Recent Progress in the Chemistry of Metal Amidinates and Guanidinates

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

Two series of boron derivatives with propiolamidinato ligands, [BPh2{C(C≡CAr)(NR)2}] (Ar = Ph, p-MeOPh, p-FPh, p-Me2NPh, 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 ZnEt2 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 BPh3, 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.

Rare-Earth Metal Complexes Supported by A Tridentate Amidinate Ligand: Synthesis, Characterization, and Catalytic Comparison in Isoprene Polymerization

To systematically investigate the dependence of the initiating group and metal size on polymerization performance, a family of rare-earth metal bis(alkyl)/bis(benzyl)/bis(amide) complexes supported by a monoanionic tridentate amidinate ligand [(2,6-iPr2C6H3)NC(Ph)N(C6H4-2-OMe]- (HL) were synthesized and well-characterized. Treatment of rare-earth metal tris(alkyl)/tris(benzyl)/tris(amide) complexes Y(CH2C6H4NMe2-o)3 or Y(CH2SiMe3)3(THF)2 or Ln[N(SiHMe2)2]3(THF)x (Ln = Sc, x = 1; Ln = Y, La, Sm, Lu, x = 2) with 1 equiv of HL gave the corresponding mono(amidinate) rare-earth metal bis(alkyl)/bis(benzyl)/bis(amide) complexes [(2,6-iPr2C6H4)NC(Ph)N(C6H4-2-OMe)]Y(CH2C6H4NMe2-o)2 (1), [(2,6-iPr2C6H4)NC(Ph)N(C6H4-2-OMe)]Y(CH2SiMe3)2(THF) (2), and [(2,6-iPr2C6H4)NC(Ph)N(C6H4-2-OMe)]Ln[N(SiHMe2)2]2(THF)n (Ln = Y, n = 1 (3); Ln = La, n = 1 (4); Ln = Sc, n = 0 (5); Ln = Lu, n = 0 (6); Ln = Sm, n = 0 (7)) in good isolated yields. These complexes were characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction. In the presence of excess AlMe3 and on treatment with 1 equiv of [Ph3C][B(C6F5)4], these complexes could serve as precatalysts for cationic polymerization of isoprene, in which the dependence of the polymerization activity and regioselectivity on the initiating group and metal size was observed.

Lanthanide complexes with a new luminescent iminophosphonamide ligand bearing phenylbenzothiazole substituents

A new iminophosphonamine Ph2P(HNPbt)(NPbt) (1, HL) bearing chromophore 2-(phen-2'-yl)-1,3-benzothiazole (Pbt) substituents was synthesized and introduced into lanthanide complexes. It was found that salt metathesis reactions between KL (2) generated in situ and LnCl3 lead to the formation of tris-iminophosphonamide complexes [LnL2]L (Ln = Y (3), Sm (4), Gd (5), Dy (6)), regardless of the 2/LnCl3 ratio. Compounds 3-6 consist of a cationic fragment [LnL2]+, where the lanthanide atom is surrounded by two rigidly κ4-coordinated ligands, and an L- anion residing in the outer coordination sphere. Iminophosphonamine 1 shows a rare excitation wavelength-dependent two-band luminescence in the solid state. For compounds containing the deprotonated form, namely potassium salt KL and complexes of Gd and Dy, a single-band luminescence with the color changing from turquoise to orange was observed. The Sm complex reveals a set of a few narrow well-resolved bands corresponding to the f-f transitions against the background of the outer-sphere ligand's emission.

Thermally Stable Terbium(II) and Dysprosium(II) Bis-amidinate Complexes

The thermostable four-coordinate divalent lanthanide (Ln) bis-amidinate complexes [Ln(Piso)2] (Ln = Tb, Dy; Piso = {(NDipp)2CtBu}, Dipp = C6H3iPr2-2,6) were prepared by the reduction of parent five-coordinate Ln(III) precursors [Ln(Piso)2I] (Ln = Tb, Dy) with KC8; halide abstraction of [Ln(Piso)2I] with [H(SiEt3)2][B(C6F5)] gave the respective Ln(III) complexes [Ln(Piso)2][B(C6F5)]. All complexes were characterized by X-ray diffraction, ICP-MS, elemental analysis, SQUID magnetometry, UV-vis-NIR, ATR-IR, NMR, and EPR spectroscopy and ab initio CASSCF-SO calculations. These data consistently show that [Ln(Piso)2] formally exhibit Ln(II) centers with 4fn5dz21 (Ln = Tb, n = 8; Dy, n = 9) valence electron configurations. We show that simple assignments of the f-d coupling to either L-S or J-s schemes are an oversimplification, especially in the presence of significant crystal field splitting. The coordination geometry of [Ln(Piso)2] is intermediate between square planar and tetrahedral. Projecting from the quaternary carbon atoms of the CN2 ligand backbones shows near-linear C···Ln···C arrangements. This results in strong axial ligand fields to give effective energy barriers to magnetic reversal of 1920(91) K for the Tb(II) analogue and 1964(48) K for Dy(II), the highest values observed for mononuclear Ln(II) single-molecule magnets, eclipsing 1738 K for [Tb(C5iPr5)2]. We tentatively attribute the fast zero-field magnetic relaxation for these complexes at low temperatures to transverse fields, resulting in considerable mixing of mJ states.

