Synthesis, structure, and catalytic activity of titanium complexes with new chiral 11,12-diamino-9,10-dihydro-9,10-ethanoanthracene-based ligands

A new series of organo-titanium complexes have been prepared from the reaction between Ti(NMe₂)₄ and C₂-symmetric ligands, (R,R)-11,12-bis(pyrrol-2-ylmethyleneamino)-9,10-dihydro-9,10-ethanoanthracene (1H₂), and (R,R)-bis(diphenylthiophosphoramino)-9,10-dihydro-9,10-ethanoanthracene (2H₂), (R,R)-11,12-bis(mesitylenesulphonylamino)-9,10-dihydro-9,10-ethanoanthracene (3H₂) and (R,R)-bis(diphenylthiophosphoramino)-1,2-cyclohexane (4H₂). Treatment of Ti(NMe₂)₄ with 1 equiv of 1H₂ gives, after recrystallization from a benzene solution, the binuclear double helicate titanium amide (1)₂[Ti(NMe₂)₂]₂⋅(5) in 71% yield. While under similar reaction conditions, reaction of Ti(NMe₂)₄ with 1 equiv of 2H₂, 3H₂ or 4H₂ gives, after recrystallization from a toluene or benzene solution, the mononuclear single helicate titanium amides (2)Ti(NMe₂)₂ (6), (3)Ti(NMe₂)₂ (7) and (4)Ti(NMe₂)₂ (8), respectively, in good yields. All new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of complexes 5-8 have further been confirmed by X-ray diffraction analyses. The titanium amides are active catalysts for the polymerization of rac-lactide, leading to the isotactic-rich polylactides.     

Synthesis, structure, and catalytic activity of titanium(IV) and zirconium(IV) amides with chiral biphenyldiamine-based ligands

A new series of titanium(IV) and zirconium(IV) amides have been prepared from the reaction between M(NMe₂)₄ (M = Ti, Zr) and C₂-symmetric ligands, (R)-2,2′-bis(pyridin-2-ylmethylamino)-6,6′-dimethyl-1,1′-biphenyl (2H₂), (R)-2,2′-bis(pyrrol-2-ylmethyleneamino)-6,6′-dimethyl-1,1′-biphenyl (3H₂), (R)-2,2′-bis(diphenylphosphinoylamino)-6,6′-dimethyl-1,1′-biphenyl (4H₂), (R)-2,2′-bis(methanesulphonylamino)-6,6′-dimethyl-1,1′-biphenyl (5H₂), (R)-2,2′-bis(p-toluenesulphonylamino)-6,6′-dimethyl-1,1′-biphenyl (6H₂), and C₁-symmetric ligands, (R)-2-(diphenylthiophosphoramino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (7H) and (R)-2-(pyridin-2-ylamino)-2′-(dimethylamino)-6,6′-dimethyl-1,1′-biphenyl (8H), which are derived from (R)-2,2′-diamino-6,6′-dimethyl-1,1′-biphenyl. Treatment of M(NMe₂)₄ with 1 equiv. of N₄-ligand, 2H₂ or 3H₂ gives, after recrystallization from an n-hexane solution, the chiral zirconium amides (2)Zr(NMe₂)₂ (9), (3)Zr(NMe₂)₂ (11), and titanium amide (3)Ti(NMe₂)₂ (10), respectively, in good yields. Reaction of Zr(NMe₂)₄ with 1 equiv of diphenylphosphoramide 4H₂ affords the chiral zirconium amide (4)Zr(NMe₂)₂ (12) in 85% yield. Under similar reaction conditions, treatment of Ti(NMe₂)₄ with 1 equiv. of sulphonylamide ligand, 5H₂ or 6H₂ gives, after recrystallization from a toluene solution, the chiral titanium amides (5)Ti(NMe₂)₂·0.5C₇H₈ (13·0.5C₇H₈) and (6)Ti(NMe₂)₂ (15), respectively, in good yields, while reaction of Zr(NMe₂)₄ with 1 equiv. of 5H₂ or 6H₂ gives the bis-ligated complexes, (5)₂Zr (14) and (6)₂Zr (16). Treatment of M(NMe₂)₄ with 2 equiv. of diphenylthiophosphoramide ligand 7H or N₃-ligand 8H gives, after recrystallization from a benzene solution, the bis-ligated chiral zirconium amides (7)₂Zr(NMe₂)₂ (17) and (8)₂Zr(NMe₂)₂ (19), and bis-ligated chiral titanium amide (8)₂Ti(NMe₂)₂ (18), respectively, in good yields. All new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of complexes 10, 12, 13, and 17-19 have further been confirmed by X-ray diffraction analyses. The zirconium amides are active catalysts for the asymmetric hydroamination/cyclization of aminoalkenes, affording cyclic amines in good to excellent yields with moderate ee values, while the titanium amides are not.     

