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Research has been conducted on the 'scorpionate' ligands. The preparation of these ligands in the form of lithium derivatives with acetate and dithioacetate groups, their synthesis and characterization have been carried out and their reactivity has been studied and discussed.

Polydentate ligands with nitrogen donor atoms have possibly given rise to the largest group of coordination complexes described. Among these ligands, amidinates represent a nitrogenated version of carboxylates and allow the formation of complexes with most elements in the periodic table, adopting chelate or bridge coordination modes. The precursors of these ligands, amidines, can present an alkynyl group as the substituent of their central atom, R'N=C(C≡CR)NHR', which provides an additional point of reactivity for these molecules, as well as a different electronic behavior compared to conventional amidines with alkyl groups on the central carbon atom of the amidine group. These propiolamidines have been obtained through classical stoichiometric organic synthesis procedures or, with greater atomic economy, through catalytic procedures based on Main Group, Transition, or Rare Earth metals. This work reviews these synthesis methods, as well as the reactivity in the obtention of new, more complex heterocyclic organic molecules.

Two series of boron derivatives with propiolamidinato ligands, [BPh 2 {C(C≡CAr)(NR) 2 }] (Ar = Ph, p -MeOPh, p -FPh, p -Me 2 NPh, or phen; R = iPr or p -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 2 as a precatalyst. Alternatively, to obtain propiolamidines with aromatic groups on the nitrogen atoms, the formation of lithiated derivatives of terminal alkynes by reaction with n -BuLi in air and at room temperature, and subsequent addition to the di- p -tolylcarbodiimide, under the same conditions and using 2-MeTHF as a sustainable solvent, has been used for the first time. After reaction with BPh 3 , the corresponding boron amidinates were obtained, which are emissive in the solution state. The influence of the different substituents introduced into the ligands on the photophysical properties of the boron compounds has been studied. One of the obtained compounds can be used as a ratiometric fluorescent pH sensor in the acidic range.

The guanidine core has been one of the most studied functional groups in medicinal chemistry, and guanylation reactions are powerful tools for synthesizing this kind of compound. In this study, a series of five guanidine-core small molecules were obtained through guanylation reactions. These compounds were then evaluated against three different strains of Escherichia coli , one collection strain from the American Type Culture Collection (ATCC) of E. coli ATCC 35218, and two clinical extended-spectrum beta-lactamase (ESBL)-producing E. coli isolates (ESBL1 and ESBL2). Moreover, three different strains of Pseudomonas aeruginosa were studied, one collection strain of P. aeruginosa ATCC 27853, and two clinical multidrug-resistant isolates (PA24 and PA35). Among Gram-positive strains, three different strains of Staphylococcus aureus , one collection strain of S. aureus ATCC 29213, and two clinical methicillin-resistant S. aureus (MRSA1 and MRSA2) were evaluated. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) experiments were reported, and the drop plate (DP) method was used to determine the number of viable suspended bacteria in a known beaker volume. The results from this assessment suggest that guanidine-core small molecules hold promise as therapeutic alternatives for treating infections caused by clinical Gram-negative and Gram-positive bacteria, highlighting the need for further studies to explore their potential. The results from this assessment suggest that the chemical structure of CAPP4 might serve as the basis for designing more active guanidine-based antimicrobial compounds, highlighting the need for further studies to explore their potential.

A synthesis of iminopyridines based on zinc has been developed. The commercially available ZnEt 2 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. The zinc amidinato intermediates underscore the critical role of zinc in this synthesis process.

