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.

Studies on the chemical reduction of polynuclear titanium(IV) nitrido complexes.

The redox chemistry of cube-type titanium(IV) nitrido complexes [{Ti4(η5-C5Me5)3(R)}(µ3-N)4] (R = η5-C5Me5 (1), N(SiMe3)2 (2), η5-C5H4SiMe3 (3), and η5-C5H5 (4)) was investigated by electrochemical methods and chemical reactions. Cyclic voltammetry studies indicate that 1-4 undergo a reversible one-electron reduction at ca. -1.8 V vs. ferrocenium/ferrocene. Thus, complex 1 reacts with sodium sand in tetrahydrofuran to produce the highly reactive ionic compound [Na(thf)6][{Ti(η5-C5Me5)}4(µ3-N)4] (5). The treatment of complexes 1-4 in toluene with one equivalent of [K(C5Me5)] in the presence of macrocycles (L) leads to C10Me10 and the formation of more stable derivatives [K(L)][{Ti4(η5-C5Me5)3(R)}(µ3-N)4] (R = η5-C5Me5, L = 18-crown-6 (6), crypt-222 (7); R = N(SiMe3)2, L = 18-crown-6 (8), crypt-222 (9); R = η5-C5H4SiMe3, L = 18-crown-6 (10), crypt-222 (11); R = η5-C5H5, L = crypt-222 (12)). However, the analogous reaction of 4 with [K(C5Me5)] and 18-crown-6 affords [{(18-crown-6)K}2(µ-η5:η5-C5H5)][{Ti4(η5-C5Me5)3(η5-C5H5)}(µ3-N)4] (13) via abstraction of one cyclopentadienide group from a putative intermediate [(18-crown-6)K(µ-η5:η5-C5H5)Ti4(η5-C5Me5)3(µ3-N)4]. In contrast to the cube-type nitrido systems 1-4, the cyclic voltammogram of the trinuclear imido-nitrido titanium(IV) complex [{Ti(η5-C5Me5)(µ-NH)}3(µ3-N)] (14) does not reveal any reversible redox event and 14 readily reacts with [K(C5Me5)] to afford C5Me5H and the diamagnetic derivative [{K(µ4-N)(µ3-NH)2Ti3(η5-C5Me5)3(µ3-N)}2] (15). The treatment of 15 with two equiv. of 18-crown-6 polyethers produces the molecular species [(L)K{(µ3-N)(µ3-NH)2Ti3(η5-C5Me5)3(µ3-N)}] (L = 18-crown-6 (16), dibenzo-18-crown-6 (17)). Complex 17 further reacts with one equiv. of dibenzo-18-crown-6 to yield the ion-separated compound [K(dibenzo-18-crown-6)2][Ti3(η5-C5Me5)3(µ3-N)(µ-N)(µ-NH)2] (18) similar to the ion pair [K(crypt-222)][Ti3(η5-C5Me5)3(µ3-N)(µ-N)(µ-NH)2] (19) obtained in the treatment of 15 with cryptand-222.

Dinitrogen Binding at a Trititanium Chloride Complex and Its Conversion to Ammonia under Ambient Conditions.

Reaction of [TiCp*Cl3 ] (Cp*=η5 -C5 Me5 ) with one equivalent of magnesium in tetrahydrofuran at room temperature affords the paramagnetic trinuclear complex [{TiCp*(µ-Cl)}3 (µ3 -Cl)], which reacts with dinitrogen under ambient conditions to give the diamagnetic derivative [{TiCp*(µ-Cl)}3 (µ3 -η1 : η2 : η2 -N2 )] and the titanium(III) dimer [{TiCp*Cl(µ-Cl)}2 ]. The structure of the trinuclear mixed-valence complexes has been studied by experimental and theoretical methods and the latter compound represents the first well-defined example of the µ3 -η1 : η2 : η2 coordination mode of the dinitrogen molecule. The reaction of [{TiCp*(µ-Cl)}3 (µ3 -η1 : η2 : η2 -N2 )] with excess HCl in tetrahydrofuran results in clean NH4 Cl formation with regeneration of the starting material [TiCp*Cl3 ]. Therefore, a cyclic ammonia synthesis under ambient conditions can be envisioned by alternating N2 /HCl atmospheres in a [TiCp*Cl3 ]/Mg(excess) reaction mixture in tetrahydrofuran.

