1. Synthesis and structure of a new bulky bis-(alkoxide) ligand on a terphenyl platform
Sudheer S Kurup, Sandra Nasser, Cassandra L Ward, Stanislav Groysman Acta Crystallogr E Crystallogr Commun. 2022 Jan 1;78(Pt 1):92-96. doi: 10.1107/S2056989021013438.
A new sterically bulky chelating bis-(alkoxide) ligand 3,3'-([1,1':4',1''-terphen-yl]-2,2''-di-yl)bis-(2,2,4,4-tetra-methyl-pentan-3-ol), (H2[OO]tBu), was prepared in a two-step process as the di-chloro-methane monosolvate, C36H50O2·CH2Cl2. The first step is a Suzuki-Miyaura coupling reaction between 2-bromo-phenyl-boronic acid and 1,4-di-iodo-benzene. The resulting 2,2''-di-bromo-1,1':4',1''-terphenyl was reacted with t BuLi and hexa-methyl-acetone to obtain the desired product. The crystal structure of H2[OO]tBu revealed an anti conformation of the [CPh2(OH)] fragments relative to the central phenyl. Furthermore, the hydroxyl groups point away from each other. Likely because of this anti-anti conformation, the attempts to synthesize first-row transition-metal complexes with H2[OO]tBu were not successful.
2. Synthesis, Characterization, and Catalytic Exploration of Mononuclear Mo(VI) Dioxido Complexes of ( Z)-1- R-2-(4',4'-Dimethyl-2'-oxazolin-2'-yl)-eth-1-en-1-ates
Anna Petrov, Jeanette A Adjei, Alan J Lough, R Stephen Wylie, Robert A Gossage Molecules. 2022 Feb 15;27(4):1309. doi: 10.3390/molecules27041309.
The coordination chemistry of the title ligands with Mo metal centers was investigated. Thus, the synthesis and characterization (NMR, X-ray diffraction) of four mononuclear formally Mo(6+) complexes of (Z)-1-R-2-(4',4'-dimethyl-2'-oxazolin-2'-yl)-eth-1-en-1-ates (L: R = -Ph, -Ph-p-NO2, -Ph-p-OMe and -t-Bu), derived from the part enols (LH), is described. The resulting air-stable MoO2L2 complexes (1-4) exist, as shown by single-crystal X-ray diffraction experiments, in the cis-dioxido-trans(N)-κ2-N,O-L conformation in the solid state for all four examples. This situation was further probed using semi-empirical PM6(tm) calculations. Complexes 1-4 represent the first Mo complexes of this ligand class and, indeed, of Group 6 metals in general. Structural and spectroscopic comparisons were made between these and related Mo(6+) compounds. Complex 1 (R = -Ph) was studied for its ability to selectively catalyze the production of poly-norbornene from the monomer in the presence of MAO. This, unfortunately, only resulted in the synthesis of insoluble, presumably highly cross-linked, polymeric and/or oligomeric materials. However, complexes 1-4 were demonstrated to be highly effective for catalyzing benzoin to benzil conversion using DMSO as the O-transfer agent. This catalysis work is likewise put into perspective with respect to analogous Mo(6+) complexes.
3. Sterically directed nitronate complexes of 2,6-di-tert-butyl-4-nitrophenoxide with Cu(ii) and Zn(ii) and their H-atom transfer reactivity
Thomas R Porter, Ellen C Hayes, Werner Kaminsky, James M Mayer Dalton Trans. 2017 Feb 21;46(8):2551-2558. doi: 10.1039/c6dt04427a.
The bulky 2,6-di-tert-butyl-4-nitrophenolate ligand forms complexes with [TptBuCuII]+ and [TptBuZnII]+ binding via the nitro group in an unusual nitronato-quinone resonance form (TptBu = hydro-tris(3-tert-butyl-pyrazol-1-yl)borate). The Cu complex in the solid state has a five-coordinate κ2-nitronate structure, while the Zn analogue has a four-coordinate κ1-nitronate ligand. 4-Nitrophenol, without the 2,6-di-tert-butyl substituents, instead binds to [TptBuCuII]+ through the phenolate oxygen. This difference in binding is very likely due to the steric difficulty in binding a 2,6-di-tert-butyl-phenolate ligand to the [TptBuMII]+ unit. TptBuCuII(κ2-O2NtBu2C6H2O) reacts with the hydroxylamine TEMPO-H (2,2,6,6-tetramethylpiperidin-1-ol) by abstracting a hydrogen atom. This system thus shows an unusual sterically enforced transition metal-ligand binding motif and a copper-phenolate interaction that differs from what is typically observed in biological and chemical catalysis.