Synthesis of 1,4-disilacyclohexa-2,5-dienes

Title compounds of the type 2,3,5,6-tetraphenyl-1,4-di-X-1,4-di-Y-1,4-disilacyclohexa-2,5-diene wherein X=Y=NMe₂ (4); X=NMe₂, Y=Cl (cis, trans-5); X=NMe₂, Y=Me [(trans)-6] and X=t-Bu, Y=Cl (trans-8) were synthesized from Si₂(NMe₂)₅Cl, sym-Si₂(NMe₂)₄Cl₂, sym-Si₂(NMe₂)₄Me₂, and sym-Si₂Cl₄(t-Bu)₂, respectively, in the presence of diphenylacetylene at 200 °C. Similarly the analogous title compound from the combination of 1-phenyl-1-propyne and Si₂(NMe₂)₅Cl [X=Y=NMe₂ (cis and trans-7) was synthesized. In all cases where cis/trans diastereomers could arise from two different silicon substituents (5, 6, 8) the trans isomer was the sole or dominant product. Evidence for the intermediacy of the silylene Si(NMe₂)₂ in these reactions was gained from a trapping experiment. Compound 4 upon treatment with SiCl₄, SiBr₄ or PI₃ provided the corresponding 1,1,4,4-tetrahalo derivatives 9a-c, respectively. Treatment of 4 with MeOH or PhOH gave the 1,1,4,4-tetramethoxy and tetraphenoxy analogues 9d and 9e, respectively. The tetrachloro derivative 9a upon LAH reduction led to the corresponding tetrahydro compound 10, while the reaction of 9a with H₂O gave the tetrahydroxy derivative 11. Allowing (trans)-6 to react with SiCl₄ provided a ca. 1:1 cis/trans ratio of the derivative 12 in which X=Cl, Y=Me, and possible pathways that rationalize this loss of stereochemistry are proposed. Synthesis of trans-13 in which X=t-Bu, Y=H was achieved by LAH reduction of 8. All of the title compounds except 8 experience free phenyl rotation at room temperature. At −30 °C this rotation in 8 is essentially halted. The molecular structures of 4, 8, 9c, 9e, 10 and 13 were determined by X-ray crystallography.     

Derivatisation of boryl substituted titanium half-sandwich complexes - Molecular structures of [Ti{(η-C5H4)B(NiPr2)N(H)tBu}Cl2(NMe2)] and [{TiCl2(μ-{OB(NHMe2)-η-C5H4})}2-μ-O]

The half-sandwich complex [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)iPr}(NMe₂)₃] (6) was prepared from (η¹-C₅H₅)B(NiPr₂)N(H)iPr (5) and [Ti(NMe₂)₄] with cleavage of one equivalent of HNMe₂ and further converted into the corresponding constrained geometry complex [Ti{(η⁵-C₅H₄)B(NiPr₂)NiPr}(NMe₂)₂] (7) by elimination of a second equivalent of HNMe₂. Reaction of the half-sandwich complexes [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)R}(NMe₂)₃] (R = iPr, tBu) with excess Me₃SiCl yielded the corresponding dichloro complexes [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)R}Cl₂(NMe₂)] (R = tBu (10), iPr (11)). The intermediate species [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)iPr}Cl(NMe₂)₂] (9) could also be spectroscopically characterised. Partial hydrolysis of 10 and 11, respectively, resulted in formation of [{TiCl₂(μ-{OB(NHMe₂)-η⁵-C₅H₄})}₂-μ-O] (12). The molecular structures of 10 and 12 have been determined by X-ray crystallographic analyses. Complex 10, when activated with MAO, was found to be a highly active styrene polymerisation catalyst while being inactive towards the polymerisation of ethylene.     

