Chemistry of boryllithium: synthesis, structure, and reactivity

A series of lithium salts of boryl anion, boryllithiums, were synthesized and characterized by NMR spectroscopy and crystallographic analysis. In addition to the parent boryllithium compound 35a, structural modification of boryllithium, using saturated C-C and benzannulated C=C backbones in the five-membered ring and mesityl groups on the nitrogen atoms, also allowed generation of the corresponding boryllithium. The solid state structures of boryllithium showed that the boron-lithium bond is polarized where the boron atom is anionic in all (35a x DME)(2), 35a x (THF)(2), 35b x (THF)(2), and 35c x (THF)(2) when compared to the structures of hydroborane 38a-c and optimized free boryl anion opt-46a-c. Dissolution of the isolated single crystals of (35a x DME)(2) and 35a x (THF)(2) in THF-d(8) showed that the boron-lithium bond remained in solution and free DME or THF molecules were observed. Temperature-dependent (11)B NMR chemical shift changes of 35a were observed in THF-d(8) or methylcyclohexane-d(14), suggesting a change of chemical shift anisotropy around the boron center. The HOMO of opt-35a x (THF)(2) had a lone pair character on the boron atom, as observed for phenyllithium, whereas the HOMO of hydroborane 38a corresponds to the pi-orbital of the boron-containing five-membered heterocycle. The polarity of the B-Li bond, estimated by AIM analysis, was similar to that of alkyllithium. Boryllithiums 35a and 35b behave as a base or a boron nucleophile in reaction with organic electrophiles via deprotonation, S(N)2-type substitution, halogen-metal exchange or electron-transfer, 1,2-addition to a carbonyl group, and S(N)Ar reaction. In the case of the reaction with CO(2), intramolecular cyclization followed by CO elimination from borylcarboxylate anion and subsequent protonation gave hydroxyboranes 64a and 64b. The characters of the carbonyl groups in the borylcarbonyl compounds 60a, 60b, 61, 62, and 63a, which were obtained from the reaction of boryllithiums 35a and 35b, were investigated by X-ray crystallography, IR, and (13)C NMR spectroscopy to show that the boryl substituent weakened the C=O bond when compared to carbon substituted analogues.     

Chemistry of sulfones: synthesis of a new chiral nucleophilic catalyst

A chiral pyrrolidinopyridine was synthesized by using Buchwald methodology. The sulfone was used to add a benzyl group, which positioned a phenyl near the reacting position.     

A base-free thorium-terminal-imido metallocene: synthesis, structure, and reactivity

The synthesis, structure, and reactivity of a base-free thorium terminal-imido metallocene have been comprehensively studied. Treatment of thorium metallocenes [{η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)}(2)ThMe(2)] and [{η(5)-1,3-(Me(3)C)(2)C(5)H(3)}(2)ThMe(2)] with RNH(2) gives diamides [{η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)}(2)Th(NHR)(2)] (R=Me (7), p-tolyl (8)) and [{η(5)-1,3-(Me(3)C)(2)C(5)H(3)}(2)Th(NH-p-tolyl)(2)] (9), respectively. Diamides 7 and 9 do not eliminate methylamine or p-toluidine, but sublime without decomposition at 150 °C under vacuum (0.01 mmHg), whereas diamide 8 is converted at 140 °C/0.01 mmHg into the primary amine p-tolyl-NH(2) and [{η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)}(2)Th=N(p-tolyl)] (10), which may be isolated in pure form. Imido metallocene 10 does not react with electrophiles such as alkylsilyl halides; however, it reacts with electron-rich or unsaturated reagents. For example, reaction of 10 with sulfur affords the metallacycle [{η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)}(2)Th{N(p-tolyl)S-S}]. Imido 10 is an important intermediate in the catalytic hydroamination of internal alkynes, and an efficient catalyst for the trimerization of PhCN. Density functional theory (DFT) studies provide a detailed understanding of the experimentally observed reactivity patterns.     

