The Challenge of Linear (E)‐Enones in the Rh‐Catalyzed,Asymmetric 1,4‐Addition Reaction of Phenylboronic Acid: A DFT Computational Analysis

Why are linear (E)‐enones such challenging substrates in the Rh‐catalyzed asymmetric arylation with boronic acids, which is one of the most important asymmetric catalysis methods? DFT computations show that these substrates adopt a specific conformation in which the largest substituent is antiperiplanar to Rh^I π‐complexed with the C?C bond within the enantioselectivity‐determining carborhodation transition state. Additionally, for such structures, there is a strong, but not exclusive, preference for s‐cis enone conformation. This folding minimizes steric interactions between the substrate and the ligand, and hence reduces the enantioselectivity. This idea is further confirmed by investigating three computation‐only substrate “probes”, one of which is capable of double asymmetric induction, and a recent computationally designed 1,5‐diene ligand. On average, excellent agreement between predicted and experimental enantioselectivity was attained by a three‐pronged approach: 1) thorough conformational search within ligand and substrate subunits to locate the most preferred carborhodation transition state; 2) including dispersion interaction and long‐range corrections by SMD/ωB97xD/DGDZVP level of theory; and 3) full substrate and ligand modeling. Based on the results, a theory‐enhanced enantioselectivity model that is applicable to both chiral diene and diphosphane ligands is proposed.     

Asymmetric Synthesis of Axially Chiral 2‐Aminobiaryls by Rhodium‐Catalyzed Benzannulation of 1‐Arylalkynes with 2‐(Cyanomethyl)phenylboronates

Asymmetric benzannulation of 1‐arylalkynes, where the aryl group is an ortho‐substituted aromatic group, with 2‐(cyanomethyl)phenylboronate was catalyzed by a rhodium complex coordinated with a chiral diene ligand to give high yields of axially chiral 2‐aminobiaryls with greater than 90 % ee.     

Rhodium(I)/Chiral Diene‐Catalyzed Enantioselective Addition of Boronic Acids to N‐Unsubstituted Isatin‐Derived Ketimines

Enantioselective addition of boronic acids to N‐unsubstituted isatin‐derived ketimines was realized using rhodium(I)/chiral diene catalysts. The reactions can be performed in the presence of catalytic amounts of a base to give adducts in high yield with high enantioselectivity. Preliminary mechanistic information including a computational model to explain the observed enantioselectivity is also provided.     

Asymmetric Conjugate Alkynylation of Cyclic α,β‐Unsaturated Carbonyl Compounds with a Chiral Diene Rhodium Catalyst

Asymmetric conjugate alkynylation of cyclic α,β‐unsaturated carbonyl compounds (ketones, esters, and amides) was realized by use of diphenyl[(triisopropylsilyl)ethynyl]methanol as an alkynylating reagent in the presence of a rhodium catalyst coordinated with a new chiral diene ligand (Fc‐bod; bod=bicyclo[2.2.2]octa‐2,5‐diene, Fc=ferrocenyl) to give high yields of the corresponding β‐alkynyl‐substituted carbonyl compounds with 95–98 % ee.     

溴化钯或乙酰丙酮羰基铑/手性配体催化醛与乙酰胺的不对称酰胺羰化反应研究

采用溴化钯为催化剂前体,与非螯合型双齿膦配体L1(DPPFF)、联吡啶型双齿膦配体L2(P-PHOS)和二茂铁基手性双膦配体L3((S,Rp)-BPPF)制备络合物催化剂,以乙酰丙酮羰基铑为催化剂前体,与手性亚磷酸酯配体L4-L6制备络合物催化剂,将其分别应用于底物环己基甲醛或苯乙醛的不对称酰胺羰化反应中,研究结果表明...     

Kinetic Studies Prove High Catalytic Activity of a Diene–Rhodium Complex in 1,4‐Addition of Phenylboronic Acid to α,β‐Unsaturated Ketones

In the 1,4‐addition of phenylboronic acid to α,β‐unsaturated ketones, [Rh(OH)(cod)]₂ has a much higher catalytic activity than [Rh(OH)(binap)]₂ (cod=1,5‐cyclooctadiene, binap=2,2′‐bis(diphenylphosphanyl)‐1,1′‐binaphthyl). Kinetic studies revealed that the rate‐determining transmetalation step in the catalytic cycle has a large rate constant when [Rh(OH)(cod)]₂ is used.     

