Mairi F. Haddow

Mild C-H Halogenation of Anilides and the Isolation of an Unusual Palladium(I)-Palladium(II) Species

Eine einfache Pd-katalysierte ortho-selektive Bromierung und Chlorierung von Aniliden gelingt unter aeroben Bedingungen bei Raumtemperatur, wenn N-Halogensuccinimide (NXS) in Gegenwart von p-Toluolsulfonsaure (PTSA) eingesetzt werden. Der orthopalladierte PTSA-Komplex ist nicht nur katalytisch aktiv, sondern geht auch einen reduktiven Prozess unter Bildung eines ungewohnlichen PdI-PdII-Tetramers ein (siehe Struktur; Pd grun, O rot, S gelb, C grau).

Frustrated Lewis Pairs beyond the Main Group: Synthesis, Reactivity, and Small Molecule Activation with Cationic Zirconocene–Phosphinoaryloxide Complexes

The extension of the frustrated Lewis pair (FLP) concept to the transition series with cationic zirconocene-phosphinoaryloxide complexes is demonstrated. Such complexes mimic the reactivity of main group FLPs in reactions such as heterolytic hydrogen cleavage, CO(2) activation, olefin and alkyne addition, and ring-opening of tetrahydrofuran. The interplay between sterics and electronics is shown to have an important role in determining the reactivity of these compounds with hydrogen in particular. The Zr-H species generated from the heterolytic activation of hydrogen is shown to undergo insertion reactions with both CO(2) and CO. Crucially, these transition metal FLPs are markedly more reactive than main group systems in many cases, and in addition to the usual array of reactions they demonstrate unprecedented reactivity in the activation of small molecules. This includes S(N)2 and E2 reactions with alkyl chlorides and fluorides, enolate formation from acetone, and the cleavage of C-O bonds to facilitate S(N)2 type reactions with noncyclic dialkyl ethers.

Frustrated Lewis Pairs beyond the Main Group: Cationic Zirconocene–Phosphinoaryloxide Complexes and Their Application in Catalytic Dehydrogenation of Amine Boranes

The cationic zirconocene-phosphinoaryloxide complexes [Cp(2)ZrOC(6)H(4)P(t-Bu)(2)][B(C(6)F(5))(4)] (3) and [Cp*(2)ZrOC(6)H(4)P(t-Bu)(2)][B(C(6)F(5))(4)] (4) were synthesized by the reaction of Cp(2)ZrMe(2) or Cp*(2)ZrMe(2) with 2-(diphenylphosphino)phenol followed by protonation with [2,6-di-tert-butylpyridinium][B(C(6)F(5))(4)]. Compound 3 exhibits a Zr-P bond, whereas the bulkier Cp* derivative 4 was isolated as a chlorobenzene adduct without this Zr-P interaction. These compounds can be described as transition-metal-containing versions of linked frustrated Lewis pairs (FLPs), and treatment of 4 with H(2) under mild conditions cleaved H(2) in a fashion analogous to that for main-group FLPs. Their reactivity in amine borane dehydrogenation also mimics that of main-group FLPs, and they dehydrogenate a range of amine borane adducts. However, in contrast to main-group FLPs, 3 and 4 achieve this transformation in a catalytic rather than stoichiometric sense, with rates superior to those for previous high-valent catalysts.

Iron(I) in Negishi Cross-Coupling Reactions

Herein we demonstrate both the importance of Fe(I) in Negishi cross-coupling reactions with arylzinc reagents and the isolation of catalytically competent Fe(I) intermediates. These complexes, [FeX(dpbz)(2)] [X = 4-tolyl (7), Cl (8a), Br (8b); dpbz = 1,2-bis(diphenylphosphino)benzene], were characterized by crystallography and tested for activity in representative reactions. The complexes are low-spin with no significant spin density on the ligands. While complex 8b shows performance consistent with an on-cycle intermediate, it seems that 7 is an off-cycle species.