Low-Valent Titanium Species Stabilized with Aluminum/Boron Hydride Fragments.

Low-valent titanium species were prepared by reaction of [TiCp*X3 ] (Cp*=η5 -C5 Me5 ; X=Cl, Br, Me) with LiEH4 (E=Al, B) or BH3 (thf), and their structures elucidated by experimental and theoretical methods. The treatment of trihalides [TiCp*X3 ] with LiAlH4 in ethereal solvents (L) leads to the hydride-bridged heterometallic complexes [{TiCp*(µ-H)}2 {(µ-H)2 AlX(L)}2 ] (L=thf, X=Cl, Br; L=OEt2 , X=Cl). Density functional theory (DFT) calculations for those compounds reveal an open-shell singlet ground state with a Ti-Ti bond and can be described as titanium(II) species. The theoretical analyses also show strong interactions between the Ti-Ti bond and the empty s orbitals of the Al atom of the AlH2 XL fragments, which behave as σ-accepting (Z-type) ligands. Analogous reactions of [TiCp*X3 ] with LiBH4 (2 and 3 equiv.) in tetrahydrofuran at room temperature and at 85 °C lead to the titanium(III) compounds [{TiCp*(BH4 )(µ-X)}2 ] (X=Cl, Br) and [{TiCp*(BH4 )(µ-BH4 )}2 ], respectively. The treatment of [TiCp*Me3 ] with 4 and 5 equiv. of BH3 (thf) produces the diamagnetic [{TiCp*(BH3 Me)}2 (µ-B2 H6 )] and paramagnetic [{TiCp*(µ-B2 H6 )}2 ] complexes, respectively.

Successive Protonation and Methylation of Bridging Imido and Nitrido Ligands at Titanium Complexes.

The reactions of nitrido complexes [{Ti(η5-C5Me5)(µ-NH)}3(µ3-N)] (1) and [{Ti(η5-C5Me5)}4(µ3-N)4] (2) with electrophilic reagents ROTf (R = H, Me; OTf = OSO2CF3) in different molar ratios have allowed the structural characterization of a series of titanium intermediates en route to the formation of the ammonium salts [NR4]OTf and [NR4][Ti(η5-C5Me5)(OTf)4]. The treatment of the trinuclear imido-nitrido complex 1 with 5.5 equiv of triflic acid in toluene at room temperature led to the dinuclear complex [Ti2(η5-C5Me5)2(µ-N)(NH3)(µ-O2SOCF3)2(OTf)] (3) and [NH4]OTf. Compound 3, along with the ammonium salts [NMe4]OTf and [NMe4][Ti(η5-C5Me5)(OTf)4] (5), was also obtained in the reaction of 1 with 8 equiv of methyl triflate in toluene at 100 °C. The trinuclear complex [Ti3(η5-C5Me5)3(µ-N)(µ-NH)2(µ-O2SOCF3)(OTf)] (4), an intermediate in the formation of 3, was isolated in the treatment of 1 with 4 equiv of MeOTf, although compound 4 was prepared in better yield by treatment of 1 with Me3SiOTf (2 equiv). Addition of a large excess of MeOTf or HOTf reagents to solutions of 3 resulted in the clean formation of ammonium salts [NR4][Ti(η5-C5Me5)(OTf)4] (R = Me (5), H (6)). Treatment of the tetranuclear nitrido complex [{Ti(η5-C5Me5)}4(µ3-N)4] (2) with 1 equiv of ROTf in toluene afforded the precipitation of the ionic compounds [{Ti(η5-C5Me5)}4(µ3-N)3(µ3-NR)][OTf] (R = H (8), Me (9)), while a large excess of HOTf led to the formation of [{Ti(η5-C5Me5)}4(µ3-N)3(µ3-NH)][Ti(η5-C5Me5)(OTf)4(NH3)] (10) by rupture of a fraction of tetranuclear molecules. Complex 2 reacted with 1 equiv of [M(η5-C5H5)(CO)3H] (M = Mo, Cr) via hydrogenation of one nitrido ligand to give the molecular derivative [{Ti(η5-C5Me5)}4(µ3-N)3(µ3-NH)] (11) and [{M(η5-C5H5)(CO)3}2], while a second 1 equiv of [M(η5-C5H5)(CO)3H] produced the ionic compounds [{Ti(η5-C5Me5)}4(µ3-N)2(µ3-NH)2][M(η5-C5H5)(CO)3] (M = Mo (12), Cr (13)) by protonation of another nitrido group. The X-ray crystal structures of 3-5, 9, 10, and 13 were determined.

