ON MIXED GROUP 14-GROUP 14 BONDS .8. ASYMMETRICALLY SUBSTITUTED COMPOUNDS AR3PB-GEAR3 AND AR3PB-PBAR3 - COMPARISON OF STRUCTURE AND PHYSICAL BEHAVIOR IN THE SERIES OF BONDS SN-SN, PB-GE, PB-SN, AND PB-PB

A general procedure for the synthesis of hexaarylated compounds of the type Ar3PbGeAr's from Ar3PbLi and Ar'3GeX in THF/ether at -60-degrees -C is given. Likewise, from Ar3PbLi and Ar'PbI the asymmetrical diplum banes Ar3PbPbAr3 could be prepared. By the use of the bulky groups Ar and Ar', the migration of aryl groups could be suppressed, avoiding th e appearance of the mixtures Pb2Ar6-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)3PbGe Ph3 (triclinic, space group P1BAR; a = 9.983(1) b = 12.201(1) c = 15.7 28(2) angstrom; alpha = 95.73(1), beta = 103.56(1), gamma = 113.06(1)d egrees; V = 1674(1) angstrom3; Z = 2; R = 0.0434) and (p-Tol)3PbGe-(p- Tol)3 (trigonal, space group R3BAR; a = 13.338(1), c = 36.55(1) angstr om; V = 5631(2) angstrom3; Z = 6; R = 0.0522) have been determined. NM R chemical shifts delta(Sn-119) and delta(Pb-207) (40 compounds) and o ne-bond couplings 1J(M-M') (16 compounds), stretching vibrations nu(M- M') and force constants f(M-M') for a diatomic oscillator (38 compound s), 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 asymmetri c diplumbanes Ar3Pb-PbAr'3, assignments of delta(Pb-207) resulted from a consideration of inductivity (comparison to PbAr4/Ar'4) and an assu med order of charge flow DELTA(Ar <-> Ar') (13 compounds). Sequences e xist for delta(Sn-119) (Pb-Sn > Sn-Sn greater-than-or-equal-to Sn-Ge), delta(Pb-207) (Pb-Pb > Pb-Sn almost-equal-to Pb-Ge), f (Sn-Ge > Sn-Sn greater-than-or-equal-to Pb-Sn, and Pb-Ge > Pb-Sn greater-than-or-equ al-to Pb-Pb), d (Sn-Ge less-than-or-equal-to Pb-Ge < Sn-Sn less-than-o r-equal-to Pb-Sn less-than-or-equal-to Pb-Pb) and reduced spin-spin co uplings 1K (Pb-Sn > Sn-Sn > Pb-Pb ''scatter''). The polarities Pb(delt a-)-Ge(delta+) and Pb(delta-)-Sn(delta+) are obvious. The enhanced ele ctronegativity of lead demonstrates the influence of its relativistica lly contracted 6s and 6p orbitals. With regard to Ar3Pb-PbAr'3, a rela tion between 1K(Pb-Pb) and the charge flow DELTA(Ar <-> Ar') is indica ted.