Catching the First Oligomerization Event in the Catalytic Formation of Polyaminoboranes: H3B·NMeHBH2·NMeH2 Bound to Iridium

We report the first insertion step at a metal center for the catalytic dehydropolymerization of H(3)B·NMeH(2) to form the simplest oligomeric species, H(3)B·NMeHBH(2)·NMeH(2), by the addition of 1 equiv of H(3)B·NMeH(2) to [Ir(PCy(3))(2)(H)(2)(η(2)-H(3)B·NMeH(2))][BAr(F)(4)] to give [Ir(PCy(3))(2)(H)(2)(η(2)-H(3)B·NMeHBH(2)·NMeH(2))][BAr(F)(4)]. This reaction is also catalytic for the formation of the free linear diborazane, but this is best obtained by an alternative stoichiometric synthesis.

Simplifying Iron–Phosphine Catalysts for Cross‐Coupling Reactions

Any old iron? Iron catalysts based on the widely available diphosphine ligand bis(diphenylphosphino)ethane have not previously fared particularly well in iron-catalyzed cross-coupling processes. However, this turns out not to be due to any inherently poor performance associated with the ligand, but rather the need to form a bis-chelate complex, either before or during the formation of an active FeI species.

Switching Pathways: Room-Temperature Neutral Solvolysis and Substitution of Amides

Stick or twist: By introducing steric hindrance at the nitrogen atom, stable linear amides bearing an electron-withdrawing α-substituent (Z = Ar, PhSO(2), P(O)(OR)(2), CN, or CO(2)R) can be induced to undergo solvolysis and substitution reactions through an elimination-addition mechanism (see picture). Key to this process is a low barrier to rotation around the amide bond and the α-substituent Z.

Paramagnetic Titanium(III) and Zirconium(III) Metallocene Complexes as Precatalysts for the Dehydrocoupling/Dehydrogenation of Amine-Boranes

Complexes of Group 4 metallocenes in the +3 oxidation state and amidoborane or phosphidoborane function as efficient precatalysts for the dehydrocoupling/dehydrogenation of amine-boranes, such as Me(2) NH⋅BH(3). Such Ti(III) -amidoborane complexes are generated in [Cp(2)Ti]-catalyzed amine-borane dehydrocoupling reactions, for which diamagnetic M(II) and M(IV) species have been previously postulated as precatalysts and intermediates.

Crystal engineering of lattice metrics of perhalometallate salts and MOFs.

The synthesis of the salt 3 and metallo-organic framework (MOF) [{(4,4′-bipy)CoBr2}n] 4 by a range of solid state (mechanochemical and thermochemical) and solution methods is reported; they are isostructural with their respective chloride analogues 1 and 2. 3 and 4 can be interconverted by means of HBr elimination and absorption. Single phases of controlled composition and general formula [4,4′-H2bipy][CoBr4-xClx] 5x may be prepared from 2 and 4 by solid—gas reactions involving HBr or HCl respectively. Crystalline single phase samples of 5x and [{(4,4′-bipy)CoBr2-xClx}n] 6x were prepared by solid-state mechanochemical routes, allowing fine control over the composition and unit cell volume of the product. Collectively these methods enable continuous variation of the unit cell dimensions of the salts [4,4′-H2bipy][CoBr4-xClx] (5x) and the MOFs [{(4,4′-bipy)CoBr2-xClx}n] (6x) by varying the bromide to chloride ratio and establish a means of controlling MOF composition and the lattice metrics, and so the physical and chemical properties that derive from it.

Selective guest recognition by a self-assembled paramagnetic cage complex

A cubic cage complex assembled from twelve bis-bidentate ligands and eight Co(II) ions provides a cavity that selectively recognises and binds coumarin in MeCN solution. The cage portals are large enough to allow guest exchange, but small enough to provide a kinetic trap; the cage paramagnetism facilitates detailed NMR analysis.