Synthesis and characterization of the octahydrotriborate complexes Cp*V(B3H8)2 and Cp*Cr(B3H8)2 and the unusual cobaltaborane cluster Cp*2Co2(B6H14)

The new compounds CpV(B(3)H(8))(2), CpCr(B(3)H(8))(2), and Cp(2)Co(2)(B(6)H(14)) have been synthesized by treating the pentamethylcyclopentadienyl complexes [CpVCl(2)](3), [CpCrCl(2)](2), and [CpCoCl](2) with NaB(3)H(8). X-ray crystallography shows that CpV(B(3)H(8))(2) and CpCr(B(3)H(8))(2) have the same ligand sets but different molecular structures: the vanadium compound contains two bidentate B(3)H(8) ligands (i.e., bound to the metal center via two vicinal hydrogen atoms), whereas the chromium compound has one bidentate B(3)H(8) ligand and one B(3)H(8) ligand bound in an unprecedented fashion via two geminal hydrogen atoms. The "gem-bound" B(3)H(8) group itself has an atypical structure consisting of a BH(2)-BH(2)-BH(3) triangle with one additional hydrogen atom bridging the unique BH(2)-BH(2) edge. The B-B distances are nearly identical within experimental error at 1.790(5), 1.792(5), and 1.786(6) Angstrom. The relationship between the electronic and molecular structures of the V and Cr compounds is briefly discussed. The structure of Cp(2)Co(2)(B(6)H(14)) can be viewed in two different ways: as a dicobalt complex in which two CpCo units are each bound to four adjacent boron atoms of an S-shaped B(6)H(14) ligand, or as an eight-vertex hypho cluster compound. In the former case, the B(6)H(14) ligand is best regarded as a dianionic bi-borallyl group H(3)B(mu-H)BH(mu-H)BHBH(mu-H)BH(mu-H)BH(3) in which one hydrogen at each end of the chain is involved in an agostic interaction. From a cluster point of view, the structure of Cp(2)Co(2)(B(6)H(14)) can be generated by removing three adjacent high-connectivity vertices from the eleven-vertex closo polyhedron. The Co-B distances vary from 2.008(5) to 2.183(4) Angstrom, and the B-B distances within in the S-shaped chain range from 1.734(8) to 1.889(6) Angstrom. Finally, a new synthesis of the known molybdenum compound Cp(2)Mo(2)(B(5)H(9)) is described; its structure as established by X-ray crystallography closely resembles that of the previously described (C(5)H(4)Me) analogue.     

Palladium-catalyzed silyl C(sp3)-H bond activation

The first transition-metal-catalyzed activation of silyl C(sp(3))-H bond was realized and synthetically applied. A variety of organic skeletons substituted with SiMe(3) groups could undergo the Pd-catalyzed intramolecular coupling reaction, resulting in an unprecedented synthetic method for yielding six-membered silacycles. It was found that the adjacent Si atom played an essential role for the activation of the C(sp(3))-H bond of the SiMe(3) group; no activation reaction of the C(sp(3))-H bond of the CMe(3) group took place under the same reaction conditions.     

Multinuclear self-assembly via half-sandwich complexes Cp*M[S2C2(B10H10)] and pyridine-based ligands

The study on transition metal mediated self-assemblies has drawn considerable attention during the past decade. This article focused on the significant progress made in the area of multinuclear supramolecular construction through pseudo-aromatic carboranyl species Cp*M[S(2)C(2)(B(10)H(10))] (M = Co, Rh, Ir) and pyridine-based ligands over the past few years. Structurally pre-defined complexes, from mono-molecules to three-dimensional frameworks, can be obtained in high yields under mild reaction conditions through self-assembly, and the structural features of solid state confirmed by X-ray crystallography are also discussed.     

Aza-oxindole synthesis by oxidative coupling of C(sp2)-H and C(sp3)-H centers

A Cu(II) mediated oxidative C(sp(2))-H and C(sp(3))-H coupling protocol gives access to aza-oxindoles in good to excellent yield in the presence of NaOtBu as base and toluene as solvent.     

