Synthesis, structure and catalytic application of lead(II) complexes in cyanosilylation reactions

Hydrothermal reactions of a lead(II) salt with 3-aminopyrazine-2-carboxylic acid (HL1) gave rise to a series of lead(II) coordination compounds (1-6) having zero, one, two and three dimensional structures. X-ray diffraction structural analyses reveal that complexes [Pb(L1)(2)](2) (1) and [Pb(L1)(OCHNH2)(eta-OCHO)](2) (2) possess dinuclear structures, containing a centre of symmetry. Complexes [Pb-2(L1)(4)(NHMeCHO)(2)](n) (3) and [Pb-2(L1)(4)](n)center dot(H2O)(n)center dot(2.5DMF)(n) (4) have 1D chain like structures, and [Pb-5(L1)(7)(eta-NO3)(mu-HCOO)(eta-HCOO)](n)center dot(DMF)(n)center dot(MeOH)(n) (5) shows a 2D sheet like structure constructed by the [Pb5O5(HCOO)] cluster and 3-aminopyrazine-2-carboxylate anions. The hydrothermal reaction of lead(II) nitrate with HL1 in DMF led to in situ formation of 3,3'-(methylenebis(azanediyl))bis(pyrazine-2-carboxylic acid) [H(2)L2] which produces the 3D framework [Pb-2(L2)(2)](n)center dot(2DMF)(n)center dot(H2O)(n) (6). The L1(-) and L2(2-) ligands bind the metal cations by means of a pyrazine N-atom and one, or both, carboxylate O-atoms. The carboxylate group of L1(-) presents a diversity of coordination modes, viz., monodentate (1 and 3), bridging mu(2) (3) and bridging mu(3) (4), monodentate bridging mu(2) (1, 2, 4, 5 and 6) and bridging chelate mu(2) (5). The carboxylate moiety of L2(2-) in 6 binds the metal in a bridging mu(2) fashion. The Pb(II) ions display coordination numbers from 5 to 8 with hemi-or holodirected coordination environments. The Pb(II) complexes act as heterogeneous catalysts for the cyanosilylation reaction, at 15 degrees C, of different aldehydes with trimethylsilyl cyanide (TMSCN) and can be recycled at least three times without losing activity.