Synthesis and Reactivity of a Neutral,Three‐Coordinate Platinum(II) Complex Featuring Terminal Amido Ligation

A crystallographically characterized three‐coordinate, formally 14 electron Pt^II complex 1 featuring terminal amido ligation is reported. Computational analysis revealed relatively weak π donation from the amide lone pair to platinum and supports a 14‐electron assignment for 1 . Stoichiometric reactivity studies confirmed the viability of net O? H and C? H addition across, as well as isonitrile insertion into, the terminal platinum–amido linkage of 1 .     

Cp*CoIII Catalyzed Site‐Selective C?H Activation of Unsymmetrical O‐Acyl Oximes: Synthesis of Multisubstituted Isoquinolines from Terminal and Internal Alkynes

The synthesis of isoquinolines by site‐selective C H activation of O‐acyl oximes with a Cp*Co^III catalyst is described. In the presence of this catalyst, the C H activation of various unsymmetrically substituted O‐acyl oximes selectively occurred at the sterically less hindered site, and reactions with terminal as well as internal alkynes afforded the corresponding products in up to 98 % yield. Whereas the reactions catalyzed by the Cp*Co^III system proceeded with high site selectivity (15:1 to 20:1), use of the corresponding Cp*Rh^III catalysts led to low selectivities and/or yields when unsymmetrical O‐acyl oximes and terminal alkynes were used. Deuterium labeling studies indicate a clear difference in the site selectivity of the C H activation step under Cp*Co^III and Cp*Rh^III catalysis.     

Multinuclear magnetic resonance study of some imidovanadium complexes

¹⁴N NMR studies were carried out for a series of mononuclear and dinuclear vanadium complexes with different types of nitrogen ligands (terminal and µ‐imido, amido, nitrido, amine). Some complexes containing ancillary phosphine moieties were also characterized by ³¹P NMR spectroscopy. The observed shieldings for terminal and bridging imido ligands are intermediate between those of nitrido and amido moieties, and the latter appear less shielded than coordinated tertiary amines. The ranges for individual ligand types are sufficiently resolved to allow the use of nitrogen chemical shifts as a structure assignment tool. The ¹⁴N NMR signals of terminal and bridging imido nitrogens displayed marked differences in their lineshapes which could be used as an additional criterion for signal assignment. Examination of substituent influences revealed the absence of a general parallelism between δ¹⁴N and δ⁵¹V, but gave evidence for parallel relationships between both quantities for complexes with formal 12VE and 16VE electron counts. Determination of ¹J(⁵¹V,¹⁴N) and ¹J(⁵¹V,³¹P) coupling constants in mononuclear complexes was feasible from simulation of ¹⁴N and ³¹P lineshapes and suggested that imido ligands exhibit generally greater couplings to vanadium than amido ligands. Analysis of the ³¹P {¹H,¹⁴N} NMR spectrum allowed us to determine ²J(⁵¹V,³¹P) for the vanadacycle cyclo(^tBuN—P?C(^tBu)—VCl₃—). It was shown that both couplings can be employed for the acquisition of two‐dimensional ³¹P,⁵¹V shift correlations. Copyright © 2001 John Wiley & Sons, Ltd.     

Gold‐Catalyzed C(sp3)?H/C(sp)?H Coupling/Cyclization/Oxidative Alkynylation Sequence: A Powerful Strategy for the Synthesis of 3‐Alkynyl Polysubstituted Furans

In sharp contrast to the gold‐catalyzed reactions of alkynes/allenes with nucleophiles, gold‐catalyzed oxidative cross‐couplings and especially C H/C H cross‐coupling have been under represented. By taking advantage of the unique redox property and carbophilic π acidity of gold, this work realizes the first gold‐catalyzed direct C(sp³) H alkynylation of 1,3‐dicarbonyl compounds with terminal alkynes under mild reaction conditions, with subsequent cyclization and in situ oxidative alkynylation. A variety of terminal alkynes including aryl, heteroaryl, alkenyl, alkynyl, alkyl, and cyclopropyl alkynes all successfully participate in the domino reaction. The protocol offers a simple and region‐defined approach to 3‐alkynyl polysubstituted furans.     

