Dataset Information

Dihydrogen Activation by Titanium Sulfide Complexes.

ABSTRACT: The titanocene sulfido complex Cp*(2)Ti(S)py (1, Cp* = pentamethylcyclopentadienyl; py = pyridine) is synthesized by addition of a suspension of S(8) to a toluene solution of Cp*(2)Ti-(CH(2)CH(2)) (2) and py. The rate of rotation of the pyridine ligand in solution was determined by (1)H NMR spectroscopy, and the structure of 1 was determined by X-ray crystallography. Complex 1 reacts reversibly with dihydrogen to give Cp*(2)Ti(H)SH (6) and py. Reaction of 1 with HD gives an equilibrium mixture of Cp*(2)Ti(D)SH and Cp*(2)Ti(H)SD; H(2) and D(2) are not formed in this reaction. 1D (1)H NMR magnetization transfer spectra and 2D EXSY (1)H NMR spectra of 6 in the presence of H(2) show that in solution the H(2), hydride, and hydrosulfido hydrogen atoms exchange. A four-center mechanism for this exchange is proposed. The EXSY studies show that the Ti-H and S-H hydrogens exchange with each other more rapidly than either of those hydrogens exchanges with external H(2). A transient dihydrogen complex intermediate is proposed to explain this observation. The infrared spectrum of 6 shows an absorption assigned to the Ti-H stretching mode at 1591 cm(-1) that shifts upon deuteration to 1154 cm(-1). Reaction of 1 with trimethylsilane, diethylsilane, or dimethylsilane gives Cp*(2)-Ti(H)SSiMe(3) (7), Cp*(2)Ti(H)SSiHEt(2) (8), or Cp*(2)Ti(H)SSiHMe(2) (9), respectively. The isotope effect for the reaction producing 7 has been measured, and a mechanism is proposed. Treatment of 1 with an additional equivalent of S(8) results in the formation of the disulfide Cp*(2)Ti(S(2)) (4). Acetylene inserts into the Ti-S bond of 4 to produce the vinyl disulfide complex 5. The structures of 4 and 5 have been determined by X-ray diffraction. Compound 4 reacts with 2 in the presence of py to produce 1. Phosphines react with 4 in the presence of H(2) to provide 6 and the corresponding phosphine sulfide. Reaction of hydrogen with 4 gives Cp*(2)-Ti(SH)(2) (3). The reactions of 1 and 4 with dihydrogen provide a model for possible mechanisms of H(2) activation by metal-sulfide hydrodesulfurization catalysts.

SUBMITTER: Sweeney ZK

PROVIDER: S-EPMC1444909 | biostudies-literature | 1999 Dec

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Dihydrogen Activation by Titanium Sulfide Complexes.

Sweeney Zachary K ZK Polse Jennifer L JL Bergman Robert G RG Andersen Richard A RA

Organometallics 19991201 26

The titanocene sulfido complex Cp*(2)Ti(S)py (1, Cp* = pentamethylcyclopentadienyl; py = pyridine) is synthesized by addition of a suspension of S(8) to a toluene solution of Cp*(2)Ti-(CH(2)CH(2)) (2) and py. The rate of rotation of the pyridine ligand in solution was determined by (1)H NMR spectroscopy, and the structure of 1 was determined by X-ray crystallography. Complex 1 reacts reversibly with dihydrogen to give Cp*(2)Ti(H)SH (6) and py. Reaction of 1 with HD gives an equilibrium mixture o ...[more]

PMID: 16633550

Similar Datasets

Project description:Homogeneous catalysis using transition metal complexes is ubiquitously used for organic synthesis, as well as technologically relevant in applications such as water splitting and CO2 reduction. The key steps underlying homogeneous catalysis require a specific combination of electronic and steric effects from the ligands bound to the metal center. Finding the optimal combination of ligands is a challenging task due to the exceedingly large number of possibilities and the non-trivial ligand-ligand interactions. The classic example of Vaska's complex, trans-[Ir(PPh3)2(CO)(Cl)], illustrates this scenario. The ligands of this species activate iridium for the oxidative addition of hydrogen, yielding the dihydride cis-[Ir(H)2(PPh3)2(CO)(Cl)] complex. Despite the simplicity of this system, thousands of derivatives can be formulated for the activation of H2, with a limited number of ligands belonging to the same general categories found in the original complex. In this work, we show how DFT and machine learning (ML) methods can be combined to enable the prediction of reactivity within large chemical spaces containing thousands of complexes. In a space of 2574 species derived from Vaska's complex, data from DFT calculations are used to train and test ML models that predict the H2-activation barrier. In contrast to experiments and calculations requiring several days to be completed, the ML models were trained and used on a laptop on a time-scale of minutes. As a first approach, we combined Bayesian-optimized artificial neural networks (ANN) with features derived from autocorrelation and deltametric functions. The resulting ANNs achieved high accuracies, with mean absolute errors (MAE) between 1 and 2 kcal mol-1, depending on the size of the training set. By using a Gaussian process (GP) model trained with a set of selected features, including fingerprints, accuracy was further enhanced. Remarkably, this GP model minimized the MAE below 1 kcal mol-1, by using only 20% or less of the data available for training. The gradient boosting (GB) method was also used to assess the relevance of the features, which was used for both feature selection and model interpretation purposes. Features accounting for chemical composition, atom size and electronegativity were found to be the most determinant in the predictions. Further, the ligand fragments with the strongest influence on the H2-activation barrier were identified.

Dataset Information

Dihydrogen Activation by Titanium Sulfide Complexes.

Publications

Dihydrogen Activation by Titanium Sulfide Complexes.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure