Topic
Steric effects
About: Steric effects is a research topic. Over the lifetime, 16112 publications have been published within this topic receiving 319615 citations. The topic is also known as: steric hindrance.
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TL;DR: The large difference in measured excited-state lifetimes for the two homoleptic Ru (II) complexes is attributed to a strong influence of steric interactions on the ligand field strength, which in turn affects the activation barriers for thermal conversion from (3)MLCT states to short-lived ( 3)MC states.
Abstract: Steric influence on the excited-state lifetimes of ruthenium complexes with bipyridyl-alkanylene-pyridyl ligands
124 citations
TL;DR: In this article, the steric repulsion of the PR2 groups within the chelating fragment was found to significantly influence the coordination geometry of [(P2)Rh], depending on the nature and length of the backbone (X).
Abstract: The complexes [(P2)Rh(hfacac)] 1 [P2 = R2P-(X)-PR2] are introduced as model compounds for the investigation of the intrinsic steric properties of the [(P2)Rh] fragment. The ligand exchange processes that occur during the syntheses of 1 from [(cod)Rh(hfacac)] and the appropriate chelating diphosphanes 3 were studied by variable-temperature multinuclear NMR spectroscopy. The molecular structures of eight examples of 1 with systematic structural variations in 3 were determined by X-ray crystallography. The steric repulsion of the PR2 groups within the chelating fragment was found to significantly influence the coordination geometry of [(P2)Rh], depending on the nature and length of the backbone (X). A linear correlation between the P-Rh-P angles in the solid state and the 103Rh chemical shifts reveals a similar geometric situation in solution. A unique molecular modeling approach was developed to define the accessible molecular surface (AMS) of the rhodium center within the flexible [(P2)Rh] fragment. The potential of this model for application in homogeneous catalysis was exemplified by the use of 1 as catalysts in a test reaction, the hydrogenation of CO2 to formic acid. Complexes 1 were found to be the most active catalyst precursors for this process in organic solvents known to date.
123 citations
TL;DR: In this paper, the preparation of the [Pd(IPr*)(3-Cl-pyridinyl)Cl2] complex was described, and the steric parameters of the ligand as well as its reactivity in the Buchwald-Hartwig amination were directly compared to other precatalysts.
123 citations
TL;DR: In this article, the first example of an organotin compound having C,Y-chelating ligands was presented, i.e., bis [1, 2-bis(ethoxycarbonyl)ethyl]tin dibromide, for which the structure in the solid state was unambiguously established by an X-ray crystal structure determination.
Abstract: Publisher Summary This chapter overviews organotin compounds containing C,Y-chelating ligands particularly, (1) structures in the solid state, (2) fluxional behavior in solution, and (3) stereochemical aspects. Attention is also given to the enhanced reactivity of tin–carbon bonds in tetraorganotin compounds as a result of intramolecular coordination. The first example of an organotin compound having C,Y-chelating ligands, i.e., bis [1, 2-bis(ethoxycarbonyl)ethyl]tin dibromide, for which the structure in the solid state was unambiguously established by an X-ray crystal structure determination. By using the steric and electronic properties of C,Y-chelating ligands, organometallic compounds that have interesting properties and special reactivities can be isolated. Special features of some of these compounds are (1) stabilization of organometallic compounds in which the metal has an unusual oxidation number, e.g., Fe(II1), Co(I1), and Ni(II1); (2) the trapping of organometallic species that are supposed to be intermediates in reactions, e.g., organoplatinum compounds in which a di-iodine molecule is coordinated end-on to platinum as a first step in oxidative-addition reactions; (3) the use of a novel organonickel compound as a catalyst in the selective Karasch addition of polyhaloalkanes to olefines; and (4) the unexpected reactivity of organocopper compounds toward acetylenes.
123 citations
TL;DR: The synthesis and reactivity of a chiral aminoborane displaying both rapid and reversible H2 activation and the catalyst shows exceptional reactivity in asymmetric hydrogenation of enamines and unhindered imines with stereoselectivities of up to 99% ee.
Abstract: We report the synthesis and reactivity of a chiral aminoborane displaying both rapid and reversible H2 activation. The catalyst shows exceptional reactivity in asymmetric hydrogenation of enamines and unhindered imines with stereoselectivities of up to 99% ee. DFT analysis of the reaction mechanism pointed to the importance of both repulsive steric and stabilizing intermolecular non-covalent forces in the stereodetermining hydride transfer step of the catalytic cycle.
123 citations