Reactivity of Scandium β-Diketiminate Alkyl Complexes with Carbon Dioxide

Abstract

The reactions of two highly air- and moisture-sensitive scandium bis­(alkyls) supported by a bulky β-diketiminato (nacnac) ligand with carbon dioxide are described. [κ2-ArNC­( t Bu)­CHC­( t Bu)­NAr]­ScR2 (Ar = 2,6- i Pr2C6H3; R = CH3, 1a; R = CH2SiMe3, 1b) react rapidly with CO2 to give mixtures of mono- and bis­(carboxylato) insertion products 2a/2b and 3a/3b depending on the stoichiometry and conditions of the reaction. Compound 2a (R = CH3) is a dimeric complex with bridging acetato groups, as determined by X-ray crystallography. These compounds were characterized by NMR spectroscopy, and 3a could be isolated in pure form. Treatment of these compounds with excess CO2 resulted in addition to the central carbon of the Sc­(nacnac) six-membered ring and displacement of the nitrogen donors to yield dimeric scandium carboxylates 4a/4b; compound 4b was characterized by X-ray crystallography. Reactions of the nacnac scandium cations formed upon abstraction of one or two methides from 1a using B­(C6F5)3 with CO2 were also explored. Although the products were qualitatively more thermally robust, eventually ligand displacement occurred in these cationic acetato complexes as well. Nevertheless, insertion products were characterizable in solution using NMR spectroscopy. Overall, this study shows the facility with which CO2 is taken up by scandium alkyls but that the nacnac ligand framework is too reactive to support chemistry aimed at catalytic conversion of CO2 into other products.

Reduction of CO2 by Pyridine Monoimine Molybdenum Carbonyl Complexes: Cooperative Metal–Ligand Binding of CO2

“…For example, Braunstein et al in 1981 obtained a similar result to ours by activation of CO 2 at a square planar Pd diphenylphophinoacetate complex. [23] Similar binding patterns of carbon dioxide have recently been reported for PNN-Ru [24] and PNP-Ru/Re [25] pincer complexes as well as β-diketiminate Sc [26] complexes.…”

Synthesis of Unsymmetrically Substituted Phosphane Oxides (R1R2P(O)H) and Phosphinous Acids (R1R2POH)

“…in 1981 obtained a similar result to ours by activation of CO 2 at a square planar Pd diphenylphosphinoacetate complex 23. Similar binding patterns of carbon dioxide have recently been reported for PNN–Ru24 and PNP–Ru/Re25 pincer complexes, as well as β‐diketiminate Sc26 complexes.…”

Boron-mediated activation of carbon dioxide

“…The final complex can be described as the insertion of one molecule of CO 2 into a Mg-H bond, whereas the second equivalent is trapped, as in a Lewis pair, between the nucleophilic methine moiety of the ligand backbone and the Lewis acidic B(C 6 F 5 ) 3 [48]. This structure is reminiscent to the structure characterized by Piers et al from the reaction of a methylborate compound with a scandium countercation also bearing a nacnac ligand [49]. [48] C N (34)(35)(36)(37) via the activation of CO 2 by the borane compounds B(C 6 F 5 ) 3 and BPh 3 and the related M-H complexes (scheme 9) [50].…”