Facile intramolecular C(sp3)-H bond activation with PdII

The treatment of bis(4-tert-butylthiazolyl)isoindoline (4-tBuBTI) with palladium acetate results in the exclusive formation of an organometallic PdII compound with C-H activated t-butyl group and a hemilabile S-coordinated thiazole donor in cis-position.     

Original palladium pincer complexes deriving from 1,3-bis(thiophosphinoyl)indene proligands: C(sp3)-H versus C(sp2)-H bond activation

A series of original 2-indenylidene palladium pincer complexes {PdL[Ind(Ph(2)P==S)(2)]} (L = HNCy(2), PPh(3), Cl(-)) have been prepared by double C-H activation of a 1,3-bis(thiophosphinoyl)indene proligand. Crystallographic analyses and DFT calculations indicate that the bonding situation of the {Pd[Ind(Ph(2)P==S)(2)]} fragment is essentially governed by the conjugated and rigid nature of the dianionic pincer ligand, the nature of the coligand having little influence. The formation of the 2-indenylidene complexes involves either a 2-indenyl pincer or a four-membered cyclometalated complex as an intermediate, suggesting that C(sp(2))-H or C(sp(3))-H bond activation takes place. However, deuterium labelling experiences show that in all cases, C(sp(3))-H bond activation occurs followed eventually by a Pd/H exchange. Nevertheless, evidence for direct C(sp(2))-H bond activation under mild conditions is obtained when a methyl group is introduced at the indene proligand to prevent C(sp(3))-H bond activation. The ensuing dissymmetrical 2-indenyl palladium pincer complex has been fully characterized.     

Platinum(II)-catalyzed cyclization sequence of aryl alkynes via C(sp3)-H activation: a DFT study

The mechanism and intermediates of hydroalkylation of aryl alkynes via C(sp(3))-H activation through a platinum(II)-centered catalyst are investigated with density functional theory at the B3LYP/[6-31G(d) for H, O, C; 6-31+G(d,p) for F, Cl; SDD for Pt] level of theory. Solvent effects on reactions were explored using calculations that included a polarizable continuum model for the solvent (THF). Free energy diagrams for three suggested mechanisms were computed: (a) one that leads to formation of a Pt(II) vinyl carbenoid (Mechanism A), (b) another where the transition state implies a directed 1,4-hydrogen shift (Mechanism B), and (c) one with a Pt-aided 1,4-hydrogen migration (Mechanism C). Results suggest that the insertion reaction pathway of Mechanism A is reasonable. Through 4,5-hydrogen transfer, the Pt(II) vinyl carbenoid is formed. Thus, the stepwise insertion mechanism is favored while the electrocyclization mechanism is implausible. Electron-withdrawing/electron-donating groups substituted at the phenyl and benzyl sp(3) C atoms slightly change the thermodynamic properties of the first half of Mechanism A, but electronic effects cause a substantial shift in relative energies for the second half of Mechanism A. The rate-limiting step can be varied between the 4,5-hydrogen shift process and the 1,5-hydrogen shift step by altering electron-withdrawing/electron-donating groups on the benzyl C atom. Additionally, NBO and AIM analyses are applied to further investigate electronic structure changes during the mechanism.     

Cp*RhIII‐Catalyzed Arylation of C(sp3)H Bonds

The first Cp*Rh^III‐catalyzed arylation of unactivated C(sp³)? H bonds is presented. The unactivated primary C(sp³)? H bond of 2‐alkylpyridines can be activated by Rh^III and further reacts with triarylboroxines to efficiently build new C(sp³)? aryl bonds. The methodology also provides a facile and efficient synthesis of unsymmetrical triarylmethanes by Rh^III‐catalyzed C(sp³)? H arylation of diarylmethanes.     

