Monomeric Three- and Four-Coordinate Magnesium Amides

Abstract

Treatment of bis(bis(trimethylsilyl)amido)bis(tetrahydrofuran)magnesium with 2 equiv of 2,3,5-collidine, 2-picoline, 4-picoline, or 3,5-lutidine in benzene at room temperature for 18 h afforded bis(bis(trimethylsilyl)amido)bis(2,3,5-collidine)magnesium (80%), bis(bis(trimethylsilyl)amido)bis(2-picoline)magnesium (70%), bis(bis(trimethylsilyl)amido)bis(4-picoline)magnesium (48%), or bis(bis(trimethylsilyl)amido)bis(3,5-lutidine)magnesium (58%), respectively. Sublimation of bis(bis(trimethylsilyl)amido)bis(2,3,5-collidine)magnesium (90 degrees C, 0.1 mmHg) and bis(bis(trimethylsilyl)amido)bis(2-picoline)magnesium (115 degrees C, 0.1 mmHg) afforded colorless crystals of bis(bis(trimethylsilyl)amido)(2,3,5-collidine)magnesium (53%) and bis(bis(trimethylsilyl)amido)(2-picoline)magnesium (46%), respectively. Treatment of bis(bis(trimethylsilyl)amido)bis(tetrahydrofuran)magnesium with 1 equiv of 2,6-lutidine in benzene at room temperature for 18 h afforded bis(bis(trimethylsilyl)amido)(2,6-lutidine)magnesium (56%). The X-ray crystal structures of bis(bis(trimethylsilyl)amido)bis(2,3,5-collidine)magnesium, bis(bis(trimethylsilyl)amido)bis(4-picoline)magnesium, bis(bis(trimethylsilyl)amido)(2-picoline)magnesium, and bis(bis(trimethylsilyl)amido)(2,6-lutidine)magnesium were determined. Bis(bis(trimethylsilyl)amido)bis(2,3,5-collidine)magnesium crystallizes in the monoclinic space group C2/c with a = 11.8410(7) Å, b = 20.5413(13) Å, c = 15.5746(10) Å, beta = 93.072(2) degrees, V = 3782.8(4) Å(3), and Z = 4. Bis(bis(trimethylsilyl)amido)bis(4-picoline)magnesium crystallizes in the triclinic space group P&onemacr; with a = 10.4914(6) Å, b = 11.8504(6) Å, c = 15.4546(9) Å, alpha = 99.3180(10) degrees, beta = 98.4180(10) degrees, gamma = 111.5320(10) degrees, V = 1718.8(2) Å(3), and Z = 2. Bis(bis(trimethylsilyl)amido)(2-picoline)magnesium crystallizes in the orthorhombic space group Pbca with a = 18.4536(14) Å, b = 15.2326(9) Å, c = 20.614(2) Å, V = 5794.6(7) Å(3), and Z = 8. Bis(bis(trimethylsilyl)amido)(2,6-lutidine)magnesium crystallizes in the orthorombic space group Pbca with a = 18.6221(13) Å, b = 15.3236(9) Å, c = 20.9085(14) Å, V = 5966.4(7) Å(3), and Z = 8. Application of the these complexes as source compounds in chemical vapor deposition processes is discussed.

Advances in alkaline earth-nitrogen chemistry

“…Aggregation of the strontium species is attributed to its higher ionic radii and subsequent higher need for steric saturation as compared to magnesium. This is also evident by a close M· · ·C interaction (3.16Å) between the strontium metal center and a trimethylsilyl group (Table 4 [41,42]. However when the sterically more demanding co-ligands 2-picoline and 2,6-lutidine were used, monomeric three coordinate species, Mg[N(SiMe 3 ) 2 ] 2 (pyr*), were obtained.…”

“…Other applications include their use as initiators in polymerization reactions for both synthetic and biodegradable polymers [8,27,28,[52][53][54][55][56][57][58][59][60][61]. The alkaline earth metal silyl amides have also been studied as potential precursors in MOCVD (metal-organic chemical vapor deposition) processes, as their low coordination numbers and relatively low molecular weight were believed to provide good volatility [42,[62][63][64]. However, frequent silicon incorporation into the resulting films rendered the precursor materials non-ideal [62][63][64].…”

CVD of MgO from a Mg(β-ketoiminate)2: Preparation, Characterization, and Utilization of an Intramolecularly Stabilized, Highly Volatile, Thermally Robust Precursor

“…Previously explored ligand platforms range from b-diketonates to amides. The b-diketonate chemistry focuses mainly on CVD precursors for use in the fabrication of group 2 metal oxides, while the amide chemistry deals mainly with the preparation of magnesium compounds for the p-type doping of group 13 nitrides [5] as components of blue light-emitting devices. The marrying of the b-diketonate and amide ligand motifs produces the b-ketoiminate hybrid.…”

A monomeric three-coordinate magnesium bis(amide)

“…Magnesium bis(amides) are typically isolated as tetrahedrally coordinated compounds of the type [MgL 2 S 2 ], where L is an amide ligand and S a donating solvent, or as dimeric species of the type [LS x Mg("-L) 2 MgLS x ] (x = 0 or 1), where Mg is in either a trigonal-planar or a tetrahedral environment [for typical examples, see Sebestl et al (1998) and Clegg et al (1997)]. Lower coordination numbers are favoured by sterically demanding amide groups.…”

“…Unusually, the Mg atom is three-coordinate, bonding to two amide units and a diethyl ether molecule in a planar manner [Mg1 lies 0.042 (1) A Ê from the N1/N2/O1 plane]. Although this coordination geometry is common in dimeric (Clegg et al, 1997) and polymeric (Andrews et al, 2000) magnesium amide solid-state structures, a search of the Cambridge Structural Database (version 5.21;Allen & Kennard, 1993) revealed only [Mg(HMDS) 2 S], (II) (S = 2-picoline or 2,6-lutidine; Sebestl et al, 1998), and the chelate [Mg t Bu{(N,N-(2,6-i Pr 2 C 6 H 3 )NC-(Me)CHC(Me)N(2,6-i Pr 2 C 6 H 3 )}] (Gibson et al, 2000), with similar three-coordinate monomeric structures. An illustration of the coordinatively unsaturated nature of these species is that, unlike (I), (II) is not isolated in the presence of solvent.…”