Ruthenium Complexes with N-Bound 2-Pyridonato Ligand as O-Donors: A New Synthetic Approach and the Effect on Reactivity.

In this study, Ru complexes [(η6-p-cymene)RuX(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(O))] (3: X=Cl; 4: X=I) were prepared with N-bound 2-pyridonato ligand by thermal base-free MeX elimination from ionic N,N-chelated Ru complexes [(η6-p-cymene)RuX(κ2-L1)](X) (1: X=Cl; 2: X=I; L1={2-[(2,6-iPr2-C6H3)N=CH]-6-(OMe)C5H3N}). The Ru complex 3 was used as O-donor for Lewis (LA) or Brönsted acids. The reactions of 3 with SnCl2, Ph3SnCl, ZnCl2 or HCl provided [(η6-p-cymene)Ru(SnCl3)(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(O→SnCl2)] (6), [(η6-p-cymene)RuCl(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(O→SnPh3Cl)] (7), and [(η6-p-cymene)RuCl(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(O→)]2(µ-ZnCl2) (8) and [(η6-p-cymene)RuCl(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(OH)}](Cl) (9). The easy conversion of the 2-pyridonato ligand in 3 to its 2-hydroxypyridine in 9 evoked testing of 3 and 4 as potential catalysts in base-free transfer-hydrogenation of ketones.

B-substituted group 1 phosphides: synthesis and reactivity.

1-Boryl-8-phosphinonaphthalenes 1-BCy2-8-PCl2-C10H6 (1) and 1-BCy2-8-PPhCl-C10H6 (2) were prepared and used as starting materials for the synthesis of B-substituted phosphides. The reduction of 1 and 2 by Mg provided neutral compounds [1-BCy-8-PCy-C10H6]2 (3) and [1-BCy2-8-PPh-C10H6]2 (4). Compound 3 represents the dimer of phosphinoborane 1-BCy-8-PCy-C10H6 while complex 4 is a rare example of a discrete B ← P coordinated diphosphine. The reduction of 2 by Na or K in THF yielded B-substituted group 1 phosphides [Na(THF)3]+[1-BCy2-8-PPh-C10H6]- (5) and {[K(THF)2]+[1-BCy2-8-PPh-C10H6]-}∞ (6), which structurally resembled bulky group 1 phosphides. Complex 5 showed easy activation of elemental chalcogens E (E = O, S, Se) to give B-substituted chalcogenophosphinites {[Na(THF)2]+[1-BCy2-8-P(E)Ph-C10H6]}2 (E = O (7), S (8), Se (9)) as the products of chalcogen insertion into the P-Na bond. Importantly no oxidation to dichalcogenophosphinates was observed. Compound 5 is tolerant of the CO polar bonds in organic substrates and the reactions of 5 with 2,3-butanedione or an acyl chloride provided {[Na(THF)2]+[1-BCy2-8-P{CHC(O)C(Me)O}Ph-C10H6]-}2 (10) and [1-BCy2-8-P{C(O)tBu}Ph-C10H6] (11). Finally, B-coordinated phosphatetrylenes [1-BCy2-8-P(SnL)Ph-C10H6] (12) and [1-BCy2-8-P(PbL)Ph-C10H6] (13) (L is {2,6-(Me2NCH2)C6H3}-) were also prepared by substitution reactions of 5.

Synthesis and reactivity of alkali metal aluminates bearing bis(organoamido)phosphane ligand.

In this study, we report a group of alkali metal aluminates bearing bis(organoamido)phosphane ligand. The starting complex {[PhP(NtBu)2]AlMe2}Li·OEt2 (1) was prepared by stepwise deprotonation of the parent PhP(NHtBu)2 by nBuLi and AlMe3. Further derivatization of aluminate 1 was performed by the virtual substitution of lithium -{[PhP(NtBu)2]AlMe2}K (2), methyl substituents - {[PhP(NtBu)2]AlH2}Li·THF (3), modification of steric bulk and induction effects on the phosphorus atom - {[tBuP(N-2,6-iPr2C6H3)2]AlMe2}Li·(OEt2)2 (4), and phosphorus atom oxidation state {[Ph(Y)P(NtBu)2]AlMe2}Li (Y = O (5), S (6), Se (7), Te (8)). The structure causing non-covalent interactions in 1-4 were evaluated with the help of theoretical calculations and topological analysis ranging from π-electron system-metal to agostic interactions of various types. The further reactions of 1 with various nucleophiles were found to be a versatile tool for the preparation of iminophosphonamides via the formation of P-E bond (E = Si, Ge, Sn, Pb, P, and C) and followed by P(III) → P(V) tautomeric shift.