Rhodium(III) Complexes Featuring Coordinated CF3 Appendages

The synthesis and characterisation of a homologous series of rhodium 2,2′-biphenyl complexes featuring intramolecular dative bonding of the nominally inert and weakly coordinating trifluoromethyl group are described. Presence of these interactions is evidenced in the solid state using X-ray diffraction, with Rh−F contacts of 2.36–2.45 Å, and in solution using NMR spectroscopy, through hindered C−CF₃ bond rotation and the presence of time-averaged ¹J_RhF and ²J_PF coupling.     

Three-Coordinate Rhodium Complexes in Low Oxidation States

The isolation of simultaneously low-coordinate and low-valent compounds is a timeless challenge for preparative chemists. This work showcases the preparation and full characterization of tri-coordinate rhodium(-I) and rhodium(0) complexes as well as a rare rhodium(I) complex. Reduction of [{Rh(μ-Cl)(IPr)(dvtms)}₂] ( 1 , IPr=1,3-bis(2,6-diisopropylphenyl)imidazolyl-2-ylidene; dvtms=divinyltetramethyldisiloxane) with KC₈ gave the trigonal complexes K[Rh(IPr)(dvtms)] and [Rh(IPr)(dvtms)], whereas the cation [Rh(IPr)(dvtms)]⁺ results from their oxidation or by abstraction of chloride from 1 with silver salts. The paramagnetic Rh⁰ complex is a unique fully metal-centered radical with the unpaired electron in the d_z2 orbital. The Rh(-I) complex reacts with PPh₃ with replacement of the NHC ligand, and behaves as a nucleophile, which upon reaction with [AuCl(PPh₃)] generates the trigonal pyramidal complex [(IPr)(dvtms)Rh-Au(PPh₃)] with a metal–metal bond between two d¹⁰ metal centers.     

Trinuclear Rhodium Complexes and Their Relevance for Asymmetric Hydrogenation

Various trinuclear rhodium complexes of the type [Rh₃(PP)₃(μ₃‐OH)_x(μ₃‐OMe)_2?x]BF₄ (where PP=Me‐DuPhos, dipamp, dppp, dppe; different ligands and μ‐bridging anions) are presented, which are formed upon addition of bases such as NEt₃ to solvate complexes [Rh(PP)(solvent)₂]BF₄. They were extensively characterized by X‐ray diffraction and NMR spectroscopy (¹⁰³Rh, ³¹P, ¹³C, ¹H). Their in situ formation resulting from basic additives (NEt₃) or basic prochiral olefins (without addition of another base) can cause deactivation of the asymmetric hydrogenation. This effect can be reversed by means of acidic additives.     

Synthesis and Structure of Heterodinuclear Rhodium and Iridium Borylene Complexes

Herein we report on the synthesis and structural characterization of a representative range of novel heterodinuclear bridging rhodium and iridium borylene complexes. The iridium borylene complexes feature an unusual coordination mode of the borylene ligand. Furthermore, the first instance of a heterodinuclear‐bridged borylene compound containing a chromium atom in the three‐membered ring is reported.     

Unprecedented Selectivity via Electronic Substrate Recognition in the 1,4‐Addition to Cyclic Olefins Using a Chiral Disulfoxide Rhodium Catalyst

From zero to hero? Sulfoxides are generally not considered useful ligand entities in asymmetric metal catalysis. However, a chiral disulfoxide as a chelating ligand in the rhodium‐catalyzed 1,4‐addition of aryl boronic acids to cyclic, α,β‐unsaturated ketones and esters gives impressive catalytic results, thus opening the door to future applications of this new chiral ligand class.

     

Discrete Supramolecular Stacks Based on Multinuclear Tweezer-Type Rhodium Complexes

By taking advantage of self-complementary π–π stacking and CH–π interactions, a series of discrete quadruple stacks were constructed through the self-aggregation of U-shaped dirhodium metallotweezer complexes featuring various planar polyaromatic ligands. By altering the conjugate stacking strength and bridging ligands, assemblies with a range of topologies were obtained, including a binuclear D-shaped macrocycle, tetranuclear open-ended cagelike frameworks, and duplex metallotweezer stacking structures. Furthermore, a rare stacking interaction resulting in selective C−H activation was observed during the self-assembly process of these elaborate architectures.