Boron-nitrogen compounds. Part 117. Pyrazaboles of the type RR'B(.mu.-pz)2BRR' and related studies

Abstract

Boron-bonded hydrogen or organylthio groups of pyrazaboles, R/sub 2/B(/mu/-pz/sup */)/sub 2/BR/sub 2/ (HPz/sup */ = pyrazole or C-substituted derivatives thereof), can be replaced by reaction with either (C/sub 2/H/sub 5/)/sub 2/O/center dot/BF/sub 3/ or CH/sub 3/OH/center dot/BF/sub 3/ to give the corresponding F/sub 2/B(/mu/-pz/sup */)/sub 2/BF/sub 2/ species. Attempts to replace boron-bonded hydrocarbon groups require much more forcing conditions and usually result in a complete breakdown of the molecule. However, under mild conditions the B-C bond is not attacked and (C/sub 6/H/sub 5/)FB(/mu/-pz)/sub 2/B(C/sub 6/H/sub 5/)F is readily obtained from the reaction of (C/sub 6/H/sub 5/)(C/sub 2/H/sub 5/S)B(/mu/-pz)/sub 2/B(C/sub 6/H/sub 5/)(SC/sub 2/H/sub 5/) with BF/sub 3/. 4,8-Dihalopyrazaboles, RXB(/mu/-ps)/sub 2/BRX, are also obtained from the reaction of dihaloboranes, RBX/sub 2/, with N-(trimethylsilyl)pyrazole, (CH/sub 3/)/sub 3/Si(pz); the halogen of the pyrazabole can be displaced readily be reaction with a Grignard reagent or an alcohol. The compound ((C/sub 2/H/sub 5/)/sub 2/N)(pz)B(/mu/-pz)/sub 2/B(N(C/sub 2/H/sub 5/)/sub 2/)(pz) was also prepared by the cited procedure. The diethylamino group of the latter species is easily displaced by reaction with pyrazole. Several additional pyrazaboles of the type RR'B(/mu/-pz)/sub 2/BBR' have been prepared. (C/sub 6/H/sub 5/)(pz)B(/mu/-pz)/sub 2/B(C/sub 6/H/sub 5/)(pz), which is accessible by various preparative routes, was separated intomore » isomers that exhibit distinctly different /sup 1/H NMR spectra. The mass spectral fragmentations of such (cis and trans) isomers are significantly different with respect to their loss of the first fragments from the parent ions. 18 references, 2 tables.« less