A straightforward and selective conversion of nitriles into highly substituted tetrahydropyridines, aminoketones or enamines by using allylmagnesium bromide as an addition partner (under neat conditions) and subsequent treatment with different aqueous-based hydrolysis protocols is reported. Refuting the conventional wisdom of the incompatibility of Grignard reagents with air and moisture, we herein report that the presence of water allows us to promote the chemoselective formation of the target tetrahydropyridines over other competing products (even in the case of highly challenging aliphatic nitriles). Moreover, the careful tuning of both the reaction media employed (acid or basic aqueous solutions for the hydrolysis protocol) and the electronic properties of the starting nitriles allowed us to design a multi-task system capable of producing either β-aminoketones or enamines in a totally selective manner. Importantly, and for the first time in the chemistry of main-group polar organometallic reagents in non-conventional protic solvents ( e.g. , water), both experimental and computational studies showed that the excellent efficiency and selectivity observed in aqueous media cannot be replicated by using standard dry volatile organic solvents (VOCs) under inert atmosphere conditions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The modular synthesis of the guanidine core by guanylation reactions using commercially available ZnEt 2 as a catalyst has been exploited as a tool for the rapid development of antitumoral guanidine candidates. Therefore, a series of phenyl-guanidines were straightforwardly obtained in very high yields. From the in vitro assessment of the antitumoral activity of such structurally diverse guanidines, the guanidine termed ACB3 has been identified as the lead compound of the series. Several biological assays, an estimation of AMDE values, and an uptake study using Fluorescence Lifetime Imaging Microscopy were conducted to gain insight into the mechanism of action. Cell death apoptosis, induction of cell cycle arrest, and reduction in cell adhesion and colony formation have been demonstrated for the lead compound in the series. In this work, and as a proof of concept, we discuss the potential of the catalytic guanylation reactions for high-throughput testing and the rational design of guanidine-based cancer therapeutic agents.

We report here the use of commercially available ZnEt 2 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- i Pr 2 C 6 H 3 ) 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(N i Pr) 2 and C(N p -tol) 2 , 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. Some of the new isoureas thus prepared have also been isolated and characterized. Kinetic and stoichiometric experiments allowed us to propose a plausible mechanism for these transformations., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

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., (© 2022 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

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.

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. The photophysical behaviors of the new mono- ( M ) and bis-guanidine ( B ) derivatives were studied through pH dependence, solvent effects, and ion sensing on steady-state spectra and time-resolved fluorescence spectroscopy. In more detail, the results demonstrate that M is a highly selective and sensitive sulfate ion receptor in real water samples and, even more importantly, its function remains unchanged at different ranges of pH. The reason behind this resides on the fluorescence quenching produced by an internal charge-transfer process when the sulfate anion is complexed with M . It is worth noting that the global and partial affinity constants (10 10 M -2 and 10 5 M -1 , respectively) of complex formation are far above from the current sulfate sensors in water (10 4 M -1 ) which give an LOD of 0.10 μM in water with an analytical range of 2.5-10 μM. On the other hand, although it would seem, at first sight, that the B derivate will be the most promising one, the possibility of having two simultaneous protonation states reduces the complex formation and, therefore, its sensitivity to sulfate anions. The results presented here offer the possibility of using a new molecule in water environments, which opens the door to infinite applications such as the detection of trace amounts of sulfate ions in food or water.