Synthesis of inventive biphenyl and azabiphenyl derivatives as potential insecticidal agents against the cotton leafworm, Spodoptera littoralis

The emergence of pest resistance of Spodoptera littoralis (order; Lepidoptera, family; Noctuidae) towards the large scale of different classes of insecticides necessitates the development of some new poly-functionalized biphenyl and azabiphenyl with highly anticipated insecticidal bioresponse. Four new biphenyl carboxamidines 4a-d and four aza-analogue picolinamidine derivatives 8a-d were designed and prepared via the treatment of their corresponding carbonitriles with lithium-bis trimethylsilylamide [LiN(TMS)2], followed by hydrolysis with hydrogen chloride. Furthermore, these compounds were elucidated by spectral data, and their toxicity and insecticidal activity were screened against Spodoptera littoralis. Whereby, toxicological and biochemical aspects of the inventively synthesized biphenyl and azabiphenyl derivatives against the cotton leafworm, Spodoptera littoralis were inspected. As regards the indomitable LC50 and LC90 values, biphenyl and aza-analogues 8d, 8a, 4b, and 8b, revealed the furthermost forceful toxic effects with LC50 values of 113.860, 146.265, 216.624, and 289.879 ppm, respectively. Whereby, their LC90 values are 1235.108, 1679.044, 2656.296, and 3381.256 ppm, respectively, and toxicity index being 22.31%, 17.36%, 11.72%, and 8.76%, respectively, comparing with the already recommended, methomyl insecticide, lannate 90% SP (LC50, 25.396 and LC90, 57.860 and toxicity index, 100%). Additionally, electrochemical parameters via DFT studies were carried out for demonstrating and elucidation of structure-activity relationship (SAR) according to highly motived compounds, descriptors, and the in vivo insecticidal activities.

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.

Semistabilized Diazatrienyl Anions from Pyridine Imines and Acetylenes: An Access to (Z)-Stilbene/Imidazopyridine Ensembles, Benzyl Imidazopyridines, and Beyond

Semistabilized diazatrienyl anions are generated by the reaction of 2-pyridylarylimines with arylacetylenes in superbase systems MO^tBu (M = Li, Na, K)/DMSO at ambient temperature for 15 min. The initial intermediate N-centered propargyl-1,3-diaza-1,3,5-trienyl anions undergo intermolecular cyclization to benzyl imidazopyridine anions (formally [3 + 2] cycloaddition), further intercepting a second molecule of the starting pyridylimines or a proton of medium to afford (Z)-stilbene/imidazopyridine ensembles and benzyl imidazopyridines. The charge distribution in all intermediate anions and their synthetic evolution are consistent with quantum-chemical analysis (B2PLYPD/6-311+G**//B3LYP/6-31+G*).

Synthesis and photophysical properties of rare earth complexes bearing silanediamido ligands Me2Si(NAryl)22− (Aryl = Dipp, Mes)

Luminescence of the newly obtained silanediamides of rare earths was investigated. The triplet states of the ligands {Me2Si(NAryl)2}2− (Aryl = Dpp, Mes) were determined by the emission of Gd complexes, and the bright emission of Tb3+ was observed.

Coordination Chemistry of Bulky Aminopryridinates with Main Group and Transition Metals

The coordination chemistry of bidentate aminopyridinato ligands (ApH), in particular 2-aminopyridines, is a highly popular area of research. Due to easy accessibility and versatility, 2-aminopyridines have played a prominent role as alternatives to cyclopentadienyl ligands in coordination chemistry. Easily modifiable steric bulks and the ability for fine-tuning of electronic effects have allowed researchers to control not only the metal-to-ligand stoichiometry but also the properties of their metal complexes. Previously, ligand redistribution was frequently observed for ligands of small steric demands. Bulky aminopyridinato ligands refer to ligands that incorporate alkyl-substituted phenyl groups at the amine/amido nitrogen and at the sixth position of the pyridine ring. The steric crowding allowed the stabilization of transition metals in unusually low oxidation conditions. One of the remarkable developments, for example, is the stabilization of metal-metal quintuple bonds by these ligands, thus providing a diamagnetic platform to study such systems chemically. Application of metal aminopyridinates in homogeneous catalysis has also broadened considerably in recent years. This review provides a comprehensive account of advances made with such ligands since their development for main group and transition elements.

