RESUMO
Salt metathesis routes to five new -N(SiMe3)2 nickel derivatives were studied to illuminate their mode of formation, structures, and spectroscopy. The reaction between NiI2 and K{N(SiMe3)2} afforded the Ni(II) and Ni(I) complexes [K][Ni{N(SiMe3)2}3] (1) and [K][Ni{N(SiMe3)2}2] (2). Dissolving 1 in tetrahydrofuran (THF) gave the Ni(II) species [K(THF)2][Ni{N(SiMe3)2}3] (3). The Ni(I) salt [K(DME)][Ni2{N(SiMe3)2}3] (4) was obtained by using NiCl2(DME) (DME = 1,2-dimethoxyethane) as the nickel source rather than NiI2. The isolation of the Ni(I) complexes 2 and 4 highlights the tendency for K{N(SiMe3)2} to function as a reducing agent. Introduction of adventitious O2 to solutions of [K][Ni{N(SiMe3)2}2] (2) gave the nickel inverse crown ether (ICE) species [K2][O(Ni{N(SiMe3)2}2)2] (5). Complex 5 is the first ICE complex of nickel and is one of four known ICE complexes for the 3d metals. The experimental results indicate that the reduced Ni(I) bis(trimethylsilyl)amides are relatively easily generated, whereas Ni(III) derivatives that might be expected from a disproportionation of a Ni(II) derivative are apparently not yet isolable by the above routes. Overall, the new species crystallize readily from the reaction mixtures, but under ambient conditions, they begin to decompose as solids within ca. 24 h, which hinders their characterization.
RESUMO
The first assortment of achiral pentafluorosulfanylated cyclobutanes (SF5-CBs) are now synthetically accessible through strain-release functionalization of [1.1.0]bicyclobutanes (BCBs) using SF5Cl. Methods for both chloropentafluorosulfanylation and hydropentafluorosulfanylation of sulfone-based BCBs are detailed herein, as well as proof-of-concept that the logic extends to tetrafluoro(aryl)sulfanylation, tetrafluoro(trifluoromethyl)sulfanylation, and three-component pentafluorosulfanylation reactions. The methods presented enable isolation of both syn and anti isomers of SF5-CBs, but we also demonstrate that this innate selectivity can be overridden in chloropentafluorosulfanylation; that is, an anti-stereoselective variant of SF5Cl addition across sulfone-based BCBs can be achieved by using inexpensive copper salt additives. Considering the SF5 group and CBs have been employed individually as nonclassical bioisosteres, structural aspects of these unique SF5-CB "hybrid isosteres" were then contextualized using SC-XRD. From a mechanistic standpoint, chloropentafluorosulfanylation ostensibly proceeds through a curious polarity mismatch addition of electrophilic SF5 radicals to the electrophilic sites of the BCBs. Upon examining carbonyl-containing BCBs, we also observed rare instances whereby radical addition to the 1-position of a BCB occurs. The nature of the key C(sp3)-SF5 bond formation step - among other mechanistic features of the methods we disclose - was investigated experimentally and with DFT calculations. Lastly, we demonstrate compatibility of SF5-CBs with various downstream functionalizations.
RESUMO
The new Ge(II) cluster [Ge6(µ3-O)4(µ2-OC6H2-2,4,6-Cy3)4](NH3)0.5 (1) and three divalent Group 14 aryloxide derivatives [Ge(OC6H2-2,4,6-Cy3)2]2 (2), [Sn(OC6H2-2,4,6-Cy3)2]2 (3), and [Pb(OC6H2-2,4,6-Cy3)2]2 (4) of the new tricyclohexylphenyloxo ligand, [(-OC6H2-2,4,6-Cy3)2]2 (Cy = cyclohexyl), were synthesized and characterized. Complexes 1-4 were obtained by reaction of the metal bissilylamides M(N(SiMe3)2)2 (M = Ge, Sn, Pb) with 2,4,6-tricyclohexylphenol in hexane at room temperature. If the freshly generated reaction mixture for the synthesis of 2 is stirred in solution for 12 h at room temperature, the cluster [Ge6(µ3-O)4(µ2-OC6H2-2,4,6-Cy3)4](NH3)0.5 (1), which features a rare Ge6O8 core that includes ammonia molecules in non-coordinating positions, is formed. Complexes 3 and 4 were also characterized via119Sn{1H} NMR and 207Pb NMR spectroscopy and feature signals at -280.3 ppm (119Sn{1H}, 25 °C) and 1541.0 ppm (207Pb, 37 °C), respectively. The spectroscopic characterization of 3 and 4 extends known 119Sn parameters for dimeric Sn(II) aryloxides, but data for 207Pb NMR spectra for Pb(II) aryloxides are rare. We present also a rare VT-NMR study of a homoleptic 3-coordinate Pb(II) aryloxide. The crystal structures of 2, 3, and 4 feature interligand Hâ¯H contacts that are similar in number to those of related transition metal derivatives despite the larger size of the group 14 elements.
RESUMO
A series of Mn(II), Fe(II), and Co(II) bisaryloxide dimers ([M(OC6H2-2,4,6-Cy3)2]2 {M = Mn (1), Fe (2), and Co (3)} were synthesized by the addition of 2,4,6-tricyclohexylphenol (HOC6H2-2,4,6-Cy3) to the silyl amido dimers [M(N(SiMe3)2)2]2 (M = Mn, Fe, Co; Cy = cyclohexyl). An unexpected and unique Co(II) phenoxide derivative (4), [Co(OC6H2-2,4,6-Cy3)(O2C6H-3,5,6-Cy3)]2, was obtained via ligand rearrangement of 3 at ca. 180 °C. This yielded 4 in which there are two unchanged, bridging phenoxide ligands as well as a terminal bidentate semiquinone ligand bound to each cobalt. Complexes 1 and 2 did not undergo such a rearrangement under the same conditions; both are thermally stable to temperatures exceeding 250 °C and feature numerous short-contact (<2.5 Å) H···H interactions consistent with the presence of dispersion stabilization. Use of the aryloxide ligand -OC6H3-2,6-Pri2 (Pri = isopropyl), which is sterically similar to -OC6H2-2,4,6-Cy3 but produces fewer close H···H interactions, gave the trimeric species [M(OC6H3-2,6-Pri2)2]3 {M = Fe (5) or Co (6)} which feature a linear array of three metal atoms bridged by aryloxides. The higher association number in 5 and 6 in comparison to that of 1-3 is due to the lower dispersion energy donor properties of the -OC6H3-2,6-Pri2 ligand and the lower stabilization it produces.