Preparation of Dimeric Monopentamethylcyclopentadienyltitanium(III) Dihalides and Related Derivatives.

The synthesis, crystal structure, and reactivity of a series of half-sandwich titanium(III) dihalide complexes [Ti(η5-C5Me5)X2] (X = Cl, Br, I) and several of its Lewis base derivatives were investigated. The reaction of the trihalides [Ti(η5-C5Me5)X3] (X = Cl (1), Br (2), I (3)) with LiAlH4 (≥1 equiv) in toluene at room temperature results in the formation of the halide-bridged dimers [{Ti(η5-C5Me5)X(µ-X)}2] (X = Cl (4), Br (5), I (6)). The treatment of 4 with [Li{N(SiMe3)2}] (≥2 equiv) at room temperature affords the precipitation of the amido titanium(III) complex [{Ti(η5-C5Me5)(µ-Cl){N(SiMe3)2}}2] (7), but analogous reactions of 4 with other lithium reagents [LiR] (R = Me, CH2SiMe3, NMe2) lead to disproportionation into titanium(IV) [Ti(η5-C5Me5)R3] and presumably titanium(II) derivatives. Similarly, complex 4 in solution at temperatures higher than 100 °C undergoes disproportionation as demonstrated by its reactions with cobaltocene and N-(4-methylbenzylidene)aniline yielding the ionic paramagnetic compound [Co(η5-C5H5)2][Ti(η5-C5Me5)Cl3] (8) and the diamagnetic diazatitanacyclopentane [Ti(η5-C5Me5)Cl{N(Ph)CH(p-tolyl)}2], respectively. Treatment of complex 4 with 2 equiv of 2,6-dimethylphenylisocyanide or tert-butylisocyanide in toluene at room temperature affords the paramagnetic titanium(III) dinuclear adducts [{Ti(η5-C5Me5)Cl(µ-Cl)(CNR)}2] (R = 2,6-Me2C6H3 (9), tBu (10)). Magnetic studies for polycrystalline 9 show that it displays a weak intramolecular antiferromagnetic coupling between the Ti ions, which is consistent with the long Ti-Ti distance of 3.857(1) Å determined by X-ray diffraction. The isocyanide ligands in complex 10 undergo a reductive coupling reaction in toluene to give the titanium(IV) iminoacyl derivative [{Ti(η5-C5Me5)Cl2}2(µ-η2:η2-tBuN═C-C═NtBu)] (11). Whereas an analogous dinuclear structure was found in the aqua titanium(III) complex [{Ti(η5-C5Me5)Cl(µ-Cl)(OH2)}2] (12), resulting from the reaction of 4 with adventitious amounts of water, compound 4 reacts with excess ammonia to give a mononuclear adduct [Ti(η5-C5Me5)Cl2(NH3)2] (13) with a robust layered pattern in the solid state.

