Steric and electronic effects in stabilizing allyl-palladium complexes of “P-N-P” ligands, X2PN(Me)PX2 (X = OC6H5 or OC6H3Me2-2,6)

The chemistry of η³-allyl palladium complexes of the diphosphazane ligands, X₂PN(Me)PX₂ [X = OC₆H₅ (1) or OC₆H₃Me₂-2,6 (2)] has been investigated.The reactions of the phenoxy derivative, (PhO)₂PN(Me)P(OPh)₂ with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = H or Me; R′ = H, R″ = Me) give exclusively the palladium dimer, [Pd₂{μ-(PhO)₂PN(Me)P(OPh)₂}₂Cl₂] (3); however, the analogous reaction with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = Ph) gives the palladium dimer and the allyl palladium complex [Pd(η³-1,3-R′,R″-C₃H₃)(1)](PF₆) (R′ = R″ = Ph) (4). On the other hand, the 2,6-dimethylphenoxy substituted derivative 2 reacts with (allyl) palladium chloro dimers to give stable allyl palladium complexes, [Pd(η³-1,3-R′,R″-C₃H₃)(2)](PF₆) [R′ = R″ = H (5), Me (7) or Ph (8); R′ = H, R″ = Me (6)].Detailed NMR studies reveal that the complexes 6 and 7 exist as a mixture of isomers in solution; the relatively less favourable isomer, anti-[Pd(η³-1-Me-C₃H₄)(2)](PF₆) (6b) and syn/anti-[Pd(η³-1,3-Me₂-C₃H₃)(2)](PF₆) (7b) are present to the extent of 25% and 40%, respectively. This result can be explained on the basis of the steric congestion around the donor phosphorus atoms in 2. The structures of four complexes (4, 5, 7a and 8) have been determined by X-ray crystallography; only one isomer is observed in the solid state in each case.     

Synthesis and structures of bimetallic silicon-containing imido alkylidene complexes of tungsten (R′O)2(ArN)WCH-SiR2-CHW(NAr)(OR′)2 (R = Me, Ph) and (R′O)2(ArN)WCH-SiMe2SiMe2-CHW(NAr)(OR′)2

Bimetallic alkylidene complexes of tungsten (R′O)₂(ArN)WCH-SiR₂-CHW(NAr)(OR′)₂ (R = Me (1), Ph (2)) and (R′O)₂(ArN)WCH-SiMe₂SiMe₂-CHW(NAr)(OR′)₂ (3) (Ar = ; R′ = CMe₂CF₃) have been prepared by the reactions of divinyl silicon reagents R₂Si(CHCH₂)₂ with known alkylidene compounds R′′-CHMo(NAr)(OR′)₂. (R′′ = Bu^t, PhMe₂C) Complexes 1-3 were structurally characterized. Ring opening metathesis polymerization (ROMP) of cyclooctene using compounds 1-3 as initiators led to the formation of high molecular weight polyoctenamers with predominant trans-units content in the case of 1 and 3 and predominant cis-units content in the case of 2.     

Dimeric and trimeric diorganosilicon chalcogenides (PhRSiE)2,3 (E = S, Se, Te; R = Ph, Me)

Ph₂SiCl₂ and PhMeSiCl₂ react with Li₂E (E = S, Se, Te) under formation of trimeric diorganosilicon chalcogenides (PhRSiE)₃ (R = Ph: 1a-3a, R = Me: cis/trans-4a (E = S), cis/trans-5a (E = Se)). In case of E = S, Se dimeric four-membered ring compounds (PhRSiE)₂ (R = Ph: 1b-2b, R = Me: cis/trans-4b (E = S), cis/trans-5b (E = Se)) have been observed as by-products. 1a-5b have been characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ²⁹Si, ⁷⁷Se, ¹²⁵Te). Four- and six-membered ring compounds differ significantly in ²⁹Si and ⁷⁷Se chemical shifts as well as in the value of ¹J_SiSe.The molecular structures of 2a, 3a and trans-5a reported in this paper are the first examples of compounds with unfused six-membered rings Si₃E₃ (E = Se, Te). The Si₃E₃ rings adopt twisted boat conformations. The crystal structure of 3a reveals an intermolecular Te-Te contact of 3.858 Å which yields a dimerization in the solid state.     

