Metal-Free Catalytic Hydrogenolysis of Chlorosilanes into Hydrosilanes with "Inverse" Frustrated Lewis Pairs.

The challenging metal-free catalytic hydrogenolysis of silyl chlorides to hydrosilanes is unlocked by using an inverse frustrated Lewis pair (FLP), combining a mild Lewis acid (Cy BCl) and a strong phosphazene base (BTPP) in mild conditions (10 bar of H , r. t.).

Catalyst-free depolymerization of polycaprolactone to silylated monoesters and iodide derivatives using iodosilanes.

The homogeneous depolymerization of polycaprolactone (PCL) with excess iodotrimethylsilane (MeSiI) proceeds without catalysts and selectively afforded I(CH)COSiMe or a mixture of I(CH)COSiMe and I(CH)COI depending on the solvent (CHCl, MeCN). The latter mixture can undergo methanolysis or hydrolysis into the valuable ester I(CH)COMe or the acid I(CH)COH. In contrast, SiHI depolymerized PCL into the fully deoxygenated species I(CH)I and -hexane.

Selective Reduction of Secondary Amides to Imines Catalysed by Schwartz's Reagent.

The partial reduction of amides is a challenging transformation that must overcome the intrinsic stability of the amide bond and exhibit high chemoselective control to avoid overreduction to amine products. To address this challenge, we describe a zirconium-catalysed synthesis of imines by the reductive deoxygenation of secondary amides. This reaction exploits the excellent chemoselectivity of Schwartz's reagent (Cp Zr(H)Cl) and utilises (EtO) SiH as a mild stoichiometric reductant to enable catalyst turnover.

Metal-Free Catalytic Hydrogenolysis of Silyl Triflates and Halides into Hydrosilanes.

The metal-free catalytic hydrogenolysis of silyl triflates and halides (I, Br) to hydrosilanes is unlocked by using arylborane Lewis acids as catalysts. In the presence of a nitrogen base, the catalyst acts as a Frustrated Lewis Pair (FLP) able to split H and generate a boron hydride intermediate capable of reducing (pseudo)halosilanes. This metal-free organocatalytic system is competitive with metal-based catalysts and enables the formation of a variety of hydrosilanes at room temperature in high yields (>85 %) under a low pressure of H (≤10 bar).

Reductive depolymerization of polyesters and polycarbonates with hydroboranes by using a lanthanum(III) tris(amide) catalyst.

The homogeneous reductive depolymerization of polyesters and polycarbonates with hydroboranes is achieved with the use of an f-metal complex catalyst. These polymeric materials are transformed into their value-added alcohol equivalents. Catalysis proceeds readily, under mild conditions, with La[N(SiMe)] (1 mol%) and pinacolborane (HBpin) and shows high selectivity towards alcohols and diols, after hydrolysis.

A Copper(I)-Catalyzed Sulfonylative Hiyama Cross-Coupling.

An air-tolerant Cu-catalyzed sulfonylative Hiyama cross-coupling reaction enabling the formation of diaryl sulfones is described. Starting from aryl silanes, DABSO and aryliodides, the reaction tolerates a large variety of polar functional groups (amines, ketones, esters, aldehydes). Control experiments coupled with DFT calculations shed light on the mechanism, characterized by the formation of a Cu(I)-sulfinate intermediate via fast insertion of a SO molecule.

Uranyl(VI) Triflate as Catalyst for the Meerwein-Ponndorf-Verley Reaction.

Catalytic transformation of oxygenated compounds is challenging in f-element chemistry due to the high oxophilicity of the f-block metals. We report here the first Meerwein-Ponndorf-Verley (MPV) reduction of carbonyl substrates with uranium-based catalysts, in particular from a series of uranyl(VI) compounds where [UO(OTf)] () displays the greatest efficiency (OTf = trifluoromethanesulfonate). [UO(OTf)] reduces a series of aromatic and aliphatic aldehydes and ketones into their corresponding alcohols with moderate to excellent yields, using PrOH as a solvent and a reductant.

Carbonylation of C-N Bonds in Tertiary Amines Catalyzed by Low-Valent Iron Catalysts.

