Fluoride Reactions with Hydrotris(pyrazolyl)borate Rhenium Oxo Complexes: Re−F vs B−F Bond Formation

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Abstract
Rhenium−oxo−fluoride complexes are readily prepared using hydrotris(3,5-dimethyl-1-pyrazolyl)borate [HB(3,5-Me2pz)3-, Tp*] as a supporting ligand. For instance, treatment of Tp*Re(O)(OH)Cl with concentrated aqueous HF cleanly forms the chloro−fluoride complex Tp*Re(O)(F)Cl. Related fluoro−iodide, fluoro−triflate, and difluoride complexes are also described. In contrast, a variety of reactions of analogous compounds with the unsubstituted hydrotris(1-pyrazolyl)borate ligand [HB(pz)3-, Tp] have failed to produce fluoro complexes. Extended refluxing of TpRe(O)I2 with an excess of NaF in acetonitrile in the air gives a modest yield of an unusual rhenium μ-pyrazolyl μ-oxo dimer, {[κ2-H(F)Bpz2]Re(O)}2(μ-pz)2(μ-O) (5) (pz = pyrazolyl). The X-ray crystal structure of 5 shows that one pyrazolyl of each Tp ligand has been substituted for fluoride. The different reactivity of the Tp and Tp* complexes is apparently due to the greater steric protection of the boron afforded by the Tp* ligand. Crystallographic data for 5: monoclinic; space group Cc; a = 19.103(4) Å, b = 10.482(2) Å, c = 14.240(3) Å, β = 114.82(3)°; Z = 4; R = 3.73%, Rw (observed data) = 4.73%; GOF = 1.20.