Gold(III) NHC Complexes for Catalyzing Dihydroalkoxylation and Hydroamination Reactions.

A gold(III) complex of an N-heterocyclic carbene based hemilabile ligand with two pendant pyrazole arms (1,3-bis((1H-pyrazol-3-yl)methyl)-2,3-dihydro-1H-imidazole, LH) was synthesized. Complex [LAu(III)Cl3] is an excellent catalyst for promoting dihydroalkoxylation at room temperature, even catalyzing this reaction at 0 °C. [LAu(III)Cl3] is one of the most efficient catalysts reported to date for the spirocyclization of alkynyl diols. Furthermore, [LAu(III)Cl3] catalyzed intra- and intermolecular hydroamination reactions, achieving good to excellent conversions. [LAu(III)Cl3] is a more efficient catalyst than a gold(I) analogue, [LAu(I)Cl]. The dependence of the quantity of weakly coordinating anion [BArF4]- ((3,5-trifluoromethyl)phenyl borate) present on catalysis efficiency was probed for the dihydroalkoxylation reaction. X-ray diffraction analysis of single crystals demonstrated the solid-state structure of gold complexes [LAu(III)Cl3] and [LAu(I)Cl], which displayed the expected square-planar and linear coordination geometries, respectively.

Synthesis, Structure, and Bonding for Bis(permethylpentalene)diiron.

The synthesis of the first homoleptic double metallocene complex of iron, Fe2Pn*2 (Pn* = permethylpentalene, C8Me6) is described. The structural and electronic properties of Fe2Pn*2 have been characterized by NMR and EPR spectroscopy, single crystal X-ray diffraction, magnetic measurements, cyclic voltammetry, and DFT calculations. Fe2Pn*2 adopts a Ci symmetry in the solid state with a Fe-Fe distance of 2.3175(9) Å, slightly lower than the sum of radii in metallic iron. Magnetic measurements in solution, and of the solid phase between 60 and 300 K, indicate that Fe2Pn*2 is a triplet (S = 1) paramagnet, with effective magnetic moments (µeff) of 3.4 and 3.48 µB, respectively. DFT calculations indicate the origin of this high magnetic moment is likely to be unquenched orbital angular momentum contributions from two SOMOs which have metal d character. Cyclic voltammetry studies demonstrate that Fe2Pn*2 can access four charge states (-1, 0, +1, +2).

Ring-opening polymerization of a strained [3]nickelocenophane: a route to polynickelocenes, a class of S = 1 metallopolymers.

We report the synthesis, reactivity studies, and ring-opening polymerization of a tricarba[3]nickelocenophane. The resulting green polynickelocene (5) possesses a -(CH2)3- spacer between the nickelocene units and is shown to be of high molecular weight. SQUID magnetometry measurements indicate that 5 is a macromolecular material with an S = 1 repeat unit.

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.

Synthesis, characterisation and redox properties of anti-bimetallic permethylpentalene complexes.

We report a series of anti-bimetallic transition metal complexes based on the permethylpentanyl (Pn*, C8Me6) ligand: anti-(MCpR5)2Pn* (where M = Fe, Co and Ni and R = H or Me). Compounds (FeCp*)2Pn* (1), (CoCp*)2Pn* (2), (NiCp*)2Pn* (3), (CoCp)2Pn* (4) and (NiCp)2Pn* (5) were fully characterised by NMR spectroscopy, X-ray crystallography, DFT calculations and cyclic voltammetry. All anti-(MCpR5)Pn* structures have diamagnetic ground states. 1, 2 and 4 have isolated non-degenerate ground states with closed shell configurations. A study of the magnetic properties of the dinickel complexes 3 and 5 reveal Boltzmann population of a Curie triplet state in the solution. Cyclic voltammetry reveals multiple reversible or quasi-reversible redox couples for all the dinuclear complexes.

Small molecule activation by frustrated Lewis pairs.

A series of frustrated Lewis pairs (FLPs) based on the Lewis acids tris(perchloroaryl)borane (BAr(Cl)), and tris(2,2',2''-perfluorobiphenyl)borane (PBB) and trialkylphosphines were prepared; their ability to effect the heterolytic cleavage of dihydrogen, insert carbon dioxide into the borohydride, and reduce the resulting formatoborate to methanol were studied. Additionally, the insertion of CO(2) into a B-OH bond is explored with the ultimate aim of developing a homogeneous, catalytic preparation of carbonates. The compound [PBB-OH][H-P((t)Bu)(3)] was characterised by single crystal X-ray crystallography.

Heterolytic activation of hydrogen using frustrated Lewis pairs containing tris(2,2',2''-perfluorobiphenyl)borane.

The extremely sterically hindered borane tris(2,2',2''-perfluorobiphenyl)borane (PBB) has been structurally characterised. In combination with bulky nitrogen bases, it forms the 'frustrated Lewis pairs' (FLPs) PBB/2,2,6,6-tetramethylpiperidine (TMP) (1), PBB/1,4-diazobicyclo[2.2.2]-octane (DABCO) (2) and PBB/2,6-lutidine (lut) (3). These novel, unquenched acid-base pairs have been shown to effect facile room temperature heterolytic cleavage of dihydrogen to form the ammonium borate salts [2,2,6,6-Me(4)C(5)H(6)NH(2)][HB(C(12)F(9))(3)] (4) and [N(C(2)H(4))(3)NH][HB(C(12)F(9))(3)] (5), and lutidinium borate [2,6-Me(2)C(5)H(3)NH][HB(C(12)F(9))(3)] (6). Although these reactions are equilibria, the reverse reaction and release of hydrogen gas was not apparent at temperatures up to 120 °C. The relative Lewis acidity of PBB has been determined using the Gutmann-Beckett method.