The first iron catalysts able to promote the formal insertion of CO into the C-N bond of amines are reported. Using low-valent iron complexes, including K [Fe(CO) ], amides are formed from aromatic and aliphatic amines, in the presence of an iodoalkane promoter. Inorganic Lewis acids, such as AlCl and Nd(OTf) , have a positive influence on the catalytic activity of the iron salts, enabling the carbonylation at a low pressure of CO (6 to 8 bars).

Activation of SO by N/Si and N/B Frustrated Lewis Pairs: Experimental and Theoretical Comparison with CO Activation.

The guanidine 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and the substituted derivatives [TBD-SiR ] and TBD-BR reacted with SO to give different FLP-SO adducts.

Complexes of the tripodal phosphine ligands PhSi(XPPh2)3 (X = CH2, O): synthesis, structure and catalytic activity in the hydroboration of CO2.

The coordination chemistry of Fe(2+), Co(2+) and Cu(+) ions was explored with the triphosphine and triphosphinite ligands PhSi{CH2PPh2}3 (1) and PhSi{OPPh2}3 (2), so as to evaluate the impact of the electronic properties of the tripodal phosphorus ligands on the structure and reactivity of the corresponding complexes. The synthesis and characterization of the complexes [Fe(κ(3)-PhSi{CH2PPh2}3)(MeCN)3][OTf]2 (3) (OTf = O3SCF3), [Fe(κ(3)-PhSi{OPPh2}3)(MeCN)3][OTf]2 (3'), [Co(κ(2)-PhSi{CH2PPh2}3)Cl2] (4), [Co(κ(3)-PhSi{OPPh2}3)Cl2] (4'), [Cu(κ(3)-PhSi{CH2PPh2}3)Br] (5) and [Cu(κ(3)-PhSi{OPPh2}3)I] (5') were carried out. The crystal structures of 3, 3', 4, 4', and of the solvates 5·3THF and 5'·THF are reported.

Advances in f-element cyanide chemistry.

This Dalton perspective gives an overview of the development of cyanide chemistry of 4f- and 5f-elements, a field which was poorly explored in contrast to the attention paid to the cyanide complexes of the d transition metals. The use of the cyanide ligand led to the discovery of mono- and polycyanide complexes which exhibit unprecedented and unexpected coordination geometries. A new type of linear metallocenes including [U(Cp*)2(CN)5](3-) (Cp* = C5Me5) and the first bent actinocenes [An(Cot)2(CN)](-) (An = Th, U; Cot = C8H8) were isolated.

U(III)-CN versus U(IV)-NC coordination in tris(silylamide) complexes.

Treatment of the metallacycle [UN*2(N,C)] [N* = N(SiMe3)2; N,C = CH2SiMe2N(SiMe3)] with [HNEt3][BPh4], [HNEt3]Cl, and [pyH][OTf] (OTf = OSO2CF3) gave the cationic compound [UN*3][BPh4] (1) and the neutral complexes [UN*3X] [X = Cl (3), OTf (4)], respectively. The dinuclear complex [{UN*(μ-N,C)(μ-OTf)}2] (5) and its tetrahydrofuran (THF) adduct [{UN*(N,C)(THF)(μ-OTf)}2] (6) were obtained by thermal decomposition of 4. The successive addition of NEt4CN or KCN to 1 led to the formation of the cyanido-bridged dinuclear compound [(UN*3)2(μ-CN)][BPh4] (7) and the mononuclear mono- and bis(cyanide) complexes [UN*3(CN)] (2) and [M][UN*3(CN)2] [M = NEt4 (8), K(THF)4 (9)], while crystals of [K(18-crown-6)][UN*3(CN)2] (10) were obtained by the oxidation of [K(18-crown-6)][UN*3(CN)] with pyridine N-oxide.

Catalytic methylation of aromatic amines with formic acid as the unique carbon and hydrogen source.

A novel methodology is presented for the direct methylation of amines, using formic acid as a unique source of carbon and hydrogen. Based on ruthenium(II) catalysts, the formation of the N-CH3 group proceeds via an efficient formylation/transfer hydrogenation pathway.

Efficient disproportionation of formic acid to methanol using molecular ruthenium catalysts.

