Cristina Santamaría

Construction of Heterometallic Cubanes [{Ti3Cp(μ3‐CMe)}(μ3‐O)3{Mo(CO)3}]

Incorporation of M(CO)(3) fragments by trinuclear Ti complexes [{Ti(3)Cp (µ(3)-CR)}(µ-O)(3)] and [{Ti(3)Cp (µ(3)-N)}(µ-NH)(3)] (Cp*=eta(5)-C(5)Me(5)) leads to the formation of an unprecedented class of heterometallic clusters with cubane structure [e.g., Eq. (a)]. Density functional calculations on these complexes indicate the existence of electron delocalization in the Ti(3)M cores (M=Cr, Mo, W).

Ammonia activation by μ3-alkylidyne fragments supported on a titanium molecular oxide model.

Ammonolysis of the μ(3)-alkylidyne derivatives [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-CR)] [R = H (1), Me (2)] produces a trinuclear oxonitride species, [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-N)] (3), via methane or ethane elimination, respectively. During the course of the reaction, the intermediates amido μ-alkylidene [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ-CHR)(NH(2))] [(R = H (4), Me (5)] and μ-imido ethyl species [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ-NH)Et] (6) were characterized and/or isolated. This achievement constitutes an example of characterization of the three steps of successive activation of N-H bonds in ammonia within the same transition-metal molecular system. The N-H σ-bond activation of ammonia by the μ(3)-alkylidyne titanium species has been theoretically investigated by DFT method on [{Ti(η(5)-C(5)H(5))(μ-O)}(3)(μ(3)-CH)] model complex. The calculations complement the characterization of the intermediates, showing the multiple bond character of the terminal amido and the bridging nature of imido ligand. They also indicate that the sequential ammonia N-H bonds activation process goes successively downhill in energy and occurs via direct hydron transfer to the alkylidyne group on organometallic oxides 1 and 2. The mechanism can be divided into three stages: (i) coordination of ammonia to a titanium center, in a trans disposition with respect to the alkylidyne group, and then the isomerization to adopt the cis arrangement, allowing the direct hydron migration to the μ(3)-alkylidyne group to yield the amido μ-alkylidene complexes 4 and 5, (ii) hydron migration from the amido moiety to the alkylidene group, and finally (iii) hydron migration from the μ-imido complex to the alkyl group to afford the oxo μ(3)-nitrido titanium complex 3 with alkane elimination.

Carbene complexes of titanium group metals — formation and reactivity

Abstract The principles in the formation of carbene complexes of titanium group metals are summarized. Characteristic examples of isolated as well as carbene complexes as intermediates are given. Selected structures and reactivity patterns are discussed. Starting from the Tebbe-type chemistry, new aspects of carbene complexes with only one or without cyclopentadienyl ligands are illustrated. In that direction, the formation of carbene complexes with N and O-donor ligands is described. Applications in co-ordination chemistry, organic syntheses and material sciences are summarized.

Complete Defluorination of 1,2,3,4‐Tetramethyl‐5‐(trifluoromethyl)cyclopentadiene by Titanium Tetrakis(dimethylamide)—Selective Formation of a Cyclic Hexanuclear Titanium Fluoroamide and 6,6‐Dimethylaminotetramethylfulvene

1,2,3,4-Tetramethyl-5-(trifluoromethyl)cyclopentadiene (Cp*CF3-H, 1) reacts with [Ti(NMe2)4] (2) under mild conditions to give [Ti(mu-NMe2)(NMe2)(mu-F)(F)]6 (3) in nearly quantitative yield. The molecular structure of 3 consists of a ring of six [TiF2(NMe2)2] edge-bridged octahedra. Titanium complexes containing the Cp*CF3 ligand, which was the primary intention of these investigations, were not observed. C5Me4=C(NMe2)2 (4) was isolated as a by-product. The complete defluorination of an aliphatic CF3 group occurs during the reaction. The reaction mechanism involves the primary formation of a difluorofulvene intermediate C5Me4=CF2 (5), which was monitored by NMR studies. Density functional theory calculations predict a highly charged C6 atom (+0.87) in 5, which is discussed as the driving force of the reaction.

