The structure of dichlorotris(triphenylphosphine)ruthenium(II): a DFT study of interaction energies and substitution mechanism

Structural and thermodynamic insights into the coordination preference of norbornadiene with the initiator complex [RuCl2(PPh3)2(piperidine)] in polymerization via olefin metathesis

The metathesis reaction has been an important tool in both organic and inorganic synthetic chemistry. More specifically in polymer chemistry, ring opening metathesis polymerization (ROMP), via the formation of an active metal-carbene species (MCHR), has been widely used. The elucidation of the mechanism for ROMP opened the way for the development of well-defined catalysts, suited to local conditions. In the present study, we employed density functional theory (DFT) to investigate three reaction pathways for the formation of a species capable of activating ROMP. The active species is formed from the [RuCl2(PPh3)2(pip)] complex in the presence of norbornadiene (NBD) and the carbene source ethyl diazoacetate (EDA). Formation of a hexacoordinated intermediate [RuCl2(PPh3)2(pip)(NBD)] is favored in the first step, with NBD doubly coordinated to the [RuCl2(PPh3)2(pip)] moiety. Analysis of donation (X → Ru) and back-donation (Ru → X) processes in the [RuCl2(PPh3)2(pip)(NBD)] complex shows that piperidine behaves as a σ donor, while NBD behaves as a π donor and the PPh3 groups act as π acceptors. The intensity of the orbital component is predominant in relation to the steric component in the complex. Thus, we propose that the reaction occurs through the formation of a hexacoordinated complex, followed by the dissociation of a PPh3 group, thus forming a complex where NBD is doubly coordinated to the metal center. Coordination of EDA leads finally to the catalyst capable of forming the metallocyclobutane intermediate required for the ROMP reaction.

Synthesis Characterization and X-ray Structure of 2-(2,6-Dichlorophenylamino)-2-imidazoline Tetraphenylborate: Computational Study

The title compound tetraphenylborate salt of clonidine (Catapres®), 2-(2,6-dichlorophenylamino)-2-imidazoline tetraphenylborate (3), was prepared in 76 % yield by the reaction of 2-(2,6-dichlorophenylamino)-2-imidazoline hydrochloride (clonidine hydrochloride) (1) with sodium tetraphenylborate (2) in deionized water through anion exchange reaction at ambient temperature. The structure of the title borate salt was characterized by UV, thermal analysis, mass and NMR analyses. White crystals of (3) suitable for an X-ray structural analysis were obtained by slow growing from acetonitrile. The molecular structure of the titled compound (3) was crystallized in the acetonitrile, P21/c, a = 9.151 (3) Å, b = 12.522 (3) Å, c = 25.493 (6) Å, β = 105.161 (13)° V = 2819.5 (13) Å3, Z = 4. A DFT quantum chemistry calculation method was employed to investigate the interaction mechanism of clonidine with tetraphenylborate. The stable configurations of the complexes of clonidine with tetraphenylborate with electrostatic interactions were obtained. Finally, the interaction strength and type of the complexes were studied through the reduced density gradient (RDG) function. This study provides new theoretical insight into the interaction mechanism and a guide for screening and designing the optimal clonidine and tetraphenylborate reacting to form the complex.