Computational and spectroscopic studies of molecular lanthanide complexes have implicated 4f orbitals in metal–ligand bonding interactions. Now, a comparative study of isostructural d-block, actinide ...

It is with a heavy heart, that we must announce the passing of George Michael Sheldrick. Everyone in crystallography knows George as a giant in the development of computing methods […]

From code on a Titan to becoming the titan of crystal structure determination

Molecular ZrIV phosphides are extremely rare, with no examples containing a one-coordinated and terminal triple-bonded phosphorus atom. We report here an isolable and relatively stable Zr phosphide complex, [(PN)2Zr≡P{μ2-Na(OEt2)}]2 (4), stemming from a cyclometalated Zr-hydride, [(PN)(PN′)Zr(H)] (2), and NaPH2. Complex 2 is prepared from two- or one-electron reductions of precursors [(PN)2ZrCl2] (1) or metastable ZrIII[(PN)2ZrCl], respectively. Oxidation of 2 with ClCPh3 (2 equiv) or I2 (1 equiv) resulted in re-formation of the PN ligand and isolation of the ZrIV complexes [(PN)2ZrX2] (X = Cl, 1; X = I, 3), whereas addition of a weak acid to 2 allowed us to intercept the hydrido-halide intermediate [(PN)2Zr(I)(H)] (X = Cl, I) spectroscopically before conversion to 1 or 3. Complex 2 exchanged with D2 (1 atm) to fully deuterate the methylene all ortho-methyl groups of the PN and PN′ ligands and the hydride. Discrete salts of 4 can be readily prepared from Na+ encapsulation with the crown ether 1,4,7,10,13,16-hexaoxacyclooctadecane (18-C-6) or cryptand 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (222-Kryptofix) to form [Na(18-C-6)(THF)2][(PN)2Zr≡P] (5) and [Na(222-Kryptofix)][(PN)2Zr≡P] (6), respectively, which were structurally and spectroscopically characterized. Compounds 4–6 demonstrate exceptionally short Zr≡P bonds (4, 2.3270(18) Å; 5, 2.291(3) Å; 6, 2.2989(17) Å) and highly downfield 31P NMR spectral resonances (4, 819 ppm; 5 and 6, 927 and 955 ppm) in accord with a terminal phosphide ligand. The Zr≡P motif in 4–6 can be stabilized via coordination to a softer Tl+ ion to form a nonsolvated phosphide [(PN)2Zr≡P{μ2-Tl}]2 (7), exhibiting a phosphide resonance at ∼711 ppm.

A concise and convergent synthesis of the isosteroidal alkaloids veratramine and 20-iso-veratramine has been accomplished. A Horner–Wadsworth–Emmons olefination joins two chiral building blocks of app...

A concise synthesis of the complex diterpene azorellolide, inspired by speculations on biosynthetic cationic cascades, is presented. The approach, guided by computation, relies on the intramolecular interception of a cyclopropylcarbinyl cation by an appended carboxylate. The successful execution of this strategy was achieved through acid-catalyzed isomerization of a β-lactone in competition with a type I dyotropic rearrangement.

During the synthesis of a new family of diimine–dioxime acenaphthene cobalt complexes a novel cis coordination mode was observed and fully characterized. The preference for the cis vs. trans coordina....

Three organometallic ligand scaffolds resulting from the insertion of 1-adamantyl isonitrile (C≡NAd; Ad = C10H15) into titanium neopentylidene complexes, [(PNP)Ti═CHtBu(X)] are described herein. Treatment of the titanium neopentylidene complex (PNP)Ti═CHtBu(OTf) (1-OTf, PNP– = N[2-PiPr2-4-methylphenyl]2–, OTf = trifluoromethanesulfonate–) with one equivalent of C≡NAd leads to the formation of a titanium η2-C,N-ketenimine, (PNP)Ti(η2-C,N-AdNCCHtBu)(OTf) (2-OTf). However, when the titanium neopentylidene neopentyl complex (PNP)Ti═CHtBu(CH2tBu) (1-Np) is added one equivalent of C≡NAd, a titanium neopentylidene κ1-N-vinylamido complex (PNP)Ti═CHtBu(κ1-N-AdNCHCHtBu) (3) is formed. In contrast, the titanium neopentylidene methyl complex (PNP)Ti═CHtBu(CH3) (1-Me) reacts with one equivalent of C≡NAd to produce a rare chelating κ2-C,N-azaalleneyl ligand, in the complex (PNP)Ti(κ2-C,N-AdNCCtBu) (4), with concurrent extrusion of methane. Independently, it is shown that treatment of 2-OTf with one equivalent of neopentyl lithium (LiNp, Np– = CH2tBu) or a half equivalent of dimethyl magnesium (MgMe2) smoothly forms complex 3 or 4, respectively, and suggests that the η2-C,N-ketenimine ligand in 2-OTf might be an intermediate ligand enroute to the neopentylidene κ1-N-vinylamido or κ2-C,N-azaalleneyl complexes. Complexes 2-OTf, 3 and 4 have been structurally and spectroscopically characterized and a proposed mechanism for the formation of complexes 3 and 4 is also described.

A concise and convergent synthesis of the isosteroidal alkaloids veratramine and 20-epi-veratramine has been accom-plished. A Horner-Wadsworth-Emmons olefination joins two chiral building blocks of ap...