Thorium- and Uranium-Mediated C–H Activation of a Silyl-Substituted Cyclobutadienyl Ligand

Abstract

Cyclobutadienyl complexes of the f-elements are a relatively new yet poorly understood class of sandwich and half-sandwich organometallic compounds. We now describe cyclobutadienyl transfer reactions of the magnesium reagent [(η4-Cb'''')Mg(THF)3] (1), where Cb'''' is tetrakis(trimethylsilyl)cyclobutadienyl, toward thorium(IV) and uranium(IV) tetrachlorides. The 1:1 stoichiometric reactions between 1 and AnCl4 proceed with intact transfer of Cb'''' to give the half-sandwich complexes [(η4-Cb'''')AnCl(μ-Cl)3Mg(THF)3] (An = Th, 2; An = U, 3). Using a 2:1 reaction stoichiometry produces [Mg2Cl3(THF)6][(η4-Cb'''')An(η3-C4H(SiMe3)3-κ-(CH2SiMe2)(Cl)] (An = Th, [Mg2Cl3(THF)6][4]; An = U [Mg2Cl3(THF)6][5]), in which one Cb'''' ligand has undergone cyclometalation of a trimethylsilyl group, resulting in the formation of an An–C σ-bond, protonation of the four-membered ring, and an η3-allylic interaction with the actinide. Complex solution-phase dynamics are observed with multinuclear nuclear magnetic resonance spectroscopy for both sandwich complexes. A computational analysis of the reaction mechanism leading to the formation of 4 and 5 indicates that the cyclobutadienyl ligands undergo C–H activation across the actinide center.

Phenylsilyl-Substituted Tetramethylcyclopentadienide Uranium Chemistry: Magnesocenes vs Grignard Reagents

“…Incorporation of Mg into actinide chloride organometallic complexes has been observed previously in structures such as {(C 5 Me 5 )­U­[μ-(CH 2 )­PPh 2 (CH 2 )]} 2 Mg­[CH 2 PMePh 2 ] 2 (μ-Cl) 2 (μ-O)­(μ 3 -O), {[(C 8 H 8 )­U] 2 [Mg­(THF) 4 ]­[U­(THF)] 2 (μ-NPh) 6 (μ-Cl) 2 } n , and [η 4 -C 4 (SiMe 3 ) 4 ]­AnCl­(μ-Cl) 3 Mg­(THF) 3 (An = U, Th) . In addition, a thorium analogue of 6 with the C 5 H 2 t Bu 3 cyclopentadienyl ligand was previously reported …”

“…Incorporation of Mg into actinide chloride organometallic complexes has been observed previously in structures such as 45 and [η 4 -C 4 (SiMe 3 ) 4 ]AnCl(μ-Cl) 3 Mg-(THF) 3 (An = U, Th). 46 In addition, a thorium analogue of 6 with the C 5 H 2 t Bu 3 cyclopentadienyl ligand was previously reported. 47 Complex 6 crystallizes in the P1̅ space group as a centrosymmetric dimer with three molecules of toluene in the unit cell.…”

Pyramidanes: newcomers to the anti-van’t Hoff–Le Bel family

“…(3) cyclobutadiene complexes of f-block elements (lanthanides and actinides). However, if numerous cyclobutadiene complexes of the elements of s-block (including tetrasila-and tetragermacyclobutadiene analogues), [33][34][35][36][37][38] d-block (including tetrasila-and tetragermacyclobutadiene analogues), 37,[39][40][41][42][43][44][45][46][47] and f-block [48][49][50][51][52][53][54][55][56][57][58][59] were reported, cyclobutadiene complexes of the p-block elements, which are commonly known as ''pyramidanes'', were without precedents until recently. 60 According to Wade's rule, 61 for the parent unsubstituted pyramidane C[C 4 H 4 ] 4n-cluster rule is to be applied.…”

“…In general, given the peculiar nature of the apical atom, one can discriminate four different types of such complexes: (1) cyclobutadiene complexes of the main group elements: s-block elements (alkali and alkaline earth metals) and p-block elements, (2) cyclobutadiene complexes of d-block elements (transition metals); (3) cyclobutadiene complexes of f-block elements (lanthanides and actinides). However, if numerous cyclobutadiene complexes of the elements of s-block (including tetrasila- and tetragermacyclobutadiene analogues), 33–38 d-block (including tetrasila- and tetragermacyclobutadiene analogues), 37,39–47 and f-block 48–59 were reported, cyclobutadiene complexes of the p-block elements, which are commonly known as “pyramidanes”, were without precedents until recently. 60…”