Isolation and Computational Studies of a Series of Terphenyl Substituted Diplumbynes with Ligand Dependent Lead-Lead Multiple-Bonding Character

摘要

A series of formally triply bonded diplumbyne analogues of alkynes of the general formula ArPbPbAr (Ar = terphenyl ligand with different steric properties) was synthesized by two routes. All diplumbyne products were synthesized by a simple reduction of the corresponding Pb(II) halide precursor ArPb(Br) by DIBAL-H with yields in the range 8-48%. For one of the diplumbynes (ArPbPbArPri4)-Pb-Pri4 (Ar-Pri4 = C6H3-2,6-(C6H3-2,6-Pr-2(i))(2)) it was shown that reduction of (ArPb)-Pb-Pri4(Br) using a magnesium(I) beta-diketiminate afforded a much improved yield in comparison (29 vs 8%) to that obtained by reduction with DIBAL-H. The more sterically crowded diplumbyne (ArPbPbArPri8)-Pb-Pri8 (Ar-Pri8= C6H-3,5-Pr-2(i)-2,6-(C6H2-2,4,6-Pr-3(i))(2)) displayed a shortened Pb-Pb bond with a length of 3.0382(5) angstrom and wide Pb-Pb-C angles of 114.73(7)degrees and 116.02(6)degrees consistent with multiple-bond character with a bond order of up to 1.5. The others displayed longer metal-metal distances and narrower Pb-Pb-C angles that were consistent with a lower bond order that approached one. Computational studies of the diplumbynes yielded detailed insight of the unusual bonding and explained their similar electronic spectra arising from the flexibility of the C-Pb-Pb-C core in solution. Furthermore, the importance of London dispersion interactions for the stabilization of the diplumbynes was demonstrated.