Tin(II) cations stabilized by non-symmetric N,N',O-chelating ligands: synthesis and stability.

A series of novel non-symmetric neutral N,N',O-chelating ligands derived from the α-iminopyridine 2-(C(R1)N(C6H3-2,6-iPr2))-6-(R2R3PO)C5H3N (L1: R1 = H, R2 = R3 = Ph; L2: R1 = Me, R2 = R3 = Ph; L3: R1 = H; R2 = Ph, R3 = EtO; L4: R1 = Me, R2 = Ph, R3 = EtO; L5: R1 = H, R2 = R3 = iPrO; L6: R1 = Me, R2 = R3 = iPrO) were synthesized. Ligands L1-6 were reacted with SnCl2 and Sn(OTf)2 with the aim of studying the influence of different R2R3PO functional groups on the Lewis base mediated ionization of SnCl2 and Sn(OTf)2. While all ligands L1-6 provided the corresponding ionic tin(II) complexes [L1-6 → SnCl]+[SnCl3]- (1-6), only ligands L1, L4 and L6 were able to stabilize tin(II) dications [L1,4,6 → Sn(H2O)][OTf]2 (7-9). The auto-ionized compounds [L3-6 → SnCl]+[SnCl3]- possessing ethylphenyl phosphinate and diisopropylphosphite substituents undergo elimination of EtCl and iPrCl, respectively, yielding compounds 10-13. These can either be interpreted as neutral tin(II)phosphinate chloride (10, 11) and tin(II)phosphonate chloride (12, 13), respectively, containing Sn-O and Sn-Cl bonds, and a PO → SnCl2 interaction, or as zwitterionic compounds, where the positive charge of the central tin atom is compensated by an [OSnCl2]- anion. Finally, DFT studies were performed to better understand the steric and electronic properties of the ligands L1-6 as well as the nature of the bonds in the resulting products, with a particular focus on complexes 10-13.

Lithium, Magnesium, and Zinc Centers N,N'-Chelated by an Amine-Amide Hybrid Ligand.

The synthesis and structure of lithium, magnesium, and zinc complexes N,N'-chelated by a hybrid amine-amido ligand ([2-(Me2NCH2)C6H4NR]-, abbreviated as LNR, where R = H, SiMe3, or Bn) are reported. The reaction of the least sterically demanding LNH with various magnesium sources gives the hexameric imide [LNMg]6 (4) by the elimination of n-butane from LNHMgnBu (2) or by the reaction of LNHLi (1) with MeMgBr. [LNH]2Mg (3) is obtained through the addition of 0.5 equiv of nBu2Mg or Mg[N(SiMe3)2]2 to LNH2 and with 1 equiv of nBu2Mg reacting to 2. Both LNHMgN(SiMe3)2 (6) and isostructural LNHZnN(SiMe3)2 (16) have been prepared using two different approaches: monodeprotonation of LNH2 by Zn/Mg[N(SiMe3)2]2 in a 1:1 ratio or ligand substitution of 2 or LNHZnEt (12) by 0.5 equiv of Sn[N(SiMe3)2]2. The reactions of 2 or 3 with 1 provide the heterotrimetallic complex [LNH]4Li2Mg (5). Benzyl- or trimethylsilyl-substituted anilines [LN(SiMe3)H (7) and LN(Bn)H (8)] with 0.5 equiv of nBu2Mg allow the formation of homoleptic bis(amides) of the [LN(R)]2Mg type (10 and 11). Nevertheless, only the silylated secondary amine 7 is able to provide the heteroleptic n-butylmagnesium amide LN(SiMe3)MgnBu (9) upon reaction with an equimolar amount of nBu2Mg. Similarly, 12, [LNH]2Zn (13), LN(R)ZnEt (17 and 18), and [LN(R)]2Zn [R = SiMe3 (19) and Bn (20)] were prepared by the monodeprotonation of LNH2 or LN(R)H using Et2Zn in the corresponding stoichiometric ratio. LNHZnI was prepared by the nucleophilic substitution of an ethyl chain in 12 by molecular iodine. A heterometallic complex, [LNH]4Li2Zn (14), analogous to 5 was prepared from 12 or 13 with 1 or 2 equiv of 1, respectively.

