Divalent Pb(0) compounds

Density functional theory (DFT) calculations have been carried out on four novel dicoordinated lead compounds PbL₂ where L is an N-heterocyclic ylidene or a five-membered cyclic ylidene (1Pb, 2Pb, 4Pb, 5Pb) and for a plumbylene-coordinated carbone CL₂ (3Pb). The theoretically predicted equilibrium geometries and the first and second proton affinities of 1Pb-5Pb are reported. Geometry optimizations have also been carried out for the complexes with one and two BH₃ ligands 1Pb(BH₃)-5Pb(BH₃) and 1Pb(BH₃)₂-5Pb(BH₃)₂, and for the transition metal complexes 1PbW(CO)₅-5PbW(CO)₅ and 1PbNi(CO)₃-5PbNi(CO)₃. The results suggest that the molecules 1Pb, 2Pb and 4Pb possess properties which identify them as divalent Pb(0) compounds (plumbylones). This comes to the fore by the theoretically predicted second PAs which are very large for a lead compound and (for 1Pb and 4Pb) by the BDE of the second BH₃ ligand. Compound 3Pb should be considered as a plumbylene-coordinated divalent C(0) compound (carbone) which has a very high second PA of 195. 1 kcal/mol. The geometry optimization of 5Pb gives an equilibrium structure which identifies the molecules as divalent Pb(II) compound, i. e., as a plumbylene.