Methods to separate the components of the equilibrium mixture of [(C5Me5)2UH]2 and [(C5Me5)2UH2]2 have been developed that allow their reductive chemistry to be studied. These actinide hydrides can act as four-, six-, and eight-electron reductants depending on the substrate with H2 as the byproduct of a H- → e- + 1/2 H2 redox couple. This hydride reduction chemistry allows complexes of redox-inactive Th4+ such as [(C5Me5)2ThH2]2 to be four- and six-electron reductants. [(C5Me5)2UH]2 and [(C5Me5)2UH2]2 cleanly reduce 2 equiv of PhEEPh (E = S, Se) to form 2 equiv of (C5Me5)2U(SPh)2 and (C5Me5)2U(SePh)2 in an overall four-electron reduction in each case. [(C5Me5)2UH]2 and [(C5Me5)2UH2]2 also effect a six-electron reduction of 3 equiv of 1,3,5,7-cyclooctatetraene to [(C5Me5)(C8H8)U]2(C8H8) and an eight-electron reduction of 2 equiv of PhNNPh to form 2 equiv of the U6+ imido complex (C5Me5)2U(NPh)2. In each reaction, H2 is a byproduct. This hydride-based reduction is also successful with the tetravalent thorium hydride [(C5Me5)2ThH2]2, which reduces 2 equiv of PhSSPh to (C5Me5)2Th(SPh)2 and 3 equiv of C8H8 to [(C5Me5)(C8H8)Th]2(C8H8) with concomitant formation of H2. X-ray crystallographic data are reported on [(C5Me5)2UH]2, [(C5Me5)2UH2]2, and (C5Me5)2U(SePh)2 as well as the thorium reduction products (C5Me5)2Th(SPh)2 and [(C5Me5)(C8H8)Th]2(C8H8).

Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) has been used to characterize the air-sensitive paramagnetic organouranium azide and nitride complexes [(C5Me5)2UN3(mu-N3)]3 and [(C5Me5)U(mu-I)2]3N, respectively. The trimetallic complex [(C5Me5)U(mu-I)2]3E had been identified by X-ray crystallography, but the data did not definitively identify E as N3- versus O2- or (OH)-, a common problem in heavy-element nitride complexes involving metals with variable oxidation states. A comparison of the 250 degrees C APCI-MS spectra of products made from NaN3 and Na15NNN showed mixed [M]+ and [M + H]+ envelopes at expected ion intensities for the 14N and 15N isotopomers. A compilation of U-C(C5Me5) and U-I bond distance data for U3+ and U4+ is also reported that shows that the ranges for the two oxidation states have significant overlap.

(C5Me5)2UMe2, 1, reacts with 1 and 2 equiv of PhEEPh (E = S, Se) to form (C5Me5)2UMe(EPh) (E = S, 2; Se, 3) and (C5Me5)2U(EPh)2 (E = S, 4; Se, 5), respectively, with concomitant formation of MeEPh. Complexes 2, 3, and 5 form at ambient temperature, but the synthesis of 4 required heating to 65 °C. Addition of 2 equiv of PhTeTePh to 1 equiv of (C5Me5)2UMe2 generated the tellurium analogue of 4 and 5, namely, (C5Me5)2U(TePh)2, 6, but when 1 was reacted with 1 equiv of PhTeTePh, C−H activation of the aryl ring occurred to form (C5Me5)2U(η 2-TeC6H4), 7, along with MeTePh and CH4.

The actinide metallocene hydrides [{(C5Me5)2UH}2] and [{(C5Me5)2ThH2}2] convert three equivalents of acetonitrile into a polydentate ligand containing a six carbon atom chain (see scheme). These reactions show that a ThIV hydride moiety can undergo chemistry similar to UIII in a multistep reaction.

The reductive reactivity of lanthanide hydride ligands in the [(C5Me5)2LnH]x complexes (Ln = Sm, La, Y) was examined to see if these hydride ligands would react like the actinide hydrides in [(C5Me5)2AnH2]2 (An = U, Th) and [(C5Me5)2UH]2. Each lanthanide hydride complex reduces PhSSPh to make [(C5Me5)2Ln(mu-SPh)]2 in approximately 90% yield. [(C5Me5)2SmH]2 reduces phenazine and anthracene to make [(C5Me5)2Sm]2(mu-eta(3):eta(3)-C12H8N2) and [(C5Me5)2Sm]2(mu-eta(3):eta(3)-C10H14), respectively, but the analogous [(C5Me5)2LaH]x and [(C5Me5)2YH]2 reactions are more complicated. All three lanthanide hydrides reduce C8H8 to make (C5Me5)Ln(C8H8) and (C5Me5)3Ln, a reaction that constitutes another synthetic route to (C5Me5)3Ln complexes. In the reaction of [(C5Me5)2YH]2 with C8H8, two unusual byproducts are obtained. In benzene, a (C5Me5)Y[(eta(5)-C5Me4CH2-C5Me4CH2-eta(3))] complex forms in which two (C5Me5)(1-) rings are linked to make a new type of ansa-allyl-cyclopentadienyl dianion that binds as a pentahapto-trihapto chelate. In cyclohexane, a (C5Me5)2Y(mu-eta(8):eta(1)-C8H7)Y(C5Me5) complex forms in which a (C8H8)(2-) ring is metalated to form a bridging (C8H7)(3-) trianion.

To compare the ligand-based reduction chemistry of (EPh)(-) ligands in a metallocene environment to the sterically induced reduction chemistry of the (C(5)Me(5))(-) ligands in (C(5)Me(5))(3)Sm, (C(5)Me(5))(2)Sm(EPh) (E = S, Se, Te) complexes were synthesized and treated with substrates reduced by (C(5)Me(5))(3)Sm: cyclooctatetraene; azobenzene; phenazine. Reactions of PhEEPh with (C(5)Me(5))(2)Sm(THF)(2) and (C(5)Me(5))(2)Sm produced THF-solvated monometallic complexes, (C(5)Me(5))(2)Sm(EPh)(THF), and their unsolvated dimeric analogues, [(C(5)Me(5))(2)Sm(mu-EPh)](2), respectively. Both sets of the paramagnetic benzene chalcogenolate complexes were definitively identified by X-crystallography and form homologous series. Only the (TePh)(-) complexes show reduction reactivity and only upon heating to 65 degrees C.

The U4+ mixed alkyl hydride complex (C5Me5)U[mu-C5Me3(CH2)2](mu-H)2U(C5Me5)2, 1, which contains a cyclopentadienyl ligand with two metalated methylene substituents, can effect four, six, and eight-electron reductions in which the combination of the two H1- ligands and the [C5Me3(CH2)2]3- moiety delivers four electrons and forms (C5Me5)1-. The reaction is formally equivalent to an alkyl hydride reductive elimination, a transformation common with transition metals not previously observed with f element compounds. This type of alkyl hydride reduction reactivity is also observed with a combination of U4+ alkyl and hydride complexes, (C5Me5)2UMe2/[(C5Me5)2UH2]2, which reduces benzene to make [(C5Me5)2U]2(C6H6), a U3+ complex formally containing a (C6H6)2- ligand.

Long sought structural data on an f‐element tuck‐in complex have been obtained for the title compound 1 that contains the first example of both tuck‐in and tuck‐over bonding in a ligand derived from C5Me5− by metalation (see scheme).