The Puzzling Monopentamethylcyclopentadienyltitanium(III) Dichloride Reagent: Structure and Properties.

Following the track of the useful titanocene [Ti(η5-C5H5)2Cl] reagent in organic synthesis, the related half-sandwich titanium(III) derivatives [Ti(η5-C5R5)Cl2] are receiving increasing attention in radical chemistry of many catalyzed transformations. However, the structure of the active titanium(III) species remains unknown in the literature. Herein, we describe the synthesis, crystal structure, and electronic structure of titanium(III) aggregates of composition [{Ti(η5-C5Me5)Cl2} n]. The thermolysis of [Ti(η5-C5Me5)Cl2Me] (1) in benzene or hexane at 180 °C results in the clean formation of [{Ti(η5-C5Me5)Cl(µ-Cl)}2] (2), methane, and ethene. The treatment of 1 with excess pinacolborane in hexane at 65 °C leads to a mixture of 2 and the paramagnetic trimer [{Ti(η5-C5Me5)(µ-Cl)2}3] (3). The X-ray crystal structures of compounds 2 and 3 show Ti-Ti distances of 3.267(1) and 3.219(12) Å, respectively. Computational studies (CASPT2//CASSCF and BS DFT methods) for dimer 2 reveal a singlet ground state and a relatively large singlet-triplet energy gap. Nuclear magnetic resonance spectroscopy of 2 in aromatic hydrocarbon solutions and DFT calculations for several [{Ti(η5-C5Me5)Cl2} n] aggregates are consistent with the existence of an equilibrium between the diamagnetic dimer [{Ti(η5-C5Me5)Cl(µ-Cl)}2] and a paramagnetic tetramer [{Ti(η5-C5Me5)(µ-Cl)2}4] in solution. In contrast, complex 2 readily dissolves in tetrahydrofuran to give a green-blue solution from which blue crystals of the mononuclear adduct [Ti(η5-C5Me5)Cl2(thf)] (4) were grown.

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.

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)nCl3-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 ß-hydride elimination to give hydride functions.

Cleavage of Dinitrogen from Forming Gas by a Titanium Molecular System under Ambient Conditions.

Simple exposure of a hexane solution of [TiCp*Me3 ] (Cp*=η5 -C5 Me5 ) to an atmosphere of commercially available and inexpensive forming gas (H2 /N2 mixture, 13.5-16.5 % of H2 ) at room temperature leads to the methylidene-methylidyne-nitrido cube-type complex [(TiCp*)4 (µ3 -CH)(µ3 -CH2 )(µ3 -N)2 ] via dinitrogen cleavage. This paramagnetic compound reacts with [D1 ]chloroform to give the titanium(IV) methylidyne-nitrido species [(TiCp*)4 (µ3 -CH)2 (µ3 -N)2 ], whereas its one-electron oxidation with AgOTf or [Fe(η5 -C5 H5 )2 ](OTf) (OTf=O3 SCF3 ) yields the diamagnetic ionic derivative [(TiCp*)4 (µ3 -CH)(µ3 -CH2 )(µ3 -N)2 ](OTf). The µ3 -nitrido ligands of the methylidyne-nitrido cubane complex can be protonated with [LutH](OTf) (Lut=2,6-lutidine) or hydrogenated with NH3 ⋅BH3 to afford µ3 -NH imido moieties.

Homo and heteropolymetallic Group 4 molecular nitrides.

