Terminal uranium(V)-nitride hydrogenations involving direct addition or Frustrated Lewis Pair mechanisms.

Despite their importance as mechanistic models for heterogeneous Haber Bosch ammonia synthesis from dinitrogen and dihydrogen, homogeneous molecular terminal metal-nitrides are notoriously unreactive towards dihydrogen, and only a few electron-rich, low-coordinate variants demonstrate any hydrogenolysis chemistry. Here, we report hydrogenolysis of a terminal uranium(V)-nitride under mild conditions even though it is electron-poor and not low-coordinate. Two divergent hydrogenolysis mechanisms are found; direct 1,2-dihydrogen addition across the uranium(V)-nitride then H-atom 1,1-migratory insertion to give a uranium(III)-amide, or with trimesitylborane a Frustrated Lewis Pair (FLP) route that produces a uranium(IV)-amide with sacrificial trimesitylborane radical anion. An isostructural uranium(VI)-nitride is inert to hydrogenolysis, suggesting the 5f1 electron of the uranium(V)-nitride is not purely non-bonding. Further FLP reactivity between the uranium(IV)-amide, dihydrogen, and triphenylborane is suggested by the formation of ammonia-triphenylborane. A reactivity cycle for ammonia synthesis is demonstrated, and this work establishes a unique marriage of actinide and FLP chemistries.

Thermally Stable Ln(II) and Ca(II) Bis(benzhydryl) Complexes: Excellent Precatalysts for Intermolecular Hydrophosphination of C-C Multiple Bonds.

A series of Ln(II) and Ca(II) bis(alkyl) complexes with bulky benzhydryl ligands, [( p- tBu-C6H4)2CH]2M(L n) (M = Sm, L = DME, n = 2 (1); M = Sm, Yb, Ca, L = TMEDA, n = 1 (2, 3, 4), were synthesized by the salt-metathesis reaction of MI2(THF) n ( n = 0-2) and [( p- tBu-C6H4)2CH]-Na+. In complex 1, the benzhydryl ligands are bound to the metal center in η2-coordination mode. Unlike complex 1, in isomorphous complexes 3 and 4, due to the coordination unsaturation of the metal center, the both benzhydryl ligands coordinate to the metal in η3-fashion. In complex 2, one ligand is η3-coordinated while the second one is η4-coordinated to the Sm(II) ion. Complexes 2-4 demonstrated unprecedented thermal stability: no evidence of decomposition was observed after heating their solutions in C6D6 at 100 °C during 72 h. Complex 1 behaves differently: thermolysis in C6D6 solution at 75 °C results in total decomposition in 8 h. Addition of DME promotes decomposition of 2-4 and makes it feasible at 40 °C. Complexes 1-4 demonstrated high catalytic activity and excellent regio- and chemoselectivities in intermolecular hydrophosphination of double and triple C-C bonds with both primary and secondary phosphines. Complexes 2 and 3 enable addition of PhPH2 toward the internal C═C bond of Z- and E-stilbenes with 100% conversion under mild conditions. Double sequential hydrophosphination of phenylacetylene with Ph2PH and PhPH2 was realized due to the application of Yb(II) complex as a catalyst.

Divalent Ytterbium Complex-Catalyzed Homo- and Cross-Coupling of Primary Arylsilanes.

Redistribution of primary silanes through C-Si and Si-H bond cleavage and reformation provides a straightforward synthesis of secondary silanes, but the poor selectivity and low efficiency severely hinders the application of this synthetic protocol. Here, we show that a newly synthesized divalent ytterbium alkyl complex exhibits unprecedentedly high catalytic activity toward the selective redistribution of primary arylsilanes to secondary arylsilanes. More significantly, this complex also effectively catalyzes the cross-coupling between electron-withdrawing substituted primary arylsilanes and electron-donating substituted primary arylsilanes to secondary arylsilanes containing two different aryls. DFT calculation indicates that the reaction always involve the exothermic formation of a hypervalent silicon upon facile addition of PhSiH3 to the Yb-E (E = C, H) bond. This hypervalent compound can easily either generate directly the Yb-Ph complex, or indirectly through the formation of Yb-H, that is the key complex for the formation of Ph2SiH2.

Cyaarside (CAs- ) and 1,3-Diarsaallendiide (AsCAs2- ) Ligands Coordinated to Uranium and Generated via Activation of the Arsaethynolate Ligand (OCAs- ).

