Rhenium(V) Dioxo Complexes with Dihydrobis(pyrazolyl)borates:  Synthesis and Reactivity toward Electrophilic Substrates

Abstract

The compounds trans,trans-[ReO2(py)4][ReO2{H2B(pz*)2}2] (pz* = pz (1), 3,5-Me2pz (2)) have been prepared by reacting trans-[ReO2(py)4]Cl with the corresponding dihydrobis(pyrazolyl)borate. Compounds 1 and 2 react with electrophilic substrates, such as ClXMe3 (X = Si, Sn), leading to the neutral monoxo derivatives [ReO(OSiMe3){H2B(pz*)2}2] (pz* = pz (3), 3,5-Me2pz (4)) and [ReO(OSnMe3){H2B(pz)2}2] (5) and regenerating trans-[ReO2(py)4]Cl. Compounds 1 and 3 crystallize from dichloromethane/n-hexane as yellow crystals, with one molecule of solvated CH2Cl2 in the case of 1. Crystallographic data: 1, triclinic space group P1̄, a = 9.419(1) Å, b = 9.584(1) Å, c = 12.652(1) Å, α = 89.03(1)°, β = 82.41(1)°, γ = 72.75(1)°, V = 1080.9(2) Å3, Z = 2; 3, monoclinic space group P21/n, a = 10.785(2) Å, b = 17.680(2) Å, c = 11.971(2) Å, β = 98.67(1)°, V = 2256.5(6) Å3, Z = 4.

Re and Tc Complexes Containing B−H···M Agostic Interactions as Building Blocks for the Design of Radiopharmaceuticals

“…Dihydrobis(2-mercapto-1-methylimidazolyl)borate ([H 2 B(tim Me ) 2 ] - 3 ) (we use the abbreviation tim Me , from the term “thioimidazolyl”, to represent the 2−mercapto-1-methylimidazolyl fragment) can provide a bidentate or tridentate facial coordination geometry, including the two thione sulfurs and one agostic hydrogen . The ligand 3 can be considered as the soft congener of dihydrobis(pyrazolyl)borate, (H 2 B(pz) 2 - ), which has been largely used in organometallic and coordination chemistry. − Contrastingly, the coordination chemistry described for poly(thioimidazolyl)borates such as 3 is quite limited and is restricted, to our knowledge, to a few complexes of late transition metals …”

Uranyl Oxo Silylation Promoted by Silsesquioxane Coordination

“…To further support our proposed mechanism, we note that oxo silylation is a well-established transformation. − Moreover, HN­(SiMe 3 ) 2 is well known to act as a [SiMe 3 ] + source. − With that said, unactivated uranyl is not known to undergo silylation with such a weakly electrophilic silyl source, suggesting that the coordination of the tripodal silsesquioxane ligand to the uranyl ion activates the uranyl ion toward oxo silylation. This activation may be a consequence of some O yl –U–O yl bending upon ligation of the silsesquioxane, which increases the O yl nucleophilicity. − In this regard, the reaction of the tripodal TREN ligand, [Li] 3 [N­(CH 2 CH 2 NR) 3 ] (R = Si t BuMe 2 ), with uranyl resulted in the isolation of an oxo substitution product, [{UO­(μ-NCH 2 CH 2 N­(CH 2 CH 2 NR) 2 )} 2 ] − , which was hypothesized to form via a reactive cis -uranyl intermediate .…”

Cationic Re(V) Oxo Complexes with Poly(pyrazolyl)borates: Synthesis, Characterization, and Stability

“…The ReO bond distance in 3 (1.620(14) Å) is relatively short and is at the low end of the range (1.65−1.70 Å), − found for neutral mono-oxo Re(V) complexes with tetrakis(pyrazolyl)borate. All of the other metrical parameters obtained for the structure of 3 are unexceptional compared to the ones obtained for other rhenium(V) mono-oxo complexes containing [η 2 -B(pz) 4 ] - , other rhenium(V) oxosiloxides, or other Re(V) complexes containing diphosphine ligands. − ,, ,, …”

“…These results clearly show that the presence of σ-donor coligands influences the reactivity of the unity “ReO 2 {B(pz) 4 }”, apparently increasing the nucleophilicity of the oxo ligands. The oxosiloxide derivatives ( 1 − 4 ) described in this work have been prepared by a method similar to the one that we have previously used to prepare the neutral compounds [ReO(OSiMe 3 ){H 2 B(pz*) 2 } 2 ] (pz* = pz, 3,5-Me 2 pz) . However, the stability of the previously described compounds [ReO(OSiMe 3 ){H 2 B(pz*) 2 } 2 ] (pz* = pz, 3,5-Me 2 pz) contrasts significantly with the reactivity found for the cationic complexes ( 1 − 4 ) described in this work.…”