Comparative Insertion Reactivity of CO, CO<sub>2</sub>, <sup>t</sup>BuCN, and <sup>t</sup>BuNC into Thorium– and Uranium–Phosphorus Bonds
Michael L. Tarlton, Iker Del Rosal, Sean P. Vilanova, Steven P. Kelley, Laurent Maron, Justin R. Walensky
Abstract
A study of the comparative reactivity of CO, CO2, tBuCN, and tBuNC with (C5Me5)2An[P(H)Mes]2 (An = Th, U) has been undertaken. While CO2 and tBuNC form identical products with both metals, namely (C5Me5)2An[κ2(O,O)-O2CPH(Mes)]2 and (C5Me5)2An[η2(tBuNC═PMes](CNtBu), respectively, differing results are obtained with CO and tBuCN. The reaction of tert-butylnitrile with (C5Me5)2U[P(H)Mes]2 in a 2:1 ratio leads to double insertion into the U–P bonds and elimination of H2PMes, forming the diketimido complex (C5Me5)2U[κ2(N,N)-(N═CtBu)2P(Mes)]. This is a case in which the analogous reaction with (C5Me5)2Th[P(H)Mes]2 affords a different product, (C5Me5)2Th[PH(Mes)][κ2(P,N)-N(H)C(CMe3)P(Mes)]. The reaction of 1 atm of CO with (C5Me5)2U[P(H)Mes]2 results in double insertion with proton migration from one phosphido ligand to one of the CO carbons to form (C5Me5)2U[(κ2(O,O)-OC═PMesC(O)(H)P(H)Mes]. This is in contrast to the previously published result of the reaction between (C5Me5)2Th[P(H)Mes]2 and CO, in which the product is similar, but both protons from the phosphido ligands migrate to one carbon atom, resulting in (C5Me5)2Th[κ2(O,O)-OC(H)2P(Mes)C(O)P(Mes)]. Density functional theory calculations demonstrate that the mechanisms are quite similar and therefore a similar product is formed, except uranium is less acidic, and the final C–H bond formation does not occur.