A titanium redox-switch enables reversible C-C bond forming and splitting reactions.

Using an Earth-abundant transition metal to mediate formation and splitting of C-C σ-bonds, in response to electrical stimuli, constitutes a promising strategy to construct complex organic skeletons. Here, we showcase how [ BuN][N] reacts with an isocyanide adduct of a tetrahedral and high-spin Ti complex, [(Tp )TiCl] (1), to enact N-atom transfer, C-N bond formation, and C-C coupling, to form a dinuclear complex, [(Tp )Ti{AdN(N)C-C(N)NAd}Ti(Tp )] (3), with two Ti ions bridged by a disubstituted oxalimidamide ligand ( Bu = -butyl, Tp = hydrotris(3--butyl-5-methylpyrazol-1-yl)borate, Ad = 1-adamantyl). Magnetic and computational studies reveal two magnetically isolated d Ti ions, and electrochemical studies unravel a reversible two-electron oxidation at -0.

Comparison of Ce(iv)/Th(iv)-alkynyl complexes and observation of a -influence ligand series for Ce(iv).

Organometallic cerium(iv) complexes have been challenging to isolate and characterize due to the strongly oxidizing nature of the cerium(iv) cation. Herein, we report two cerium(iv) alkynyl complexes, [Ce(TriNOx)(C[triple bond, length as m-dash]C-SiMe)] (1-Ce) and [Ce(TriNOx)(C[triple bond, length as m-dash]C-Ph)] (1-Ce) (TriNOx = (2--butylhydroxylaminato)benzylamine), that include terminal alkyne moieties. The isostructural thorium analogue [Th(TriNOx)(C[triple bond, length as m-dash]C-SiMe)] (1-Th) was also synthesized and compared with 1-Ce in bond distance, C-NMR spectra, vibrational spectra and electronic structure.

Carbon Dioxide Capture and Functionalization from a Molecular Ti(III) Oxo Anion.

Carbon dioxide capture and functionalization sequesters carbon dioxide in more robust products and offers a viable route to reducing greenhouse gas emissions. We present herein a unique molecular Ti oxo anion that reversibly binds CO to allow both its sequestration and functionalization. The reduction of [(PN)Ti═O] (1) [PN = (2-PPr-4-methylphenyl)(mesityl)amide] with KC and 2.

Reactivity Profile of a Formally Dicobalt(0) Complex Bound by a Redox-Active Macrocycle.

In this article, we discuss the synthesis, characterization, and reactivity of a neutral dicobalt complex, , supported by a highly reduced, redox-active macrocyclic ligand. The reducing equivalents stored within the ligand framework proved capable of activating a wide scope of small molecule substrates. The addition of a weak acid, lutidinium triflate, led to the clean formation of a bridging hydride that was found to undergo fluxional geometric changes in solution, while exposure of to H resulted in a rare example of net binuclear oxidative addition to give two bridging hydrides.

Breaking a Lewis Acidity Trend for Rare Earths by Excited State Quenching.

Facilitating different chemistries between the rare earth (RE = La-Lu, Sc, Y) ions is of significant interest for their separations. While the bulk of attention has been on maximizing the small differences in their ground state chemistry, interest is beginning to shift toward the differences in their electronic excited states. In this work, we demonstrate modulation of the photostationary state of an azobenzene derivative, Na, via chelation to a series of REDO3A (DO3A = 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) complexes.

4f-orbital covalency enables a single-crystal-to-single-crystal ring-opening isomerization in a Ce-cyclopropenyl complex.

Metal-ligand bonding interactions for f-element compounds are typically highly polarized with only minor covalent character. Whereas the 5d/6d orbitals are known to be chemically accessible for dative bonding, recent quantum chemical and spectroscopic analyses have indicated appreciable 4f/5f-orbital involvement in certain metal-ligand bonds. However, 4f-orbital covalency has not been compellingly linked to distinctive modes of chemical reactivity via rigorous comparative study and mechanistic investigation.

Titanium Phosphinidene and Phosphide Moieties from Oxidative Phosphorylation and Desilylation.

A unique entry into mononuclear titanium complexes bearing phosphinidene and phosphide ligand moieties is reported. Reaction of [K(crypt)][(PN)TiCl] (, crypt = 2.2.

Unusually air-stable copper(i) complexes showing high selectivity for carbon monoxide.

