Di([5]trovacenyl)ethyne, Di([5]trovacenyl)butadiyne, and Di-1,4-([5]trovacenylethynyl)benzene:  Electrocommunication and Magnetocommunication Mediated by C⋮C, C⋮CC⋮C and C⋮CC₆H₄C⋮C Spacers

Abstract

The synthesis of dinuclear derivatives of trovacene (eta7-C7H7)V(eta5-C5H5) (1.) is reported, in which ethynyl (6..), butadiynyl (7..), and 1,4-di(ethynyl)phenyl (8..) groups serve as spacers between paramagnetic (S = 1/2) [5]trovacenyl units. The mononuclear precursors [5]trovacenylcarbaldehyde (2.) and [5]trovacenylacetylene (4.) are also described. Structural characterization by X-ray diffraction has been performed for 4., 6.., 7.., and 8.. Electronic communication as gleaned from cyclic voltammetry only manifests itself in the reduction processes where redox splitting deltaE1/2(0/ 1-, 1-/2-) is resolved for 6.. (deltaE1/2 = 150 mV) and indicated for 7.. (deltaE1/2 < or approximately 80 mV). Magnetocommunication leads to exchange coupling of the two electron spins which reside in vanadium centered orbitals. The values JEPR(6..) = (-)0.92, JEPR(7..) = (-)0.56, and JEPR(8..) = (-)0.005 cm(-1) are derived from the 51V hyperfine patterns. Accordingly, attenuation of exchange interaction by oligoalkyne spacers is weak, corresponding to a factor of 0.6 only per added --C triple bond C-- unit. In the determination of very weak long distance exchange interactions, EPR excels because of the range 5 x 10(-4) < or approximately J < or approximately 1.5 cm(-1) accessible in the case of 51V as a reporting magnetic nucleus and because competing intermolecular exchange is quenched in dilute fluid solution. This is demonstrated by the value Jchi(7..) = -3.84 cm(-1) obtained from a magnetic susceptibility study, which exceeds JEPR(7..) by a factor of 7. The small magnitude of spin exchange interaction between trovacene units reflects the fact that the spin bearing V3dz2 orbital is virtually orthogonal to the pi-perimeter ligand orbitals and weakly overlapping only with the a1g(sigma) ring orbitals, creating two bottlenecks for spin-exchange in the spacer-containing ditrovacenes.

Electro‐ and Magnetocommunication in [5,5]Ditrovacenyls, [(η7‐C7H7)V(η5‐C5H4‐X‐η5‐C5H4)V(η7‐C7H7)], Mediated by the Spacers X=(Z)CHCH, (E)CHCH, >CCH2, CH2CH2, and CH2

“…The preparation of formyl [5]trovacene (12C), [1] its titanium-mediated carbonyl olefination by means of (C 5 H 5 ) 2 Ti-(CH 3 ) 2 [11a] to yield vinyl [5]trovacene (13C), and reductive coupling to 1,2-di( [5]trovacenyl)ethane (15C) are outlined in Scheme 2. For the synthesis of 17CC, it proved advantageous to prepare the bridging ligand dicyclopentadienylmethane Scheme 1.…”

“…In the crystals of formyl [5]trovacene (12C) [1] rotational disorder of the h 5 -C 5 H 4 C(O)H ligand was encountered as depicted in Figure 1. In both forms, the formyl substituents are coplanar with the cyclopentadienyl ring.…”

“…Physical measurements were carried out with the instruments described previously. [1] Crystallographic data are given in Table 3. Treatment of hydrogen atoms: for (E)-9CC, isotropic refinement; for (Z)-9CC, riding model; for 11CC, isotropic refinement, 7-ring H calculated; for 12C refined, disorder calculated; and for 15CC isotropic refinement.…”

“…[1] The present paper focusses on ethylene as a spacer: the question raised is how the three different ways (1,1-, (E)-1,2-, and (Z)-1,2-) of connecting two [5]trovacenyl groups to ethylene are reflected in the redox properties and the magnetic behavior of the products? The synthesis and properties of the important intermediates acetyl [5]trovacene (8C) and formyl [5]trovacene (12C), and that of the reference molecule vinyl [5]trovacene (13C) will also be described.…”

A journey into the electrochemistry of vanadium compounds

“…Successively, [5]trovacenyl units were connected with different spacers: boron [244], silicon [245] and tin [246], a carbonyl group [247], methylene, ethylene and various groups with double bonds [248], triple bonds and extensively conjugated triple bonds [249] to the most recent, octamethylferrocene-1,1 -diyl [250]. Up to four [5]-trovacenyl groups were assembled into a benzene ring [251].…”