No abstract

The synthesis and characterization of a stable, acyclic two-coordinate silylene, Si(SArMe6 )2 [ArMe6 = C6H3-2,6(C6H2-2,4,6-Me3)2], by reduction of Br2Si(SArMe6 )2 with a magnesium(I) reductant is described. It features a V-shaped silicon coordination with a S–Si–S angle of 90.52(2)° and an average Si–S distance of 2.158(3) Å. Although it reacts readily with an alkyl halide, it does not react with hydrogen under ambient conditions, probably as a result of the ca. 4.3 eV energy difference between the frontier silicon lone pair and 3p orbitals.

The synthesis, spectroscopic and structural characterization of an extensive series of acyclic, monomeric tetrylene dichalcogenolates of formula M(ChAr)2 (M = Si, Ge, Sn, Pb; Ch = O, S, or Se; Ar = bulky m-terphenyl ligand) are described. They were found to possess several unusual features-the most notable of which is their strong tendency to display acute interligand, Ch-M-Ch, bond angles that are often well below 90°.Furthermore, and contrary to normal steric expectations, the interligand angles were 2 found to become narrower as the size of the ligand was increased. Experimental and structural data in conjunction with high-level DFT calculations, including corrections for dispersion effects, led to the conclusion that dispersion forces play a key role in stabilizing their acute interligand angles.

The first-row transition-metal(II) dithiolates M(SAr) [Ar = CH-2,6-(CH-2,6-iPr); M = Cr (1), Mn (3), Fe (4), Co (5), Ni (6), and Zn (7)] and Cr(SAr) [2; Ar = CH-2,6-(CH-2,4,6-Me)] and the ligand-transfer reagent (NaSAr) (8) are described. In contrast to their M(SAr) (M = Cr, Mn, Fe, Co, Ni, and Zn; Ar = CH-2,6-(CH-2,4,6-iPr)) congeners, which differ from 1 and 3-6 in having p-isopropyl groups on the flanking aryl rings of the terphenyl substituents, compounds 1 and 4-6 display highly bent coordination geometries with S-M-S angles of 109.802(2)° (1), 120.2828(3)° (4), 91.730(3)° (5), and 92.68(2)° (6) as well as relatively close metal-flanking aryl ring η interactions with metal-centroid distances of 2.11477(6) Å (1), 1.97188(3) Å (2), 2.15269(6) Å (4), 1.62058(9) Å (5), and 1.724(8) Å (6). However, the d (Mn) and d (Zn) complexes 3 and 7 display linear or near-linear coordination with no close metal-ligand distances. The nonlinear geometries of 1 and 4-6 also contrast with those of their Ar-substituted alkoxo and amido congeners, which have strictly linear coordination. Complexes 1-7 were synthesized by the reaction of the lithium or sodium thiolate salt with the metal dihalide or, in the case of 3, by the reaction of the thiol with the amido complex Mn[N(SiMe)]. All compounds were characterized by electronic spectroscopy, X-ray crystallography, and magnetic measurements using Evans' method and SQUID magnetometry. It was concluded that, despite the large bulk of the Ar substituents, the absence of p-isopropyl groups on the flanking rings of the ligand permits close secondary metal-flanking ring distances. The compounds are characterized by more intense colors and display magnetic moments that are generally lower than the spin-only values, in agreement with the covalent character of the close metal-flanking ring η interactions.

The complexes, Pb(ChAr(Pri4))2 (Ch = O (1), S (2); Ar(Pri4) = C6H3-2,6-(C6H3-2,6-Pr(i)2)2) were synthesized by alcoholysis and salt metathesis routes and represent the first fully characterized monomeric, two-coordinate, lead dichalcogenolates in the solid state. Structural studies showed that the S-Pb-S angle (77.21(4)°) is about 22° narrower than the corresponding O-Pb-O angle. (207)Pb NMR and electronic spectroscopy show that the separation between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) decreases from the bisaryloxo plumbylene to the bisthiolato derivative. Reaction of LiSAr(Me6) with PbBr2 in a 2:1 ratio led not to Pb(SAr(Me6))2, but to a mixture of the monothiolato lead(II) complex, {Pb(Br)(μ-SAr(Me6))}2 (3) and the lithium tristhiolato plumbate, LiPb(SAr(Me6))3 (4). 3 and 4 were isolated and purified by fractional recrystallization, and both were characterized by X-ray crystallography and spectroscopic studies.