New Plumbylenes and a Plumbylene Dimer with a Short Lead−Lead Separation^†^,1

The diarylplumbylene R2Pb:  (3), R = 2-tBu-4,5,6-Me3C6H, and the rearranged alkylarylplumbylene RR‘Pb:, R = 2,4,6-tBu3C6H2, R‘ = CH2C(CH3)2-3,5-tBu2C6H3, were synthesized and characterized by NMR and UV/vis spectroscopy, as well as by X-ray crystallography. Treatment of 3 with the disilylplumbylene R‘‘2Pb:, R‘‘ = Si(SiMe3)3, furnished the heteroleptic plumbylene RR‘‘Pb:  (8), which, in the solid state, forms the plumbylene dimer RR‘‘PbPbRR‘‘ (9). The X-ray structure analysis of 9 reveals a trans-bent angle of 46.5° and a Pb...Pb separation of 3.37 Å, the shortest observed so far between the lead atoms of two plumbylenes

Effect of Chelate Ring Expansion on Jahn–Teller Distortion and Jahn–Teller Dynamics in Copper(II) Complexes

The expanded ligand <i>N</i>,<i>N</i>′-dimethyl-<i>N</i>,<i>N</i>′-dipyridin-2-yl-pyridin-2,6-diamine (ddpd) coordinates to copper­(II) ions in a meridional fashion giving the dicationic complex <i>mer</i>-[Cu­(ddpd)₂]­(BF₄)₂ (<b>1</b>). In the solid state at temperatures below 100 K the cations of <b>1</b> localize in Jahn–Teller elongated CuN₆ polyhedra with the longest Cu–N bond pointing in the molecular <i>x</i> or <i>y</i> directions while the <i>z</i> axis is constrained by the tridentate ddpd ligand. The elongated polyhedra are ordered in an antiferrodistortive way giving an idealized zincblende structure. At higher temperature dynamically averaged (fluxional) polyhedra in the molecular <i>x</i>/<i>y</i> directions are observed by multifrequency variable temperature electron paramagnetic resonance (EPR) and by variable temperature X-ray diffraction studies. Compared to [Cu­(tpy)₂]²⁺ (tpy = 2,2′;6′,2″-terpyridine) the Jahn–Teller splitting 4δ₁ of <b>1</b> is larger. This is very probably caused by the much more favorable orbital overlap in the Cu–N bonds in <b>1</b> which results from the larger bite angle of ddpd as compared to tpy. The “freezing-in” of the Jahn–Teller dynamics of <b>1</b> (<i>T</i> ≈ 100 K) occurs at higher temperature than observed for [Cu­(tpy)₂]²⁺ (<i>T</i> < 77 K) which is also probably due to the larger Jahn–Teller distortion of <b>1</b> resulting in a larger activation barrier

Persistent Radicals of Trivalent Tin and Lead

In this report we present synthetic, crystallographic, and new electron paramagnetic resonance (EPR) spectroscopic work that shows that the synthetic route leading to the recently reported, first persistent plumbyl radical •PbEbt3 (Ebt = ethylbis(trimethylsilyl)silyl), that is, the oxidation of the related PbEbt3-anion, was easily extended to the synthesis of other persistent molecular mononuclear radicals of lead and tin. At first, various novel solvates of homoleptic potassium metallates KSnHyp3 (4a), KPbHyp3 (3a), KSnEbt3 (4b), KPbIbt3 (3c), and KSnIbt3 (4c) (Hyp = tris(trimethylsilyl)silyl, Ibt = isopropylbis(trimethylsilyl)silyl), as well as some heteroleptic metallates, such as [Li(OEt2)2][SnnBuHyp2] (3d), [Li(OEt2)2][PbnBuHyp2] (4d), [Li(thf)4][PbPhHyp2] (3e), and [K(thf)7][PbHyp2{N(SiMe3)2}] (3f), were synthesized and crystallographically characterized. Through oxidation by tin(II) and lead(II) bis(trimethylsilyl)amides or the related 2,6-di-tert-butylphenoxides, they had been oxidized to yield in most cases the corresponding radicals. Five novel persistent homoleptically substituted radicals, that is, •SnHyp3 (2a), •PbHyp3 (1a), •SnEbt3 (2b), •SnIbt3 (2c), and •PbIbt3 (1c), had been characterized by EPR spectroscopy. The stannyl radicals 2a and 2c as well as the plumbyl radical 1c were isolated as intensely colored crystalline compounds and had been characterized by X-ray diffraction. Persistent heteroleptically substituted radicals such as •PbHyp2Ph (1e) or •PbHyp2Et (1g) had also been generated, and some selected EPR data are given for comparison. The plumbyl radicals •PbR3 exhibit a clean monomolecular decay leading to the release of a temperature-dependent stationary concentration of branched silyl radicals. They may thus serve as tunable sources of these reactive species that may be utilized as reagents for mild radical silylations and/or as initiators for radical polymerizations. We present EPR-spectroscopic investigations for the new tin- and lead-containing compounds giving detailed insights into their electronic and geometric structure in solution, as well as structural studies on the crystalline state of the radicals, some of their anionic precursors, and some side-products