We report the reactivity of N -phosphinoguanidines of the formula (HNR)(Ph 2 PNR)C(NAr) (R = i Pr and Ar = 2,6- i Pr 2 C 6 H 3 [Dipp] for 1a , R = i Pr and Ar = 2,4,6-Me 3 C 6 H 2 [Mes] for 1b , and R = Cy and Ar = Dipp for 1c ), prepared in high yields from the corresponding trisubstituted guanidines, toward main group metal alkyls AlMe 3 , ZnEt 2 , Mg n Bu 2 , and n BuLi to obtain novel phosphinoguanidinato and phosphinimine-amidinato compounds. Reactions of 1a - c with AlMe 3 at room temperature led to the kinetic phosphinoguanidinato products [Al{κ 2 - N,N '-(NR)C(NAr)(NRPPh 2 )}Me 2 ] ( 2a - c ), whereas the mild heating (60-80 °C) of solutions of 2a - c give the thermodynamic phosphinimine-amidinato products [Al{κ 2 - N,N '-(NR)C(NAr)(PPh 2 NR)}Me 2 ] ( 3a - c ) after ligand rearrangement. The reactions of equimolar amounts of 1a - c and ZnEt 2 initially give solutions containing unstable phosphinoguanidinato compounds [Zn{κ 2 - N,P -(NR)C(NAr)(NRPPh 2 )}Et] ( 4a - c ), which rearrange upon mild heating to the phosphinimine-amidinato derivatives [Zn{κ 2 - N,N '-(NR)C(NAr)(PPh 2 NR)}Et] ( 6a - c ). Bis(phosphinoguanidinato) compounds [Zn{κ 2 - N,P -(NR)C(NAr)(NRPPh 2 )} 2 ] ( 5a - c ) can be obtained under mild conditions (<45 °C) in THF, whereas bis(phosphinimine-amidinato) compounds [Zn{κ 2 - N,N '-(NR)C(NAr)(PPh 2 NR)} 2 ] ( 7a - c ) are also accessible under more forcing conditions (55-100 °C) from (i) ZnEt 2 and 1b , c (2 equiv), (ii) 6a and 1a , or (iii) 5b , c . Equimolar mixtures of Mg n Bu 2 and 1a - c in THF at room temperature give unstable phosphinimine-amidinato monoalkyl products [Mg{κ 2 - N,N '-(NR)C(NAr)(PPh 2 NR)} n Bu(THF) 2 ] ( 8a - c ), whereas 2 equiv of 1a , b are required to reach the bischelate compounds [Mg{κ 2 - N,N '-(N i Pr)C(NAr)(PPh 2 N i Pr)} 2 ] ( 9a , b ). Finally, phosphinoguanidinato compounds [Li{κ 2 - N,P -(NR)C(NDipp)(NRPPh 2 )}(THF) 2 ] ( 10a , c ) were obtained in the reactions of 1a , c with n BuLi in THF under ambient conditions. The removal of the solvent from solutions of 10a , c under partial vacuum leads to the dinuclear compounds [Li 2 {μ-κ 2 - N,N ':κ 1 - N - (NR)C(NDipp)(NRPPh 2 )} 2 (THF) 2 ] ( 11a , c ) after the decoordination of one of the THF molecules in 10a , c and dimerization. Heating solutions of 10a , c at 60 °C triggers ligand rearrangement to give phosphinimine-amidinato compounds [Li{κ 2 - N,N '-(NR)C(NDipp)(PPh 2 NR)}(THF) 2 ] ( 12a , c ). We also propose a mechanism for the ligand rearrangement reaction from 10a to give 12a , supported by DFT calculations, which fits nicely with our experimental results. It essentially involves a carbodiimide deinsertion reaction followed by a [3 + 2] cycloaddition between the resulting lithium phosphino-amide and the carbodiimide.

