On mixed group 14-group 14 bonds. 8. Asymmetrically substituted compounds Ar3Pb-GeAr′3 and Ar3Pb-PbAr′3: Comparison of structure and physical behavior in the series of bonds Sn-Sn, Pb-Ge, Pb-Sn, and Pb-Pb

Article abstract of DOI:10.1021/om00019a033

A general procedure for the synthesis of hezaarylated compounds of the type Ar₃PbGeAr′₃ from Ar₃PbLi and Ar′₃GeX in THF/ether at -60°C is given. Likewise, from Ar₃PbLi and Ar′PbI the asymmetrical diplumbanes Ar₃PbPbAr′₃ could be prepared. By the use of the bulky groups Ar and Ar′, the migration of aryl groups could be suppressed, avoiding the appearance of the mixtures Pb₂Ar_6-nAr′_n (n = 0-6). Nonetheless, the resulting diplumbanes Ar₃Pb-PbAr′₃ were always partially contaminated with some symmetric Pb₂Ar₆ and Pb₂Ar′₆. The structures of (p-Tol)₃PbGePh₈ (triclinic, space group P1; a = 9.983(1) b = 12.201(1) c = 15.728(2) A?; α = 95.73(1), β = 103.56(1), γ = 113.06(1)°; V = 1674(1) A?³; Z = 2; R = 0.0434) and (p-Tol)₃PbGe-(p-Tol)₃ (trigonal, space group R3; a - 13.338(1), c = 36.55(1) A?; V = 5631(2) A?³; Z = 6; R = 0.0522) have been determined. NMR chemical shifts δ(¹¹⁹Sn) and δ(²⁰⁷Pb) (40 compounds) and one-bond couplings ¹J(M-M′) (16 compounds), stretching vibrations ν(M-M′) and force constants f(M-M′) for a diatomic oscillator (38 compounds), and bond distances d(M-M′) (18 compounds) are compared for all six combinations M/M′ = Ge/Sn/Pb of Ar₃M-M′Ar′₃. Concerning the asymmetric diplumbanes Ar₃Pb-PbAr′₃, assignments of δ(²⁰⁷Pb) resulted from a consideration of inductivity (comparison to PbAr₄/Ar′₄) and an assumed order of charge flow Δ(Ar ? Ar′) (13 compounds). Sequences exist for δ(¹¹⁹Sn) (Pb-Sn > Sn-Sn ≥ Sn-Ge), δ(²⁰⁷Pb) (Pb-Pb > Pb-Sn ≈ Pb-Ge), f (Sn-Ge > Sn-Sn ≥ Pb-Sn, and Pb-Ge > Pb-Sn ≥ Pb-Pb), d (Sn-Ge ≤ Pb-Ge < Sn-Sn ≤ Pb-Sn ≤ Pb-Pb) and reduced spin-spin couplings ¹K (Pb-Sn > Sn-Sn > Pb-Pb scatter ). The polarities Pb^δ--Ge^δ+and Pb^δ- - Sn^δ+ are obvious. The enhanced electronegativity of lead demonstrates the influence of its relativistically contracted 6s and 6p orbitals. With regard to Ar₃Pb-PbAr′₃, a relation between ¹K(Pb-Pb) and the charge flow Δ(Ar ? Ar′) is indicated.