Allison M. Mills

Modular diphosphine ligands based on bisphenol A backbones

A straightforward two-step synthesis is used to obtain new phosphorus-containing ligands based on readily available bisphenol A type backbones. Five diphosphine ligands have been prepared in good yields. An X-ray crystallographic study is presented for ligand 5. Preliminary results on rhodium-catalyzed hydroformylation exemplify the use of these ligands for homogeneous catalysis.

Metathesis of olefin-substituted pyridines: the metalated NCN-pincer complex in a dual role as protecting group and scaffold.

Pincer-palladium(II) and -platinum(II) cat- ions, YCY-M (YCY (2,6-(YCH2)2C6H3) ;Y NMe2, SPh; M Pd II ,P t II ), bound to diolefin-substituted pyridines (3,5- or 2,6-substitution) were successfully synthesized, and subsequently used in olefin meta- thesis (RCM) as a model study for template-directed synthesis of macrocycles. Especially a 3,5-disubstitut- ed pyridine bound to a NCN-Pt II -center (5a) gave a fast metathesis reaction, while the same reaction with the Pd II analogue (4a) was much slower and less selective (isomerization products were formed). Fur- thermore, it was found that 2,6-diolefin-substituted pyridines (4b, 5b, 5c) gave slow metathesis reactions, which is mainly ascribed tosteric hindrance during the ring-closing step. In all cases where prolonged reaction times were required an isomerization pro- cess, most likely assisted by cationic pincer-M II species, was observed as a competing reaction. 1 HN MR spectroscopy experiments revealed that pyridines are stronger bound to a cationic NCN-Pt II -center than toits Pd II -analogue. This aspect is of crucial importance when these pincer-pyridine complexes are applied in metathesis, since free pyridine in solution deactivates the Ru-metathesis catalyst. For the tem- plated construction of macrocycles, a strong M-N(py) bond is also important since it determines the selectivity for the desired product. In addition, these results open a new research field in which organo- metallic (pincer) complexes are used as protecting groups for strong Lewis-basic groups in catalysis. From failed attempts to prepare macrocycles using hexakis(SCS-Pd II -(1a)) complex 14, and from the results obtained with the monometallic pincer com- plexes in RCM, it can be concluded that the most suitable candidate for constructing macrocycles should comprise 2,6-diolefin-substituted pyridines bound to a multi-(NCN-Pt II )-template. In such a system, intrapyridine metathesis (steric hindrance) as well as isomerization reactions (strong M-N(py) bond) are suppressed.

A pyrazole-containing verdazyl radical ligand Meprv: structure of its precursor prvH3 and its bis(2,2'-bipyridine)ruthenium(II) complex.

Abstract Reaction between 1,1′-dimethyl carbonic dihydrazide and pyrazole-3-carboxaldehyde gave 1,5-dimethyl-3-(3′-pyrazolyl)-6-oxotetrazane (prvH 3 ), which crystallizes in the orthorhombic space group Pca 2 1 , with a =10.7745(4), b =8.1745(2) and c =10.6625(3) A. Dehydrogenation of prvH 3 in methanol by 1,4-benzoquinone afforded the methylated radical 1,5-dimethyl-3-(1′-methyl-3′-pyrazolyl)-6-oxoverdazyl (Meprv), which reacted with cis -[Ru(bpy) 2 Cl 2 ] and NaBPh 4 to yield the cation [Ru(bpy) 2 (Meprv)] 2+ as its BPh 4 salt. The absence of luminescence and the electrochemical behavior of this complex imply that the lowest 3 MLCT (metal to ligand charge transfer) excited state is located on the electron-deficient Meprv ligand.

Synthesis, structure and magnetic properties of a linear-chain manganese(II) complex [Mn(μ-Cl)2(mppma)]n, where mppma is N-(3-methoxypropyl)-N-(pyridin-2-ylmethyl)amine

Abstract N-(3-methoxypropyl)-N-(pyridin-2-ylmethyl)amine (abbreviated as mppma) and its complex [Mn(μ-Cl)2(mppma)]n have been synthesized. Single-crystal X-ray diffraction analysis has revealed that in the complex, mppma acts as a didentate ligand bound to the Mn(II) ion through two nitrogen atoms; [MnCl2(mppma)] units are connected by double chloride bridges to form one-dimensional zigzag chains of edge-sharing distorted MnCl4(mppma) octahedra. The temperature-dependent magnetic susceptibility data have been explained with Fisher model, with parameters J=−0.25 cm−1 and g=1.99, indicating weak antiferromagnetic coupling.

