Reactivity of the Dimer [{RuCl(μ-Cl)(η3:η3-C10H16)}2] (C10H16 = 2,7-Dimethylocta-2,6-diene-1,8-diyl) toward Guanidines: Access to Ruthenium(IV) and Ruthenium(II) Guanidinate Complexes

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. In addition to occurring in a plethora of natural compounds, and thus in compounds of pharmacological use, guanidines allow a wide variety of coordination modes to different metal centers along the periodic table, with their monoanionic chelate derivatives being the most common. In this review, we focused on the organometallic chemistry of guanidinato compounds, discussing selected examples of coordination modes, reactivity and uses in catalysis or materials science. We believe that these amazing ligands offer a new promise in Organometallic Chemistry.

The chemistry of guanidinate complexes of the platinum group metals

In this Perspective article, recent advances in the chemistry of platinum group metal complexes containing mono- and dianionic guanidinate ligands, i.e. [(RN)2C-NR2]- and [(RN)2C[double bond, length as m-dash]NR]2-, respectively, are presented. Synthetic and structural aspects, reactivity studies, and applications of these compounds are discussed.

Selective Three-Component Coupling for CO2 Chemical Fixation to Boron Guanidinato Compounds

A selective three-component coupling was employed to fix carbon dioxide to boron guanidinato compounds. The one-pot reaction of carbon dioxide, carbodiimides, and borylamines (ArNH)BC₈H₁₄ afforded the corresponding 1,2-adducts {R(H)N}C{N(Ar)}(NR)(CO₂)BC₈H₁₄. Alternatively, the reaction with p-MeOC₆H₄NC or 2,6-Me₂C₆H₃NC gave the corresponding isocyanide 1,1-adducts { i-PrHN}C{N(p-Me-C₆H₄)}(N i-Pr){CNAr}BC₈H₁₄. The molecular structures of products (2,6- i-Pr₂C₆H₃NH)BC₈H₁₄ 7, { i-Pr(H)N}C{N(p-MeC₆H₄)}(N i-Pr)(CO₂)BC₈H₁₄ 9, {Cy(H)N}C{N( p-MeC₆H₄)}(Cy)(CO₂)BC₈H₁₄ 13, and { i-PrHN}C{N( p-MeC₆H₄)}(N i-Pr){CNR″}BC₈H₁₄ (R″ = p-MeOC₆H₄, 2,6-Me₂C₆H₃) 14 and 15 were established by X-ray diffraction. Density functional theory calculations at the M05-2X level of theory revealed that CO₂ fixation and formation of the corresponding adduct is exothermic and proceeds via a nonchelate boron guanidinato intermediate.

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, (Me₂N)C(NⁱPr)₂BCy₂ (1) and {ⁱPr(H)N}C(NⁱPr){N(p-^tBu-C₆H₄)}BCy₂ (2), and two bisboron guanidinates(2-), {ⁱPr(BCy₂)N}C(NⁱPr){N(p-^tBu-C₆H₄)}BCy₂ (3) and {ⁱPr(C₈H₁₄B)N}C(NⁱPr){N(p-Me-C₆H₄)}BC₈H₁₄ (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-BC₈H₁₄)₂. Compounds 1-4 easily insert aromatic isonitriles, XylNC (Xyl = 2,6-Me₂-C₆H₃) and (p-MeO-C₆H₄)NC, to give the expected diazaboroles 5-12, some of them being structurally characterised by X-ray diffraction. Interestingly, the BC₈H₁₄ derivatives 11 and 12 are in a fast temperature-dependent equilibrium with the de-insertion products, whose thermodynamic parameters are reported here. A correlation between these equilibria and the puckered heterocyclic structure found in the solid state for 11, and confirmed by DFT calculations, is also established. Reactions of the aforementioned guanidinates with CO are more sluggish or even precluded, and only one product, {ⁱPr(H)N}C{N(p-^tBu-C₆H₄)}(NⁱPr)(CO)BCy₂ (13), could be isolated in moderate yields. The 1,2-insertions of benzaldehyde in compounds 1, 2 and 4 are reversible reactions in all cases, and only one of the insertion products, {ⁱPr(H)N}C{N(p-^tBu-C₆H₄)}(NⁱPr)(PhHCO)BCy₂ (16a), was isolated and diffractrometrically characterised. Likewise, CO₂ reversibly inserts into a N-B bond of 2 to give {ⁱPr(H)N}C{N(p-^tBu-C₆H₄)}(NⁱPr)(CO₂)BCy₂ (19) with a conversion of ca. 9%. In all these equilibria, de-insertion is always favoured upon increasing the temperature.

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. The process starts with the interaction of tris(pentafluorphenyl)borane and the amine to form the corresponding adduct, [(C6F5)3B-NRH2] , followed by a straightforward proton transfer to one of the nitrogen atoms of the carbodiimide, (i)PrN[double bond, length as m-dash]C[double bond, length as m-dash]N(i)Pr, to produce, in two consequent steps, a guanidine-borane adduct, [(C6F5)3B-NRC(N(i)PrH)2] . The rupture of this adduct liberates the guanidine product RNC(N(i)PrH)2 and interaction with additional amine restarts the catalytic cycle. DFT studies have been carried out in order to study the thermodynamic characteristics of the proposed pathway. Significant borane adducts with amines and guanidines have been isolated and characterized by multinuclear NMR in order to study the N-B interaction and to propose the existence of possible Frustrated Lewis Pairs. Additionally, the molecular structures of significant components of the catalytic cycle, namely 4-tert-butylaniline-[B(C6F5)3] adduct and both free and [B(C6F5)3]-bonded 1-(phenyl)-2,3-diisopropylguanidine, and respectively, have been established by X-ray diffraction.

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

Solutions of some of the title compounds reached an equilibrium with the aminoboranes and the corresponding carbodiimides at room temperature.

Bis(allyl)-ruthenium(iv) complexes with phosphinous acid ligands as catalysts for nitrile hydration reactions

The preparation of bis(allyl)-Ru(iv) complexes with phosphinous acid ligands is presented, as well as their application as catalysts in the base-free hydration of organonitriles in water.