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 HC=CCH2C(CH3)(CH2PPh2 )2(7) and H2C=CHCH2C(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)(3)SiC=CCH2 (CH3)(CH2PPh2)(2)}PdCl2] (8) and [{(CH3)(3)SiC=CCH2C(CH3)(CH2PPh2)(2)}PtCl2] (9) as well as [{H2C=CHCH2C(CH3)(CH2PPh2)(2)}PdI2] (14b), all of which were characterized by X-ray diffraction. Reaction of Si[(CH2)(3)SiMe2Cl](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=CCH2C(CH3)(CH2PPh2)(2)](4) (15) which was converted to the metallated derivative G[0]-[C=CCH2C(CH3)(CH2PPh2)(2)PdCl2](4) (16). Since the fixation of the alkenyl-functionalized diphosphine ligand 13 to the SiH-silane Si[(CH2)(3)SiMe2H](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, H2C=CHCH2C(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).