雙鉬五重鍵與腈類之碳-氫鍵活化反應及與炔、腈之三元[2+2+2]環化加成反應研究

Reactions of Mo-Mo Quintuple Bond with Alkynes and Nitriles: C-H Bond Activation and Three-component [2+2+2] Cycloaddition

簡彥庭(Chien, Yen Ting)

指導教授 ： 蔡易州

國立清華大學/理學院/化學系/碩士(2016年)

摘要

本論文的目的為探討具雙氮基眯配基的雙鉬五重鍵錯合物Mo2[μ-η2-HC(N-2,6-iPr2C6H3)2]2 (1)與各種腈類及炔類的反應，找出能成功進行三元[2+2+2]環化加成反應的條件，同時探討其選擇性及可能反應機制。
當錯合物1與兩當量的異丙腈、環己腈或三級丁腈反應時，皆進行分子內碳-氫鍵活化反應，並非合環反應，分離得到的產物為 [κ1-NC-R]2Mo2(H)
[μ-κ2-HC(N-2,6-iPr2C6H3)(N-2-iPr-6-CH(κ1-CH2)CH3-C6H3)][μ-κ2-HC(N-2,6-iPr2C6H3)2] (R = iPr (2), Cy (3), tBu (4))；而當錯合物1與三當量的乙腈反應時，分離得到的產物為[μ-κ1:η2-CH2CN][μ-κ2-NC(CH3)C(CH3)N]Mo2(H)[μ-κ2-HC(N-2,6- iPr2C6H3)2]2 (6)，除了進行少見的腈類頭對尾[2+2+2]環化加成反應之外，還有另一當量的乙腈以特殊形式與鉬金屬進行配位，由上可知，立體阻礙是錯合物1與兩當量腈類反應後能否進行[2+2+2]環化加成反應的重要因素；接著將錯合物6與苯乙炔反應，可以成功置換配位的乙腈而得到[κ1-CCPh][μ-κ2-NC(CH3)C(CH3)N]Mo2(H)[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (7)；接著嘗試將錯合物1與立障較大兩當量三甲基氰矽烷反應，分離得到的產物為[κ1-NC-TMS][κ1-NC]Mo2[μ-κ2-HC(N-2,6-iPr2C6H3)(N-2-iPr-6-CH(κ1-CH2)CH3-C6H3)][μ-κ2-HC(N-2,6-iPr2C6H3)2] (8)，有趣的是除了進行分子內碳-氫鍵活化，還可觀察到腈類碳、氮原子的反轉；而後將錯合物1與兩當量氰乙酸甲酯反應，並非進行碳-氫鍵活化，分離得到的產物為Mo2{μ-η2:η2-N(H)C[CHC(OMe)]O}2[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (9)，是一常見的腈類與雙核金屬鍵結及配位的形式。
當錯合物1、內炔與末端炔類反應時，會進行[2+2+2]環化加成反應。錯合物1與3-己炔先進行[2+2]環化加成反應，得到四員環C2Mo2錯合物Mo2(μ-η2-EtCCEt)[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (10)。接著，錯合物10與苯乙炔、丙炔酸乙酯或1-戊炔反應，皆作[4+2]環化加成反應得到六員環C4Mo2碳-碳耦合錯合物Mo2[μ-κ2-5,6-Et2-3-RC4H][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = Ph (11), COOEt (12), Pr (13))；當錯合物Mo2(μ-κ2-MeCCPh)[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (14)與三甲基矽乙炔、對氟苯基乙炔、對甲氧基苯基乙炔、環丙基乙炔、環己基乙炔或3-乙炔噻吩反應時，一樣會進行[4+2]環化加成反應，但會得到兩種六員環結構異構物Mo2[μ-κ2-6-Me-5-Ph-3-RC4H][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = TMS (15), 4-FPh (18), 4-MeOPh (20), 2-thiophene (24))以及Mo2[μ-κ2-6-R-4-Me-3-PhC4H][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = TMS (16), 4-FPh (17), 4-MeOPh (19), cyclopropyl (21), cyclohexyl (22), 2-thiophene (23))。由錯合物11-13可以得知，末端炔類加成之位向受立體阻礙的影響，而從錯合物15-24可以得知，內炔加成之位向與末端炔類的電子效應有關。簡而言之，錯合物1、內炔與末端炔類[2+2+2]環化加成反應中，內炔的位向受電子效應影響，末端炔的位向受立體效應影響。而當錯合物14及錯合物Mo2(μ-κ2-PhCCPh)[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (25)分別與1,6-庚二炔反應，也會進行合環反應，可以得到四核雙六員環錯合物{Mo2[μ-κ2-HC(N-2,6-iPr2C6H3)2](μ-κ2-4-Ph-3-PhC4H)}2-6-(CH2)3 (R = Ph (26), Me (27))。
當錯合物1、內炔與特定腈類反應時，也能成功進行三元[2+2+2]環化加成反應。錯合物10與一當量丙腈及乙腈反應，可以進行[4+2]環化加成反應且得到類似吡啶(pyridine)結構的六員環錯合物Mo2[μ-κ2-NC(R)C(Et)C(Et)][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = Et (30), Me (31))；而錯合物14與一當量丙腈或苯乙腈反應，同樣可以進行合環反應，得到六員環錯合物Mo2[μ-κ2-NC(R)C(Ph)C(Me)][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = Et (33), CH2Ph (35))。由以上結果可以得知，腈類本身的電子效應讓六員環產物有單一的選擇性。錯合物10及14分別與兩當量乙腈反應，可以得到類似錯合物6的結構[μ-κ1:η2-CH2CN][μ-κ2-NC(Me)C(R1)C(R2)]Mo2(H) [μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R1 = R2 = Et (32), R1 = Ph, R2 = Me (34))，除了進行三元[2+2+2]合環反應之外，第三當量的乙腈在另一側以特殊形式與鉬金屬進行配位。

