Synthesis of Globular Precursors

Abstract

o-Carborane (C2 B10 H12 ) was adapted to perform as the core of globular macromolecules, dendrons or dendrimers. To meet this objective, precisely defined substitution patterns of terminal olefin groups on the carborane framework were subjected to Heck cross-coupling reactions or hydroboration leading to hydroxyl terminated arms. These led to new terminal groups (chloro, bromo, and tosyl leaving groups, organic acid, and azide) that permitted ester production, click chemistry, and oxonium ring opening to be performed as examples of reactions that demonstrate the wide possibilities of the globular icosahedral carboranes to produce new dendritic or dendrimer-like structures. Polyanionic species were obtained in high yield through the ring-opening reaction of cyclic oxonium compound [3,3'-Co(8-C4 H8 O2 -1,2-C2 B9 H10 )(1',2'-C2 B9 H11 )] by using terminal hydroxyl groups as nucleophiles. These new polyanionic compounds that contain multiple metallacarborane clusters at their periphery may prove useful as new classes of compounds for boron neutron capture therapy with enhanced water solubility and as cores to make a new class of high-boron globular macromolecules.

m-Carborane as a Novel Core for Periphery-Decorated Macromolecules

“…Table 3 shows a downfield shift (∆δ = +10.1 ppm) of the B(9,10) resonances of 9,10-(allyl) 2 -1,7-closo-C 2 B 10 H 10 (3) vs the corresponding B(9,10)-H ones in the parent m-carborane. A similar downfield (∆δ = +10.6 ppm) is reported for the B(9,12) vertexes of 9,12-(allyl) 2 -1,2-closo-C 2 B 10 H 10 with respect to the B(9,12)-H vertexes of the parent o-carborane [14]. The 11 B{ 1 H} NMR spectrum provides information on the electron density surrounding B atoms in the cluster vertexes, so it can be concluded that the effect of a B-allyl vertex concerning to the former B-H in the 11 B{ 1 H} NMR of both isomers is almost the same, ∆δ +10.6 ppm and +10.1 ppm, for oand m-, respectively.…”

“…Therefore, di-branched m -carborane derivatives ( Scheme 2 ) with precise patterns of substitution are prepared by judicious choice of the synthetic procedure using similar conditions to the preparation of o -carborane derivatives present in previous work [ 14 ].…”

“…Compound 8 was obtained in 81% yield by avigorous stirring of 5, with excess of NaN3 and [Nbu4]Cl in a mixture of toluene and water, at reflux for 24-48 h. An example of the click reaction on 8 was the compound 9 synthesis in 86% yield by simple reaction with phenylaceylene, sodium ascorbate, and hydrated CuSO4 as a catalyst in a mixture of dioxane/water. Therefore, di-branched m-carborane derivatives (Scheme 2) with precise patterns of substitution are prepared by judicious choice of the synthetic procedure using similar conditions to the preparation of o-carborane derivatives present in previous work [14].…”

“…This procedure does not proceed equally for all B-Hs, for instance, at the B (3,6) vertices, which are the most electron-deficient vertexes, their functionalization does not take place by using the same process at the other cluster's vertices [8,11]. Substitution on these positions can be achieved via the deboration-capping multistep reaction or via the metallation procedure [11-13. The diverse regioreactivity of o-carborane, has been exploited and adapted to make o-carborane an exceptional core for developing a large variety of multibranched molecules, globular macromolecules, dendrimers (Figure 2b), and so on [14][15][16][17][18]. Moreover, new versatile synthons have been explored through the multi-functionalization of B and Cc atoms jointly, which make the ocarborane clusters an exciting platform for new materials [6,8,[18][19][20][21][22][23][24][25].…”

“…Substitution on these positions can be achieved via the deboration-capping multistep reaction or via the metallation procedure [ 11 , 12 , 13 ]. The diverse regioreactivity of o -carborane, has been exploited and adapted to make o -carborane an exceptional core for developing a large variety of multibranched molecules, globular macromolecules, dendrimers ( Figure 2 b), and so on [ 14 , 15 , 16 , 17 , 18 ]. Moreover, new versatile synthons have been explored through the multi-functionalization of B and C c atoms jointly, which make the o -carborane clusters an exciting platform for new materials [ 6 , 8 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ].…”