Bis(η⁶‐phosphabenzene)vanadium: Synthesis, Structure, Redox Properties, and Conformational Flexibility

Abstract

Dedicated to Professor Kurt Dehnicke on the occasion of his 60th birthdayThe unsubstituted heteroarenes analogous to pyridine namely phospha-, arsa-, stiba-, and bismabenzenes,r21 a class of compounds that has been developed by Ashe ZZI, offer the coordination chemist a rich field of activity. The heterocycles C,H,E (E = element ofgroup 15) are ambidentate, since, in principle, they can bind to metals via the lone a-electron pair at E (q') and/or via the n-electron sextet (q6). In the case of the pyridine ligand a-coordination clearly predominates, since bis(q6-pyridine)chromium 1 can be obtained only if complexation is effected via an intermediate in which the N atom is sterically blocked by neighboring trimethylsilyl groups. ['] In the synthesis of bis(q6-arsabenzene)chromium The readiness of phosphabenzene to undergo q6-coordination manifests itself, inter alia, in that on heating the q'-complex 5 rearranges almost quantitatively to the q6-complex 4.[4bl We therefore engaged in the synthesis of binary phosphabenzene-transition-metal complexes and report here on the first representative of this series.I5I In order to study a possible conformational preference unaffected by steric effects we have chosen unsubstituted phosphabenzene 6 as ligand.t6' Metal atom-ligand cocondensation affords bis(q6-phosphabenzene)vanadium 7 in the form of reddish-brown, sublimable crystals, whose air-sensitivity is noticeably reduced compared to that of the free ligand 6 [Eq.

Phospha‐Organic Chemistry: Panorama and Perspectives

“…[233] 2,2'-Biphosphinines (BP), easily obtained by CÀC homocoupling of the 2-zirconium derivatives, [234] also give a wide range of very stable homoleptic chelates:…”

Bonding situation and stability of η1- and η6-bonded heteroarene complexes M(η1-EC5H5)6 and M(η6-EC5H5)2 (M=Cr, Mo, W; E=N, P, As, Sb, Bi)

“…Negative values indicate that M(g 6 -EC 5 H 5 ) 2 is more favored than M(g 1 -EC 5 rene complexes. Numerous studies have been carried out for substituted analogues which are not considered in our work since they exhibit ligand-specific effect on the relative stability.…”

“…The coordination chemistry of this class of ligands has systematically been investigated in experimental studies of Elschenbroich [5][6][7][8][9][10][11][12][13] with the focus on the preparation of neutral compounds. The results show that the phosphinine ligand prefers the g 6 -binding mode in complexes with early metals of the first transition metal row while in complexes of late transition metals g 1 coordination via the lone pair is favored [5][6][7]. The group-6 metals chromium and molybdenum which are in the middle of the transition metals rows are particularly interesting because they exhibit a diverse binding mode with heteroarene ligands.…”

Unprecedented triphosphinine iron interactions: Intramolecular electron transfer, reactivity round a corner, and a low-activated ring element exchange reaction

“…In 3 ; L 3 = h 6 -arene) but monocyclic arene ligands like benzene or toluene have been identified as h 4 -ligands with respect to iron only in the case of highly reactive [(h 6 -arene)(h 4 -arene)Fe] species which decompose in the range of À50 to À60 8C [7,8]. The phosphorus atom of 2c thus causes a stabilization effect that equals that of a noncoordinated naphthalene ring with its aromatic p 6 -electron system.…”

“…No trace of Fe-p-complexes has been observed for that ligand. On the other hand, even in the absence of shielding o-substituents, sandwich complex [(h 6 -C 5 H 5 P) 2 V] is formed as the only isolable product of vanadium vapor and C 5 H 5 P again [3]. Depending on both, the size of o-substituents and the specific transition metal, a delicate balance of the two principal ligand properties of phosphinine and its derivatives can be stated.…”