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

Abstract

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 Ar Pri 4 PbPbAr Pri 4 (Ar Pri 4 = C 6 H 3 -2,6-(C 6 H 3 -2,6-Pr i 2 ) 2 ) it was shown that reduction of Ar Pri 4 Pb(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 Ar Pri 8 PbPbAr Pri 8 (Ar Pri 8 = C 6 H-3,5-Pr i 2 -2,6-(C 6 H 2 -2,4,6-Pr i 3 ) 2 ) displayed a shortened Pb−Pb bond with a length of 3.0382(5) Å and wide Pb−Pb−C angles of 114.73(7)°and 116.02( 6)°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.

Bonding Relationship between Silicon and Germanium with Group 13 and Heavier Elements of Groups 14–16

“…After this discovery, several research groups independently reported the synthesis of phosphasilenes depicted in Figure 5 (96)(97)(98)(99)(100). [72b-f,73] Recently, Scheschkewitz et al [74a] synthesized cyclic phosphasilene by the reaction of disilenide (101) with NHC-stabilized P(I) cation (102) (1 : 1 ratio) led to the formation of donorstabilized cyclic phosphasilene (103, Scheme 35).…”

“…Recently, Grimme, Power and co‐workers isolated a formally triple bonded terphenyl substituted diplumbyne analogue of alkynes by a simple reduction of the corresponding Pb(II) halide precursor by DIBAL−H [102] . The sterically crowded diplumbyne Ar Pri8 PbPbAr Pri8 (Ar Pri8 =C 6 H‐3,5‐Pr i 2 ‐2,6‐(C 6 H 2 ‐2,4,6‐Pr i 3 ) 2 ) displayed the shortest Pb−Pb bond with a length of 3.0382(5) Å and wide Pb−Pb−C angles of 114.73(7)° and 116.02(6)°, consistent with the multiple‐bond character, with a bond order up to 1.5.…”

Main Group Multiple Bonds for Bond Activations and Catalysis

“…Recent studies by Power and co‐workers showed the reversibility of distannyne–stannylene in toluene solutions [111] as well as the reversibility of dihydrogen activation by distannynes [112] . Despite diplumbylenes being the first example of a heavier E 14 –E 14 triple bond, it was only recently that further examples emerged [113] . A combined experimental and theoretical study found that London dispersion forces [31] were important in the stabilisation of diplumbylenes.…”

“…Those which are less trans ‐bent contain increased multiple bond character compared with their more trans ‐bent counterparts (i.e. closer to 90°) [113] …”

“…[112] Despite diplumbylenes being the first example of aheavier E 14 -E 14 triple bond, it was only recentlyt hat further examples emerged. [113] Ac ombined experimentala nd theoretical study found that London dispersion forces [31] were important in the stabilisation of diplumbylenes. Those which are less trans-bent contain increased multiple bond character compared with their more trans-bent counterparts (i.e.…”