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The authors express their gratitude for the service of Ibex and Shaheen 2 High-Performance Computing Facilities as well as the continued financial support from King Abdullah Univ. of Science and Technology (KAUST).

The mechanism of Rh-catalyzed intermolecular annulation of aryl-substituted diazenecarboxylates and alkenes was investigated using density functional theory (DFT) (PCM-M062X/6-311+G(d,p)//M062X/6-31G(d)). The acetate ligand (OAc)-assisted C–H activation via the formation of a five-membered rhodacycle (I-TS1; ΔG⧧ = 19.4 kcal/mol) is more favorable compared to that via a four-membered intermediate (II-TS1; ΔG⧧ = 27.8 kcal/mol). Our results also revealed that the seven-membered intermediate (I-3, ΔGrel = −6.8 kcal/mol) formed after the alkene insertion could undergo a coordination switch with the adjacent nitrogen atom (via TScs; ΔG⧧ = 16.5 kcal/mol) to produce a thermodynamically stable six-membered intermediate (II-3, ΔGrel = −10.4 kcal/mol), eventually leading to a cyclization process followed by a barrierless ligand-assisted protonation to yield the final product. The β-hydride elimination product was found to be kinetically and thermodynamically undesirable. The rate-determining step is identified as th...

Hydrogenation of esters under mild conditions was achieved using air-stable ruthenium PN3-pincer complexes containing an aminophosphine arm. High efficiency was achieved even in the presence of water. DFT studies suggest a bimolecular proton shuttle mechanism which allows H2 to be activated by the relatively stable catalyst with a reasonably low transition state barrier.

Density functional theory (DFT) was used to elucidate the mechanism of n-butane hydrogenolysis (into propane, ethane, and methane) on well-defined zirconium hydrides supported on SBA15 coordinated to the surface via N-donor surface pincer ligands: [(≡SiNH−)(≡SiO−)ZrH2] (A), [(≡SiNH−)2ZrH2] (B), [(≡SiNH−)(≡SiO−)2ZrH] (C), [(≡SiNH−)2(≡SiO−)ZrH] (D), [(≡SiN═)(≡Si–O−)ZrH] (E), and [(≡SiN═)(≡SiNH−)ZrH] (F). The roles of these hydrides have been investigated in C–H/C–C bond activation and cleavage. The dihydride A linked via a chelating [N,O] surface ligand was found to be more active than B, linked to the chelating [N,N] surface ligand. Moreover, the dihydride zirconium complexes are also more active than their corresponding monohydrides C–F. The C–C cleavage step occurs preferentially via β-alkyl transfer, which is the rate-limiting step in the alkane hydrogenolysis. The energetics of the comparative pathways over the potential energy surface diagram (PES) reveals the hydrogenolysis of n-butane into propane a...

The one-electron oxidations of two dimers of half-sandwich osmium carbonyl complexes have been examined by electrochemistry, spectro-electrochemistry, and computational methods. The all-terminal carbonyl complex Os2Cp2(CO)4 (1, Cp = η5-C5H5) undergoes a reversible one-electron anodic reaction at E1/2 = 0.41 V vs ferrocene in CH2Cl2/0.05 M [NBu4][B(C6F5)4], giving a rare example of a metal–metal bonded radical cation unsupported by bridging ligands. The IR spectrum of 1+ is consistent with an approximately 1:1 mixture of anti and gauche structures for the 33 e– radical cation in which it has retained all-terminal bonding of the CO ligands. Density functional theory (DFT) calculations, including orbital-occupancy-perturbed Mayer bond-order analyses, show that the highest-occupied molecular orbitals (HOMOs) of anti-1 and gauche-1 are metal–ligand delocalized. Removal of an electron from 1 has very little effect on the Os–Os bond order, accounting for the resistance of 1+ to heterolytic cleavage. The Os–Os bo...

Copper(I) fluoride complexes ligated by phenanthroline derivatives have been synthesized and structurally characterized by X-ray crystallography. These complexes adopt as either ionic or neutral forms in the solid state, depending on the steric bulkiness of the substituent groups on the phenanthroline ligands. These complexes react with primary and secondary alkyl bromides to produce the corresponding alkyl fluorides in modest to good yields. This new method is compatible with a variety of important functional groups such as ether, thioether, amide, nitrile, methoxyl, hydroxyl, ketone, ester, and heterocycle moieties.

An effective model of cooperative effect of silver for the copper-catalyzed trifluoromethylation of activated and unactivated aryl iodides to trifluoromethylated arenes using Me3SiCF3 was achieved with a broad substrate scope.