Synthesis, characterization, and reactivity of new types of constrained geometry group 4 metal complexes derived from picolyl-substituted dicarbollide ligand systems

The syntheses of group 4 metal complexes containing the picolyldicarbollyl ligand Dcab^PyH [nido-7-HNC₅H₄(CH₂)-8-R-7,8-C₂B₉H₁₀] (2) are reported. New types of constrained geometry group 4 metal complexes (Dcab^Py)MCl₂, [{(η⁵-RC₂B₉H₉)(CH₂)(η¹-NC₅H₄)}MCl₂] (M = Ti, 3; Zr, 4; R = H, a; Me, b), were prepared by the reaction of 2 with M(NMe₂)₂Cl₂ (M = Ti, Zr). The reaction of 2 with M(NMe₂)₄ in toluene afforded (Dcab^Py)M(NMe₂)₂, [{(η⁵-RC₂B₉H₉)(CH₂)(η¹-NC₅H₄)}M(NMe₂)₂] (M = Ti, 5; Zr, 6; R = H, a; Me, b), which readily reacted with Me₃SiCl to yield the corresponding chloride complexes (Dcab^Py)MCl₂ (M = Ti, 3; Zr, 4; R = H, a; Me, b). The structures of the diamido complexes (Dcab^Py)M(NMe₂)₂ (M = Ti, 5; Zr, 6) were established by X-ray diffraction studies of 5a, 5b, and 6a, which verified an η⁵:η¹-bonding mode derived from the dicarbollylamino ligand. Related constrained geometry catalyst CGC-type alkoxy titanium complexes, (Dcab^Py)Ti(OⁱPr)₂ (7), were synthesized by the reaction of 2 with Ti(OⁱPr)₄. Sterically less demanding phenols such as 2-Me-C₆H₄OH replaced the coordinated amido ligands on (Dcab^Py)Ti(NMe₂)₂ (5a) to yield aryloxy stabilized CGC complexes (Dcab^Py)Ti(OPh^Me)₂(Ph^Me  =  2- Me-C₆H₄, 8). NMR spectral data suggested that an intramolecular Ti-N coordination was intact in solution, resulting in a stable piano-stool structure with two aryloxy ligands residing in two of the leg positions. The aryloxy coordinations were further confirmed by single crystal X-ray diffraction studies on complexes (Dcab^Py)Ti(OPh^Me)₂ (8).     

Titanium complexes bearing bidentate benzimidazole-containing ligands and their behavior in ethylene polymerization

A series of potentially bidentate benzimidazolyl ligands of the type (Bim)CH₂D (where Bim = benzimidazolyl and D = NMe₂L1, NEt₂L2, NPrⁱ₂L3, OMe L4 and SMe L5) has been reacted with Ti(NMe₂)₄ to give five- and six-coordinate Ti(IV) complexes of the type [(Bim)CH₂D]Ti(NMe₂)₃ and [(Bim)CH₂D]₂Ti(NMe₂)₂, respectively. The X-ray structures of [(Bim)CH₂OMe]Ti(NMe₂)₃, [(Bim)CH₂NMe₂]₂Ti(NMe₂)₂ and [(Bim)CH₂OMe)]₂Ti(NMe₂)₂ are reported along with an evaluation of their behavior in ethylene polymerization.     

Endo and exo cyclometallated iron carbonyl complexes derived from N-(N′-methyl-2-pyrrolylmethylidene)-2-thienylmethylamine

The reaction of N-(N′-methyl-2-pyrrolylmethylidene)-2-thienylmethylamine (1) with Fe₂(CO)₉ in refluxing toluene gives endo cyclometallated iron carbonyl complexes 2 and 5, exo cyclometallated iron carbonyl complex 3, and unexpected iron carbonyl complex 4. Complexes 2, 3, and 5 are geometric isomers. Complex 5 differs from complex 2 in the switch of the original substituent from α to β position of the pyrrolyl ring, and the pyrrolyl ring bridges to the diiron centers in μ-(3,2-η¹:η²) coordination mode in stead of μ-(2,3-η¹:η²). In complex 4, the pyrrolyl moiety of the original ligand 1 has been displaced by a thienyl group, which comes from the same ligand. Single crystals of 2, 3, and 5 were subjected to the X-ray diffraction analysis. The major product 2 undergoes: (i) thermolysis to recover the original ligand 1; (ii) reduction to form a hydrogenation product, 6, of the original ligand; (iii) substitution to form a monophosphine-substituted complex 7; (iv) chemical as well as electrochemical oxidation to produce a carbonylation product, γ-butyrolactam 8.     