The disproportionation of formic acid to methanol was unveiled in 2013 using iridium catalysts. Although attractive, this transformation suffers from very low yields; methanol was produced in less than 2% yield, because the competitive dehydrogenation of formic acid (to CO2 and H2) is favored. We report herein the efficient and selective conversion of HCOOH to methanol in 50% yield, utilizing ruthenium(II) phosphine complexes under mild conditions.

U-CN versus Ce-NC coordination in trivalent complexes derived from M[N(SiMe3)2]3 (M = Ce, U).

Reactions of [MN*3] (M = Ce, U; N* = N(SiMe3)2) and NR4CN (R = Me, Et, or (n)Bu) or KCN in the presence of 18-crown-6 afforded the series of cyanido-bridged dinuclear compounds [NEt4][(MN*3)2(μ-CN)] (M = Ce, 2a, and U, 2b), [K(18-crown-6)(THF)2][(CeN*3)2(μ-CN)] (2'a), and [K(18-crown-6)][(UN*3)2(μ-CN)] (2'b), and the mononuclear mono-, bis-, and tris(cyanide) complexes [NEt4][MN*3(CN)] (M = Ce, 1a(Et), and U, 1b(Et)), [NMe4][MN*3(CN)] (M = Ce, 1a(Me), and U, 1b(Me)), [K(18-crown-6)][MN*3(CN)] (M = Ce, 1'a, and U, 1'b), [N(n)Bu4]2[MN*3(CN)2] (M = Ce, 3a, and U, 3b), [K(18-crown-6)]2[MN*3(CN)2] (M = Ce, 3'a, and U, 3'b), and [N(n)Bu4]2[MN*2(CN)3] (M = Ce, 4a, and U, 4b). The mono- and bis(cyanide) complexes were found to be in equilibrium. The formation constant of 3'b (K3'b) from 1'b at 10 °C in THF is equal to 5(1) × 10(-3), and -ΔH3'b = 104(2) kJ mol(-1) and -ΔS3'b = 330(5) J mol(-1) K(-1).

Nitrite complexes of the rare earth elements.

The coordination chemistry of the nitrite anion has been investigated with rare earth elements, and the resulting complexes were structurally characterized. Among them, the first homoleptic examples of nitrite complexes of samarium, ytterbium and yttrium are described. The coordination behavior of the nitrite ion is directly controlled by the ionic radius of the metal cation.

Regioselective and stereospecific deuteration of bioactive aza compounds by the use of ruthenium nanoparticles.

An efficient H/D exchange method allowing the deuteration of pyridines, quinolines, indoles, and alkyl amines with D2 in the presence of Ru@PVP nanoparticles is described. By a general and simple procedure involving mild reaction conditions and simple filtration to recover the labeled product, the isotopic labeling of 22 compounds proceeded in good yield with high chemo- and regioselectivity. The viability of this procedure was demonstrated by the labeling of eight biologically active compounds.

Revisiting the chemistry of the actinocenes [(η8-C8H8)2An] (An = U, Th) with neutral Lewis bases. Access to the bent sandwich complexes [(η8-C8H8)2An(L)] with thorium (L = py, 4,4'-bipy, tBuNC, R4phen).

In stark contrast to uranocene, (Cot)2Th reacts with neutral mono- or bidentate Lewis bases to give the bent sandwich complexes (Cot)2Th(L) (L = py, 4,4'-bipy, tBuNC, phen, Me4phen). DFT calculations in the gas phase show that, for both U and Th, formation of the bent compound (Cot)2An(L) should be facile, the linear and bent forms being close in energy.

Bent thorocene complexes with the cyanide, azide and hydride ligands.

Reaction of the linear thorocene with NC(-), N3(-) and H(-) led to the bent derivatives [(Cot)2Th(X)](-) (X = CN, N3) and the bimetallic [{(Cot)2Th}2(μ-H)](-), whereas only [(Cot)2U(CN)](-) could be formed from (Cot)2U.

Nitrite complexes of uranium and thorium.