We report two Cu(i)-tren host molecules with unusual air-stability, as revealed by strong preference for axial CO binding over bent O. Spectroscopy, electrochemical, and X-ray crystal structure analyses indicate that the phenyl rotators of the capsule select for small axial ligands.

Synthesis and Characterization of Solvated and Base-Free Cerium(III) Mixed-Sandwich Complexes.

A series of solvated complexes: [(CH)Ln(CMeR)(DME)] Ln = La, R = -Me; () Ln = Ce, R = -Me, -SiMe, -H; (, , ), [(dbCOT)Ln(CMe)(DME)] (), (dbCOT = dibenzocyclooctadienide; Ln = Ce, La), [(dbCOT)Ce(CMeH)(DME)] () and [(hdcCOT)Ce(CMe)(DME)] () (hdcCOT = hexahydrodicyclopentacyclooctatetraenide) and base-free mixed-sandwich complexes [(CH)Ce(CMe)] (), [(CH)Ce(CMeH) () and [(hdcCOT)Ce(CMe)] () of the early lanthanide metals cerium and lanthanum comprising variable cyclopentadienide (Cp) and cyclooctatetraenide (COT) ligands is described. To evaluate the effect of cyclopentadienide and cyclooctatetraenide ligands on the characteristics of these complexes, their solid-state structural, electrochemical, and photophysical properties were studied and accompanied by theoretical calculations. To further evaluate the effect of ligands on the topology of the complexes and the reducing properties of the complexes, syntheses of several base-free congeners were pursued, which led to isolation of the first base-free monomeric and polymeric Ce(III) mixed-sandwich compounds.

Molecular Phosphide Complexes of Zirconium.

Molecular Zr phosphides are extremely rare, with no examples containing a one-coordinated and terminal triple-bonded phosphorus atom. We report here an isolable and relatively stable Zr phosphide complex, [(PN)Zr≡P{μ-Na(OEt)}] (), stemming from a cyclometalated Zr-hydride, [(PN)(PN')Zr(H)] (), and NaPH. Complex is prepared from two- or one-electron reductions of precursors [(PN)ZrCl] () or metastable Zr[(PN)ZrCl], respectively.

Mechanistic Investigation of the Ce(III) Chloride Photoredox Catalysis System: Understanding the Role of Alcohols as Additives.

Photocatalytic C-H activation is an emerging area of research. While cerium chloride photocatalysts have been extensively studied, the role of alcohol additives in these systems remains a subject of ongoing discussion. It was demonstrated that the photocatalyst [NEt][CeCl] () produces •Cl and added alcohols exhibit zero-order kinetics.

Pnictogen-based vanadacyclobutadiene complexes.

The reactivity of the V[triple bond, length as m-dash]C Bu multiple bonds in the complex (dBDI)V[triple bond, length as m-dash]C Bu(OEt) (C) (dBDI = ArNC(CH)CHC(CH)NAr, Ar = 2,6- PrCH) with unsaturated substrates such as N[triple bond, length as m-dash]CR (R = Ad or Ph) and P[triple bond, length as m-dash]CAd leads to the formation of rare 3d transition metal compounds featuring α-aza-vanadacyclobutadiene, (dBDI)V(κ- , - BuC(R)N) (R = Ad, 1; R = Ph, 2) and β-phospha-vanadacyclobutadiene moieties, (dBDI)V(κ- , - BuPAd) (3). Complexes 1-3 are characterized using multinuclear and multidimensional NMR spectroscopy, including the preparation of the 50% N-enriched isotopologue (dBDI)V(κ- , - BuCC(Ad)N) (1-N). Solid-state structural analysis is used to determine the dominant resonance structures of these unique pnictogen-based vanadacyclobutadienes.

C-H/F bond activation and borylation with iron.

Reduction of [K{(pyrrpyr)Fe}(μ-N)] (1) with two equiv. of KC in the presence of crown-ether 18-C-6 yields the N adduct [{K(18-C-6)}(pyrrpyr)Fe(N)] (2). Complex 2 heterolytically splits the C-H bond of benzene to form [{K(18-C-6)}(pyrrpyr)Fe(CH)] (3), whereby usage of a diboron Bpin promotes hydride elimination to form the salt [K(18-C-6)HBPin] (4).

Controlling the Size of Molecular Copper Clusters Supported by a Multinucleating Macrocycle.

