1,2-Diiodo-4,5-dimethyl­benzene

The structure of the title compound, C8H8I2, conforms closely to the mm2 symmetry expected for the free mol­ecule and is the first reported structure of a diiodo­dimethyl­benzene. Repulsion by neighboring I atoms and the neighboring methyl groups opposite to them results in a slight elongation of the mol­ecule along the approximate twofold rotation axis that bis­ects the ring between the two I atoms. In the extended structure, the mol­ecules form inversion-related pairs which are organized in approximately hexa­gonal close-packed layers and the layers then stacked so that mol­ecules in neighboring layers abut head-to-tail in a manner that optimizes dipole–dipole inter­actions

Cationic and neutral four-coordinate alkylidene complexes of vanadium(IV) containing short V:C bonds

Kinetically stable, four-coordinate V(IV) neopentylidene complexes such as [(Nacnac)V:CHtBu(THF)](BPh4) (Nacnac- = [Ar]NC(Me)CHC(Me)N[Ar], Ar = 2,6-(CHMe2)2C6H3), which was prepd. by oxidatively induced alpha-H abstraction from [(Nacnac)V(CH2tBu)2] with AgBPh4 in THF, contain the shortest V:C bonds known to date. [on SciFinder (R)

Four-coordinate alkylidene, alkylidyne and phosphinidene complexes of vanadium: One and two-electron oxidatively-induced alpha-hydrogen abstraction reactions

One electron oxidn. of the beta-Diketiminate vanadium (III) bis-neopentyl complex (Nacnac)V(CH2tBu)2 (Nacnac-=[Ar]NC(Me)CHC(Me)N[Ar], Ar=2,6-(CHMe2)2C6H3) promotes alpha-abstraction to afford the cationic four-coordinate neopentylidene vanadium complex [(Nacnac)V=CHtBu(THF)][BPh4]. The neutral vanadium neopentylidene complex (Nacnac)V=CHtBu(I) was prepd. by the reaction of cationic complex [(Nacnac)V=CHtBu(THF)][BPh4] with I-. This family of alkylidene complexes are one electron paramagnets and display well-resolved EPR spectra at room temp. The thermal stability of these systems was explored in addn. to its reactivity. In conjunction with the above studies, novel four-coordinate vanadium(IV) phosphinidene complexes (Nacnac)V=PR(CH2tBu) (R=2,4,6-iPr3C6H2, 2,4,6-tBuC6H2) were also prepd. from salt metathesis of (Nacnac)V=CHtBu(I) with LiPHR. Solid and soln. magnetic measurements, EPR spectra, and single crystal X-ray diffraction studies have been carried out for all the complexes described. Two electron-oxidn. and double alpha-hydrogen abstraction starting from (Nacnac)V(CH2tBu)2 lead to the first four coordinate neopentylidyne complex (Nacnac)V.tplbond.CtBu(Otf) which showed a distinct alkylidyne carbon resonance at 375 ppm at -50 DegC. [on SciFinder (R)

Computational Transition-State Design Provides Experimentally Verified Cr(P,N) Catalysts for Control of Ethylene Trimerization and Tetramerization

Computational design of molecular homogeneous organometallic catalysts followed by experimental realization remains a significant challenge. Here, we report the development and use of a density functional theory transition-state model that provided quantitative prediction of molecular Cr catalysts for controllable selective ethylene trimerization and tetramerization. This computational model identified a general class of phosphine monocyclic imine (P,N)-ligand Cr catalysts where changes in the ligand structure control 1-hexene versus 1-octene selectivity. Experimental ligand and catalyst synthesis as well as reaction testing quantitatively confirmed predictions

Hydrogen Production Using Nickel Electrocatalysts with Pendant Amines: Ligand Effects on Rates and Overpotentials

A Ni-based electrocatalyst for H₂ production, [Ni­(8P^Ph₂N^C₆H₄Br)₂]­(BF₄)₂, featuring eight-membered cyclic diphosphine ligands incorporating a single amine base, 1-<i>para</i>-bromophenyl-3,7-triphenyl-1-aza-3,7-diphosphacycloheptane (8P^Ph₂N^C₆H₄Br) has been synthesized and characterized. X-ray diffraction studies reveal that the cation of [Ni­(8P^Ph₂N^C₆H₄Br)₂(CH₃CN)]­(BF₄)₂ has a distorted trigonal bipyramidal geometry. In CH₃CN, [Ni­(8P^Ph₂N^C₆H₄Br)₂]²⁺ is an electrocatalyst for reduction of protons, and it has a maximum turnover frequency for H₂ production of 800 s^–1 with a 700 mV overpotential (at <i>E</i>_cat/2) when using [(DMF)­H]­OTf as the acid. Addition of H₂O to acidic CH₃CN solutions of [Ni­(8P^Ph₂N^C₆H₄Br)₂]²⁺ results in an increase in the turnover frequency for H₂ production to a maximum of 3300 s^–1 with an overpotential of 760 mV at <i>E</i>_cat/2. Computational studies carried out on [Ni­(8P^Ph₂N^C₆H₄Br)₂]²⁺ indicate the observed catalytic rate is limited by formation of nonproductive protonated isomers, diverting active catalyst from the catalytic cycle. The results of this research show that proton delivery from the exogenous acid to the correct position on the proton relay of the metal complex is essential for fast H₂ production

Studies of a Series of [Ni(P^R₂N^Ph₂)₂(CH₃CN)]²⁺ Complexes as Electrocatalysts for H₂ Production: Substituent Variation at the Phosphorus Atom of the P₂N₂ Ligand

A series of [Ni(P^R₂N^Ph₂)₂(CH₃CN)](BF₄)₂ complexes containing the cyclic diphosphine ligands [P^R₂N^Ph₂ = 1,5-diaza-3,7-diphosphacyclooctane; R = benzyl (Bn), <i>n</i>-butyl (<i>n-</i>Bu), 2-phenylethyl (PE), 2,4,4-trimethylpentyl (TP), and cyclohexyl (Cy)] have been synthesized and characterized. X-ray diffraction studies reveal that the cations of [Ni(P^Bn₂N^Ph₂)₂(CH₃CN)](BF₄)₂ and [Ni(P^{<i>n</i>‑Bu}₂N^Ph₂)₂(CH₃CN)](BF₄)₂ have distorted trigonal bipyramidal geometries. The Ni(0) complex [Ni(P^Bn₂N^Ph₂)₂] was also synthesized and characterized by X-ray diffraction studies and shown to have a distorted tetrahedral structure. These complexes, with the exception of [Ni(P^Cy₂N^Ph₂)₂(CH₃CN)](BF₄)₂, all exhibit reversible electron transfer processes for both the Ni(II/I) and Ni(I/0) couples and are electrocatalysts for the production of H₂ in acidic acetonitrile solutions. The heterolytic cleavage of H₂ by [Ni(P^R₂N^Ph₂)₂(CH₃CN)](BF₄)₂ complexes in the presence of <i>p</i>-anisidine or <i>p</i>-bromoaniline was used to determine the hydride donor abilities of the corresponding [HNi(P^R₂N^Ph₂)₂](BF₄) complexes. However, for the catalysts with the most bulky R groups, the turnover frequencies do not parallel the driving force for elimination of H₂, suggesting that steric interactions between the alkyl substituents on phosphorus and the nitrogen atom of the pendant amines play an important role in determining the overall catalytic rate