A bipyridyl thorium metallocene: synthesis, structure and reactivity

The synthesis, structure and reactivity of a new bipy thorium metallocene have been studied. The reduction of the thorium chloride metallocene [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)ThCl(2) (1) with potassium graphite in the presence of 2,2'-bipyridine gives the purple bipy metallocene [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th(bipy) (2) in good yield. Complex 2 has been fully characterized by various spectroscopic techniques, elemental analysis and X-ray diffraction analysis. Complex 2 reacts cleanly with trityl chloride, silver halides and diphenyl diselenide, leading to the halide metallocenes [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)ThX(2) (X = Cl (1), Br (3), I (4)) and [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th(F)(μ-F)(3)Th[η(5)-1,3-(Me(3)C)(2)C(5)H(3)](F)(bipy) (5), and selenido metallocene [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th(SePh)(2) (6), in good conversions. In addition, 2 cleaves the C[double bond, length as m-dash]S bond of CS(2) to give the sulfido complex, [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)ThS (7), which further undergoes an irreversible dimerization or nucleophilic addition with CS(2), leading to the dimeric sulfido complex {[η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th}(μ-S)(2) (8) and dimeric trithiocarbonate complex {[η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th}(μ-CS(3))(2) (10) in good yields, respectively.     

1,2-BN cyclohexane: synthesis, structure, dynamics, and reactivity

BN/CC isosterism has emerged as a viable strategy to increase the structural diversity of carbon-based compounds. We present the first synthesis and characterization of the parent 1,2-BN cyclohexane, the BN-isostere of cyclohexane. 1,2-BN cyclohexane is an air- and water-stable compound that cleanly forms a trimer with release of dihydrogen when thermally activated. We also demonstrate that 1,2-BN cyclohexane has a lower activation barrier for ring inversion than cyclohexane due to BN/CC isosterism.     

Phosphido pincer complexes of platinum: synthesis, structure and reactivity

A series of platinum(II) complexes supported by the tridentate bis(phosphine)phosphido ligand bis(2-diisopropylphosphinophenyl)phosphide) [(i)Pr-PPP] have been synthesized and characterized (1-4). X-Ray structural studies of [(i)Pr-PPP]PtCl (1) and [(i)Pr-PPP]PtCH(3) (3) complexes show meridional [(i)Pr-PPP] ligands around approximately square-planar platinum centers. Structural data and NMR analysis highlight a strong trans influence for the phosphido phosphorous donor, comparable to that of the anionic aryl carbon of the classic PCP pincer complexes. A series of thermally stable [PPP]Pt(IV) compounds, including [PPP]Pt(CH(3))(2)X [X = I (5) and SbF(6) (6)], were also synthesized. The study of the binding affinity of SO(2) and NO to complex 1 has also been addressed.     

A well-defined hydrocarbon-soluble calcium hydroxide: synthesis, structure, and reactivity

Controlled hydrolysis of a (beta-diketiminate)calcium-amide gave a heteroleptic (beta-diketiminate)calcium-hydroxide complex that is remarkably stable against ligand exchange and formation of Ca(OH)2. The structure of this dimeric complex shows OH- units that symmetrically bridge the Ca2+ ions. This hydrocarbon-soluble calcium hydroxide reacted rapidly with CO2 to produce a gel from which amorphous CaCO3 slowly separated. This reaction behavior allows for sol-gel coating with CaCO3 from an organic solvent. Reaction with benzophenone did not lead to nucleophilic attack of OH- to the carbonyl but gave a red benzophenone adduct instead.     

An unprecedented lanthanide phosphinidene halide: synthesis, structure and reactivity

The synthesis and structural characterization of an unprecedented lanthanide phosphinidene species [(THF)(3)(I)Nd(mu-PC(6)H(3)-2,6-(i)Pr(2))](2) are described; the phosphinidene moiety in this complex reacts as a carbene.     

Lewis acid-assisted nucleophilic substitution of fullerene epoxide

[Structure: see text] A 1,4-bis(phenyl)-1,4-dihydro[60]fullerene resulting from an efficient nucleophilic substitution has been obtained by reaction of a fullerene epoxide, C60O, with nucleophilic aromatic compounds in the presence of boron trifluoride etherate as a Lewis acid.     

Silatranes: a review on their synthesis, structure, reactivity and applications

This critical review summarizes progress of the rapidly developing and very active field of silatrane chemistry. The first part of the review deals with general synthetic approaches used to synthesize different silatranes. The most interesting feature of silatranes, i.e., variation of Si-N bond length on the basis of the axial substituent of Si, and other structural features, are described in the second part with special emphasis on crystallographic and theoretical studies. It is followed by a discussion on the reactivity of various silatranes. Silatranes have now gained acceptance for a wide variety of applications which are summarized in the last section of review. Some of them have extensive interest due to their medical use to heal wounds or stimulate hair-growth (pilotropic activity), biological properties, pharmacological properties e.g. antitumor, anticancer, antibacterial, anti-inflammatory, fungicidal activity, stimulating effect in animal production and seed germination effects. The review focuses on the extended potential of silatranes in sol-gel processes, mesoporous zeotypes, atomic force microscopy, commercial products such as adhesion promoters, polymer formation and rubber compositions. This critical review will be helpful for general researchers, experts, advanced undergraduates and newcomers working on silatrane chemistry as this review presents greater emphasis on synthesis and characterization, structural properties, reactivity and applications of silatranes in the field of biology, material science, sol-gel chemistry, pharmaceutics, agriculture and medicine (311 references).     