The use of a nonrigid, pyridyldialdimine-derived macrocyclic ligand (PDAI) enabled the synthesis of well-defined mono-, di-, tri-, and tetra-nuclear Cu(I) complexes in good yields through rational synthetic means. Starting from mono- and diargentous PDAI complexes, transmetalation to Cu(I) proceeded smoothly with formation of AgX (X = Cl, I) salts to generate mono-, di-, and trinuclear copper complexes. Monodentate supporting ligands (MeCN, xylNC, PMe, PPh) were found to either transmetallate with or bind various di- and trinuclear clusters.

Molecular Bis(chalcogenido) Titanates of Te, Se, and S.

A series of titanate cisoid bis(chalcogenidos) (Ch = Te, Se, and S) complexes supported by the β-diketiminate ligand BDI = [ArNC(CH)]CH (Ar = 2,6-PrCH) are readily assembled via treatment of the Ti precursor (BDI)Ti(CHSiMe) with 2.5 equiv of elemental "Ch" source and 1 equiv of reductant in the presence of crown-ether. In the absence of the electride, Te or S addition to (BDI)Ti(CHSiMe) results instead in the isolation of a mononuclear tellurido-tellurolate [(BDI)Ti(=Te)(TeCHSiMe)] and the bridging sulfido-thiolate complex [(BDI)Ti(SCHSiMe)(μ-S)], respectively.

Synthesis and Luminescence Studies of a Tethered, Trigonal, Silver(I) Tris(alkyne) Complex.

The synthesis and characterization of a tris(alkyne) ligand, tris[2-(trimethylsilyl)ethynyl-4--butylbenzyl]amine (), and its silver(I) hexafluorophosphate complex, , are reported. The solid-state structure and luminescence properties of indicate relatively strong silver(I)-alkyne interactions between the metal cation and . No significant changes in the bond angles or lengths were observed upon metalation of with Ag, indicating a relatively unstrained ligand-metal motif.

Bifunctional Ligands: Evaluating the Role of Acidic Protons in the Secondary Coordination Sphere.

To evaluate bifunctional ligand reactivity involving NH acidic sites in the secondary coordination sphere, complexes where the proton has been substituted with a methyl group (NMe) are often investigated. An alternative strategy involves substitution of the NH group for an O. This contribution considers and compares the merits of these approaches; the synthesis and characterization of cationic square-planar Rh carbonyl complexes bearing diprotic bispyrazole pyridine ligand L1, and the bis-methylated pyrazole pyridine ligand L1Me are described.

A Vanadium Methylidene.

Examples of stable 3d transition metal methylidene complexes are extremely rare. Here we report an isolable and stable vanadium methylidene complex, [(PNP)V(=NAr)(=CH)] (PNP = N[2-PPr-4-methylphenyl], Ar = 2,6-PrCH), via H atom transfer (HAT) from [(PNP)V(NHAr)(CH)] or [(PNP)V(=NAr)(CH)] using two or one equivalents of the TEMPO radical (TEMPO = (2,2,6,6-tetramethylpiperidin-1-yl)oxyl), respectively. Alternatively, the vanadium methylidene moiety can also be formed via the treatment of transient [(PNP)V=NAr] with the Wittig reagent, HCPPh.

Divalent Titanium via Reductive N-C Coupling of a Ti Nitrido with π-Acids.

The nitrido-ate complex [(PN)Ti(N){μ-K(OEt)}] (1) (PN=(N-(2-PPr-4-methylphenyl)-2,4,6-MeCH) reductively couples CO and isocyanides in the presence of DME or cryptand (Kryptofix222), to form rare, five-coordinate Ti complexes having a linear cumulene motif, [K(L)][(PN)Ti(NCE)] (E=O, L=Kryptofix222, (2); E=NAd, L=3 DME, (3); E=NBu, L=3 DME, (4); E=NAd, L=Kryptofix222, (5)). Oxidation of 2-5 with [Fc][OTf] afforded an isostructural Ti center containing a neutral cumulene, [(PN)Ti(NCE)] (E=O, (6); E=NAd (7), NBu (8)) and characterization by CW X-band EPR spectroscopy, revealed unpaired electron to be metal centric. Moreover, 1e reduction of 6 and 7 in the presence of Kryptofix222cleanly reformed corresponding discrete Ti complexes 2 and 5, which were further characterized by solution magnetization measurements and high-frequency and -field EPR (HFEPR) spectroscopy.

