Avelino Martín

SELF-ASSEMBLY OF DOUBLE-HELICAL COMPLEXES OF 2,2'-6',2''-6'',2'''-QUATERPYRIDINE (QTPY) - THE X-RAY CRYSTAL-STRUCTURES OF [CU2(QTPY)2][PF6]2 AND [AG2(QTPY)2][BF4]2

Abstract 2,2′:6′,2″:6″,2‴-Quaterpyridine (qtpy) forms double-helical binuclear complexes with metal ions adopting a pseudo-tetrahedral geometry; it is not necessary to design a sterically constrained ligand for this purpose, as the crystal structures of [Cu2(qtpy)2][PF6]2 and [Ag2 (qtpy)2][BF4]2 demonstrate; the role of the substituents is not to control the assembly of the helix, but to control its pitch.

2,2′ : 6′,2″ : 6″,2‴-Quaterpyridine (qtpy): a versatile ligand in metallosupramolecular chemistry; crystal and molecular structures of [Ni(qtpy)(OH2)2][BF4]2, [Pd(qtpy)][PF6]2, [Cu2(qtpy)2][Pf6]2 and [Ag2(qtpy)2][BF4]2

The co-ordination behaviour of 2,2′ : 6′,2″ : 6″,2‴-quaterpyridine (qtpy) has been systematically studied. Double-helical dinuclear complexes were only obtained with ions bearing a low charge or a low charge-to-radius ratio and which have no electronically imposed preference for geometries in which the ligand can present a planar donor set. The double-helical complexes [Cu2(qtpy)2][PF6]2 and [Ag2(qtpy)2][BF4]2 have been structurally characterised, as have the mononuclear species [Ni(qtpy)(OH2)2][BF4]2 and [Pd(qtpy)][PF6]2. Complexes with zinc(II) and cadmium(II) are mononuclear but it is suggested that a double-helical dinuclear complex is formed with mercury(II).

Dialkylamido derivatives of [(η5-C5Me5)TiCl3], [(η5-C5Me5) TiCl22(μ-O)] and [(η5-C5Me5)TiCl3(μ-O)3]: X-ray crystal structure of [(η5-C5Me5)Ti(NMe2)3]

Abstract Reactions of [(η5-C5Me5)TiCl3] with dialkyl and diarylamido-lithium complexes in 1:1, 1:2 or 1:3 molar ratios afford the mono(pentamethylcyclopentadienyl)titanium(IV) dialkylamido- complexes [(η5-C5Me5)TiCl3-n(NR2)n (n = 1; R = Me or SiMe3) (n = 2, R = Me or Ph) (n = 3, R = Me or Et). Similar reactions of [(η5-C5Me5)TiCl 22(μ-O)] and [(η5-C5Me5)TiCl3(μ-O)3] gave the corresponding complexes [(η5-C5Me5)TiCl2-n(NR2)ni2(μ-O)] (n = 1; R = Me or Ph) (n = 2, R = Me) and [(η5-C5Me5)3Ti3Cl3-n(NMe2)n(μ-O) 3] (n = 1 or 3). The crystal structure of [(η5-C5Me5)Ti(NMe2)3] has been established by X-ray crystallography and is shown to be monomeric with the typical three-legged piano- stool structure.

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).

Monopentamethylcyclopentadienyltitanium(IV) halo-alkoxides, alkyl-alkoxides and acetylacetonates

Abstract Reactions of (C 5 Me 5 )TiCl 3 with lithium alkoxides in 1:1 or 1:2 molar ratio have given the halo-alkoxides (C 5 Me 5 )TiCl 3− n (OR) n ( n = 1, R = Me, SiPh 3 ; n = 2, R = SiPh 3 ) and (C 5 Me 5 )TiCl (O 2 R′)(R′ = C 6 H 4 , C 6 H 3 -4- t Bu). Protonolysis of (C 5 Me 5 TiMe 3 with HOSiPh 3 and Hacac gives (C 5 Me 5 )TiMe(OSiPh 3 ) 2 and (C 5 Me 5 )TiMe 2 (acac), and (C 5 Me 5 )TiCl 2 Me likewise gives (C 5 Me 5 )TiCl 2 (OC 6 H 3 -2.6-Me 2 ) and (C 5 Me 5 )TiCl 2 (acac). The crystal structure of (C 5 Me 5 )TiCl 2 (OC 6 H 3 -2,6-Me 2 ) has been determined and shows it to be monomeric, with a symmetry plane, a TiO distance of 1.785(2) A, and a TiOC angle of 162.3(2)°.

