32 research outputs found
Nickel-Catalyzed Coupling Reactions of Alkyl Electrophiles, Including Unactivated Tertiary Halides, To Generate Carbon–Boron Bonds
Through the use of a catalyst formed in situ from NiBr2·diglyme and a pybox ligand (both of which are commercially available), we have achieved our first examples of coupling reactions of unactivated tertiary alkyl electrophiles, as well as our first success with nickel-catalyzed couplings that generate bonds other than C–C bonds. Specifically, we have determined that this catalyst accomplishes Miyaura-type borylations of unactivated tertiary, secondary, and primary alkyl halides with diboron reagents to furnish alkylboronates, a family of compounds with substantial (and expanding) utility, under mild conditions; indeed, the umpolung borylation of a tertiary alkyl bromide can be achieved at a temperature as low as −10 °C. The method exhibits good functional-group compatibility and is regiospecific, both of which can be issues with traditional approaches to the synthesis of alkylboronates. In contrast to seemingly related nickel-catalyzed C–C bond-forming processes, tertiary halides are more reactive than secondary or primary halides in this nickel-catalyzed C–B bond-forming reaction; this divergence is particularly noteworthy in view of the likelihood that both transformations follow an inner-sphere electron-transfer pathway for oxidative addition
Nickel-Catalyzed Enantioconvergent Borylation of Racemic Secondary Benzylic Electrophiles
Nickel‐catalyzed cross‐coupling has emerged as the most versatile approach to date for achieving enantioconvergent carbon–carbon bond formation using racemic alkyl halides as electrophiles. In contrast, there have not yet been reports of the application of chiral nickel catalysts to the corresponding reactions with heteroatom nucleophiles to produce carbon–heteroatom bonds with good enantioselectivity. Herein, we establish that a chiral nickel/pybox catalyst can borylate racemic secondary benzylic chlorides to provide enantioenriched benzylic boronic esters, a highly useful family of compounds in organic synthesis. The method displays good functional group compatibility (e.g., being unimpeded by the presence of an indole, a ketone, a tertiary amine, or an unactivated alkyl bromide), and both of the catalyst components (NiCl_2⋅glyme and the pybox ligand) are commercially available
Nickel-Catalyzed Enantioconvergent Borylation of Racemic Secondary Benzylic Electrophiles
Nickel‐catalyzed cross‐coupling has emerged as the most versatile approach to date for achieving enantioconvergent carbon–carbon bond formation using racemic alkyl halides as electrophiles. In contrast, there have not yet been reports of the application of chiral nickel catalysts to the corresponding reactions with heteroatom nucleophiles to produce carbon–heteroatom bonds with good enantioselectivity. Herein, we establish that a chiral nickel/pybox catalyst can borylate racemic secondary benzylic chlorides to provide enantioenriched benzylic boronic esters, a highly useful family of compounds in organic synthesis. The method displays good functional group compatibility (e.g., being unimpeded by the presence of an indole, a ketone, a tertiary amine, or an unactivated alkyl bromide), and both of the catalyst components (NiCl_2⋅glyme and the pybox ligand) are commercially available
Controlled Synchronization of One Class of Nonlinear Systems under Information Constraints
Output feedback controlled synchronization problems for a class of nonlinear
unstable systems under information constraints imposed by limited capacity of
the communication channel are analyzed. A binary time-varying coder-decoder
scheme is described and a theoretical analysis for multi-dimensional
master-slave systems represented in Lurie form (linear part plus nonlinearity
depending only on measurable outputs) is provided. An output feedback control
law is proposed based on the Passification Theorem. It is shown that the
synchronization error exponentially tends to zero for sufficiantly high
transmission rate (channel capacity). The results obtained for synchronization
problem can be extended to tracking problems in a straightforward manner, if
the reference signal is described by an {external} ({exogenious}) state space
model. The results are applied to controlled synchronization of two chaotic