Synthesis, structures and preliminary biological screening of bis(diphenyl)chlorotin complexes and adducts: Ph2ClSn-CH2-R-CH2-SnClPh2, R = p-C6H4, CH2CH2

The reaction between ClCH₂-R-CH₂Cl, R = p-C₆H₄, and [Ph₃Sn]⁻Li⁺ yields Ph₃Sn-CH₂-R-CH₂-SnPh₃ (1) in high yield. The related known compound R = CH₂CH₂ (1a) is synthesized by the reaction of the di-Grignard reagent BrMg(CH₂)₄MgBr with two equivalents of Ph₃SnCl. Cleavage of a single Sn-Ph group at each tin centre of both compounds using HCl/Et₂O yields the corresponding bis-chlorostannanes Ph₂ClSn-CH₂-R-CH₂-SnClPh₂, R = (CH₂)₄ (2) and R = C₆H₄ (3), respectively. Compounds 1, 2 and 3 are crystalline solid materials and their single crystal X-ray structures are reported. In the solid state both 2 and 3 form self-assembled ladder structures involving alternating intermolecular Cl-Sn?Cl and Cl?Sn-Cl bonded chains at both ends of the distannanes with 5-coordinate tin atoms. Recrystallization of 3 from CH₂Cl₂ in the presence of DMF yields the bis-DMF adduct (4) in which no self-assembled structures were noted. Evaluation of the chlorostannanes 2 and 3 against a suite of bacteria, Staphylococcus aureus, Escherichia coli and Photobacterium phosphoreum is reported and compared to the related mono-chlorostannanes Ph₂(CH₃)SnCl and Ph₂(PhCH₂)SnCl.     

Reverse Kocheshkov reaction - Redistribution reactions between RSn(OCH2CH2NMe2)2Cl (R = Alk, Ar) and PhSnCl3: Experimental and DFT study

A series of organotin compounds bearing two intramolecular N → Sn coordination bonds RSn(OCH₂CH₂NMe₂)₂Cl (R = Me (4), n-Bu (5), Mes (6)) were synthesized in good yields. These compounds as well as 2 (R = Ph) react with PhSnCl₃ to give redistribution products RPhSnCl₂ and (Me₂NCH₂CH₂O)₂SnCl₂ (3). The direction of redistribution reactions is reverse to Kocheshkov reaction. DFT calculations have shown that the driving force of the reactions is formation of intramolecular N → Sn coordination bonds in (RO)₂SnCl₂ (3), the Lewis acid stronger than RSn(OR)₂Cl (2, 4-6). The mechanism of the redistribution reaction between 2 and PhSnCl₃ consists of two steps: (1) initial exchange of OCH₂CH₂NMe₂ and Cl to give PhSn(OCH₂CH₂NMe₂)Cl₂ (7) followed by (2). Ph and OCH₂CH₂NMe₂ exchange.     

Formation and structural characterization of mercury complexes from Te(R)CH2SiMe3 (R = Ph, CH2SiMe3) and HgCl2

The reaction of HgCl₂ and Te(R)CH₂SiMe₃ [R = CH₂SiMe₃ (1), Ph (2)] in ethanol yielded a mononuclear complex [HgCl₂{Te(R)CH₂SiMe₃}₂] (R = Ph, 3a; R = CH₂SiMe₃, 3b). The recrystallization of 3a or 3b from CH₂Cl₂ produced a dinuclear complex [Hg₂Cl₂(μ-Cl)₂{Te(R)CH₂SiMe₃}₂] (R = Ph, 4a; R = CH₂SiMe₃, 4b). When 3a was dissolved in CH₂Cl₂, the solvent quickly removed, and the solid recrystallized from EtOH, a stable ionic [HgCl{Te(Ph)CH₂SiMe₃}₃]Cl·2EtOH (5a·2EtOH) was obtained. Crystals of [HgCl₂{Te(CH₂SiMe)₂}]·2HgCl₂·CH₂Cl₂ (6b·2HgCl₂·CH₂Cl₂) were obtained from the CH₂Cl₂ solution of 3b upon prolonged standing. The complex formation was monitored by ¹²⁵Te-, and ¹⁹⁹Hg NMR spectroscopy, and the crystal structures of the complexes were determined by single crystal X-ray crystallography.     

