Synthesis and properties of a new class of highly reactive trivalent actinide organometallic compounds. Derivatives of bis(pentamethylcyclopentadienyl)uranium(III)

Synthesis and characterization of a new and electronically unusual uranium metallacyclocumulene, (C5Me5)2U(η4-1,2,3,4-PhC4Ph)

“…As illustrated in Scheme 1, only a handful of such metallacycle complexes have been reported for thorium and uranium. In 1981, Marks and co-workers reported the synthesis of the uranium metallacyclopentadiene complex (C 5 Me 5 ) 2 U( 2 -1,4-C 4 Ph 4 ) from the reaction of (C 5 Me 5 ) 2 UCl 2 and two equivalents of PhCCPh with excess reducing equivalents provided by Na/Hg, [9] and also by salt metathesis between (C 5 Me 5 ) 2 UCl 2 and 1,4-dilithiotetraphenylbutadiene. [10] Several years later in 2005, the Evans group showed that the sterically crowded complexes (C 5 Me 5 ) 3 U, [(C 5 Me 5 ) 2 U][(µ-Ph) 2 BPh 2 ], and [(C 5 Me 5 ) 2 U] 2 (- 6 : 6 -C 6 H 6 ) could all reduce PhCCPh to give (C 5 Me 5 ) 2 U( 2 -1,4-C 4 Ph 4 ).…”

Phenylsilane as a safe, versatile alternative to hydrogen for the synthesis of actinide hydrides

“…26 For example, the classic route to the dihydride dimer complexes 1 and 2 involves treating the known alkyl complexes (C 5 Me 5 ) 2 AnMe 2 (An = Th (3), U (4)) with H 2 ; the uranium derivative (2) must be stored under H 2 as it is prone to loss of H 2 and formation of [(C 5 Me 5 ) 2 U(m-H)] 2 (5). 12,27 Having stable and easy-to-handle liquid surrogates for H 2 as hydriding reagents would be synthetically more convenient, thereby enabling future progress in the field of actinide hydride chemistry. 28 Using the [(C 5 Me 5 ) 2 An(H)(m-H)] 2 (An = Th (1), U ( 2)) systems as a platform, we now demonstrate that phenylsilane (PhSiH 3 ) is a safe, versatile alternative to H 2 for the synthesis of actinide hydride complexes from the corresponding alkyl precursors.…”

“…The formation of complexes 11 and 12 establishes that the (C 5 Me 5 ) 2 AnMe 2 /phenylsilane reduction combination provides an attractive synthetic strategy for accessing chemistry previously reported for very reactive low-valent uranium and thorium species. For example, the reductive coupling of PhCRCPh to (C 4 Ph 4 ) 2À to prepare complex 12 has been achieved in the past, but requires either sterically crowded complexes such as (C 5 Me 5 ) 3 U, 31 [(C 5 Me 5 ) 2 U][(m-Ph) 2 BPh 2 ], 31 and [(C 5 Me 5 ) 2 U] 2 (m-Z 6 :Z 6 -C 6 H 6 ) 31 (which are capable of transferring multiple electrons to a substrate), or the reaction of (C 5 Me 5 ) 2 UCl 2 combined with excess reducing equivalents provided by Na/Hg, 27 and KC 8 , 27 or salt metathesis between (C 5 Me 5 ) 2 UCl 2 and 1,4-dilithiotetraphenylbutadiene. 12 Although complex 12 has been known for nearly 30 years, only very recently has the synthesis of the thorium analogue (11) been realized.…”

The synthesis and versatile reducing power of low-valent uranium complexes

“…Complexes of the form (Cp R )2UX (X = halide) are most commonly isolated via oneelectron reduction of (Cp R )2UX2 species 64,65 or by reaction of two equiv of M(Cp R ) (M = alkali metal) with a uranium(III) halide. 8,30,[66][67][68][69][70] Dimerization 64,65 or ate complex formation 8,71,72 are often observed in these species with varying effects on resultant reactivity. Uranium(III) metallocenium species 73 Due to the unstable nature typical of divalent uranium complexes, as well as a lack of simple uranium(II) precursors, isolation of uranium(II) complexes has been reported exclusively via reduction of uranium(III) species already incorporating supporting ligands.…”