Synthesis and structure of amido- and imido(pentafluorophenyl)borane zirconocene and hafnocene complexes: N-H and B-H activation

Half-Sandwich Zirconium and Hafnium Amidoborane Complexes: Precursors of Hydride Derivatives

Half-sandwich zirconium(IV) and hafnium(IV) complexes with amidoborane and hydride ligands have been isolated in the stoichiometric reactions of mono(pentamethylcyclopentadienyl)metal alkyl and amido derivatives with the amine-boranes NHR2BH3 (R2 = H2, Me2, HtBu). Treatment of the tris(trimethylsilylmethyl) complexes [M(η5-C5Me5)(CH2SiMe3)3] with NH3BH3 (3 equiv) gives the seven-coordinate species [M(η5-C5Me5)(NH2BH3)3] (M = Zr (1), Hf (2)) with three κ2N,H-NH2BH3 ligands. The tris(neophyl) [M(η5-C5Me5)(CH2CMe2Ph)3] or tris(dimethylamido) [M(η5-C5Me5)(NMe2)3] derivatives react with NHMe2BH3 (≥3 equiv) to afford bis(dimethylamidoborane) hydride complexes [M(η5-C5Me5)H(NMe2BH3)2] (M = Zr (3), Hf (4)) via thermally unstable [M(η5-C5Me5)(NMe2BH3)3] species. The reaction of [M(η5-C5Me5)(NMe2)3] and NH2tBuBH3 (≥4 equiv) affords analogous mixed amidoborane hydride derivatives [M(η5-C5Me5)H(NHtBuBH3)(NMe2BH3)] (M = Zr (5), Hf (6)) with κ2N,H-NHtBuBH3 and κ3N,H,H-NMe2BH3 ligands. The addition of NHR2BH3 (≥1 equiv) on the mono(dimethylamido) complexes [M(η5-C5Me5)Cl2(NMe2)] in hexane leads to the precipitation of the ionic compounds [(NHR2)2BH2][{M(η5-C5Me5)Cl2}2(μ-H)3] (R2 = Me2, M = Zr (7), Hf (8); R2 = HtBu, M = Zr (9), Hf (10)). Molecular hydride species [Cl2(η5-C5Me5)M(μ-Cl)(μ-H)2M(η5-C5Me5)Cl(NH2tBu)] (M = Zr (11), Hf (12)) could be isolated from mixtures of complexes [M(η5-C5Me5)Cl2(NMe2)] and lower ratios of NH2tBuBH3. The zirconium complex 11 decomposes in solution to give the mononuclear tert-butylamido derivative [Zr(η5-C5Me5)Cl2(NHtBu)] (13) along with other byproducts.

Mechanistic insights into dehydrocoupling of amine boranes using dinuclear zirconocene complexes

Catalytic dehydrocoupling of H₃B·NMe₂H using Cp₂Zr(Cl)(μ-Me₃SiC₃SiMe₃)Zr(Cl)Cp₂ (1)/MeLi was studied. Spectroscopic monitoring and stoichiometric experiments show the formation and interconversion of several catalytically active Zr species.

Ammonia-Borane Derived BN Fragments Trapped on Bi- and Trimetallic Titanium(III) Systems

Titanium(III) complexes containing unprecedented (NH₂ BH₂ NHBH₃ )^2- and {N(BH₃ )₃ }^3- ligands have been isolated, and their structures elucidated by a combination of experimental and theoretical methods. The treatment of the trimethyl derivative [TiCp*Me₃ ] (Cp*=η⁵ -C₅ Me₅ ) with NH₃ BH₃ (3 equiv) at room temperature gives the paramagnetic dinuclear complex [{TiCp*(NH₂ BH₃ )}₂ (μ-NH₂ BH₂ NHBH₃ )], which at 80 °C leads to the trinuclear hydride derivative [{TiCp*(μ-H)}₃ {μ₃ -N(BH₃ )₃ }]. The bonding modes of the anionic BN fragments in those complexes, as well as the dimethylaminoborane group trapped on the analogous trinuclear [{TiCp*(μ-H)}₃ (μ₃ -H)(μ₃ -NMe₂ BH₂ )], have been studied by X-ray crystallography and density functional theory (DFT) calculations.

