New Experimental Insight into the Nature of Metal-Metal Bonds in Digallium Compounds: J Coupling between Quadrupolar Nuclei.

Multiple bonding between atoms is of ongoing fundamental and applied interest. Here, we report a multinuclear ((1) H, (13) C, and (71) Ga) solid-state magnetic resonance spectroscopic study of digallium compounds which have been proposed, albeit somewhat controversially, to contain single, double, and triple Ga-Ga bonds. Of particular relevance to the nature of these bonds, we have carried out two-dimensional (71) Ga J/D-resolved NMR experiments which provide a direct measurement of J((71) Ga,(71) Ga) spin-spin coupling constants across the gallium-gallium bonds.

The tipping point of the inert pair effect: experimental and computational comparison of In(I) and Sn(II) bis(imino)pyridine complexes.

The autoionization reaction of neutral bis(imino)pyridine and SnX2 led to three compounds [{ArN[double bond, length as m-dash]CPh}2(NC5H3)]SnX(+)SnX3(-) (Ar = 2,6-(2,5-(t)Bu2C6H3), X = Cl, Br; Ar = 2,6-(2,6-Me2C6H3), X = Cl) which display, within the same species, cations and anions possessing Sn(ii) centers. Computational analysis compared the ligated Sn(ii) cations with bis(imino)pyridine In(i) complexes that showed unprecedented weak metal-ligand covalent interactions, consistent with the In(i) 5s(2) electrons remaining as an inert nonbonding pair. Analysis of the metal-ligand bonding indicates that the chloride ligand of the Sn(ii) complex induces promotion of the metal 5s(2) electron pair to a stereochemically active hybridized orbital, which, in turn, allows strong coordination of the bis(imino)pyridine to Sn.

Noncovalent interactions of metal cations and arenes probed with thallium(I) complexes.

The synthesis, characterization, and computational analysis of Tl(I) complexes bearing the bis(imino)pyridine scaffold, [{ArN═CPh}2(NC5H3)]Tl(+)(OTf)(-) (Ar = 2,6-Et2C6H33, 2,5-(t)Bu2C6H3, 4), are reported. The cations of these species showed long Tl-N and Tl-OTf distances indicating only weak or no ligand coordination. Computational analysis of the interactions between the Tl cation and the ligands (orbital populations, bond order, and energy decomposition analysis) point to only minimal covalent interactions of the cation with the ligands.

Solid-state thermolysis of a fac-rhenium(I) carbonyl complex with a redox non-innocent pincer ligand.

The development of rhenium(I) chemistry has been restricted by the limited structural and electronic variability of the common pseudo-octahedral products fac-[ReX(CO)3L2] (L2 = α-diimine). We address this constraint by first preparing the bidentate bis(imino)pyridine complexes [(2,6-{2,6-Me2C6H3N=CPh}2C5H3N)Re(CO)3X] (X = Cl 2, Br 3), which were characterized by spectroscopic and X-ray crystallographic means, and then converting these species into tridentate pincer ligand compounds, [(2,6-{2,6-Me2C6H3N=CPh}2C5H3N)Re(CO)2X] (X = Cl 4, Br 5). This transformation was performed in the solid-state by controlled heating of 2 or 3 above 200 °C in a tube furnace under a flow of nitrogen gas, giving excellent yields (≥95 %).

The interplay of metal and supporting ligand in labile coordination to pincer complexes of Ag(I).

The bis(imino)pyridine scaffold provides support for the synthesis and characterization of unique Ag(I) pincer complexes [{ArN=CPh}(2)(NPh)]Ag(+)(OTf)(-) (Ar = 2,5-(t)Bu(2)C(6)H(3)3; 2,6-(i)Pr(2)C(6)H(3) 4). The bonding interactions between the cation-anion and between the bis(imino)pyridine ligand and the Ag centre are presented. Coordination of pyridine, toluene, 2-butyne and cyclooctene to the Ag centre led to the isolation and crystallographic characterization of labile transient adduct species.

Single-molecule magnet behavior with a single metal center enhanced through peripheral ligand modifications.

