An effective way of teaching undergraduates a full complement of research skills is through a multiweek advanced laboratory experiment. Here we outline a comprehensive set of experiments adapted from current primary literature focusing on organic and inorganic synthesis, catalysis, reactivity, and reaction kinetics. The catalyst, bis(2(2'-hydroxyphenyl)-2-oxazoline)oxorhenium(V) tetrapentafluorophenylborate (1) is isolated through a multistep reaction starting with the formation of the ligand, 2-(2'-hydroxyphenyl)-2-oxazoline (2), followed by complexation of a Re-oxo precursor to form chlorobis(2-(2'-hydroxyphenyl)-2-oxazoline)oxorhenium(V) (3). Both Re(V) oxo complexes are diathagnetic and allow for NMR analysis. Complex 1 is an air-stable and highly active catalyst for two reactions: (1) hydrosilylation of carbonyls and (2) hydrolysis of Et3SiH to form Et3SiOH and H-2 gas. Students monitor the evolution of hydrogen gas in the second reaction and use the data to investigate the reaction kinetics in order to obtain the complete rate law and the second-order rate constant for the catalytic reaction. The complete project provides a wealth of opportunities to focus on experimental skills, fundamental concepts in inorganic and organic chemistry, catalysis, reactivity, and experimental kinetics. KEYWORDS: Upper-Division Undergraduate, Laboratory Instruction, Synthesis, Catalysis, Kinetics, NMR. Spectroscopy, Organic Chemistry, Inorganic Chemistry, Communication/Writing

The effect of oxidatively stable L- and X-type additives on the activity of Cp*Ir catalyst precursors in the C-H activation of arenes has been studied. Turnover numbers for C-H activation of up to 65 can thus be achieved, as determined by H/D exchange in MeOH-D4. In particular, carbonate additives are found to enhance the C-H activation reactivity of Cp*Ir(H2O)3(OTf)2 () more significantly than L-type ligands investigated in this study. Based on these studies, Cp*Ir/carbonate systems are developed that catalyze the aerobic Csp(3)-H oxygenation of alkyl arenes, employing air as oxidant.

In this paper the reactivity of the previously reported metallacyclopentane complex [Mo(NPh)(o-(Me3SiN)(2)C6H4)(CH2)(4)] (1) is reported. Complex I reacts with acetylenes via ethylene exchange to form novel Mo imido metallacyclopentene complexes, [Mo(NPh)(O-(Me3SiN)(2)C6H4)(CRCR'(CH2)(2))(4)] (R = Ph, R' = H, 4a; R = H, R' = Ph, 4b; R, R' = CO2Et, 4c). The kinetics of the formation of 4c from 1, in the presence of excess diethyl acetylenedicarboxylate (DEAC), was examined. The activation parameters for the formation of 4c were found to be Delta H-not equal = 20.5(2.3) kcal mol(-1) and Delta S-not equal = -14.8(6.6) cal (mol K)(-1). The metallacyclopentadiene complex [(NPh)Mo(C(Ph)CHCHC(Ph)){o-(Me3SiN)(2)C6H4}] (7) was synthesized by the oxidative coupling of two phenylacetylene molecules. Compound 7 is active as a catalyst for the cyclotrimerization of phenylacetylene. X-ray crystal structures of 1, 4b, and 7 are reported.

We describe herein the novel application of a transition metal oxo complex, a cationic oxorhenium(V) oxazoline, in the production of molecular hydrogen (H2) from the catalytic hydrolytic oxidation of organosilanes. The main highlights of the reaction are quantitative hydrogen yields, low catalyst loading, ambient conditions, high selectivity for silanols, water as the only co-reagent, and no solvent requirement. The amount of hydrogen produced is proportional to the water stoichiometry. Thus, reaction mixtures of polysilyl organics such as HC(SiH3)3 and water contain potentially >6 wt % hydrogen. Kinetic and isotope labeling experiments have revealed a new mechanistic paradigm for the activation of Si-H bonds by oxometalates.