Gold(I) phosphido complexes: synthesis, structure, and reactivity

Deprotonation of the phosphine complexes Au(PHR(2))Cl with aqueous ammonia gave the gold(I) phosphido complexes [Au(PR(2))](n)() (PR(2) = PMes(2) (1), PCy(2) (2), P(t-Bu)(2) (3), PIs(2) (4), PPhMes (5), PHMes (6); Mes = 2,4,6-Me(3)C(6)H(2), Is = 2,4,6-(i-Pr)(3)C(6)H(2), Mes = 2,4,6-(t-Bu)(3)C(6)H(2), Cy = cyclo-C(6)H(11)). (31)P NMR spectroscopy showed that these complexes exist in solution as mixtures, presumably oligomeric rings of different sizes. X-ray crystallographic structure determinations on single oligomers of 1-4 revealed rings of varying size (n = 4, 6, 6, and 3, respectively) and conformation. Reactions of 1-3 and 5 with PPN[AuCl(2)] gave PPN[(AuCl)(2)(micro-PR(2))] (9-12, PPN = (PPh(3))(2)N(+)). Treatment of 3 with the reagents HI, I(2), ArSH, LiP(t-Bu)(2), and [PH(2)(t-Bu)(2)]BF(4) gave respectively Au(PH(t-Bu)(2))(I) (14), Au(PI(t-Bu)(2))(I) (15), Au(PH(t-Bu)(2))(SAr) (16, Ar = p-t-BuC(6)H(4)), Li[Au(P(t-Bu)(2))(2)] (17), and [Au(PH(t-Bu)(2))(2)]BF(4) (19).     

Thieno[3,4-b]pyrazines: synthesis,structure, and reactivity

A general synthetic route has been developed for the efficient preparation of 2,3-disubstituted thieno[3,4-b]pyrazines. These methods eliminate problems in the preparation of the precursor 3,4-diaminothiophene and utilize alpha-diones prepared through the reaction of the appropriate organocuprates with oxalyl chloride. This combination allows the convenient preparation of thieno[3,4-b]pyrazine and its 2,3-disubstituted analogues (where substituent = methyl, hexyl, octyl, decyl, dodecyl, and phenyl) in high yield. Characterization of the structure and reactivity of this class of compounds is also described, including the results of structural, electrochemical, and pK(a) studies.     

Thorium oxo and sulfido metallocenes: synthesis, structure, reactivity, and computational studies

The synthesis, structure, and reactivity of thorium oxo and sulfido metallocenes have been comprehensively studied. Heating of an equimolar mixture of the dimethyl metallocene [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)ThMe(2) (2) and the bis-amide metallocene [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)Th(NH-p-tolyl)(2) (3) in refluxing toluene results in the base-free imido thorium metallocene, [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)Th═N(p-tolyl) (4), which is a useful precursor for the preparation of oxo and sulfido thorium metallocenes [η(5)-1,2,4-(Me(3)C)(3)C(5)H(2)](2)Th═E (E = O (5) and S (15)) by cycloaddition-elimination reaction with Ph(2)C═E (E = O, S) or CS(2). The oxo metallocene 5 acts as a nucleophile toward alkylsilyl halides, while sulfido metallocene 15 does not. The oxo metallocene 5 and sulfido metallocene 15 undergo a [2 + 2] cycloaddition reaction with Ph(2)CO, CS(2), or Ph(2)CS, but they show no reactivity with alkynes. Density functional theory (DFT) studies provide insights into the subtle interplay between steric and electronic effects and rationalize the experimentally observed reactivity patterns. A comparison between Th, U, and group 4 elements shows that Th(4+) behaves more like an actinide than a transition metal.     

