Intermolecular Interactions in (Arene)chromium Carbonyl Compounds: Prediction of Chiral Crystal Packing from Racemate Structure

Six X-ray crystal structures are reported, all containing substituted triphenylmethanol derivative 4 either alone or as its mono or bis(chromium tricarbonyl) complexes. All four chromium complexes studied crystallize with two independent molecules in the crystallographic asymmetric unit. It is demonstrated that from the X-ray crystal structure of the acentric racemic (±)-(1pR,1‘ ‘R)(1pS,1‘ ‘S)-[Cr(CO)3(η6-t-BuC6H3(CMeOMe)CPh2OH)], (±)-3, it is possible to deduce the 4-fold helical structure of the chiral (−)-(1pR,1‘ ‘R) isomer, (−)-3. The bimetallic derivatives demonstrate the ability to control intermolecular interactions by the positioning of relative stereochemistry

An Improved Aldehyde Linker for the Solid Phase Synthesis of Hindered Amides

A novel aldehyde dual-linker system has been developed for the solid phase synthesis of sterically hindered amides. The linker [5-(4-formyl-3-hydroxyphenoxy)pentanoic acid] exploits an intramolecular oxygen−nitrogen acyl transfer mechanism to prepare compounds that are unattainable with current commercially available linkers. A dual linker system, exploiting the hyper-acid labile Sieber amide linker as part of the construct, enabled the initial reductive alkylation reactions of hindered amines and their subsequent acylation with a range of carboxylic acids with varying stereoelectronic properties to be monitored. Simple acylation conditions (HBTU/HOBt/NMM) sufficed to provide near quantitative reaction of test acids with support-bound hindered amines, reaction conditions which failed when commercial linkers were used

Interplay between Core and Peripheral Chirality in Polyethers

A chiral-base mediated reaction has been used to synthesise the polyethers illustrated and their enantiomers; CD spectroscopy revealed that the homochiral isomers A may be viewed as a C3-symmetric arrangement of fixed paddles while the heterochiral isomers B form a C3-symmetric arrangement of rotating paddles

Novel Structures and Pauson−Khand Activities of N-Heterocyclic Carbene Dicobalt Complexes

N-Heterocyclic carbene derivatives of dicobalt octacarbonyl have been synthesized for the first time and tested in the Pauson−Khand reaction. Two complexes with both NHC and PPh3 ligands represent the only examples of structurally characterized dicobalt hexacarbonyl complexes with two different non-CO ligands

Identification of an Asymmetric Pauson−Khand Precatalyst

X-ray crystallographic analysis of red crystals formed on mixing octacarbonyldicobalt(0) and BINAP, combined with NMR evidence obtained from a catalytic asymmetric Pauson−Khand reaction, suggests that this complex is a precatalyst to this reaction and leads to a new hypothesis for the role of axially chiral diphosphanes in the catalytic asymmetric Pauson−Khand reaction

Novel Structures and Pauson−Khand Activities of N-Heterocyclic Carbene Dicobalt Complexes

N-Heterocyclic carbene derivatives of dicobalt octacarbonyl have been synthesized for the first time and tested in the Pauson−Khand reaction. Two complexes with both NHC and PPh3 ligands represent the only examples of structurally characterized dicobalt hexacarbonyl complexes with two different non-CO ligands

Identification of an Asymmetric Pauson−Khand Precatalyst

X-ray crystallographic analysis of red crystals formed on mixing octacarbonyldicobalt(0) and BINAP, combined with NMR evidence obtained from a catalytic asymmetric Pauson−Khand reaction, suggests that this complex is a precatalyst to this reaction and leads to a new hypothesis for the role of axially chiral diphosphanes in the catalytic asymmetric Pauson−Khand reaction

Pendant Alkenes Promote Cobalt−Cobalt Bond Cleavage in (Alkyne)(binap)tetracarbonyldicobalt(0) Complexes

Heating (alkyne)(binap)tetracarbonyldicobalt(0) complexes bearing pendant alkenes leads to cleavage of the cobalt−cobalt bond and generation of the mononuclear hydride (binap)(CO)2CoH at 45−55 °C

Pendant Alkenes Promote Cobalt−Cobalt Bond Cleavage in (Alkyne)(binap)tetracarbonyldicobalt(0) Complexes

Heating (alkyne)(binap)tetracarbonyldicobalt(0) complexes bearing pendant alkenes leads to cleavage of the cobalt−cobalt bond and generation of the mononuclear hydride (binap)(CO)2CoH at 45−55 °C