Boron Complexes with Propiolamidinato Ligands: Synthesis, Structure, and Photophysical Properties.

Two series of boron derivatives with propiolamidinato ligands, [BPh{C(C≡CAr)(NR)}] (Ar = Ph, -MeOPh, -FPh, -MeNPh, or phen; R = iPr or -tolyl), were synthesized and structurally characterized. The corresponding propiolamidine (or propargylamidine) proligands have been obtained through sustainable methods. One is the catalytic hydroalkynylation of diisopropylcarbodiimide with different terminal alkynes, using simple ZnEt as a precatalyst.

Zinc amidinate-catalysed cyclization reaction of carbodiimides and alkynes. An insight into the mechanism.

A synthesis of iminopyridines based on zinc has been developed. The commercially available ZnEt was employed as a precatalyst for this process. A mechanism has been proposed on the basis of Density Functional Theory (DFT) studies and stoichiometric reactions.

ZnEt as a Precatalyst for the Addition of Alcohols to Carbodiimides.

We report here the use of commercially available ZnEt as an efficient precatalyst for the addition of alcohols to carbodiimides to obtain a wide range of isoureas under mild conditions. In an initial screening using methanol and commercial carbodiimides as substrates, the bulky isourea (OMe)(NHDipp)C(NDipp) (Dipp = 2,6-PrCH) was prepared for the first time using a catalytic method, and its structure confirmed by an X-ray diffraction analysis. Then, the efficiency of the precatalyst was tested with two carbodiimides, C(NPr) and C(N-tol), toward a series of alkylic and arylic alcohols and diols, with different steric and electronic properties, including the presence of other functional groups, usually with excellent conversions, especially for the more reactive aromatic carbodiimide.

Guanidinates as Alternative Ligands for Organometallic Complexes.

For decades, ligands such as phosphanes or cyclopentadienyl ring derivatives have dominated Coordination and Organometallic Chemistry. At the same time, alternative compounds have emerged that could compete either for a more practical and accessible synthesis or for greater control of steric and electronic properties. Guanidines, nitrogen-rich compounds, appear as one such potential alternatives as ligands or proligands.

Aerobic/Room-Temperature-Compatible s-Block Organometallic Chemistry in Neat Conditions: A Missing Synthetic Tool for the Selective Conversion of Nitriles into Asymmetric Alcohols.

Highly-efficient and selective one-pot/two-step modular double addition of different highly polar organometallic reagents (RLi/RMgX) to nitriles en route to asymmetric tertiary alcohols (without the need for isolation/purification of any halfway reaction intermediate) has been studied, for the first time, in the absence of external/additional organic solvents (neat conditions), at room temperature and under air/moisture (no protecting atmosphere is required), which are generally forbidden reaction conditions in the field of highly-reactive organolithium/organomagnesium reagents. The one-pot modular tandem protocol demonstrated high chemoselectivity with a broad range of nitriles, as no side reactions (Li/halogen exchange, ortho-lithiations or benzylic metalations) were detected. Finally, this protocol could be scaled up, thus proving that this environmentally friendly methodology is amenable for a possible applied synthesis of asymmetric tertiary alcohols under bench type reaction conditions and in the absence of external organic solvents.

Novel Fluorescence Guanidine Molecules for Selective Sulfate Anion Detection in Water Complex Samples over a Wide pH Range.

Quantitative analysis of sulfate anions in water still remains an important challenge for the society. Among all the methodologies, the most successful one is based on optical supramolecular receptors because the presence of small concentrations of sulfate anion modifies the photophysical properties of the receptor. In this case, fluorescence anion sensors have been designed by the incorporation of guanidine motifs into fluorenyl cores.

Reactivity of -Phosphinoguanidines of the Formula (HNR)(PhPNR)C(NAr) toward Main Group Metal Alkyls: Facile Ligand Rearrangement from -Phosphinoguanidinates to Phosphinimine-Amidinates.