Treatment of [{Ti(η(5)-C5Me5)(µ-NH)}3(µ3-N)] (1) with zirconium or hafnium tetrachloride adducts [MCl4(thf)2] affords complexes [Cl3M{(µ3-N)(µ3-NH)2Ti3(η(5)-C5Me5)3(µ3-N)}] (M = Zr (2), Hf (3)). Titanium chloride complexes [Cl2Ti{(µ3-N)2(µ3-NH)Ti3(η(5)-C5Me5)3(µ3-N)}] (4) and [(Me2NH)ClTi{(µ3-N)3Ti3(η(5)-C5Me5)3(µ3-N)}] (5) are obtained by reaction of 1 with [TiCl4-x(NMe2)x] (x = 2, 3). The dimethylamine ligand in 5 is displaced by pyridine to give the analogue complex [(py)2ClTi{(µ3-N)3Ti3(η(5)-C5Me5)3(µ3-N)}] (6). Treatment of the titanium chloride complexes 4 and 5 with sodium cyclopentadienide or lithium bis(trimethylsilyl)amide reagents leads to the cube-type nitrido derivatives [RTi{(µ3-N)3Ti3(η(5)-C5Me5)3(µ3-N)}] (R = η(5)-C5H5 (7), N(SiMe3)2 (8)). The reaction of the zirconium trichloride complex 2 with [Tl(C5H5)] yields exclusively the dichloride-monocyclopentadienyl derivative [(η(5)-C5H5)Cl2Zr{(µ3-N)(µ3-NH)2Ti3(η(5)-C5Me5)3(µ3-N)}] (9). However, the treatment of 2 with excess [Na(C5H5)] causes further chloride replacement in 9 and subsequent cyclopentadiene elimination to give [(η(5)-C5H5)Zr{(µ3-N)3Ti3(η(5)-C5Me5)3(µ3-N)}] (10) via intermediates [(η(5)-C5H5)2ClZr{(µ3-N)Ti3(η(5)-C5Me5)3(µ-NH)2(µ3-N)}] (11) and [(η(5)-C5H5)ClZr{(µ3-N)2(µ3-NH)Ti3(η(5)-C5Me5)3(µ3-N)}] (12). Treatment of 2 or 9 with [Mg(C5H5)2] leads to the magnesium derivative [(η(5)-C5H5)Mg(µ-Cl)2(η(5)-C5H5)Zr{(µ4-N)(µ3-N)(µ3-NH)Ti3(η(5)-C5Me5)3(µ3-N)}] (13), which can be visualized as a result of the incorporation of one [Mg(η(5)-C5H5)Cl] moiety to complex 12. In contrast to the metathesis process with [M(C5H5)x] derivatives and subsequent C5H6 eliminations, the reaction of 2 with potassium pentamethylcyclopentadienide in toluene produces the paramagnetic derivative [K(µ-Cl)3Zr{(µ3-N)(µ3-NH)2Ti3(η(5)-C5Me5)3(µ3-N)}] (14) and C10Me10. Complex 14 reacts with one equivalent of 18-crown-6 or cryptand-222 to give the molecular complex [(18-crown-6)K(µ-Cl)3Zr{(µ3-N)(µ3-NH)2Ti3(η(5)-C5Me5)3(µ3-N)}] (15) or the ion pair [K(crypt-222)][Cl3Zr{(µ3-N)(µ3-NH)2Ti3(η(5)-C5Me5)3(µ3-N)}] (16). The X-ray crystal structures of 2, 8, 13 and 15 have been determined.

Crystal structure of (1,3-di-tert-butyl-η(5)-cyclo-penta-dien-yl)tri-methyl-hafnium(IV).

The mol-ecule of the title organometallic hafnium(IV) com-pound, [Hf(CH3)3(C13H21)] or [HfMe3(η(5)-C5H3-1,3- (t) Bu2)], adopts the classical three-legged piano-stool geometry for mono-cyclo-penta-dienylhafnium(IV) derivatives with the three methyl groups bonded to the Hf(IV) atom at the legs. The C atoms of the two tert-butyl group bonded to the cyclo-penta-dienyl (Cp) ring are 0.132 (5) and 0.154 (6) Šabove the Cp least-squares plane. There are no significant inter-molecular inter-actions present between the mol-ecules in the crystal structure.

Heterometallic complexes with cube-type [MTi3N4] cores containing Group 10 metals in a variety of oxidation states.