B?H,C?H,and B?C Bond Activation: The Role of Two Adjacent Agostic Interactions

Tuning the nature of the linker in a L∼BHR phosphinoborane compound led to the isolation of a ruthenium complex stabilized by two adjacent, δ‐C H and ε‐B_sp2 H, agostic interactions. Such a unique coordination mode stabilizes a 14‐electron “RuH₂P₂” fragment through connected σ‐bonds of different polarity, and affords selective B H, C H, and B C bond activation as illustrated by reactivity studies with H₂ and boranes.     

Rhodium(III)‐Catalyzed C?C and C?O Coupling of Quinoline N‐Oxides with Alkynes: Combination of C?H Activation with O‐Atom Transfer

[Cp*Rh^III]‐catalyzed C H activation of arenes assisted by an oxidizing N O or N N directing group has allowed the construction of a number of hetercycles. In contrast, a polar N O bond is well‐known to undergo O‐atom transfer (OAT) to alkynes. Despite the liability of N O bonds in both C H activation and OAT, these two important areas evolved separately. In this report, [Cp*Rh^III] catalysts integrate both areas in an efficient redox‐neutral coupling of quinoline N‐oxides with alkynes to afford α‐(8‐quinolyl)acetophenones. In this process the N O bond acts as both a directing group for C H activation and as an O‐atom donor.     

Reaction mechanism of palladium‐catalyzed silastannation of allenes by density functional theory

The reaction mechanism of Pd(0)‐catalyzed allenes silastannation reaction is investigated by the density functional method B3LYP. The overall reaction mechanism is examined. For the allene insertion step, the Pd Si bond is preferred over the Pd Sn bond. The electronic mechanism of the allene insertion into Pd Si bond to form σ‐vinylpalladium (terminal‐insertion) and σ‐allylpalladium (internal‐insertion) insertion products is discussed in terms of the electron donation and back‐donation. It is found that the electron back‐donation is significant for both terminal‐ and internal‐insertion. During allene insertion into Pd Si bond, internal‐insertion is preferred over terminal‐insertion. By using methylallene, the regio‐selectivity for the monosubstituted allene insertion into Pd Si and Pd Sn bond is analyzed. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009     

Synthesis of Annelated Phospholes through Intramolecular C?H Activation by Monovalent Phosphorus

Electrophilic terminal phosphinidene complexes [Ar‐Ar‐P‐W(CO)₅] (Ar‐Ar: biaryl or an analogue thereof) undergo a spontaneous insertion of the phosphorus atom into the vicinal C H bonds to give annelated phospholes. Twelve examples are described, including biphenyl, thienyl, pyrrolyl, and benzofuryl groups as biaryl moieties. The activation energy of the insertion reaction is quite low (about 2 kcal mol⁻¹).     

A Two‐Coordinate Cobalt(II) Imido Complex with NHC Ligation: Synthesis,Structure, and Reactivity

The synthesis, structural characterization, and reactivity of the first two‐coordinate cobalt complex featuring a metal–element multiple bond [(IPr)Co(NDmp)] ( 4 ; IPr=1,3‐bis(2′,6′‐diisopropylphenyl)imidazole‐2‐ylidene; Dmp=2,6‐dimesitylphenyl) is reported. Complex 4 was prepared from the reaction of [(IPr)Co(η²‐vtms)₂] (vtms=vinyltrimethylsilane) with DmpN₃. An X‐ray diffraction study revealed its linear C Co N core and a short Co N distance (1.691(6) Å). Spectroscopic characterization and calculation studies indicated the high‐spin nature of 4 and the multiple‐bond character of the Co N bond. Complex 4 effected group‐transfer reactions to CO and ethylene to form isocyanide and imine, respectively. It also facilitated E H (E=C, Si) σ‐bond activation of terminal alkyne and hydrosilanes to produce the corresponding cobalt(II) alkynyl and cobalt(II) hydride complexes as 1,2‐addition products.     

