Synthesis, Characterization, and Structural Studies of Multimetallic Ferrocenyl Carbene Complexes of Group VII Transition Metals

Fischer carbene complexes of the group VII transition metals (Mn and Re) containing at least two or three different transition metal substituents, all in electronic contact with the carbene carbon atom, were synthesized. The structural features and their relevance to bonding in the carbene multimetal compounds were investigated, as they represent indicators of possible reactivity sites in polymetallic carbene assemblies. For complexes of the type [MLx{C(OR)R′}] (MLx = MnCp(CO)2 or Re2(CO)9), ferrocenyl (Fc) was chosen as the R′ substituent, while the OR substituent was systematically varied between an ethoxy or a titanoxy group, to yield the complexes 1a (MLx = MnCp(CO)2, R = Et, R′ = Fc), 2a (MLx = MnCp(CO)2, R = TiCp2Cl, R′ = Fc), 3a (MLx = Re2(CO)9, R = Et, R′ = Fc), and 4a (MLx = Re2(CO)9, R = TiCp2Cl, R′ = Fc). Direct lithiation of the ferrocene with n-BuLi/TMEDA at elevated temperatures, followed by the Fischer method of carbene preparation, resulted in formation of the novel biscarbene complexes with bridging ferrocen-1,1′-diyl (Fc′) substituents [{π-Fe(C5H4)2-C,C′}{C(OEt)MLx}2] (1b, MLx = MnCp(CO)2; 3b, MLx = Re2(CO)9) or the unusual bimetallacyclic bridged biscarbene complexes [{π-TiCp2O2−O,O′}{π-Fe(C5H4)2-C,C′}{CMLx}2] (2b, MLx = MnCp(CO)2; 4b, MLx = Re2(CO)9). The target compounds that were isolated displayed a variety of different geometric isomers and conformations. The greater reactivity of the binary dirhenium acylates in solution, compared to that of the cyclopentadienyl manganese acylate, resulted in a complex reaction mixture. Although the stabilization of hydroxycarbene or hydrido-acyl intermediates of dirhenium carbonyls could not be achieved, their existence in solution was confirmed by the isolation of [(π-H)2−(Re(CO)4{C(O)Fc})2] (8), the unique dichloro-bridged biscarbene complex fac-[(π-Cl)2-(Re(CO)3{C(OEt)Fc})2] (6), the known hydrido complex [Re3(CO)14H] (5), the acyl complex [Re(CO)5{C(O)Fc}] (7), and the aldehyde-functionalized eq-[Re2(CO)9{C(OTiCp2Cl)(Fc′CHO)}] (9).

本工作合成了第7族过渡金属（锰Mn与铼Re）的费舍尔卡宾配合物（Fischer carbene complexes），该类配合物至少包含两个或三个不同的过渡金属取代基，且所有取代基均与卡宾碳原子存在电子相互作用。针对该类配合物的结构特征及其在多金属卡宾化合物成键机制研究中的关联意义展开了探究——这类配合物可作为多金属卡宾组装体中潜在反应位点的表征指标。对于通式为[MLₓ{C(OR)R′}]的配合物（其中MLₓ为MnCp(CO)₂或Re₂(CO)₉），研究选用二茂铁基（ferrocenyl, Fc）作为R′取代基，并对OR取代基进行系统调控，分别采用乙氧基与钛氧基，最终得到配合物1a（MLₓ = MnCp(CO)₂，R = Et，R′ = Fc）、2a（MLₓ = MnCp(CO)₂，R = TiCp₂Cl，R′ = Fc）、3a（MLₓ = Re₂(CO)₉，R = Et，R′ = Fc）与4a（MLₓ = Re₂(CO)₉，R = TiCp₂Cl，R′ = Fc）。通过在升温条件下用正丁基锂（n-butyllithium, n-BuLi）/四甲基乙二胺（tetramethylethylenediamine, TMEDA）对二茂铁进行直接锂化，再结合费舍尔卡宾制备法，成功制备了以桥联二茂铁-1,1′-二基（bridging ferrocen-1,1′-diyl, Fc′）为取代基的新型双卡宾配合物[{π-Fe(C₅H₄)₂-C,C′}{C(OEt)MLₓ}₂]（1b，MLₓ = MnCp(CO)₂；3b，MLₓ = Re₂(CO)₉），以及非常规的双金属环桥联双卡宾配合物[{π-TiCp₂O₂−O,O′}{π-Fe(C₅H₄)₂-C,C′}{CMLₓ}₂]（2b，MLₓ = MnCp(CO)₂；4b，MLₓ = Re₂(CO)₉）。所分离得到的目标化合物展现出多种不同的几何异构体与构象。相较于环戊二烯基锰酰基配合物，双核铼酰基化合物在溶液中具有更高的反应活性，因此其反应体系更为复杂。尽管未能实现羰基二铼配合物的羟基卡宾或氢酰基中间体的稳定分离，但通过分离得到[(π-H)₂-(Re(CO)₄{C(O)Fc})₂]（8）、独特的二氯桥联双卡宾面式（fac）配合物fac-[(π-Cl)₂-(Re(CO)₃{C(OEt)Fc})₂]（6）、已知氢桥三核铼羰基配合物[Re₃(CO)₁₄H]（5）、酰基配合物[Re(CO)₅{C(O)Fc}]（7）以及醛基官能化的边式（eq）配合物eq-[Re₂(CO)₉{C(OTiCp₂Cl)(Fc′CHO)}]（9），证实了这类中间体在溶液中的存在。