A new N-heterocyclic carbene architecture comprising a 1,4-naphthoquinone annulated to 1,3-dimesitylimidazolylidene (NpQ-NHC) was synthesized in two high yielding steps from commercially available starting materials. The free NpQ-NHC was characterized (solution and solid-state) and was used to synthesize various Rh and Ag complexes that ranged in pi-electron density. Enabled by the quinone moiety, the pi-systems of these complexes were analyzed using infrared spectroscopy and cyclic voltammetry. In contrast to previous reports, pi-backbonding was found to be non-negligible and was directly influenced by the metal's electronic character.

A series of group 10 bis(benzimidazolylidene) complexes featuring chelating N-(o-phenol) moieties were synthesized and characterized. The ligand was prepared in 85% overall yield from 1-fluoro-2-nitrobenzene using a short SNAr/reductive cyclization/alkylation reaction sequence. Direct metalation of the respective benzimidazolium precursor with Ni(II), Pd(II), and Pt(II) salts under ambient atmosphere at 50−80 °C provided the discrete chelating complexes in excellent yields (≥91%). Whereas chelation occurred spontaneously in the case of the Ni complex, an intermediate displaying ligation from the NHCs without chelation from pendent phenol groups was isolated and characterized when Pd was used. This complex was subsequently converted to its chelated form upon treatment with base. The effect of chelation was measured via thermogravimetric analysis and found to enhance the stability of the complex by 24 °C. The chelation also did not significantly effect overall electronic characteristics. A similar reaction sequence was observed when Pt was used, but the respective intermediate could not be isolated. Chelated Ni, Pd, and Pt complexes were characterized by X-ray crystallography and found to exhibit cis configurations about their respective square-planar metal centers. Based on these model systems, a new class of main-chain organometallic polymers comprised of a benzobis(imidazolylidene) ligand with chelating phenolate moieties and group 10 transition metals was synthesized and characterized. The respective bis(bidentate) ligand was prepared from 1,5-dichloro-2,4-dinitrobenzene in three chromatography-free steps in 78% overall yield from commercially-available starting materials and used as monomer. Consistent with the model studies, direct metalation of the monomer was accomplished by addition of a stoichiometric amount of metal(II) salt under basic conditions, which resulted in excellent yields (≥95%) of the respective organometallic polymers with molecular weights up to 363,000 g/moL (relative to polystyrene standards). The polymers were found to be exceptionally air- and moisture-stable and displayed thermal stabilities exceeding 350 °C (under nitrogen), as measured by thermogravimetric analysis. Electronic absorption measurements indicated the λmax values of these polymers ranged between 312 and 322 nm, depending on the incorporated transition metal, and were bathochromically shifted by up to 27 nm relative to their corresponding model complexes.

The first acyclic diaminocarbene (ADC) featuring N-aryl groups, as well as two complexes containing this ligand, (ADC)RhCl(1,5-cis,cis-cyclooctadiene) and (ADC)RhCl(CO)2, were synthesized and characterized. Insight into controlling conformational diversity in acyclic diaminocarbenes with N-aryl groups through judicious N substitution was also explored.

No abstract

Additional Information on Synthesis of IsHP(BH 3 )CH 2 PHIs(BH 3 ) (1-BH 3 )As mentioned in the experimental section, use of a slight excess of IsMgBr (2.4 equiv) ensured complete 1,2diarylation of Cl 2 PCH 2 PCl 2 , but subsequent formation of IsH during the workup hindered crystallization of 1-BH 3 . In that case (starting with 2.24 g (10.3 mmol) of Cl 2 PCH 2 PCl 2 ), the following procedure was used to obtain the product as a solid.Removal of the solvent from crude 1-BH 3 (formed on addition of BH 3 -THF to crude 1) gave an oily mass. 31 P NMR analysis showed two peaks corresponding to the diastereomers of the diphosphine diborane (δ -31.8, -33.9, 1:1). The mass was diluted with ca. 100 mL of pentane and allowed to stand for one week. A white precipitate (106 mg) was collected by filtration. 31 P NMR analysis of both the solid and solution showed the presence of 1-BH 3 and minor impurities. After removing the solvent from the solution, the oily mass was dissolved in 5 mL of pentane and then the solvent was removed under reduced pressure. This process was repeated until the oily mass took on a chalky appearance and was no longer translucent. At this point the mass was redissolved in 5 mL of pentane and a small amount of white precipitate appeared. The slurry was passed through a 0.5 x 2.0 cm Celite pipet column, which collected the white precipitate while the brown solution passed through. The column was washed with 5 mL more pentane and the pentane washings were collected -some of the white solid seemed to dissolve with this wash. Finally the Celite column was washed with 5 mL of Et 2 O, which was then removed in vacuo to afford 0.185 g of a white solid. A sample of 5 mg of the white solid was dissolved in 0.7 mL of Et 2 O, and 31 P NMR analysis of the material showed two peaks corresponding to the two diastereomers of the diphosphine diborane (δ -32.1 (minor), -33.9 (major), 1:10) and a minor species corresponding to a diphosphine monoborane (δ -29.5, -103.3 (< 5%)). After 24 h, this sample had reverted to a spectrum very similar in appearance to the original reaction solution, now with a 7:10 ratio of diastereomers. The pentane was removed S7 from the washings in vacuo and the above protocol (addition/removal of pentane followed by a Celite column) was repeated to afford another 0.554 g of a white solid (0.739 g total (1.44 mmol, 14.0% yield from Cl 2 PCH 2 PCl 2 )). Further repetitions proved unfruitful. Additional Information on Synthesis of rac-and meso-MiniPhos 5, IsMePCH 2 PMeIsPt-Catalyzed Synthesis of MiniPhos 5: Background Reactions Coupling of PHMeIs and CH 2 I 2 in the presence of NaOSiMe 3 but without a Pt catalyst was monitored by 31 P NMR spectroscopy for 96 h. After this time, signals were identified at δ -53.4 (1%), -53.9 (<1%), -56.6 (<1%), -61.4 (<1%), -107.4 (<1%). The low conversion without the catalyst suggests that the background is not significant in the catalytic reaction. Similarly, the reaction of MeI with IsHPCH 2 PHIs (1) and NaOSiMe 3 in the absence of a Pt catalyst was monitored...