Rhodium Complexes Containing a Tridentate Bis(8-quinolyl)methylsilyl Ligand: Synthesis and Reactivity

Synthesis of a series of rhodium complexes bearing a tridentate bis(8-quinolyl)methylsilyl (NSiN)
ligand is reported. Bis(8-quinolyl)methylsilane (1) reacted with (PPh3)3RhCl via oxidative addition at
the Si−H bond to afford (NSiN)Rh(H)Cl(PPh3) (2). Several coordinatively unsaturated, 16-electron
complexes were synthesized, including the cationic complex [(NSiN)Rh(H)(PPh3)][B(C6F5)4] (3) and
the neutral complex (NSiN)Rh(CH2Ph)2 (12). The X-ray structures of 3 and 12 reveal a square-pyramidal
geometry about the Rh center, with the silyl group occupying an apical position. The dicationic complex
[(NSiN)Rh(CH3CN)3][OTf]2 (11), synthesized by reaction of [(NSiN)RhCl2]2 (10) with 2 equiv of AgOTf
in acetonitrile, exhibits moderate activity as a catalyst for alkene hydrogenation and for H/Cl exchange
between Ph3SiH and CH2Cl2. Complex 2 reacts with 2 equiv of PhCH2MgCl in benzene to afford (NSiN)Rh(CH2Ph)Cl(PPh3) (6). Chlorination of 2 by DBU in CH2Cl2 afforded the solvent-activated Rh(III)
product (NSiN)RhCl2(PPh3) (8). Similarly, with PMe3/CH2Cl2 as the chlorinating reagent, [(NSiN)Rh(PMe3)2Cl]Cl (9) was obtained. The low-valent complex (NSiN)Rh(COD) (14; COD = 1,5-cyclooctadiene)
was synthesized via the reaction of 1 with (COD)Rh(η3-CH2Ph) in benzene. The COD ligand was replaced
by the phosphine-based dppe ligand, resulting in the thermally more stable complex (NSiN)Rh(dppe)
(18; dppe = Ph2PCH2CH2PPh2).

本文报道了一系列搭载三齿双(8-喹啉基)甲基硅基（NSiN）配体的铑配合物的合成工作。双(8-喹啉基)甲基硅烷（化合物1）与三苯基膦氯化铑((PPh₃)₃RhCl)通过Si−H键的氧化加成反应，得到配合物(NSiN)Rh(H)Cl(PPh₃)（化合物2）。本研究合成了多种配位不饱和的16电子配合物，包括阳离子配合物[(NSiN)Rh(H)(PPh₃)][B(C₆F₅)₄]（化合物3）与中性配合物(NSiN)Rh(CH₂Ph)₂（化合物12）。X射线晶体结构分析表明，配合物3与12的铑中心呈现四方锥几何构型，硅基配体占据轴向顶点位置。由二聚体[(NSiN)RhCl₂]₂（化合物10）与2当量三氟甲磺酸银（AgOTf）在乙腈中反应制得的二阳离子配合物[(NSiN)Rh(CH₃CN)₃][OTf]₂（化合物11），在烯烃加氢反应以及三苯基硅烷（Ph₃SiH）与二氯甲烷（CH₂Cl₂）之间的氢氯交换反应中展现出中等催化活性。配合物2与2当量苄基氯化镁（PhCH₂MgCl）在苯溶剂中反应，得到配合物(NSiN)Rh(CH₂Ph)Cl(PPh₃)（化合物6）。配合物2在二氯甲烷中经1,8-二氮杂双环[5.4.0]十一碳-7-烯（DBU）氯化，得到溶剂活化的三价铑产物(NSiN)RhCl₂(PPh₃)（化合物8）。同理，以三甲基膦/二氯甲烷（PMe₃/CH₂Cl₂）作为氯化试剂，可得到配合物[(NSiN)Rh(PMe₃)₂Cl]Cl（化合物9）。低价态铑配合物(NSiN)Rh(COD)（化合物14；COD=1,5-环辛二烯）由化合物1与(COD)Rh(η³-苄基)在苯中反应合成。该配合物中的COD配体可被膦基配体dppe取代，得到热稳定性更优的配合物(NSiN)Rh(dppe)（化合物18；dppe=1,2-双(二苯基膦基)乙烷，Ph₂PCH₂CH₂PPh₂）。