Asymmetric Organocatalytic Direct C(sp2)?H/C(sp3)?H Oxidative Cross‐Coupling by Chiral Iodine Reagents

An asymmetric organocatalytic direct C H/C H oxidative coupling reaction of N¹,N³‐diphenylmalonamides has been well established by using chiral organoiodine compounds as catalysts, wherein four C H bonds were stereoselectively functionalized to give structurally diverse spirooxindoles with high levels of enantioselectivity. More importantly, the findings indicated that chiral hypervalent organoiodine reagents can serve as alternative catalysts for the creation of enantioselective functionalization of inactive C H bonds.     

Palladium(0)/PAr3‐Catalyzed Intermolecular Amination of C(sp3)?H Bonds: Synthesis of β‐Amino Acids

An intermolecular C(sp³) H amination using a Pd⁰/PAr₃ catalyst was developed. The reaction begins with oxidative addition of R₂N OBz to a Pd⁰/PAr₃ catalyst and subsequent cleavage of a C(sp³) H bond by the generated Pd NR₂ intermediate. The catalytic cycle proceeds without the need for external oxidants in a similar manner to the extensively studied palladium(0)‐catalyzed C H arylation reactions. The electron‐deficient triarylphosphine ligand is crucial for this C(sp³) H amination reaction to occur.     

Copper‐Catalyzed Site‐Selective Intramolecular Amidation of Unactivated C(sp3)?H Bonds

The intramolecular dehydrogenative amidation of aliphatic amides, directed by a bidentate ligand, was developed using a copper‐catalyzed sp³ C H bond functionalization process. The reaction favors predominantly the C H bonds of β‐methyl groups over the unactivated methylene C H bonds. Moreover, a preference for activating sp³ C H bonds of β‐methyl groups, via a five‐membered ring intermediate, over the aromatic sp² C H bonds was also observed in the cyclometalation step. Additionally, sp³ C H bonds of unactivated secondary sp³ C H bonds could be functionalized by favoring the ring carbon atoms over the linear carbon atoms.     

Metallacyclopentadienes and related heterocycles via 1,1‐organoboration of alkyn‐1‐ylmetal compounds

Metallacyclopentadienes (metalloles) containing M = Si, Ge, Sn, Pb, Ti, Pt can be prepared by 1,1‐organoboration of alkyn‐1‐ylmetal compounds L_nM CC R¹(R¹ = H, alkyl, aryl, silyl, etc; L depends on M, and can be hydrogen, alkyl, aryl, Cl, Br, amino groups, a chelating diphosphane, and one or more L can be again alkynyl groups). These reactions proceed via activation of the M C bond(s) by an electron‐deficient triorganoborane BR₃ (R = alkyl, aryl; non‐cyclic, monocyclic, bicyclic, and tricyclic boranes), at first intermolecular and then intramolecular. In the course of these reactions, the M C bonds are cleaved, zwitterionic alkynylborate‐like intermediates are formed, in which the metal‐containing fragments are coordinated side‐on to the CC bonds. In most cases, the 1,1‐organoboration reactions tolerate various functional groups at the alkyne as well as at the metal. The characterization of intermediates and final products by X‐ray structural analysis and by multinuclear magnetic resonance spectroscopy (NMR) is documented and described. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:188–208, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20222     

