- Formation of a hydride containing amido-zincate using pinacolborane
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Amido-zincates containing hydrides are underexplored yet potentially useful complexes. Attempts to access this type of zincate through combining amido-organo zincates and pinacolborane (HBPin)viaZn-C/H-BPin exchange led instead to preferential formation of amide-BPin and/or [amide-BPin(Y)]?(Y = Ph, amide, H), when the amide is hexamethyldisilazide or 2,2,6,6-tetramethylpiperidide and the hydrocarbyl group was phenyl or ethyl. In contrast, the use of a dipyridylamide (dpa) based arylzinc complex led to Zn-C/H-BPin metathesis being the major outcome. Independent synthesis and full characterisation of two LnLi[(dpa)ZnPh2] (L = THF,n= 3; L = PMDETA,n= 1) complexes,1and3, respectively, enabled reactivity studies that demonstrated that these species display zincate type reactivity (by comparison to the lower reactivity of the neutral complex (Me-dpa)ZnPh2,4, Me-dpa = 2,2′-dipyridyl-N-methylamine). This included1performing the rapid deprotonation of 4-ethynyltoluene and also phenyl transfer to α,α,α-trifluoroacetophenone in contrast to neutral complex4. Complex1reacted with one equivalent of HBPin to give predominantly PhBPin (ca.90%) and a lithium amidophenylzincate containing a hydride unit, complex7-A, as the major zinc containing product. Complex7-Atransfers hydride to an electrophile preferentially over phenyl, indicating it reacts as a hydridozincate. Attempts to react1with >1 equivalent of HBPin or with catecholborane led to more complex outcomes, which included significant borane and dpaZn substituent scrambling, two examples of which were crystallographically characterised. While this work provides proof of principle for Zn-C/H-BPin exchange as a route to form an amido-zincate containing a hydride, amido-organozincates that undergo more selective Zn-C/H-BPin exchange still are required.
- Ingleson, Michael J.,Nichol, Gary S.,Uzelac, Marina,Yuan, Kang
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p. 14018 - 14026
(2021/10/19)
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- β-Oxo-δ-diimine Nickel Complexes: A Comparison of Tautomeric Active Species in Ethylene Polymerization Catalysis
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A series of mono- and bimetallic Ni alkyl complexes of a β-oxo-δ-diimine (BODDI) ligand are reported. The monometallic complexes have a second binding pocket, of which the free "arm" can exist as either an enamine (e.g., 8, BODEI, β-oxo-δ-enamineiminato) or imine (e.g., 3, BODII, β-oxo-δ-imineiminato) tautomer. The identity of the tautomer in the secondary Ni coordination sphere has a significant effect on ethylene polymerization behavior: the enamine tautomer, which hydrogen bonds to the central O atom and is in conjugation with the N,O backbone chelate, is significantly more electron rich and yields a much lower molecular weight polymer than the imine tautomer, which rotates away from Ni to a distal position and has little effect on polymerization. Deprotonation of the second binding pocket with M(HMDS) (M = Li, Na, K) yields the Ni-alkali metal heterobimetallic complexes 3Li, 3Na, and 3K. The deprotonated alkali metal enamides display ethylene polymerization behavior similar to the neutral imine complex because the enamide arm can also distally rotate to minimize interaction with the Ni coordination sphere upon activation.
- Chiu, Hsin-Chun,Pearce, Adam J.,Dunn, Peter L.,Cramer, Christopher J.,Tonks, Ian A.
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supporting information
p. 2076 - 2085
(2016/07/07)
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- Elimination of butylcycloheptylprodigiosin as a known natural product inspired by an evolutionary hypothesis for cyclic prodigiosin biosynthesis
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The cyclic prodigiosins are an important family of bioactive natural products that continue to be the subject of numerous structural, synthetic, and biosynthetic studies. In particular, the structural assignments of the isomeric cyclic prodigiosins butylcycloheptylprodigiosin (BCHP) and streptorubin B have been the cause of significant confusion. Herein, we report detailed studies regarding the electron impact (EI) mass spectra of synthetic BCHP and streptorubin B that have allowed us to distinguish the two compounds in the absence of quality historical isolation NMR data. On the basis of these fragmentation differences, the status of BCHP as a natural product is challenged. The proposed mechanism of fragmentation is supported by the EI mass spectra of synthetic pentyl-chain analogues of BCHP and streptorubin B, X-ray crystallography, and DFT calculations. Elimination of BCHP from the prodigiosin family supports a proposed evolutionary hypothesis for the surprising biosynthesis of cyclic prodigiosins.
- Jones, Brian T.,Hu, Dennis X.,Savoie, Brett M.,Thomson, Regan J.
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p. 1937 - 1945
(2013/11/19)
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- Crystalline 10,10-Bis((2-fluoro-4-pyridinyl)methyl)-9(10H)-Anthracenone and an improved process for preparing the same
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The present invention relates to processes for the synthesis of a crystalline polymorph of 10,10-Bis((2-fluoro-4-pyridinyl)methyl)-9(10H)-Anthracenone in high purity. The product is useful in the synthesis of pharmaceutical compounds for the reduction of cholinergic system dysfunction.
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- Tetrasubstituted Tetrazenes (Me3E)2N-N=N-N(EMe3)2 (E = Si, Ge, Sn): Reactivity
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By substitution of the silyl, germyl, or stannyl groups, (Me3Si)2N-N=N-N(SiMe3)2 (1) reacts with variable amounts of trifluoroacetic acid to form (Me3Si)4-nN4Hn, (Me3Ge)2N-N=N-N(GeMe)2 (2) with variable amounts of methanol to form (Me3Ge)4-nN4Hn, and (Me3Sn)2N-N=N-N(SnMe3)2 (3) with variable amounts of trimethylchlorosilane to give (Me3Sn)4-nN4(SiMe3)n (n = 1-4).The reaction of 1 with benzenesulfonyl isocyanate leads by substitution and cyclization to silylated 5-hydroxytetrazole 12.Substitution in connection with thermolysis of the substitution products formed is found in the reaction of 1 with methanol, aluminium chloride, or nitrosyl chloride and in the reaction of 3 with trimethylstannane, acetone, or nitrosobenzene.By oxidation of 1 with chlorine, bromine, or p-benzoquinone and of 3 with p-benzoquinone or oxygen, all tetrazene nitrogen is envolved.The reduction of 1 with hydrogen or alkali metals leads to nitrogen and (Me3Si)2NH or (Me3Si)2NM.
- Wiberg, Nils,Bayer, Heiner,Vasisht, Sham Kumar,Meyers, Rene
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p. 2916 - 2927
(2007/10/02)
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