The rhenium oxo complex [Re(O)(hoz)2][TFPB], 1 (where hoz = 2-(2'-hydroxyphenyl)-2-oxazoline(-) and TFPB = tetrakis(pentafluorophenyl)borate) catalyzes the hydrosilation of aldehydes and ketones under ambient temperature and atmosphere. The major organic product is the protected alcohol as silyl ether. Isolated yields range from 86 to 57%. The reaction requires low catalyst loading (0.1 mol %) and proceeds smoothly in CH2Cl2 as well as neat without solvent. In the latter condition, the catalyst precipitates at the end of reaction, allowing easy separation and catalyst recycling. Re(O)(hoz)(H), 3, was prepared, and its involvement in an ionic hydrosilation mechanism was evaluated. Complex 3 was found to be less hydridic than Et3SiH, refuting its participation in catalysis. A viable mechanism that is consistent with experimental findings, rate measurements, and kinetic isotope effects (Et3SiH/Et3SiD = 1.3 and benzaldehyde-H/benzaldehyde-D = 1.0) is proposed. Organosilane is activated via eta2-coordination to rhenium, and the organic carbonyl adds across the coordinated Si-H bond [2 + 2] to afford the organic reduction product.

The synthesis and characterization of the bis(isocyanide) complexes (RNC)(2)Mo(NPh)(o-(Me3SiN)(2)C6H4) (2: 2a, R = (BuNC)-Bu-t; 2b, R = 2,6-dimethylphenyl) and the subsequent reactivity of these complexes with excess isocyanide have been reported. An X-ray crystal structure of (RNC)2Mo(NPh)(o-(Me3SiN)2C6H4) (R = 2,6-dimethylphenyl) is reported. Treatment of 2a with excess tent-butyl isocyanide resulted in the formation of the tris(isocyanide) complex ((BuNC)-Bu-t)(3)Mo(NPh)(o-(Me3SiN)(2)C6H4) (3). Complex 3 exists in solution in equilibrium with 2a. Using a two-site exchange mechanism the activation barrier for the dissociative exchange of tBuNC has been calculated. The X-ray crystal structure of ((BuNC)-Bu-t)(3)Mo(NPh)(o-(Me3SiN)(2)C6H4) is reported. Computational studies (ONIOM) performed on 3 reveal that pi conflicts in this complex results in the lengthening of the Mo-N(amido)(cis) bond relative to the Mo-N(amido)(trans) bond. Treatment of 2b with excess 2,6-dimethylphenyl isocyanide results in the slow insertion of the isocyanide ligands into the Mo-N bond of the chelating diamide ligand, resulting in a novel chelating iminocarbamoyl bis(isocyanide) complex, 4. An X-ray crystal structure of 4 is reported.

Reaction of AlMe3 with the imido compounds Mo(NPh)(o-(SiMe3N)(2)C6H4)(CH2)(4) (1) and Mo(NPh)(o-(SiMe3N)(2)C6H4)L (2; L = diphenylacetylene) results in the transfer of the diamide ligand to the Al, giving the unusual arene complexes 3 and 4.

The monomeric alkyne complexes (eta(2)-alkyne)Mo(NPh)(o-(Me3SiN)(2)C6H4) (3) have been synthesized by the displacement of isobutylene from (eta(2)-isobutylene)Mo(NPh)(o-(Me3SiN)(2)C6H4) (2). The alkyne fragment in these complexes is oriented perpendicular to the Mo=N bond of the cis imido ligand, as confirmed by an X-ray structural analysis of 3e. The deshielded nature of the chemical shifts of the (x-carbons and terminal protons of the alkyne, fragments in these complexes strongly suggests the participation of the alkyne pi(perpendicular to) electrons in the Mo - alkyne interaction. The alkyne fragment in 3 rotates freely about the Mo - alkyne bond, resulting in the fluxional behavior of these complexes at room temperature. An activation barrier of 13.2 kcal/mol for the alkyne rotation was measured using VT NMR spectroscopy. Computational studies using a two-layer ONIOM model, and the B3LYP hybrid functional, provided insight into the Mo-alkyne bonding. The transition state for alkyne rotation has been calculated and is characterized by a parallel orientation of the alkyne fragment to the cis imido ligand. A natural bond orbital (NBO) population analysis reveals that alkyne pi(perpendicular to) donation to Mo is more extensive in the transition state than in the ground state. Weaker Mo-N(imido) bonds are also observed in the transition state, because pi donation from the alkyne ligand competes with imido pi donation.