New Aspects in the Coordination Chemistry of Magnesium Hydrazides

Abstract

The coordination chemistry of alkaline earth metal hydrazides has been investigated, and the synthesis and crystal structures of monomeric magnesium bis[N-phenyl-NЈ,NЈ-bis-(trimethylsilyl)hydrazide] (1) and dimeric magnesium bis [N,N-dimethyl-NЈ-(trimethylsilyl)hydrazide] (2) are presented. An unusual coordination sphere of the magnesium atom was observed in the first structurally characterized monomer magnesium hydrazide 1, a highly reactive comLow-coordinated compounds of main-group metals are highly desired to study their structural chemistry and reactivity. They are considered to be potential candidates for the synthesis of ceramic composite materials by CVD techniques. Different ligand systems have been investigated to achieve low-coordinated, volatile compounds. [1,2] Hydrazines are interesting ligands due to an additional donor atom in the α-position, and metalated hydrazines exhibit a different coordination chemistry than the corresponding amides. Due to a second nitrogen atom in the adjacent α-position, intramolecular (A), as well as intermolecular (B) coordination of the metal centers is possible by the ligands.The structural chemistry of the amides of group-1, -2 and -13 metals has already been widely characterized and indicates the formation of oligomeric or polymeric ring and cage structures. [3Ϫ5] Some recent aspects of the coordination chemistry of alkali metal hydrazides have been reported, [6Ϫ8] and the syntheses of aluminium and gallium hydraziedes were studied as possible precursors for AlN [3] and GaN. [10,11] These metal hydrazides share some common features with the corresponding amides, but also show significant differences in their coordination chemistry. Monomeric magnesium complexes containing monoanionic bidentate ligands are rare and the coordination chemistry of [a] Institute for Inorganic Chemistry FR 8.11, pound with side-on coordinated hydrazide ligands forming a bent butterfly-type structure. The Mg−N distances range from 1.92 to 2.45 Å and intramolecular C−H···Mg interactions in the range 2.42 to 2.63 Å are observed. This structural motif is unprecedented in the coordination chemistry of magnesium hydrazides.alkaline earth metal hydrazides is quite unexplored. The alkaline earth metal hydrazides were studied in order to compare the structures with the corresponding alkali metal hydrazides.In this report, the structures of two magnesium hydrazides are presented. The aim was to investigate the coordination chemistry of alkaline earth metal hydrazides without the influence of donor solvents on the coordination sites at the metal atoms, hence a straightforward synthesis of the corresponding compounds was carried out. The deprotonation of the hydrazines was achieved by a solution of dibutylmagnesium in hexane according to Equations (1) and (2). This gave magnesium bis[N-phenyl-NЈ,NЈ-bis(trimethylsilyl)hydrazide] (1) and magnesium bis[N,N-dimethyl-NЈ-(trimethylsilyl)hydrazide] (2).

Volatile Imido−Hydrazido Compounds of the Refractory Metals Niobium, Tantalum, Molybdenum, and Tungsten

“…Fischer et al spectroscopically observed a substitution of only one chloro ligand by Li-TDMH but reported neither a synthesis nor a full characterization of the product . Recently, Sachdev prepared [Mg(N(SiMe 3 )NMe 2 ) 2 ] 2 from dibutylmagnesium and H-TDMH . This magnesium dihydrazide is capable of exchanging two chloro ligands of [Ta(N t Bu)Cl 3 Py 2 ], giving [Ta(N t Bu)(TDMH) 2 Cl] ( 2a ) in very high yield (Figure ).…”

Volatile Imido−Hydrazido Compounds of the Refractory Metals Niobium, Tantalum, Molybdenum, and Tungsten

“…Fischer et al spectroscopically observed a substitution of only one chloro ligand by Li-TDMH but reported neither a synthesis nor a full characterization of the product . Recently, Sachdev prepared [Mg(N(SiMe 3 )NMe 2 ) 2 ] 2 from dibutylmagnesium and H-TDMH . This magnesium dihydrazide is capable of exchanging two chloro ligands of [Ta(N t Bu)Cl 3 Py 2 ], giving [Ta(N t Bu)(TDMH) 2 Cl] ( 2a ) in very high yield (Figure ).…”

