Jonathan D. Egbert

Copper N-heterocyclic carbene complexes in catalysis

N-Heterocyclic carbene ligated copper complexes act as catalysts in a variety of reactions. A brief overview of this rich chemistry is given here. Of particular note is the ability of Cu(NHC) complexes to functionalize carbonyls, alkenes and alkynes. With growth in the number of Cu(NHC) derived complexes, the catalytic possibilities involving these complexes are ever growing. We feel the full potential of these (for the most part) simply accessed complexes has yet to be fully achieved. The litany of reactions which Cu(NHC) catalyst facilitate are outlined here.

Activation of Hydrogen by Palladium(0): Formation of the Mononuclear Dihydride Complex trans‐[Pd(H)2(IPr)(PCy3)]

An even split: In sharp contrast with the general behavior of Pd(0) complexes, [Pd(IPr)(PCy(3))] is able to activate the H-H bond. The resulting trans-[Pd(H)(2)(IPr)(PCy(3))] is the first isolated mononuclear dihydride palladium compound. Its formation is supported by multinuclear NMR spectroscopy, density functional calculations, and X-ray diffraction studies. The stability and reactivity of this new species are examined.

Deuteration of boranes: catalysed versus non-catalysed processes

A dichotomy in the reactivity of B-H bonds is reported. A bis(N-heterocyclic carbene)-ligated iridium(III) complex can effect rapid deuteration of boronate esters at room temperature with low catalyst loadings; however, borane and 9-BBN both undergo deuteration in the absence of catalyst, and do not react with the iridium complexes. This is proposed to result from the inductive electron-withdrawing properties of the boronic ester substituents. Deuterated boronic esters can be accessed rapidly at room temperature with only very low loadings of iridium catalyst.

Protonation Studies of a Mono-Dinitrogen Complex of Chromium Supported by a 12-Membered Phosphorus Macrocycle Containing Pendant Amines

The reduction of fac-[CrCl3(P(Ph)3N(Bn)3)], (1(Cl3)), (P(Ph)3N(Bn)3 = 1,5,9-tribenzyl-3,7,11-triphenyl-1,5,9-triaza-3,7,11-triphosphacyclododecane) with Mg in the presence of dmpe (dmpe = 1,2-bis(dimethylphosphino)ethane) affords the first example of a monodinitrogen Cr(0) complex, Cr(N2)(dmpe)(P(Ph)3N(Bn)3), (2(N2)), containing a pentaphosphine coordination environment. 2(N2) is supported by a unique facially coordinating 12-membered phosphorus macrocycle containing pendant amine groups in the second coordination sphere. Treatment of 2(N2) at -78 °C with 1 equiv of [H(OEt2)2][B(C6F5)4] results in protonation of the metal center, generating the seven-coordinate Cr(II)-N2 hydride complex, [Cr(H)(N2)(dmpe)(P(Ph)3N(Bn)3)][B(C6F5)4], [2(H)(N2)](+). Treatment of 2((15)N2) with excess triflic acid at -50 °C afforded a trace amount of (15)NH4(+) from the reduction of the coordinated (15)N2 ligand (electrons originate from Cr). Electronic structure calculations were employed to evaluate the pKa values of three protonated sites of 2(N2) (metal center, pendant amine, and N2 ligand) and were used to predict the thermodynamically preferred Cr-NxHy intermediates in the N2 reduction pathway for 2(N2) and the recently published complex trans-[Cr(N2)2(P(Ph)4N(Bn)4)] upon the addition of protons and electrons.

Tandem deuteration/hydrosilylation reactions catalyzed by a rhodium carbene complex under solvent-free conditions

The complex [Rh(I(t)Bu)(2)HCl] has been shown to be an active catalyst in the hydrosilylation of carbonyl and imine complexes. This reactivity, combined with the previously reported H/D exchange catalyzed by these complexes allows for a one pot, two step reaction using a single catalyst for both H/D exchange and hydrosilylation. Using triethylsilane, [Rh(I(t)Bu)(2)Cl] catalyst, and D(2) gas, deuterated silyl-ethers can be synthesized in an atom-economical, solvent-free reaction.