While β-diketiminate (BDI or 'nacnac') ligands have been widely adopted to stabilize a wide range of metal ions in multiple oxidation states and coordination numbers, in several occurrences these ...ligands do not behave as spectators and participate in reactivity. Besides unwanted decomposition processes, BDI redox non-innnocence and unusual metal-ligand cooperative activation of substrates yielding attractive reactivity have been reported. This feature article will provide a comprehensive analysis of the various transformations involving BDI ligand platforms in coordination compounds across the periodic table.
While β-diketiminate (BDI or 'nacnac') ligands have been widely adopted to stabilize a wide range of metal ions in multiple oxidation states and coordination numbers, in several occurrences these ligands do not behave as spectators and participate in reactivity.
A method for the synthesis of substituted cycloalkanes was developed using diols and secondary alcohols or ketones via a cascade hydrogen borrowing sequence. A non-noble and air-stable manganese ...catalyst (2 mol %) was used to perform this transformation. Various substituted 1,5-pentanediols (3–4 equiv) and substituted secondary alcohols (1 equiv) were investigated to prepare a collection of substituted cyclohexanes in a diastereoselective fashion. Similarly, cyclopentane, cyclohexane, and cycloheptane rings were constructed from substituted 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol, and sterically hindered ketones following a (4 + 1), (5 + 1), and (6 + 1) strategy, respectively. This reaction provides an atom economic methodology to construct two C–C bonds at a single carbon center generating high-value cycloalkanes from readily available alcohols as feedstock using an earth-abundant metal catalyst.
The new homoleptic ate U(III) siloxide K(18c6)U(OSi(O t Bu)3)4 2 was prepared in 69% yield by reduction of U(OSi(O t Bu)3)4 3 with KC8. The reaction of the neutral U(III) siloxide complex U(OSi(O t ...Bu)3)2(μ-OSi(O t Bu)3)2 1 with adamantyl azide leads to the isolation of the dinuclear U(VI) imido complex U2(NAd)4(OSi(O t Bu)3)4 4. The X-ray crystal structure shows the presence of a “cation–cation interaction” between the two U(NAd)22+ groups. In contrast the reactions of 2 with the trimethylsilyl and adamantyl azides afford the U(V) imido complexes K(18c6)U(NSiMe3)(OSi(O t Bu)3)4 5-TMS and K(18c6)U(NAd)(OSi(O t Bu)3)4 5-Ad pure in 48% and 66% yield, respectively. The reaction of 2 with CsN3 in THF at −40 °C yields a mixture of products from which the azido U(IV) complex K(18c6)U(N3)(OSi(O t Bu)3)4 7 and the μ-nitrido diuranium(V) complex KU(μ-N)(OSi(O t Bu)3)2 8 were isolated. The crystal structure of 8 shows the presence of a rare U2N2 core with two nitrido atoms bridging two uranium centers in a diamond-shaped geometry. In contrast, the reaction of 1 with CsN3 affords the diuranium(IV) complex Cs{(μ-N)U(OSi(O t Bu)3)32} 9 presenting a nitrido ligand bridging two uranium and one cesium cations. These results show the importance of the coordination environment in the outcome of the reaction of U(III) with azides.
A highly efficient catalyst–base pair for the C–H arylation of free (NH)-indoles in the C-3 position is reported. Ligand-free palladium acetate coupled with lithium hexamethyldisilazide (LiHMDS) ...catalyzed the regiospecific, i.e. 100% regioselective, C-3 arylation of indoles with high turnover numbers. This catalytic system has been successfully applied to a wide range of substrates, including various functional aryl halides and indolic cores. The unique role of LiHMDS as both a base and unexpected transient directing group has been revealed experimentally and elucidated computationally, in line with a Heck-type insertion–elimination mechanism.
This work describes the development of easy-to-prepare cobalt nanoparticles (NPs) in solution as promising alternative catalysts for alkene hydrosilylation with the industrially relevant tertiary ...silane 1,1,1,3,5,5,5-heptamethyltrisiloxane (MDHM). The Co NPs demonstrated high activity when used at 30 °C for 3.5–7 h in toluene, with catalyst loadings 0.05–0.2 mol %, without additives. Under these mild conditions, a set of terminal alkenes were found to react with MDHM, yielding exclusively the anti-Markovnikov product in up to 99% yields. Additionally, we demonstrated the possibility of using UV irradiation to further activate these cobalt NPs not only to enhance their catalytic performances but also to promote tandem isomerization–hydrosilylation reactions using internal alkenes, among them unsaturated fatty ester (methyl oleate), to produce linear products in up to quantitative yields.
The metal-mediated redox transformation of CO2 in mild conditions is an area of great current interest. The role of cooperativity between a reduced metal center and a Lewis acid center in ...small-molecule activation is increasingly recognized, but has not so far been investigated for f-elements. Here we show that the presence of potassium at a U, K site supported by sterically demanding tris(tert-butoxy)siloxide ligands induces a large cooperative effect in the reduction of CO2. Specifically, the ion pair complex K(18c6)U(OSi(OtBu)3)4, 1, promotes the selective reductive disproportionation of CO2 to yield CO and the mononuclear uranium(IV) carbonate complex U(OSi(OtBu)3)4(μ-κ2:κ1-CO3)K2(18c6), 4. In contrast, the heterobimetallic complex U(OSi(OtBu)3)4K, 2, promotes the potassium-assisted two-electron reductive cleavage of CO2, yielding CO and the U(V) terminal oxo complex UO(OSi(OtBu)3)4K, 3, thus providing a remarkable example of two-electron transfer in U(III) chemistry. DFT studies support the presence of a cooperative effect of the two metal centers in the transformation of CO2.
