Unrealized concepts of masked alkylidenes in (PNP)FeXY systems and alternative approaches to LnXmFe(IV)=CHR
Unrealized concepts of masked alkylidenes in (PNP)FeXY systems and alternative approaches to LnXmFe(IV)=CHR
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DOI：
10.1016/j.poly.2020.114460
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发表时间：
2020-05
期刊：
影响因子：
2.6
通讯作者：
Gregory M. George;P. T. Wolczanski;S. MacMillan;T. Cundari
中科院分区：
文献类型：
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作者：
Gregory M. George;P. T. Wolczanski;S. MacMillan;T. Cundari
用铁（II）卤化物处理PNP配体得到伪四面体{(Ph2PCH2)2NR}FeX2（R″=tBu,1a-X; Me,1b-X）和{(iBu2PCH2)2NR″}FeX2（R″=tBu,2a-X; Me,2b-X）配合物，它们可以单烷基化和二烷基化得到各种{(Ph2PCH2)2NR″}FeCl(R) (R″=tBu,3a-R; Me,3b-R), {(iBu2PCH2)2NR″}FeCl(R) (R″=tBu,4a-R; Me,4b-R), {(Ph2PCH2)2NtBu}Fe(neoPe)2（5a-neoPe）和{(iBu2PCH2)2NtBu}Fe(1-nor)2（6a-nor）。所有的配合物都是高自旋（S= 2），对{(Ph2PCH2)2NMe}FeCl2（1b-Cl）、{(iBu2PCH2)2NtBu}FeCl2（2a-Cl）和{(iBu2PCH2)2NtBu}FeCl(1-nor) （4a-nor）的结构研究揭示了PNP配体的椅形构象，计算出这些配体通过扭转船作为计算最小值对船形具有适度的障碍。试图将这些配合物转化为两性离子NCRR '含铁物质作为“掩膜烷基烯”未能实现。其他方法包括结构表征的抗磁性{(iBu2PCH2)2NtBu}(CO)2FeCl(COneoPe)(8)，羰基化产物4a- neope和低价{(Ph2PCH2CH2)2NtBu}Fe((H2C=CHSiMe2)2O)(9)也失败了。给出了烷基烷的轨道能量和重叠的分析。共价被认为是复分解过程中烷基烯向元环丁烷转化的关键特征。
Treatment of PNP ligands with iron(II) halides yielded pseudo tetrahedral {(Ph2PCH2)2NR}FeX2(R″ =tBu,1a-X; Me,1b-X) and {(iBu2PCH2)2NR″}FeX2(R″ =tBu,2a-X; Me,2b-X) complexes, which could be mono- and dialkylated to afford various {(Ph2PCH2)2NR″}FeCl(R) (R″ =tBu,3a-R; Me,3b-R), {(iBu2PCH2)2NR″}FeCl(R) (R″ =tBu,4a-R; Me,4b-R), {(Ph2PCH2)2NtBu}Fe(neoPe)2(5a-neoPe) and {(iBu2PCH2)2NtBu}Fe(1-nor)2(6a-nor). All of the complexes were high spin (S= 2), and structural studies of {(Ph2PCH2)2NMe}FeCl2(1b-Cl), {(iBu2PCH2)2NtBu}FeCl2(2a-Cl), and {(iBu2PCH2)2NtBu}FeCl(1-nor) (4a-nor), revealed chair conformations for the PNP ligands, which were calculated to have modest barriers to boat configurations via twist-boats as calculational minima. Attempts to convert these complexes to zwitterionic NCRR′Fe-containing species as “masked alkylidenes” failed to materialize. Alternative approaches involving structurally characterized diamagnetic {(iBu2PCH2)2NtBu}(CO)2FeCl(COneoPe) (8), the carbonylation product of4a-neoPe, and low-valent {(Ph2PCH2CH2)2NtBu}Fe((H2C=CHSiMe2)2O) (9) also failed. An analysis of orbital energies and overlap is given for alkylidenes. Covalence is identified as a crucial feature necessary for the alkylidene to metalacyclobutane transformation in metathesis.