FUNCTIONALIZED ETHER DERIVATIVES OF HOCH2C(CH2PPH2)(3) AND RELATED TRIPOD LIGANDS - SYNTHESIS AND COORDINATION CHEMISTRY

Neopentane-derived tripod ligands of the general type HOCH2C(CH2PPh2)( CH2Y)(CH(2)Z) (1; Y, Z = PPh2, SR) are notoriously resistant to ether formation at their hydroxy group. Two routes have been found, which al low the transformation of 1 into ether functionalized tripod ligands R OCH2C(CH2PPh2)(CH2Y)(CH(2)Z) (Y = Z = PPh2: 5, Y = Z = SR: 8). One of these strategies relies upon the eta 3 coordination of 1 in 1 . Mo(CO) (3) (2). By this way the donor groups are efficiently protected and th e steric encumbrance of the CH2OH group at the backbone of the ligands is greatly reduced by fixing three arms of the neopentane scaffolding to the metal center. After deprotonation, reaction with electrophiles will produce the corresponding ether derivatives ROCH2C(CH2PPh2) (CH( 2)Z)(2) (3). Mesylation of 2 leads to MeSO2OCH2C(CH2PPh2)(3). Mo(CO)(3 ) (4), which reacts with alkoxides to produce 3 in a sequence of rever sed polarity. Ligands 5 [ROCH2C(CH2PPh2)(3)] are liberated from 3 by U V irridation of their solutions in the presence of pyridine N-oxide. D irect etherification of 1 is also possible in some cases after deproto nation of 1 by KOtBu and subsequent reaction with an electrophile RX i n the narrow temperature range between -10 and +20 degrees C. By this way, omega-methyl polyglycol ether functions are easily introduced res ulting in H3C(OC2H4)(n)OCH2C(CH2PPh2)(3) (5g, h).