Coordination-Mode Control of Bound Nitrile Radical Complex Reactivity: Intercepting End-on Nitrile−Mo(III) Radicals at Low Temperature

Binding of Nitriles and Isonitriles to V(III) and Mo(III) Complexes: Ligand vs Metal Controlled Mechanism

The synthesis and structures of nitrile complexes of V(N[^tBu]Ar)₃, 2 (Ar = 3,5-Me₂C₆H₃), are described. Thermochemical and kinetic data for their formation were determined by variable temperature Fourier transform infrared (FTIR), calorimetry, and stopped-flow techniques. The extent of back-bonding from metal to coordinated nitrile indicates that electron donation from the metal to the nitrile plays a less prominent role for 2 than for the related complex Mo(N[^tBu]Ar)₃, 1. Kinetic studies reveal similar rate constants for nitrile binding to 2, but the activation parameters depend critically on the nature of R in RCN. Activation enthalpies range from 2.9 to 7.2 kcal·mol^-1, and activation entropies from -9 to -28 cal·mol^-1·K^-1 in an opposing manner. Density functional theory (DFT) calculations provide a plausible explanation supporting the formation of a π-stacking interaction between a pendant arene of the metal anilide of 2 and the arene substituent on the incoming nitrile in favorable cases. Data for ligand binding to 1 do not exhibit this range of activation parameters and are clustered in a small area centered at ΔH^‡ = 5.0 kcal·mol^-1 and ΔS^‡ = -26 cal·mol^-1·K^-1. Computational studies are in agreement with the experimental data and indicate a stronger dependence on electronic factors associated with the change in spin state upon ligand binding to 1.

pH-controlled crystal growth of copper/gemini surfactant complexes with bipyridine groups

pH-controlled crystal growth of two copper complexes with different coordination modes is successfully manipulated by means of pH adjustment.

Bis(μ(2)-η:η-2,4,6-trimethyl-benzonitrile)-bis-[(N-isopropyl-3,5-dimethyl-anilido)molybdenum(III)](Mo-Mo)

The title compound, [Mo₂(C₁₁H₁₆N)₄(C₁₀H₁₁N)₂], is a dinuclear molybdenum complex with a formal metal–metal bond [Mo⋯Mo separation = 2.5946 (8) Å], four anilide-type ligands and two bridging mesityl nitrile groups. There are two inversion symmetric mol­ecules in the unit cell (an inversion center is localized at the mid-point of the Mo—Mo bond), each with approximate non-crystallographic C_2h symmetry. The mol­ecules contain disordered isopropyl and 3,5-C₆H₃Me₂ groups on different anilido ligands; the major component having an occupancy of 0.683 (7). The complex was obtained in low yield as the product from the reaction between the bridging pyrazine adduct of molybdenum tris­-anilide ([μ₂-(C₄H₄N₂){Mo(C₁₁H₁₆N)₃}₂]) and mesityl nitrile with a loss of one anilido ligand.

Enthalpy vs Entropy Driven Complexation of Homoallylic Alcohols by Rh(I) Complexes

The thermodynamics of binding between several homoallylic alcohols and simple olefinic Rh(I) compounds was examined with (1)H NMR spectroscopy and ITC. (1)H NMR titrations revealed moderate binding of these alcohols with [Rh(COD)(2)](+) (1) and [Rh(COD)(CH(3)CN)(2)](+) (3), but weaker binding with [Rh(NBD)(2)](+) (2). ITC indicated that the complexation with [Rh(COD)(2)](+) is mainly governed by enthalpy whereas binding with [Rh(COD)(CH(3)CN)(2)](+) is entirely driven by entropy. The thermodynamic parameters for the homoallylic alcohol binding of Rh(I) complexes 1-3 are consistent with crystallographic data.