Reaction of the trivalent uranium complex [((Ad,Me ArO)3 N)U(DME)] with one molar equiv [Na(OCAs)(dioxane)3 ], in the presence of 2.2.2-crypt, yields [Na(2.2.2-crypt)][{((Ad,Me ArO)3 N)UIV (THF)}(µ-O){((Ad,Me ArO)3 N)UIV (CAs)}] (1), the first example of a coordinated η1 -cyaarside ligand (CAs- ). Formation of the terminal CAs- is promoted by the highly reducing, oxophilic UIII precursor [((Ad,Me ArO)3 N)U(DME)] and proceeds through reductive C-O bond cleavage of the bound arsaethynolate anion, OCAs- . If two equiv of OCAs- react with the UIII precursor, the binuclear, µ-oxo-bridged U2 IV/IV complex [Na(2.2.2-crypt)]2 [{((Ad,Me ArO)3 N)UIV }2 (µ-O)(µ-AsCAs)] (2), comprising the hitherto unknown µ:η1 ,η1 -coordinated (AsCAs)2- ligand, is isolated. The mechanistic pathway to 2 involves the decarbonylation of a dimeric intermediate formed in the reaction of 1 with OCAs- . An alternative pathway to complex 2 is by conversion of 1 via addition of one further equiv of OCAs- .

Small molecule activation with divalent samarium triflate: a synergistic effort to cleave O2.

The divalent samarium triflate salt does not react with CO2 or water, but does react with traces of O2 or N2O to form a tetrameric bis-oxo samarium motif. The reaction with O2 is a 4e- reductive cleavage where the electrons are coming from four different samarium centers. This highlights a rare synergistic effect for cleaving O2, which has no precedent in divalent lanthanide complexes. Additionally, the addition of CO2 to the tetrameric bis-oxo intermediate leads to the formation of a tetrameric bis-carbonate samarium triflate. Thus, the concomitant reaction of CO2 with traces of O2 leads to the same bis-carbonate tetrameric assembly.

Steric control in the metal-ligand electron transfer of iminopyridine-ytterbocene complexes.

A systematic study of reactions between Cp*2Yb(THF) (Cp* = η5-C5Me5, 1) and iminopyridine ligands (IPy = 2,6-iPr2C6H3N[double bond, length as m-dash]CH(C5H3N-R), R = H (2a), 6-C4H3O (2b), 6-C4H3S (2c), 6-C6H5 (2d)) featuring similar electron accepting properties but variable denticity and steric demand, has provided a new example of steric control on the redox chemistry of ytterbocenes. The reaction of the unsubstituted IPy 2a with 1, either in THF or toluene, gives rise to the paramagnetic species Cp*2YbIII(IPy)˙- (3a) as a result of a formal one-electron oxidation of the YbII ion along with IPy reduction to a radical-anionic state. The reactions of 1 with substituted iminopyridines 2b-d, bearing aryl or hetero-aryl dangling arms on the 6 position of the pyridine ring occur in a non-coordinating solvent (toluene) only and afford coordination compounds of a formally divalent ytterbium ion, coordinated by neutral IPy ligands Cp*2YbII(IPy)0 (3b-d). The X-ray diffraction studies revealed that 2a-c act as bidentate ligands; while the radical-anionic IPy in 3a chelates the YbIII ion with both nitrogens, neutral IPy ligands in 3b and 3c participate in the metal coordination sphere through the pyridine nitrogen and O or S atoms from the furan or thiophene moieties, respectively. Finally, in complex 3d the neutral IPy ligand formally adopts a monodentate coordination mode. However, an agostic interaction between the YbII ion and an ortho C-H bond of the phenyl ring has been detected. Imino-nitrogens in 3b-d are not involved in the metal coordination. Variable temperature magnetic measurements on 3a are consistent with a multiconfigurational ground state of the Yb ion and suggest that the largest contribution arises from the 4f13-radical configuration. For complexes 3b and 3c the data of magnetic measurements are indicative of a YbII-closed shell ligand electronic distribution. Complex 3d is characterized by a complex magnetic behavior which does not allow for an unambiguous estimation of its electronic structure. The results are rationalized using DFT and CSSCF calculations. Unlike diazabutadiene analogues, 3a does not undergo a solvent mediated metal-ligand electron transfer and remains paramagnetic in THF solution. On the other hand, complexes 3b-d readily react with THF to afford 1 and free IPy 2b-d.

SO2 and SO3 reactions with [(C5Me5)2Sm-O-Sm(C5Me5)2]: a DFT investigation and comparison with CO2 reactivity.

Recently, it was shown that samarocene oxide [Cp*2Sm-O-SmCp*2] with Cp* = C5Me5 could react with organic and inorganic anhydrides. The reactions of [Cp*2Sm-O-SmCp*2] with SO2 and SO3 are reported using DFT calculations and compared with the reactivity of CO2. These reactions exhibit similar features yielding [Cp*2-Sm-(µ-η1:η2-OSO2)-SmCp*2] similar to [Cp*2-Sm-(µ-η1:η2-OCO2)-SmCp*2] and [Cp*2-Sm-(µ-η2:η2-O2SO2)-SmCp*2] complexes.