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Neutral and Cationic Complexes of Silicon(IV) Halides with Phosphine Ligands.

ABSTRACT: The reaction of SiI₄ and PMe₃ in n-hexane produced the yellow salt, [SiI₃(PMe₃)₂]I, confirmed from its X-ray structure, containing a trigonal bipyramidal cation with trans-phosphines. This contrasts with the six-coordination found in (the known) trans-[SiX₄(PMe₃)₂] (X = Cl, Br) complexes. The diphosphines o-C₆H₄(PMe₂)₂ and Et₂P(CH₂)₂PEt₂ form six-coordinate cis-[SiI₄(diphosphine)], which were also characterized by X-ray crystallography, multinuclear NMR, and IR spectroscopy. Reaction of trans-[SiX₄(PMe₃)₂] (X = Cl, Br) with Na[BAr^F] (BAr^F = [B{3,5-(CF₃)₂C₆H₃}₄]) produced five-coordinate [SiX₃(PMe₃)₂][BAr^F], but while Me₃SiO₃SCF₃ also abstracted chloride from trans-[SiCl₄(PMe₃)₂], the reaction products were six-coordinate complexes [SiCl₃(PMe₃)₂(OTf)] and [SiCl₂(PMe₃)₂(OTf)₂] with the triflate coordinated. X-ray crystal structures were obtained for [SiCl₃(PMe₃)₂][BAr^F] and [SiCl₂(PMe₃)₂(OTf)₂]. The charge distribution across the silicon species was also examined by natural bond orbital (NBO) analyses of the computed density functional theory (DFT) wavefunctions. For the [SiX₄(PMe₃)₂] and [SiX₃(PMe₃)₂]⁺ complexes, the positive charge on Si decreases and the negative charge on X decreases going from X = F to X = I. Upon going from [SiX₄(PMe₃)₂] to [SiX₃(PMe₃)₂]⁺, i.e., removal of X^-, there is an increase in positive charge on Si and a decrease in negative charge on the X centers (except for the case X = F). The positive charge on P shows a slight decrease.

SUBMITTER: King RP

PROVIDER: S-EPMC9597660 | biostudies-literature | 2022 Oct

REPOSITORIES: biostudies-literature

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Neutral and Cationic Complexes of Silicon(IV) Halides with Phosphine Ligands.

King Rhys P RP Dyke John M JM Levason William W Reid Gillian G

Inorganic chemistry 20221012 42

The reaction of SiI4 and PMe3 in n-hexane produced the yellow salt, [SiI3(PMe3)2]I, confirmed from its X-ray structure, containing a trigonal bipyramidal cation with trans-phosphines. This contrasts with the six-coordination found in (the known) trans-[SiX4(PMe3)2] (X = Cl, Br) complexes. The diphosphines o-C6H4(PMe2)2 and Et2P ...[more]

PMID: 36222839

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Project description:Copper(I) imidate and amidate complexes of chelating N,N-donor ligands, which are proposed intermediates in copper-catalyzed amidations of aryl halides, have been synthesized and characterized by X-ray diffraction and detailed solution-phase methods. In some cases, the complexes adopt neutral, three-coordinate trigonal planar structures in the solid state, but in other cases they adopt an ionic form consisting of an L 2Cu (+) cation and a CuX 2 (-) anion. A tetraalkylammonium salt of the CuX 2 (-) anion in which X = phthalimidate was also isolated. Conductivity measurements and (1)H NMR spectra of mixtures of two complexes all indicate that the complexes exist predominantly in the ionic form in DMSO and DMF solutions. One complex was sufficiently soluble for conductance measurements in less polar solvents and was shown to adopt some degree of the ionic form in THF and predominantly the neutral form in benzene. The complexes containing dative nitrogen ligands reacted with iodoarenes and bromoarenes to form products from C-N coupling, but the ammonium salt of [Cu(phth) 2] (-) did not. Similar selectivities for stoichiometric and catalytic reactions with two different iodoarenes and faster rates for the stoichiometric reactions implied that the isolated amidate and imidate complexes are intermediates in the reactions of amides and imides with haloarenes catalyzed by copper complexes containing dative N,N ligands. These amidates and imidates reacted much more slowly with chloroarenes, including chloroarenes that possess more favorable reduction potentials than some bromoarenes and that are known to undergo fast dissociation of chloride from the chloroarene radical anion. The reaction of o-(allyloxy)iodobenzene with [(phen) 2Cu][Cu(pyrr) 2] results in formation of the C-N coupled product in high yield and no detectable amount of the 3-methyl-2,3-dihydrobenzofuran or 3-methylene-2,3-dihydrobenzofuran products that would be expected from a reaction that generated free radicals. These data and computed reaction barriers argue against mechanisms in which the haloarene reacts with a two-coordinate anionic copper species and mechanisms that start with electron transfer to generate a free iodoarene radical anion. Instead, these data are more consistent with mechanisms involving cleavage of the carbon-halogen bond within the coordination sphere of the metal.

Dataset Information

Neutral and Cationic Complexes of Silicon(IV) Halides with Phosphine Ligands.

Publications

Neutral and Cationic Complexes of Silicon(IV) Halides with Phosphine Ligands.

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