Treatment of [{Ti(η5-C5Me5)(µ-NH)}3(µ3-N)] (1) with one equivalent of [Ni(cod)2] (cod = 1,5-cyclooctadiene) in toluene at 60­80 °C and subsequent addition of diphenylacetylene, trans-stilbene or triphenylphosphane afforded the nickel(0) complexes [LNi{(µ3-NH)3Ti3(η5-C5Me5)3(µ3-N)}] (L = PhCCPh (2), PhCH≡CHPh (3), PPh3 (4)). The nickel(II) complex [I2Ni{(µ3-NH)3Ti3(η5-C5Me5)3(µ3-N)}] (5) was prepared by analogous addition of iodine to the solution obtained from the heating of 1 and [Ni(cod)2]. Treatment of 1 with one equivalent of [Pd(dba)2] (dba = dibenzylideneacetone) in toluene at room temperature led to the palladium(0) complex [(dba)Pd{(µ3-NH)3Ti3(η5-C5Me5)3(µ3-N)}] (6). Compound 6 reacted immediately with chloroform-d1 to give the palladium dichloride derivative [Cl2Pd{(µ3-NH)2Ti3(η5-C5Me5)3(µ-NH)(µ3-N)}] (7), which was prepared by treatment of 1 with [PdCl2(cod)] at room temperature. Addition of iodine to a toluene solution of 6 afforded the analogous palladium(II) derivative [I2Pd{(µ3-NH)2Ti3(η5-C5Me5)3(µ-NH)(µ3-N)}] (8). Complex 6 reacted with two equivalents of dimethylacetylenedicarboxylate (dmad) to give the metallacyclopentadiene palladium(II) complex [{(MeOOC)4C4}Pd{(µ3-NH)2Ti3(η5-C5Me5)3(µ-NH)(µ3-N)}] (9) via oxidative coupling. The treatment of 1 with [Pt(nbe)3] (nbe = norbornene) in toluene at room temperature gave the platinum(0) complex [(nbe)Pt{(µ3-NH)3Ti3(η5-C5Me5)3(µ3-N)}] (10). Compound 10 reacted with excess iodine to afford the platinum(IV) ionic derivative [I3Pt{(µ3-NH)3Ti3(η5-C5Me5)3(µ3-N)}]2(I3)(I5) (11) via an intermediate platinum(II) complex [I2Pt{(µ3-NH)2Ti3(η5-C5Me5)3(µ-NH)(µ3-N)}] (12). The X-ray crystal structures of 5, 8, 9 and 11 have been determined.

Partial hydrogenation of a tetranuclear titanium nitrido complex with ammonia borane.

The treatment of [{Ti(η(5)-C5Me5)}4(µ3-N)4] with NH3BH3 leads to the paramagnetic imidonitrido complex [{Ti(η(5)-C5Me5)}4(µ3-N)3(µ3-NH)], which can also be obtained by stepwise proton and electron transfer with HOTf and [K(C5Me5)].

Reactivity with electrophiles of imido groups supported on trinuclear titanium systems.

