Highly Efficient Rh(I) Homo- and Heterogeneous Catalysts for C-N Couplings via Hydrogen Borrowing.

Rhodium(I) complexes were explored as catalysts for the hydrogen borrowing reactions of amines and alcohols. Bidentate carbene-triazole ligands were readily synthesized via "click" reactions which allowed a diversity of ligand backbones to be accessed. The catalytic transformations are highly efficient, able to reach completion in under 6 h, and promote C-N bond formation across a range of primary alcohol and amine substrates. Moreover, site-selective catalysis can be achieved using substrates with more than one reactive site. A rhodium(I) complex covalently attached to a carbon black surface was also deployed in the hydrogen borrowing coupling reaction of aniline with benzyl alcohol. This represents the first report of a heterogeneous rhodium catalyst used for hydrogen borrowing.

Incorporation of 5-hydroxyindazole into the self-polymerization of dopamine for novel polymer synthesis.

Investigation into the mussel-inspired polymerization of dopamine has led to the realization that other compounds possessing potential quinone structures could undergo similar self-polymerizations in mild buffered aqueous conditions. To this end, 5-hydroxyindazole was added to a dopamine polymerization matrix in varying amounts, to study its incorporation into a polydopamine coating of silica particles. Solid-state (13) C NMR spectroscopy confirmed the presence of the indazole in the polymer shell when coated onto silica gel. SEM and DLS analysis also confirmed that the presence of the indazole in the reaction matrix yielded monodisperse polymer-coated particles, which retained their polymer shell upon HF etching, except when high levels of the indazole were used. Characterization data and examination of incorporation mechanism suggests that the 5-hydroxyindazole performs the function of a chain-terminating agent. Cytotoxicity studies of the polymer particles containing 5-hydroxyindazole showed dramatically lower toxicity levels compared to polydopamine alone.

Simple and reactive Ir(i) N-heterocyclic carbene complexes for alkyne activation.

Two simple unsymmetrical monometallic Ir(i) complexes with an N-heterocyclic carbene ligand and an analogous bimetallic Ir(i) complex were synthesised. These complexes were found to be extremely active catalysts for a range of C-X (X = N or O) and Si-N bond forming reactions involving alkyne and imine activation for dihydroalkoxylation, hydroamination and hydrosilylation reactions. These catalysts exhibited reaction rates far exceeding those of other Rh(i) and Ir(i) complexes previously reported. In addition, a small change to the ligand design (phenyl vs. mesityl) substantially affected both the reactivity and product selectivity of the catalyst. The Ir(i) complex bearing a mesitylene wingtip provided unprecedented regioselectivity in the dihydroalkoxylation reaction and a new kinetic product from the typical hydrosilylation protocol of 2-benyzlpyrroline to produce an N-silylaminoalkene. Our mechanistic studies indicated that this transformation proceeded via a dehydrogenative coupling mechanism.

Diastereoselective Synthesis and Conformational Analysis of (2R)- and (2S)-Fluorostatines: An Approach Based on Organocatalytic Fluorination of a Chiral Aldehyde.

Stereoselectively fluorinated analogues of the amino acid statine have been efficiently synthesized. The key step is an organocatalytic electrophilic fluorination of a chiral ß-oxygenated aldehyde, which provided a test of both diastereoselectivity and chemoselectivity. The target statine analogues were found to adopt unique conformations influenced by the fluorine gauche effect, rendering them potentially valuable building blocks for incorporation into bioactive peptides.

Cationic Rh and Ir complexes containing bidentate imidazolylidene-1,2,3-triazole donor ligands: synthesis and preliminary catalytic studies.

A series of new cationic Rh(I), Rh(III) and Ir(III) complexes containing hybrid bidentate N-heterocyclic carbene­1,2,3-triazolyl donor of general formulae [Rh(CaT)(COD)]BPh4 (2a­d), [Rh(CaT)(CO)2]BPh4 (3a­d) and [M(CaT)(Cp*)Cl]BPh4 (M = Rh, 4a­d; M = Ir, 5a­c), where CaT = bidentate N-heterocyclic carbene­triazolyl ligands, COD = 1,5-cyclooctadiene and Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl, were synthesised. The imidazolium­1,2,3-triazolyl pre-ligands (1a­c and 1e­i) were readily prepared using the Cu(I) catalysed 'click reaction' between phenyl azide or benzyl azides with propargyl functionalised imidazolium salts. The single crystal solid state structures of complexes 2a­d; 3a­b; 4a­d and 5a­b confirm the bidentate coordination of the NHC­1,2,3-triazolyl ligand with the NHC coordinating via the 'normal' C2-carbon and the 1,2,3-triazolyl donor coordinating via the N3' atom to form six membered metallocycles. These complexes are the first examples of Rh and Ir complexes containing the hybrid NHC­1,2,3-triazolyl ligands which exhibit a bidentate coordination mode. A number of these complexes showed limited efficiency as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine to 2-methylpyrroline.