Mary F. Mahon

Ruthenium-catalyzed meta sulfonation of 2-phenylpyridines

A selective catalytic meta sulfonation of 2-phenylpyridines was found to occur in the presence of (arene)ruthenium(II) complexes upon reaction with sulfonyl chlorides. The 2-pyridyl group facilitates the formation of a stable Ru-C(aryl) σ bond that induces a strong para-directing effect. Electrophilic aromatic substitution proceeds with the sulfonyl chloride to furnish a sulfone at the position meta to the chelating group. This new catalytic process offers access to atypical regioselectivity for reactions involving chelation-assisted cyclometalation.

Synthesis, Electronic Structure, and Magnetism of (Ni(6-Mes) 2 ) + :A Two-Coordinate Nickel(I) Complex Stabilized by Bulky N‑Heterocyclic Carbenes

The two-coordinate cationic Ni(I) bis-N-heterocyclic carbene complex [Ni(6-Mes)2]Br (1) [6-Mes =1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene] has been structurally characterized and displays a highly linear geometry with a C-Ni-C angle of 179.27(13)°. Density functional theory calculations revealed that the five occupied metal-based orbitals are split in an approximate 2:1:2 pattern. Significant magnetic anisotropy results from this orbital degeneracy, leading to single-ion magnet (SIM) behavior.

Catalytic Hydrodefluorination of Aromatic Fluorocarbons by Ruthenium N-Heterocyclic Carbene Complexes

The catalytic hydrodefluorination (HDF) of hexafluorobenzene, pentafluorobenzene, and pentafluoropyridine with alkylsilanes is catalyzed by the ruthenium N-heterocyclic carbene (NHC) complexes Ru(NHC)(PPh(3))(2)(CO)H(2) (NHC = SIMes (1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) 13, SIPr (1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) 14, IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) 15, IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) 16). Catalytic activity follows the order 15 > 13 > 16 > 14, with 15 able to catalyze the HDF of C(6)F(5)H with Et(3)SiH with a turnover number of up to 200 and a turnover frequency of up to 0.86 h(-1). The catalytic reactions reveal (i) a novel selectivity for substitution at the 2-position in C(6)F(5)H and C(5)F(5)N, (ii) formation of deuterated fluoroarene products when reactions are performed in C(6)D(6) or C(6)D(5)CD(3), and (iii) a first-order dependence on [fluoroarene] and zero-order relationship with respect to [R(3)SiH]. Mechanisms are proposed for HDF of C(6)F(6) and C(6)F(5)H, the principal difference being that the latter occurs by initial C-H rather than C-F activation.

Group 2 Promoted Hydrogen Release from NMe2H⋅BH3: Intermediates and Catalysis

Abstract Both homo‐ and heteroleptic alkyl and amide complexes of the Group 2 elements Mg and Ca are shown to be active for the catalytic dehydrocoupling of Me2NH⋅BH3. Reactions of either magnesium dialkyls or the β‐diketiminate complex [HC{(Me)CN(Dipp)}2MgnBu] with four or two equivalents of Me2NHBH3, respectively, produce compounds containing the [H3BNMe2BH2Me2N]− ion, which coordinates to the magnesium centers through Mg—N and Mg⋅⋅⋅HB interactions in both the solution and solid states. Thermolysis of these compounds at 60 °C produces the cyclic product [(H2BNMe2)2] and, it is proposed, magnesium hydrido species by an unprecedented δ‐hydride elimination process. Calcium‐based species, although less reactive than their magnesium‐based counterparts, are found to engage in similar dehydrocoupling reactivity and to produce a similar distribution of products under thermally promoted catalytic conditions. A mechanism for these observations is presented that involves initial production and insertion of H2B=NMe2 into polarized M—N bonds as the major B—N bond‐forming step. The efficacy of this insertion and subsequent β‐ or δ‐hydride elimination steps is proposed to be dependent upon the charge density and polarizing capability of the participating Group 2 center, providing a rationale for the observed differences in reactivity between magnesium and calcium.

Silver phosphanes partnered with carborane monoanions: Synthesis, structures and use as highly active lewis acid catalysts in a hetero-Diels-Alder reaction

