Metal-nitrogen multiple bonds. V. Crystal structure of potassium nitridopentachloroosmate(VI)(K2OsNCl5)

A Terminal Osmium(IV) Nitride: Ammonia Formation and Ambiphilic Reactivity

Low-valent osmium nitrides are discussed as intermediates in nitrogen fixation schemes. However, rational synthetic routes that lead to isolable examples are currently unknown. Here, the synthesis of the square-planar osmium(IV) nitride [OsN(PNP)] (PNP=N(CH2 CH2 P(tBu)2 )2 ) is reported upon reversible deprotonation of osmium(VI) hydride [Os(N)H(PNP)](+) . The Os(IV) complex shows ambiphilic nitride reactivity with SiMe3 Br and PMe3 , respectively. Importantly, the hydrogenolysis with H2 gives ammonia and the polyhydride complex [OsH4 (HPNP)] in 80 % yield. Hence, our results directly demonstrate the role of low-valent osmium nitrides and of heterolytic H2 activation for ammonia synthesis with H2 under basic conditions.

Uranium-ligand multiple bonding in uranyl analogues, [L═U═L]n+, and the inverse trans influence

The societal importance of uranium complexes containing the uranyl moiety [O═U═O](2+) continues to grow with the ongoing international nuclear enterprise and associated accumulating legacy waste. Further studies of the electronic structure of uranyl and its analogues are imperative for the development of crucial technologies, including lanthanide/actinide extractants and chemical and environmental remediation methodologies. Actinide oxo halides are a subset of the growing class of actinyl (uranyl) analogues. The understanding of their electronic structures links the detailed spectroscopic studies of uranyl, indicating the role of the pseudocore 6p orbitals in U-O bonding, to hypotheses about the 6p orbitals' role in the chemical bonding of uranyl analogues. These actinide oxo halides are a very small class of actinide compounds that present the inverse trans influence (ITI). This class of complexes was, until recently, limited to two crystallographically characterized compounds, namely, [UCl(5)O][PPh(4)] and [PaCl(5)O][NEt(4)](2). These complexes are important because they give a readily and clearly defined experimental observable: the difference between the M-X(trans) and M-X(cis) (here X = Cl) bond lengths in the solid state. This bond metric is a sensitive probe for the role of 6p, 6d, and 5f orbitals, as well as electrostatic interactions, in determining their electronic structure. This Viewpoint Article reviews the theoretical, experimental, and synthetic work on the ITI in actinide complexes and contextualizes it within broader studies on the electronic structure of uranyl and its analogues. Furthermore, our recent work on the ITI in high-valent uranium(V/VI) oxo and imido complexes is described as a whole. This work builds on the extant synthetic literature on the ITI and provides design parameters for the synthesis and characterization of high-valent uranium-ligand multiple bonds.

Electronic structures and spectroscopic properties of nitrido-osmium(VI) complexes with acetylide ligands [OsN(CCR)4]− RH, CH3, and Ph by density functional theory calculation

Electronic structures and spectroscopic properties of a series of nitrido-osmium (VI) complex ions with acetylide ligands, [OsN(C[Triple Bond]CR)(4)](-) (R[Double Bond]H, (1), CH(3) (2), and Ph (3)) were investigated theoretically. The structures of the complexes were fully optimized at the B3LYP and CIS level for the ground states and excited states, respectively. The calculated bond lengths of Os[Triple Bond]N (1.639 A in 1, 1.642 A in 2, and 1.643 A in 3) and Os-C (2.040 A in 1, 2.043 A in 2, and 2.042 A in 3) in ground state agree well with the experimental results. The bond length of Os[Triple Bond]N bond is lengthened by ca. 0.13 A in the A (3)B(2) excited state compared to the (1)A(1) ground state, which is consistent with the lower vibration frequency of nu(Os-N) ( approximately 780 cm(-1)) in the excited state than that ( approximately 1175 cm(-1)) in the ground state. Among the calculated dipole-allowed absorptions at lambda>250 nm, the intense absorption at 261 nm for 1, 266 nm for 2, and 300 nm for 3 were attributed to the (1)[pi(C[Triple Bond]C)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C)], (1)[pi(C[Triple Bond]C)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C)], and (1)[pi(C[Triple Bond]CPh)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]CPh)], respectively. The lowest energy absorption at lambda(max)=393 nm for 1, 400 nm for 2, and 400 nm for 3 were assigned as (1)[d(xy)(Os)+pi(C[Triple Bond]C)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C)], (1)[d(xy)(Os)+pi(C[Triple Bond]C)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C)], and (1)[d(xy)(Os)+pi(C[Triple Bond]CPh)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]CPh)], respectively. The calculated phosphorescence emission at lambda(max)=581 nm for 1, 588 nm for 2, and 609 nm for 3 were originated from (3)[(pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C))(1)(d(xy)(Os)+pi(C[Triple Bond]C))(1)], (3)[(pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C))(1)(d(xy)(Os)+pi(C[Triple Bond]C))(1)], and (3)[(pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]CPh))(1)(d(xy)(Os)+pi(C[Triple Bond]CPh))(1)] excited state, respectively.

