Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Abstract The reaction between thecloso-gallacarborane, 1-(t-C4H9)-1-Ga-2,3-(SiMe3)2-2,3-C2B4H4 (1), and 2,2′-bipyrimidine in a molar ratio of 1∶1 in dry benzene produced the unbridged donor-acceptor complex 1-(2,2′-C8H6N4)-1-(t-C4H9)-1-Ga-2,3-(SiMe3)2-2, 3-C2B4H4 (2) as a pale-yellow crystalline solid in 81% yield. The spectroscopic data of2 are almost identical to those of the bridged species 1,1′-(2,2′-C8 H6N4)-[1-(t-C4H9)-1-Ga-2,3-(SiMe3)2-2,3-C2 B4H4]2 (3). However, the single-crystal X-ray structure of2 reveals that the complex consists of only one distorted gallacarborane unit and a bipyrimidine molecule, that acts as a bidentate ligand. The apical gallium in2 is displaced further away from the centroidal position above the carborane than it is in 1. Despite the steric hindrance imposed by the bulky trimethylsilyl groups on the cage carbons, the Ga-C(t-buty) bond is tilted toward the cage carbon atoms. Complex2 crystallizes in the monoclinic space groupP21 witha=11.279 (3),b=10.060 (3),c=11.911 (3) Å,β=94.94 (2)°,V=1346.5 (6) Å3,Z=2,D x=1.24g cm−3, λ(MoKα) F(000)= 528, andT=220 K. Full-matrix least-squares refinement for2 converged at R=0.036 andRw= 0.045 for 3032 observed reflections. Molecular orbital calculations showed that antibonding interactions between the gallium and carborane cage carbons, induced by base complexation, are a contributing factor to the gallium's slip distortion that is found in2.
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