The Synthesis of Novel Gallium Carbenes, Nitrenes, Phosphinidenes and Alkoxides

<p>In the present study, synthetic routes to formal double bonds between gallium and carbon (fig 1), nitrogen (fig 2), and phosphorus (fig 3) have been investigated. These synthetic routes utilised the monoanionic, four electron donor, β-diketiminate (BDI) ligand to provide both steric and electronic stabilisation to three coordinate gallium complexes. The known di-substituted β-diketiminatogallium complexes: [(BDI)GaMe₂] and [(BDI)Ga(NHPh)₂], as well the new complexes: [(BDI)GaBn₂], [(BDI)Ga(NHDMP)₂] (DMP = 2,6-Me₂C₆H₃), [(BDI)Ga(NHDIPP)₂] (DIPP = 2,6-iPr₂C₆H₃), [(BDI)Ga(PHPh)₂] were examined for their reactivity towards the α-proton elimination mechanism for the formation of multiple bonds that is observed in transition metals. All of these complexes were shown to be unreactive towards α-proton elimination. The di-substituted β-diketiminato-gallium complex [(BDI)GaMe₂] was subjected to various aniline derivatives to investigate if the methyl ligands exhibited the same reactivity as di-methyl transition metal complexes, where the methyl ligands could deprotonate the aniline to form a metal-imido complex. This complex was found to have no reactivity with anilines. The mono-substituted β-diketiminato-gallium complex [(BDI)Ga(NHDMP)Cl] was tested for its reactivity with ⁿBuLi to abstract the amide proton and eliminate LiCl to form a gallium imido complex. While the ¹H NMR spectrum of the reaction mixture showed that a reaction had occurred, the products could not be isolated for characterisation. Another mono-substituted β-diketiminato-gallium complex [(BDI)Ga(PHPh)Cl] was also tested for its reactivity with ⁿBuLi to abstract the phosphide proton and eliminate LiCl to form a gallium phosphinidene complex. The ¹H NMR spectrum and ³¹P NMR spectrum of the isolated complex revealed that it still contained a phosphide proton, however the gallium centre now appeared to be bonded to a former methine carbon of an isopropyl group of the BDI ligand (fig 32). This bond may have formed through metathesis between an intermediate containing a gallium-phosphorus double bond, and the C-H bond of the isopropyl group. Further mechanistic studies could confirm if an intermediate such as [fig 3] is formed, and the synthetic strategy altered to isolate it. The synthesis of β-diketiminato-gallium-alkoxide complexes was also attempted, however the products of these synthesises could not be isolated due to solubility issues, potentially due to polymerisation.</p>

The Synthesis of Novel Gallium Carbenes, Nitrenes, Phosphinidenes and Alkoxides

<p>In the present study, synthetic routes to formal double bonds between gallium and carbon (fig 1), nitrogen (fig 2), and phosphorus (fig 3) have been investigated. These synthetic routes utilised the monoanionic, four electron donor, β-diketiminate (BDI) ligand to provide both steric and electronic stabilisation to three coordinate gallium complexes. The known di-substituted β-diketiminatogallium complexes: [(BDI)GaMe₂] and [(BDI)Ga(NHPh)₂], as well the new complexes: [(BDI)GaBn₂], [(BDI)Ga(NHDMP)₂] (DMP = 2,6-Me₂C₆H₃), [(BDI)Ga(NHDIPP)₂] (DIPP = 2,6-iPr₂C₆H₃), [(BDI)Ga(PHPh)₂] were examined for their reactivity towards the α-proton elimination mechanism for the formation of multiple bonds that is observed in transition metals. All of these complexes were shown to be unreactive towards α-proton elimination. The di-substituted β-diketiminato-gallium complex [(BDI)GaMe₂] was subjected to various aniline derivatives to investigate if the methyl ligands exhibited the same reactivity as di-methyl transition metal complexes, where the methyl ligands could deprotonate the aniline to form a metal-imido complex. This complex was found to have no reactivity with anilines. The mono-substituted β-diketiminato-gallium complex [(BDI)Ga(NHDMP)Cl] was tested for its reactivity with ⁿBuLi to abstract the amide proton and eliminate LiCl to form a gallium imido complex. While the ¹H NMR spectrum of the reaction mixture showed that a reaction had occurred, the products could not be isolated for characterisation. Another mono-substituted β-diketiminato-gallium complex [(BDI)Ga(PHPh)Cl] was also tested for its reactivity with ⁿBuLi to abstract the phosphide proton and eliminate LiCl to form a gallium phosphinidene complex. The ¹H NMR spectrum and ³¹P NMR spectrum of the isolated complex revealed that it still contained a phosphide proton, however the gallium centre now appeared to be bonded to a former methine carbon of an isopropyl group of the BDI ligand (fig 32). This bond may have formed through metathesis between an intermediate containing a gallium-phosphorus double bond, and the C-H bond of the isopropyl group. Further mechanistic studies could confirm if an intermediate such as [fig 3] is formed, and the synthetic strategy altered to isolate it. The synthesis of β-diketiminato-gallium-alkoxide complexes was also attempted, however the products of these synthesises could not be isolated due to solubility issues, potentially due to polymerisation.</p>

