2 research outputs found
Utilizing the 8‑Methoxycyclooct-4-en-1-ide Unit As a Hydrogen Atom Acceptor en Route to “Metal–Borane Pincers”
The synthesis and characterization of palladium and platinum
complexes
containing the neutral ligand HBÂ(mp)<sub>2</sub> (where mp = 2-mercaptopyridyl)
are presented. Addition of 2 equiv of NaÂ[H<sub>2</sub>BÂ(mp)<sub>2</sub>] to [MÂ(Cl)Â(COE<sup>OMe</sup>)]<sub>2</sub> (where M = Pt, Pd; COE<sup>OMe</sup> = 8-methoxycyclooct-4-en-1-ide) in the presence of 2 equiv
of PPh<sub>3</sub> leads to the formation of the metal–borane
pincer complexes [PtÂ{Îş<sup>3</sup><i>SBS</i>-HBÂ(mp)<sub>2</sub>}Â(PPh<sub>3</sub>)] and [PdÂ{Îş<sup>3</sup><i>SBS</i>-HBÂ(mp)<sub>2</sub>}Â(PPh<sub>3</sub>)]. In these reactions, a hydrogen
migration reaction occurs from the borohydride ligand to the metal
center, eventually leading to the elimination of the COE<sup>OMe</sup> unit from the metal center. X-ray crystallographic characterization
of the two isostructural complexes reveals a rare <i>mer</i>-κ<sup>3</sup><i>S</i>,<i>B</i>,<i>S</i> coordination mode with short platinum– and palladium–boron
distances: 2.098(4) and 2.091(3) Ă…, respectively (the shorter
distances of two independent complexes in the unit cells of both structures).
The complexes [PdÂ{Îş<sup>3</sup><i>S</i>,<i>B</i>,<i>S</i>-HBÂ(mp)<sub>2</sub>}Â(PPh<sub>3</sub>)] and [PtÂ{Îş<sup>3</sup><i>S</i>,<i>B</i>,<i>S</i>-HBÂ(mp)<sub>2</sub>}Â(PPh<sub>3</sub>)] are the first examples of metal–borane
complexes featuring a pincer-type coordination where one hydrogen
substituent remains at the boron center
Silver and Palladium Complexes Containing Ditopic N‑Heterocyclic Carbene–Thione Ligands
The mixed donor N-heterocyclic carbene (NHC)/thione ligand
precursors [1-(3-R-2<i>H</i>-imidazol-1-yl-2-thione)Âmethyl-3-R-2<i>H</i>-imidazol-2-ium]ÂX, [H<b>CS</b><sup><b>R</b></sup>]ÂX (R = methyl, benzyl; X = Br, I), have been utilized to prepare
a range of silver and palladium complexes. The coordination of <b>CS</b><sup><b>R</b></sup> to silverÂ(I) salts has been explored,
providing dimeric complexes of the type [AgXÂ(<b>CS</b><sup><b>R</b></sup>)]<sub>2</sub> (where R = methyl, benzyl; X = Br, I).
Structural characterization of [AgXÂ(<b>CS</b><sup><b>Bn</b></sup>)]<sub>2</sub> revealed a bidentate coordination mode for the
mixed donor ligand and dinuclear structures where the silver centers
are bridged by two bromido centers. Palladium complexes bearing one
or two <b>CS</b><sup><b>R</b></sup> ligands have additionally
been prepared either directly, utilizing [PdÂ(OAc)<sub>2</sub>] as
precursor, or via transmetalation strategies. The dicationic complexes
[PdÂ(<b>CS</b><sup><b>R</b></sup>)<sub>2</sub>]Â[X]<sub>2</sub> and neutral complexes [PdX<sub>2</sub>(<b>CS</b><sup><b>R</b></sup>)] (where R = methyl, benzyl; X = Br, I, PF<sub>6</sub>) have been synthesized and fully characterized. The <b>CS</b><sup><b>R</b></sup> ligand in the aforementioned complexes
does not undergo transformation of the NHC unit to a urea function,
which had been found to occur in the previously reported copper complexes.
Palladium complexes containing both NHC/thione and bis-phosphine ligands
were also prepared. Complexes of the type [PdÂ(<b>CS</b><sup><b>Me</b></sup>)Â(L<sub>2</sub>)]Â[X]<sub>2</sub> and [PdXÂ(<b>CS</b><sup><b>Me</b></sup>)Â(L<sub>2</sub>)]Â[X] (where L<sub>2</sub> = dppe, dppp; X = Br, OAc, I, PF<sub>6</sub>) were obtained.
The presence of the bis-phosphine appears to destabilize the coordination
of the NHC/thione ligand and as a consequence leads to its elimination
from the complex