Structurally rigidified cobalt bis(dicarbollide) derivatives, a chiral platform for labelling of biomolecules and new materials.

We report the difunctional modification of an anionic cobalta bis(dicarbollide)(1-) cluster with a B(8,8')-oxygen bridging unit that provides structural rigidity and an organic alkylazide substituent(s) on the carbon atoms of the metallacarborane cage. These ions present a good binding motif for incorporation into organic molecules using Huisgen-Sharpless (2+3) cycloaddition reactions. In addition, the compounds are chiral, as verified by separation of enantiomers using HPLC on chiral stationary phases (CSPs) and provide a high electrochemical peak in the window located outside of typical signals of biomolecules.

Reversible addition of tin(II) amides to nitriles.

Lappert's stannylene (Sn[N(SiMe3)2]2) has been reacted with various nitriles, dinitriles and trinitriles with the formation of heteroleptic amidotin(II) amidinates of the general formulae [RC(NSiMe3)2]SnN(SiMe3)2, R'{[C(NSiMe3)2]SnN(SiMe3)2}2 and R''{[C(NSiMe3)2]SnN(SiMe3)2}3, where R = Ph (1), 2-(CN)-C6H4 (2), 3-(CN)-C6H4 (3); R' = 1,3-C6H4 (4), 1,4-C6H4 (5) and R'' = 1,3,5-C6H3 (6). The reactions of amidotin(II) benzamidinate 1 with an excess of benzonitrile proceed to homoleptic tin(II) bis(benzamidinate) [PhC(NSiMe3)2]2Sn, which reversibly eliminates benzonitrile and 1 when warmed. The premise of reversibility has been supported by a multinuclear time-dependent NMR study and a theoretical (DFT) description. On the other hand, magnesium(II) bis(benzamidinate) [PhC(NSiMe3)2]2Mg (8) and lanthanum(II) tris(benzamidinate) [PhC(NSiMe3)2]3La (7) have been synthesised from appropriate metal hexamethyldisilazides and benzonitrile.

Synthesis and optical properties of N→Ga coordinated gallium boroxines.

Reactions of the N,C,N-chelated organogallium amide LGa(NEt2)2 (1), where L is {2,6-(Me2NCH2)2C6H3}-, with organoboronic acids RB(OH)2 yielded molecular gallium boroxines LGa(O3B2R2) (2: R = OH, 3: R = Ph, 4: R = 4-MeO-C6H4, 5: R = 4-CHO-C6H4, 6: R = Fc), neutral analogues of gallaborates. The molecular structures revealed the presence of a six-membered central GaB2O3 ring. The film forming properties of 5 allowed the deposition of transparent thin films by a spin coating method. The thicknesses, refractive index, energy of the optical gap (Eoptg), activation energy of surface electrical conductivity (Esa) and pre-exponential factor (σ0) of the thin layers of 5 were measured and they are close to those found for related oxygen glass. Finally, GBO 5 was also used as an additive to printing ink and a thin film of 5 was prepared by the gravure printing technique.

N-Donor stabilized tin(II) cations as efficient ROP catalysts for the synthesis of linear and star-shaped PLAs via the activated monomer mechanism.