We study two metal-free catalysts for the reduction of CO 2 with four different hydroboranes and try to identify mechanistically relevant intermediate species. The catalysts are the phosphinoborane Ph 2 P(CH 2 ) 2 BBN ( 1 ), easily accessible in a one-step synthesis from diphenyl(vinyl)phosphine and 9-borabicyclo[3.3.1]nonane (H-BBN), and its formaldehyde adduct Ph 2 P(CH 2 ) 2 BBN(CH 2 O) ( 2 ), detected in the catalytic reduction of CO 2 with 1 as the catalyst but properly prepared from compound 1 and p -formaldehyde. Reduction of CO 2 with H-BBN gave mixtures of CH 2 (OBBN) 2 ( A ) and CH 3 OBBN ( B ) using both catalysts. Stoichiometric and kinetic studies allowed us to unveil the key role played in this reaction by the formaldehyde adduct 2 and other formaldehyde-formate species, such as the polymeric BBN(CH 2 ) 2 (Ph 2 P)(CH 2 O)BBN(HCO 2 ) ( 3 ) and the bisformate macrocycle BBN(CH 2 ) 2 (Ph 2 P)(CH 2 O)BBN(HCO 2 )BBN(HCO 2 ) ( 4 ), whose structures were confirmed by diffractometric analysis. Reduction of CO 2 with catecholborane (HBcat) led to MeOBcat ( C ) exclusively. Another key intermediate was identified in the reaction of 2 with the borane and CO 2 , this being the bisformaldehyde-formate macrocycle (HCO 2 ){BBN(CH 2 ) 2 (Ph 2 P)(CH 2 O)} 2 Bcat ( 5 ), which was also structurally characterized by X-ray analysis. In contrast, using pinacolborane (HBpin) as the reductant with catalysts 1 and 2 usually led to mixtures of mono-, di-, and trihydroboration products HCO 2 Bpin ( D ), CH 2 (OBpin) 2 ( E ), and CH 3 OBpin ( F ). Stoichiometric studies allowed us to detect another formaldehyde-formate species, (HCO 2 )BBN(CH 2 ) 2 (Ph 2 P)(CH 2 O)Bpin ( 6 ), which may play an important role in the catalytic reaction. Finally, only the formaldehyde adduct 2 turned out to be active in the catalytic hydroboration of CO 2 using BH 3 ·SMe 2 as the reductant, yielding a mixture of two methanol-level products, [(OMe)BO] 3 ( G , major product) and B(OMe) 3 ( H , minor product). In this transformation, the Lewis adduct (BH 3 )Ph 2 P(CH 2 ) 2 BBN was identified as the resting state of the catalyst, whereas an intermediate tentatively formulated as the Lewis adduct of compound 2 and BH 3 was detected in solution in a stoichiometric experiment and is likely to be mechanistically relevant for the catalytic reaction.

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. Stoichiometric reactions, kinetic studies, and DFT calculations have allowed us to propose a plausible mechanism involving a heterocyclic amidinate intermediate with a three center-two electron B-H-B bond.

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.

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)BC 8 H 14 afforded the corresponding 1,2-adducts {R(H)N}C{N(Ar)}(NR)(CO 2 )BC 8 H 14 . Alternatively, the reaction with p-MeOC 6 H 4 NC or 2,6-Me 2 C 6 H 3 NC gave the corresponding isocyanide 1,1-adducts { i-PrHN}C{N(p-Me-C 6 H 4 )}(N i-Pr){CNAr}BC 8 H 14 . The molecular structures of products (2,6- i-Pr 2 C 6 H 3 NH)BC 8 H 14 7, { i-Pr(H)N}C{N(p-MeC 6 H 4 )}(N i-Pr)(CO 2 )BC 8 H 14 9, {Cy(H)N}C{N( p-MeC 6 H 4 )}(Cy)(CO 2 )BC 8 H 14 13, and { i-PrHN}C{N( p-MeC 6 H 4 )}(N i-Pr){CNR″}BC 8 H 14 (R″ = p-MeOC 6 H 4 , 2,6-Me 2 C 6 H 3 ) 14 and 15 were established by X-ray diffraction. Density functional theory calculations at the M05-2X level of theory revealed that CO 2 fixation and formation of the corresponding adduct is exothermic and proceeds via a nonchelate boron guanidinato intermediate.

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.

Expanding the possibilities of the use of simple and available ZnEt 2 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. The hydroalkynylation reaction has been coupled with isocyanate (and isothiocyanate) insertion and intramolecular hydroamination to obtain imidazolidin-2-ones (or thione). The structures of different plausible intermediates have been determined by X-ray diffraction studies.