Coinage Metal Complexes of Tris(pyrazolyl)methanide-Based Redox-Active Metalloligands

A series of coinage metal complexes containing the redox-active metalloligands [RuCp^X(κ³<i>N</i>-Tpmd)] {κ³<i>N</i>-Tpmd = κ³<i>N</i>-[C­(pz)₃] with pz = pyrazolyl; [RuCp­(Tpmd)] (<b>2a</b>) and [RuCp*­(Tpmd)] (<b>2b</b>)} are presented. <b>2a</b> and <b>2b</b> are isolable, relatively stable compounds, despite the fact that they feature a “naked” carbanion at the bridgehead position of the κ³<i>N</i>-coordinated tris­(pyrazolyl)­methanide ligand scaffold. As expected, both complexes act as κ¹<i>C</i> ligands toward coinage metal fragments to yield dinuclear complexes of the general formula [RuCp^X(μ-Tpmd)­{MX}] (μ-Tpmd = μ-κ¹<i>C</i>:κ³<i>N</i>-[C­(pz)₃]; M = Au, X = Cl, Cp^X = C₅H₅ (<b>3a</b>) or C₅Me₅ (<b>3b</b>); M = Au, X = CN, Cp^X = C₅H₅ (<b>4a</b>) or C₅Me₅ (<b>4b</b>); M = Cu, X = OC­(O)­Me, Cp^X = C₅H₅ (<b>5a</b>); M = Cu, X = Si­(SiMe₃)₃, Cp^X = C₅H₅ (<b>6a</b>) or C₅Me₅ (<b>6b</b>); M = Ag, X = SC­(S)­NEt₂, Cp^X = C₅H₅ (<b>7a</b>), M = Au, X = CC–Ar, Cp^X = C₅H₅ {Ar = C₆H₅ (<b>8a</b>), 4-NH₂-C₆H₄ (<b>9a</b>), 3,5-(CF₃)₂-C₆H₃ (<b>10a</b>)}). All complexes under study were fully characterized by common spectroscopic techniques; the structural parameters of <b>2a</b>, <b>3a</b>, <b>5a</b>, <b>6a</b>, <b>7a</b>, and <b>10a</b> were determined by X-ray diffraction. Coordination of the {MX} fragment leads to electronic effects on the metalloligand unit, as reflected by the corresponding ¹H and ¹³C NMR spectra. Density functional theory calculations were performed in order to elucidate a conceivable interplay between the metal atoms. The bonding characteristics within the {MX} fragment are only marginally affected upon electronic excitation of the ruthenium-based metalloligand. However, some effect of the influence of {MX} on the <i>E</i>⁰_1/2(Ru^II/Ru^III) value was detected with the aid of cyclic voltammetry measurements. A strong Lewis-acidic metal fragment such as GaCl₃ (<b>11a</b>) leads to an <i>E</i>⁰_1/2 value of 0.37 V, while electron-richer coinage metal fragments facilitate the oxidation of the ruthenium center significantly (<i>E</i>⁰_1/2 = 0.14–0.23 V). This dependence suggests an interaction between both metals due to their close spatial proximity