A Solid−Gas Route to Polymorph Conversion in Crystalline [Fe^II(η⁵-C₅H₄COOH)₂]. A Diffraction and Solid-State NMR Study

Crystalline form I (monoclinic) and form II (triclinic) of ferrocene dicarboxylic acid [Fe(η5-C5H4COOH)2] have been employed in solid−gas reactions at room temperature with the gaseous bases NH3, NH2(CH3), and NH(CH3)2. The two crystal forms behave in exactly the same way in the solid−gas reaction, generating the same products, identified as the anhydrous crystalline salts [NH4]2[Fe(η5-C5H4COO)2] (1), [NH3CH3]2[Fe(η5-C5H4COO)2] (2), and [NH2(CH3)2]2[Fe(η5-C5H4COO)2] (3). Interestingly though, all these crystals revert via vapor release exclusively to the metastable crystalline form I. Starting materials and products have been investigated by single-crystal and powder diffraction and by 13C, 15N CPMAS and 1H MAS methods

A Solid−Gas Route to Polymorph Conversion in Crystalline [Fe^II(η⁵-C₅H₄COOH)₂]. A Diffraction and Solid-State NMR Study

Crystalline form I (monoclinic) and form II (triclinic) of ferrocene dicarboxylic acid [Fe(η5-C5H4COOH)2] have been employed in solid−gas reactions at room temperature with the gaseous bases NH3, NH2(CH3), and NH(CH3)2. The two crystal forms behave in exactly the same way in the solid−gas reaction, generating the same products, identified as the anhydrous crystalline salts [NH4]2[Fe(η5-C5H4COO)2] (1), [NH3CH3]2[Fe(η5-C5H4COO)2] (2), and [NH2(CH3)2]2[Fe(η5-C5H4COO)2] (3). Interestingly though, all these crystals revert via vapor release exclusively to the metastable crystalline form I. Starting materials and products have been investigated by single-crystal and powder diffraction and by 13C, 15N CPMAS and 1H MAS methods

Facile Activation of Dihydrogen by a Phosphinito-Bridged Pt(I)−Pt(I) Complex

The phosphinito-bridged Pt(I) complex [(PHCy2)Pt(μ-PCy2){κ2P,O-μ-P(O)Cy2}Pt(PHCy2)](Pt−Pt) (1) reversibly adds H2 under ambient conditions, giving cis-[(H)(PHCy2)Pt1(μ-PCy2)(μ-H)Pt2(PHCy2){κP-P(O)Cy2}](Pt−Pt) (2). Complex 2 slowly isomerizes spontaneously into the corresponding more stable isomer trans-[(PHCy2)(H)Pt(μ-PCy2)(μ-H)Pt(PHCy2){κP-P(O)Cy2}](Pt−Pt) (3). DFT calculations indicate that the reaction of 1 with H2 occurs through an initial heterolytic splitting of the H2 molecule assisted by the phosphinito oxygen with breaking of the Pt−O bond and hydrogenation of the Pt and O atoms, leading to the formation of the intermediate [(PHCy2)(H)Pt(μ-PCy2)Pt(PHCy2){κP-P(OH)Cy2}](Pt−Pt) (D), where the two split hydrogen atoms interact within a six-membered Pt−H···H−OP−Pt ring. Compound D is a labile intermediate which easily evolves into the final dihydride complex 2 through a facile (9−15 kcal mol−1, depending on the solvent) hydrogen shift from the phosphinito oxygen to the Pt−Pt bond. Information obtained by addition of para-H2 on 1 are in agreement with the presence of a heterolytic pathway in the 1 → 2 transformation. NMR experiments and DFT calculations also gave evidence for the nonclassical dihydrogen complex [(PHCy2)(η2-H2)Pt(μ-PCy2)Pt(PHCy2){κP-P(O)Cy2}](Pt−Pt) (4), which is an intermediate in the dehydrogenation of 2 to 1 and is also involved in intramolecular and intermolecular exchange processes. Experimental and DFT studies showed that the isomerization 2 → 3 occurs via an intramolecular mechanism essentially consisting of the opening of the Pt−Pt bond and of the hydrogen bridge followed by the rotation of the coordination plane of the Pt center with the terminal hydride ligand

¹⁵N Magnetic Resonance Hyperpolarization via the Reaction of Parahydrogen with ¹⁵N-Propargylcholine

¹⁵N-Propargylcholine has been synthesized and hydrogenated with para-H₂. Through the application of a field cycling procedure, parahydrogen spin order is transferred to the ¹⁵N resonance. Among the different isomers formed upon hydrogenation of ¹⁵N-propargylcholine, only the nontransposed derivative contributes to the observed N-15 enhanced emission signal. The parahydrogen-induced polarization factor is about 3000. The precise identification of the isomer responsible for the observed ¹⁵N enhancement has been attained through a retro-INEPT (¹⁵N–¹H) experiment. <i>T</i>₁ of the hyperpolarized ¹⁵N resonance has been estimated to be ca. 150 s, i.e., similar to that reported for the parent propargylcholine (144 s). Experimental results are accompanied by theoretical calculations that stress the role of scalar coupling constants (<i>J</i>_HN and <i>J</i>_HH) and of the field dependence in the formation of the observed ¹⁵N polarized signal. Insights into the good cellular uptake of the compound have been gained