Reversible C-C Bond Formation, Halide Abstraction, and Electromers in Complexes of Iron Containing Redox-Noninnocent Pyridine-imine Ligands.

The exploration of pyridine-imine (PI) iron complexes that exhibit redox noninnocence (RNI) led to several interesting discoveries. The reduction of (PI)FeX2 species afforded disproportionation products such as (dmpPI)2FeX (dmp = 2,6-Me2-C6H3, X = Cl, Br; 8-X) and (dippPI)2FeX (dipp = 2,6-iPr2-C6H3, X = Cl, Br; 9-X), which were independently prepared by reductions of (PI)FeX2 in the presence of PI. The crystal structure of 8-Br possessed an asymmetric unit with two distinct electromers, species with different electronic GSs: a low-spin (S = 1/2) configuration derived from an intermediate-spin S = 1 core antiferromagnetically (AF) coupled to an S = 1/2 PI ligand, and an S = 3/2 center resulting from a high-spin S = 2 core AF-coupled to an S = 1/2 PI ligand. Calculations were used to energetically compare plausible ground states. Polydentate diazepane-PI (DHPI) ligands were applied to the synthesis of monomeric dihalides (DHPI)FeX2 (X = Cl, 1-Cl2; X = Br, 1-Br2); reduction generated the highly distorted bioctahedral dimers (DHPA)2Fe2X2 ((3-X)2) containing a C-C bond formed from imine coupling; the monomers 1-X2 could be regenerated upon Ph3CX oxidation. Dihalides and their reduced counterparts were subjected to various alkyl halides and methyl methacrylate (MMA), generating polymers with little to no molecular weight control, indicative of simple radical-initiated polymerization.

Design and reactivity of pentapyridyl metal complexes for ammonia oxidation.

Oxidation of NH3 to N2 by pentapyridyl metal complexes via hydrogen atom abstraction was investigated computationally. Quantum chemical analysis reveals insights on orbital symmetry requirements for efficient NH3 oxidation. The most promising complex, [(PY5)Mo(NH3)]2+, was studied experimentally. It shows conversion of NH3 to N2 upon treatment with 2,4,6-tri-tert-butylphenoxyl radical.

Redox non-innocence permits catalytic nitrene carbonylation by (dadi)Ti[double bond, length as m-dash]NAd (Ad = adamantyl).

Application of the diamide, diimine {-CH[double bond, length as m-dash]N(1,2-C6H4)N(2,6-iPr2-C6H3)}2 m ((dadi) m ) ligand to titanium provided adducts (dadi)TiL x (1-L x ; L x = THF, PMe2Ph, (CNMe)2), which possess the redox formulation [(dadi)4-]Ti(iv)L x , and 22 πe- (4n + 2). Related complexes containing titanium-ligand multiple bonds, (dadi)Ti[double bond, length as m-dash]X (2 [double bond, length as m-dash]X; X = O, NAd), exhibit a different dadi redox state, [(dadi)2-]Ti(iv)X, consistent with 20 πe- (4n). The Redox Non-Innocence (RNI) displayed by dadi m impedes binding by CO, and permits catalytic conversion of AdN3 + CO to AdNCO + N2. Kinetics measurements support carbonylation of 2 [double bond, length as m-dash]NAd as the rate determining step. Structural and computational evidence for the observed RNI is provided.

Nitrene Insertion into C-C and C-H Bonds of Diamide Diimine Ligands Ligated to Chromium and Iron.

The impact of redox non-innocence (RNI) on chemical reactivity is a forefront theme in coordination chemistry. A diamide diimine ligand, [{-CH=N(1,2-C6H4)NH(2,6-iPr2C6H3)}2](n) (n = 0 to -4), (dadi)(n), chelates Cr and Fe to give [(dadi)M] ([1Cr(thf)] and [1Fe]). Calculations show [1Cr(thf)] (and [1Cr]) to have a d(4) Cr configuration antiferromagnetically coupled to (dadi)(2-)*, and [1Fe] to be S = 2. Treatment with RN3 provides products where RN is formally inserted into the C-C bond of the diimine or into a C-H bond of the diimine. Calculations on the process support a mechanism in which a transient imide (imidyl) aziridinates the diimine, which subsequently ring opens.