Aluminum five‐ and six‐coordination in bis(acetylacetonato)aminoalkoxides

Reactions of bis(acetylacetonato)aluminum(III)‐di‐μ‐isopropoxo‐di‐isopropoxo aluminum(III), [(CH₃COCHCOCH₃)₂Al(μ‐OPrⁱ)₂Al(OPrⁱ)₂] with aminoalcohols, (HO R NR¹R²) in 1:1 and 1:2 molar ratios in refluxing anhydrous benzene yielded binuclear complexes of the types [(CH₃COCHCOCH₃)₂Al(μ‐OPrⁱ)₂Al(O R NR¹R²)(OPrⁱ)] and [(CH₃COCHCOCH₃)₂Al(μ‐OPrⁱ)₂Al(O R NR¹R²)₂] (R   (CH₂)₃ , R¹ = R² = H; R =  CH₂C(CH₃)₂ , R¹ = R² = H; R =  (CH₂)₂ , R¹ = H, R² =  CH₃; and R   (CH₂)₂ , R¹ = R² = CH₃), respectively. All these compounds are soluble in common organic solvents and exhibit sharp melting points. Molecular weight determinations reveal their binuclear nature in refluxing benzene. Plausible structures have been proposed on the basis of elemental analysis, molecular weight measurements, IR, NMR (¹H, ¹³C, and ²⁷Al), and FAB mass spectral studies. ²⁷Al NMR spectra show the presence of both five‐ and six‐coordinated aluminum sites. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:518–522, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10184     

New phosphoric triamides: Chlorine substituents effects and polymorphism

New phosphoric triamides 1–10 were synthesized by the reaction of N‐2,4‐dichlorobenzoyl phosphoramidic dichloride with various cyclic aliphatic amines, and the products were characterized by ¹H, ¹³C, ³¹P NMR, and IR spectroscopy and elemental analysis. Surprisingly, the ¹H NMR spectra of compounds 1–7 demonstrate long‐range ⁴J(H,H) coupling constant from 1.5 to 1.9 Hz. Comparison of the NMR and IR spectra of N‐benzoyl, N‐4‐chlorobenzoyl, and N‐2,4‐dichlorobenzoyl phosphoric triamide analogues indicates that N‐2,4‐dichlorobenzoyl derivatives have the most upfield δ(³¹P) and the highest ν(CO) values. The crystal structures of 3 , 4 , 6 , 6a , and 10 have been determined by X‐ray crystallography. Interestingly, the structures of 6 and 6a are polymorphic. All structures form dimers through strong, intermolecular  PO···H N hydrogen bonds. The dimers connect to each other via weak C H···Cl and C H···OH bonds to produce two‐dimensional polymeric chains for 4 and three‐dimensional networks for others. Among new synthesized N‐2,4‐dichlorobenzoyl phosphoric triamides, one indicated polymorphism. All structures were characterized by ¹H, ¹³C, ³¹P NMR, and infrared spectroscopy and elemental analysis. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:168–180, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20592     

A DFT Study on the Mechanism of Rh2II,II‐Catalyzed Intramolecular Amidation of Carbamates

The potential‐energy surfaces of the reactions of dirhodium tetracarboxylate (Rh₂^II,II) catalyzed nitrene (NR) insertion into C H bonds were examined by a DFT computational study. A pure Becke exchange functional (B88) rather than a hybrid exchange functional (B3, BHandH) was found to be appropriate for the calculation of the energy difference between the singlet and triplet Rh₂^II,II–NH nitrene species. Rh₂^II,II–NR¹ (R¹=(S)‐2‐methyl‐1‐butylformyl) is thermodynamically more favorable with a free energy lower than that of Rh₂^II,II–N(PhI)R¹. The singlet and triplet states of Rh₂^II,II–NR¹ have similar stability. Singlet Rh₂^II,II–NR¹ undergoes a concerted NR insertion into the C H bond with simultaneous formation of the N H and N C bonds during C H bond cleavage; triplet Rh₂^II,II–NR¹ undergoes H atom abstraction to produce a diradical, followed by subsequent bond formation by diradical recombination. The singlet pathway is favored over the triplet in the context of the free energy of activation and leads to the retention of the chirality of the C atom in the NR insertion product. The reactivities of the C H bonds toward the nitrene‐insertion reaction follow the order tertiary>secondary>primary. Relative reaction rates were calculated for the six reaction pathways examined in this work.     

