- Neutral and Anionic Monomeric Zirconium Imides Prepared via Selective C=N Bond Cleavage of a Multidentate and Sterically Demanding β-Diketiminato Ligand
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A sterically encumbering multidentate β-diketiminato ligand, tBuL2 (tBuL2=[ArNC(tBu)CHC(tBu)NCH2CH2N(Me)CH2CH2NMe2]?, Ar=2,6-iPr2C6H3), is reported in this study along with its coordination chemistry to zirconium(IV). Using the lithio salt of this ligand, Li(tBuL2) (4), the zirconium(IV) precursor (tBuL2)ZrCl3 (6) could be readily prepared in 85 % yield and structurally characterized. Reduction of 6 with 2 equiv of KC8 resulted in formation of the terminal and mononuclear zirconium imide-chloride [C(tBu)CHC(tBu)NCH2CH2N(Me)CH2CH2NMe2]Zr(=NAr)(Cl) (7) as the result of reductive C=N cleavage of the imino fragment in the multidentate ligand tBuL2 by an elusive ZrII species (tBuL2)ZrCl (A). The azabutadienyl ligand in 7 can be further reduced by 2 e? with KC8 to afford the anionic imide [K(THF)2]{[CH(tBu)CHC(tBu)NCH2CH2N(Me)CH2CH2N(Me)CH2]Zr=NAr} (8-2THF) in 42 % isolated yield. Complex 8-2THF results from the oxidative addition of an amine C?H bond followed by migration to the vinylic group of the formal [C(tBu)CHC(tBu)NCH2CH2N(Me)CH2CH2NMe2]? ligand in 7. All halides in 6 can be replaced with azides to afford (tBuL2)Zr(N3)3 (9) which was structurally characterized, and reduction with two equiv of KC8 also results in C=N bond cleavage of tBuL2 to form [C(tBu)CHC(tBu)NCH2CH2N(Me)CH2CH2NMe2]Zr(=NAr)(N3) (10), instead of the expected azide disproportionation to N3? and N2. Solid-state single crystal structural studies confirm the formation of mononuclear and terminal zirconium imido groups in 7, 8-Et2O, and 10 with Zr=NAr distances being 1.8776(10), 1.9505(15), and 1.881(3) ?, respectively.
- Kurogi, Takashi,Chu, Jiaxiang,Chen, Yaofeng,Mindiola, Daniel J.
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p. 2629 - 2638
(2019/07/04)
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- Sequence-Specific Osmium Reagents for Polynucleotides. 2. A Method for Thymine-Cytosine Pairs
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We have modified the dinucleoside monophosphate, deoxythymidylyldeoxycytidine (d-TpC), by replacement of the exocyclic amino group of cytosine with a series of ligands, H2N(CH2)nN(CH3)CH2CH2N(CH3)2, where n = 2, 4, and 6.The kinetics of the reactions of these modified dinucleoside monophosphates with osmium tetroxide were measured.The modified nucleotides react with osmium tetroxide 4200, 7900, and 1200 times faster than the unmodified species for n = 6, 4, and 2, respectively.The products of the reactions are macrocyclic oxoosmium (VI) esters for which 360-MHz proton NMR spectra are reported.
- Ford, H.,Chang, C.-H.,Behrman, E.J.
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p. 7773 - 7779
(2007/10/02)
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