Synthesis and characterisation of bis- and tris-(pyrazol-1-yl)borate acetyl complexes of FeII and RuII and isolation of an intermediate of B–N bond hydrolysis

Abstract
Complexes cis,trans-[MI(Me)(CO)2(PMe3)2] (M = Fe 1a or Ru 1b), in CH2Cl2, reacted with K[(pz)2BH2] and Na[(pz)3BH] affording the acetyl complexes trans-[M(COMe){(pz)2BH2}(CO)(PMe3)2] 2a and 2b and trans-[M(COMe){κ2-(pz)3BH}(CO)(PMe3)2] 3a and 3b, respectively. If the reactions are carried out in polar solvents decomposition of both starting materials occurs. Upon standing in n-hexane solution, the free pyrazol-1-yl arm in complex 3a displaces a co-ordinated PMe3 forming [Fe(COMe){κ3-(pz)3BH}(CO)(PMe3)] 4a. The analogous ruthenium complex was formed directly from the tricarbonyl complex fac-[RuI(Me)(CO)3(PMe3)] 5 with Na[(pz)3BH]. One of the intermediates of the decomposition of a pyrazolyl donor, trans-[Fe(COMe){κ2-(mpz)OB(C8H14)}(CO)(PMe3)2] 6 (mpz = 3-methylpyrazolyl), was isolated from the reaction of 1a with K[(mpz)2B(C8H14)]. This complex was fully characterised both in solution (IR, multinuclear and multidimensional NMR spectroscopy) and in the solid state (X-ray single-crystal diffraction).

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