Didentate phosphine ligands with alkenyl and alkynyl linker units as building blocks for dendrimer fixation

Using diethyl-2-methylmalonate as a starting material, the two diphosphines HCCCH2C(CH3)(CH2PPh2)2 (7) and H2CCHCH2C(CH3)(CH2PPh2)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 [{(CH3)3SiCCCH2C(CH3)(CH2PPh2)2}PdCl2] (8) and [{(CH3)3SiCCCH2C(CH3)(CH2PPh2)2}PtCl2] (9) as well as [{H2CCHCH2C(CH3)(CH2PPh2)2}PdI2] (14b), all of which were characterized by X-ray diffraction. Reaction of Si[(CH2)3SiMe2Cl]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]-[CCCH2C(CH3)(CH2PPh2)2]4 (15) which was converted to the metallated derivative G[0]-[CCCH2C(CH3)(CH2PPh2)2PdCl2]4 (16). Since the fixation of the alkenyl-functionalized diphosphine ligand 13 to the SiH-silane Si[(CH2)3SiMe2H]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, H2CCHCH2C(CH3)(CH2Cl)2 (12) was used. Hydrosilation of G[0]-[H]4 with four molar equivalents of 12 readily gave the functionalized dendrimer G[0]-[CH2CH2CH2C(CH3)(CH2Cl)2]4 (17) which was then reacted with eight equivalents of LiPPh2 to yield the phosphinated derivative G[0]-[CH2CH2CH2C(CH3)(CH2PPh2)2]4 (18).