Influence of the [2.1.1]-(2,6)-pyridinophane macrocycle ring size constraint on the structure and reactivity of copper complexes

The macrocycle [2.1.1]-(2,6)-pyridinophane (L) binds to CuCl to give a monomeric molecule with tridentate binding of the ligand but in a distorted tetrahedral "3 + 1" geometry, where one nitrogen forms a longer (by 0.12 A) bond to Cu. In dichloromethane solvent this pyridine donor undergoes facile site exchange with a second pyridine in the macrocycle, to give time-averaged mirror symmetry. Both experimental and density functional theory studies of the product of chloride abstraction, using NaBAr(F)(4) in CH(2)Cl(2), show that the Cu(+) binds in a trigonal pyramidal, not planar, arrangement in LCu(+). This illustrates the ability of macrocyclic ligand constraint to impose an electronically unfavorable geometry on 3-coordinate Cu(I). LCuBAr(F)(4) and a triflate analogue LCu(I)(OTf) readily react with oxygen in dichloromethane to produce, in the latter case, a hydroxo-bridged dimer [LCu(II)(micro-OH)](2)(OTf)(2), of the intact (unoxidized) ligand L. Since the analogous LCuCl does not react as fast with O(2) in CH(2)Cl(2), outer-sphere electron transfer is concluded to be ineffective for oxidation of cuprous ion here.     

Aggregation and solvation of a lithium aryloxide

{Li[OC₆H₃-2,6-(^tBu)₂]THF}₂, synthesized from phenol and LiH, is shown by X-ray crystallography to exist in the solid as a centrosymmetric dimer with two bridging phenoxides. Terminal THF ligands (envelope conformation) complete trigonal planar coordination about Li. The THF ligand plane lies in the Li₂(-O)₂ plane, while the phenyl ligands are perpendicular to this same Li₂O₂ plane. This explains the unusual¹H NMR chemical shifts of the THF ligand. THF binds to Li as a dipole rather than using one of the two ether lone pairs. Crystallographic data (–160°C):a=18.799(3) Å,b=18.758(6),c=15.697(5), andZ=4 in space groupPbca (no. 61). The final quality indices areR(F)=6.2% andR _w (F)=5.9% for 1535 unique data.     

Influence of chelate substituents on the structure and spin state of unsaturated [N(SiMe2CH2PtBu2)2]Ru-X

Density functional theory calculations on the conformational preferences in the two fused five-membered rings of anionic N(SiR2CH2PR'2)2 chelated to RuX+ are compared to several experimental structures (X=halide). The calculations consider the structures of both singlet and triplet states and reveal that both the four tBu groups and the crowded juncture (N(SiMe2)2) of the two rings must be included computationally to understand the observed structures. Computational experiments with different substituents R and R' show the reality of N-->Ru pi donation. The cases where X=H and CH3 are also studied.     

Radical (NO) and nonradical (N(2)O) reagents convert a ruthenium(IV) nitride to the same nitrosyl complex

The ruthenium(IV) nitride complex (PNP)RuN (PNP = (tBu2PCH2-SiMe2)2N-) reacts rapidly with 2NO to form (PNP)Ru(NO) and N2O, via no detectable intermediate. The linear nitrosyl complex has a planar structure. In a slower reaction, (PNP)RuN reacts with N2O by O-atom transfer (established by 15N labeling) to give the same nitrosyl complex and N2. Density functional theory (B3LYP) calculations show both reactions to be very thermodynamically favorable. Analysis of possible intermediates in each reaction shows that radical (PNP)RuN(NO) has much spin density on nitride N (hence, N2-), while one 2 + 3 metallacycle, (PNP)RuN3O, has the wrong connectivity to form a product. Instead, an intermediate with a doubly bent N2O (hence, a two-electron reduced N-nitrosoimide form) brings the O atom in proximity to the nitride N on the path to a product.