Synthetic and Structural Studies of Ethyl Zinc β-Amidoenoates and β-Ketoiminates

A set of heteroleptic ethyl zinc β-amidoenoates (1, 2) and β-ketoiminates (3) of the form [LZnEt]2 with varying steric bulk have been synthesised via the reaction of diethylzinc with β-aminoenoate ligands HL1 and HL2 and β-ketoimine HL3. These complexes have been characterised via 1H and 13C NMR, mass spectrometry and single-crystal X-ray diffraction, which unambiguously determined all three structures as dimeric species in the solid state. We observe the unusual dimerisation of 1 and 2 through coordination of the central zinc atom to the methine carbon of the second monomer, which gives these complexes high reactivity. The thermal properties of complex 3 are explored via thermal gravimetric analysis (TGA), to investigate their potential as single-source precursors to zinc oxide, which shows that 3 has a significantly lower decomposition temperature as compared to its bis-ligated counterpart [Zn(L3)2], which gives 3 promise as a single-source precursor to zinc oxide.

Picket fence porphyrin challenges. Unexpected atropisomerism

The synthesis and structural analysis of two new bis imidazole-ligated iron(II) porphyrinates are reported. The reacting porphyrin used in the studies was the four-coordinate [Formula: see text] atropisomer of [Fe(TpivPP)] (picket fence porphyrin); the axial ligands are 2-methylimidazole and 1,2-dimethylimidazole. Crystal structure analysis revealed that the [Fe(TpivPP)(2-MeHIm)[Formula: see text]] complex had a strongly ruffled porphyrin core that accommodated the hindered ligands on both the picket side and the open face of the porphyrin. Reaction with 1,2-dimethylimidazole with the four-coordinate [Fe(TpivPP)] starting material led to an isomerized form of the picket fence porphyrin. The structure analysis showed that the product obtained was the [Formula: see text] atropisomer. Strong ruffling caused by the bulky 1,2-dimethylimidazole ligand must allow the requisite rotation about the methine carbon to phenyl carbon single bond and yields what is probably the most stable form of the complex. The relative orientation of the two axial ligands in both complexes are approximately perpendicular to each other. Other structural parameters are in general accord with six-coordinate iron(II) porphyrinates.

Study of tacticity and thermal rearrangement of low molecular weight 1,2- polybutadiene by NMR

Low molecular wieght 1,2-polybutadiene (Aldrich) tacticity was determined by 13CNMR (100.6 MHz). It was found that the olefinic methylene carbon has the highest splitting and a combination of pentad and heptad sequences was determined which is in agreement with the theoretical calculations. For the first time aliphatic methine carbon assignment of 1,2-polybutadiene was performed. Furthermore, olefinic methine carbon assignment was also performed and the results were compared with the theoretical calculations. For all carbons Bernoullian and first-order Markov-chain propagation statistics were used to fit the experimental data and a good agreement was obtained indicating an atactic polymer (Pm= 0.467). It was shown that the most probable reaction before gelation which happens by heating the polymer under vacuum at 250°C, is crosslinking accompanied with methyl group formation. The decrease in double bond intensity of the pendant group together with constant cis and trans double bond intensities were observed. During heating the syndiotactic triad sequences are consumed indicating that no cyclization has happened.