Organometallic and related imidotitanium compounds containing a pendant arm functionalised benzamidinate ligand

Chloride ligand substitution reactions of tert-butyl- and arylimido-titanium complexes supported by the pendant arm functionalised N-trimethylsilyl benzamidinate ligand Me₃SiNC(Ph)NCH₂CH₂CH₂NMe₂ are described. Reaction of previously-described [Ti(N^tBu){Me₃SiNC(Ph)NCH₂CH₂CH₂NMe₂}Cl] (1) with PhLi afforded thermally sensitive [Ti(N^tBu){Me₃SiNC(Ph)NCH₂CH₂CH₂NMe₂}Ph] (2). The corresponding reaction of 1 with MeLi afforded [Ti(N^tBu){Me₃SiNC(Ph)NCH₂CH₂CH₂NMe₂}Me] (3) detected by ¹H-NMR spectroscopy but this compound could not be isolated. Reaction of 1 with LiCH₂SiMe₃ gave a complex mixture, but with LiN(SiMe₃)₂ and LiO-2,6-C₆H₃Me₂ the compounds [Ti(N^tBu){Me₃SiNC(Ph)NCH₂CH₂CH₂NMe₂}X] (X=N(SiMe₃)₂ (4) or O-2,6-C₆H₃Me₂ (5)) were isolated. The X-ray structure of 5 was determined. Reaction of the homologous compound [Ti(N^tBu){Me₃SiNC(Ph)NCH₂CH₂NMe₂}Cl] (6) (containing a 2-carbon atom chain in the pendant arm) with MeLi or PhLi were unsuccessful although the aryloxide compound [Ti(N^tBu){Me₃SiNC(Ph)NCH₂CH₂NMe₂}(O-2,6-C₆H₃Me₂)] (7) could be isolated from the reaction of 6 with LiO-2,6-C₆H₃Me₂. Reaction of the 3-carbon pendant arm arylimido compound [Ti(N-2,6-C₆H₃Me₂){Me₃SiNC(Ph)NCH₂CH₂CH₂NMe₂}Cl] (8) with MeLi afforded thermally sensitive [Ti(N-2,6-C₆H₃Me₂){Me₃SiNC(Ph)NCH₂CH₂CH₂NMe₂}Me] (9), and although the analogous phenyl homologue was elusive, the aryloxide derivative [Ti(N-2,6-C₆H₃Me₂){Me₃SiNC(Ph)NCH₂CH₂CH₂NMe₂}(O-2,6-C₆H₃Me₂)] (10) was successfully isolated and structurally characterised. Comparison of the X-ray structures of 5 and 10 show unexpectedly large differences between the TiNR and TiOAr bond lengths in the two compounds.     

Diazaallyls of group 4 metals based on trans-1,2-diaminocyclohexane

Amination of 1-bromo-2-methylpyridine with trans-1,2-diaminocyclohexane gives the corresponding bis(aminopyridine) H₂L¹. Conversion of the same diamine to the N,N′-bis(amino-4,4-dimethylthiazoline) H₂L² is also completed in three steps. The analogous aminooxazoline is however inaccessible, although the aminocyclohexane analogue is prepared readily. The proligand H₂L¹ forms bis(aminopyridinato) alkyl complexes of the type [ZrL¹R₂] (R = CH₂Ph, CH₂Bu^t). The molecular structure of the neopentyl complex shows that the chiral backbone leads to a puckering of the N₄Zr coordination sphere, which contrasts with the related cyclohexyl-bridged Schiff-base complexes which are essentially planar. [ZrL²(CH₂Bu^t)₂] - the first aminothiazolinato complex - is formed similarly. A comparison of the structures of [ZrL¹(CH₂Bu^t)₂] and [ZrL²(CH₂Bu^t)₂] indicates that the latter has a fully delocalised N-C-N system, rather similar to a bis(amidinate). Reaction of H₂L² with [Ti(NMe₂)₄] gives [TiL²(NMe₂)₂] which appears to be C₂-symmetric like the above complexes according to NMR spectra, but has one uncoordinated thiazoline unit in the solid state. This is a result of increased ring strain at the smaller titanium metal centre.     

Understanding the role of an easy-to-prepare aldimine-alkyne carboamination catalyst, [Ti(NMe2)3(NHMe2)][B(C6F5)4]