Bis(imino)pyridine pincer ligands in conjunction with two isothiocyanate ligands have been used to prepare two mononuclear Co(II) complexes. Both complexes have a distorted square-pyramidal geometry with the Co(II) centers lying above the basal plane. This leads to significant spin-orbit coupling for the d(7) Co(II) ions and consequently to slow relaxation of the magnetization that is characteristic of Single-Molecule Magnet (SMM) behavior.

Novel pincer complexes of Ag(I), coordination of toluene and their comparison with indium analogues.

The bis(imino)pyridine scaffold provides for the synthesis and characterization of the unique Ag(I) pincer complexes [{ArN=CPh}(2)(NPh)]Ag(+)(OTf)(-) (Ar = 2,5-(t)Bu(2)C(6)H(3); 2,6-(i)Pr(2)C(6)H(3)). The similar covalent radii of Ag(I) and In(I), prompted a bonding comparison of these species with their In(I) analogues. Coordination of toluene to the Ag center revealed the stronger Lewis acidity of the metal site in these compounds relative to In(I) analogues.

Harnessing low-valent metal centers through non-bonding orbital interactions.

The synthesis, characterization, and computational analysis of a series of low-valent, In(I) complexes bearing the bis(imino)pyridine scaffold, {Ar'N=CPh}(2)(NC(5)H(3)), is reported. A stepwise steric reduction of the aryl groups on the imine substituents around the coordination site, (Ar' = 2,5-(t)Bu(2)C(6)H(3), 2,6-(i)Pr(2)C(6)H(3), 2,6-(CH(3)CH(2))(2)C(6)H(3)) is explored through the spectroscopic and crystallographic examination of complexes [{Ar'N=CPh}(2)(NC(5)H(3))]In(+)(OTf)(-) (1-3). Compounds 1-3 displayed long In-N and In-OTf distances indicating only weak or no coordination.

Disubstituted 1,8-diamidonaphthalene ligands as a flexible, responsive, and reactive framework for tantalum complexes.

Deprotonated N,N'-disubstituted 1,8-diaminonaphthalenes (R(2)DAN(2-); R = (CH(3))(2)CH, C(6)H(5), 3,5-Me(2)C(6)H(3)) were incorporated into Ta(V) complexes employing two methods. The direct proton transfer reaction of the parent amine, 1,8-(RNH)(2)C(10)H(6), with TaMe(3)Cl(2) led to elimination of methane and formation of TaCl(3)[1,8-(RN)(2)C(10)H(6)] (1, 2). Reaction of the dilithiated amido species, Li(2)R(2)DAN, with TaMe(3)Cl(2) or [Ta(NEt(2))(2)Cl(3) ] yielded TaMe(3)[1,8-(RN)(2)C(10)H(6)] (3, 4) and TaCl(NEt(2))(2)[1,8-(RN)(2)C(10)H(6)] (5, 6), respectively.

Disproportionation and radical formation in the coordination of "GaI" with bis(imino)pyridines.

Attempted coordination of "Ga(I)I" with two new sterically bulky, aryl substituted bis(imino)pyridine ligands lead to Ga(III) species [2,6-{ArN=CPh}(2)(NC(5)H(3))]GaI(2)(+)GaI(4)(-) (Ar = 2,5-(t)Bu(2)C(6)H(3), 2,6-(i)Pr(2)C(6)H(3) = Dipp) arising from thermodynamically favorable disproportionation reactions. Examination of these reactions lead to isolation of a neutral radical species [2,6-{DippN=CPh}(2)(NC(5)H(3))]GaI(2). Both EPR spectroscopy and DFT calculations on this compound indicate that the unpaired electron is localized in a di(imino)pyridine pi* orbital of an anionic ligand with nearly zero contribution from the Ga or I centers.

SERS detection and boron delivery to cancer cells using carborane labelled nanoparticles.

Water-soluble carborane functionalized nanoparticles also co-functionalized with targeting antibodies have been prepared. We demonstrate tumour cell targeting with anti-EGFR antibodies and delivery of a high concentration of boron using SERS imaging. This suggests these materials have a therapeutic potential in addition to multimodal imaging capabilities.