A salt metathesis synthetic strategy is used to access rare tantalum/coinage metal (Cu, Ag, Au) heterobimetallic complexes. Specifically, complex Li(THF)2Ta(C t Bu)(CH2 t Bu)3, 1, reacts with ...(IPr)MCl (M = Cu, Ag, Au, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) to afford the alkylidyne-bridged species Ta(CH2 t Bu)3(μ-C t Bu)M(IPr) 2-M. Interestingly, π-bonding of group 11 metals to the TaC moiety promotes a rare alkylidyne alkyl to bis-alkylidene tautomerism, in which compounds 2-M are in equilibrium with Ta(CH t Bu)(CH2 t Bu)2(μ-CH t Bu)M(IPr) 3-M. This equilibrium was studied in detail using NMR spectroscopy and computational studies. This reveals that the equilibrium position is strongly dependent on the nature of the coinage metal going down the group 11 triad, thus offering a new valuable avenue for controlling this phenomenon. Furthermore, we show that these uncommon bimetallic couples could open attractive opportunities for synergistic reactivity. We notably report an uncommon deoxygenative carbyne transfer to CO2 resulting in rare examples of coinage metal ketenyl species, ( t BuCCO)M(IPr), 4-M (M = Cu, Ag, Au). In the case of the Ta/Li analogue 1, the bis(alkylidene) tautomer is not detected, and the reaction with CO2 does not cleanly yield ketenyl species, which highlights the pivotal role played by the coinage metal partner in controlling these unconventional reactions.
A novel heterobimetallic tantalum/iridium hydrido complex, {Ta(CH2 t Bu)3}{IrH2(Cp*)} 1, featuring a very short metal–metal bond, has been isolated through an original alkane elimination route from ...Ta(CH t Bu)(CH2 t Bu)3 and Cp*IrH4. This molecular precursor has been used to synthesize well-defined silica-supported low-coordinate heterobimetallic hydrido species SiOTa(CH2 t Bu)2{IrH2(Cp*)}, 5, and SiOTa(CH2 t Bu)H{IrH2(Cp*)}, 6, using a surface organometallic chemistry (SOMC) approach. The SOMC methodology prevents undesired dimerization as encountered in solution and leading to a tetranuclear species {Ta(CH2 t Bu)2}(Cp*IrH)2, 4. This approach therefore allows access to unique low-coordinate species not attainable in solution. These original supported Ta/Ir species exhibit drastically enhanced catalytic performances in H/D exchange reactions with respect to (i) monometallic analogues as well as (ii) homogeneous systems. In particular, material 6 promotes the H/D exchange between fluorobenzene and C6D6 or D2 as deuterium sources with excellent productivity (TON up to 1422; TOF up to 23.3 h–1) under mild conditions (25 °C, sub-atmospheric D2 pressure) without any additives.
The direct activation of C-H bonds has been a rich and active field of organometallic chemistry for many years. Recently, incredible progress has been made and important mechanistic insights have ...accelerated research. In particular, the use of heterobimetallic complexes to heterolytically activate C-H bonds across the two metal centers has seen a recent surge in interest. This perspective article aims to orient the reader in this fast moving field, highlight recent progress, give design considerations for further research and provide an optimistic outlook on the future of catalytic C-H functionalization with heterobimetallic complexes.
The activation of C-H bonds by heterobimetallic compounds is a rich area of research that has recently received increased attention. This perspective highlights recent advances and aims to guide the reader in this rapidly evolving field.
We report the synthesis and comprehensive study of the electronic structure of a unique series of dinuclear group 5 cyclo-tetraphosphide inverted sandwich complexes. White phosphorus (P4) reacts with ...niobium(III) and tantalum(III) β-diketiminate (BDI) tert-butylimido complexes to produce the bridging cyclo-P4 phosphide species {(BDI)(NtBu)M2(μ‑η3:η3P4)} (1, M = Nb; 2, M = Ta) in fair yields. 1 is alternatively synthesized upon hydrogenolysis of (BDI)Nb(NtBu)Me2 in the presence of P4. The trinuclear side product {(BDI)NbNtBu3(μ‑P12)} (3) is also identified. Protonation of 1 with HOEt2B(C6F5)4 does not occur at the phosphide ring but rather involves the BDI ligand to yield {(BDI#)Nb(NtBu)2(μ‑η3:η3P4)}B(C6F5)42 (4). The monocation and dication analogues {(BDI)(NtBu)Nb2(μ‑η3:η3P4)}{B(ArF)4} n (5, n = 1; 6, n = 2) are both synthesized by oxidation of 1 with AgBArF. DFT calculations were used in combination with EPR and UV–visible spectroscopies to probe the nature of the metal–phosphorus bonding.
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