The tetrahedral geometry of organolead(IV) compounds can be readily transformed by using an organic ligand containing a dangling-arm oxygen functionality. The acidity of the Pb center results in so-called secondary bonding between O and Pb thereby pushing the geometry at Pb toward a trigonal bipyramidal (tbp) structure. Replacing a phenyl group by a chlorine atom dramatically enhances this phenomenon. Thus for (o-methoxybenzyl) triphenyllead (4), and (o-methoxybenzyl)diphenyllead chloride (5), the Pb–O internuclear distances are 3.362(4) and 2.845(3) Å, respectively; 83% (4) and 70% (5) of the sum of the van der Waals Pb and O radii. Within the group 14 element congeners the structural analysis of the (o-methoxybenzyl)triphenylE compounds, E = Si, Ge, Sn, and now Pb, demonstrates the relative acidities of E are Si < Ge < Sn < Pb.

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Treatment of 8-NH 2 -BODIPY, 1 a, (BODIPY = boron,methyl]-1H-pyrrolato-kN]-) with NaH, followed by addition of acylchlorides, R.-C(= O)Cl, R = CH 3 , CH 2 Cl, Ph, produces the corresponding 8-amido-BODIPYs, RC(= O)NH-BODIPYs in good yield, R = Me, 2 (62 %); ClCH 2 , 3 (52 %); Ph, 4 (74 %). Structural and spectroscopic analyses indicate a lack of N-lone pair delocalization to the BODIPY core (normally exhibited by the parent 8-amino-BODIPYs) as a result of the BODIPY-NH + = CR-O À contribution to the amide structure. The new materials 2, 3, and 4 exhibit C8-N bond lengths significantly longer than the those in related 8-amino-BODIPYs, average 1.407 Å vs 1.327 Å; and the N-Cacyl bond lengths in the region associated with regular amides, average 1.38 Å. This lack of 8-N-BODIPY pi interaction results in a significant bathochromic shift in the absorbance spectra (modelled by empirically corrected Time Dependent-Density Functional Theory (TD-DFT) calculations) and removes the well-established blue emission for 8-amino-BODIPYs and the new materials revert to the "normal" green emission generally noted for 8substituted-BODIPYs.[a] L. Figure 1. (a) 8-R-BODIPYs; (b) 8-NHR-BODIPY illustrating hemicyanin resonance contribution B, R = H (1 a); iPr (1 b); iBu (1 c).ChemistrySelect Full Papers % 1 b 406 462 16 % 1 c 406 450 26 % ChemistrySelect Full Papers