“Embroidered” Square Pyramidal Coordination Caps for Nickel(II): Mono-, Di- and Tetrafunctionalisation of a Tetrapodal Pentadentate Ligand with an NN4 Donor Set
✍ Scribed by Christian Dietz; Frank W. Heinemann; Andreas Grohmann
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 383 KB
- Volume
- 1999
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Tetrapodal pentadentate ligand / Ligand periphery / Polydentate amine complex / Nickel / Podand / Schiff base
The tetrapodal pentaamine ligand 2,6-bis(1Ј,3Ј-diamino-2Ј-acetylacetone, to give the new ligand 6 which, likewise, is hexadentate in its Ni II complex {[( 6)Ni](PF 6 ) 2 } (7). In this case, methylprop-2Ј-yl)pyridine
(1), which contains four equivalent primary amino groups, can be derivatised partly however, the N/O-functional sidearm is not deprotonated. Rather, it is coordinated as the keto-imine tautomer, making or completely by Schiff base condensation with suitable carbonyl compounds. The new ligands thus obtained are 7 a rare example of a metal complex containing this structural fragment. Two-fold functionalisation of 1 is mononucleating, as shown by the X-ray crystal structures of their respective nickel(II) complexes. Reaction of 1 with 1 observed upon reaction with acetone, regardless of whether the ketone is present in stoichiometric amounts or in excess, equiv. of salicylaldehyde and subsequent reduction allows the selective modification of one of the four sidearms. The to give the pentadentate ligand 8 with two diagonally juxtaposed isopropylidene-imine units. The complex isolated resulting ligand 2 is hexadentate and uninegative in its nickel(II) complex {[( 2)Ni]PF 6 } (3) with both the secondary with this ligand {[(8)Ni](PF 6 ) 2 } (9) contains pentacoordinate
Ni II , the sixth coordination site being blocked by the rigidly amine and the phenoxide functionalities coordinated to the metal centre. The unreduced Schiff base form of the ligand, positioned isopropylidene groups. When reacted with 4 equiv. of trans-cinnamaldehyde, all the primary amino 4, does not form a complex with nickel(II) as readily, and only a small quantity of the mixed salt {[( 4)Ni](1)Ni-groups in 1 condense to give the four-fold Schiff base 10, which acts as a pentadentate podand towards nickel(II). In (H 2 O) 2 (PF 6 )} (5) has been obtained. While the overall coordination of 4 resembles that of 2, there is considerably this complex, {[( 10)Ni(OH 2 )]Br 2 } (11), an aqua ligand completes the coordination octahedron. All ligands are stable more strain in the appended chelate ring, due to the presence of the C=N double bond. Modification of one arm towards hydrolysis when coordinated to the metal, despite the presence of alkyl-imine groups in some cases. in 1 can also be achieved by condensation with 1 equiv. of them as head groups in functional metal complexes. All ba- [a]