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The synthesis and structure of lithium, magnesium, and zinc complexes

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.

Amidotin(ii) benzamidinates were prepared via addition of Sn[N(SiMe3)2]2 to mono-, di- and trinitriles. A reversible addition of [PhC(NSiMe3)2]SnN(SiMe3)2 with an excess of benzonitrile to its homoleptic [PhC(NSiMe3)2]2Sn was studied by NMR and DFT.

Direct synthesis of magnesium amidinates of the general formula [RNC(R1)NR]MgR2 has been performed from appropriate carbodimide and Grignard reagents (R = iPr, Cy, pTol; R1 = Me, nBu; R2 = nBu, Cl, I). Magnesium bisamidinates of the composition [RNC(R1)NR]2Mg(solvent)2 are accessible from [RNC(R1)NR]MgR2 and via the Schlenk-like equilibrium in coordinating solvents. The only isolated amidinatomagnesium halide, preserved in the dinuclear form of {[pTolNC(Me)N-pTol]Mg(THF)}2-μ-(THF)-μ-(Cl)2, has been obtained from the reaction of pTol-N[double bond, length as m-dash]C[double bond, length as m-dash]N-pTol with MeMgCl(THF)n in hexane. The reaction of pTol-N[double bond, length as m-dash]C[double bond, length as m-dash]N-pTol with two equivalents of MeMgI gives an unprecedented dinuclear cyclic adduct {μ-[pTolNC(Me)N-pTol][MgI(OEt2)]2-μ-Me}. The structures of these complexes have been investigated by NMR spectroscopy, sc-XRD and theoretical methods. Selected complexes have been tested as initiators of ring-opening polymerization reactions with various substrates, the copolymerization of oxiranes and CO2 as well as the esterification of lactides.

Complexes of main group metals containing amidinate and guanidinate ligands with an additional functional/donor group are reviewed. Amino-, imino-, amido-, alkoxy-, phenoxy-, carboranyl- and carbene-amidinates along with metal amidinates and a heterocyclic moiety, guanidinates(1−) containing an amino group and a doubly deprotonated guanidinates reveal various structures and ligand coordination modes such as monodentate–anisobidentate–isobidentate–tridentate. The survey of chemical shifts of the central carbon atoms in 13 C NMR spectra is provided. Some of those complexes are especially applicable in ring opening polymerization of cyclic esters, lactones and polymerization of olefins.

Reactivity of trimethylaluminium, dimethylaluminium chloride and methylaluminium dichloride with N,N′-diisopropyl-, N,N′-dicyclohexyl- or N,N′-bis(diisopropylphenyl) carbodiimide (Dipp-N C N-Dipp) via the nucleophilic addition mechanism was studied. Six aluminium(III) complexes containing amidinato ligands were prepared and isolated. All reactions as well as the purity and structural confirmation of products were monitored using 1H and 13C NMR techniques. Reactions of prepared [Dipp-N-C(Me)–N-Dipp]AlMeCl with potassium mirror or pivalonitrile were also investigated. Molecular structures of five aluminium(III) mono- or bisamidinates and two dinuclear oxo-aluminium(III) amidinato by-products displaying four- or five-coordinated aluminium atom were determined by X-ray diffraction techniques.

Series of bisamidinato and bisguanidinato tin(IV) diolates prepared from 1,2-diones (3,5-di-tert-butyl-o-benzoquinone, 3,4,5,6-tetrachloro-1,2-benzoquinone, 9,10-phenanthrenedione, acenaphthenequinone, 1,2-diphenylethanedione) and {Cy-NC(n-Bu)N-Cy}2Sn or {pTol-NC[N(SiMe3)2]N-pTol}2Sn, respectively, were used as efficient initiators for ring-opening polymerization of e-caprolactone. Moderate to good efficiency of selected compounds in trimethylene carbonate polymerization was also observed.