α-Iminopyridine ligands L1 (2-(CHN(C6H2-2,4,6-Ph3))C5H4N), L2 (2-(CHN(C6H2-2,4,6-tBu3))C5H4N) and L3 (1,2-(C5H4N-2-CHN)2CH2CH2) differing by the steric demand of the substituent on the imine CHN group and by the number of donating nitrogen atoms were utilized to initiate a Lewis base mediated ionization of SnCl2 in an effort to prepare ionic tin(II) species [L1-3 → SnCl][SnCl3]. The reaction of L1 and L2 with SnCl2 led to the formation of neutral adducts [L1 → SnCl2] (2) and [L2 → SnCl2] (3). The preparation of the desired ionic compounds was achieved by subsequent reactions of 2 and 3 with an equivalent of SnCl2 or GaCl3. In contrast, ligand L3 containing four donor nitrogen atoms showed the ability to ionize SnCl2 and also Sn(OTf)2, yielding [L3 → SnCl][SnCl3] (7) and [L3 → Sn(H2O)][OTf]2 (8). The study thus revealed that the reaction is dependent on the type of the ligand. The prepared complexes 4-8 together with the previously reported [{2-((CH3)CN(C6H3-2,6-iPr2))-6-CH3O-C5H3N}SnCl][SnCl3] (1) were tested as catalysts for the ROP of L-lactide, which could operate via an activated monomer mechanism. Finally, a DFT computational study was performed to evaluate the steric and electronic properties of the ionic tin(II) species 1 and 4-8 together with their ability to interact with the L-lactide monomer.

Access to cationic polyhedral carboranes via dynamic cage surgery with N-heterocyclic carbenes.

Polyhedral boranes and heteroboranes appear almost exclusively as neutral or anionic species, while the cationic ones are protonated at exoskeletal heteroatoms or they are instable. Here we report the reactivity of 10-vertex closo-dicarbadecaboranes with one or two equivalents of N-heterocyclic carbene to 10-vertex nido mono- and/or bis-carbene adducts, respectively. These complexes easily undergo a reaction with HCl to give cages of stable and water soluble 10-vertex nido-type cations with protonation in the form of a BHB bridge or 10-vertex closo-type cations containing one carbene ligand when originating from closo-1,10-dicarbadecaborane. The reaction of a 10-vertex nido mono-carbene adduct with phosphorus trichloride gives nido-11-vertex 2-phospha-7,8-dicarbaundecaborane, which undergoes an oxidation of the phosphorus atom to P = O, while the product of a bis-carbene adduct reaction is best described as a distorted C2B6H8 fragment bridged by the (BH)2PCl2+ moiety.

Thiaborane Icosahedral Barrier Increased by the Functionalization of all Terminal Hydrogens in closo-1-SB11H11.

The electrophilic substitution of icosahedral closo-1-SB11H11 with methyl iodide has resulted in two B-functionalized thiaboranes, 7,12-I2-2,3,4,5,6,8,9,10,11-(CH3)9-1-closo-SB11 and 7,8,12-I3-2,3,4,5,6,9,10,11-(CH3)8-closo-1-SB11, with the former being significantly predominant. These two icosahedral thiaboranes are the first cases of polysubstituted polyhedral boron clusters with another vertex that differs from B and C. Such polyfunctionalizations have increased the earlier observed thiaborane icosahedral barrier, not exhibiting any reactivity toward bases, unlike the parent thiaborane. The search for methylation pathways has revealed that the complete B11-methylation is impossible, like in the case of decaborane(14), where this seems to be a result of the positively charged upper parts of these two molecules.

Oxidative addition of cyanogen bromide to C,N-chelated and Lappert's stannylenes.

Stannylenes of L2Sn type bearing either C,N-chelating (1, L = LCN = 2-(N,N-dimethylaminomethyl)phenyl) or bulky amido (2, L = LN = N(SiMe3)2) ligands react with cyanogen bromide (Br-C[triple bond, length as m-dash]N) via an oxidative-addition reaction to give monomeric six-coordinate (LCN)2Sn(Br)CN (1a) and four-coordinate (LN)2Sn(Br)CN (2a) stannanes in moderate yields. In solution, both 1a and 2a undergo instantaneous bromido-cyanido ligand redistribution reactions, leading to mixtures containing 1a, (LCN)2SnBr2 (1b) and (LCN)2Sn(CN)2 (1c) or 2a, (LN)2SnBr2 (2b) and (LN)2Sn(CN)2 (2c), respectively. The prepared species were characterised by multinuclear NMR spectroscopy in solution (1a-c and 2a-c) and in the solid state (1a-c). The crystal structures of 1a/b/c, 2a/b/c and sole 2b were determined by XRD analyses. DFT calculations and QTAIM analysis were also carried out to corroborate the experimental results.