Several trinuclear titanium complexes bearing amido µ-NHR, imido µ-NR, and nitrido µn-N ligands have been prepared by reaction of [{Ti(η(5)-C5Me5)(µ-NH)}3(µ3-N)] (1) with 1 equiv of electrophilic reagents ROTf (R = H, Me, SiMe3; OTf = OSO2CF3). Treatment of 1 with triflic acid or methyl triflate in toluene at room temperature affords the precipitation of compounds [Ti3(η(5)-C5Me5)3(µ3-N)(µ-NH)2(µ-NH2)(OTf)] (2) or [Ti3(η(5)-C5Me5)3(µ3-N)(µ-NH)(µ-NH2)(µ-NMe)(OTf)] (3). Complexes 2 and 3 exhibit a fluxional behavior in solution consisting of proton exchange between µ-NH2 and µ-NH groups, assisted by the triflato ligand, as could be inferred from a dynamic NMR spectroscopy study. Monitoring by NMR spectroscopy the reaction course of 1 with MeOTf allows the characterization of the methylamido intermediate [Ti3(η(5)-C5Me5)3(µ3-N)(µ-NH)2(µ-NHMe)(OTf)] (4), which readily rearranges to give 3 by a proton migration from the NHMe amido group to the NH imido ligands. The treatment of 1 with 1 equiv of Me3SiOTf produces the stable ionic complex [Ti3(η(5)-C5Me5)3(µ3-N)(µ-NH)2(µ-NHSiMe3)][OTf] (5) with a disposition of the nitrogen ligands similar to that of 4. Complex 5 reacts with 1 equiv of [K{N(SiMe3)2}] at room temperature to give [Ti3(η(5)-C5Me5)3(µ3-N)(µ-N)(µ-NH)(µ-NHSiMe3)] (6), which at 85 °C rearranges to the trimethylsilylimido derivative [Ti3(η(5)-C5Me5)3(µ3-N)(µ-NH)2(µ-NSiMe3)] (7). Treatment of 7 with [K{N(SiMe3)2}] affords the potassium derivative [K{(µ3-N)(µ3-NH)(µ3-NSiMe3)Ti3(η(5)-C5Me5)3(µ3-N)}] (8), which upon addition of 18-crown-6 leads to the ion pair [K(18-crown-6)][Ti3(η(5)-C5Me5)3(µ3-N)(µ-N)(µ-NH)(µ-NSiMe3)] (9). The X-ray crystal structures of 2, 5, 6, and 8 have been determined.

Redox-active behavior of the [{Ti(η(5)-C5Me5)(µ-NH)}3(µ3-N)] metalloligand.

Treatment of [Cl3Y{(µ3-NH)3Ti3(η(5)-C5Me5)3(µ3-N)}] with [K(C5Me5)] in toluene gives C10Me10 and the paramagnetic [K(µ-Cl)3Y{(µ3-NH)3Ti3(η(5)-C5Me5)3(µ3-N)}] (3) derivative. Crystallization of 3 in pyridine affords the potassium-free [Cl2(py)2Y{(µ3-NH)3Ti3(η(5)-C5Me5)3(µ3-N)}] (4) complex. Whereas the reaction of 3 with 1 equiv of 18-crown-6 leads to the molecular complex [(18-crown-6)K(µ-Cl)3Y{(µ3-NH)3Ti3(η(5)-C5Me5)3(µ3-N)}] (5), the analogous treatment of 3 with cryptand-222 affords the ion pair [K(crypt-222)][Cl3Y{(µ3-NH)3Ti3(η(5)-C5Me5)3(µ3-N)}] (6). The X-ray crystal structures of 4, 5, and 6 have been determined. Density functional theory (DFT) calculations have elucidated the electronic structure of these species, which should be regarded as containing trivalent Y bonded to the {(µ3-NH)3Ti3(η(5)-C5Me5)3(µ3-N)} metalloligand radical anion.

Copper(I) and silver(I) complexes supported by the tridentate [{Ti(η(5)-C5Me5)(µ-NH)}3(µ3-N)] metalloligand.