關鍵字

三元環化加成 ； 鉬 ； 腈炔類

並列摘要

The goals of this thesis are to study the reactions of the quintuply bonded dimolybdenum complex, Mo2[μ-η2-HC(N-2,6-iPr2C6H3)2]2 (1), with various nitriles and alkynes, from which [2+2+2] cycloaddition involving the Mo-Mo quintuple bond with interesting selectivity is found and possible mechanisms are discussed herein.
When 1 reacts with two equivalents of isobutyronitrile, cyclohexanecarbonitrile, or pivalonitrile, intramolecular C-H bond activation is observed and [κ1-NC-R]2Mo2(H)[μ-κ2-HC(N-2,6-iPr2C6H3)(N-2-iPr-6-CH(κ1-CH2)CH3-C6H3)][μ-κ2-HC(N-2,6-iPr2C6H3)2] (R = iPr (2), Cy (3), tBu (4)) are isolated. In contrast, when 1 reacts with three equivalents of acetonitrile, [2+2+2] cycloaddition involving the Mo-Mo quintuple bond leads to the isolation of the cycloadduct [μ-κ1:η1-CH2CN][μ-κ2-NC(CH3)C(CH3)N]Mo2(H)[μ-κ2-HC(N-2,6- iPr2C6H3)2]2 (6). Not only does it generate an unusual head-to-tail [2+2+2] cycloaddtion, but also one molecule of acetonitrile coordinates to the Mo2 unit by an unprecedented coordination mode. Presumably, steric hindrance of alkyl nitriles is the main factor determining whether two equivalents of nitriles will undergo [2+2+2] cycloaddition with 1. Upon treatment with phenylacetylene, the CH2CN ligand of 6 is replaced “PhCC” to give [κ1-CCPh][μ-κ2-NC(CH3)C(CH3)N]Mo2(H)[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (7). Furthermore, reacting 1 with two equivalents of trimethylsilylformonitrile, we isolate [κ1-NC-TMS][κ1-NC]Mo2[μ-κ2-HC(N-2,6-iPr2C6H3)(N-2-iPr-6-CH(κ1-CH2)
CH3-C6H3)][μ-κ2-HC(N-2,6-iPr2C6H3)2] (8), which not only shows intramolecular C-H bond activation, but also a swap of carbon and nitrogen atoms of the nitrile is observed. On the other hand, reaction of 1 with two equivalents of methyl-cyanoacetate leads to the isolation of the complex Mo2{μ-η2:η2-N(H)C[CHC(OMe)]O}2[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (9), which doesn’t undergo intramolecualr C-H bond activation, but a common coordination mode of nitrile to metal is observed.
The reactions of 1 with internal and terminal alkynes lead to [2+2+2] cycloaddition. First, 1 undergoes a [2+2] cycloaddition reaction with one equivalent of 3-hexyne to give the four-membered ring complex Mo2(μ-η2-EtCCEt)[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (10). When 10 subsequently reacts with phenylacetylene, ethyl propiolate, or 1-pentyne, [4+2] six-membered ring complexes, Mo2[μ-κ2-5,6-Et2-3-RC4H][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = Ph (11), COOEt (12), Pr (13)), are isolated. When Mo2(μ-κ2-MeCCPh)[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (14) reacts with trimethylsilylacetylene, 