Transformation of various multicenter bondings within bicapped-square antiprismatic motifs: Z-rearrangement.

Reported herein are mutual rearrangements in the whole series of seven bicapped-square antiprismatic closo-C2B8H10 by means of high-quality computations that disprove the earlier postulated dsd (diamond-square-diamond) scheme for these isomerizations. The experimentally existing closo-1,2-C2B8H10 was able to be converted to 1,6-, and 1,10-isomers by pyrolysis, and the dsd (diamond-square-diamond) mechanism was offered as an explanation of these processes. However, these computations disprove the postulated dsd scheme for these isomerizations that take place in the ten-vertex closo series. Experimentally observed thermal rearrangements, both in the parent and substituted closo-1,2-C2B8H10, closo-1-CB9H10-, and closo-B10H102-, indirectly support these refined computations. All these processes are based on the new concept of the so-called Z-mechanism, being consistent with a transition state of a boat shape with an open hexagonal belt that results from the initial breakage of three bonds. Such bond breakings and the consequent bond formations bring to mind the shape of the letter Z. In effect, the pattern of multicenter bonding shifts from reactant through a transition state to product. The molecular rearrangements that are available experimentally favour either the axial or equatorial isomers, and this ratio depends on temperature and the type of cluster and its substitution.

Cobalt Bis(dicarbollide) Alkylsulfonamides: Potent and Highly Selective Inhibitors of Tumor Specific Carbonic Anhydrase IX.

Invited for this month's cover is a collaboration from three institutes from the Czech Academy of Sciences: Institute of Inorganic Chemistry, Institute of Organic Chemistry and Biochemistry, and Institute of Molecular Genetics, and the University of Pardubice. The cover picture shows a family of potent and selective CA IX inhibitors that combines the structural motif of a bulky inorganic cobalt bis(dicarbollide) polyhedral ion with a propylsulfonamido anchor group. Read the full text of the article at 10.1002/cplu.202000574.

Cobalt Bis(dicarbollide) Alkylsulfonamides: Potent and Highly Selective Inhibitors of Tumor Specific Carbonic Anhydrase IX.

Carbonic anhydrase IX (CAIX) is an enzyme expressed on the surface of cells in hypoxic tumors. It plays a role in regulation of tumor pH and promotes thus tumor cell survival and occurrence of metastases. Here, derivatives of the cobalt bis(dicarbollide)(1-) anion are reported that are based on substitution at the carbon sites of the polyhedra by two alkylsulfonamide groups differing in the length of the aliphatic connector (from C1 to C4, n=1-4), which were prepared by cobalt insertion into the 7-sulfonamidoalkyl-7,8-dicarba-nido-undecaborate ions. Pure meso- and rac-diastereoisomeric forms were isolated. The series is complemented with monosubstituted species (n=2). Synthesis by a direct method furnished similar derivatives (n=2, 3), which are chlorinated at the B(8,8') boron sites. All compounds inhibited CAIX with subnanomolar inhibition constants and showed high selectivity for CAIX. The best inhibitory properties were observed for the compound with n= 3 and two substituents present in rac-arrangement with Ki =20 pM and a selectivity index of 668. X-ray crystallography was used to study interactions of these compounds with the active site of CAIX on the structural level.

Ferrocene donor linked to pyridine/pyridinium acceptor via a systematically enlarged π-linker.

Nine chromophores with ferrocene donor and pyridine/pyridinium acceptors have been prepared and further investigated. The performed X-ray analysis showed partially polarized and geometrically oblate pyridine unit. An extension of the π-system and N-quaternization were revealed as suitable tools for exclusive manipulation of the LUMO with the almost steady HOMO. Whereas the electrochemical HOMO-LUMO gap can be tuned from 3.01 to 1.49 eV, the high- and low-energy absorption bands were found within the range of 280-402/456-547 nm. The pyridinium chromophores showed distinct negative solvatochromism. A thorough DFT analysis has been performed; it turned out that ferrocene donor is capable of two principal D-A interactions, whose employment depends on the appended electron-withdrawing moiety.

