Palladium Complexes of Phosphane-Functionalised Carbosilane Dendrimers as Catalysts in a Continuous-Flow Membrane Reactor

Abstract

Phosphane‐functionalised carbosilane dendrimers 9, 10, 11, 12, 13, 19 and 20 have been synthesised, and their palladium complexes have been used as catalysts in the allylic substitution reaction. The catalytic sites at the periphery of the dendrimer support are readily accessible to the substrate, which is reflected − also for the larger dendrimeric systems − in the high catalytic activity. Moreover, the higher generations are sufficiently large to be retained by a nanofilter, and dendrimeric catalysts 13 and 20 have been applied in a continuous‐flow membrane reactor. The stability of the palladium complexes of the phosphane‐functionalised dendrimers is crucial for application in a continuous process of this type, and appeared to be very sensitive to small changes in the dendrimeric structure. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Design and synthesis of tris[bis(benzylammonium)aryl]phosphines with bulky meta-substituents

“…The mixture was allowed to warm up to room temperature, and was stirred for 16 h. Degassed H 2 O (100 mL) was added and the organic layer was separated. The aqueous layer was extracted twice with CH 2 Cl 2 (2£75 mL), the combined organic fractions were dried over MgSO 4 and evaporated in vacuo, affording crude 2 as a yellow oil. To this oil, THF (100 mL) was added and the solution was cooled to 08C.…”

“…OvP(NCN) 3 (3) and SvP(NCN) 3 (4) were alkylated with MeI in CH 2 Cl 2 at room temperature (Scheme 2). The respective products precipitated from the reaction mixtures as light yellow powders, which could be filtered off.…”

“…Homogeneous catalysts based on dendrimers functionalized with phosphines at the periphery were reported by many authors. 3 Illustrative examples were developed in the groups of Van Leeuwen, 4 Reetz, 5 Togni, 6 and Majoral, 7 as well as in our group. 8 Phosphine ligands of which the phosphorus center is part of the dendrimer backbone, were reported by the groups of Dubois and Kakkar, respectively.…”

Phosphine-functionalized dendrimers for transition-metal catalysis

“…We studied the application of both periphery- [48,49] and core-functionalized dendritic systems [50] in the allylic substitution using continuous and batch processes. The stability of the catalyst appeared to be an important issue, especially with respect to practical applications of these types of immobilized systems (Table 4).…”

Design and Synthesis of Tris[bis(benzylammonium)aryl]phosphines with Bulky meta-Substituents.

“…The crude product was further purified by crystallization from hexane and obtained as colorless crystals (1.21 g, 33%). 3 (4). SvP(NCN) 3 was prepared similarly to the synthesis described above for OvP(NCN) 3 , starting from Br-NCN (1) (4.54 g, 16.75 mmol) and PBr 3 (0.44 mL, 4.68 mmol).…”