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).