No abstract

Keywords: Phosphane ligands / Hydrogenation / Catalysis / Dendrimers / Rhodium 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

Using diethyl-2-methylmalonate as a starting material, the two diphosphines HC᎐ ᎐ ᎐ CCH 2 C(CH 3 )(CH 2 PPh 2 ) 2 (7) and H 2 C᎐ ᎐ CHCH 2 C(CH 3 )(CH 2 PPh 2 ) 2 (13), containing alkynyl and alkenyl unit in the ligand backbone were prepared in multistep syntheses. These two ligands were employed in the synthesis of [{(CH 3), all of which were characterized by X-ray diffraction. Reaction of Si[(CH 2 ) 3 SiMe 2 Cl] 4 (= "G[0]-[Cl] 4 ") with four molar equivalents of the in situ lithiated alkynyl diphosphine 7 cleanly yielded the four-fold functionalized derivative G[0]-[C᎐ ᎐ ᎐ CCH 2 C(CH 3 )(CH 2 PPh 2 ) 2 ] 4 (15) which was converted to the metallated derivative G[0]-[C᎐ ᎐ ᎐ CCH 2 -C(CH 3 )(CH 2 PPh 2 ) 2 PdCl 2 ] 4 (16). Since the fixation of the alkenyl-functionalized diphosphine ligand 13 to the SiHsilane Si[(CH 2 ) 3 SiMe 2 H] 4 (= "G[0]-[H] 4 ") by Pt-catalyzed hydrosilation proved to be unsuccessful due to the negative interference of the phosphine with Karstedt's catalyst, the chloro-substituted precursor of 13, H 2 C᎐ ᎐ CHCH 2 C(CH 3 )-(CH 2 Cl) 2 (12) was used. Hydrosilation of G[0]-[H] 4 with four molar equivalents of 12 readily gave the functionalized dendrimer G[0]-[CH 2 CH 2 CH 2 C(CH 3 )(CH 2 Cl) 2 ] 4 (17) which was then reacted with eight equivalents of LiPPh 2 to yield the phosphinated derivative G[0]-[CH 2 CH 2 CH 2 C(CH 3 )(CH 2 PPh 2 ) 2 ] 4 (18). Scheme 1 Synthesis of the alkynyl diphosphine 7 from diethyl-2methylmalonate. DALTON