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

Complexes cis,trans-[MI(Me)(CO)(2)(PMe3)(2)] (M = Fe la or Ru Ib), in CH2Cl2, reacted with K[(pz)(2)BH2] and Na[(pz)(3)BH] affording the acetyl complexes trans-[M(COMe){(pz)(2)BH2}(CO)(PMe3)(2)] 2a and 2b and trans-[M(CoMe){kappa(2)-(pz)(3)BH} (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){kappa(3)-(pz)(3)BH}(CO)(PMe3)] 4a. The analogous ruthenium complex was formed directly from the tricarbonyl complex fac-[RuI(Me)(CO)(3)(PMe3)] 5 with Na[(pz)(3)BH]. One of the intermediates of the decomposition of a pyrazolyl donor, trans-[Fe(COMe){kappa(2)-(mpz)-OB(C8H14)}(CO)(PMe3)(2)] 6 (mpz = 3-methylpyrazolyl), was isolated from the reaction of 1a with K[(mpz)(2)-B(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).