Tetrazole Ring Substitution at Carbon and Boron Sites of the Cobalt Bis(dicarbollide) Ion Available via Dipolar Cycloadditions.

Herein, we describe the synthesis of two families of compounds accessible from [3 + 2] cycloaddition reactions of known B8-substituted isonitrilium and new C1-alkylnitrile and C(1,1')-dialkylnitrile derivatives of the [(1,2-C2B9H11)2-3,3'-Co(III)]- ion with an azide ion that produce a tetrazole ring substitution at the cobaltacarborane cage. In addition, we outline the important differences in reactivity observed for the two types [B-isonitrilium/C-(alkyl)nitrile] of cobaltacarborane derivatives. The first family of compounds described corresponds to C5-atom-boronated tetrazole rings, with the five-membered moiety in the second type being doubly substituted at the N1 and C5 positions. This substitution opens cobaltacarborane chemistry to a new type of functional group at the cage of potential utility as structural blocks for use in medicinal chemistry or materials science. Our study includes single-crystal X-ray structures of the starting nitriles and both families of tetrazole derivatives, and the structural features that arise from the substitutions are discussed.

Direct Introduction of an Alkylsulfonamido Group on C-sites of Isomeric Dicarba-closo-dodecaboranes: The Influence of Stereochemistry on Inhibitory Activity against the Cancer-Associated Carbonic Anhydrase IX Isoenzyme.

Carbonic anhydrase IX (CA IX), a tumor-associated metalloenzyme, represents a validated target for cancer therapy and diagnostics. Herein, we report the inhibition properties of isomeric families of sulfonamidopropyl-dicarba-closo-dodecaboranes group(s) prepared using a new direct five-step synthesis from the corresponding parent cages. The protocol offers a reliable solution for synthesis of singly and doubly substituted dicarba-closo-dodecaboranes with a different geometric position of carbon atoms. The closo-compounds from the ortho- and meta-series were then degraded to corresponding 11-vertex dicarba-nido-undecaborate(1-) anions. All compounds show in vitro enzymatic activity against CA IX in the low nanomolar or subnanomolar range. This is accompanied by clear isomer dependence of the inhibition constant (Ki ) and selectivity towards CA IX. Decreasing trends in Ki and selectivity index (SI ) values are observed with increasing separation of the cage carbon atoms. Interactions of compounds with the active sites of CA IX were explored with X-ray crystallography, and eight high-resolution crystal structures uncovered the structural basis of inhibition potency and selectivity.

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.

Electrophilic Methylation of Decaborane(14): Selective Synthesis of Tetramethylated and Heptamethylated Decaboranes and Their Conjugated Bases.

The paper reports specific syntheses of methylated decaborane(14), nido-B10H14 (1), derivatives. The reaction of 1 with an excess of neat MeI and AlCl3 yields 1,2,3,4-Me4-nido-B10H10 (2) essentially quantitatively when performed at room temperature. Heating the same mixture to 120 °C provides 1-I-2,3,4,5,7,8,10-Me7-nido-B10H6 (3a). The formation of analogous 1-CF3SO2O-2,3,4,5,7,8,10-Me7-nido-B10H6 (3b) is achieved by heating 1 or 2 with an excess of MeSO3CF3 in the presence of a catalytic amount of HOSO2CF3 to 120 °C. Compounds 2 and 3 can be deprotonated to yield the corresponding anions [1,2,3,4-Me4-nido-B10H9]- (2-), [1-I-2,3,4,5,7,8,10-Me7-nido-B10H5]- (3a-), and [1-CF3SO2O-2,3,4,5,7,8,10-Me7-nido-B10H5]- (3b-). The structure of all the compounds isolated has been unambiguously confirmed by multinuclear (11B and 1H) NMR measurements, and the structures of 2-, 3a, 3a-, and 3b have been established by X-ray diffraction analyses. The very high volatility of 2 has made it impossible to apply X-ray diffraction in this case; therefore, its structure has been derived computationally using the ab initio/GIAO/NMR tool. DFT-based computational protocols have also outlined the reason why it is impossible to obtain an octamethyl derivative of 1 experimentally.