Pincer oxazolines: emerging tools in coordination chemistry and catalysis--where to next?

Transition metal complexes of monodentate 2-oxazolines containing long chain alkyl groups. The crystal structure of trans-PdCl2(κ 1-N-rac-2-heptadecyl-4,5-dihydro-5-methyl-2-oxazole)2

The synthesis, characterisation and properties of several divalent metal complexes (Co, Ni, Pd) containing 2-oxazoline ligands L1–L3, appended with long chain alkyl and/or ester groups, is reported. The X-ray crystal structure aspects of one such complex, trans-PdCl2(rac-2-heptadecyl-4,5-dihydro-5-methyl-2-oxazole)2 (i.e. PdCl2(L1)2: 3), is described. This latter material contains one of the longest alkyl chains to be crystallographically characterised appended to an oxazoline ligand. The complexes reported herein represent the first transition metal derivatives of these high molecular weight, long chain and presumably low polarity monodentate oxazoline ligands. A combination of spectral and theoretical calculations (semi-empirical PM6(tm) level of theory) are used to support the proposed structure in the case of the hydrates of NiCl2 and CoBr2 complexes derived from L1. A trio of PdCl2 complexes of the ligand set are likewise detailed. Complex 3 is shown to be a useful pre-catalyst for the promotion of a Heck coupling reaction between bromobenzene and styrene under typical conditions.

Synthesis and characterisation of κ2-N,O-oxazoline-enolate complexes of nickel(ii): explorations in coordination chemistry and metal-mediated polymerisation

The synthesis and characterisation (UV-Vis, IR, X-ray diffraction, etc.) of a series of Ni(ii) complexes derived from both known and novel 2-acylmethyl-2-oxazolines (2a-g: i.e., (Z)-1-R-2-(4,4'-dimethyl-2'-oxazolin-2'-yl)eth-1-en-1-ol; R = -Ph, -2-furanyl, -p-NO2-Ph, -t-Bu, -2-thiofuranyl, p-NC-Ph, -CF3) is reported. These Ni materials (3a-g) represent the first group 10 metal complexes of this ligand class. All derivatives reported are paramagnetic (S = 1) compounds of formulae Ni(κ2-N,O-L)2 where L represents an enolate of structure (Z)-1-R-2-(4',4'-dimethyl-2'-oxazolin-2'-yl)eth-1-en-1-ate formed via proton loss from 2. The air- and moisture-stable metal complexes feature a less typical distorted seesaw-shaped disposition of binding atoms around the metal centre for six structurally characterised (X-ray) examples. Preliminary investigations indicate that 3a (R = -Ph) is a useful catalysts for olefin polymerisation in the presence of alkylaluminum reagents.

The crystal structure of diaqua-(N-(2-hydroxy-5-nitrobenzyl)iminodiacetato-κ4-N,O,O′,O′′)chromium(III) based on synchrotron data, C11H13CrN2O9

C11H13CrN2O9, orthorhombic, Pbca (no. 61), a = 6.7740(14) Å, b = 12.309(3) Å, c = 32.776(7) Å, V = 2732.9(10) Å3, Z = 8, Rgt(F) = 0.0302, wRref(F2) = 0.0867, T = 100(2) K.

Oxazolines as Dual-Function Traceless Chromophores and Chiral Auxiliaries: Enantioselective Photoassisted Synthesis of Polyheterocyclic Ketones

2-(o-Amidophenyl)oxa- and -thiazolines undergo excited-state intramolecular proton transfer (ESIPT), generating aza-o-xylylenes capable of intramolecular [4+2] and [4+4] cycloadditions with tethered unsaturated pendants. Facile hydrolysis of the primary photoproducts, spiro-oxazolidines and thiazolidines, under mild conditions unmasks a phenone functionality. Variations in linkers allow for access to diverse core scaffolds in the primary photoproducts, rendering the approach compatible with the philosophy of diversity-oriented synthesis. Chiral oxazolines, readily available from the corresponding amino alcohols, yield enantioenriched keto-polyheterocycles of complex topologies with enantiomeric excess values up to 90%.

Cobalt(ii) and copper(ii) supramolecular networks with a 1-iminoisoindoline asymmetric pincer

The first synthesis and characterization of cobalt(ii) and copper(ii) complexes with an in situ prepared novel asymmetric trinitrogen isoindoline-based pincer type ligand, N-(2-picolyl)isoindoline-1-(2-picolyl)imine (pap), are reported.

Isolation of a potassium bis(1,2,3-triazol-5-ylidene)carbazolide: a stabilizing pincer ligand for reactive late transition metal complexes

The synthesis and X-ray crystal structure of a potassium adduct of a monoanionic CNC-pincer ligand featuring two mesoionic carbenes is reported. Owing to the peculiar electronic and steric properties of this ligand, the first neutral stable Ni(II)-hydride, and an unusual Cu(II) complex displaying a seesaw geometry, have been isolated.