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Synthesis and Structural Characterization of Phosphine-Borane-Stabilized Dicarbanions with either Rigid or Flexible Spacers

Lookup NU author(s): Dr Keith Izod, Dr Casey Dixon, Dr Ross Harrington, Dr Ulrich Baisch

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Abstract

The reaction between 1,2-C6H4(CH2CO2 and 2 equiv of in situ generated [R2P(BH3)]Li in THF gives the corresponding o-phenylene-bridged bis(phosphine-boranes) 1,2-C6H4{CH2P(BH3)R-2}(2) (R = iPr (1a), Ph (2a), Cy (3a)). Treatment of 1a-3a with 2 equiv of nBuLi and 2 equiv of tmeda yields the corresponding phosphine boranestabilized carbanion (PBC) complexes [1,2-C6H4{CHP(BH3)R-2}(2)][Li(tmeda)](2).nL (R = iPr, n = 0 (lb); R = Ph, nL THF (2b); R = Cy, nL = 2PhCH(3) (3b)). In contrast, treatment of la with 2 equiv of MeK, followed by 2 equiv of pmdeta, yields the monodeprotonation product [1,2-C6F14{CHP(BH3)iPr(2)}{CH2P(BH3)iPr(2)}][K(pmdeta)] (lc), due to a competing side reaction with the solvent. Treatment of la and 3a with the less aggressive metalating agent PhCH2K gives the corresponding dipotassium salts, the latter of which was isolated as the adduct [1,2-C6H4{CHP(BH3)Cy-2}(2)][K(pmdeta)]2 (3c). X-ray crystallography reveals that lb-3b adopt similar structures in which the lithium ions are coordinated by the carbanion centers and the borane hydrogen atoms of the phosphine borane-stabilized carbanions. The potassium ion in lc is coordinated by the carbanion center and by B-H center dot center dot center dot K contacts with both borane groups, whereas the two potassium ions in 3c exhibit multihapto interactions with the aromatic ring of the PBC ligand, along with B H.-K contacts. The reaction between CISiMe2CH2CH2SiMe2C1 and 2 equiv of in situ generated [R2P(BH3)CH2]Li gives the bis(phosphine boranes) [CH2SiMe2CH2P(BH3)R-2}(2) (R = Me (4a), Ph (5a)). Treatment of 4a or 5a with 2 equiv of nBuLi in THF readily yields the 1,6-dicarbanion complexes [CH2SiMe2CHP(BH3)R-2](2)[Li(THF)(2)](2) (R = Me (4b), Ph (5b)). A similar reaction of 5a, 2 equiv of PhCH2K, and 2 equiv of pmdeta in THF gives the potassium complex [CH2SiMe2CHP(BH3)Ph-2](2)[K(pmdeta)](2) (Sc). Complex 5b adopts a linear structure in the solid state, while Sc adopts an unusual polycyclic structure by virtue of bridging K center dot center dot center dot H B H center dot center dot center dot K contacts.

Publication metadata

Author(s): Izod K, Dixon CM, McMeekin E, Rodgers L, Harrington RW, Baisch U

Publication type: Article

Publication status: Published

Journal: Organometallics

Year: 2014

Volume: 33

Issue: 1

Pages: 378-386

Print publication date: 13/01/2014

Online publication date: 19/12/2013

Acceptance date: 17/11/2013

ISSN (print): 0276-7333

ISSN (electronic): 1520-6041

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/om4011142

DOI: 10.1021/om4011142

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