Chua systems via a communication channel with limited capacity.Comment: 8 pages, 2 figure
Modern microwave methods in solid state inorganic materials chemistry: from fundamentals to manufacturing
No abstract available
Nickel-Catalyzed Coupling Reactions of Alkyl Electrophiles, Including Unactivated Tertiary Halides, To Generate Carbon–Boron Bonds
Through the use of a catalyst formed in situ from NiBr[subscript 2]·diglyme and a pybox ligand (both of which are commercially available), we have achieved our first examples of coupling reactions of unactivated tertiary alkyl electrophiles, as well as our first success with nickel-catalyzed couplings that generate bonds other than C–C bonds. Specifically, we have determined that this catalyst accomplishes Miyaura-type borylations of unactivated tertiary, secondary, and primary alkyl halides with diboron reagents to furnish alkylboronates, a family of compounds with substantial (and expanding) utility, under mild conditions; indeed, the umpolung borylation of a tertiary alkyl bromide can be achieved at a temperature as low as −10 °C. The method exhibits good functional-group compatibility and is regiospecific, both of which can be issues with traditional approaches to the synthesis of alkylboronates. In contrast to seemingly related nickel-catalyzed C–C bond-forming processes, tertiary halides are more reactive than secondary or primary halides in this nickel-catalyzed C–B bond-forming reaction; this divergence is particularly noteworthy in view of the likelihood that both transformations follow an inner-sphere electron-transfer pathway for oxidative addition.National Institute of General Medical Sciences (U.S.) (Grant R01-GM62871
Nickel-Catalyzed Coupling Reactions of Alkyl Electrophiles, Including Unactivated Tertiary Halides, To Generate Carbon–Boron Bonds
Through the use of a catalyst formed in situ from NiBr<sub>2</sub>·diglyme and a pybox ligand (both of which are commercially
available), we have achieved our first examples of coupling reactions
of unactivated tertiary alkyl electrophiles, as well as our first
success with nickel-catalyzed couplings that generate bonds other
than C–C bonds. Specifically, we have determined that this
catalyst accomplishes Miyaura-type borylations of unactivated tertiary,
secondary, and primary alkyl halides with diboron reagents to furnish
alkylboronates, a family of compounds with substantial (and expanding)
utility, under mild conditions; indeed, the umpolung borylation of
a tertiary alkyl bromide can be achieved at a temperature as low as
−10 °C. The method exhibits good functional-group compatibility
and is regiospecific, both of which can be issues with traditional
approaches to the synthesis of alkylboronates. In contrast to seemingly
related nickel-catalyzed C–C bond-forming processes, tertiary
halides are <i>more</i> reactive than secondary or primary
halides in this nickel-catalyzed C–B bond-forming reaction;
this divergence is particularly noteworthy in view of the likelihood
that both transformations follow an inner-sphere electron-transfer
pathway for oxidative addition
Obtaining of hydroxylated fullerenes Y@C82OX(OH)Y, Y2@C82OX(OH)Y, Y2C2@C82OX(OH)Y and electrophysical characteristic of composite film based thereon
The article presents, for the first time, the results of the research on composite film obtained from
hydroxylated endohedral metallofullerenes (EMF) Y@C82, Y2@C82, with Y2C2@C82 and highest fullerenes
as dopant. The composite film has been established to have electric conductivity and to be
a ferroelectric with the value of residual polarization of ~0.75 mkC/cm2. The impedance spectroscopy
of this sample allowed us to determine dispersion of dielectric permittivity and conductivity
in the range of frequencies of 0.5Hz–100MHz. It is stated that the value of the high-frequency
dielectric permittivity of films is e' = 2.8. However, with reduction in the electric field frequency,
real and imaginary parts of e increase to values ~10^4–10^5. Such increase in dielectric permittivity
is connected with increase in polarizing caused by accumulation of mobile electric charges (electrons
of ions, protons) on boundaries of the structural defects of a film, which are divided by thin
dielectric interlayers. The film is solid electrolyte with the ionic conductivity of ~5*10^(-7) S/cm