Osmium(VI) Nitrido and Osmium(IV) Phosphoraniminato Complexes Containing Schiff Base Ligands

A series of osmium(VI) nitrido complexes containing Schiff base ligands, [Os(VI)(N)(L)Cl] (L = salophen or salen), have been synthesized by reaction of the ligand with [NBu(n)(4)][Os(VI)(N)Cl(4)] in the presence of 2,6-dimethylpyridine. The nu(Os&tbd1;N) for the salophen complexes occur at around 1070 cm(-)(1) and are insensitive to the nature of the substituents present on the Schiff base ligand. The structures of [Os(N)(salophen)(MeOH)]ClO(4) and [Os(N)(5,5-Cl(2)salophen)(MeOH)]ClO(4) have been determined by X-ray crystallography, and the Os&tbd1;N bond distances are 1.651 and 1.66 Å, respectively. The osmium(VI) nitrido complexes react rapidly with triphenylphosphine to produce the corresponding osmium(IV) phosphoraniminato complexes, [Os(IV)(NPPh(3))(L)Cl]. The osmium(IV) complexes exhibit reversible Os(V/IV) and Os(IV/III) couples in cyclic voltammetry. The E(1/2) values show linear correlations with the Hammett constants sigma(p) of the substituents on the Schiff base ligand. The structure of [Os(IV)(NPPh(3))(salophen)Cl] has been determined by X-ray crystallography. The rather long Os-N(P) bond length (1.92 Å) and acute Os-N-P bond angle (149.6 degrees ) suggest that there is no significant multiple-bond character in the Os-N bond. The kinetics of nitrogen atom transfer from a series of 5,5'-disubstituted salophen nitrido complexes to PPh(3) have been studied in CH(3)CN at 25.0 degrees C by stopped-flow spectrophotometric method. The following rate law was obtained: -d[Os(VI)]/dt = k(2)[Os(VI)][PPh(3)]. The reactivities of the complexes were found to follow a Hammett correlation of log(k(X)/k(H)) with sigma(p), with a rho value of 1.9 +/- 0.1. The positive rho value is consistent with a transition state involving electrophilic attack by the nitrido ligand on the phosphorus atom.

Influence of heme-surrounding amino acid residues on the manganese (V)-nitrido bond in manganese-substituted hemoproteins: resonance Raman evidence for porphyrin core expansion and reduction of the manganese(V)-nitrido stretching force constant

Nitridomanganese(V) protoporphyrin IX was prepared by hypochlorite oxidation of the corresponding manganese(III) protoporphyrin IX derivative in the presence of ammonium ion and by photolysis of the corresponding azidomanganese(III) complex. Myoglobin and horseradish peroxidase containing this novel protoporphyrin derivative were prepared for the first time. These remarkably stable species were examined by electronic absorption, electron paramagnetic resonance, and resonance Raman spectroscopies. The MnV-N stretching modes of the nitridomanganese(V)-substituted myoglobin and horseradish peroxidase were observed at 1010 and 1003 cm-1, respectively, by resonance Raman spectroscopy, while the MnV-N stretching frequency for nitridomanganese(V) protoporphyrin IX in 0.1 N aqueous NaOH was found at 1046 cm-1. The equilibrium dissociation energies of MnV-N bonds in these complexes were estimated from vibrational overtone spacings by introducing the Morse potential energy function, were found to be around 4.5 eV, and seemed independent of the surroundings of the manganese porphyrin, although its force constant decreased from 7.3 to 6.7 mdyn/A upon incorporation into apoprotein. The porphyrin ring modes of these nitridomanganese(V) derivatives were influenced greatly upon incorporation into apoproteins, suggestive of the occurrence of porphyrin core expansion. Upon this core expansion the MnV center moves into the mean plane of porphyrin plane, but the access of nitrido (N) toward MnV is restricted due to a steric hindrance from porphyrin pyrrole nitrogens. The resulting stretched MnV-N bond might cause lowering of the MnV-N stretching frequency upon incorporation into apoprotein.