Experimental and Theoretical Investigations of Catalytic Alkyne Cross-Metathesis with Imidazolin-2-iminato Tungsten Alkylidyne Complexes

The imidazolin-2-iminato tungsten alkylidyne complexes [Me3CC≡W(NImR)(OR′)2] (4a: R = tBu, R′ = CMe3; 4b: R = Dipp, R′ = CMe3; 5a: R = tBu, R′ = CMe(CF3)2; 5b: R = Dipp, R′ = CMe(CF3)2 have been prepared from [Me3CC≡W(OCMe3)3] (2) and [Me3CC≡W{OCMe(CF3)2}3(dme)] (3, dme = 1,2-dimethoxyethane) by reaction with the lithium reagents Li(NImtBu) and Li(NImDipp), generated with MeLi from 1,3-di-tert-butylimidazolin-2-imine (ImtBuNH) or 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine (ImDippNH), respectively. Reaction of 3 with Li[N(tBu)Ar]·OEt2 (Ar = 3,5-dimethylphenyl) afforded the amido complex [Me3CC≡W{N(tBu)Ar}{OCMe(CF3)2}2] (6). Addition of Li[OCPh(CF3)2] to [Me3CC≡WCl3(dme)] (1) produced the dme-free complex [Me3CC≡W{OCPh(CF3)2}3] (7), which, upon treatment with Li(NImtBu), gave the alkylidene complex 8, presumably formed by activation and addition of an ortho-C−H bond across the W≡C bond in the intermediate alkylidyne complex. Treatment of 1 with Li[OC(CF3)3] led to the substitution of only two chloride ligands and formation of cis-[Me3CC≡WCl{OC(CF3)3}2(dme)] (9), which exhibits long-range through-space 19F−19F coupling between the fluorine atoms of the two OC(CF3)3 ligands. Reaction of 9 with Li(NImtBu) resulted in partial cleavage of the ImtBuN ligand and ligand redistribution to afford the dinuclear tungsten alkylidyne complex 10. The propylidyne complex [EtC≡W(NImtBu){OCMe(CF3)2}2] (12) was obtained by treatment of 5a with 3-hexyne, which proceeded via the metallacyclobutadiene complex 11. Complex 5a is able to rapidly catalyze alkyne cross-metathesis of 3-heptyne to give a statistical 1:2:1 mixture of 3-hexyne, 3-heptyne and 4-octyne. The catalytic homodimerization of 1-phenylpropyne under vacuum-driven conditions was studied for 5a, 5b and 6 at 30 and 80 °C. The molecular structures of complexes 2, 3, 4a, 4b, 5b, 8, 9, 10 and 12 were determined by single crystal X-ray diffraction. High-level DFT calculations employing the B3LYP functional have been carried out for a series of experimentally studied and other alkylidyne complexes by choosing alkyne metathesis of 2-butyne as the model reaction.

以[Me3CC≡W(OCMe3)3](2)和[Me3CC≡W{OCMe(CF3)2}3(dme)](3, dme = 1,2-二甲氧基乙烷)为原料，通过与锂试剂Li(NImtBu)和Li(NImDipp)反应，分别由1,3-二叔丁基咪唑啉-2-亚胺(ImtBuNH)或1,3-双(2,6-二异丙基苯基)咪唑啉-2-亚胺(ImDippNH)与MeLi作用生成，合成了咪唑啉-2-亚胺钨烷基炔基络合物[Me3CC≡W(NImR)(OR′)2](4a: R = tBu, R′ = CMe3; 4b: R = Dipp, R′ = CMe3; 5a: R = tBu, R′ = CMe(CF3)2; 5b: R = Dipp, R′ = CMe(CF3)2)。将络合物3与Li[N(tBu)Ar]·OEt2(Ar = 3,5-二甲基苯基)反应，得到了酰胺络合物[Me3CC≡W{N(tBu)Ar}{OCMe(CF3)2}2](6)。将Li[OCPh(CF3)2]加到[Me3CC≡WCl3(dme)](1)中，产生了无dme的络合物[Me3CC≡W{OCPh(CF3)2}3](7)，经Li(NImtBu)处理后，生成了烷基炔基络合物8，推测是通过中间烷基炔基络合物中W≡C键上邻位-C−H键的活化与加成形成的。将1与Li[OC(CF3)3]反应，仅替换了两个氯配体，并形成了顺式-[Me3CC≡WCl{OC(CF3)3}2(dme)](9)，该络合物展示了两个OC(CF3)3配体氟原子之间的长程空间19F−19F偶合。将9与Li(NImtBu)反应，导致了ImtBuN配体的部分断裂和配体重新分布，从而提供了二核钨烷基炔基络合物10。通过将5a与3-己炔处理，获得了丙炔络合物[EtC≡W(NImtBu){OCMe(CF3)2}2](12)，该反应通过金属环丁二烯络合物11进行。络合物5a能够快速催化3-庚炔的烷基炔基交叉偶联反应，生成3-己炔、3-庚炔和4-辛炔的1:2:1的统计混合物。在真空驱动条件下，对5a、5b和6在30和80°C下进行的1-苯基丙炔的催化同分异构化进行了研究。通过单晶X射线衍射确定了络合物2、3、4a、4b、5b、8、9、10和12的分子结构。通过选择2-丁炔的烷基炔基交叉偶联反应作为模型反应，对一系列实验研究和其他烷基炔基络合物进行了使用B3LYP函数的高水平DFT计算。