Preparation, crystal structures, EPR and reflectance spectra of two new charge-transfer salts, [CpFeCpCH2N(CH3)3]4[XMo12O40] · nCH3CN (n = 0 for X = P or n = 1 for X = Ge)

Two new charge-transfer salts, [CpFeCpCH₂N(CH₃)₃]₄[PMo₁₂O₄₀] · CH₃CN (1) and [CpFeCpCH₂N(CH₃)₃]₄[GeMo₁₂O₄₀] (2), were synthesized by the traditional solution synthetic method and their structures were determined by single-crystal X-ray analysis. Salt 1 belongs to the triclinic space group P1, and salt 2 belongs to the triclinic space group . There exist the complex interactions of the cationic ferrocenyl donor and Keggin polyanion in the solid state. The solid state UV-Vis diffuse reflectance spectra indicate the presence of a charge-transfer band climbing from 450 nm to well beyond 900 nm for 1, a charge-transfer band from 460 to 850 nm with λ_max = 630 nm for 2.The EPR spectra of salts 1 and 2 at 77 K show a signal at g = 2.0048 and 1.9501, respectively, ascribed to the delocalization of one electron in reduced Keggin ion in salt 1 and the Mo^VI in [GeMo₁₂O₄₀]⁴⁻ is partly reduced to Mo^V owing to the charge-transfer transitions taking place between the ferrocenyl donors and the POM acceptors. The two compounds were also characterized by IR spectroscopy and cyclic voltammetry.     

Aqueous syntheses of [(Cp-R)M(CO)3] type complexes (Cp = cyclopentadienyl, M = Mn, Tc, Re) with bioactive functionalities

We describe reactions of [^99mTc(H₂O)₃(CO)₃)]⁺ (1) with Diels-Alder products of cyclopentadiene such as “Thiele’s acid” (HCp-COOH)₂ (2) and derivatives thereof in which the corresponding [(Cp-COOH)^99mTc(CO)₃)] (3) complex did form in water. We propose a metal mediated Diels-Alder reaction mechanism. To show that this reaction was not limited to carboxylate groups, we synthesized conjugates of 2 (HCp-CONHR)₂ (4a-c) (4a, R = benzyl amine; 4b, R = N_α-Boc-l-2,3-diaminopropionic acid and 4c, R = glycine). The corresponding ^99mTc complexes [(4a)^99mTc(CO)₃)] 6a, [(4b)^99mTc(CO)₃)] 6b and [(4c)^99mTc(CO)₃)] 6c have been prepared along the same route as for Thiele’s acid in aqueous media demonstrating the general applicability of this synthetic strategy. The authenticity of the ^99mTc complexes on the no carrier added level have been confirmed by chromatographic comparison with the structurally characterized manganese or rhenium complexes.Studies of the reaction of 1 with Thiele’s acid bound to a solid phase resin demonstrated the formation of [(Cp-COOH)^99mTc(CO)₃)] 3 in a heterogeneous reaction. This is the first evidence for the formation of no carrier added ^99mTc radiopharmaceuticals containing cyclopentadienyl ligands via solid phase syntheses. Macroscopically, the manganese analogue 5a and the rhenium complexes 5b-c have been prepared and characterized by IR, NMR, ESI-MS and X-ray crystallography for 5a (monoclinic, P2₁/c, a = 9.8696(2) Å, b = 25.8533(4) Å, c = 11.8414(2) Å, β = 98.7322(17)°) in order to unambiguously assign the authenticity of the corresponding ^99mTc complexes.     

New stable germylenes, stannylenes, and related compounds: 6. Heteroleptic germanium(II) and tin(II) compounds [(SiMe3)2N-E-OCH2CH2NMe2]n (E = Ge, n = 1; Sn, n = 2): synthesis and structure

New stable heteroleptic germanium(II) and tin(II) compounds [(SiMe₃)₂N-E¹⁴-OCH₂CH₂NMe₂]_n (E¹⁴ = Ge, n = 1 (1), Sn, n = 2 (2)) have been synthesized and their crystal structures have been determined by X-ray diffraction analysis. While compound 1 is monomer stabilized by intramolecular Ge ← N coordination, compound 2 is associated to dimer via intermolecular dative Sn ← O interactions.     