Dehydropolymerisation of methylamine borane using a dinuclear 1,3-allenediyl bridged zirconocene complex

The dinuclear zirconocene chloride complex 1 is a highly active precatalyst for the dehydropolymerisation of methylamine borane. Comparison with mononuclear Zr chlorides and related dinuclear complexes suggests that the nature of the bridging motif is essential for the unique reactivity of 1.

Crystal structure and Hirshfield analysis of the 4-(di-methyl-amino)-pyridine adduct of 4-meth-oxy-phenyl-borane

The title compound [systematic name: 4-(di-methyl-amino)-pyridine-4-meth-oxy-phenyl-borane (1/1)], C14H19BN2O, contains two independent mol-ecules in the asymmetric unit. Both molecules exhibit coplanar, mostly sp2-hybridized meth-oxy and di-methyl-amino substituents on their respective aromatic rings, consistent with π-donation into the aromatic systems. The B-H groups exhibit an intra-molecular close contact with a C-H group of the pyridine ring, which may be evidence of electrostatic attraction between the hydridic B-H and the electropositive aromatic C-H. There appears to be weak C-H⋯π(arene) inter-actions between two of the H atoms of an amino-methyl group and the meth-oxy-substituted benzene ring of the other independent mol-ecule, and another C-H⋯π (arene) inter-action between one of the pyridine ring H atoms and the same benzene ring.

Group 4 Half-Sandwich Tris(trimethylsilylmethyl) Complexes: Thermal Decomposition and Reactivity with N,N-Dimethylamine-Borane

The thermal decomposition of group 4 trimethylsilylmethyl derivatives [M(η⁵-C₅Me₅)(CH₂SiMe₃)₃] (M = Ti (1), Zr (2), Hf (3)) in solution and their reactivity with N,N-dimethylamine-borane were investigated. Heating of hydrocarbon solutions of compounds 2 and 3 at 130-200 °C results in the elimination of SiMe₄ and the clean formation of the singular alkylidene-alkylidyne zirconium and hafnium compounds [{M(η⁵-C₅Me₅)}₃{(μ-CH)₃SiMe}(μ₃-CSiMe₃)] (M = Zr (4), Hf (5)). The reaction of 2 and 3 with NHMe₂BH₃ (≥1 equiv) at room temperature affords the dialkyl(dimethylamidoborane) complexes [M(η⁵-C₅Me₅)(CH₂SiMe₃)₂(NMe₂BH₃)] (M = Zr (6), Hf (7)). Compounds 6 and 7 are unstable in solution and decompose with formation of the alkyl(dimethylamino)borane [B(CH₂SiMe₃)H(NMe₂)] (8), SiMe₄, and other minor byproducts, including the tetranuclear zirconium(III) octahydride complex [{Zr(η⁵-C₅Me₅)}₄(μ-H)₈] (9) in the decomposition of 6. Addition of NHMe₂BH₃ to the titanium tris(trimethylsilylmethyl) derivative 1 gives the trinuclear mixed valence Ti(II)/Ti(III) tetrahydride complex [{Ti(η⁵-C₅Me₅)(μ-H)}₃(μ₃-H)(μ₃-NMe₂BH₂)] (10) at 45-65 °C. While the complete conversion of 1 under argon atmosphere requires excess NHMe₂BH₃ (up to 15 equiv), complex 10 is readily prepared with 3 equiv of NHMe₂BH₃ under a hydrogen atmosphere indicating that the formation of 10 involves hydrogenolysis of 1 in the presence of (NMe₂BH₂)₂. In absence of amine-borane, the reaction of 1 with H₂ leads to the tetranuclear titanium(III) octahydride [{Ti(η⁵-C₅Me₅)}₄(μ-H)₈] (11), which upon addition of NHMe₂BH₃ and subsequent heating at 65 °C affords complex 10. The X-ray crystal structures of 2, 4, 5, 10, and 11 were determined.

Isolable zirconium hydride species in the reaction of amido complexes with amine-boranes

Mono-, di- and trinuclear zirconium hydride species have been isolated in the treatment of amido complexes [Zr(η⁵-C₅Me₅)(NMe₂)_nCl_3-n] (n = 3, 1) with amine-borane adducts NHR₂BH₃ (R₂ = Me₂, HtBu). The reactions involve the formation of amidoborane ligands with ZrH-B interactions which readily undergo β-hydride elimination to give hydride functions.

s-Block amidoboranes: syntheses, structures, reactivity and applications

The highly versatile amidoborane compounds of the group 1 and 2 metals are reviewed, with an emphasis on their synthesis, structures and reactivity.