Visible-light photolytic synthesis of multinuclear and dendritic iron-nitrile cationic complexes

How do nitriles compare with isoelectronic alkynyl groups in the electronic communication between iron centers bridged by phenylenebis- and -tris(nitrile) ligands? An electronic and crystal-structure study

Density functional theory (DFT) calculations on the model [{FeCp(dpe)}(2){1,4-C(6)H(4)(CN)(2)}](2+) (3(2+); dpe = diphosphinoethane) of salts of the cations [{FeCp(dppe)}(2){1,4-C(6)H(4)(CN)(2)}](2+) (1(2+); dppe = 1,2-bis[diphenyldiphosphino]ethane) and [{FeCp*(CO)(2)}(2){1,4-C(6)H(4)(CN)(2)}](2+) (2(2+)), for which the X-ray crystal structures have been determined, as well as on its isomer [{FeCp(dpe)}(2){1,3-C(6)H(4)(CN)(2)}](2+) (4(2+)) and on the related complex [{FeCp(dpe)}(3){1,3,5-C(6)H(3)(CN)(3)}](3+) (5(2+)), indicate that the highest occupied molecular orbitals (HOMOs) of these compounds are localized on the metal centers with negligible participation of the C(6) ring. Thus, the poly(nitrile)phenylene ligand efficiently quenches the electronic communication between the metal centers. This is at variance with the related isoelectronic polyacetylene phenylene complexes, in which the iron centers have been shown to be electronically coupled. Consistently, apart from the case of 3(3+), which shows some degree of delocalization, all of the oxidized forms of 3(2+), 4(2+), and 5(2+) can be described as class II, localized mixed-valent species, in agreement with the electrochemical data showing two close oxidation potentials around 1 V vs FeCp*(2). This is at variance with the p-phenylene-bridged biethynyldiiron analogue, for which extended electronic delocalization was earlier shown to provide greater degree of delocalization of the mixed valency. Time-dependent DFT calculations on 3(2+), 4(2+), and 5(2+) indicate that the lowest-energy absorption band is associated with metal-to-ligand charge-transfer transitions involving the metallic HOMOs and the two lowest unoccupied molecular orbitals that derive from the lowest π*(phenylene) orbitals with some π*(CN) bonding admixture.

4-Benzyloxy-3-methoxybenzonitrile

In the mol­ecule of the title compound, C₁₅H₁₃NO₂, the aromatic rings are oriented at a dihedral angle of 81.65 (3)°. In the crystal structure, weak inter­molecular C—H⋯N hydrogen bonds link the mol­ecules into chains along the b axis.

4,4'-[Thio-phene-2,5-diylbis(ethyne-2,1-di-yl)]dibenzonitrile

In the solid state, the title compound, C(22)H(10)N(2)S, forms centrosymmetric dimers by pairs of non-classical C-H⋯S hydrogen bonds linking approximately coplanar mol-ecules. The benzene ring involved in this inter-action makes a dihedral angle of only 7.21 (16)° with the thio-phene ring, while the other benzene ring is twisted somewhat out of the plane, with a dihedral angle of 39.58 (9)°. The hydrogen-bonded dimers stack on top of each other with an inter-planar spacing of 3.44 Å. C-H⋯N hydrogen bonds link together stacks that run in approximately perpendicular directions. Each mol-ecule thus inter-acts with 12 adjacent mol-ecules, five of them approaching closer than the sum of the van der Waals radii for the relevant atoms. Optimization of the inter-stack contacts contributes to the non-planarity of the mol-ecule.