We report the reactivity of -phosphinoguanidines of the formula (HNR)(PhPNR)C(NAr) (R = Pr and Ar = 2,6-PrCH [Dipp] for , R = Pr and Ar = 2,4,6-MeCH [Mes] for , and R = Cy and Ar = Dipp for ), prepared in high yields from the corresponding trisubstituted guanidines, toward main group metal alkyls AlMe, ZnEt, MgBu, and BuLi to obtain novel phosphinoguanidinato and phosphinimine-amidinato compounds. Reactions of - with AlMe at room temperature led to the kinetic phosphinoguanidinato products [Al{κ-'-(NR)C(NAr)(NRPPh)}Me] (-), whereas the mild heating (60-80 °C) of solutions of - give the thermodynamic phosphinimine-amidinato products [Al{κ-'-(NR)C(NAr)(PPhNR)}Me] (-) after ligand rearrangement. The reactions of equimolar amounts of - and ZnEt initially give solutions containing unstable phosphinoguanidinato compounds [Zn{κ--(NR)C(NAr)(NRPPh)}Et] (-), which rearrange upon mild heating to the phosphinimine-amidinato derivatives [Zn{κ-'-(NR)C(NAr)(PPhNR)}Et] (-).

PhPCHCHB(CH) and Its Formaldehyde Adduct as Catalysts for the Reduction of CO with Hydroboranes.

We study two metal-free catalysts for the reduction of CO with four different hydroboranes and try to identify mechanistically relevant intermediate species. The catalysts are the phosphinoborane PhP(CH)BBN (), easily accessible in a one-step synthesis from diphenyl(vinyl)phosphine and 9-borabicyclo[3.3.

9-Borabicyclo[3.3.1]nonane: a metal-free catalyst for the hydroboration of carbodiimides.

The commercial 9-borabicyclo[3.3.1]nonane dimer is used as the first example of a metal-free catalyst for the monohydroboration of carbodiimides with pinacol borane.

Unusual ligand rearrangement: from N-phosphinoguanidinato to phosphinimine-amidinato compounds.

Novel N-phosphinoguanidines (HNiPr)(Ph2PNiPr)C(NAr) (Ar = 2,6-iPr2C6H3, 2,4,6-Me3C6H2) react with AlMe3 to afford phosphinimine-amidinato derivatives, via an unprecedented rearrangement of an initial N-phosphinoguanidinato intermediate. A reasonable mechanism has been proposed for this transformation, supported by DFT calculations, involving carbodiimide de-insertion followed by a [3+2] cycloaddition.

Carbodiimides as catalysts for the reduction of CO with boranes.

Carbodiimides catalyse the reduction of CO2 with H-BBN or BH3·SMe2 to give either mixtures of CH2(OBBN)2 and CH3OBBN or (MeOBO)3 and B(OMe)3 under mild conditions (25-60 °C, 1 atm CO2). Stoichiometric reactions and theoretical calculations were performed to unveil the mechanism of these catalytic processes.

Simple ZnEt as a catalyst in carbodiimide hydroalkynylation: structural and mechanistic studies.

Expanding the possibilities of the use of simple and available ZnEt as a catalyst, the hydroalkynylation of carbodiimides with a variety of alkynes to obtain unsaturated substituted amidines is described in this work. Different stoichiometric studies allow proposing that amidinate complexes are intermediates in this catalytic process, produced by easy activation of the C-H bond of the alkyne and formation of alkynyl derivatives followed by a carbodiimide insertion step. Kinetics studies allowed the generation of a rate law for the hydroalkynylation of N,N'-diisopropylcarbodiimide with phenylacetylene which is second order in [carbodiimide], first order in [catalyst] and zero order in [alkyne], with a negligible PhC[triple bond, length as m-dash]CH/PhC[triple bond, length as m-dash]CD isotopic effect, consistent with a rate-determining state involving carbodiimide insertion.

Insertion reactions of small unsaturated molecules in the N-B bonds of boron guanidinates.

We report here 1,1- and 1,2-insertion reactions of small unsaturated molecules in the N-B bonds of two boron guanidinates, (MeN)C(NPr)BCy (1) and {Pr(H)N}C(NPr){N(p-Bu-CH)}BCy (2), and two bisboron guanidinates(2-), {Pr(BCy)N}C(NPr){N(p-Bu-CH)}BCy (3) and {Pr(CHB)N}C(NPr){N(p-Me-CH)}BCH (4), the latter being prepared for the first time by double deprotonation of the corresponding guanidine with the 9-borabicyclo[3.3.1]nonane dimer, (H-BCH).

Synthesis, characterization, DNA interactions and antiproliferative activity on glioblastoma of iminopyridine platinum(II) chelate complexes.

A series of iminopyridine platinum chelate compounds has been prepared and characterized by NMR spectroscopy and single-crystal X-ray diffraction. The complexes were evaluated in C6 tumoral cells as an in vitro model for glioblastoma multiforme. The DNA-binding properties of these complexes were studied by UV-Vis absorption and fluorescence spectroscopy and Density Functional Theory calculations were performed in an effort to rationalize the observed properties at the molecular level.

