No abstract

The influence of nuclearity and charge of chiral Rh diene complexes on the activity and enantioselectivity in catalytic asymmetric 1,2-additions of organoboron reagents to Ntosylimines and 1,4-additions to enones was investigated. For this purpose, cationic dimeric Rh(I) complex [(Rh(1)) 2 Cl]SbF 6 and cationic monomeric Rh(I) complex [RhOH 2 (2)]SbF 6 were synthesized from oxazolidinone-substituted 3-phenylnorbornadiene ligands 1 and 2, which differ in the substitution pattern at oxazolidinone C-5′ (CMe 2 vs CH 2 ) and compared with the corresponding neutral dimeric and monomeric Rh(I) complexes [RhCl(1)] 2 and [RhCl(2)]. Structural, electronic, and mechanistic insights were gained by X-ray crystallography, cyclic voltammetry (CV), X-ray absorption spectroscopy (XAS), and DFT calculations. CV revealed an increased stability of cationic vs neutral Rh complexes toward oxidation. Comparison of solid-state and solution XAS (extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES)) data showed that the monomeric Rh complex [RhCl(2)] maintained its electronic state and coordination sphere in solution, whereas the dimeric Rh complex [RhCl(1)] 2 exchanges bridging chloro ligands by dioxane molecules in solution. In both 1,2-and 1,4-addition reactions, monomeric Rh complexes [RhCl(2)] and [RhOH 2 (2)]SbF 6 gave better yields as compared to dimeric complexes [RhCl(1)] 2 and [(Rh(1)) 2 Cl]SbF 6 . Regarding enantioselectivities, dimeric Rh species [RhCl(1)] 2 and [(Rh(1)) 2 Cl]SbF 6 performed better than monomeric Rh species in the 1,2-addition, while the opposite was true for the 1,4-addition. Neutral Rh complexes performed better than cationic complexes. Microemulsions improved the yields of 1,2-additions due to a most probable enrichment of Rh complexes in the amphiphilic film and provided a strong influence of the complex nuclearity and charge on the stereocontrol. A strong nonlinear-like effect (NLLE) was observed in 1,2-additions, when diastereomeric mixtures of ligands 1 and epi-1 were employed. The pronounced substrate dependency of the 1,4-addition could be rationalized by DFT calculations.

Reported herein is the coordination of rhenium complexes to tetrazine ligand in [ReCl(CO)3(TzPy)] [1] (TzPy = 3-(2-pyridyl)-1,2,4,5-tetrazine) and the rates of addition of different dienophiles to the tetrazine.

Organometallic complexes are frequently deposited on solid surfaces, but little is known about how the resulting complex−solid interactions alter their properties. Here, a series of complexes of the type Cu(dppf)(L x ) + (dppf = 1,1′-bis(diphenylphosphino)ferrocene, L x = monoand bidentate ligands) were synthesized, physisorbed, ion-exchanged, or covalently immobilized on solid surfaces and investigated by 31 P MAS NMR spectroscopy. Complexes adsorbed on silica interacted weakly and were stable, while adsorption on acidic γ-Al 2 O 3 resulted in slow complex decomposition. Ion exchange into mesoporous Na-[Al]SBA-15 resulted in magnetic inequivalence of 31 P nuclei verified by 31 P-31 P RFDR and 1 H-31 P FSLG HETCOR. DFT calculations verified that a MeCN ligand dissociates upon ion exchange. Covalent immobilization via organic linkers as well as ion exchange with bidentate ligands both lead to rigidly bound complexes that cause broad 31 P CSA tensors. We thus demonstrate how the interactions between complexes and functional surfaces determine and alter the stability of complexes. The applied Cu(dppf)(L x ) + complex family members are identified as suitable solid-state NMR probes for investigating the influence of support surfaces on deposited inorganic complexes.