Construction of Heterometallic Cubanes [{Ti3Cp*3(μ3‐CR)}(μ3‐O)3{Mo(CO)3}] (R=H, Me; Cp*=η5‐C5Me5) and [{Ti3Cp*3(μ3‐N)}(μ3‐NH)3{M(CO)3}] (M=Cr, Mo, W); Crystal Structure of [{Ti3Cp*3(μ3‐CMe)}(μ3‐O)3{Mo(CO)3}]

Der Einbau von M(CO)3-Fragmenten in die dreikernigen Ti-Komplexe [{Ti3Cp*3(μ3-CR)}(μ-O)3] und [{Ti3Cp*3(μ3-N)}(μ-NH)3] (Cp*=η5-C5Me5) fuhrt zu einer neuen Klasse von Heterometallclustern mit Cubanstruktur [z. B. Gl. (a)]. Dichtefunktionalrechungen deuten auf eine Elektronendelokalisierung in den Ti3M-Gerusten hin (M=Cr, Mo, W).

Allyl derivatives of [{Ti(η5-C5Me5)(μ-O)Cl)}3]: X-ray crystal structure of [{Ti(η5-C5Me5)(μ-O)(CH2CH=CHMe)}3]

Abstract Reactions of [{Ti( η 5 -C 5 Me 5 )( μ -O)Cl} 3 ] ( 1 ) with Grignard reagents, RMgCl (R = allyl (CH 2 CHCH 2 ), crotyl (CH 2 CHCHMe)), in diverse ratios and conditions allow the characterization of the allyl oxotrimers [{Ti( η 5 -C 5 Me 5 )( μ -O)} 3 R n Cl 3− n ] ( n = 3, R = allyl, 2 ; n = 1, R = allyl, 4 ; n = 2, R = allyl, 5 ; n = 3, R = crotyl, 7 ). The complexes [{Ti( η 5 -C 5 Me 5 )( μ -O)} 3 ( π -C 3 H 5 ) 3 ] ( 2 ) and [{Ti( η 5 -C 5 Me 5 )( μ -O)} 3 ( π -C 3 H 5 ) 2 Cl] ( 5 ) undergo thermal rearrangements, in a regio- and stereoselective way, to give the derivatives [{Ti( η 5 -C 5 Me 5 )( μ -O)} 3 ( μ 2 -CH 2 CH(CH 2 CHCH 2 )CH 2 }X]X = allyl ( 3 ) and X = Cl ( 6 ) respectively. These processes involve the migration of one allyl group to the β-carbon of the adjacent allyl ligand and the formation of a 2-allyl-1,3-propanediyl unit bridging two titanium atoms. The crystal structure of [{Ti( η 5 -C 5 Me 5 )( μ -O)} 3 ( σ -CH 2 CHCHMe 3 ] ( 7 ) has been studied by X-ray crystallography and can be described as three Ti( η 5 -C 5 Me 5 )( σ -crotyl) units linked through oxygen bridges forming a nearly planar Ti 3 O 3 ring.

Organotitanium oxides as Lewis acidic supports of metal carbonyl species: [{Ti3(η5-C5Me5)3(µ-O)3Me}{(µ-OC)M(CO)2(η5-C5H5)}2](M = Mo, W)

Reaction of [{Ti(η5-C5Me5)(µ-O)}3(µ3-CH)]1 with [M(η5-C5H5)(CO)3H](M = Mo, W) leads to the formation of Lewis acid carbonyl adducts [{Ti3(η5-C5Me5)3(µ-O)3Me}{(µ-OC)M(CO)2(η5-C5H5)}2]4, 5 showing the transformation of the µ3-methylidyne group into a Me group through the µ-methylene intermediates [{Ti3(η5-C5Me5)3(µ-O)3(µ-CH2)}(µ-OC)M(CO)2(η5-C5H5)]2, 3.

Co-complexation of lithium gallates on the titanium molecular oxide {[Ti(η5-C5Me5)(μ-O)}3(μ3-CH)].