Half-sandwich complexes of osmium containing guanidine-derived ligands

Pyridinyl- and phosphano-guanidino complexes of formula [(η6-p-cymene)OsCl(H2L)][SbF6] (cymene = MeC6H4iPr; H2L = N,N'-bis(p-Tolyl)-N''-(2-pyridinylmethyl)guanidine, H2L1 (1) and N,N'-bis(p-Tolyl)-N''-(2-diphenylphosphanoethyl)guanidine, H2L2 (2)) have been prepared from the dimer [{(η6-p-cymene)OsCl}2(μ-Cl)2] and H2L in the presence of NaSbF6. Treatment of complex 2 with HCl renders the phosphano-guanidinium complex [(η6-p-cymene)OsCl2(H3L2)][SbF6] (3). Compounds 1 and 2 react with AgSbF6 rendering the cationic aqua complexes [(η6-p-cymene)Os(H2L)(OH2)][SbF6]2 (H2L = H2L1 (4), H2L2 (5)). Addition of monodentate ligands L to compound 4 affords complexes of formula [(η6-p-cymene)Os(H2L1)L][SbF6]2 (L = py (6), 4-(NHMe)py (7), CO (8), P(OMe)3 (9)). Treatment of complexes 4 and 5 with NaHCO3 renders the monocationic complexes [(η6-p-cymene)Os(κ3N,N',N''-HL1)][SbF6] (10) and [(η6-p-cymene)Os(κ3N,N',P-HL2)][SbF6] (11), respectively, in which the HL ligand adopts a fac-κ3 coordination mode. The new complexes have been characterised by analytical and spectroscopic means, including the determination of the crystal structures of the compounds 1-4, 6, 8, and 11, by X-ray diffractometric methods. The phosphano-guanidino complexes 2 and 5 exhibit a temperature dependent fluxional process in solution. The new 18 electron complexes 1, 2, 6, and 8-10 are active catalysts for the Friedel-Crafts reaction between trans-β-nitrostyrene and N-methyl-2-methylindole. Conversions greater than 90% were obtained. Proton NMR studies support a mechanism involving the Brønsted-acid activation of trans-β-nitrostyrene through the NH functionalities of the coordinated guanidine ligands.

Lithium and Dilithium Guanidinates, a Starter Kit for Metal Complexes Containing Various Mono- and Dianionic Ligands

Comparative studies of the synthesis of lithium guanidinates via nucleophilic addition of lithium amides to carbodiimides were performed. Four combinations of small or sterically crowded carbodiimide and sterically crowded lithium amide or lithium amide containing an adjacent amino donor group give ten different types of complexes. In particular, 2,6-[(CH₃)₂CH]₂C₆H₃NHLi (DipNHLi, 1) reacts with (CH₃)₂CHN═C═NCH(CH₃)₂ upon the formation of the dissymmetric dimeric complex 2 with four-coordinate Li atoms. In contrast, 1 with DipN═C═NDip gives the mononuclear lithium guanidinate 3 with two-coordinate lithium by κ¹-guanidinate, solvent molecule, and additional interaction with a π-electron cloud of one of the Dip groups. Analogous reactions of 2-[(CH₃)₂NCH₂]C₆H₄NHLi (7) yield complexes 8 and 9, where the adjacent amino donors are always coordinated. Further deprotonation of 2, 3, 8, and 9 leads to dilithium guanidinates(2-)-4, 5, 10, and 11, among which only 5, containing three Dip groups, is monomeric with contacts to two π-electron systems of Dip groups. The rest of the complexes are tetranuclear with different structural patterns. In the central parts of molecules, toward which the nitrogen atoms of the guanidinates are oriented, lithium atoms are usually pseudotetrahedral, but trigonal in peripheral parts. Adjacent solvent molecules, chelating amino groups, and π-electron systems of Dip groups are coordinated in order to complete coordination polyhedra. Complexes 4 and 5 deoligomerize in solution upon the formation of fluxional monomeric dilithium species. Conversely, 11 is a dimer in solution due to the strong donation of an amino group. The silylated lithium amide {2-[(CH₃)₂NCH₂]C₆H₄}[(Si(CH₃)₃]NLi (12) reacts with both carbodiimides to give dinuclear 13 obtained from diisopropylcarbodiimide and monomeric 14 from the second carbodiimide. Complexes 13 and 14 structurally resemble 8 and 9, with the highest degree of the localization of π-electron density within the N₃C guanidinate system, η³-contact to the Dip ring, and a lack of the solvent molecule in 14.

