POP-Pincer Silyl Complexes of Group 9: Rhodium versus Iridium

9,9-Dimethyl-4,5-bis­(diisopropyl­phosphino)­xanthene (xant­(PiPr2)2) derivatives RhCl­{xant­(PiPr2)2} (1) and IrHCl­{xant­(PiPr2)­[iPrPCH­(Me)CH2]} (2) react with diphenylsilane and triethylsilane to give the saturated d6-compounds RhHCl­(SiR3)­{xant­(PiPr2)2} (SiR3 = SiHPh2 (3), SiEt3 (4)) and IrHCl­(SiR3)­{xant­(PiPr2)2} (SiR3 = SiHPh2 (5), SiEt3 (6)). Complexes 3 and 5 undergo a Cl/H position exchange process via the MH­{xant­(PiPr2)2} (M = Rh (8), Ir (E)) intermediates. The rhodium complex 3 affords the square planar d8-silyl derivative Rh­(SiClPh2)­{xant­(PiPr2)2} (7), whereas the iridium derivative 5 gives IrH2(SiClPh2)­{xant­(PiPr2)2} (9), which is stable. In agreement with the formation of 7, the reactions of 8 with silanes are a general method to prepare square planar d8-rhodium-silyl derivatives. Thus, the addition of triethylsilane and triphenylsilane to 8 initially leads to the dihydrides RhH2(SiR3)­{xant­(PiPr2)2} (SiR3 = SiEt3 (10), SiPh3 (11)), which lose molecular hydrogen to afford Rh­(SiR3)­{xant­(PiPr2)2} (SiR3 = SiEt3 (12), SiPh3 (13)). Treatment of 7 with NaBArF4·2H2O leads to the cationic five-coordinate d6-species [RhH­{Si­(OH)­Ph2}­{xant­(PiPr2)2}]­BArF4 (14) through a silylene intermediate. According to the participation of the latter in the formation of 14, this cation is an efficient catalyst precursor for the monoalcoholysis of diphenylsilane with a wide range of alcohols, reaching turnover frequencies at 50% of conversion between 4000 and 76 500 h–1. The X-ray structures of 3, 6, 7, 9, 12, and 14 are also reported.9,9-二甲基-4,5-双(二异丙基膦)呫吨（xant(PiPr2)2）的衍生物RhCl{xant(PiPr2)2}（化合物1）与IrHCl{xant(PiPr2)[iPrPCH(Me)CH2]}（化合物2），可与二苯基硅烷和三乙基硅烷发生反应，生成饱和d6构型配合物RhHCl(SiR3){xant(PiPr2)2}（SiR3=SiHPh2（3）、SiEt3（4））与IrHCl(SiR3){xant(PiPr2)2}（SiR3=SiHPh2（5）、SiEt3（6））。配合物3和5可通过MH{xant(PiPr2)2}（M=Rh（8）、Ir（E））中间体发生氯/氢位置交换过程。其中，铑配合物3生成平面正方形d8构型的硅基衍生物Rh(SiClPh2){xant(PiPr2)2}（7），而铱配合物5则得到稳定的IrH2(SiClPh2){xant(PiPr2)2}（9）。与化合物7的生成规律相符，化合物8与硅烷的反应是制备平面正方形d8构型铑硅基配合物的通用方法。具体而言，向化合物8中加入三乙基硅烷和三苯基硅烷，初始会生成二氢化物RhH2(SiR3){xant(PiPr2)2}（SiR3=SiEt3（10）、SiPh3（11）），该产物经脱分子氢后可得到Rh(SiR3){xant(PiPr2)2}（SiR3=SiEt3（12）、SiPh3（13））。采用NaBArF4·2H2O处理化合物7，可通过硅烯中间体得到阳离子型五配位d6物种[RhH{Si(OH)Ph2}{xant(PiPr2)2}]BArF4（14）。鉴于该硅烯中间体参与了化合物14的生成，该阳离子可作为高效催化前体，用于二苯基硅烷与多种醇的单醇解反应，在转化率达50%时的周转频率可达4000~76500 h–1。本文还报道了化合物3、6、7、9、12和14的X射线晶体结构。