1,4-Dialkyl-1,4-diazabutadienes: their reactions with aluminum and indium halides

Abstract

Reactions of 1,4-bis[(S) methylbenzyl]-1,4-diazabutadiene (1), 1,4-bis[(R) 1 0 -chlorobutan-2 0 -yl]-1,4-diazabutadiene (2), 1,4-bis[(S,S) 1 0 -chloro-1 0 -phenyl-propan-2 0 -yl]-1,4-diazabutadiene (3), and 1,4-di-tert-butyl-1,4diazabutadiene (4) with aluminum and indium halides were performed. Reaction of 1,4-diazabutadienes 1-4 with two equivalents of aluminum halides in toluene afforded ionic aluminum coordination compounds (5-10) which in THF solution are transformed into 1,3-dialkyl-2-methaneiminealkyl imidazolium heterocycles (11-14) by condensation of two 1,4-diazabutadienes and elimination of amine hydrochloride. Equimolar reactions of 1-4 with InCl 3 in dry acetonitrile at À78 1C afforded the neutral and diamagnetic InCl 3 coordination compounds (15-18), which are stable in the solid state under dry conditions, but in THF solution are slowly transformed into the corresponding 1,3-dialkyl-imidazolium heterocycles 19-22. The X-ray diffraction analyses of compounds 2, 3, 10, 11, 14 and 17 are described.Quantum mechanical calculations were performed in order to find the minimum energy conformers of 1,4-diazabutadienes, 1,3-dialkyl-2-methaneiminealkyl imidazolium and 1,3-dialkyl-imidazolium derivatives as well as the aluminum and indium coordination compounds.Scheme 1 Neutral, anion and dianionic oxidation states of 1,4diazabutadienes.

Synthesis and Characterization of Neutral Ligand α-Diimine Complexes of Aluminum with Tunable Redox Energetics

“…There is no systematic trend in these metrics across the complexes. The C–C bond distances in our compounds are slightly longer than those reported for either the [(dipp-DAB)­AlI 2 ]­[I] [C–C = 1.442(13) Å; C–N = 1.325(12) and 1.289(11) Å] or [( t Bu-DAB)­AlClMe]­[AlCl 3 Me] [C–C = 1.459(9) Å; C–N = 1.284(7) and 1.279(8) Å] neutral ligand complex, although the C–N distances are in better agreement. Our bonding metrics also compare well to the average C–C (1.51 Å) and C–N (1.28 Å) bond distances reported for the neutral ligand complex [(dmp-BIAN) 3 Al]­[PF 6 ] 3 .…”

“…The Al–N distances in the [Al­(L Ar ) 2 Cl 2 ]­AlCl 4 complexes average 2.05 Å, which is slightly longer than the corresponding average bond length in either [(diip-DAB)­AlI 2 ]­[I] (Al–N ave = 1.92 Å) or [( t Bu-DAB)­AlClMe]­[AlCl 3 Me] (Al–N = 1.96 Å) . These distances for the neutral ligand complexes are all longer than the average Al–N distances in previously reported singly (1.90 Å) ,,,,, and doubly (1.82 Å) − ,, reduced aluminum α-diimine adducts, as is anticipated from the lesser Coulombic attraction between the aluminum­(III) ion and neutral ligand.…”

“…The average C−C and C−N bond distances in the α-diimine ligands for the complexes are 1.50 and 1.29 Å, respectively, confirming that the ligands remain fully oxidized across the series. 36 There is no systematic trend in these metrics across the complexes 23 These distances for the neutral ligand complexes are all longer than the average Al−N distances in previously reported singly (1.90 Å) 20,21,24,30,31,37 and doubly (1.82 Å) [20][21][22]24,30 reduced aluminum α-diimine adducts, as is anticipated from the lesser Coulombic attraction between the aluminum(III) ion and neutral ligand. A similar trend was observed for the iminopyridine complexes reported by Berben, 12−14 The Al-BIAN complexes show a similar trend in the Al−N bond distance with changing ligand oxidation state.…”

“…Interestingly, the analogous reaction between t Bu-DAB and [Al­(C 5 Me 5 )] 4 gives Al­( t Bu-DAB 2– )­( t Bu-DAB – ) as the major product. Neutral ligand DAB complexes have also been prepared: The reaction of t Bu-DAB with 2 equiv of AlMeCl 2 gives [( t Bu-DAB)­AlClMe]­[AlCl 3 Me] and the 1:1 reaction between dipp-DAB [dipp-DAB = N , N ′-bis­(2,6-diisopropylphenyl)-1,4-diazabutadiene] and AlI 3 gives [(dipp-DAB)­AlI 2 ]­[I] . Jones and co-workers also demonstrated that the singly reduced (dipp-DAB – )­AlI 2 complex could be prepared by using an Al/AlI 3 mixture as the metal source.…”

High molecular weight PE elastomers through 4,4-difluorobenzhydryl substitution in symmetrical α-diimino-nickel ethylene polymerization catalysts

“…Several isomers are possible for L1–L5 on the basis of Z , E -isomerism about the CN bonds, s-cis / s-trans isomerism and anti / syn isomerism as a result of hindered rotation of the N -aryl groups (Scheme 2). 5 g , h , j ,6 c ,15 Given that L2 (R 1 = Me, R 2 = Et) shows peaks for one compound in its 1 H NMR spectrum (see Fig. S2†), it would suggest that E , E / Z , E and s-cis / s-trans interconversions for both L2 - anti and L2 - syn are fast on the laboratory timescale at room temperature.…”