid with the methylidene ligand in the apical position and THF coordinated trans to the imido ligand. Exposure of 5 to ethylene generated the tungstacyclobutane complex, W(NAr)(C3H6)(Me(2)Pyr)(OR) (6), whose structure is analogous to that of 2. Treatment of 5 with PMe3 yielded yellow 5(PMe3) an X-ray study of which revealed it to be a square pyramid with the methylidene ligand in the apical position and the phosphine trans to the pyrrolide. These studies suggest that metallacyclobutane intermediates in metathesis reactions with MAP species are likely to contain axial imido and phenoxide ligands, that metallacycles are formed when an olefin approaches the metal in a MAP species trans to the pyrrolide, and that the configuration at the metal inverts as a consequence of each forward metathesis step.