The reaction of the group-13 alkyls ER3 (E = Al, Ga, In; R = CH2t-Bu, CH2 SiMe3) with the platinum-complex [(dcpe)Pt(H)(CH2t-Bu)]

The reactions of the sterically demanding group-13 alkyls ER₃ (E = Al, Ga, In; R = CH₂t-Bu, CH₂SiMe₃) with the platinum-complex [(dcpe)Pt(H)(CH₂t-Bu)] were re-investigated. The bimetallic compounds [(dcpe)Pt(ER₂)(R)] (3: E = Ga, R = CH₂SiMe₃; 5: E = In, R = CH₂t-Bu; dcpe = bis(dicyclohexylphosphino)ethane) with direct σ(Pt-E) bonds were obtained by oxidative addition of an E-C bond to the coordinatively unsaturated fragment [(dcpe)Pt] produced in situ by thermolysis of the starting complex [(dcpe)Pt(CH₂t-Bu)(H)]. The single crystal structure determination reveals a Pt-Ga bond length of 2.376(2) Å and a Pt-In bond length of 2.608(1) Å. All new compounds were characterised by elemental analysis, ³¹P and ¹⁹⁵Pt NMR spectroscopy. Interestingly, the Pt-Ga compound 3 slowly transforms into the platinum alkyl/hydride isomer {(dcpe)Pt(μ₂-H)[CH₂Si(CH₃)₂ CH₂Ga(CH₂SiMe₃)₂]} (4) during crystallization from solution at room temperature. The X-ray single crystal structure analysis revealed both complexes 3 and 4 coexisting in the unit cell in a 1:1 relation. The inaccessibility of analytically pure samples of the Pt-Al complex {(dcpe)Pt[Al(CH₂t-Bu)₂](CH₂t-Bu)} (6), postulated as intermediate of the reaction of [(dcpe)Pt(H)(CH₂t-Bu)] with Al(CH₂t-Bu) on the basis of ³¹P and ¹⁹⁵Pt NMR data, is attributed to an enhanced tendency to isomerisation into the alkyl/hydride Pt/Al congener of 4. A brief DFT analysis of the bonding situation of the model complex [(dhpe)Pt(GaMe₂)(Me)] (1M) revealed, that the contribution of π(Pt-Ga) back-bonding is negligible.     

Mixed-metal single-molecule magnets: Syntheses, structure, and magnetic properties of [Mn8Fe4O12(O2CR)16(H2O)4] (R = CH2Cl, CH2Br, CHCl2)

Three mixed-metal single-molecule magnets containing [Mn₈Fe₄O₁₂]¹⁶⁺ cores are synthesized and characterized. The reaction of FeCl₂·4H₂O with KMnO₄ and RCOOH (R = CH₂Cl, CH₂Br) in H₂O gives [Mn₈Fe₄O₁₂(O₂CR)₁₆(H₂O)₄] (R = CH₂Cl (1), CH₂Br (2)) in yields of 43% and 40%, respectively. Treatment of complex 1 with an excess of CHCl₂COOH in CH₂Cl₂ gives [Mn₈Fe₄O₁₂(O₂CCHCl₂)₁₆(H₂O)₄]·CH₂Cl₂·10H₂O (3·CH₂Cl₂·10H₂O) in a yield of 83%. The X-ray structure analysis reveals that all three complexes consist of a trapped-valence dodecanuclear core comprising 4Mn^III, 4Fe^III, and 4Mn^IV ions. DC magnetic susceptibility and magnetization measurements indicate that all three complexes exhibit intramolecular antiferromagnetic interaction, resulting in an S = 4 ground state. In addition, frequency-dependent out-of-phase AC magnetic susceptibility signals at low temperature for complexes 1, 2, and 3 are indicative of their single-molecule magnetism behavior.     

New versatile organyltellurium(IV) halides: Synthesis and X-ray structural features of the telluronium tellurolate salts [PhTe(CH3)2]2[TeX6] (X = Cl, Br) and [Ph3Te][PhTeX4] (X = Cl, Br, I)

TeX₄ (X = Cl, Br) react in HCl/HBr with [Ph(CH₃)₂Te]X (X = Cl, Br) to give [PhTe(CH₃)₂]₂[TeCl₆] (1) and [PhTe(CH₃)₂]₂[TeBr₆] (2). The reaction of PhTeX₃ (X = Cl, Br, I) in cooled methanol with [(Ph)₃Te]X (X = Cl, Br, I) leads to [Ph₃Te][PhTeCl₄] (3), [Ph₃Te][PhTeBr₄] (4) and [Ph₃Te][PhTeI₄] (5). In the lattices of the telluronium tellurolate salts 1 and 2, octahedral TeCl₆ and TeBr₆ dianions are linked by telluronium cations through Te?Cl and Te?Br secondary bonds, attaining bidimensional (1) and three-dimensional (2) assemblies. The complexes 3, 4 and 5 show two kinds of Te?halogen secondary interactions: the anion-anion interactions, which form centrosymmetric dimers, and two identical sets of three telluronium-tellurolate interactions, which accomplish the centrosymmetric fundamental moiety of the supramolecular arrays of the three compounds, with the tellurium atoms attaining distorted octahedral geometries. Also phenyl C-H?halogen secondary interactions are structure forming forces in the crystalline structures of compounds 3, 4 and 5.     