Copper(I) and silver(I) ionic compounds [(L)M{(µ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)}][O(3)SCF(3)] containing [MTi(3)N(4)] cube-type cations have been prepared by reaction of [(CF(3)SO(2)O)M{(µ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)}] (M = Cu (2), Ag (3)) with a variety of donor molecules L. Treatment of complexes 2 and 3 with NH(3) in toluene at room temperature gives the ammonia adducts [(H(3)N)M{(µ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)}][O(3)SCF(3)] (M = Cu (4), Ag (5)), whose X-ray crystal structures reveal two cube-type cations associated through hydrogen bonding interactions between the ammine ligands and one oxygen atom of each trifluoromethanesulfonate anion. Analogous treatment of 2 and 3 with 1 equiv of pyridine, 2,6-dimethylphenylisocyanide, tert-butylisocyanide, or triphenylphosphane gives the ionic compounds [(L)M{(µ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)}][O(3)SCF(3)] (L = py, M = Cu (6), Ag (7); L = CNAr, M = Cu (8), Ag (9); L = CNtBu, M = Cu (10), Ag (11); L = PPh(3), M = Cu (12), Ag (13)). The reactions of 2 and 3 with methylenebis(diphenylphosphane) (dppm) in a 1:1 ratio lead to the single-cube complexes [(dppm)M{(µ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)}][O(3)SCF(3)] (M = Cu (14), Ag (15)), whereas in a 2:1 ratio give the bisphosphane-bridged double-cube compounds [{M(µ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)}(2)(µ-dppm)][O(3)SCF(3)](2) (M = Cu (16), Ag (17)). Similarly, treatment of 2 or 3 with a half equivalent of ethane-1,2-diylbis(diphenylphosphane) (dppe) affords double-cube derivatives [{M(µ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)}(2)(µ-dppe)][O(3)SCF(3)](2) (M = Cu (18), Ag (19)). The X-ray crystal structures of 4, 5, 10, 14, 15, and 18 have been determined.

Electrophilic attack on trinuclear titanium imido-nitrido systems.

Alkylation of [{Ti(η(5)-C(5)Me(5))(µ-NH)}(3)(µ(3)-N)] with MeOTf occurs at the imido ligands to produce the methylamido derivative [Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)(µ-NH)(2)(µ-NHMe)(OTf)] which readily rearranges to form the methylimido complex [Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)(µ-NH)(µ-NH(2))(µ-NMe)(OTf)].

Molecular nitrides with titanium and rare-earth metals.

A series of titanium-group 3/lanthanide metal complexes have been prepared by reaction of [{Ti(η(5)-C(5)Me(5))(µ-NH)}(3)(µ(3)-N)] (1) with halide, triflate, or amido derivatives of the rare-earth metals. Treatment of 1 with metal halide complexes [MCl(3)(thf)(n)] or metal trifluoromethanesulfonate derivatives [M(O(3)SCF(3))(3)] at room temperature affords the cube-type adducts [X(3)M{(µ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)}] (X = Cl, M = Sc (2), Y (3), La (4), Sm (5), Er (6), Lu (7); X = OTf, M = Y (8), Sm (9), Er (10)). Treatment of yttrium (3) and lanthanum (4) halide complexes with 3 equiv of lithium 2,6-dimethylphenoxido [LiOAr] produces the aryloxido complexes [(ArO)(3)M{(µ(3)-NH)(3)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)}] (M = Y (11), La (12)). Complex 1 reacts with 0.5 equiv of rare-earth bis(trimethylsilyl)amido derivatives [M{N(SiMe(3))(2)}(3)] in toluene at 85-180 °C to afford the corner-shared double-cube nitrido compounds [M(µ(3)-N)(3)(µ(3)-NH)(3){Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)}(2)] (M = Sc (13), Y (14), La (15), Sm (16), Eu (17), Er (18), Lu (19)) via NH(SiMe(3))(2) elimination. A single-cube intermediate [{(Me(3)Si)(2)N}Sc{(µ(3)-N)(2)(µ(3)-NH)Ti(3)(η(5)-C(5)Me(5))(3)(µ(3)-N)}] (20) was obtained by the treatment of 1 with 1 equiv of the scandium bis(trimethylsilyl)amido derivative [Sc{N(SiMe(3))(2)}(3)]. The X-ray crystal structures of 2, 7, 11, 14, 15, and 19 have been determined. The thermal decomposition in the solid state of double-cube nitrido complexes 14, 15, and 18 has been investigated by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) measurements, as well as by pyrolysis experiments at 1100 °C under different atmospheres (Ar, H(2)/N(2), NH(3)) for the yttrium complex 14.