A series of tin(IV) guanidinates were prepared by a (4+1) oxidative cycloaddition of four 1,2-diones (3,5-di-tert-butyl-o-benzoquinone, 3,4,5,6-tetrachloro-1,2-benzoquinone, 9,10-phenanthrenedione, 1,2-diphenylethanedione) or by an oxidative addition of a C–Br bond (from 2-bromo-1,3-diphenylpropane-1,3-dione followed by rearrangement) and a Cl–Cl bond (Cl2 generated from (dichloro-λ3-iodanyl)benzene) with {pTol-NC[N(SiMe3)2]N-pTol}2Sn (1). The reactivity of five pentane-1,3-diones and dimethyl malonate with compound 1 was assessed on the basis of the effect of 1,3-diones on the reaction mechanism in comparison with 1,2-diones. In contrast with oxidation reactions observed for compounds containing conjugated C═O bonds, the reactions of the tin(II) guanidinate with 1,3-diones revealed a high ability for ligand substitution. All the tin compounds prepared were characterized, and ligand substitution reactions were monitored using 1H, 13C, and 119Sn NMR spectroscopy. The molecular structures of one tin(II) and five tin(IV) guanidinato complexes investigated were determined by X-ray diffraction. All tin(IV) compounds display six- or seven-coordination. The UV–vis absorption spectra were recorded and simulated by TDDFT methods in order to get insight into the origin of the nontypical colors of the target tin(IV) diolato-guanidinates and their keto-functionalized precursors.

Lithium amidinate complexes bearing different peripheral substituents on both nitrogen atoms (iPr and Dipp (2,6-di(isopropyl)phenyl-) and pendant, potentially coordinating group originated from the 2-(N,N-dimethylaminomethyl)phenyl moiety, at the central carbon atom were prepared by addition of the 2-(N,N-dimethylaminomethyl)phenyllithium to the appropriate carbodiimides. The structure of the isopropyl group substituted lithium amidinates is dimeric with bidentate amidinate unit and four-coordinated lithium atom. On contrary the Dipp group substituted lithium amidinate is monomeric with trigonal planar geometry of the lithium atom, monodentately bound amidinate unit and coordinated pendant arm.

Lithium n-butyl amidinates (formally lithium salts of N',N-disubstituted amidoimides of pentanoic acid) with various substituents were prepared and characterized in solution by 1H, 7Li, 13C and 15N NMR spectra parameters in C6D6, THF-d8 and Et2O-d10. The characteristic spectral parameters were compared with parent carbodiimides and amidines prepared by hydrolysis, where large solvent effects were described. Five of studied compounds were studied by X-ray diffraction techniques in the solid state. Lithium n-butyl amidinates containing less bulky substituents like isopropyl or cyclohexyl crystallize with Et2O or THF as centrosymmetric dimers with mutually parallel amidinate moieties. The lithium N,N'-bis[2,6-di(propan-2-yl)phenyl]n-butylamidinate crystallizes from Et2O solution as an asymmetric dimer. The first unit is composed by one ligand coordinated to one of lithium atoms. The lithium atom is also coordinated by one of the nitrogen atoms of the second ligand. The second nitrogen atom of the same ligand is coordinated to the second lithium atom which is also connected to the Et2O molecule and the aromatic ring of the ligand in a η3-fashion. The same compound crystallizes from the THF solution as a monomeric bis-tetrahydrofuranate.

Two ethylene-bridged methylaluminium amidinates and one aluminium amidinate containing three terminal trimethylstannyl-ethynyl groups interconnected by π-coordinated potassium ions were prepared in situ. The re-oxidation of the ethylene-bridged compound by iodine followed by further reduction using the same activation procedure demonstrated the versatility of the approach. The reactivity of an ethylene-bridged methylaluminum amidinate towards HCl was examined to demonstrate the building block concept. DFT calculations were performed to gain insight into the mechanism of the in situ activation of diphenylacetylene.