Synthesis, characterization, and catalytic activities in syndiospecific polymerization of styrene for half-sandwich titanium complexes with non-Cp tridentate dianionic ligands MeN(CH2CR2O)2

New half-titanocenes, Cp^∗TiCl[(OCR₂CH₂)NMe(CH₂CR^′₂O)] [R,R′ = H (1), R,R′ = Me, H, (2), R,R′ = Me (3)], were prepared from Cp^∗TiCl₃ (4) with the corresponding alcohols in the presence of triethylamine. X-ray analysis shows that 1 has slightly distorted trigonal bipyramidal geometry around Ti. These complexes exhibited moderate catalytic activities for syndiospecific styrene polymerization in the presence of MAO and the activity increased in the order: 2 > 1 > 4 > 3 (at 50 °C), 1 > 2 > 4 > 3 (at 70 °C and 90 °C).     

New synthetic route to polyphosphine ligands bearing 1,2,4,5-tetrakis(phosphino)benzene framework: structural characterizations of 1,4-(PPh2)2-2,5-(PR2)2-C6F2 (R = Ph, Pr, Et)

Reactions of 1,4-dibromo-2,5-difluorobenzene with two equivalents of lithium diisopropylamide at low temperature (T < −90 °C) followed by a quench with a slight excess of ClPPh₂ afford 1,4-dibromo-2,5-bis(diphenylphosphino)-3,6-difluorobenzene (1) in good yields. Reacting 1 with two equivalents of BuLi followed by a quench with a slight excess of ClPR₂ yield novel 1,2,4,5-tetrakis(phosphino)-3,6-difluorobenzenes 1,4-(PPh₂)₂-2,5-(PR₂)₂-C₆F₂ (R = Ph (2a); R = ⁱPr (2b); R = Et (2c)) in moderate yields. Compounds 1 and 2a-c were characterized by multinuclear NMR spectroscopy and elemental analyses. In addition, molecular structures of 2a-c have been determined by single crystal X-ray crystallography. Phosphorus atoms of PPh₂/PR₂ substituents in 2a-c are displaced from the plane of the central phenyl ring due to steric interactions with neighboring groups.     

Dihalogen-halogenomethyl complexes of indium(III) X2InCH2X (X = Br, I): Simultaneous coordination of soft and hard ligands

Halogenomethyl-dihalogen-indium(III) compounds X₂InCH₂X (X = Br, I) obtained from indium monohalides and methylene dihalides were reacted with the soft donor ligands dialkylsulfides, R₂S (R = CH₃, CH₂Ph) to afford the corresponding dialkylsulfonium methylide complexes of InX₃, X₃InCH₂SR₂ (X = Br, R = CH₃, 1; X = I, R = CH₃, 2; X= I, R = CH₂Ph, 3). Compound 1 was reacted with the hard donor ligands dimethylsulfoxide or triphenylphosphine oxide to give the corresponding 1:1 adduct, Br₃(L)InCH₂S(CH₃)₂ (L = (CH₃)₂SO, 4; L = (C₆H₅)₃PO, 5). Compounds 1-5 were fully characterized in solution by NMR spectroscopy and in the solid state by X-ray methods.     

Pentabenzylcyclopentadienyl molybdenum and tungsten hydrides: Syntheses, structures and electrochemistry of [MHCp(CO)2(L)] (L = CO, PMe3, PPh3)

Complexes [MHCp^Bz(CO)₂(PR₃)] (R = CH₃, M = Mo (1); M = W (2); R = Ph, M = Mo (3); Cp^Bz = C₅(CH₂Ph)₅) were prepared by thermal decarbonylation of the corresponding [MHCp^Bz(CO)₃] in the presence of trimethyl- or triphenyl-phosphine. In solution the NMR spectra of all compounds show the presence of cis and trans isomers that interconvert at room temperature. In the solid state the molecular structures obtained for compounds 1 and 2 correspond to the trans isomers, while for 3 the cis isomer is present.The electrochemistry of [MoHCp^Bz(CO)₂(PMe₃)] (1), [MoHCp^Bz(CO)₃] (5), [WHCp^Bz(CO)₃] (6), [WCp^Bz(CO)₃]₂ (7), and [MCp^Bz(CO)₃(CH₃CN)]BF₄ (8), is described. The cleavage of M-H bonds takes place upon oxidation or reduction. Cations [MCp^Bz(CO)₂L(CH₃CN)]⁺ form in solvent-assisted M-H bond breaking upon oxidation of [MHCp^Bz(CO)₂L] (L = PMe₃, CO). Reduction of [MHCp^Bz(CO)₃] gives [MCp^Bz(CO)₃]⁻ and H₂. The presence of one PMe₃ ligand lowers the reduction potential and precludes the observation of reduction waves.     