An Alkyne‐Appended,Click‐Ready PtII Complex with an Unusual Arrangement in the Solid State

To better understand the range of cellular interactions of Pt^II‐based chemotherapeutics, robust and efficient methods to track and analyze Pt targets are needed. A powerful approach is to functionalize Pt^II compounds with alkyne or azide moieties for post‐treatment conjugation through the azide–alkyne cycloaddition (click) reaction. Herein, we report an alkyne‐appended cis‐diamine Pt^II compound, cis‐[Pt(2‐(5‐hexynyl)amido‐1,3‐propanediamine)Cl₂] ( 1 ), the X‐ray crystal structure of which exhibits a combination of unusual radially distributed CH/π(CC) interactions, Pt Pt bonding, and NH:O/NH:Cl hydrogen bonds. In solution, 1 exhibits no Pt alkyne interactions and binds readily to DNA. Subsequent click reactivity with nonfluorescent dansyl azide results in a 70‐fold fluorescence increase. This result demonstrates the potential for this new class of alkyne‐modified Pt compound for the comprehensive detection and isolation of Pt‐bound biomolecules.     

Anagostic Interactions under Pressure: Attractive or Repulsive?

Square‐planar d⁸‐ML₄ complexes might display subtle but noticeable local Lewis acidic sites in axial direction in the valence shell of the metal atom. These sites of local charge depletion provide the electronic prerequisites to establish weakly attractive 3c–2e M⋅⋅⋅H C agostic interactions, in contrast to earlier assumptions. Furthermore, we show that the use of the sign of the ¹H NMR shifts as major criterion to classify M⋅⋅⋅H C interactions as attractive (agostic) or repulsive (anagostic) can be dubious. We therefore suggest a new characterization method to probe the response of these M⋅⋅⋅H C interactions under pressure by combined high pressure IR and diffraction studies.     

HNgBeF3 (Ng = Ar‐Rn): Superhalogen‐supported noble gas insertion compounds

Ab initio and density functional theory‐based calculations are performed to study the structure, stability, and nature of bonding of superhalogen‐supported noble gas (Ng) compounds of the type HNgY where (Ng = Ar‐Rn; Y = BeF₃). Here, BeF₃ acts as the superhalogen. Calculations show that the HNgBeF₃ spontaneously dissociates into product following the dissociation channels: HNgBeF₃ → HBeF₃ + Ng and HNgBeF₃ → Ng + HF + BeF₂. The transition states are optimized and the energy barriers are computed to show the metastable behavior of HNgBeF₃. HNgBeF₃ molecules are kinetically stable with respect to the first dissociation process having energy barriers of 1.0, 5.0, 10.6, and 13.9 kcal/mol for Ar, Kr, Xe, and Rn analogues, respectively, at CCSD(T)/Aug‐cc‐pVTZ level. These calculations suggest that the HXeBeF₃ and HRnBeF₃ can be shown to be stable up to ∼100 K temperature with a half‐life of ∼10² seconds. The nature of H Ng and two different types of Ng F bonds in HNgBeF₃ molecules is explored through the natural bond orbital and electron density analyses. The large Wiberg bond index (WBI) values for the H Ng bond indicate the formation of almost a single bond in between H‐atoms and Ng‐atoms, whereas small WBI values for the two Ng F bonds indicate a noncovalent interaction in between them. The electron density analysis further supports the covalency of the H Ng bond and noncovalent interaction in the two Ng F bonds in HNgBeF₃.     

Self‐assembling directed synthesis of a novel terephthalamide‐bridged ladderlike polysiloxane

A novel, soluble terephthalamide‐bridged ladderlike polysiloxane ( L ) was synthesized successfully for the first time by stepwise coupling polymerization. The process involved the hydrogen‐bonding self‐assembly of amido groups, which resulted in the formation of a more highly ordered polymeric structure. A novel monomer, bis(3‐methyldimethoxysilylpropyl) terephthalamide ( M ), was prepared by a hydrosilylation reaction in the presence of dicyclopentadienyl platinum dichloride as a catalyst. The structures of the monomer ( M ) and the polymer ( L ) were characterized by Fourier transform infrared, ¹H NMR, ¹³C NMR, ²⁹Si NMR, mass spectrometry, X‐ray diffraction, differential scanning calorimetry, and vapor pressure osmometry. All the characterization data indicated that the synthesized polymer ( L ) possessed an ordered ladderlike structure. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3161–3170, 2002