Seven tin(IV) amidinates were prepared and isolated from the reactions of tin(II) bisamidinate [Cy–NC(nBu)N–Cy]2Sn with a series of various 1,2-diones ((4 + 1) oxidative cycloaddition mechanism) and chlorine/oxygen molecules, respectively. The ligand substitution effect of (non)symmetric 1,3-diones to starting stannylene as well as intermolecular CO2 activation via prepared dimeric stannoxane is also reported. All the prepared tin containing compounds as well as ligand substitution reactions were investigated by the multinuclear NMR (1H, 13C, and 119Sn) spectroscopic techniques. Molecular structures of one tin(II) and seven tin(IV) amidinates investigated were determined by X-ray diffractions and also evaluated by DFT methods. The UV–vis absorption spectra of all desired colored tin(IV) diolates and its diketo precursors were recorded and simulated by TD-DFT methods.

Reactions of bis[bis(trimethylsilyl)amino]tin and the dimer of [bis(trimethylsilyl)amino]tin chloride with various carbodiimides give pure corresponding tin(II) guanidinates in essentially quantitative yields. Heteroleptic bis(trimethylsilyl)amido ({R-NC[N(SiMe3)2]N-R}SnN(SiMe3)2)- and chloro-substituted ({R-NC[N(SiMe3)2]N-R}SnCl) tin(II) guanidinates were obtained from reactions of N,N′-diisopropyl-, N,N′-dicyclohexyl-, N,N′-bis(4-methylphenyl)-, and N-[3-(dimethylamino)propyl]-N′-ethylcarbodiimides, respectively. Homoleptic tin(II) guanidinates {R-NC[N(SiMe3)2]N-R}2Sn were obtained from the N,N′-bis(4-methylphenyl)- and N-[3-(dimethylamino)propyl]-N′-ethyl-substituted carbodiimides. Similar reactions of N,N′-bis(2,6-diisopropylphenyl)- and N,N′-bis(trimethylsilyl)carbodiimide, respectively, having the bulkiest substituents of the series, failed to take place under various conditions. The complexes prepared were characterized as monomers in solution by 1H, 13C, and 119Sn NMR spectroscopy in C6D6 and THF-...

The structure of the title compound, C9H6I2N2, contains two symmetry-independent molecules. The interplanar angles between the imidazole and phenyl ring planes are 16.35 (3) and 17.48 (6)°. Molecules are connected via N—H...N hydrogen bonds to form zigzag chains along the b axis. The title compound is the first example of a structurally characterized 4,5-diiodoimidazole with an organic substituent in the 2-position and without protection on the N—H group of imidazole.

The new class of homo- and heteroleptic n-butyl-N,N'-disubstituted amidinato group 14 metal(II) complexes were prepared by salt elimination from starting lithium amidinates and metal(II) chlorides both in stoichiometric ratio 2:1 and 1:1, respectively. The target amidinates contain less bulky isopropyl or cyclohexyl as well as a sterically demanding aromatic substituent. Desired 1:1 Pb(II) complexes are not accessible by the described procedure. Ligand transfer from Pb to Sn is taking place if homoleptic Pb(II) compounds are reacted with SnCl(2). Prepared tetrylenes were characterized by (1)H, (13)C, (119)Sn and (207)Pb NMR spectroscopy in C(6)D(6) or THF-d(8). X-Ray diffraction studies of one heteroleptic Ge(II) monomeric where the coordination polyhedron of the three coordinated germanium atoms is a trigonal pyramid, two different dimeric structures of heteroleptic Sn(II) complexes, one amidine hydroiodide byproduct and the oxidation product of the heteroleptic chloro Sn(II) amidinate as a tetranuclear species with two Sn(IV) and two Sn(II) atoms in central Sn(2)O(2) planar ring were performed on appropriate single crystals. The dimer of one of the heteroleptic stannylenes reveals a new type of monomeric units connection, weak Sn-Cl contact and an interaction of the tin atom with delocalized N-C(C)-N system of the amidinato ligand of the second molecule.