Compounds with mixed ligand systems as precursors for thermal synthesis of III-V extended solids: Halo-pnictido, alkyl-pnictido, and siloxo-pnictido complexes of gallium and indium.

Abstract

The compounds MN(SiMe$\rm\sb3)\sb2Cl\sb2\cdot$base (1: M = Ga, base = thf; 2: M = In, base = pyridine) were synthesised. Compound 1 disproportionated to gallium trichloride while 2 did not show any thermal reactivity. The compounds (Ga(R)$\sb2$N(SiMe$\sb3)\sb2\rbrack\sb2$ (3: R = $\rm\sp{n}$Bu, 4: R = $\rm\sp{t}$Bu) were synthesised. Complex 4 decomposed into several products at 400$\sp\circ$C, while 3 thermolysed to form hexagonal GaN at 400$\sp\circ$C, after annealing at 900$\sp\circ$C. Phosphido analogues of these, $\rm\lbrack Ga(\sp{n}Bu)(R)P(SiMe\sb3)\sb2\rbrack\sb2$ (5: R = $\rm\sp{n}$Bu, 6: R = Cl) as well as (($\rm\sp{n}Bu)\sb2InP(SiMe\sb3)\sb2\rbrack\sb2$ (7) were synthesised. Complex 5 thermally rearranged to GaP at 250$\sp\circ$C. NMR studies determined that although the side product $\rm Me\sb3SiCl$ was formed in the thermolysis of 6, several products resulted and the desired phosphinido was isolated. The thermolysis of 7 at 400$\sp\circ$C produced both InP and In$\sp0.$ A series of primary amido gallium alkyl complexes: $\rm\lbrack\sp{t}Bu\sb2Ga(\mu$-N(H)$\rm\sp{t}Bu)\rbrack\sb2$ (8), $\rm\lbrack\sp{n}Bu\sb2Ga(N(H)\sp{t}Bu)\rbrack\sb2$ (9), $\rm\sp{n}Bu\sb2Ga\lbrack NH$(2.6-$\rm Me\sb2C\sb6H\sb3)1py$ (10) and $\rm\sp{n}Bu\sb2Ga\lbrack NH$(2,6-$\rm Me\sb2C\sb6H\sb3)\rbrack\sb2\lbrack Li(Et\sb2O)\rbrack$ (11) were synthesised.. Thermolysis of 8 at 120$\sp\circ$C gave a compound which $\sp1$H NMR characterisation suggested was $\rm\lbrack\sp{t}BuGaN\sp{t}Bu\rbrack\sb{x},$ but the extreme air sensitivity of this compound precluded characterization. Compound 9 was robust to thermolysis. Compounds 10 and 11 formed many products upon thermolysis at 170$\sp\circ$C and 155$\sp\circ$C respectively. The siloxide compounds M(OSiMe$\sb3)\sb{3-x}Cl\sb{x}\cdot$py (12: M = Ga, X = 0; 13: M = Ga, X = 1, 14: M = In, X = 0; 15: M = In, X = 1) were synthesised. All demonstrated elimination of $\rm(Me\sb3Si)\sb2O$ as determined by $\sp1$H NMR and MS, with only 12 forming any undesirable side-products. Thermolysis products were not isolated. A series of trimethylsilylamido-siloxo complexes: $\rm Ga(N(SiMe\sb3)\sb2)(OSiMe\sb3)\sb2py$ (17), $\rm\lbrack Li(thf)\sb2\rbrack\lbrack Ga(N(SiMe\sb3)\sb2)(OSiMe\sb3)\sb2Cl\rbrack$ (16), $\rm\lbrack Li(py)\sb2\rbrack\lbrack In(N(SiMe\sb3)\sb2)(OSiMe\sb3)\sb2Cl\rbrack$ (18), and $\rm\lbrack Li(py\sb2\rbrack\lbrack In(N(SiMe\sb3)\sb2)(OSiMe\sb3)\sb3\rbrack$ (19) were synthesised. 17 thermolised to a grey powder, which evolves into hexagonal GaN upon heating at 900$\sp\circ$C. Thermolysis experiments of compounds 16, 18, and 19 indicate a more complex rearrangement process than for 17; they do not proceed smoothly to yield the III-V nitride. Lastly, $\rm\lbrack In(N(SiMe\sb3)\sb2)(\mu\sp2$-$\rm O)\rbrack\sb{x},$ (20) was prepared from hexane in the absence of coordinating base. It was characterised by $\sp1$H NMR, elemental analysis and MS, but its crystallinity precluded a single-crystal XRD to establish the extent of oligomerisation.