EPR spectroscopic characterization of persistent germyl-substituted Pb(iii)- and Sn(iii)-radicals

Abstract

In this report we present the synthesis and the detailed electron paramagnetic resonance (EPR) spectroscopic characterization of novel trivalent lead- and tin-based radicals comprising sterically demanding germyl substituents. The investigated radicals are derived from the recently reported trihypersilyl-substituted tetryl radicals *PbHyp3 and *SnHyp3. The tetryl radicals *Pb(Ge(SiMe3)3)3 (8), *Pb(Ge(SiMe3)3)2Si(SiMe3)3 (9), *PbGe(SiMe3)3(Si(SiMe3)3)2 (10), and *Sn(Ge(SiMe3)3)3 (11) show substitution patterns derived from stepwise (9, 10) or complete (8, 11) substitution of hypersilyl groups (Hyp = Si(SiMe3)3) in *PbHyp3 and *SnHyp3 by homologous hypergermyl groups (Hge = Ge(SiMe3)3). They were generated through oxidation of the corresponding potassium tetranides KPbR3 and KSnR3 (R = Hyp, Hge), which in turn had been synthesized employing nucleophilic addition of KHyp or KHge to PbHyp2 or to the novel tetrylenes PbHge2 (1) and SnHge2 (12). The gained EPR spectroscopic data give insights into the influence of the substitution pattern on the geometric and electronic properties of the lead-centered species. With an increasing number of germyl substituents, the spin-orbit coupling to the central atom increases resulting in larger g(iso)-values and larger g-anisotropies while the 209Pb hyperfine splitting constants A(iso) decrease. These decreasing splitting constants are indicative of a diminished s-character of the singly occupied molecular orbital (SOMO) and to a molecular geometry running from slightly pyramidal to almost planar. Interestingly, already one germyl substituent (for radical 10) dominates most of the mentioned properties. For stannyl radical 11 a similar trend is seen for the spin-orbit coupling, while the (117/119)Sn hyperfine splittings unexpectedly increase from SnHyp3 to SnHge3.