We report here 1,1- and 1,2-insertion reactions of small unsaturated molecules in the N-B bonds of two boron guanidinates, (Me 2 N)C(N i Pr) 2 BCy 2 (1) and { i Pr(H)N}C(N i Pr){N(p- t Bu-C 6 H 4 )}BCy 2 (2), and two bisboron guanidinates(2-), { i Pr(BCy 2 )N}C(N i Pr){N(p- t Bu-C 6 H 4 )}BCy 2 (3) and { i Pr(C 8 H 14 B)N}C(N i Pr){N(p-Me-C 6 H 4 )}BC 8 H 14 (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-BC 8 H 14 ) 2 . Compounds 1-4 easily insert aromatic isonitriles, XylNC (Xyl = 2,6-Me 2 -C 6 H 3 ) and (p-MeO-C 6 H 4 )NC, to give the expected diazaboroles 5-12, some of them being structurally characterised by X-ray diffraction. Interestingly, the BC 8 H 14 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, { i Pr(H)N}C{N(p- t Bu-C 6 H 4 )}(N i Pr)(CO)BCy 2 (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, { i Pr(H)N}C{N(p- t Bu-C 6 H 4 )}(N i Pr)(PhHCO)BCy 2 (16a), was isolated and diffractrometrically characterised. Likewise, CO 2 reversibly inserts into a N-B bond of 2 to give { i Pr(H)N}C{N(p- t Bu-C 6 H 4 )}(N i Pr)(CO 2 )BCy 2 (19) with a conversion of ca. 9%. In all these equilibria, de-insertion is always favoured upon increasing the temperature.

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. The most promising drug candidate displayed a similar potency in inducing cell death to the clinically used reference compound and showed significant inhibition of glioblastoma cell proliferation. Moreover, this compound had a safer profile than cisplatin on non-tumoral cells., (Copyright © 2016 Elsevier Inc. All rights reserved.)

To advance the catalytic applications of s-block mixed-metal complexes, sodium magnesiate [NaMg(CH 2 SiMe 3 ) 3 ] (1) is reported as an efficient precatalyst for the guanylation of a variety of anilines and secondary amines with carbodiimides. First examples of hydrophosphination of carbodiimides by using a Mg catalyst are also described. The catalytic ability of the mixed-metal system is much greater than that of its homometallic components [NaCH 2 SiMe 3 ] and [Mg(CH 2 SiMe 3 ) 2 ]. Stoichiometric studies suggest that magnesiate amido and guanidinate complexes are intermediates in these catalytic routes. Reactivity and kinetic studies imply that these guanylation reactions occur via (tris)amide intermediates that react with carbodiiimides in insertion steps. The rate law for the guanylation of N,N'-diisopropylcarbodiimide with 4-tert-butylaniline catalyzed by 1 is first order with respect to [amine], [carbodiimide], and [catalyst], and the reaction shows a large kinetic isotopic effect, which is consistent with an amine-assisted rate-determining carbodiimide insertion transition state. Studies to assess the effect of sodium in these transformations denote a secondary role with little involvement in the catalytic cycle., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The synthesis of novel dialkylboron guanidinates is reported: the symmetrical compounds, (Me 2 N)C(NR) 2 BR' 2 [R = i Pr, R' = Nrb (1); R = Cy, R' = Nrb (2); R = i Pr, R' = Cy (3); R = R' = Cy (4); R = 2,6- i Pr 2 -C 6 H 3 ; R' = Cy (5); Nrb = exo-2-norbornyl] and the asymmetrically coordinated { i Pr(H)N}C(N i Pr)(NAr)BCy 2 [Ar = Ph (6), 4-Me-C 6 H 4 (7), 4- t Bu-C 6 H 4 (8)] were prepared by the salt metathesis method from the appropriate lithium guanidinates and chloroboranes. Moreover, the bis(dicyclohexylboron)guanidinate(-2) { i Pr(Cy 2 B)N}C(N i Pr){N(4- t Bu-C 6 H 4 )}BCy 2 (9) was also prepared from the corresponding dilithium guanidinate Li 2 [{N(4- t Bu-C 6 H 4 )}C(N i Pr) 2 ] and ClBCy 2 . 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' 2 fragment, the latter displaying an additional BCy 2 attached to the exocyclic N atom. Solutions of compounds 1-4 reached an equilibrium with the aminoboranes Me 2 NBR' 2 [R' = Nrb (10), Cy (11)] and the corresponding carbodiimides, which was slow at 25 °C. The thermodynamic parameters for these equilibria are also reported. The activation parameters for the equilibrium for compound 1 have been calculated after a kinetic study. Compounds 5-8, with one or two N-aryl fragments bound to a B centre, are more robust and need higher temperatures (80 °C) and prolonged times to give similar carbodiimide de-insertion reactions.