A series of gold(III) and palladium(II) heterometallic complexes with new iminophosphorane ligands derived from ferrocenyl-phosphanes [{Cp-P(Ph2)=N-Ph}2Fe] (1), [{Cp-P(Ph2)=N-CH2-2-NC5H4}2Fe] (2) and [{Cp-P(Ph2)=N-CH2-2-NC5H4}Fe(Cp)] (3) have been synthesized and structurally characterized. Ligands 2 and 3 afford stable coordination complexes [AuCl2(3)]ClO4, [{AuCl2}2(2)](ClO4)2, [PdCl2(3)] and [{PdCl2}2(2)]. The complexes have been evaluated for their antripoliferative properties in human ovarian cancer cells sensitive and resistant to cisplatin (A2780S/R), in human breast cancer cells (MCF7) and in a non-tumorigenic human embryonic kidney cell line (HEK-293T). The highly cytotoxic trimetallic derivatives M2Fe (M = Au, Pd) are more cytotoxic to cancer cells than their corresponding monometallic fragments. Moreover, these complexes were significantly more cytotoxic than cisplatin in the resistant A2780R and the MCF7 cell lines. Studies of the interactions of the trimetallic compounds with DNA and the zinc-finger protein PARP-1 indicate that they exert anticancer effects in vitro based on different mechanisms of actions with respect to cisplatin.
The development of efficient catalytic methods to cleave the relatively unreactive C-O bonds of ethers remains an important challenge in catalysis. Building on our group's recent work, we report the dehydroaryloxylation of aryl alkyl ethers using pincer iridium catalysts. This method represents a rare fully atom-economical method for ether C-O bond cleavage.
We present a simple
linear model for ranking the drop weight impact
sensitivity of organic explosives that is based explicitly on chemical
kinetics. The model is parameterized to specific heats of explosion, Q, and Arrhenius kinetics for the onset of chemical reactions
that are obtained from gas-phase Born-Oppenheimer molecular dynamics
simulations for a chemically diverse set of 24 molecules. Reactive
molecular dynamics simulations sample all possible decomposition pathways
of the molecules with the appropriate probabilities to provide an
effective reaction barrier. In addition, the calculations of effective
trigger linkage kinetics can be accomplished without prior physical
intuition of the most likely decomposition pathways. We found that
the specific heat of explosion tends to reduce the effective barrier
for decomposition in accordance with the Bell-Evans-Polanyi principle,
which accounts naturally for the well-known correlations between explosive
performance and sensitivity. Our model indicates that sensitive explosives
derive their properties from a combination of weak trigger linkages
that react at relatively low temperatures and large specific heats
of explosion that further reduce the effective activation energy.
Aryl alkyl ethers, which are widely used throughout the chemical industry, are typically produced via the Williamson ether synthesis. Olefin hydroaryloxylation potentially offers a much more atom-economical alternative. Known acidic catalysts for hydroaryloxylation, however, afford very poor selectivity. We report the organometallic-catalyzed intermolecular hydroaryloxylation of unactivated olefins by iridium "pincer" complexes. These catalysts do not operate via the hidden Brønsted acid pathway common to previously developed transition-metal-based catalysts. The reaction is proposed to proceed via olefin insertion into an iridium-alkoxide bond, followed by rate-determining C-H reductive elimination to yield the ether product. The reaction is highly chemo- and regioselective and offers a new approach to the atom-economical synthesis of industrially important ethers and, potentially, a wide range of other oxygenates.
The
selective functionalization of alkanes and alkyl groups is
a major goal of chemical catalysis. Toward this end, a bulky triphosphine
with a central secondary phosphino group, bis(2-di-t-butyl-phosphinophenyl)phosphine (tBuPHPP),
has been synthesized. When complexed to iridium, it adopts a meridional
(“pincer”) configuration. The secondary phosphino H
atom can undergo migration to iridium to give an anionic phosphido-based–pincer
(tBuPPP) complex. Stoichiometric reactions of the (tBuPPP)Ir complexes reflect a distribution of steric bulk around
the iridium center in which the coordination site trans to the phosphido
group is quite crowded; one coordination site cis to the phosphido
is even more crowded; and the remaining site is particularly open.
The (tBuPPP)Ir precursors are the most active catalysts
reported to date for dehydrogenation of n-alkanes,
by about 2 orders of magnitude. The electronic properties of the iridium
center are similar to that of well-known analogous (RPCP)Ir
catalysts. Accordingly, DFT calculations predict that (tBuPPP)Ir and (tBuPCP)Ir are, intrinsically, comparably active
for alkane dehydrogenation. While dehydrogenation by (RPCP)Ir proceeds through an intermediate trans-(PCP)IrH2(alkene), (tBuPPP)Ir follows a pathway proceeding
via cis-(PPP)IrH2(alkene), thereby circumventing
unfavorable placement of the alkene at the bulky site trans to phosphorus.
(tBuPPP)Ir and (tBuPCP)Ir, however, have analogous
resting states: square planar (pincer)Ir(alkene). Alkene coordination
at the crowded trans site is therefore unavoidable in the resting
states. Thus, the resting state of the (tBuPPP)Ir catalyst
is destabilized by the architecture of the ligand, and this is largely
responsible for its unusually high catalytic activity.
Understanding the factors that affect explosive sensitivity is paramount to the safe handling and development of new explosives molecules. Erythritol tetranitrate (ETN) is an explosive that recently has attracted significant attention in the explosives community because of its ease of synthesis and physical properties. Herein, we report the synthesis of ETN derivatives using azide, nitramine, and nitrate ester functional groups. Impact, spark, and friction sensitivity measurements, computationally calculated explosive properties, and the crystal structure analysis of the ETN derivatives are reported. Mixing explosive functional groups led to changes in the explosive sensitivity, explosive performance as well as physical properties including melting point and physical state at room temperature. Overall, we have demonstrated that combining functional groups can enable the tuning of explosive and physical properties of a molecule. This tunability can potentially aid in the development of new explosives in which characteristics are varied to meet certain specifications.
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