Actinide Metals with Multiple Bonds to Carbon: Synthesis, Characterization, and Reactivity of U(IV) and Th(IV) Bis(iminophosphorano)methandiide Pincer Carbene Complexes

Treatment of ThCl4(DME)2 or UCl4 with 1 equiv of dilithiumbis(iminophosphorano) methandiide, [Li2C(Ph2PNSiMe3)2] (1), afforded the chloro actinide carbene complexes [Cl2M(C(Ph2PNSiMe3)2)] (2 (M = Th) and 3 (M = U)) in situ. Stable PCP metal–carbene complexes [Cp2Th(C(Ph2PNSiMe3)2)] (4), [Cp2U(C(Ph2PNSiMe3)2)] (5), [TpTh(C(Ph2PNSiMe3)2)Cl] (6), and [TpU(C(Ph2PNSiMe3)2)Cl] (7) were generated from 2 or 3 by further reaction with 2 equiv of thallium(I) cyclopentadienide (CpTl) in THF to yield 4 or 5 or with 1 equiv of potassium hydrotris(pyrazol-1-yl) borate (TpK) also in THF to give 6 or 7, respectively. The derivative complexes were isolated, and their crystal structures were determined by X-ray diffraction. All of these U (or Th)–carbene complexes (4–7) possess a very short M (Th or U)carbene bond with evidence for multiple bond character. Gaussian 03 DFT calculations indicate that the MC double bond is constructed by interaction of the 5f and 6d orbitals of the actinide metal with carbene 2p orbitals of both π and σ character. Complex 3 reacted with acetonitrile or benzonitrile to cyclo-add CN to the Ucarbon double bond, thereby forming a new C–C bond in a new chelated quadridentate ligand in the bridged dimetallic complexes (9 and 10). A single carbon–U bond is retained. The newly coordinated uranium complex dimerizes with one equivalent of unconverted 3 using two chlorides and the newly formed imine derived from the nitrile as three connecting bridges. In addition, a new crystal structure of [CpUCl3(THF)2] (8) was determined by X-ray diffraction.