The syntheses and structures of some main group complexes of the sterically hindered N,N′-bis(2,6-diisopropylphenyl)-4-toluamidinate ligand

“…This geometry has only been observed before in rigidly held porphyrin coordinated 43 magnesium metal centres and two unusual compounds from Lappert and Sachdev; the 1-azallyl species [Mg(Me 3 SiNC (Bu t )C(H)SiMe 3 ) 2 ] 44 and the hydrazide compound [Mg{PhNN(SiMe 3 ) 2 } 2 ]. 45 The former of these exhibits considerable closing of the planes created by the NCC 1-azallyl donor and the MgN 2 C 2 metallacycle (ca. 461), 44 while the latter displays amide nitrogen to magnesium contacts (mean value; 1.92 A ˚) that radically contrast with the mean Mg-N amine contacts (2.42 A ˚).…”

“…461), 44 while the latter displays amide nitrogen to magnesium contacts (mean value; 1.92 A ˚) that radically contrast with the mean Mg-N amine contacts (2.42 A ˚). 45 These 'secondary' lengths are outside of the combined covalent radii of magnesium and nitrogen (ca. 2.1 A ˚)46 and do not suggest explicit four-coordination of the metal.…”

“…2.1 A ˚)46 and do not suggest explicit four-coordination of the metal. Accordingly, neither 'non-porphyrin' [43][44][45] example demonstrates the 'symmetrical' planarity of 2, wherein the MgNCN metallocycles exhibit a maximum rms deviation from planarity of below 0.001 A ˚(N(1) and N(2) exhibit deviations of 0.0001(11) A ˚). Further, there are no obvious MgÁ Á ÁH-C agostic contacts that could rationalise the adopted geometry, the closest MgÁ Á ÁC and MgÁ Á ÁH distances being those of C( 7) and H(7) (3.888(3) and 3.07 A ˚, respectively).…”

Mixed hydrazido amido/imido complexes of tantalum, hafnium and zirconium: potential precursors for metal nitrideMOCVD

“…The structure of 8 is very similar to the recently published dimeric complex [Mg(tdmh) 2 ] 2 . 14 Numerous examples of lithiumhydrazido complexes are known and compound 8 matches the typical structural properties. 15…”

Volatile Imido−Hydrazido Compounds of the Refractory Metals Niobium, Tantalum, Molybdenum, and Tungsten

“…Fischer et al spectroscopically observed a substitution of only one chloro ligand by Li-TDMH but reported neither a synthesis nor a full characterization of the product . Recently, Sachdev prepared [Mg(N(SiMe 3 )NMe 2 ) 2 ] 2 from dibutylmagnesium and H-TDMH . This magnesium dihydrazide is capable of exchanging two chloro ligands of [Ta(N t Bu)Cl 3 Py 2 ], giving [Ta(N t Bu)(TDMH) 2 Cl] ( 2a ) in very high yield (Figure ).…”

The syntheses and structures of some main group complexes of the sterically hindered N,N′-bis(2,6-diisopropylphenyl)-4-toluamidinate ligand

“…This geometry has only been observed before in rigidly held porphyrin coordinated 43 magnesium metal centres and two unusual compounds from Lappert and Sachdev; the 1-azallyl species [Mg(Me 3 SiNC (Bu t )C(H)SiMe 3 ) 2 ] 44 and the hydrazide compound [Mg{PhNN(SiMe 3 ) 2 } 2 ]. 45 The former of these exhibits considerable closing of the planes created by the NCC 1-azallyl donor and the MgN 2 C 2 metallacycle (ca. 461), 44 while the latter displays amide nitrogen to magnesium contacts (mean value; 1.92 A ˚) that radically contrast with the mean Mg-N amine contacts (2.42 A ˚).…”

“…461), 44 while the latter displays amide nitrogen to magnesium contacts (mean value; 1.92 A ˚) that radically contrast with the mean Mg-N amine contacts (2.42 A ˚). 45 These 'secondary' lengths are outside of the combined covalent radii of magnesium and nitrogen (ca. 2.1 A ˚)46 and do not suggest explicit four-coordination of the metal.…”

