Cooperative Metal–Ligand Hydroamination Catalysis Supported by C–H Activation in Cyclam Zr(IV) Complexes

Synthesis, Characterization, and Reactivity Studies of New Cyclam-Based Y(III) Complexes

[(Bn2Cyclam)Y(N(SiMe3)2)] was prepared by reaction of H2Bn2Cyclam with Y[N(SiMe3)2]3. The protonation of the macrocycle ligand in [(Bn2Cyclam)Y(N(SiMe3)2)] is observed upon reaction with [HNMe3][BPh4] leading to the formation of [(HBn2Cyclam)Y(N(SiMe3)2)][BPh4]. DFT analysis of [(Bn2Cyclam)Y(N(SiMe3)2)] showed that the HOMO is located on the anionic nitrogen atoms of the cyclam ring indicating that protonation follows orbital control. Addition of H2Bn2Cyclam and H2(3,5-tBu2Bn)2Cyclam to a 1:3 mixture of YCl3 and LiCH2SiMe3 in THF resulted in the formation of [((C6H4CH2)BnCyclam)Y(THF)(µ-Cl)Li(THF)2] and [Y{(η3-3,5-tBu2Bn)2Cyclam}Li(THF)], respectively. The reaction of H23,5-tBu2Bn2Cyclam with Y(CH2SiMe3)3(THF)2 was studied and monitored by a temperature variation NMR experiment revealing the formation of [(3,5-tBu2Bn2Cyclam)Y(CH2SiMe3)]. Preliminary catalytic assays have shown that [Y{(η3-3,5-tBu2Bn)2Cyclam}Li(THF)] is a very efficient catalyst for the intramolecular hydroamination of 2,2-diphenyl-pent-4-enylamine.

Synthesis and Characterization of New Cyclam-Based Zr(IV) Alkoxido Derivatives

In this study, new mono- and di-alkoxido zirconium(IV) complexes supported by tetradentate dianionic cyclam ligands were synthesized and characterized. These compounds were obtained by reaction of the parent Zr(IV) dichlorido species with one or two equivalents of the corresponding lithium alkoxido, whereas (3,5-Me2Bn2Cyclam)Zr(OPh)2 was prepared by protonolysis of the orthometallated species (3,5-Me-C6H4CH2)2Cyclam)Zr with phenol. The solid-state molecular structures of (Bn2Cyclam)ZrCl(OtBu) and (4-tBuBn2Cyclam)Zr(OiPr)2 show a trigonal prismatic geometry around the metal centers. (Bn2Cyclam)Zr(SPh)(OtBu) and (Bn2Cyclam)ZrMe(OiPr) were prepared by reaction of (Bn2Cyclam)ZrCl(OR) (R = iPr, tBu) with one equivalent of LiSPh or MeMgCl, respectively. The reactions of (Bn2Cyclam)Zr(OiPr)2 and (4-tBuBn2Cyclam)Zr(OiPr)2 with carbon dioxide suggested the formation of species that correspond to the addition of four CO2 molecules.

Synthesis of and Metal Complexation with a Chiral Cyclam

Tetraazamacrocycles, like cyclam 1, are well-studied polyamine ligands for metal ions that were first developed to model biological processes. Despite being studied for nearly 60 years, the development of chiral variants of 1 has been limited. We report the synthesis of a chiral variant of 1, the tetraazamacrocycle 2. Outlined herein are the synthesis of 2, a preliminary study of its complexation with metal ions, and the properties of the resulting metal complexes.

Synthesis, Conformational Analysis, and Complexation Study of an Iminosugar-Aza-Crown, a Sweet Chiral Cyclam Analog

A new family of chiral C₂ symmetric tetraazamacrocycles, coined ISAC for IminoSugar Aza-Crown, incorporating two iminosugars adopting a ⁴C₁ conformation is disclosed. Multinuclear NMR experiments on the corresponding Cd²⁺ complex show that the ISAC is a strong chelator in water and its tetramine cavity adopts a conformation similar to that of the parent Cd–cyclam complex. Similar behavior is observed with Cu²⁺ in solution, with enhanced stability compared to the Cu–cyclam complex.

Synthesis, Structures, and Solution Dynamics of Titanium and Zirconium Complexes Carrying a Bis(indolyl) and Two Diethylamido Ligands

Indolyl is the anionic species obtained from the deprotonation of the N-H group of indole. Group 4 transition-metal complexes that carry indolyl-based polydentate ligands represent promising homogeneous catalysts for, e.g., olefin polymerization, hydroamination, and nitrogen-fixation reactions due to the weak π-donation and electron-withdrawing properties, as well as the low basicity of indolyl. In this study, we systematically investigated the synthesis and structures of titanium and zirconium complexes that carry deprotonated 2,2'-bis(indolyl)methane ligands (henceforth: bis(indolyl) ligands) and two diethylamido ligands. We found that the coordination geometry of the indolyl nitrogen atom in such bis(indolyl) ligands is affected by the steric impact of the substituents attached to the central aromatic ring. Moreover, we examined the dynamics of such bis(indolyl) ligands in solution for the corresponding zirconium complexes, and the mechanism was discussed in conjunction with DFT calculations. The results of this study suggest that bis(indolyl) ligands may also serve as coordinatively flexible ancillary ligands, and indicate the feasibility of an expansion from bis(indolyl) to bis(indolyl)-donor ligands.

Polymer-Anchored Bifunctional Pincer Catalysts for Chemoselective Transfer Hydrogenation and Related Reactions

A series of polymer-supported cooperative PC(sp³ )P pincer catalysts was synthesized and characterized. Their catalytic activity in the acceptorless dehydrogenative coupling of alcohols and the transfer hydrogenation of aldehydes with formic acid as a hydrogen source was investigated. This comparative study, examining homogeneous and polymer-tethered species, proved that carefully designing a link between the support and the catalytic moiety, which takes into consideration the mechanism underlying the target transformation, might lead to superior heterogeneous catalysis.