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.

Reaction of imines with N-iodosuccinimide (NIS): unexpected formation of stable 1 : 1 complexes

Imines react with N-iodosuccinimide (NIS) to afford unexpected 1 : 1 complexes and the structure of one of these was determined by single-crystal X-ray diffraction; the reaction seems to be very general for substituted cyclic imines with solid stable complexes obtained in high yields; this is the first reported example of a halogen bonding interaction involving the C=N bond and NIS.

Synthesis and molecular structure of the first organometallic nitride cubane: [{Ti(η5-C5Me5)}4(µ3-N)4]

The ammonolysis of [Ti(η5-C5Me5)(NMe2)3] at 90 °C affords the nitride complex [{Ti(η5-C5Me5)}4(µ3-N)4]; the X-ray crystal structure analysis shows a Ti4N4 core clearly similar to the structural motif of cubic titanium nitride.

Insertion of Isocyanide into Metal−Carbon Bonds of Alkylchloro(pentamethylcyclopentadienyl)niobium- and -tantalum Complexes − X-ray Structure of [TaCp*Cl2(CH2CMe2Ph){η2-C(CH2CMe2Ph)=N(2,6-Me2C6H3)}] and Unexpected Decomposition of Alkyldichloro(η2-iminoacyl) Complexes of Tantalum

Methylation of NbCp*Cl2Me2 using excess ZnMe2 gives NbCp*ClMe3 (1) which has been found to exhibit a Berry pseudorotation process on the NMR time scale (log A = 12.2 ± 0.3, Ea = 12.2 ± 0.4 kcal·mol−1, ΔH≠ = 11.6 ± 0.4 kcal·mol−1, ΔS≠ = −4.4 ± 1.3 e.u., ΔG≠298K = 12.9 kcal·mol−1). Alternatively, lithium dimethylamide reacts with NbCp*Cl2Me2 to form NbCp*Me2(NMe2)2 (2) which decomposes in solution under the elimination of methane to give the (dimethylamido)methylazaniobacyclopropane derivative NbCp*Me(NMe2)(η2-CH2NMe) (3). Reaction of NbCp*Cl2Me2 with 1 equiv. of 2,6-Me2C6H3NC results in a double methyl group migration to give the dichloroazaniobacyclopropane complex [NbCp*Cl2{η2-CMe2N(2,6-Me2C6H3)}] (4). Dialkyldichloro complexes TaCp*Cl2R2 [Cp* = η5-C5Me5; R = CH2SiMe3 (5), CH2CMe2Ph (6), CH2CMe3 (7), CH2C6H5 (8)] were obtained by treating TaCp*Cl4 with the requisite amounts of the appropriate alkylating agents. Reactions of the dialkyldichloro complexes TaCp*Cl2R2 (5−8) with 1 equiv. of 2,6-Me2C6H3NC resulted in migration of only one of the two alkyl groups to give (alkyl)dichloro(η2-iminoacyl) complexes [TaCp*Cl2R{η2-C(R)=NAr}] [Ar = 2,6-Me2C6H3; R = CH2SiMe3 (9), CH2CMe2Ph (10), CH2CMe3 (11), CH2C6H5 (12)]. The molecular structure of complex 10 has been determined by X-ray diffraction analysis. The η2-iminoacyl complexes 9−12 decompose in [D6]benzene or n-hexane solutions to give [TaCp*Cl2{N(2,6-Me2C6H3)}] and the corresponding trans or cis olefins R′−CH=CH−CH2−R′ [R′ = SiMe3 (9o), CMe2Ph (10o), CMe3 (11o), C6H5 (12o)]. A mechanism for this reaction is proposed. All the new compounds have been characterized by IR spectrophotometry, 1H- and 13C{1H}-NMR spectroscopy, and elemental analysis.

Molecular structure of trichloro(η5-pentamethylcyclopentadienyl)zirconium(IV)

Abstract X-ray analysis of the yellow, air-unstable, crystalline compound Cp★ZrCl3 (1) which results from the reaction of ZrCl4 with Cp★SiMe3 confirms the presence of two Cp★ZrCl3 moieties related by a centre of symmetry with two chlorine atoms bridging the metals. 1 is therefore a dimer, despite the molecular structure of [CpZrCl3] which was found to be a polymer.