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2020

Dakermanji, S. J.; Westendorff, K. S.; Pert, E. K.; Wilson, K. B.; Myers, J. T.; Wilde, J. H.; Dickie, D. A.; Welch, K. D.; Harman, W. D. Spatial Recognition Within Terpenes: Redox and H-bond Promoted Linkage Isomerizations and the Selective Binding of Complex Alkenes. Organometallics 2020, 39, 1961-1975.
Publisher's Version
doi: 10.1021/acs.organomet.0c00151

A method for the resolution of η2-alkene-complex isomers of the type MoTp(NO)(DMAP)(η2-alkene) and WTp(NO)(PMe3)(η2-alkene) (where Tp = hydridotris(pyrazolyl)borate and DMAP = 4-(dimethylamino)pyridine) has been explored. Alkene and polyene compounds form as a mixture of kinetically trapped isomers. For both types of complexes, it was found that addition of either a fluorinated alcohol or one-electron oxidant reduces the number of isomers in solution. Accelerated ligand exchange was also observed, although these reactions were accompanied by significant decomposition.

2019

Combee, L. A.; Johnson, S. L.; Laudenschlager, J. E.; Hilinski, M. K. Rh(II)-Catalyzed Nitrene-Transfer [5 + 1] Cycloadditions of Aryl-Substituted Vinylcyclopropanes. Organic Letters 2019, 21, 2307–2311.
Publisher's Version
doi: 10.1021/acs.orglett.9b00594

Formal [5 + 1] cycloadditions between aryl-substituted vinylcyclopropanes and nitrenoid precursors are reported. The method, which employs Rh2(esp)2 as a catalyst, leads to the highly regioselective formation of substituted tetrahydropyridines. Preliminary mechanistic studies support a stepwise, polar mechanism enabled by the previously observed Lewis acidity of Rh-nitrenoids. Overall, this work expands the application of nitrene-transfer cycloaddition, a relatively underexplored approach to heterocycle synthesis, to the formation of six-membered rings.

Krantz, K. E.; Weisflog, S. L.; Yang, W.; Dickie, D. A.; Frey, N. C.; Webster, C. E.; Gilliard Jr., R. J. Extremely twisted and bent pyrene-fused N-heterocyclic germylenes. Chemical Communications 2019, 55, 14954-14957.
Publisher's Version
doi: 10.1039/c9cc08703f

The first examples of pyrene-fused Janus-type N-heterocyclic germylenes (NHGe) are reported. Remarkably, the pyrene linker and the germanium containing rings are extremely twisted, with “twist angles” up to 64°. Coordination of a Lewis base modifies the twisting of pyrene to an overall bent core (141° bend angle).

 
Walley, J. E.; Wong, Y. O.; Freeman, L. A.; Dickie, D. A.; Gilliard Jr., R. J. N-Heterocyclic Carbene-Supported Aryl- and Alk- oxides of Beryllium and Magnesium. Catalysts 2019, 9, 934.
Publisher's Version
doi: 10.3390/catal9110934

Recently, we have witnessed significant progress with regard to the synthesis of molecular alkaline earth metal reagents and catalysts. To provide new precursors for light alkaline earth metal chemistry, molecular aryloxide and alkoxide complexes of beryllium and magnesium are reported. The reaction of beryllium chloride dietherate with two equivalents of 1,3-diisopropyl-4,5-dimethylimidizol-2-ylidine (sIPr) results in the formation of a bis(N-heterocyclic carbene) (NHC) beryllium dichloride complex, (sIPr)2BeCl2 (1). Compound 1 reacts with lithium diisopropylphenoxide (LiODipp) or sodium ethoxide (NaOEt) to form the terminal aryloxide (sIPr)Be(ODipp)2 (2) and alkoxide dimer [(sIPr)Be(OEt)Cl]2 (3), respectively. Compounds 2 and 3 represent the first beryllium alkoxide and aryloxide species supported by NHCs. Structurally related dimers of magnesium, [(sIPr)Mg(OEt)Brl]2 (4) and [(sIPr)Mg(OEt)Me]2 (5), were also prepared. Compounds 1-5 were characterized by single crystal X-ray diffraction studies, 1H, 13C, and 9Be NMR spectroscopy where applicable.