4-fluorophenylacetylene, 4-methoxyphenylacetylene, cyclopropylacetylene, cyclohexylacetylene, or 3-ethynylthiophene, [4+2] cycloaddition products can also be isolated along with their stereoisomers, Mo2[μ-κ2-6-Me-5-Ph-3-RC4H][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = TMS (15), 4-FPh (18), 4-MeOPh (20), 2-thiophene(24)) and Mo2[μ-κ2-6-R-4-Me-3-PhC4H][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = TMS (16), 4-FPh (17), 4-MeOPh (19), cyclopropyl (21), cyclohexyl (22), 2-thiophene (23)). The characterization of 11-13 suggests that the stereo orientation of terminal alkynes be affected by their steric hindrance. In contrast, the characterization of 15-24 shows that the stereo orientation of internal alkynes is controlled by electronic effect. In short, the electronic effect controls the stereo orientation of the first alkyne molecule and the steric effect controls the stereo orientation of the second one. Notably, when 14 or Mo2(μ-κ2-PhCCPh)[μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (25) reacts with 1,6-heptadiyne, the [4+2] cycloaddition and the dimeric complexes {Mo2[μ-κ2-HC(N-2,6-iPr2C6H3)2](μ-κ2-4-Ph-3-PhC4H)}2-6-(CH2)3 (R = Ph (26), Me (27)) are isolated.
It is worthy noting that reactions of 10 and internal alkynes and small nitrile result in three-component [2+2+2] cycloaddition as well. When 10 reacts with one equivalent of propionitrile or acetonitrile, [4+2] cycloaddition can be achieved and the pyridine-liked six-membered ring complexes Mo2[μ-κ2-NC(R)C(Et)C(Et)][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = Et (30), Me (31)) can be obtained. Likewise, reactions of 14 with one equivalent of propionitrile and benzyacetionitrile gives the [4+2] cycloaddition products, Mo2[μ-κ2-NC(R)C(Ph)C(Me)][μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R = Et (33), CH2Ph (35)). On the basis of the results above, we know that the electronic effect of nitriles dominates the high selectivity of the cycoaddition reactions. Finally, when 10 and 14 respectively react with two equivalents of acetonitrile, the cycloadducts [μ-κ1:η2-CH2CN][μ-κ2-NC(Me)C(R1)C(R2)]Mo2(H) [μ-κ2-HC(N-2,6-iPr2C6H3)2]2 (R1 = R2 = Et (32), R1 = Ph, R2 = Me (34)) are isolated, which are similar to 6.

並列關鍵字

[2+2+2] cycloaddition ； three-component

參考文獻

1. Smaglik, P., Nature 2000, 406, 807.

5. Domínguez, G.; Pérez-Castells, J. Chem. Soc. Rev. 2011, 40, 3430−3444.

6. Varela, J. A.; Saá, C. Chem. Rev. 2003, 103, 3787−3801.

7. Cotton, F. A.; Curtis, N. F.; Harris, C. B.; Johnson, B. F. G.; Lippard, S. J.; Mague, J. T.; Robinson, W. R.; Wood, J. S., Science 1964, 145, 1305.

8. Cotton, F. A.; Lippard, S. J., J. Am. Chem. Soc. 1964, 86, 4497.