Nickel(II) acetylacetonate
Encyclopedia
Nickel acetylacetonate is a coordination complex with the formula [Ni(acac)2]3. This dark green solid reacts with water to give the dihydrate Ni(acac)2·2H2O.
Structure: Ni(II), bonded to two bidentate acetylacetonate (acac) ligands. Acac is a β-diketone that forms one oxygen-nickel covalent bond with the metal centre, and one oxygen-nickel coordinated bond. The Ni-O bonds are equivalent. It exists in two different configurations, one of which is its monomeric dihydrate, with two water ligands. Dehydration gives a trimer, [Ni(acac)2]3. Geometry at Ni is octahedral in both anhydrous and dihydrate.
Ni(acac)2·2H2O also exhibits a tetragonally distorted octahedral geometry by coordinating to two additional solvent molecules, resulting in two isomers in the cis and trans form (Fig 1.). The trans isomer is preferred over the cis isomer (which was only found when pyridine N-oxide was used as the solvent. In the trans isomer, the X group occupies the axial position, forming Ni-O bonds in ethanol solvents. These axial bonds are greater in length (2.1000Å) than the equatorial Ni-O bonds (2.0085 Å and 1.9961Å).
, yielding a blue-green hydrate Ni(CH3COCHCOCH3)2·2H2O. A range of solvents may be used in the reaction, depending on which of the isomers (trans or cis) of the hydrate is desired. Subliming Ni(acac)2·2H2O at 170-210 °C under reduced pressure (0.2-0.4 mmHg) gives the anhydrous form.
and dimethyl acetylenedicarboxylate.
One reaction involving the trimer occurs when [Ni(acac)2]3 is reacted with N,N-dimethylaminoethanol, which has the ability to coordinate through oxygen and nitrogen donors.
Structure: Ni(II), bonded to two bidentate acetylacetonate (acac) ligands. Acac is a β-diketone that forms one oxygen-nickel covalent bond with the metal centre, and one oxygen-nickel coordinated bond. The Ni-O bonds are equivalent. It exists in two different configurations, one of which is its monomeric dihydrate, with two water ligands. Dehydration gives a trimer, [Ni(acac)2]3. Geometry at Ni is octahedral in both anhydrous and dihydrate.
Structure and properties
The nickels in Ni(acac)2 have tetragonally distorted octahedral geometry, caused by the difference in the length of the Ni-O bonds of bridging oxygens, and non-bridging oxygens. Ni(acac)2 has a trinuclear structure that contains two nickel-nickel bonds. The trimeric structure of the compound is the smallest unit in which all nickel centers can obtain an octahedral coordination. The trimer is only formed if intramolecular sharing of oxygen centers between pairs of nickel centers occurs. For bulkier ligands, trimeric structures would not be precluded by steric hindrance. The molecules are almost centrosymmetric, despite the noncentrosymmetric space group of the host, which is uncommon.Ni(acac)2·2H2O also exhibits a tetragonally distorted octahedral geometry by coordinating to two additional solvent molecules, resulting in two isomers in the cis and trans form (Fig 1.). The trans isomer is preferred over the cis isomer (which was only found when pyridine N-oxide was used as the solvent. In the trans isomer, the X group occupies the axial position, forming Ni-O bonds in ethanol solvents. These axial bonds are greater in length (2.1000Å) than the equatorial Ni-O bonds (2.0085 Å and 1.9961Å).
Synthesis
Bis(2,4-pentanedionato)nickel(II) is prepared by reacting nickel chloride with acetylacetoneAcetylacetone
Acetylacetone is an organic compound that famously exists in two tautomeric forms that rapidly interconvert. The less stable tautomer is a diketone formally named pentane-2,4-dione. The more common tautomer is the enol form. The pair of tautomers rapidly interconvert and are treated as a single...
, yielding a blue-green hydrate Ni(CH3COCHCOCH3)2·2H2O. A range of solvents may be used in the reaction, depending on which of the isomers (trans or cis) of the hydrate is desired. Subliming Ni(acac)2·2H2O at 170-210 °C under reduced pressure (0.2-0.4 mmHg) gives the anhydrous form.
- NiCl2 + 2CH3COCH2COCH3 + 2H2O → Ni(CH3COCHCOCH3)2·2H2O + 2HCl
- 3Ni(CH3COCHCOCH3)2·2H2O → [Ni(CH3COCHCOCH3)2]3 + 6H2O
Reactions
Ni(acac)2·2H2O reacts quickly, with a high yield at a methine position, producing diamides from isocyanates. Related reactions occur with diethyl azodicarboxylateDiethyl azodicarboxylate
Diethyl azodicarboxylate, conventionally abbreviated as DEAD and sometimes as DEADCAT, is an organic compound with the structural formula CH3CH2O2CN=NCO2CH2CH3. Its molecular structure consists of a central azo functional group, RN=NR, flanked by two ethyl ester groups. This orange-red liquid is a...
and dimethyl acetylenedicarboxylate.
- Ni(acac)2·2H2O + 2PhNCO → Ni(O2C5Me2C(O)NHPh)2 + 2H2O
One reaction involving the trimer occurs when [Ni(acac)2]3 is reacted with N,N-dimethylaminoethanol, which has the ability to coordinate through oxygen and nitrogen donors.
- 3[Ni(acac)2]3 + 6Me2NCH2CH2OH → 3[Ni(acac)2(OCH2CH2NMe2)] + 3H2