Metathetical reaction of AgSCN with a series of trans-dihalido-bis(carbene) nickel(II) complexes in CH3CN readily afforded the novel diisothiocyanato-bis(carbene) complexes [Ni(NCS)2(NHC)2] (trans-2a, NHC = 1,3-diisopropylbenzimidazolin-2-ylidene; trans-2b, NHC = 1,3-diisobutylbenzimidazolin-2-ylidene; trans-2c, NHC = 1,3-dibenzylbenzimidazolin-2-ylidene; cis-2d, NHC = 1,3-di(2-propenyl)benzimidazolin-2-ylidene; cis-2e, NHC = 1-propyl-3-methylbenzimidazolin-2-ylidene) as greenish-yellow powders in moderate to good yields. While dihalido-bis(carbene) Ni(II) complexes exclusively form trans-complexes, a trans−cis isomerization occurs upon halido−isothiocyanato exchange with complexes bearing less bulky carbene ligands, i.e., cis-2d/e. DFT calculations indicated that this isomerization can be attributed to a reduced energy difference between trans- and cis-isomers of diisothiocyanato complexes. All complexes have been characterized by multinuclear NMR spectroscopy, ESI mass spectrometry, and X-ray diffractio...

A series of N-heterocyclic carbene (NHC) complexes CpMo(CO)2(NHC)X (NHC = IMe = 1,3-dimethylimidazol-2-ylidene, X = Br, 1; NHC = 1,3-dipropylimidazol-2-ylidene, X = Br, 2; NHC = IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, X = Br, 3; NHC = IBz = 1,3-dibenzylimidazol-2-ylidene, X = Br, 4a, and X = Cl, 4b; NHC = 1-methyl-3-propylimidazol-2-ylidene, X = Br, 5) and [CpMo(CO)2(IMes)(CH3CN)][BF4] (6) have been synthesized and fully characterized. The stability of metal−NHC ligand bonds in these compounds under oxidative conditions has been investigated. The thermally stable Mo(VI) dioxo NHC complex [CpMoO2(IMes)][BF4] (9) has been isolated by the oxidation of the ionic complex 6 by TBHP (tert-butyl hydrogen peroxide). Complex 6 can be applied as a very active (TOFs up to 3400 h−1) and selective olefin epoxidation catalyst. While under oxidative conditions (in the presence of TBHP), compounds 1−5 decompose into imidazolium bromide and imidazolium polyoxomolybdate. The formation of polyoxomolybdate as...

Zirconocene−1-aza-1,3-diene complexes, [Me2Si(C5H4)2]Zr[N(Ar)CH═CHCH(Ph)] (Ar = Ph, 2a; Ar = p-MeOC6H4, 2b) and Cp2Zr[N(Ar)CH═CHCH(Ph)] (Ar = Ph, 3a; Ar = p-MeOC6H4, 3b), have been synthesized and ...

Density functional theory (DFT) calculations using the KMLYP method on a series of pincer PCP−rhodium dihydrogen complexes have been employed to model and examine the proposed mechanisms for the pincer PCP−rhodium complexes mediated hydrogenation of carbon dioxide (CO2). The relative energies of dihydrogen rotamers and dihydride isomers were evaluated together with T1 values to determine the molecular structures of these complexes. We have investigated possible pathways for the CO2 reduction processes involving the formation of rhodium dihydride species. Although the dihydrogen complexes are more stable than the corresponding dihydride isomers, the reduction of CO2 has to proceed through the dihydride structures.

A series of mono(cyclopentadienyl)titanium TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) complexes were investigated by density functional theory (DFT) calculations to study the influence of the ligands on the Ti−O bond energies. Mono-Cp complexes with pendant amino groups were found to possess significantly weaker Ti−O bonds than those lacking pendant donor ligands. On the basis of DFT predictions, a novel mono-Cp pendant dimethylamino complex, CpNTiCl2(TEMPO) (12; CpN = C5H4CH2CH2N(CH3)2), was identified as a mono-Cp titanium TEMPO complex with a weak Ti−O bond (25 kcal/mol). The calculated bond energy of this complex is comparable to that of Cp2TiCl(TEMPO) (3; 17 kcal/mol). Thermolysis of 12 in the presence of CCl4 at 100 °C resulted in the formation of CpNTiCl3, consistent with the predicted low Ti−O bond energy.

The Os−Os dimer [Cp(CO)2Os]2 was synthesized in good yield by reaction of Cp(CO)2OsI with NaK. The related Cp* dimer [Cp*(CO)2Os]2 (Cp* = η5-C5Me5) was prepared by reaction of Cp*(CO)2OsH with 2,2‘-azobis(isobutyrylnitrile) (AIBN). In contrast to [Cp(CO)2Os]2, which has only terminal CO ligands, spectroscopic and crystallographic data indicate that [Cp*(CO)2Os]2 has two bridging CO ligands. Reaction of tetraisopropylcyclopentadiene with [(CO)3OsI]2 provides (iPr4C5H)(CO)2OsI, which can be converted to (iPr4C5H)(CO)2OsH through reduction with NaK followed by treatment with EtOH. Reaction of (iPr4C5H)(CO)2OsH with AIBN gives [(iPr4C5H)(CO)2Os]2, which is much more soluble than [Cp*(CO)2Os]2. DFT (B3LYP) calculations on these Os−Os dimers reveal the energetics of different geometrical isomers. The anti and gauche isomers of [Cp(CO)2Os]2, with terminal CO ligands, are significantly more stable than the trans and cis isomers with bridging CO ligands, while the stability of the anti isomer of [Cp*(CO)2Os]2 is s...