1,6-烯炔和1,2-雙(二苯基膦)乙烷釕金屬錯合物的反應性

Abstract

在一般的金屬乙炔基錯合物反應中，中性的金屬乙炔基錯合物和親電子基作用，親電子基會攻擊乙炔基錯合物的beta碳，而得到陽離子金屬亞乙烯基錯合。本實驗針對一系列釕金屬乙炔基錯合物Cp(dppe)Ru-C≡CCH(OMe)C(R1)(R2)CH2C(R3)=C(R4)(R5) (4a, R1 = Ph, R2 = Ph, R3 = H, R4 = H, R5 = H; 4b, R1 = Ph, R2 = CH3, R3 = H, R4 = H, R5 = H; 4d, R1 = Ph, R2 = Ph, R3 = H, R4 = CH3, R5 = CH3)進行研究，此乙炔基另一端含有雙鍵，其雙鍵上或者無其他取代基或者是接有兩個甲基取代。實驗發現其和親電子基的反應與一般的金屬乙炔基錯合物不同，其具有獨特的反應性。此類釕金屬乙炔基錯合物於0oC的乙醚中與含水氟硼酸反應得到alpha碳上加成羥基之碳烯釕金屬錯合物[Cp(dppe)Ru=C(OH)CH=CHC(R1)(R2)CH2C(R3)=C(R4)(R5)][BF4] (5a, R1 = Ph, R2 = Ph, R3 = H, R4 = H, R5 = H; 5b, R1 = Ph, R2 = CH3, R3 = H, R4 = H, R5 = H; 5d, R1 = Ph, R2 = Ph, R3 = H, R4 = CH3, R5 = CH3)。透過1H-NMR、31P-NMR和X-ray的鑑定發現，乙炔基錯合物會先進行質子化反應得到釕金屬亞乙烯基錯合物，接著脫去甲醇分子，形成釕金屬亞丙二烯基錯合物中間物，再與氟硼酸中少量的水反應，使羥基加成在乙炔基錯合物的alpha碳上，產生含羥基之碳烯錯合物5a、5b及5d。 另外，雙鍵含有兩個甲基取代之釕金屬乙炔基錯合物4d，具有新穎的反應性。錯合物4d溶解於氘取代之三氯甲烷時，室溫下通入氧氣，氧分子很容易與4d 作用，幾乎完全反應產生中性釕金屬醯基錯合物8和丙酮分子。經由1H-NMR、31P-NMR、13C-NMR及X-ray的鑑定結果，推測可能的反應機構應為錯合物4d的1,6-烯炔與氧氣作用形成六圓環的中間物A，兩個氧原子分別加成在原本1,6-烯炔的頭尾，而形成丙酮及釕金屬醯基錯合物8。 大部分氧氣加成反應中，氧分子必須先進行光激發至單重態才能加成，再加熱分解。然而在本研究中，利用釕金屬乙炔基錯合物與氧氣環化，不需要以光激發氧氣分子，在黑暗中即可進行加成反應。相較於傳統的氧氣加成反應，錯合物4d僅需在溫和的條件下，數分鐘內就可以完全反應，得到氧氣加成的產物。

A series of ruthenium acetylide complexes Cp(dppe)Ru-C≡CCH(OMe)C(R1)(R2)CH2C(R3)=C(R4)(R5) (4a, R1 = Ph, R2 = Ph, R3 = H, R4 = H, R5 = H; 4b, R1 = Ph, R2 = CH3, R3 = H, R4 = H, R5 = H; 4d, R1 = Ph, R2 = Ph, R3 = H, R4 = CH3, R5 = CH3) containing pendant olefinic group, which has either none or with various substituted methyl groups, were prepared. Interestingly, these acetylide complexes display novel reactivity. Treatment of the acetylide complexes 4a, 4b and 4d with HBF4 in ether/H2O at 0oC, caused surprising transformation. Protonation of 4a, 4b and 4d generated the hydroxycarbene complexes 5a, 5b and 5d [Cp(dppe)Ru=C(OH)CH=CHC(R1)(R2)CH2C(R3)=C(R4)(R5)][BF4] (5a, R1 = Ph, R2 = Ph, R3 = H, R4 = H, R5 = H; 5b, R1 = Ph, R2 = CH3, R3 = H, R4 = H, R5 = H; 5d, R1 = Ph, R2 = Ph, R3 = H, R4 = CH3, R5 = CH3), respectively. It seems that the acetylide alpha-carbon atom was attacked by a hydroxyl group. Possibly the vinylidene complex eliminates MeOH, and the presence of H2O brings about the attack of the hydroxyl group at alpha-carbon to give the hydroxycarbene complexes 5a, 5b and 5d. Astonishingly, with the presence of two methyl groups at the terminal carbon of the tethering allyl group, the ruthenium acetylide complex 4d displays novel reactivity. Oxygen molecule readily reacts with 4d to yield the neutral acyl ruthenium complex 8 and acetone. When oxygen was gently bubbled through a CDCl3 solution of the acetylide complex 4d at room temperature, the terminal three-carbon-unit in 4d was smoothly cleaved and the acyl complex 5d was formed in almost quantitative yield. A C–C bond formation between beta-carbon and the internal carbon of the allylic group gives an intermediate A. The intermediate, then, isomerizes to give the acyl product, which is accompanied with elimination of acetone. Previously, photo activation of oxygen to singlet state was required in most oxygen addition reactions, which were commonly followed by a thermal decomposition. However, in our enyne case, no photoexcitation of oxygen is required. This reaction of oxygen with the 1,6-enyne ligand in 4d was achieved under mild condition in less than 10 min.