Capturing In+ monomers in a neutral weakly coordinating environment.

The application of a new bis(imino)pyridine ligand allowed the isolation and characterization of [{2,4-(t)Bu(2)C(6)H(3)N=CPh}(2)(NC(5)H(3))]In(+)(OTf)(-) as the first low-valent, main-group metal complex of this ligand scaffold. Structural analysis revealed a unique monomeric In(I) species with a surprisingly long metal-ligand bond. In conjunction with a density functional theory investigation, this complex is shown to display only nominal donor-acceptor interactions between the metal and the neutral ligand.

Analysis of the critical step in catalytic carbodiimide transformation: proton transfer from amines, phosphines, and alkynes to guanidinates, phosphaguanidinates, and propiolamidinates with Li and Al catalysts.

While lithium amides supported by tetramethylethylenediamine (TMEDA) are efficient catalysts in the synthesis of substituted guanidines via the guanylation of an amine with carbodiimide, as well as the guanylation of phosphines and conversion of alkynes into propiolamidines, aluminum amides are only efficient catalysts for the guanylation of amides. Density functional theory (DFT) calculations were used to explain this difference in activity. The origin of this behavior is apparent in the critical step where a proton is transferred from the substrate to a metal guanidinate.

Amidolithium and amidoaluminum catalyzed synthesis of substituted guanidines: an interplay of DFT modeling and experiment.

The synthesis of substituted guanidines is of significant interest for their use as versatile ligands and for the synthesis of bioactive molecules. Lithium amides supported by tetramethylethylenediamine have recently been shown to catalyze the guanylation of amines with carbodiimide. In this report, density functional theory (DFT) calculations are used to provide insight into the mechanism of this transformation.

Atom efficient cyclotrimerization of dimethylcyanamide catalyzed by aluminium amide: a combined experimental and theoretical investigation.

A novel method for the cyclotrimerization of dimethylcyanamide to form hexamethylmelamine has been developed using an aluminium amide catalyst; detailed DFT modelling of the catalytic cycle supports a triple insertion, nucleophilic ring closure, deinsertion mechanism.

Diamidonaphthalene-supported pnictogenium cations: synthesis of an N-heterocyclic stibenium cation by a novel protonation route.

A 1,8-bis(alkylamido)naphthalene framework has been applied to the construction of N-heterocyclic arsenium and stibenium cations; a novel synthetic route, involving protonation of an ancillary amido ligand, was used to generate the base-stabilized stibenium cation.

Synthesis and molecular and extended structures for a diaminonaphthalene-derived bis(amido)stannylene.

The cyclic bis(amido)tin(II) compound Sn[1,8-((iPrN)2C10H6] (2) was isolated from the reaction of Li2[1,8-((iPrN)2C10H6] (1) and SnCl2. Solid-state structural analysis of 2 showed it to be a mononuclear species with a pyramidal Sn center as part of a nonplanar metallaheterocycle. The packing diagram of 2 revealed an extended one-dimensional head-to-tail chain structure with short intermolecular Sn/arene-C interactions.

The insertion of carbodiimides into Al and Ga amido linkages. Guanidinates and mixed amido guanidinates of aluminum and gallium.

The insertion of carbodiimides into existing metal-heteroatom bonds is an important preparative route for the synthesis of useful ligand systems such as amidinates and guanidinates. Our interest lies in multiple insertions at one metal center and the mechanisms of insertion and rearrangement. We have synthesized and characterized [Me(2)NC(N(i)Pr)(2)](n)M(NMe(2))(3)(-)(n) (n = 1, 2, 3; M = Al, Ga).

Catalytic C=N bond metathesis of carbodiimides by group 4 and 5 imido complexes supported by guanidinate ligands.

A family of guanidinate-supported imido metal complexes are novel, effective catalysts for C=N metathesis of alkyl and aryl carbodiimides and evidence suggests that this reaction proceeds via a sequential addition/elimination pathway.

Constructing a stable carbene with a novel topology and electronic framework.