“…2.1 A ˚)46 and do not suggest explicit four-coordination of the metal. Accordingly, neither 'non-porphyrin' [43][44][45] example demonstrates the 'symmetrical' planarity of 2, wherein the MgNCN metallocycles exhibit a maximum rms deviation from planarity of below 0.001 A ˚(N(1) and N(2) exhibit deviations of 0.0001(11) A ˚). Further, there are no obvious MgÁ Á ÁH-C agostic contacts that could rationalise the adopted geometry, the closest MgÁ Á ÁC and MgÁ Á ÁH distances being those of C( 7) and H(7) (3.888(3) and 3.07 A ˚, respectively).…”

Mixed hydrazido amido/imido complexes of tantalum, hafnium and zirconium: potential precursors for metal nitrideMOCVD

“…The structure of 8 is very similar to the recently published dimeric complex [Mg(tdmh) 2 ] 2 . 14 Numerous examples of lithiumhydrazido complexes are known and compound 8 matches the typical structural properties. 15…”

Volatile Imido−Hydrazido Compounds of the Refractory Metals Niobium, Tantalum, Molybdenum, and Tungsten

“…Fischer et al spectroscopically observed a substitution of only one chloro ligand by Li-TDMH but reported neither a synthesis nor a full characterization of the product . Recently, Sachdev prepared [Mg(N(SiMe 3 )NMe 2 ) 2 ] 2 from dibutylmagnesium and H-TDMH . This magnesium dihydrazide is capable of exchanging two chloro ligands of [Ta(N t Bu)Cl 3 Py 2 ], giving [Ta(N t Bu)(TDMH) 2 Cl] ( 2a ) in very high yield (Figure ).…”

The syntheses and structures of some main group complexes of the sterically hindered N,N′-bis(2,6-diisopropylphenyl)-4-toluamidinate ligand

“…This geometry has only been observed before in rigidly held porphyrin coordinated 43 magnesium metal centres and two unusual compounds from Lappert and Sachdev; the 1-azallyl species [Mg(Me 3 SiNC (Bu t )C(H)SiMe 3 ) 2 ] 44 and the hydrazide compound [Mg{PhNN(SiMe 3 ) 2 } 2 ]. 45 The former of these exhibits considerable closing of the planes created by the NCC 1-azallyl donor and the MgN 2 C 2 metallacycle (ca. 461), 44 while the latter displays amide nitrogen to magnesium contacts (mean value; 1.92 A ˚) that radically contrast with the mean Mg-N amine contacts (2.42 A ˚).…”

“…461), 44 while the latter displays amide nitrogen to magnesium contacts (mean value; 1.92 A ˚) that radically contrast with the mean Mg-N amine contacts (2.42 A ˚). 45 These 'secondary' lengths are outside of the combined covalent radii of magnesium and nitrogen (ca. 2.1 A ˚)46 and do not suggest explicit four-coordination of the metal.…”

“…2.1 A ˚)46 and do not suggest explicit four-coordination of the metal. Accordingly, neither 'non-porphyrin' [43][44][45] example demonstrates the 'symmetrical' planarity of 2, wherein the MgNCN metallocycles exhibit a maximum rms deviation from planarity of below 0.001 A ˚(N(1) and N(2) exhibit deviations of 0.0001(11) A ˚). Further, there are no obvious MgÁ Á ÁH-C agostic contacts that could rationalise the adopted geometry, the closest MgÁ Á ÁC and MgÁ Á ÁH distances being those of C( 7) and H(7) (3.888(3) and 3.07 A ˚, respectively).…”

Mixed hydrazido amido/imido complexes of tantalum, hafnium and zirconium: potential precursors for metal nitrideMOCVD

“…The structure of 8 is very similar to the recently published dimeric complex [Mg(tdmh) 2 ] 2 . 14 Numerous examples of lithiumhydrazido complexes are known and compound 8 matches the typical structural properties. 15…”