Group 12 metal aryl selenolates. Crystal and molecular structure of [2-(Et2NCH2)C6H4]2Se2 and [2-(Me2NCH2)C6H4Se]2M (M = Zn, Cd)

Diorganodiselenide [2-(Et₂NCH₂)C₆H₄]₂Se₂ (1) was obtained by hydrolysis/oxidation of the corresponding [2-(Et₂NCH₂)C₆H₄]SeLi derivative. The treatment of [2-(Et₂NCH₂)C₆H₄]₂Se₂ with elemental sodium in THF resulted in [2-(Et₂NCH₂)C₆H₄]SeNa (2). Reactions between alkali metal selenolates [2-(R₂NCH₂)C₆H₄]SeM′ (R = Me, Et; M′ = Li, Na) and MCl₂ (M = Zn, Cd) in a 2:1 molar ratio resulted in the [2-(R₂NCH₂)C₆H₄Se]₂M species [R = Me, M = Zn (3), Cd (4); R = Et, M = Zn (5), Cd (6)]. The new compounds were characterized by multinuclear NMR (¹H, ¹³C, ⁷⁷Se, ¹¹³Cd) and mass spectrometry. The crystal and molecular structures of 1, 3 and 4 revealed monomeric species stabilized by N → Se (for 1) and N → M (for 3 and 4) intramolecular interactions.     

Assembly molecular architectures based on structural variation of metalloligand [Cu(PySal)2] (PySal = 3-pyridylmethylsalicylideneimino)

A versatile neutral metalloligand [Cu(PySal)₂] (1) (PySal = 3-pyridylmethylsalicylidene-imino) was exploited as a building unit to construct five complexes {Cu[Cu(PySal)₂]₂}(ClO₄)₂ (2), {Cd[Cu(PySal)₂]₂(H₂O)₂]} (NO₃)₂ · 2H₂O · 4CH₃OH (3), {Zn[μ₂-Cu(PySal)₂]Cl₂}_n · nCH₃OH (4), {Hg[μ₂-Cu(PySal)₂]I₂}_n (5) and {Cd[μ₂-Cu(PySal)₂]Cl₂}_n · nCH₂Cl₂ (6). [Cu(PySal)₂] acts as a chelating ligand in discrete complexes 2 and 3 with unbound anions, but as a bis-monodentate bridging ligand in polymers 4, 5 and 6 when halogen anions coordinated cooperatively to metal cations. The coordination geometry of Cu²⁺ is well-defined square planar in bridging [Cu(PySal)₂], analogous to that in free metalloligand (1), but it is distorted square planar in chelating [Cu(PySal)₂].     

Crystal structure and spectral characterization of hexanuclear oxo titanium(IV) clusters: [Ti6O6(OSi(CH3)3)6(OOCR)6] (R = Bu,CH2Bu,C(CH3)2Et)

Hexanuclear oxo titanium(IV) siloxo carboxylate complexes with the general formula [Ti₆O₆(OSi(CH₃)₃)₆(OOCR)₆] (R = Bu^t (1), CH₂Bu^t (2), C(CH₃)₂Et (3)) were synthesized in quantitative yield, by the reaction of Ti(OSiMe₃)₄ with the appropriate organic acid. Crystal structure determination revealed that molecules of 1–3 are composed of [Ti₆-(μ₃-O)₆] cores stabilized by six syn–syn carboxylato bridges and six terminal siloxide ligands. Each metal atom is surrounded by six oxo atoms, capping the triangular faces of the distorted octahedron. Spectral characterization (IR, NMR) of 1–3 revealed a significant non-equivalence of the carboxylate group interactions, resulting from the asymmetry of the Ti-μ-OOC bonds of the syn–syn bridges. The thermal stability of the studied compounds was determined from TGA/DTA analysis.