Thermal transformations of B10H12(NH3)2, B10H12(C5H5N)2, and B10H12(C9H7N)2

Conclusions For B₁₀H₁₂L₂, where L=NH₃, C₅H₅N, or C₉H₇N, features of thermal transformations in the range 25–850°C and the composition of the pyrolysis products are determined. The latter are x-ray amorphous phases, containing nitride, carbide, boron carbide, boron, and carbon.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2481–2484, November, 1988.     

Measurement of barriers to aryl rotation in Cp(CO)2FeCHC6H5+ and Cp(CO)2FeCH(p-CH3C6H4)+

The first observation of barriers to rotation about the C_arylC_carbene bonds in aryl-substituted metal carbene complexes is reported. Using variable temperature ¹H NMR, barriers of 9.1 and 10.4 kcal/mol have been determined for Cp(CO)₂FeCHC₆H₅⁺ and Cp(CO)₂FeCH(p-CH₃C₆H₄)⁺, respectively. The data clearly indicate a geometry of the complex in which the aryl ring lies coplanar with FeC_carbeneC_ipso plane.     

Photochemically induced radical transformation of C(sp3)-H bonds to C(sp3)-CN bonds

A general protocol for direct transformation of unreactive C(sp(3))-H bonds to C(sp(3))-CN bonds has been developed. The C-H activation was effected by photoexcited benzophenone, and the generated carbon radical was subsequently trapped with tosyl cyanide to afford the corresponding nitrile in a highly efficient manner. The present methodology is widely applicable to versatile starting materials and, thus, serves as a powerful tool for selective one-carbon elongation for construction of architecturally complex molecules.     

Condensed tantalaborane clusters: synthesis and structures of [(Cp*Ta)2B5H7{Fe(CO)3}2] and [(Cp*Ta)2B5H9{Fe(CO)3}4

The reaction of [(Cp*Ta)(2)B(4)H(9)(μ-BH(4))] (1; Cp* = η(5)-C(5)Me(5)) with [Fe(2)(CO)(9)] in hexane yielded [(Cp*Ta)(2)B(5)H(7){Fe(CO)(3)}(2)] (2) and [(Cp*Ta)(2)B(5)H(9){Fe(CO)(3)}(4)] (3) in moderate yield. Cluster 2 represents the first example of a bicapped pentagonal-bipyramidal metallaborane with a deformed equatorial plane, and 3 can be described as a fused cluster in which two pentagonal-bipyramidal units are fused through a common 3-vertex triangular face. Compounds 2 and 3 have been characterized by mass spectrometry and IR, (1)H, (11)B, and (13)C NMR spectroscopy, and the geometric structures were unequivocally established by crystallographic analysis.     

Tandem dual C(sp3)-H/C(sp2)-H functionalization: a radical cyclization of 2-isocyanobiphenyl with ether to 6-alkylated phenanthridine

<正>1 General experimental details 1H NMR and 13 C NMR spectra were measured on 400 MHz spectrometer, using CDCl3 as the solvent with tetramethylsilane(TMS) as the internal standard at room temperature. Chemical shifts(δ) are given in ppm relative to TMS, the coupling constants J are given in Hz. HRMS were recorded on a TOF LC/MS equipped with electrospray ionization(ESI) probe operating in positive or negative ion mode.     

Native amine-directed site-selective C(sp3)-H arylation of primary aliphatic amines with aryl iodides

Direct C(sp³)-H functionalization of N-unprotected aliphatic amines represents one of the most efficient and straightforward strategies for amine synthesis. Despite some recent progress in this field, the NH₂-directed γ-C(sp³)-H arylation of primary aliphatic amines except α-amino esters remained an unmet challenge. In this report, we established a simple and efficient method for site-selective C(sp³)-H arylation of primary aliphatic amines by aryl iodides. In the presence of only 5 mol% Pd(OAc)₂, a wide range of aliphatic amines including O-benzyl and O-silyl amino alcohols were arylated at γ- or δ-positions by aryl iodides containing a broad scope of functional groups. The synthetic application of this method had also been demonstrated by large-scale synthesis, the synthesis of a fingolimod analogue, and the conjugation with natural d-menthol and fluorescent 1,8-naphthalimide.