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.

Synthesis and characterization of 2-t-butylimino-functionalized indolyl rare-earth metal amido complexes for the catalytic addition of terminal alkynes to carbodiimides: the dimeric complexes with the alkynide species in the μ–η1:η2 bonding modes

Dimeric complexes [(μ–η¹:η²-RCC)REL2]₂ (L = 2-(^tBuNCH)C₈H₅N), with alkynyl in the μ–η¹:η² modes, were isolated in the study of the catalytic reaction.

Formation and structural characterization of a potassium amidino-guanidinate

The first potassium amidino-guanidinate complex, catena-poly[[bis-(μ-1-amidinato-N,N',N'',N'''-tetra-iso-propyl-guanidinato-κ5 N 1:N 1,N 2:N 2,N 4)dipotassium]-μ-1,2-di-meth-oxy-ethane-κ2 O:O'], [K2(C14H32N4)2(C4H10O2)] n or [{ i PrN= CHN( i Pr)N(N i Pr)2K}2(μ-DME)] n where DME is 1,2-di-meth-oxy-ethane, has been synthesized and structurally characterized. The title compound was isolated in 76% yield from a reaction of N,N'-diiso-propyl-carbodi-imide with potassium hydride in DME. The single-crystal X-ray structure determination of the title compound revealed a polymeric chain structure comprising cage-like dimeric units, with the amidino-guanidinate ligand displaying a mixed σ-/π-coordination mode.

Synthesis and structural characterization of four di-chlorido-bis-(cyclo-propyl-alkynyl-amidine)-metal complexes

Deliberate hydrolysis of lithium cyclo-propyl-alkynylamidinates, Li[c-C3H5-C≡C(NR')2] [R' = i Pr, Cy = cyclo-hex-yl)], afforded the hitherto unknown neutral cyclo-propyl-alkynyl-amidine derivatives c-C3H5-C≡C-C(NR')(NHR') [R' = i Pr (1), Cy (2)]. Subsequent reactions of 1 or 2 with metal(II) chlorides, MCl2 (M = Mn, Fe, Co), provided the title complexes di-chlorido-bis-(3-cyclo-propyl-N,N'-diisopropyl-prop-2-ynamidine)-manganese(II), [MnCl2(C12H20N2)2], (3), di-chlorido-bis-(3-cyclo-propyl-N,N'-diisopropyl-prop-2-ynamidine)-iron(II), [FeCl2(C12H20N2)2], (4), di-chlorido-bis-(N,N'-di-cyclo-hexyl-3-cyclo-propyl-prop-2-ynamidine)-iron(II), [FeCl2(C18H28N2)2], (5), and di-chlorido-bis-(N,N'-di-cyclo-hexyl-3-cyclo-propyl-prop-2-ynamidine)-cobalt(II), [CoCl2(C18H28N2)2], (6), or more generally MCl2[c-C3H5-C≡C-C(NR')(NHR')]2 [R' = i Pr, M = Mn (3), Fe (4); R' = Cy, M = Fe (5), Co (6)] in moderate yields (30-39%). Besides their spectroscopic data (IR and MS) and elemental analyses, all complexes 3-6 were structurally characterized. The two isopropyl-substituted complexes 3 and 4 are isotypic, and so are the cyclo-hexyl-substituted complexes 5 and 6. In all cases, the central metal atom is coordinated by two Cl atoms and two N atoms in a distorted-tetra-hedral fashion, and the structure is supported by intra-molecular N-H⋯Cl hydrogen bonds.

New synthetic strategies leading to [RNPNR]- anions and the isolation of the [P(Nt-Bu)3]3- trianion

New and straightforward synthetic paths for the syntheses of [RNPNR]- anions (R = t-Bu (1) or CPh3 (6)) in the form of their tmeda- or thf-coordinated lithium salts are described. The attempts to isolate the sodium analogue [(Ph3CNPNCPh3)Na·(thf)x] (8) remained unsuccessful probably due to its high reactivity although its formation in the reaction of the parent cis-[(Ph3CNP)2(Ph3CNH)2] (5) with 2 eq. of sodium naphthalenide was corroborated by NMR spectroscopy. Importantly, when an excess of sodium naphthalenide was used in the reaction with 5, [(Ph3C)Na(thf)3] (9) was obtained along with a complex mixture of other by-products indicating the cleavage of the C-N bond in the starting material. Furthermore, the synthesis and the structural characterization of the [P(Nt-Bu)3]3- trianion as its trilithium salt [P(Nt-Bu)3Li3]2 (10) has been successfully achieved.