Molybdenum amido complexes with single Mo-N bonds: synthesis,structure, and reactivity

Reactions of the complex [MoCl(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (1) (phen=1,10-phenanthroline) with potassium arylamides were used to synthesize the amido complexes [Mo(N(R)Ar)(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (R=H, Ar=Ph, 2 a; R=H, Ar=p-tolyl, 2 b; R=Me, Ar=Ph; 2 c). For 2 b the Mo-N(amido) bond length (2.105(4) A) is consistent with it being a single bond, with which the metal attains an 18-electron configuration. The reaction of 2 b with HOTf affords the amino complex [Mo(eta(3)-C(3)H(4)-Me-2)(NH(2)(p-tol))(CO)(2)(phen)]OTf (3-OTf). Treatment of 3-OTf with nBuLi or KN(SiMe(3))(2) regenerates 2 b. The new amido complexes react with CS(2), arylisothiocyanates and maleic anhydride. A single product corresponding to the formal insertion of the electrophile into the Mo-N(amido) bond is obtained in each case. For maleic anhydride, ring opening accompanied the formation of the insertion product. The reaction of 2 b with maleimide affords [Mo(eta(3)-C(3)H(4)-Me-2)[NC(O)CH=CHC(O)](CO)(2)(phen)] (7), which results from simple acid-base metathesis. The reaction of 2 b with (p-tol)NCO affords [[Mo(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)](2)(eta(2)-MoO(4))] (8), which corresponds to oxidation of one third of the metal atoms to Mo(VI). Complex 8 was also obtained in the reactions of 2 b with CO(2) or the lactide 3,6-dimethyl-1,4-dioxane-2,5-dione. The structures of the compounds 2 b, 3-OTf, [Mo(eta(3)-C(3)H(4)-Me-2)[SC(S)(N(H)Ph)](CO)(2)(phen)] (4), [Mo(eta(3)-C(3)H(4)-Me-2)[SC(N(p-tol))(NH(p-tol))](CO)(2)(phen)] (5 a), and [Mo(eta(3)-C(3)H(4)-Me-2)[OC(O)CH=CHC(O)(NH(p-tol))](CO)(2)(phen)] (6), 7, and 8 (both the free complex and its N,N'-di(p-tolyl)urea adduct) were determined by X-ray diffraction.     

Synthesis and reactivity of highly nucleophilic pyridines

3,4,5-Triamino-substituted pyridines are avid for electrophiles but are still willing to give them back. In these compounds three amino groups conjoin their forces into the heterocyclic nitrogen, making it a powerful Lewis base. A short and efficient synthesis is described, and the origin of its unique activity in nucleophilic organocatalysis is rationalized by kinetics and thermodynamic quantifications.     

Spectroscopic parameters of nucleophilic and electrophilic reactivity

Reactions of a distinct charge transfer nature (exampled by those between N,N-dimethylaniline and N-methyl cations) are associated with charge transfer bands, in the visible, of energy hν = I ? E + C where I is the ionisation energy of the nucleophile, E is the electron affinity of the electrophile and C is a correction term. As an example, the reaction between N,N-dimethylaniline and N-methylacridinium chloride is examined in detail. Tables of I are given for anions in adiponitrile solution and of hν for cations in dimethylaniline/alcohol solution; low values of I correspond with greater nucleophilic activity and low values of hν with greater electrophilic activity.     

An unusually robust triple bond: synthesis, structure and reactivity of 3-alkynylcyclopropenes

Several 1,2-diphenyl- and 1,2,3-triphenyl-3-alkynylcyclopropenes have been prepared in moderate to very good yields by the reaction of acetylenic nucleophiles with the appropriate cyclopropenylium salt. Single crystal X-ray structures of four of the cyclopropenes were obtained. Stereoselective reduction of the triple bond failed in all cases, whereas model compounds lacking the cyclopropene moiety were reduced successfully. A rational for this lack of reactivity is proposed. The solution-phase thermochemistry of the 3-alkynyl-1,2,3-triphenylcyclopropenes was explored, affording 3-alkynyl-1H-indenes in moderate to good yields.     

Cobalt N-heterocyclic carbene alkyl and acyl compounds: synthesis, molecular structure and reactivity

The N-heterocyclic-carbene containing cobalt carbonyl compound [Co(IMes)(CO)3(Me)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene), 1, has been synthesised by tertiary phosphine displacement from [Co(PPh3)(CO)3(Me)]. Subsequent carbonylation afforded the acyl derivative [Co(IMes)(CO)3(COMe)], 2. Similarly, the compound [Co(IMes)(CO)3(COEt)], 3, has been synthesised. The compounds 2 and 3 have been shown to react with dihydrogen to form the cobalt hydride compound [Co(IMes)(CO)3(H)], 4. The molecular structures of compounds 1 and 2 have been determined.