Carbon Dioxide Reduction by Terminal Tantalum Hydrides: Formation and Isolation of Bridging Methylene Diolate Complexes

Abstract

The preparation of tantalaziridine-hydride complex (Ar[(t)BuCH(2)]N)(2)(eta(2)-(t)Bu(H)CNAr)TaH (1) is reported (Ar = 3,5-Me(2)C(6)H(3)). While stable for months in the solid state at -35 degrees C, in solution this complex undergoes partial conversion to isomeric hydride (Ar[(t)BuCH(2)]N)(2)(kappa(2)-CH(2)C(Me)(2)CH(2)NAr)TaH (2). Although 1 and 2 exist in equilibrium in benzene solution, complex 2 can be isolated cleanly from 1 by selective precipitation using cold n-pentane; solid-state structures for both 1 and 2 are presented. Exposure of 1 to ca. 1 atm of CO(2) results in the production of methylene diolate complex {(Ar[(t)BuCH(2)]N)(2)(eta(2)-(t)Bu(H)CNAr)Ta}(2)(mu-OCH(2)O) as a mixture of rac and meso diastereomers (3r,m). Similar reactivity for the Nb congener of 1 is reported herein. Further-more, methylene diolate complex {(Ar[(t)BuCH(2)]N)(2)(kappa(2)-CH(2)C(Me)(2)CH(2)NAr)Ta}(2)(mu-OCH(2)O) (4) is produced from 2 upon treatment with CO(2) and was characterized crystallographically. Complexes 3r,m (and the Nb analogues) as well as 4 establish the feasibility of the formation of methylene diolate products from CO(2) and two terminal transition-metal hydrides. Reaction of formate (Ar[(t)Bu]N)(3)TiOC(O)H with 1 generates the related, structurally characterized heterobimetallic complex (Ar[(t)BuCH(2)]N)(2)(eta(2)-(t)Bu(H)CNAr)TaOCH(2)OTi(N[(t)Bu]Ar)(3) (5), which further contributes to the class of complexes reported herein that effectively stabilizes an unusual H(2)CO(2)(2-) ligand between two metal centers.

A Molecular CO2 Reduction Catalyst Based on Giant Polyoxometalate {Mo368}

“…Thus, it is necessary to find out a new pathway which can produce energy without hampering the environment and burning fossil fuels. With this end in view if we convert a greenhouse gas like CO 2 to energy rich material it would be very interesting and helpful for a sustainable environment and economy (Khenkin et al, 2010 ; Rankin and Cummins, 2010 ; Wang W. et al, 2011 ; Bontemps et al, 2012 ; Kuhl et al, 2012 ; Ohtsu and Tanaka, 2012 ; Wesselbaum et al, 2012 ; Xi et al, 2012 ; Arai et al, 2013 ; Costentin et al, 2013 ; Asadi et al, 2014 ; Blondiaux et al, 2014 ; Herrero et al, 2014 ; Kim et al, 2014 ; Kou et al, 2014 ; Lu et al, 2014 ; Studt et al, 2014 ; Zhang et al, 2014 ; Gao et al, 2015 ; Kornienko et al, 2015 ; Liu et al, 2015 ; Marszewski et al, 2015 ; Matlachowski and Schwalbe, 2015 ; Roberts et al, 2015 ; Sypaseuth et al, 2015 ; Iwase et al, 2016 ; Kuriki et al, 2017 ). However, the challenge is as CO 2 is a very stable oxide of carbon at its stable oxidation state, a large amount of energy is required to activate CO 2 .…”

Borane‐Mediated Carbon Dioxide Reduction at Ruthenium: Formation of C1 and C2 Compounds

“…However, our system broadens the panel of compounds accessible from CO 2 reduction 20. Indeed, whereas acetals are key structures that have been studied in various CO 2 reduction processes,4a–c, 6a, 7 a species such as 10 has not been reported with boron so far,4h and compound 11 represents the first direct reductive coupling of two CO 2 units 21. Mechanistic investigation shows that borane coordination competes with CO 2 insertion and that decarbonylation is readily achieved, which ultimately results in catalyst deactivation.…”

Terminal phosphinidene formation via tantalaziridine complexes

“…16 However, the targeted complex could be obtained only in low isolated yields (< 20%). A second approach involved the treatment of the previously reported tantalaziridine hydride complex (Ar[ t BuCH 2 ]N) 2 (η 2 -t BuC(H)NAr)TaH (2, Scheme 2) 15 with primary phosphine PhPH 2 in an effort to effect net H 2 extrusion concomitant with formation of 1. 5a,8d,17 Again, the desired phosphinidene 1 was identified in the product mixture of this observably slow reaction, but the yield was low in situ and work-up was complicated by a side reaction of the H 2 byproduct with the starting hydride 2, which produced the bridging hydride dimer [(Ar[ t BuCH 2 ]N) 3 Ta(μ-H)] 2 .…”