New Palladium-Catalyzed Cross-Coupling Routes to Carbon Functionalized Metallatricarbadecaboranes

A general method for the synthesis of cage-carbon-functionalized cyclopentadienyl iron and cyclopentadienyl ruthenium tricarbadecaboranyl complexes has been developed that employs palladium-catalyzed Sonogashira, Heck, and Stille cross-coupling reactions directed at a cage-carbon haloaryl substituent. The key Li+[6-(p-XC6H4)-nido-5,6,9-C3B7H9-] (X = I (1), Br (2), Cl (3)) haloaryl tricarbadecaboranyl anionic ligands were synthesized in high yields via the reaction of the arachno-4,6-C2B7H12- anion with the corresponding p-halobenzonitriles (p-XC6H4-CN). The reactions of the salts 1-3 with (eta(5)-C5H5)Fe(CO)(2)I and (eta(5)-C5H5)Ru(CH3CN)(3)PF6 were then used to produce the haloaryl complexes 1-(eta(5)-C5H5)-2-(p-XC6H4)-closo-1,2,3,4-MC3B7H9 (M = Fe, X = I (4), Dr (5), Cl (6) and M = Ru, X = I (7), Br (8), Cl (9)). The sonication-promoted Sonogashira coupling reactions of 4 with terminal alkynes catalyzed by Pd(dppf)(2)Cl-2/CuI yielded the alkynyl-linked derivatives 1-(eta(5)-C5H5)-2-p-RC6H4-closo-1,2,3,4-FeC3B7H9 (R = (PhC C)- (10), (CH3CH2C(O)OCH2C C)- (11), (eta(5)-C5H5)Fe(eta(5)-C5H4C C))- (12)). Heck reactions of 4 with terminal alkenes catalyzed by Pd(PPh3)(2)Cl-2 yielded the alkene-functionalized products 1-(eta(5)-C5H5)-2-p-RC6H4-closo-1,2,3,4-FeC3B7H9 (R = (PhCH2CH = CH)- (13), (CH3(CH2)(2)CH = CH)- (14)), while the Stille cross-coupling reactions of 4 with organotin compounds catalyzed by Pd(PPh3)(2)Cl-2 afforded the complexes 1-(eta(5)-C5H5)-2-p-RC6H4-closo-1,2,3,4-FeC3B7H9 (R = Ph- (15), (CH2 = CH)- (16), (CH2 = CHCH2)- (17)). These reactions thus provide facile and systematic access to a wide variety of new types of functionalized metallatricarbadecaboranyl complexes with substituents needed for potential metallocene-like biomedical and/or optoelectronic applications.