Linkage isomers of dibromobis(1-(2-methoxyethyl)tetrazole)copper(II) containing either a bromide or a unique tetrazole bridge

The ligand 1-(2-methoxyethyl)tetrazole (teeOMe) reacts with copper(II) bromide to form two different isomers with the formula [Cu(teeOMe)2Br2]n. The coordination details on the crystal packing are determined by the solvent from which the compound crystallises. In methanol, green crystals of α-[Cu(teeOMe)2Br2] (1) are formed, and these have been characterised by X-ray crystallography (at three temperatures) and magnetic susceptibility measurements. The crystal structure of 1 is built up from square-planar trans-[Cu(teeOMe)2Br2] units. Additional weak axial interactions between the copper centers and the N(2) tetrazole atoms of neighbouring complexes link the [Cu(teeOMe)2Br2] units into two-dimensional layers. Compound 1 displays paramagnetic behaviour (C = 0.41 cm3 K mol−1). In ethanol, yellow–brown crystals of β-[Cu(teeOMe)2Br2] (2) are formed, and these have been characterised by magnetic susceptibility measurements, in addition to IR, ligand field and EPR spectroscopy. The observed magnetic behaviour (C = 0.41 cm3 K mol−1, θ = 30.5 K and J/kB = 16.4 K) is consistent with a structure containing two-dimensional bromide-bridged copper(II) grids. It is proposed that in 2 the square-planar [Cu(teeOMe)2Br2] units are connected via axial Cu–Br interactions, as deduced from comparison of the magnetic properties.

Template-Directed Synthesis of Macroheterocycles by Ring-Closing Metathesis of Olefin-Substituted Pyridines in the Coordination Sphere of a Triplatinum Complex *

Mono- and tris-3,5- and 2,6-pyridinediyl-containing macroheterocycles were synthesized by metathesis of olefin-substituted pyridines in the coordination sphere of mono- and tris-platinum complexes, respectively. Tris(2,6-pyridinediyl)-containing macroheterocycles were hydrogenated over palladium catalyst. The hydrogenated macrocycle was used as ligand for the triplatinum template. The structure of the resulting complex was established by X-ray analysis.

Coordination chemistry and X-ray studies with novel sterically constrained diphosphonite ligands

The coordination of two novel, sterically constrained diphosphonite ligands towards different palladium, platinum and rhodium precursors has been studied. Complexes of this hitherto unexplored class of diphosphonites, based on rigid xanthene backbones, have been characterized by X-ray crystallography as well as by NMR and IR spectroscopy. A short and concise overview is given on the scarce literature on phosphonite related chemistry. Structural differences in the complexes obtained due to steric influences of the ligands are discussed. Ligand 1, bearing 2-tert-butylphenolate groups, led to orthometallated complexes cis-[MCl{1-κ3C,P,P}] (M = Pd, Pt) and to trans-[RhCl(CO)(1)]. These complexes were compared with those formed with ligand 2, bearing 2,2′-dioxo-3,3′-di-tert-butyl-5,5′-dimethoxy-1,1′-biphenyl groups, preventing orthometallation. The complexes trans-{PdCl2(2)], cis-[PtCl2(2)] and trans-[RhCl(CO)(2)] were structurally characterized. Valuable data were collected on chemical shifts, Pt–P coupling constants, as well as CO stretch frequencies of Rh–CO complexes as important tools for structural characterization of such complexes.

[5-Benzyl-3-phenyl-2-(2-pyridyl-κN)thiazolidin-4-one-κS]dichloropalladium(II)

The palladium(II) centre in the title compound, [PdCl(2)(C(21)H(18)N(2)OS)], is coordinated to the pyridyl N atom and to the thiazolidinone S atom of the 5-benzyl-3-phenyl-2-(2-pyridyl)thiazolidin-4-one ligand, resulting in a five-membered chelate ring. Two cis-chloro ligands complete the square-planar coordination environment of the metal. Although the geometry at the Pd centre is essentially planar, the N-Pd-S bite angle of 85.20 (8) degrees causes deviations in the cis angles from the ideal value of 90 degrees. Opposite enantiomers form one-dimensional chains in the cell via a short S.O intermolecular interaction.