Effects of Remote Ligand Substituents on the Structures, Spectroscopic, and Magnetic Properties of Two-Coordinate Transition-Metal Thiolate Complexes.

The first-row transition-metal(II) dithiolates M(SAriPr4)2 [AriPr4 = C6H3-2,6-(C6H3-2,6-iPr2)2; M = Cr (1), Mn (3), Fe (4), Co (5), Ni (6), and Zn (7)] and Cr(SArMe6)2 [2; ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2] and the ligand-transfer reagent (NaSAriPr4)2 (8) are described. In contrast to their M(SAriPr6)2 (M = Cr, Mn, Fe, Co, Ni, and Zn; AriPr6 = C6H3-2,6-(C6H2-2,4,6-iPr3)2) 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 η6 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 d5 (Mn) and d10 (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 AriPr4-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(SiMe3)2]2. 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 AriPr4 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 η6 interactions.

Studies on the Activation and Hydrosilylation Catalysis of RhCl3(Bu2S)3.

RhCl3(Bu2S)3 is an industrial precatalyst utilized in the curing of some solventless silicone-release coatings formulations. The catalyst requires no additional inhibitor, in contrast to typical Pt formulations, and so questions arose about how fast the catalyst could trigger curing if it were used in a more activated form. Studies on the activation of RhCl3(Bu2S)3 revealed multiple intermediates, of which [RhCl(Bu2S)2]2 and [RhHCl(SiMe(OSiMe3)2) (Bu2S)2]2 were isolated. [RhHCl(SiMe(OSiMe3)2)(Bu2S)2]2 is the most activated form of the precatalyst, showing a brief induction period. Various experiments were performed to analyze the nature of the catalyst, including Hg poisoning, addition of poison ligands, and comparisons versus Rh nanoparticles. The data tend to be more consistent with a molecular catalyst than Rh nanoparticles. Data are also provided that support the active catalyst containing a RhxClx(Bu2S)2x fragment, although the exact identity of the active catalyst is not yet determined.

Lewis base assisted B-H bond redistribution in borazine and polyborazylene.

Lewis bases react with borazine and polyborazylene, yielding borane adducts. In the case of NH3 (l), ammonia-borane (AB) is formed and quantified using NMR spectroscopy against an internal standard. Calculations indicate that the formation of B(NH2)3 may provide the driving force of this redistribution. Given the complexity and expense of currently known spent AB regeneration pathways, it is suggested that this redistribution chemistry be used to recover AB and improve regeneration methods.

Dispersion forces and counterintuitive steric effects in main group molecules: heavier group 14 (Si-Pb) dichalcogenolate carbene analogues with sub-90° interligand bond angles.

The synthesis and 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, including two new acyclic silylenes) 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 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 an important role in stabilizing their acute interligand angles.

Stable plumbylene dichalcogenolate monomers with large differences in their interligand angles and the synthesis and characterization of a monothiolato Pb(II) bromide and lithium trithiolato plumbate.

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.

Isolation of a stable, acyclic, two-coordinate silylene.

The synthesis and characterization of a stable, acyclic two-coordinate silylene, Si(SAr(Me(6)))(2) [Ar(Me(6)) = C(6)H(3)-2,6(C(6)H(2)-2,4,6-Me(3))(2)], by reduction of Br(2)Si(SAr(Me(6)))(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.