Actinide Complexes Possessing Six-Membered N-Heterocyclic Iminato Moieties: Synthesis and Reactivity

Abstract

A novel class of ligand systems possessing a sixmembered N-heterocyclic iminato [perimidin-2-iminato (Pr R N, where R = isopropyl, cycloheptyl)] moiety is introduced. The complexation of these ligands with early actinides (An = Th and U) results in powerful catalysts [(Pr R N)An(N{SiMe 3 ) 2 } 3 ] (3−6) for exigent insertion of alcohols into carbodiimides to produce the corresponding isoureas in short reaction times with excellent yields. Experimental, thermodynamic, and kinetic data as well as the results of stoichiometric reactions provide cumulative evidence that supports a plausible mechanism for the reaction.

Hydroboration of Aldehydes, Ketones, and Carbodiimides Promoted by Mono(imidazolin‐2‐iminato) Hafnium Complexes

“…We have shown that if throughout a catalytic insertion process the system initiates with a metal‐oxygen bond, however, after the catalytic transformation, a different metal‐oxygen bond is obtained, ideally and thermodynamically speaking, the system is thermoneutral as regards to the M–O bond however, the system must be able to reach the necessary energy of activation to be able to catalyze the transformation …”

Benzimidazolin-2-iminato Hafnium Complexes: Synthesis, Characterization, and Catalytic Addition of Alcohols to Carbodiimides

“…Hafnium complexes have mainly been used for the catalytic homo- and copolymerization of α-olefins − and as Lewis acid catalysts in various organic transformations including the polymerization of cyclic esters. − More recently, Hf–MOF complexes have been utilized in the catalytic activation of small molecules. − Among the group-IV metals, hafnium is considered to be the most oxophilic metal when compared with zirconium and titanium, as illustrated by their corresponding metal–oxygen bond dissociation energies (Ti–O = 666 kJ/mol, Zr–O = 766 kJ/mol, and Hf–O = 801 kJ/mol) . Hence, the strong metal–oxygen bond and the high electrophilicity of the metal have precluded the use of organometallic complexes of hafnium in processes involving oxygen-containing moieties with acidic protons. − We have postulated that if, during a stoichiometric or a catalytic process, we start with a metal–oxygen bond and after the transformation we end up with a different metal–oxygen bond, then, theoretically, we are not paying thermodynamically for the M–O bond; however, we need to have the energy of activation to be able to execute the process. − …”

“…Catalytic additions of E–H (NH, PH, SH, CH, etc.) moieties to carbodiimides have received substantial interest in recent years, and various types of catalysts have been used such as main-group metal centers, copper, lanthanides, actinides, ,,,, and titanium . Inspired by the observation that hafnium–oxygen moieties can be an active motif in catalytic processes, ,,− ,,− ,,,− we started to design our ligands toward the synthesis of hafnium complexes.…”

Recent Advances of Imidazolin-2-iminato in Transition Metal Chemistry

“…The efforts are on to extend the members of the Nheterocyclic imine class either by introducing the phenyl ring at the backbone of the imidazole ring or extend its ring size (IV-VI) (Scheme 2). [49][50][51] The synthesis, catalytic applications and, the significance of transition metal complexes containing imidazolin-2-iminato ligands in the field of homogeneous catalysis are briefly presented in this review. Catalytic applications, covered in the current review are olefin polymerization, hydroamination, ring-opening metathesis (ROP), hydroboration, and metathesis reactions.…”

“…Further, the future scopes and possible structural modifications of the transition metal complexes bearing imidazolin-2-iminato/Nheterocyclic iminato moieties by altering ring size are also presented herein. [49][50][51] Staudinger reaction [53] of 1,3-di-tert-butyl imidazolin-2-ylidene 1a with N3Si(CH3)3 in boiling toluene for 72 hours to afford the N-silylated 2-iminoimidazoline 2a (Scheme 3). The formation of carbenes (1a and 1b) were identified in 1 H NMR as the appearance of two backbone NCH protons in high-field shifts of -0.74 ppm (1a, R 1 = H) and -0.72 ppm (1b, R 1 = H) upon the formation of corresponding imine 2a and 2b respectively.…”