Facile Synthesis of Uranium Complexes with a Pendant Borane Lewis Acid and 1,2‐Insertion of CO into a U−N Bond

Abstract

In this contribution, we illustrate uranium complexes bearing a pendant borate (i.e. 1 and 2) or a pendant borane (i.e. 3 and 4) moiety via reaction of the highly strained uranacycle I with various 3-coordinate boranes. Complexes 3 and 4 represent the first examples of uranium complexes with a pendant borane Lewis acid. Moreover, complex 3 was capable of activation of CO, delivering a new CO activation mode, and an abnormal CO 1,2-insertion pathway into a UÀ N bond. The importance of the pendant borane moiety was confirmed by the controlled experiments.Recent findings about uranium complexes bearing N/P [1] or O/P [2] double-layer ligands demonstrated the relevance of pendant or secondary-sphere coordinating sites in terms of the construction of uranium-transition metal bonds. The secondary binding sites are dominated by the basic phosphino groups that coordinate to the elements, particularly those soft metals spanning the periodic table, [3] thus allowing for the hard-soft heterometallic bonding that would otherwise not be favored. Moreover, recent reports have opened up the prospect of such heterometallic clusters in small molecule activation, such as N 2 . [4] However, f-metal complexes bearing a pendant Lewis acidic borane moiety serving as the secondary binding site are thus far not reported. The stagnation stands out against the backdrop of the boom in d-metal complexes comprising one or several pendant Lewis acidic borane moieties. [5] For instance, the dangling Ph 2 P(CH 2 ) 2 B(C 8 H 14 ) of complex A is indispensable to further mediate reductive coupling of CO to form a CÀ C bond in the presence of NaHBEt 3 (Figure 1a, top). [6] Drover and co-workers demonstrated that the appended borane moiety has great impact on the ability of the hydride complexes [BH] + in hydride transfer, as well as the oxidative addition behavior at the Ni 0 center in B. [7] Very recently, Chu, Szymczak and the co-workers successfully applied a pendant 9-BBN (borabicyclo[3.3.1]nonyl) group to stabilize the reactive Ni II imido intermediates (Ni=NR) thanks to the presence of the secondary BÀ N interactions (C), and thus achieved the intermolecular 1,2-C Ar -H-addition or intramolecular 1,2-C benzylic -H-addition across the