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)(η-OCHO)]2 (2) possess dinuclear structures, containing a centre of symmetry. Complexes [Pb2(L1)4(NHMeCHO)2]n (3) and [Pb2(L1)4]n·(H2O)n·(2.5DMF)n (4) have 1D chain like structures, and [Pb5(L1)7(η-NO3)(μ-HCOO)(η-HCOO)]n·(DMF)n·(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) [H2L2] which produces the 3D framework [Pb2(L2)2]n·(2DMF)n·(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 μ2 (3) and bridging μ3 (4), monodentate bridging μ2 (1, 2, 4, 5 and 6) and bridging chelate μ2 (5). The carboxylate moiety of L2(2−) in 6 binds the metal in a bridging μ2 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 °C, of different aldehydes with trimethylsilyl cyanide (TMSCN) and can be recycled at least three times without losing activity.
Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001, Lisbon, Portugal. anirbanchem@gmail.com fatima.guedes@tecnico.ulisboa.pt pombeiro@tecnico.ulisboa.pt.
Anirban
A
Karmakar
Susanta
S
Hazra
M Fátima C
MF
Guedes da Silva
Armando J L
AJ
Pombeiro