Collision of H(2) with the unusual nickel complex, (PNP)Ni(+), where PNP = ((t)Bu(2)PCH(2)SiMe(2))(2)N, forms a rare dihydrogen complex of the d(8) configuration which then rearranges to heterolytically cleave the H-H bond. Experimental studies support a short H/H distance in the coordinated diatomic, and DFT calculations show that the transition state for heterolysis, in spite of the fact that this involves an amide nitrogen located trans to the H(2), has the H/H bond fully split, and has all the geometric features of Ni(IV), but this is a local maximum, not a minimum.

The ligand class 2,2'-pyridylpyrrolide is surveyed, both for its structural features and its electronic structure, when attached to monovalent K, Cu, Ag, Au, and Rh. The influence of pyrrolide ring substituents is studied, as well as the question of push/pull interaction between the pyridyl and pyrrolide halves. The π donor ability of the pyrrolide is found to be less than that of an analogous phenyl. However, in contrast to the phenyl analog, the HOMO is pyrrolide π in character for pyridylpyrrolide complexes of copper and rhodium, while it is conventionally metal localized for planar, d(8) rhodium pyridylphenyl. Monovalent three-coordinate copper complexes show great deviations from Y-shaped toward T-shaped structures, including cases where the pyridyl ligand bonds only weakly.

The synthesis and characterization of a Cu(I) complex with a cis-bidentate monoanionic nitrogenous ligand, 2-pyridylpyrrolide, L, is reported. This shows binding of one base B = MeCN or CO per copper in a species LCu(B), but this readily releases the volatile ligand under vacuum with aggregation of transient LCu to a mixture of two enantiomers of a chiral trimer: a zwitterion containing inequivalent Cu(I) centers, possible via a new bonding mode of pyridylpyrrolide, and one with nitrogen lone pairs donating to two different metals. Density functional theory calculations show the energetics of both ligand binding and aggregation (including dimer and monomer alternatives), as well as the ability of this ligand to rotate away from planarity to accommodate a bridging structural role. The trimer serves as a synthon for the simple fragment LCu.

Exchange of deuterium in d6-benzene with all C-H sites in (PNP)Ru(OTf), where PNP is N(SiMe2CH2PtBu2)2 and OTf is OSO2CF3, is rapid at 22 degrees C. Although intact planar triplet (PNP)Ru(OTf) binds N2 only very weakly, these reagents are observed to react rapidly to give a diamagnetic 1:1 adduct whose structure has one tBu C-H bond cleaved: the carbon binds to Ru but the hydrogen is on the PNP nitrogen, creating a secondary amine ligand bound to RuII. It is suggested that the benzene C-D cleavage and the N2 product of tBu C-H bond heterolysis both derive from a common intermediate, [HN(SiMe2CH2PtBu2)(SiMe2CH2PtBuCMe2CH2)] Ru(OTf); the formation energy and structure of this species are discussed on the basis of DFT results.

Radical cyclization reactions at a peri position were used for the synthesis of polyaromatic compounds. Depending on the choice of reaction conditions and substrate, this flexible approach led to Bu Sn-substituted phenalene, benzanthrene, and olympicene derivatives. Subsequent reactions with electrophiles provided synthetic access to previously inaccessible functionalized polyaromatic compounds.

A versatile synthetic route to distannyl-substituted polyarenes was developed via double radical periannulations. The cyclization precursors were equipped with propargylic OMe traceless directing groups (TDGs) for regioselective Sn-radical attack at the triple bonds. The two peri-annulations converge at a variety of polycyclic cores to yield expanded difunctionalized polycyclic aromatic hydrocarbons (PAHs). This approach can be extended to triple peri-annulations, where annulations are coupled with a radical cascade that connects two preexisting aromatic cores via a formal C-H activation step. The installed Bu3Sn groups serve as chemical handles for further functionalization via direct cross-coupling, iodination, or protodestannylation, and increase solubility of the products in organic olvents. Photophysical studies reveal that the Bu3Sn-substituted PAHs are moderately fluorescent, and their protodestannylation serves as a chemical switch for high fluorescence. DFT calculations identified the most likely possible mechanism of this complex chemical transformation involving two independent peri-cyclizations at the central core. File list (2) download file view on ChemRxiv double_periannulation_02_16_20.pdf (2.09 MiB) download file view on ChemRxiv double_periannulation_SI.pdf (6.34 MiB)

Halogenated trifluoroacetylacetylenes have been synthesized for the first time. It was shown that they undergo formally forbidden by the orbital symmetry rules [2+2] cycloaddition reac tions with nonactivated alkenes in the absence of light and catalyst. A possible mechanism for this transformation is suggested.

The reaction of (PNP)NiH, where PNP is ((t)Bu2PCH2SiMe2)2-N(-1), with CO2 occurs over a period of hours at 25 degrees C to form (POP)NiH(NCO), which involves transposition of the initial amide nitrogen and one oxygen of CO2.