BORON-NITROGEN COMPOUNDS .125. PYRAZOLE COMPLEXES OF 3-COORDINATED BORANES

Both BF3and B(C2H5)3form 1:1 molar complexes with pyrazole (=Hpz) and C-substituted derivatives thereof (=Hpz*). Provided the pyrazole is a relatively strong base, the BF3complexes slowly decompose on prolonged standing at room temperature with the elimination of HF to form the corresponding dimeric 1-pyrazolylboranes = pyrazaboles, e.g., F2B(μ-pz)2BF2. Deprotonation of Hpz-B(C2H5)3with NaH yields the ion [(C2H5)3B(pz)]-, and the salt K[(C2H5)2B(pz)2] is obtained on heating of an equimolar mixture of Hpz B(C2H5)3and Kpz in Hpz. Species of the type K[R2B(pz)2] are also obtained by the reaction of (dimethyl- amino)diorganylboranes, (CH3)2NBR2, with Kpz and Hpz; they were converted to the representative Pd complexes Pd[(μ- pz)2B(C2H5)2]2and R2B(μ-pz)2Pd(π-CH2CHCH2) (R = C2H5, n-C3H7, C6H5), respectively. Interaction of (CH3)2NBR2with 1 molar equiv of Hpz gives 1:1 complexes of the type (CH3)2HN-BR2(pz), which can react with an additional molar equivalent of Hpz at elevated temperatures to form Hpz-BR2(pz) = R2B(pz)2H, or form mixtures of the desired compound with the pyrazabole relative R2B(μ-pz)[μ-N(CH3)2]BR2. Steric factors may prevent the intermediate formation of the 1:1 complexes to lead directly to Hpz-BR2(pz). The complexes Hpz-BR2(pz) can be thermolyzed to yield the pyrazaboles R2B(μ-pz)2BR2. However, whereas the reaction of [(CH3)2NBF2]2with Hpz ultimately yields the pyrazabole F2B(μ-pz)2BF2, the reaction of the cited aminoborane with Hpz and Kpz causes redistribution of fluorine and K[F3B(pz)] is obtained as the only product containing B-F bonds. The complex (pz)2B(C2H5)(H2NCH3) is formed on reaction of the borazine (C2H5BNCH3)3with a large excess of Hpz, and H- (pz)3B(NHCH3) is obtained in analogous fashion originating from the borazine [(CH3)2NBNCH3]3. The reaction of [(C- H3)2NNH]3B with excess of Hpz yields the complex (CH3)2NNH2-B(pz)3. © 1990, American Chemical Society. All rights reserved.