A series of reactivity studies of the carboamination pre-catalyst [Ti(NMe₂)₃(NHMe₂)][B(C₆F₅)₄] as well as the preparation of other catalysts are reported in this work. Treatment of [Ti(NMe₂)₃(NHMe₂)][B(C₆F₅)₄] with the aldimines Ar′NCHtol (Ar′ = 2,6-Me₂C₆H₃, tol = 4-MeC₆H₄), and depending on the reaction conditions, results in isolation of [Me₂NCHR′][B(C₆F₅)₄] (1) or (Me₂N)₂CHtol, as well as the asymmetric titanium dimer [(Me₂N)₂(HNMe₂)Ti(μ₂-N[2,6-Me₂C₆H₃])₂Ti(NHMe₂)(NMe₂)][B(C₆F₅)₄] (2). Protonation of CpTi(NMe₂)₃ and Cp^∗Ti(NMe₂)₃ results in isolation of the salts, [CpTi(NMe₂)₂(NHMe₂)][B(C₆F₅)₄] (3) and [Cp^∗Ti(NMe₂)₂(NHMe₂)][B(C₆F₅)₄] (4), respectively. Treatment of compounds 3 or 4 with H₂N[2,6-ⁱPr₂C₆H₃] results in formation of the imido salts [CpTi(N[2,6-ⁱPr₂C₆H₃])(NHMe₂)₂][B(C₆F₅)₄] (5) (58% yield) or [Cp^∗Ti(N[2,6-ⁱPr₂C₆H₃])(NHMe₂)₂][B(C₆F₅)₄] (6). When Ti(NMe₂)₄ is treated with [Et₃Si][B(C₆F₅)₄], the salt [Ti(NMe₂)₃(N[SiEt₃]Me₂)][B(C₆F₅)₄] (7) is obtained, and treatment of the latter with [2,6-ⁱPr₂C₆H₃]NCHtol produces the imine adduct [Ti(NMe₂)₃(κ¹-[2,6-ⁱPr₂C₆H₃]NCHtol)][B(C₆F₅)₄] (8). The carboamination catalytic activity of complexes 2-7 was investigated and compared to [Ti(NMe₂)₃(NHMe₂)][B(C₆F₅)₄]. Likewise, a proposed mechanism to the active carboamination catalyst stemming from [Ti(NMe₂)₃(NHMe₂)][B(C₆F₅)₄] is described.     

Platinum-catalyzed double silylations of alkynes with bis(dichlorosilyl)methanes

Bis(dichlorosilyl)methanes 1 undergo the two kind reactions of a double hydrosilylation and a dehydrogenative double silylation with alkynes 2 such as acetylene and activated phenyl-substituted acetylenes in the presence of Speier’s catalyst to give 1,1,3,3-tetrachloro-1,3-disilacyclopentanes 3 and 1,1,3,3-tetrachloro-1,3-disilacyclopent-4-enes 4 as cyclic products, respectively, depending upon the molecular structures of both bis(dichlorosilyl)methanes (1) and alkynes (2). Simple bis(dichlorosilyl)methane (1a) reacted with alkynes [R¹-CC-R²: R¹ = H, R² = H (2a), Ph (2b); R¹ = R² = Ph (2c)] at 80 °C to afford 1,1,3,3-tetrachloro-1,3-disilacyclopentanes 3 as the double hydrosilylation products in fair to good yields (33-84%). Among these reactions, the reaction with 2c gave a trans-4,5-diphenyl-1,1,3,3-tetrachloro-1,3-disilacyclopentane 3ac in the highest yield (84%). When a variety of bis(dichlorosilyl)(silyl)methanes [(Me_nCl_3 − nSi)CH(SiHCl₂)₂: n = 0 (1b), 1 (1c), 2 (1d), 3 (1e)] were applied in the reaction with alkyne (2c) under the same reaction conditions. The double hydrosilylation products, 2-silyl-1,1,3,3-tetrachloro-1,3-disilacyclopentanes (3), were obtained in fair to excellent yields (38-98%). The yields of compound 3 deceased as follows: n = 1 > 2 > 3 > 0. The reaction of alkynes (2a-c) with 1c under the same conditions gave one of two type products of 1,1,3,3-tetrachloro-1,3-disilacyclopentanes 3 and 1,1,3,3-tetrachloro-1,3-disilacyclopent-4-enes (4): simple alkyne 2a and terminal 2b gave the latter products 4ca and 4cb in 91% and 57% yields, respectively, while internal alkyne 2c afforded the former cyclic products 3cc with trans form between two phenyl groups at the 3- and 4-carbon atoms in 98% yield, respectively. Among platinum compounds such as Speier’s catalyst, PtCl₂(PEt₃)₂, Pt(PPh₃)₂(C₂H₄), Pt(PPh₃)₄, Pt[ViMeSiO]₄, and Pt/C, Speier’s catalyst was the best catalyst for such silylation reactions.     

Novel sandwich complexes of zirconium [C9H5(SiMe3)2](C5Me4R)ZrCl2 (R = CH3, CH2CH2NMe2): Synthesis and reduction behavior

Novel half-sandwich [C₉H₅(SiMe₃)₂]ZrCl₃ (3) and sandwich [C₉H₅(SiMe₃)₂](C₅Me₄R)ZrCl₂ (R = CH₃ (1), CH₂CH₂NMe₂ (2)) complexes were prepared and characterized. The reduction of 2 by Mg in THF lead to (η⁵-C₉H₅(SiMe₃)₂)[η⁵:η²(C,N)-C₅Me₄CH₂CH₂N(Me)CH₂]ZrH (7). The structure of 7 was proved by NMR spectroscopy data. Hydrolysis of 2 resulted in the binuclear complex ([C₅Me₄CH₂CH₂NMe₂]ZrCl₂)₂O (6). The crystal structures of 1 and 6 were established by X-ray diffraction analysis.     