Dialkylboron guanidinates: syntheses, structures and carbodiimide de-insertion reactions.

The synthesis of novel dialkylboron guanidinates is reported: the symmetrical compounds, (MeN)C(NR)BR' [R = Pr, R' = Nrb (1); R = Cy, R' = Nrb (2); R = Pr, R' = Cy (3); R = R' = Cy (4); R = 2,6-Pr-CH; R' = Cy (5); Nrb = exo-2-norbornyl] and the asymmetrically coordinated {Pr(H)N}C(NPr)(NAr)BCy [Ar = Ph (6), 4-Me-CH (7), 4-Bu-CH (8)] were prepared by the salt metathesis method from the appropriate lithium guanidinates and chloroboranes. Moreover, the bis(dicyclohexylboron)guanidinate(-2) {Pr(CyB)N}C(NPr){N(4-Bu-CH)}BCy (9) was also prepared from the corresponding dilithium guanidinate Li[{N(4-Bu-CH)}C(NPr)] and ClBCy. The structures of compounds 1, 3, 6 and 9 were confirmed by X-ray diffraction and all displayed a chelate coordination of the guanidinate ligand to the BR' fragment, the latter displaying an additional BCy attached to the exocyclic N atom.

Tris(pentafluorophenyl)borane as an efficient catalyst in the guanylation reaction of amines.

Tris(pentafluorophenyl)borane, [B(C6F5)3], has been used as an efficient catalyst in the guanylation reaction of amines with carbodiimide under mild conditions. A combined approach involving NMR spectroscopy and DFT calculations was employed to gain a better insight into the mechanistic features of this process. The results allowed us to propose a new Lewis acid-assisted Brønsted acidic pathway for the guanylation reaction.

Toward the Prediction of Activity in the Ethylene Polymerisation of ansa-Bis(indenyl) Zirconocenes: Effect of the Stereochemistry and Hydrogenation of the Indenyl Moiety.

A combined experimental and quantum chemical study has been performed on rac- and meso-[Zr{1-Me Si(3-η -C H Et) }Cl ] (rac- and meso-1) and their hydrogenated forms (rac- and meso-2) to understand ligand effects and guide ligand design for more active ansa-bis(indenyl) zirconocenes for the polymerisation of ethylene. The rac-ansa-zirconocene rac-[Zr(1-Me Si{3-Et-(η -C H )} )Cl ] (rac-2) has been prepared and fully characterised by NMR spectroscopy and elemental analysis. The molecular structure of rac-2 has also been determined by single-crystal XRD.

Mixed amido-/imido-/guanidinato niobium complexes: synthesis and the effect of ligands on insertion reactions.

The new monoguanidinato complexes [Nb(NMe2)2{N(2,6-(i)Pr2C6H3)}{(NR)(NR')C(NMe2)}] (R = R' = (i)Pr, 2; R = (t)Bu, R' = Et, 3) were obtained by the insertion reaction of either diisopropylcarbodiimide or 1-tert-butyl-3-ethylcarbodiimide with the triamido precursor [Nb(NMe2)3(N-2,6-(i)Pr2C6H3)] (1) bearing a bulky imido moiety. The μ-oxo derivative [{N(2,6-(i)Pr2C6H3)}{(N(i)Pr)2C(NMe2)}(NMe2)Nb]2(μ-O) (2a) was formed by an unexpected hydrolysis reaction of the amido niobium compound 2. Alternatively, monoguanidinato complexes [Nb(NMe2)2{N(2,6-(i)Pr2C6H3)}{(N(i)Pr)2C(NHR)}] (R = (i)Pr, 4, (n)Bu, 5) can be obtained by protonolysis of 1 with N,N',N''-alkylguanidines [(NH(i)Pr)2C(NR)] (R = (i)Pr, (n)Bu).

Guanidines: from classical approaches to efficient catalytic syntheses.

From organosuperbases capable of base-catalyzing organic reactions, through versatile 'ligand-sets' for use in coordination chemistry, to fundamental entities in medicinal chemistry, guanidines are amongst the most interesting, attractive, valuable, and versatile organic molecules. Since the discovery of these compounds, synthetic chemists have developed new methodologies that are mainly based on multi-step and stoichiometric reactions. Despite the fact that these methodologies are still being used by the interested scientific and industrial communities, drawbacks such as the poor availability of precursors, low yields, and use and production of undesirable substances highlight the need for safe, simple and efficient syntheses of these entities.