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Tuning the structure, reactivity and magnetic communication of nitride-bridged uranium complexes with the ancillary ligands.

ABSTRACT: Molecular uranium nitride complexes were prepared to relate their small molecule reactivity to the nature of the U[double bond, length as m-dash]N[double bond, length as m-dash]U bonding imposed by the supporting ligand. The U4+-U4+ nitride complexes, [NBu4][{(( t BuO)3SiO)3U}2(?-N)], [NBu4]-1, and [NBu4][((Me3Si)2N)3U}2(?-N)], 2, were synthesised by reacting NBu4N3 with the U3+ complexes, [U(OSi(O t Bu)3)2(?-OSi(O t Bu)3)]2 and [U(N(SiMe3)2)3], respectively. Oxidation of 2 with AgBPh4 gave the U4+-U5+ analogue, [((Me3Si)2N)3U}2(?-N)], 4. The previously reported methylene-bridged U4+-U4+ nitride [Na(dme)3][((Me3Si)2)2U(?-N)(?-?2-C,N-CH2SiMe2NSiMe3)U(N(SiMe3)2)2] (dme = 1,2-dimethoxyethane), [Na(dme)3]-3, provided a versatile precursor for the synthesis of the mixed-ligand U4+-U4+ nitride complex, [Na(dme)3][((Me3Si)2N)3U(?-N)U(N(SiMe3)2)(OSi(O t Bu)3)], 5. The reactivity of the 1-5 complexes was assessed with CO2, CO, and H2. Complex [NBu4]-1 displays similar reactivity to the previously reported heterobimetallic complex, [Cs{(( t BuO)3SiO)3U}2(?-N)], [Cs]-1, whereas the amide complexes 2 and 4 are unreactive with these substrates. The mixed-ligand complexes 3 and 5 react with CO and CO2 but not H2. The nitride complexes [NBu4]-1, 2, 4, and 5 along with their small molecule activation products were structurally characterized. Magnetic data measured for the all-siloxide complexes [NBu4]-1 and [Cs]-1 show uncoupled uranium centers, while strong antiferromagnetic coupling was found in complexes containing amide ligands, namely 2 and 5 (with maxima in the ? versus T plot of 90 K and 55 K). Computational analysis indicates that the U(?-N) bond order decreases with the introduction of oxygen-based ligands effectively increasing the nucleophilicity of the bridging nitride.

SUBMITTER: Palumbo CT

PROVIDER: S-EPMC6853081 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Tuning the structure, reactivity and magnetic communication of nitride-bridged uranium complexes with the ancillary ligands.

Palumbo Chad T CT Barluzzi Luciano L Scopelliti Rosario R Zivkovic Ivica I Fabrizio Alberto A Corminboeuf Clémence C Mazzanti Marinella M

Chemical science 20190813 38

Molecular uranium nitride complexes were prepared to relate their small molecule reactivity to the nature of the U[double bond, length as m-dash]N[double bond, length as m-dash]U bonding imposed by the supporting ligand. The U4+-U4+ nitride complexes, [NBu4][{(( t BuO)3SiO)3U}2(μ-N)], [NBu4]-1, and [NBu4][((Me3Si)2N)3U}2(μ-N)], 2, wer ...[more]

PMID: 31803458

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Project description:The series of complexes [XRu(CO)(L-L)(L')2][PF6] (X = H, TFA, Cl; L-L = 2,2'-bipyridyl, 1,10-phenanthroline, 5-amino-1,10-phenanthroline and 4,4'-dicarboxylic-2,2'-bipyridyl; L'2 = 2PPh3, Ph2 PC2H4PPh2, Ph2PCH?CHPPh2) have been synthesized from the starting complex K[Ru(CO)3(TFA)3] (TFA = CF3CO2) by first reacting with the phosphine ligand, followed by reaction with the L-L and anion exchange with NaPF6. In the case of L-L = phenanthroline and L'2 = 2PPh3, the neutral complex Ru(Ph3P)(CO)(1,10-phenanthroline)( TFA)2 is also obtained and its solid state structure is reported. Solid state structures are also reported for the cationic complexes where L-L = phenanthroline, L2 = 2PPh3 and X = Cl and for L-L = 2,2'-bipyridyl, L2 = 2PPh3 and X = H. All the complexes were characterized in solution by a combination of 1H and 31P NMR, IR, mass spectrometry and elemental analyses. The purpose of the project was to synthesize a series of complexes that exhibit a range of excited-state lifetimes and that have large Stokes shifts, high quantum yields and high intrinsic polarizations associated with their metal-to-ligand charge-transfer (MLCT) emissions. To a large degree these goals have been realized in that excited-state lifetimes in the range of 100 ns to over 1 ?s are observed. The lifetimes are sensitive to both solvent and the presence of oxygen. The measured quantum yields and intrinsic anisotropies are higher than for previously reported Ru(II) complexes. Interestingly, the neutral complex with one phosphine ligand shows no MLCT emission. Under the conditions of synthesis some of the initially formed complexes with X = TFA are converted to the corresponding hydrides or in the presence of chlorinated solvents to the corresponding chlorides, testifying to the lability of the TFA Ligand. The compounds show multiple reduction potentials which are chemically and electrochemically reversible in a few cases as examined by cyclic voltammetry. The relationships between the observed photophysical properties of the complexes and the nature of the ligands on the Ru(II) is discussed.

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Tuning the structure, reactivity and magnetic communication of nitride-bridged uranium complexes with the ancillary ligands.

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Tuning the structure, reactivity and magnetic communication of nitride-bridged uranium complexes with the ancillary ligands.

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