Chlorogermylenes and -stannylenes stabilized by diimidosulfinate ligands: synthesis, structures, and reactivity

The reaction of the lithium salt of N,N'-di-tert-butyldiimidosulfinate ([PhS(N^tBu)₂]Li) having a phenyl group on the sulphur atom with ECl₂·(dioxane) (E = Ge, Sn) afforded the corresponding chlorogermylene [PhS(N^tBu)₂]GeCl 1 and -stannylene [PhS(N^tBu)₂]SnCl 2, respectively. In contrast, treatment of the N,N'-bis(trimethylsilyl)diimidosulfinate ion ([PhS(NSiMe₃)₂]^-) with ECl₂·(dioxane) resulted in the unexpected formations of six-membered 1,3-bis(chlorogermylene) [PhS(NSiMe₃)₂(η¹-η¹-GeCl)₂[μ-NSPh(NHSiMe₃)] 7 and -stannylene [PhS(NSiMe₃)₂(η¹-η¹-SnCl)₂[μ-NSPh(NHSiMe₃)] 8. The structures of these chlorometallylene derivatives were fully characterized on the basis of their NMR spectroscopic data and X-ray diffraction. In the crystalline states of 1 and 2, the diimidosulfinate ligands chelate to the metal centre to form slightly hinged four-membered EN₂S rings. On the other hand, X-ray analyses of 7 and 8 revealed that the central six-membered E₂N₃S rings adopt a distorted boat-conformation, and one diimidosulfinate ligand coordinates to the metal centre in a bridging monodentate μ-η¹-η¹-fashion. As the reactivity of 1 and 2, the oxidation of 1 with elemental chalcogen (S₈ or Se) afforded the corresponding tetra-coordinated germanium compounds [PhS(N^tBu)₂]Ge([double bond, length as m-dash]Ch)Cl 3 (Ch[double bond, length as m-dash]S) and 4 (Ch[double bond, length as m-dash]Se). In sharp contrast, the reactions of 2 with elemental chalcogen resulted in the formation of four-membered Sn₂Ch₂ ring compounds, 1,3,2,4-dichalcogenadistannetanes {(PhS(N^tBu)₂)SnCl(μ-Ch)}₂5 (Ch[double bond, length as m-dash]S) and 6 (Ch[double bond, length as m-dash]Se).

Interaction of an imidazolium-2-amidinate (NHC-CDI) zwitterion with zinc dichloride in dichloromethane: role as ligands and C–Cl activation promoters

Investigation of the interaction of a NHC-CDI zwitterion with ZnCl₂ in dichloromethane led to the serendipitous discovery of a highly selective, double C–Cl activation of dichloromethane.

Three new types of transition metal carboranylamidinate complexes

Three new types of transition metal carboranylamidinate complexes are reported.

Synthesis and crystal structures of two new tin bis-(carboranylamidinate) complexes

Reaction of 2 equiv. of the lithium carboranylamidinate Li[o-(C2H10B10)C(NCy)(NHCy)] with SnCl2 in THF afforded the stannylene compound bis(N,N'-dicyclohexylamidinatocarboranate)tin(II), SnII[o-(C2H10B10)C(NCy)(NHCy)]2 (1). A similar reaction of SnCl4 with 2 equiv. of Li[o-(C2H10B10)C(N i Pr)(NH i Pr)] unexpectedly afforded the known solvated penta-chlorido-stannate(IV) salt [Li(THF)4][SnCl5(THF)] as the main reaction product. Small amounts of the new chlorido-tin(IV) bis-(carboranylamidinate) bis(N,N'-diiso-propylamidinatocarboranate)chloridotin(IV), SnIVCl[o-(C2H10B10)C(N i Pr)(NH i Pr)][o-(C2H10B10)C(N i Pr)2] (2), were isolated as a by-product. Single-crystal X-ray structure analysis revealed a κC,κN-chelating coordination of the carboranylamidinate ligands in both 1 and 2. The Sn atom in 1 adopts a pseudo-trigonal-bipyramidal coordination under participation of a stereoactive lone pair. In 2, a trigonal-bipyramidal coordination of Sn is completed by a chlorido ligand.

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.