Polyborane reactions in ionic liquids

The main objective of my research has been to apply the unique advantages of ionic liquids in polyborane reactions. Ionic liquids have a number of unusual properties that make them attractive substitutes for conventional solvents for organic and inorganic syntheses. By applying the ionic liquid (bmimCl)/toluene biphasic condition, efficient, high yield, one step routes to functionalized o-carboranes by alkyne-decaborane insertion reactions have been developed. This method works for both internal and terminal alkynes, the reaction takes less than 20 min for many alkynes. It works for many functional alkynes which cannot be synthesized by conventional method. Computational studies by Yoon and experimental data for these reactions along with studies of the reactions of B10H13 – salts with alkynes support a reaction sequence involving: (1) the initial ionic liquid promoted formation of the B10H 13– anion; (2) addition of B10H 13– to the alkyne to form an arachno-R,R\u27-C 2B10H13– anion; and (3) protonation of arachno-R,R\u27-C2B10H13 – to form the final neutral 1-R-2-R\u27-1,2-C2B 10H10 product with loss of hydrogen. Studies of the decaborane and arachno-4,6-C2B7H13 reactions with polar alkynes in ionic liquids further supports the initial ionic liquid promoted formation of an anion, same as proposed in the decaborane-alkyne insertion reactions. The ionic liquid based reactions of 4-(Me2S)- arachno-B9H13 with alkynes also lead to insertion and dehydrogenation to 1-Ph-closo-1,2-C2B 8H9, a new compound. In this process, ionic liquids promoted both alkyne-insertion and dehydrogenation. Several new routes to n-B18H22 have been developed, via (1) 4-(Me2S)-arachno-B 9H13 pyrolysis in ionic liquids; (2) metal oxidation of [Me 4N+][B9H12-] assisted by ionic liquids and (3) iodine oxidation of [Me4N+][B 9H12-]. Ionic liquids were also found to promote dehydrogenation processes at lower temperatures, and facilitate arachno-4-CB8H14 to nido-1-CB 8H12 and nido-5,6-C2B8H 12 to closo-1,2-C2B8H10 cage conversions. A dehydrogenation cage condensation reaction of arachno-4,6-C2B7H13 with primary/secondary amineboranes was found to give unique nido-6-(R2N)-5,7-C 2B8H11 compounds containing a B=N double bond. The application of ionic liquid based methods for phosphacarbaborane syntheses provide a new, one step, high-yield route to phosphacarbaboranes, without adding deprotonation reagents. These methods work well for PCl 3 and PhPCl2 insertions into arachno-4,6-C 2B7H13, arachno-CB8H 14, and nido-5,6-C2B8H12 . The initial step in the mechanism is proposed to be similar to that in decaborane dehydrogenative alkyne-insertions in ionic liquids, involving the ionic liquid promoted ionization of the carboranes to form anions. These anions then react via metathesis and elimination reactions with PhPCl 2 and PCl3 leading to insertions. The biphasic conditions also facilitated product separation. These results also show that ionic liquids may have the potential to be applied for even broader areas of polyborane reactions