Synthesis of aluminum alkoxide and bis-alkoxide compounds containing bidentate pyrrolyl ligands

A series of aluminum alkoxide and bis-alkoxides compounds were synthesized and characterized. Reacting 1 with 1 and 2 equiv. of t-butanol in methylene chloride generates [C₄H₃N(CH₂NMe₂)-2]₂Al(O-t-Bu) (2) and [C₄H₃N(CH₂NMe₂)-2-H-C₄H₃N(CH₂NMe₂)-2]Al(O-t-Bu)₂ (3) in 47% and 54% yield, respectively. The ¹H NMR spectrum of 2 exhibits two singlets for NMe₂ and CH₂N at δ 2.52 and 3.84, respectively, representing the symmetrical manner of molecular structure 2 in a solution. Compound 3 is not thermal stable in solution which decompose into substituted pyrrole ligand C₄H₄N(CH₂NMe₂)-2 and unknown aluminum alkoxides. Reacting 1 with 2 equiv. of triphenylsilanol in methylene chloride generates a tetra-coordinated aluminum “ate” compound [C₄H₃N(CH₂NMe₂)-2-H- C₄H₃N(CH₂NMe₂)-2]Al(OSiPh₃)₂ (4) in 49% yield. The ¹H NMR spectra of 4 at room temperature show a broad signal at δ 1.57 for NMe₂ fragments and the signals for CH₂N were not observed. VT ¹H NMR spectra of 4 show the NMe₂ fragments became two singlets (δ 1.27 and 2.12) and the CH₂N exhibited two doublets (δ 2.44 and 3.56) at 240 K. The fluxional energy barrier (ΔG^‡) is estimated at ca. 50 kJ/mol. The molecular structures of compounds 3 and 4 are determined by single-crystal X-ray diffractometer.     

Synthesis and structural studies of some titanium and zirconium complexes with chiral bis(amide), amidinate or bis(amidinate) ligands

Reaction of bis(amide) sodium Na₂[(1R,2R)-(−)-1,2-(NSiMe₃)₂-C₆H₁₀] (Na₂[L¹]) with Ti(OiPr)₂Cl₂ in different conditions gave mixed-ligand complexes [Ti(OiPr)Cl][L¹] (1) or [Ti(OiPr)₂Cl]₂[L¹] (2); 2 is a dinuclear titanium example in which Ti atoms are bridged by nitrogen and oxygen atoms simultaneously forming a distorted rhombic core. Reaction of the amine-amidinate ligand (1R,2R)-(−)-1-Li[NC(Ph)N(SiMe₃)]-2-(NHSiMe₃)-C₆H₁₀(Li[L²]) or rarely linked bis(amidinate) ligand Li₂[(1R,2R)-(−)-1,2-{NC(Ph)N(SiMe₃)}₂-C₆H₁₀](Li₂[L³]) with ZrCl₄ yielded the unbridged and bridged bis(amidinate) complexes ZrCl₂[L²]₂ (3) and [ZrCl₂(THF)][L³] (4), respectively; Moreover, the reaction of (1R,2R)-(−)-1-Li[NC(Ph)N(SiMe₃)]-2-Li(NSiMe₃)C₆H₁₀(Li₂[L²]) with Ti(OiPr)₂Cl₂ gave a new type of tridentate amido-amidinate product [Ti(OiPr)₂][L²] (6), which is a distinct model compared to [Ti(OiPr)₂Cl][L²] (5) yielded from Li[L²]. All the products have been characterized by X-ray crystallography and the structural studies are presented detailedly comparing with relevant compounds.     

