RESUMO
The mixed-sandwich U(III) complexes [U(eta-C8H6{SiiPr(3)-1,4}2)(eta-CpR)(THF)] (R=Me5, Me4H) react with CO2 to give free CO and the U(IV) carbonate products [U(eta-C8H6{SiiPr(3)-1,4}2)(eta-CpR)]2(micro-eta1:eta2-CO3)]; the latter has been structurally characterised for R=Me4H; a 25% molar excess of the U(III) reductant gives a mixture of the carbonate and squarate [U(eta-C8H6{SiiPr(3)-1,4}2)(eta-C5Me4H)]2(micro-eta2:eta2-C4O4) products-the first synthesis of an oxocarbon from a CO2 carbon source.
RESUMO
The stoichiometric reaction of 1 equiv of CO with [(U(eta-C8H6{SiiPr3-1,4}2)(eta-Cp*)] affords the linear diuranium ynediolate complex [(U(eta-C8H6{SiiPr3-1,4}2)(eta-Cp*)]2(mu-eta1:eta1-C2O2) which does not react with further CO to give the deltate derivative [(U(eta-C8H6{SiiPr3-1,4}2)(eta-Cp*)]2(mu-eta1:eta2-C3O3). Spectroscopic and computational studies suggest a plausible mechanism for the formation of the deltate complex, in which a "zig-zag" diuranium ynediolate species is the key intermediate.
RESUMO
A macrocyclic organosamarium(II) complex has been shown to provide the first example of the reductive disproportionation of carbon dioxide, giving a bimetallic carbonate complex and carbon monoxide in a facile reaction under ambient conditions.
RESUMO
Computational studies on the reductive activation of a mixture of CO and NO by the U(iii) complex [U(η-C8H6{Si(i)Pr3-1,4}2)(η-Cp*)], which affords a mixture of [U(η-C8H6{Si(i)Pr3-1,4}2)(η-Cp*)]2(µ-OCN)21 and [U(η-C8H6{Si(i)Pr3-1,4}2)(η-Cp*)]2(µ-O) 2, show that the reaction proceeds via an initial attack of CO on a µ-η(2):η(2) coordinated NO, side-on bridged between two uranium centres. This leads to the formation of the bridging oxo complex 2 and the cyanate radical; coordination of the latter to the starting complex and dimerisation affords 1. The DFT studies also predict the existence of the monocyanate-bridged, mixed valence species [U(η-C8H6{Si(i)Pr3-1,4}2)(η-Cp*)]2(µ-OCN) 3, which has now been experimentally observed.
RESUMO
Calculations reveal a multistep pathway towards formation of linear [U](2)-(µ-η(1):η(1)-C(2)O(2)); [U] = U(η-C(8)H(6){SiH(3)-1,4}(2))(η-Cp). However formation of deltate-bridged [U](2)-(µ-η(1):η(2)-C(3)O(3)) requires an alternative mechanism, involving a side-on [U](2)-(µ-η(2):η(2)-CO) complex and whereby the bridging units of [U](2)-(µ-η(2):η(2)-C(n)O(n)) intermediates (n = 1, 2) react directly with free CO.
RESUMO
The role of U((η-C(8)H(6){Si(i)Pr(3)-1,4}(2))(η-C(5)Me(5)) and U((η-C(8)H(6){Si(i)Pr(3)-1,4}(2))(η-C(5)Me(4)H) in the reductive di- tri- and tetramerization of CO has been modelled using density functional methods and U(C(8)H(8))(C(5)H(5)) as the metal fragment. The orbital structure of U(C(8)H(8))(C(5)H(5)) is described. CO binding to form a monocarbonyl U(C(8)H(8))(C(5)H(5))(CO) is found, by a variety of methods, to place spin density on the CO ligand via back-bonding from the U5f orbitals. A possible pathway for formation of the yne diolate complex [U(C(8)H(8))(C(5)H(5))](2)C(2)O(2) is proposed which involves dimerization of U(C(8)H(8))(C(5)H(5))CO via coordination of the CO O atoms to the opposing U atoms followed by C-C bond formation to form a zig-zag intermediate, stable at low temperatures. The intermediate then unfolds to form the yne diolate. The structures of [U(C(8)H(8))(C(5)H(5))]C(2)O(2), the deltate complex [U(C(8)H(8))(C(5)H(5))]C(3)O(3) and the squarate complex [U(C(8)H(8))(C(5)H(5))]C(4)O(4) are optimized and provide good models for the experimental compounds. The reaction of further CO with a zig-zag intermediate to form deltate and squarate complexes was explored using Th(C(8)H(8))(C(5)H(5)) as a model and low energy pathways are proposed.