Tripodal Phosphane Ligands with Novel Linker Units and Their Rhodium Complexes as Building Blocks for Dendrimer Catalysts

An efficient strategy for the backbone functionalization of a tripodal phosphane ligand which allows its attachment to solid supports and polymers has been developed. Using pentaerythrol ( 1 ) as the starting material, the functionalized phosphane tripod HOCH 2 CH 2 OCH 2 C(CH 2 PPh 2 ) 3 ( 9 ) was obtained in good yield in a four‐step synthesis. Reaction of 9 with [Mo(CO) 3 (MeCN) 3 ] and [Rh(COD) 2 ][A] gave the complexes [{HOCH 2 CH 2 OCH 2 C(CH 2 PPh 2 ) 3 }Mo(CO) 3 ] ( 10 ) and [{HOCH 2 CH 2 OCH 2 C(CH 2 PPh 2 ) 3 }Rh(COD)][A] (A = BF 4 : 11a , PF 6 : 11b ), respectively, two of which were characterised by X‐ray diffraction. The carbosilane dendrimer Si{(CH 2 ) 3 SiMe 2 Cl} 4 “G[0]‐[Cl] 4 ” ( 12 ) and its first generation analogue Si[(CH 2 ) 3 SiMe{(CH 2 ) 3 SiMe 2 Cl} 2 ] 4 “G[1]‐[Cl] 8 ” ( 15 ) were reacted with, respectively, four and eight molar equivalents of the lithium alkoxy derivative of 9 giving the two functionalized dendrimers G[0]‐[OCH 2 CH 2 Otriphos] 4 ( 13 ) and G[1]‐[OCH 2 CH 2 Otriphos] 8 ( 16 ). These were metallated with four and eight molar equivalents of [Rh(COD) 2 ][BF 4 ] in CH 2 Cl 2 , selectively yielding the metallated dendrimers G[0][OCH 2 CH 2 OtriphosRh(COD)BF 4 ] 4 ( 14 ) and G[1]‐[OCH 2 CH 2 OtriphosRh(COD)BF 4 ] 8 ( 17 ). Comparative catalytic hydrogenation of styrene and 1‐hexene using [Rh(triphos)(COD)][BF 4 ] ( 11a) and the metallodendrimers 14 and 17 showed that the fixation to the low generation dendrimers did not alter the catalytic hydrogenation properties of the catalysts. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)