Dimolybdenum complexes containing anions of N,N′-bis(pyrimidine-2-yl)formamidine and N-(2-pyrimidinyl)formamide

The reactions of Mo₂(O₂CCH₃)₄ with different equivalents of N,N′-bis(pyrimidine-2-yl)formamidine (HL1) and N-(2-pyrimidinyl)formamide (HL2) afforded dimolybdenum complexes of the types Mo₂(O₂CCH₃)(L1)₂(L2) (1) trans-Mo₂(L1)₂(L2)₂ (2) cis-Mo₂(L1)₂(L2)₂ (3) and Mo₂(L2)₄ (4). Their UV–Vis and NMR spectra have been recorded and their structures determined by X-ray crystallography. Complexes 2 and 3 establish the first pair of trans and cis forms of dimolybdenum complexes containing formamidinate ligands. The L1 ligands in 1–3 are bridged to the metal centers through two central amine nitrogen atoms, while the L2 ligands in 1–4 are bridged to the metal centers via one pyrimidyl nitrogen atom and the amine nitrogen atom. The Mo–Mo distances of complexes 1 [2.0951(17) Å], 2 [2.103(1) Å] and 3 [2.1017(3) Å], which contain both Mo?N and Mo?O axial interactions, are slightly longer than those of complex 4 [2.0826(12)–2.0866(10) Å] which has only Mo?O interactions.     

A comparative study of metallating agents in the synthesis of [C,N,N′]-cycloplatinated compounds derived from biphenylimines

The reactions of ligands 4-C₆H₅C₆H₄CHNCH₂CH₂NMe₂ (1a) and 2-C₆H₅C₆H₄CHNCH₂CH₂NMe₂ (1b) in front of cis-[PtCl₂(dmso)₂] or cis-[PtPh₂(SMe₂)₂] produced compounds [PtCl₂{4-C₆H₅C₆H₄CHNCH₂CH₂NMe₂}] (2aCl) and [PtCl₂{2-C₆H₅C₆H₄CHNCH₂CH₂NMe₂}] (2bCl) or [PtPh₂{4-C₆H₅C₆H₄CHNCH₂CH₂NMe₂}] (2aPh) and [PtPh₂{2-C₆H₅C₆H₄CHNCH₂CH₂NMe₂}] (2bPh). From all these compounds, the corresponding cyclometallated [C,N,N′] platinum(II) compounds 3aCl, 3bCl, 3aPh and 3bPh were obtained although under milder conditions and with higher yields for the phenyl derivatives. The reaction of compounds 3aPh and 3bPh with methyl iodide gave cyclometallated [C,N,N′] platinum(IV) compounds 4aPh and 4bPh of formula [PtMePhI{C₆H₅C₆H₃CHNCH₂CH₂NMe₂}]. Compounds 3aCl and 3bCl containing a chloro ligand, although unreactive towards methyl iodide, undergo oxidative addition of chlorine to produce the corresponding platinum(IV) compounds [PtCl₃{4-C₆H₅C₆H₃CHNCH₂CH₂NMe₂}] (6aCl and 6bCl). All compounds were characterised by NMR spectroscopy and crystal structures of compounds 3bCl and 6bCl are also reported.     

Zirconium and hafnium amide, alkoxide, and pyrrolyl complexes manifesting with pyrrolyl-linked N-donor ligands: Syntheses, characterization, and ring opening polymerization of ε-caprolactone

A series of zirconium and hafnium alkoxide and amide complexes containing symmetrical tridentate pyrrolyl ligand, [C₄H₂NH(2,5-CH₂NMe₂)₂] have been synthesized conveniently by treatment of 2,6-di-tert-butylphenol, tert-butanol or pyrrole in pentane and their reactivity over ring opening polymerization of ε-caprolactone have been carried out. Reactions of [C₄H₂NH(2,5-CH₂NMe₂)₂] with M(NEt₂)₄ (M = Zr or Hf) originate [C₄H₂N(2,5-CH₂NMe₂)₂]M(NEt₂)₃ (1, M = Zr; 2, M = Hf). Furthermore, reactions of [C₄H₂N(2,5-CH₂NMe₂)₂]M(NEt₂)₃ with 2,6-di-tert-butylphenol, tert-butanol or pyrrole afford [C₄H₂N(2,5-CH₂NMe₂)₂]M(OC₆H₃-2,6-^tBu₂)(NEt₂)₂ (3, M = Zr; 4, M = Hf), [C₄H₂N(2,5-CH₂NMe₂)₂]M(O^tBu)₃ (5, M = Zr; 6, M = Hf) and [C₄H₂N(2,5-CH₂NMe₂)₂]M(C₄H₄N)₃ (7, M = Zr; 8, M = Hf), respectively, in satisfactory yield. All the complexes have been characterized by NMR spectra as well 3, 4 and 6 subjected to the X-ray diffraction analysis. Complexes 3-8 have been used as initiators for the ring-opening polymerization of ε-caprolactone and observed broad PDI values (1.84-2.75) representing multiple reactivity centers of these complexes.     

