Boranes as Lewis Bases and the Synthesis of Metallaboratranes

43395-B3
Boranes as Lewis Bases and the Synthesis of Metallaboratranes

Daniel Rabinovich, University of North Carolina (Charlotte)

The tris- and bis(mercaptoimidazolyl)borate ligand systems have been used to prepare the first examples of nickel mononitrosyl complexes supported by these sulfur-donor ligands, namely (Tm^R)Ni(NO) and (Bm^R)Ni(PPh₃)(NO). FT-IR spectroscopy studies indicate a considerable degree of backbonding from the metal centers to the NO groups, which suggests that these ligands are more electron releasing than their nitrogen-donor analogues, i.e., the poly(pyrazolyl)borates. The synthesis and characterization of the first Bm^R complexes of Cu(I), Ag(I), and Au(I), including phosphine and diphosphine derivatives, has been completed and will be published in due course. Similarly, the preparation of the first Bm^R compounds of indium and bismuth, including halide, dithiocarbamate and xanthate derivatives, and preliminary thermogravimetric analysis (TGA) studies suggesting they can be cleanly converted to the corresponding binary sulfides M₂S₃ (M = In, Bi) will be reported shortly.

We have also been involved in the synthesis of neutral bis(mercaptoimidazolyl)methanes (Bmm^R), ligands whose known coordination chemistry is limited to a few main group metal complexes and, more recently, a few compounds of rhenium, rhodium and silver. The first copper complexes with the Bmm^Me ligand have been synthesized, including (Bmm^Me)CuX and (Bmm^Me)Cu(PPh₃)X (X = Cl, Br, I) derivatives. The (Bmm^Me)CuX compounds cleanly react with bis(pyrazolyl)borate (Bp^RR') ligands (R = R' = H or Me) to produce the mixed-donor complexes (Bmm^Me)Cu(Bp^RR'). These neutral complexes contain unusual [CuS₂N₂] cores where both sulfur donor groups are heterocyclic thiones and, as such, are excellent structural models for the copper-binding site in methanobactin. An interesting lead(II) complex, [Pb₂(Bmm^Me)₅(OClO₃)](ClO₄)₃, which is the first dinuclear Bmm^Me species to be isolated, has also been reported.

The tert butyl amine adducts of the mono and bis(mercaptoimidazolyl)boranes B(mim^Me)_nH_3-n (n = 1, 2) have been prepared from Bu^tNH₂.BH₃ and methimazole (Hmim^Me). Similarly, the dimethylamine adduct of B(mim^Me)₃ has been prepared from methimazole and B(NMe₂)₃. Multiple attempts to obtain metallaboratrane complexes of cobalt, rhodium, iridium, and platinum –metals for which such species are known– remain elusive but we are currently exploring alternative routes that may yield the base-free borane B(mim^Me)₃, or at least a significantly more labile adduct thereof.

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Home > Reports Back to Table of Contents 43395-B3 Boranes as Lewis Bases and the Synthesis of Metallaboratranes Daniel Rabinovich, University of North Carolina (Charlotte) The tris- and bis(mercaptoimidazolyl)borate ligand systems have been used to prepare the first examples of nickel mononitrosyl complexes supported by these sulfur-donor ligands, namely (Tm^R)Ni(NO) and (Bm^R)Ni(PPh₃)(NO). FT-IR spectroscopy studies indicate a considerable degree of backbonding from the metal centers to the NO groups, which suggests that these ligands are more electron releasing than their nitrogen-donor analogues, i.e., the poly(pyrazolyl)borates. The synthesis and characterization of the first Bm^R complexes of Cu(I), Ag(I), and Au(I), including phosphine and diphosphine derivatives, has been completed and will be published in due course. Similarly, the preparation of the first Bm^R compounds of indium and bismuth, including halide, dithiocarbamate and xanthate derivatives, and preliminary thermogravimetric analysis (TGA) studies suggesting they can be cleanly converted to the corresponding binary sulfides M₂S₃ (M = In, Bi) will be reported shortly. We have also been involved in the synthesis of neutral bis(mercaptoimidazolyl)methanes (Bmm^R), ligands whose known coordination chemistry is limited to a few main group metal complexes and, more recently, a few compounds of rhenium, rhodium and silver. The first copper complexes with the Bmm^Me ligand have been synthesized, including (Bmm^Me)CuX and (Bmm^Me)Cu(PPh₃)X (X = Cl, Br, I) derivatives. The (Bmm^Me)CuX compounds cleanly react with bis(pyrazolyl)borate (Bp^RR') ligands (R = R' = H or Me) to produce the mixed-donor complexes (Bmm^Me)Cu(Bp^RR'). These neutral complexes contain unusual [CuS₂N₂] cores where both sulfur donor groups are heterocyclic thiones and, as such, are excellent structural models for the copper-binding site in methanobactin. An interesting lead(II) complex, [Pb₂(Bmm^Me)₅(OClO₃)](ClO₄)₃, which is the first dinuclear Bmm^Me species to be isolated, has also been reported. The tert butyl amine adducts of the mono and bis(mercaptoimidazolyl)boranes B(mim^Me)_nH_3-n (n = 1, 2) have been prepared from Bu^tNH₂.BH₃ and methimazole (Hmim^Me). Similarly, the dimethylamine adduct of B(mim^Me)₃ has been prepared from methimazole and B(NMe₂)₃. Multiple attempts to obtain metallaboratrane complexes of cobalt, rhodium, iridium, and platinum –metals for which such species are known– remain elusive but we are currently exploring alternative routes that may yield the base-free borane B(mim^Me)₃, or at least a significantly more labile adduct thereof. Back to top Terms of Use Security Privacy Contact Copyright © 2008 American Chemical Society

43395-B3 Boranes as Lewis Bases and the Synthesis of Metallaboratranes

43395-B3
Boranes as Lewis Bases and the Synthesis of Metallaboratranes