The first examples of inorganic nitrite complexes of the natural actinides are described, including the structures of the homoleptic thorium(IV) [PPh(4)](2)[Th(NO(2))(6)] and the uranyl(VI) [PPh(4)](2)[UO(2)(NO(2))(4)] complexes; the nitrite ligand can adopt two different coordination modes in the coordination sphere of the uranyl ion and is unstable towards reduction.

Iodide, azide, and cyanide complexes of (N,C), (N,N), and (N,O) metallacycles of tetra- and pentavalent uranium.

In contrast to the neutral macrocycle [UN*(2)(N,C)] (1) [N* = N(SiMe(3))(3); N,C = CH(2)SiMe(2)N(SiMe(3))] which was quite inert toward I(2), the anionic bismetallacycle [NaUN*(N,C)(2)] (2) was readily transformed into the enlarged monometallacycle [UN*(N,N)I] (4) [N,N = (Me(3)Si)NSiMe(2)CH(2)CH(2)SiMe(2)N(SiMe(3))] resulting from C-C coupling of the two CH(2) groups, and [NaUN*(N,O)(2)] (3) [N,O = OC(═CH(2))SiMe(2)N(SiMe(3))], which is devoid of any U-C bond, was oxidized into the U(V) bismetallacycle [Na{UN*(N,O)(2)}(2)(μ-I)] (5). Sodium amalgam reduction of 4 gave the U(III) compound [UN*(N,N)] (6). Addition of MN(3) or MCN to the (N,C), (N,N), and (N,O) metallacycles 1, 4, and 5 led to the formation of the anionic azide or cyanide derivatives M[UN*(2)(N,C)(N(3))] [M = Na, 7a or Na(15-crown-5), 7b], M[UN*(2)(N,C)(CN)] [M = NEt(4), 8a or Na(15-crown-5), 8b or K(18-crown-6), 8c], M[UN*(N,N)(N(3))(2)] [M = Na, 9a or Na(THF)(4), 9b], [NEt(4)][UN*(N,N)(CN)(2)] (10), M[UN*(N,O)(2)(N(3))] [M = Na, 11a or Na(15-crown-5), 11b], M[UN*(N,O)(2)(CN)] [M = NEt(4), 12a or Na(15-crown-5), 12b].

Towards high-valent uranium compounds from metallacyclic uranium(IV) precursors.

Treatment of [NaUN*(C,N)(2)] [N* = N(SiMe(3))(2); C,N = CH(2)SiMe(2)N(SiMe(3))] with I(2) led to the formation of the larger metallacycle [UN*(N{SiMe(3)}SiMe(2)CH(2)CH(2)SiMe(2)N{SiMe(3)})I] resulting from U-C cleavage and C-C coupling. Reaction of [NaUN*(O,N)(2)] [O,N = OC(=CH(2))SiMe(2)N(SiMe(3))] with I(2) afforded the U(V) complex [Na{UN*(O,N)(2)}(2)(μ-I)] which was converted into the mononuclear azido derivative [NaUN*(O,N)(2)(N(3))]. This latter was not transformed into the neutral U(VI) derivative in the presence of I(2) but afforded [U(V)(N{SiMe(3)}SiMe(2)C{CHI}O)(2)I(THF)], resulting from a cascade of addition, substitution and protonolysis reactions.

Exploring the uranyl organometallic chemistry: from single to double uranium-carbon bonds.

Uranyl organometallic complexes featuring uranium(VI)-carbon single and double bonds have been obtained from uranyl UO(2)X(2) precursors by avoiding reduction of the metal center. X-ray diffraction and density functional theory analyses of these complexes showed that the U-C and U=C bonds are polarized toward the nucleophilic carbon.

Investigating the electronic structure and bonding in uranyl compounds by combining NEXAFS spectroscopy and quantum chemistry.

The nature of the reactivity of the "yl" oxygens has been a subject of constant interest for a long time in uranyl chemistry. Thus, the electron-donor ability of the equatorial ligands plays an important role in the nature of the uranyl U=O bond. In this paper, a combination of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and both ground-state and time-dependent density functional theory (DFT) calculations have been used to examine the effect of equatorial plane ligation on the U=O bonding in two uranyl complexes: [UO(2)(py)(3)I(2)] and [UO(2)(CN)(5)][NEt(4)](3).