Synthesis and protonolysis of neutral aluminum dihydride compounds stabilized by tridentate-substituted pyrrolyl ligands: Synthesis, structural characterization and ring-opening polymerization of ?-caprolactone

A series of aluminum compounds containing tridentate pyrrolyl ligands were obtained from related aluminum dihydride compounds via protonolysis. Treatment of tetranuclear aluminum compound [C₄H₂N{2,5-(CH₂NMe₂)₂}Al₂H₅]₂ (1) with two equivalents of [C₄H₃N{2,5-(CH₂NMe₂)₂}] in methylene chloride at 0 °C led to the formation of [C₄H₂N{2,5-(CH₂NMe₂)₂}]AlH₂ (2). Similarly, when the deuterated aluminum compound 1D was used, the corresponding aluminum compound [C₄H₂N{2,5-(CH₂NMe₂)₂}]AlD₂ (2D) could be isolated. The reaction of 2 with one or two equivalents of phenylethyne, triphenylmethanethiol, 2,6-diisopropylaniline, or triphenylsilanol generated mononuclear aluminum compounds [[C₄H₂N{2,5-(CH₂NMe₂)₂}]AlRR′ (3, R = -CCPh, R′ = H; 4, R = R′ = -CCPh; 5, R = -SCPh₃, R′ = H; 6, R = R′ = -SCPh₃; 7, R = -NH(2,6-ⁱPr₂Ph), R′ = H; 8, R = R′ = -NH(2,6-ⁱPr₂Ph); 9, R = -OSiPh₃, R′ = H; 10, R = R′ = -OSiPh₃). Related Al-D compounds of 3, 5, 7 and 9 were also synthesized and corresponding IR spectroscopic data well matched in comparison of the stretching frequencies of Al-H and Al-D. The molecular structures of 2D, 4, 5, 5D, 7, and 10 have been determined by X-ray crystallography. Compounds 2, 5, and 7 initiated the ring-opening polymerization of ?-caprolactone and produced high-molecular weight of poly-?-caprolactone.     

Synthesis and reactivity of ruthenium complexes with 1,1′-dithiolate ligands

Reactions of [Ru(PPh₃)₃Cl₂] with ROCS₂K in THF at room temperature and at reflux gave the kinetic products trans-[Ru(PPh₃)₂(S₂COR)₂] (R = ⁿPr 1, ⁱPr 2) and the thermodynamic products cis-[Ru(PPh₃)₂(S₂COR)₂] (R = ⁿPr 3, ⁱPr 4), respectively. Treatment of [RuHCl(CO)(PPh₃)₃] with ROCS₂K in THF afforded [RuH(CO)-(S₂COR)(PPh₃)₂] (R = ⁿPr 5, ⁱPr 6) as the sole isolable products. Reaction of [RuCl₂(PPh₃)₃] with tetramethylthiuram disulfide [Me₂NCS₂]₂ gave a Ru(III) dithiocarbamate complex, [Ru(PPh₃)₂(S₂CNMe₂)Cl₂] (7). This reaction involved oxidation of ruthenium(II) to ruthenium(III) by the disulfide group in [Me₂NCS₂]₂. Treatment of 7 with 1 equiv. of [M(MeCN)₄][ClO₄] (M = Cu, Ag) gave the stable cationic ruthenium(III)-alkyl complexes [Ru{C(NMe₂)QC(NMe₂)S}(S₂CNMe₂)(PPh₃)₂][ClO₄] (Q = O 8, S 9) with ruthenium-carbon bonds. The crystal structures of complexes 1, 2, 4·CH₂Cl₂, 6, 7·2CH₂Cl₂, 8, and 9·2CH₂Cl₂ have been determined by single-crystal X-ray diffraction. The ruthenium atom in each of the above complexes adopts a pseudo-octahedral geometry in an electron-rich sulfur coordination environment. The 1,1′-dithiolate ligands bind to ruthenium with bite S-Ru-S angles in the range of 70.14(4)-71.62(4)°. In 4·CH₂Cl₂, the P-Ru-P angle for the mutually cis PPh₃ ligands is 103.13(3)°, the P-Ru-P angles for other complexes with mutually trans PPh₃ ligands are in the range of 169.41(4)-180.00(6)°. The alkylcarbamate [C(NMe₂)QC(NMe₂)S]⁻ (Q = O, S) ligands in 8 and 9 are planar and bind to the ruthenium centers via the sulfur and carbon atoms from the CS and NC double bonds, respectively. The Ru-C bond lengths are 1.975(5) and 2.018(3) Å for 8 and 9·2CH₂Cl₂, respectively, which are typical for ruthenium(III)-alkyl complexes. Spectroscopic properties along with electrochemistry of all complexes are also reported in the paper.