We present the results of a multi-year study of the high-amplitude δ Scuti (HADS) star GSC 03144-595. The star was observed between June and September in 2011 and 2014 for 13 nights and 28 nights, respectively. Based on our results, we argue that GSC 03144-595 is a new triple-mode radially pulsating HADS, only the fifth discovered and only the second that has a fundamental frequency in the traditional δ Scuti regime. While the frequencies and amplitudes of the fundamental and first harmonic were found to be unchanged between 2011 and 2014, we found that the amplitude of the second harmonic increased by 44%, a form of evolution not previously seen. This finding suggests that the second harmonic may be transient, thus explaining the scarcity of triple-mode HADS stars.
We
describe the template-free synthesis of the bis(pyridine-dienamine)
proligand [4,5-(m-xylylenediamine)NH–C(CH)(9-butyl-octahydroacridine)]2 (2′), a variant of Burrows’s macrocyclic
bis(pyridine-diimine) (bis-PDI) ligand [2,6-(m-xylylenediamine)NC(py)]2 (A), using octahydroacridine as the ligand backbone.
The octahydroacridine backbone favors macrocyclization by constraining
the PDI units in the (s-cis)2 conformation.
The template-free synthesis of 2′ enables facile
access to a wide array of bis-PDI and bis(pyridine-dienamido) (bis-PDE)
metal complexes. Five-coordinate binuclear bis-PDI (2)M2Cl4 complexes {2 = [4,5-(m-xylylenediamine)NC(9-butyl-octahydroacridine)]2; M = Zn, Co, or Fe} and a four-coordinate bis-PDI [(2)Pd2Br2][B(3,5-(CF3)2-Ph)4]2 complex were synthesized and
characterized. (2)Zn2Cl4 undergoes
macrocyclic ring inversion on the nuclear magnetic resonance (NMR)
time scale with a free energy barrier ΔG
⧧ of 15.5(3) kcal/mol at 295 K. In contrast, (2)Fe2Cl4 and (2)Co2Cl4 undergo slow ring inversion on the NMR chemical
shift time scale at 295 K. The amine elimination reaction of 2′ with Zr(NMe2)4 yields the
bis-PDE complex (2′-4H)Zr2(NMe2)4, which was alkylated with AlMe3 and
Al(CH2SiMe3)3 to generate (2′-4H)Zr2Me4 and (2′-4H)Zr2(CH2SiMe3)2(NMe2)2, respectively.
The synthesis and
ethylene reactivity of a new family of dinuclear Co2Br4 and Fe2Br4 complexes supported by binucleating
macrocyclic bis(pyridine-diimine) (PDI) ligands that contain 4,4″-R2-3,3″-o-terphenyl linkers (1, R = H; 2, R = Me; 3, R = iPr) are described. In the solid state, (1–3)M2Br4 (M = Zn, Fe, Co) adopt C
s
-skew-syn structures in which the (PDI)M planes are skewed 49–82°
relative to each other and both middle rings of the o-terphenyl bridges are on the same side of the molecule. The metal–metal
distances range between 5.7600(8) and 6.232(1) Å. In solution,
(1)M2Br4 (M = Zn, Co, Fe) undergo
a fluxional process that permutes the two inequivalent (PDI)M units,
while (2)M2Br4 and (3)M2Br4 are static and adopt C
s
-symmetric structures similar to those
observed in the solid state. Activation of (2)Fe2Br4 and (3)Fe2Br4 with MMAO-12 or triisobutylaluminum (TIBA) in the presence of ethylene
generates catalysts that produce solid polyethylene (M
w
= 4500–280000 Da), which contrasts
with the reported production of α-olefins by analogous mononuclear
(PDI)FeCl2 catalysts. (3)Fe2Br4/TIBA and (3)Fe2Br4/MMAO-12
produce polyethylenes with broad molecular weight distributions (MWDs)
due to chain transfer to Al. (3)Co2Br4/1000 TIBA and (3)Co2Br4/1000 MMAO-12 also produce polyethylenes with broad MWDs. However,
in these cases chain transfer to Al is not operative and the broad
MWDs result from multisite behavior.
The
synthesis of the phosphine-arenesulfonate Pd(II) fluoride complex
(PO-OMe)PdF(lut) (2, PO-OMe = P(2-OMe-Ph)2(2-SO3-5-Me-Ph), lut = 2,6-lutidine) and its reactions
with electron-deficient olefins are described. The reaction of (PO-OMe)PdBr(lut)
(1) with AgF affords 2 as an 82:18 mixture
of cis-P,F and trans-P,F isomers. 2 isomerizes to a 1:2 cis-P,F:trans-P,F equilibrium mixture in CD2Cl2 solution
at room temperature in ca. 3 days. 2 reacts with vinyl
fluoride (VF) to afford (PO-OMe)Pd(CH2CHF2)(lut)
(3), which exists as the cis-P,C isomer. 2 reacts with
vinyl bromide (VBr) to yield 1 and VF by initial fluoropalladation
to form (PO-OMe)Pd(CH2CHBrF)(lut) (4, not
observed) followed by β-Br elimination. 2 reacts
with vinyl acetate to yield (PO-OMe)Pd{CH2CHF(OAc)}(lut)
(5), which reacts further to form the C-bound enolate
complex (PO-OMe)Pd{CH2C(O)H}(lut) (6) and acetyl fluoride. 2 reacts with vinyl benzoate
in an analogous fashion. DFT analysis of the reaction of the model
complexes cis-P,F- and trans-P,F-(PH2O)PdF(py) (C1 and C2, PH2O– = o-PH2C6H4SO3
–) with VF supports
a mechanism involving substitution of lutidine by VF followed by migratory
insertion into the Pd–F bond. An alternative mechanism comprising
substitution of fluoride by VF to generate (PO-OMe)Pd(VF)(lut)+ and F–, followed by exo attack of F– on the bound VF was found to be energetically prohibitive.
DFT analysis of the reaction of the model complexes cis-P,F- and trans-P,F-(PH2O)PdF(VBr)
(C10 and C13) supports an insertion/β-Br
elimination mechanism.
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