The perimidine skeleton provides a framework for the isolation of a novel, stable carbene possessing a unique molecular architecture and electronic structure. The remarkable steric environment and exceptional electron-donating ability for the carbene-carbon are revealed through structural and spectroscopic characterization of the parent carbene and two sterically encumbered rhodium-carbene complexes, L2RhCl{C[NCH(CH3)2]2(C10H6)} (5 L2 = COD; 6 L = CO).

Synthesis and structural investigation of N,N',N' '-trialkylguanidinato-supported zirconium(IV) complexes.

The addition of 2 equiv of N,N',N' '-triisopropylguanidine (guanH(2)) to Zr(CH(2)Ph)(4) produced the bis(guanidinato)bis(benzyl)zirconium complex [((i)PrNH)C(N(i)Pr)(2)](2)Zr(CH(2)Ph)(2) (1). The mono(guanidinato) complex [((i)PrN)(2)C(NH(i)Pr)]ZrCl(3) (2) was accessible by the reaction of 2 equiv of guanH(2) with ZrCl(4). Guanidinium hydrochloride, [C(NH(i)Pr)(3)]Cl, is a byproduct of this reaction.

Catalytic construction and reconstruction of guanidines: Ti-mediated guanylation of amines and transamination of guanidines.

Bis(guanidinate) titanium imido complexes [{(Me2N)C(NiPr)2}2TiNAr'] (Ar' = 2,6-Me2C6H3 (1a); C6F5 (1b)) are competent catalysts for the guanylation of a variety of arylamines with carbodiimide. The reversible [2 + 2] addition of iPrN=C=NiPr to 1b is demonstrated and is proposed to be part of the catalytic cycle. Compounds 1a and 1b are also effective precatalysts for the transamination of trialkylguanidines with arylamines to yield aryldialkylguanidines.

Synthesis and characterization of iron complexes with monoanionic and dianionic N,N',N' '-trialkylguanidinate ligands.

Trisubstitued N,N',N' '-tri(alkyl)guanidinate anions have been used in the synthesis of a family of Fe(II) and Fe(III) complexes. Complexes FeCl[((i)PrN)(2)C(HN(i)Pr)](2) (1), [Fe[micro-((i)PrN)(2)C(HN(i)Pr)][((i)PrN)(2)C(HN(i)Pr)]](2) (2), and [Fe[mgr;-(CyN)(2)C(HNCy)][(CyN)(2)C(HNCy)]](2) (3) were prepared from the reaction of the appropriate lithium tri(alkyl)guanidinate and FeCl(3) or FeBr(2). The complex [FeBr[micro-(CyN)(2)C(HNCy)]](2) (4), an apparent intermediate in the formation of 3, has also been isolated and characterized.

Insertion Routes to Tetrasubstituted Guanidinate Complexes of Ta(V) and Nb(V).

The preparation and characterization of guanidinate-containing complexes of Nb and Ta is described. The direct reactions of M(NMe(2))(5) with either dicyclohexylcarbodiimide (CyN=C=NCy) and diisopropylcarbodiimide ((i)PrN=C=N(i)Pr) proceeded smoothly at room temperature under nitrogen to yield [RNC(NMe(2))NR]M(NMe(2))(4) (M = Ta, Nb; R = Cy, (i)Pr). The spectroscopic characterization of these materials is consistent with a symmetrical chelating bidentate guanidinate anion bonded to a pseudo-octahedral metal center.

Transition Metal Complexes of Guanidinate Dianions: Reactions between Guanidines and M(NMe(2))(5) (M = Ta, Nb).

The protonation of two metal-amido groups of M(NMe(2))(5) with trialkylguanidines yielded a series of novel complexes with formulas [RNC(NR)NR]M(NMe(2))(3) (1-4) (M = Ta, Nb; R = isopropyl, cyclohexyl). These complexes contained dianionic N,N',N' '-trialkylguanidinate ligands which were coordinated in a chelating bidentate mode. A single-crystal X-ray study of [CyNC(NCy)NCy]Ta(NMe(2))(3) (3) (C(25)H(51)N(6)Ta, triclinic, P&onemacr;, a = 9.