Amide and lithium aryloxide gallates [Li(+){RGaPh(3)}(-)] (R = NMe(2), O-2,6-Me(2)C(6)H(3)) react with the μ(3)-alkylidyne oxoderivative ligand [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-CH)] (1) to afford the gallium-lithium-titanium cubane complexes [{Ph(3)Ga(μ-R)Li}{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-CH)] [R = NMe(2) (3), O-2,6-Me(2)C(6)H(3) (4)]. The same complexes can be obtained by treatment of the [Ph(3)Ga(μ(3)-O)(3){Ti(η(5)-C(5)Me(5))}(3)(μ(3)-CH)] (2) adduct with the corresponding lithium amide or aryloxide, respectively. Complex 3 evolves with formation of 5 as a solvent-separated ion pair constituted by the lithium dicubane cationic species [Li{(μ(3)-O)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-CH)}(2)](+) together with the anionic [(GaPh(3))(2)(μ-NMe(2))](-) unit. On the other hand, the reaction of 1 with Li(p-MeC(6)H(4)) and GaPh(3) leads to the complex [Li{(μ(3)-O)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-CH)}(2)][GaLi(p-MeC(6)H(4))(2)Ph(3)] (6). X-ray diffraction studies were performed on 1, 2, 4, and 5, while trials to obtain crystals of 6 led to characterization of [Li{(μ(3)-O)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-CH)}(2)][PhLi(μ-C(6)H(5))(2)Ga(p-MeC(6)H(4))Ph] 6a.

Group 13 organoderivatives supported on a metallic oxide model

The [{TiCp*(micro-O)}3(mu3-CH)] (1) metalloligand, (Cp* = eta5-C5Me5), coordinates in a 1:1 ratio to [AlMe3] or 9-BBN to give [{Me3Al}{(mu3-O)(mu-O)2(TiCp)2(TiCp)3(mu3-CH)}](2) or [{(C8H14)B}(mu-H) {(mu3-O)(mu-O)2(TiCp*)3(mu3-CH)}](4), respectively, partial hydrolysis of 2 leads to the new hydroxo-aluminium derivative [{MeAl} {(mu-OH)(mu3-O)}2{(mu-O)2(TiCp*)3-(mu3-CH)}2](3).

An Effective Route to Dinuclear Niobium and Tantalum Imido Complexes

Thermal treatment of the trichloro complexes [MCl3(NR)py2] (R = tBu, Xyl; M = Nb, Ta) (Xyl = 2,6-Me2C6H3) under vacuum affords the dinuclear imido species [MCl2(μ-Cl)(NR)py]2 (R = tBu, Xyl; M = Nb 1, 3; Ta 2, 4) with loss of pyridine. Complexes 1-4 can be easily transformed to the mononuclear starting materials [MCl3(NR)py2] (R = tBu, Xyl; M = Nb, Ta) upon reaction with pyridine. While reactions of compounds 1 and 2 with a series of alkylating reagents render the mononuclear peralkylated imido complexes [MR3(NtBu)] (R = Me, CH2Ph, CH2CMe3, CH2CMePh, CH2SiMe3), the analogous treatment with allylmagnesium chloride results in the formation of the dinuclear niobium(IV) derivative [(NtBu)(η3-C3H5)M(μ-C3H5)(μ-Cl)2M(NtBu)py2] (5). Additionally, the treatment of the starting materials 1 and 2 with the organosilicon reductant 1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene yields the pyridyl-bridged dinuclear derivatives [M2Cl2(μ-Cl)2(NtBu)2py2]2(μ-NC4H4N)2 (M = Nb 6, Ta 7). Controlled hydrolysis reaction of 1 and 2 affords the oxo chlorido-bridged products [MCl(μ-Cl)(NtBu)py]2(μ-O) (M = Nb 8, Ta 9) in a quantitative way, while the treatment of these latter with one more equivalent of pyridine led to complexes [MCl2(NtBu)py2]2(μ-O) (M = Nb 10, Ta 11). Structural study of these dinuclear imido derivatives has been also performed by X-ray crystallography.