Reversible O-H Bond Activation by Tripodal tris(Nitroxide) Aluminum and Gallium Complexes.

Herein, we report the preparation and characterization of the Group 13 metal complexes of a tripodal tris(nitroxide)-based ligand, designated (TriNOx)M (M = Al (), Ga (), In ()). Complexes and both activate the O-H bond of a range of alcohols spanning a ∼10 p unit range via an element-ligand cooperative pathway to afford the zwitterionic complexes (HTriNOx)M-OR. Structures of these alcohol adduct products are discussed.

Vanadium Alkylidyne Initiated Cyclic Polymer Synthesis: The Importance of a Deprotiovanadacyclobutadiene Moiety.

Reported is the catalytic cyclic polymer synthesis by a 3d transition metal complex: a V(V) alkylidyne, [(dBDI)V≡CBu(OEt)] (), supported by the deprotonated β-diketiminate dBDI (dBDI = ArNC(CH)CHC(CH)NAr, Ar = 2,6-PrCH). Complex is a precatalyst for the polymerization of phenylacetylene (PhCCH) to give cyclic poly(phenylacetylene) (-PPA), whereas its precursor, complex [(BDI)V≡CBu(OTf)] (; BDI = [ArNC(CH)]CH, Ar = 2,6-PrCH, OTf = OSOCF), and the zwitterion [((CF)B-dBDI)V≡CBu(OEt)] () exhibit low catalytic activity despite having a neopentylidyne ligand. Cyclic polymer topologies were verified by size-exclusion chromatography (SEC) and intrinsic viscosity studies.

Metallacyclobuta-(2,3)-diene: A Bidentate Ligand for Stream-line Synthesis of First Row Transition Metal Catalysts for Cyclic Polymerization of Phenylacetylene.

Described here is a direct entry to two examples of 3d transition metal catalysts that are active for the cyclic polymerization of phenylacetylene, namely, [(BDI)M{κ -C,C-(Me SiC SiMe )}] (2-M) (BDI=[ArNC(CH )] CH , Ar=2,6- Pr C H ; M=Ti, V). Catalysts are prepared in one step by the treatment of [(BDI)MCl ] (1-M, M=Ti, V) with 1,3-dilithioallene [Li (Me SiC SiMe )]. Complexes 2-M have been spectroscopically and structurally characterized and the polymers that are catalytically formed from phenylacetylene were verified to have a cyclic topology based on a combination of size-exclusion chromatography (SEC) and intrinsic viscosity studies.

Tellurolate: an effective Te-atom transfer reagent to prepare the triad of group 5 metal bis(tellurides).

We show in this work how lithium tellurolate Li(X)TeCHSiMe (X = THF, = 1, 1; X = 12--4, = 2, 2), can serve as an effective Te-atom transfer reagent to all group 5 transition metal halide precursors irrespective of the oxidation state. Mononuclear and bis(telluride) complexes, namely (PNP)M(Te) (M = V; Nb, 3; Ta, 4; PNP = N[2-PPr-4-methylphenyl]), are reported herein including structural and spectroscopic data. Whereas the known complex (PNP)V(Te) can be readily prepared from the trivalent precursor (PNP)VCl, two equiv.

Observing Similarities and Differences in the Properties of Isostructural Niobium(V)/Tantalum(V) Coordination Compounds with Strong Pi-Donor Ligands.

While niobium and tantalum are found together in their mineral ores, their respective applications in technology require chemical separation. Nb/Ta separations are challenging due to the similar reactivities displayed by these metals in the solution phase. Coordination complexes of these metals have been studied in the contexts of catalysis, small-molecule activation, and functional group insertion reactivity; relatively few studies exist directly comparing the properties of isostructural Nb/Ta complexes.

Investigating Metal-Metal Bond Polarization in a Heteroleptic Tris-Ylide Diiron System.

This article describes the synthesis, characterization, and S-atom transfer reactivity of a series of -symmetric diiron complexes. The iron centers in each complex are coordinated in distinct ligand environments, with one (Fe) bound in a pseudo-trigonal bipyramidal geometry by three phosphinimine nitrogens in the equatorial plane, a tertiary amine, and the second metal center (Fe). Fe is coordinated, in turn, by Fe, three ylidic carbons in a trigonal plane, and, in certain cases, by an axial oxygen donor.