Terry Chu

Oxidative Addition of σ Bonds to an Al(I) Center

The Al(I) compound NacNacAl (1, NacNac = [ArNC(Me)CHC(Me)NAr](-) and Ar = 2,6-Pr(i)2C6H3) reacts with H-X (X = H, Si, B, Al, C, N, P, O) σ bonds of H2, silanes, borane (HBpin, pin = pinacolate), allane (NacNacAlH2), phosphine (HPPh2), amines, alcohol (Pr(i)OH), and Cp*H (Cp* = pentamethylcyclopentadiene) to give a series of hydride derivatives of the four-coordinate aluminum NacNacAlH(X), which are characterized herein by spectroscopic methods (NMR and IR) and X-ray diffraction. This method allows for the syntheses of the first boryl hydride of aluminum and novel silyl hydride and phosphido hydride derivatives. In the case of the addition of NacNacAlH2, the reaction is reversible, proving the possibility of reductive elimination from the species NacNacAlH(X).

A Coordination Compound of Ge0 Stabilized by a Diiminopyridine Ligand

Reduction of the cationic Ge(II) complex [dimpyrGeCl][GeCl3] (dimpyr=2,6-(ArN=CMe)2NC5H3, Ar=2,6-iPr2C6H3) with potassium graphite in benzene affords an air sensitive, dark green compound of Ge(0), [dimpyrGe], which is stabilized by a bis(imino)pyridine platform. This compound is the first example of a complex of a zero-valent Group 14 element that does not contain a carbene or carbenoid ligand. This species has a singlet ground state. DFT studies revealed partial delocalization of one of the Ge lone pairs over the π*(C=N) orbitals of the imines. This delocalization results in a partial multiple-bond character between the Ge atom and imine nitrogen atoms, a fact supported by the X-ray crystallography and IR spectroscopy data.

Oxidative Addition and Reductive Elimination at Main-Group Element Centers

Oxidative addition and reductive elimination are key steps in a wide variety of catalytic reactions mediated by transition-metal complexes. Historically, this reactivity has been considered to be the exclusive domain of d-block elements. However, this paradigm has changed in recent years with the demonstration of transition-metal-like reactivity by main-group compounds. This Review highlights the substantial progress achieved in the past decade for the activation of robust single bonds by main-group compounds and the more recently realized activation of multiple bonds by these elements. We also discuss the significant discovery of reversible activation of single bonds and distinct examples of reductive elimination at main-group element centers. The review consists of three major parts, starting with oxidative addition of single bonds, proceeding to cleavage of multiple bonds, and culminated by the discussion of reversible bond activation and reductive elimination. Within each subsection, the discussion is arranged according to the type of bond being cleaved or formed and considers elements from the left to the right of each period and down each group of the periodic table. The majority of results discussed in this Review come from the past decade; however, earlier reports are also included to ensure completeness.

Oxidative Cleavage of C=S and P=S Bonds at an AlI Center: Preparation of Terminally Bound Aluminum Sulfides

The treatment of cyclic thioureas with the aluminum(I) compound NacNacAl (1; NacNac=[ArNC(Me)CHC(Me)NAr]- , Ar=2,6-Pri2 C6 H3 ) resulted in oxidative cleavage of the C=S bond and the formation of 3 and 5, the first monomeric aluminum complexes with an Al=S double bond stabilized by N-heterocyclic carbenes. Compound 1 also reacted with triphenylphosphine sulfide in a similar manner, which resulted in cleavage of the P=S bond and production of the adduct [NacNacAl=S(S=PPh3 )] (8). The Al=S double bond in 3 can react with phenyl isothiocyanate to furnish the cycloaddition product 9 and zwitterion 10 as a result of coupling between the liberated carbene and PhN=C=S. All novel complexes were characterized by multinuclear NMR spectroscopy, and the structures of 5, 9, and 10 were confirmed by X-ray diffraction analysis. The nature of the Al=S bond in 5 was also probed by DFT calculations.

Oxidative Addition of Disulfides, Alkyl Sulfides, and Diphosphides to an Aluminum(I) Center

The aluminum(I) compound NacNacAl (1) reacts with diphenyl disulfide and diethyl sulfide to form the respective four-coordinate bis(phenyl sulfide) complex NacNacAl(SPh)2 (2) and alkyl thiolate aluminum complex NacNacAlEt(SEt) (3). As well, reaction of 1 with tetraphenyl diphosphine furnishes the bis(diphenyl phosphido) complex NacNacAl(PPh2)2 (4). Production of 3 and 4 are the first examples of C(sp(3))-S and R2P-PR2 activation by a main-group element complex. All three complexes were characterized by multinuclear NMR spectroscopy and X-ray crystal structure analysis. Furthermore, a variable-temperature NMR spectroscopic study was undertaken on 4 to study its dynamic behavior in solution.