Synthesis and spectra of (p-benzoquinone diimine)pentaammineosmium(II) with a low barrier to rotation about the nitrogen-carbon double bond

Abstract

Synthesis and Spectra of (p-Benzoquinone diimine)pentaammineosmium(II) with a Low Barrier to Rotation about the N=C Bond

First binuclear complex of an N,N′,N″,N‴-tetraalkyl 2,5-diamino-1,4-benzoquinonediimine

“…Such differences are also observed in pbenzoquinonediimine systems. 7 Complex 7 is the first example of a binuclear complex bridged with ligands of type 2a and extends previous results on related mononuclear complexes. 18,19 The electronic spectrum of 7 reveals a metal-toligand charge transfer (MLCT) absorption at l max = 504 nm.…”

“…The delocalization pathway also differs from that in complexes where the metal centres are linked by substituted p-benzoquinonediimines. 6,7 This important feature may be of wider occurrence in such systems than previously believed. 16,17 The molecular structure of 7 indicates that p-backbonding from the Pt orbitals into a p* orbital of the quinonediimine is occurring: the N(1)NC(1), C(1)-C(3A), C(3A)NC(2A) and C(2A)-N(2A) bonds of the bridge show alternating lengthening and shortening relative to those of the free ligand (Table 1).…”

“…Such compounds are expected to increase the scope of bonding patterns and electronic delocalization compared to other bridging nitrogen ligands such as terpyridine systems, 4 Creutz-Taube species 5 and p-benzoquinonediimine-bridged ligands. 6,7 The direct use of 2b has been shown to be unsuitable since coordination of metal fragments renders the benzoquinonediimine bridge more susceptible to nucleophilic attack. 8 In contrast, N-substitution by electron-donating groups should lead to more stable complexes toward dioxygen and/or water.…”

Syntheses and structures of novel zerovalent ruthenium monodentate amine complexes †

“…Table 1 Selected bond distances (Å) for complexes 5a, 5d, 5e and 6a 5a 5d 5e 6a 11) Ru-C( 12) C( 1)-C(2) C( 7)-C( 8) C( 8)-C( 9) C( 9)-C( 10) C( 10)-C( 11) C( 11)-C( 12) C( 12)-C( 13) C( 13)-C( 14) C( 14)-C( 7) 266(3) 2.136(3) 2.206(3) 1.448(4) 1.401(5) 1.426(5) 1.399(5) 1.426(5) 1.394( 5) 1.490( 5 a Definitions: Ctr(1-2), the center of C(1) and C(2); Ctr (7)(8), the center of C( 7) and C(8); Ctr(9-10), the center of C(9) and C (10); Ctr (11)(12), the center of C( 11) and C (12). Syntheses of other [Ru(η 4 -cot)(dmfm)(L) 2 ] were unsuccessful.…”

Benzoquinonediimine ligands: Synthesis, coordination chemistry and properties

“…Furthermore, the introduction of methyl groups at the iminium extremity (2a) and extension of conjugation using a central naphthalene ring (3) are efficient methods to further red-shift the absorption up to the orange spectral range (λmax = 568 and 599 nm, respectively). Afterwards, the same group reported in 1985 analogous complexes introducing osmium(II) (2b), and consequently evidenced the negligible effect of the transition metal on the absorption properties [27]. Scheme 1.…”