Four Lewis acidic silver phosphane complexes partnered with [1-closo-CB(11)H(12)](-) and [1-closo-CB(11)H(6)Br(6)](-) have been synthesised and studied by solution NMR and solid-state X-ray diffraction techniques. In the complex [Ag(PPh(3))(CB(11)H(12))] (1), the silver is coordinated with the carborane by two stronger 3c-2e B-H-Ag bonds, one weaker B-H-Ag interaction and a very weak Ag.C(arene) contact in the solid state. In solution, the carborane remains closely connected with the [Ag(PPh(3))](+) fragment, as evidenced by (11)B chemical shifts. Complex 2 [Ag(PPh(3))(2)(CB(11)H(12))](2) adopts a dimeric motif in the solid state, each carborane bridging two Ag centres. In solution at low temperature, two distinct complexes are observed that are suggested to be monomeric [Ag(PPh(3))(2)][CB(11)H(12)] and dimeric [Ag(PPh(3))(2)(CB(11)H(12))](2). With the more weakly coordinating anion [CB(11)H(6)Br(6)](-) and one phosphane, complex 3 [Ag(PPh(3))(CB(11)H(6)Br(6))] is isolated. Complex 4, [Ag(PPh(3))(2)(CB(11)H(6)Br(6))], has been characterised spectroscopically. All of the complexes have been assessed as Lewis acids in the hetero-Diels-Alder reaction of N-benzylideneaniline with Danishefskys diene. Exceptionally low catalyst loadings for this Lewis acid catalysed reaction are required (0.1 mol %) coupled with turnover frequencies of 4000 h(-1) (quantitative conversion to product after 15 minutes using 3 at room temperature). Moreover, the reaction does not occur in rigorously dry solvent as addition of a substoichiometric amount of water (50 mol %) is necessary for turnover of the catalyst. It is suggested that a Lewis assisted Brønsted acid is formed between the water and the silver. The effect of changing the counterion to [BF(4)](-), [OTf](-) and [ClO(4)](-) has also been studied. Significant decreases in reaction rate and final product yield are observed on changing the anion from [CB(11)H(6)Br(6)](-), thus demonstrating the utility of weakly coordinating carborane anions in organic synthesis.

A method for the prediction of the crystal structure of ionic organic compounds—the crystal structures of o-toluidinium chloride and bromide and polymorphism of bicifadine hydrochloride

The crystal structures of o-toluidinium chloride (1), o-toluidinium bromide (2) and two polymorphs of bicifadine hydrochloride (3) have been determined. The polymorphs of 3 differ in their molecular conformation and in their mode of packing. Crystallisation studies and quantum mechanical calculations show that the more readily crystallisable polymorph grows from the thermodynamically most stable conformer. On heating, conversion to the second polymorph takes place just below the melting point. The crystal structures of 1, 2 and the first polymorph of 3 have been successfully predicted using a procedure that is suitable for simple ionic organics.

Salalen aluminium complexes and their exploitation for the ring opening polymerisation of rac-lactide

In this paper we report the first use of Al(III) salalen complexes for the ring opening polymerisation of rac-lactide. Polylactides with narrow polydispersities (PDIs range from 1.04-1.65) and moderate degrees of stereoselectivity were formed. Eight salalen Al(III) complexes have been prepared and fully characterised by solution-state NMR spectroscopy and, where appropriate, single crystal X-ray diffraction. With ligand 3H(2) either a monomeric or dimeric Al(III) species was formed, the dimeric species was favoured at low concentrations. The complexes were tested for the ring opening polymerisation of rac-lactide in toluene at 80 or 100 °C. Interestingly, various tacticities of polymer were formed, which were dependent upon the nature of the group bound to the amine nitrogen centre.

A hydride-rich magnesium cluster.

High-de-hydride! A straightforward reaction between a magnesium silylamido/N-heterocyclic carbene adduct and phenylsilane provides a {Mg(4)H(6)} cluster molecule that may be regarded as a combination of two magnesium dihydride and two magnesium monohydride moieties.

Beryllium-Induced CN Bond Activation and Ring Opening of an N-Heterocyclic Carbene†

Berylliant! Interaction of a well-defined adduct of MeBeH and an N-heterocyclic carbene (NHC) with PhSiH 3 results in complete rupture of the heterocycle, and activation of the NHC through effective BeH 2 insertion into a C-N bond of the heterocycle (see scheme; Ar=2,6- diisopropylphenyl, IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene).

Group 4 Salalen Complexes and Their Application for the Ring-Opening Polymerization of rac-Lactide

In this paper, we report the preparation and characterization of a series of unsymmetrical group 4 metal complexes based on ONNO salalen-type ligands. In these examples, the ligand is unsymmetrical with an amine and an imine nitrogen center. All complexes {except Hf(3)(O(i)Pr)(2)} adopt a beta-cis configuration in the solid state, which is also in agreement with solution-state NMR spectroscopic measurements. The complexes have been tested for the ROP of rac-lactide (both in solution and under melt conditions). Narrow polydispersities have been seen (1.07-1.82). The Ti(IV) complexes produce atactic PLA, whereas the Zr(IV) complexes form PLA with a heterotactic bias. Hf(IV) complexes have been shown to produce isotactic PLA with a P(m) of 0.75. The kinetics for all initiators have been investigated and are discussed.