Synthesis of highly charged organometallic dendrimers and their characterization by electrospray mass spectrometry and single-crystal X-ray diffraction

Four new carbosilane dendrimers terminated with 12, 24, 36, and 72 benzyl groups have been synthesized and characterized by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. These dendrimers were capped with Cp*Ru+ to yield polycations containing charges of 12+, 24+, 36+, and 72+. The charged dendrimers comprise the largest such structures thus far characterized by electrospray ionization (ESI) mass spectrometry. Additionally, for the first time full resolution of individual isotopic distributions has been achieved using ESI FT-ICR techniques, thereby providing unambiguous confirmation of the charges and nuclearities of the dendrimers. The first-generation, ruthenium-containing dendrimer (G1-Ru-12) was also characterized by single-crystal X-ray diffraction. This polycation has a molecular volume significantly larger than any dendrimer thus far characterized by this technique.