Hexacoordinated MIV (M=Ti,Zr, Hf) Tetrachlorido Complexes with Chelating Dithienylethane Based 1,2 Diketone Ligand – π-Conjugation as Decisive Factor for Axial Chirality Mode

1,2-bis(2,5-dimethylthiophen-3-yl)ethane-1,2-dione ( 1 , DTEthane) reacts with MCl₄ metal precursors of group four (M=Ti, Zr, Hf) via coordination of the carbonyl groups. The molecular structure of complex 2–4 were determined in scXRD studies in the solid state and characterized by means of multi-nuclear and multi-dimensional NMR spectroscopy in solution. While the resulting titanium complex [TiCl₄(DTEthane)] 2 shows a monomeric structure, where 1 binds in a bidentate fashion, complexes with a Zr ( 3 ) and Hf ( 4 ) center have dimeric scaffolds in which the ligands adopt a bridging mode. Quantum chemical calculations using density functional theory (G16, B97D3/def2-TZVP) were used to evaluate the general trend of dimer formation (Ti<Zr<Hf). The molecular structures derived from both scXRD and the DFT optimized structures reveal the carbonyl groups in conjugation with the adjacent thiophene substituent. As a result, they are coplanar and rotation about the two C−C axes (C1−C7; C8−C9) is restricted allowing for only one chiral axis along C7−C8. This gains special importance with respect to previously described complexes carrying the closely related 1,2-endiolato ligand (1,2-bis(2,5-dimethylthiophen-3-yl)ethene-1,2-diolate), in which no coplanarity of the thiophene rings to their neighboring metallacycle was observed allowing for two chiral axes. Noteworthy, further DFT calculations addressing the pathway of racemization found transition states, which are characterized by contrary rotations of both thiophene rings and a loss of conjugation rather than a direct rotation around the axis C7−C8.     

CCC-N-heterocyclic carbene pincer complexes: Synthesis, characterization and hydroamination activity of a hafnium complex

Our methodology for the stoichiometric preparation of CCC-NHC pincer complexes of Zr has been extended to Hf. The CCC^Bu-NHC pincer Hf complex has been characterized by X-ray crystal structure analysis. Catalytic activity in the intramolecular hydroamination/cyclization of unactivated alkenes is reported and compared to the recently reported Zr analog. An improved, scaled-up CuO-catalyzed aryl amination of 1,3-dibromobenzene and an improved salt formation methodology for preparation of bis(butyl-imidazolium)benzene are reported also.     

Zirconium((IV)) and Hafnium((IV)) Porphyrin and Phthalocyanine Complexes as New Dyes for Solar Cell Devices

Metalloporphyrin and metallophthalocyanine dyes ligating Hf(IV) and Zr(IV) ions bind to semiconductor oxide surfaces such as TiO(2) via the protruding group IV metal ions. The use of oxophylic metal ions with large ionic radii that protrude from the macrocycle is a unique mode of attaching chromophores to oxide surfaces in the design of dye-sensitized solar cells (DSSCs). Our previous report on the structure and physical properties of ternary complexes wherein the Hf(IV) and Zr(IV) ions are ligated to both a porphyrinoid and to a defect site on a polyoxometalate (POM) represents a model for this new way of binding dyes to oxide surfaces. The Zr(IV) and Hf(IV) complexes of 5,10,15,20-tetraphenylporphyrin (TPP) with two ligated acetates, (TPP)Hf(OAc)(2) and (TPP)Zr(OAc)(2), and the corresponding metallophthalocyanine (Pc) diacetate complexes, (Pc)Hf(OAc)(2) and (Pc)Zr(OAc)(2), were evaluated as novel dyes for the fabrication of dye-sensitized solar cells. Similarly to the ternary complexes with the POM, the oxide surface replaces the acetates to affect binding. In DSSCs the Zr(IV) phthalocyanine dye performs better than the Zr(IV) porphyrin dye, and reaches an overall efficiency of ~ 1.0%. The Hf(IV) dyes are less efficient. The photophysical properties of these complexes in solution suggested energetically favorable injection of electrons into the conduction band of TiO(2) semiconductor nanoparticles, as well as a good band gap match with I(3) (-)/I(-) pair in liquid 1-butyl-3-methyl imidazolium iodide. The combination of blue absorbing TPP with the red absorbing Pc complexes can increase the absorbance of solar light in the device; however, the overall conversion efficiency of DSSCs using TiO(2) nanoparticles treated with a mixture of both Zr(IV) complexes is comparable, but not greater than, the single (Pc)Zr. Thus, surface bound (TPP)Zr increases the absorbance in blue region of the spectra, but at the cost of diminished absorbance in the red in this DSSC architecture.     

Catalytic hydroamination of fullerene C<Subscript>60</Subscript> with primary and secondary amines

Catalytic 1,2-hydroamination of fullerene C₆₀ with primary and secondary amines in the presence of Ti, Zr, and Hf complexes gave the corresponding alkyl-, aryl-, and hetarylaminodihydrofullerenes.     

Periodic Trends in the Agostic Interaction in Zirconium and Hafnium Methylidene Hydride Halide Complexes

The reactions of methyl chloride and bromide with laser‐ablated Zr and Hf atoms during deposition in excess Ne, Ar, or Kr are investigated, and the products are examined by matrix IR spectroscopy and density functional theory calculations. The methylidene complexes, [CH₂?MHX] (M=Zr and Hf, X=Cl and Br), are formed along with the methyl metal halide complexes, [CH₃? MX]. The amounts of both types of complexes increase upon photolysis and in the early stages of annealing. Two sets of methylidene absorptions observed in Ar and Kr matrices form a persistent photoreversible system. The most stable C₁ and slightly higher energy planar structures of the methylidene complex in the singlet ground state trapped in the matrix reproduce the characteristics of the two sets of absorptions. Agostic distortion of the methylidene complexes decreases in the order Ti, Zr, Hf and increases in the order F, Cl, and Br; the C?Zr and Zr? H stretching frequencies increase, and the bonds become shorter. This observation favors the characterization of the agostic interaction as a reorganization of charge.     

Catalytic thermal and photo-induced CH and CC activation reactions of alkanes with ansa amido functionalized half-sandwich complexes and methylalumoxane

In the literature most of the dehydrogenation reactions of alkanes are described as CH activation reactions of cyclooctane. The best results of CH activation reactions have been found for the reaction of MAO activated metallocene complexes and cyclooctane at temperatures over 300 °C.The application of ansa amido functionalized half sandwich compounds of the type Ind′Si(Me)2NtBuMCl2 (Ind′= monosubstituted indenyl); M = Ti, Zr, Hf) for CH and CC activation reactions is completely unknown in the literature.In contrast to the dehydrogenation reactions of cyclooctane and the metallocene complexes of the group 4 metals, where the zirconocene complexes give higher TONs than the titanocene complexes the ansa amido functionalized titanium complexes give more than two times higher TONs than the corresponding Zr or Hf complexes. The ansa amido functionalized ligand increases the TONs for the Ti complexes and decreases the TONs of the Zr complexes.In contrast to the metallocene complexes, the ansa amido functionalized dichloride complexes of Ti show also a higher activity than the corresponding Zr complexes. It is known that the photolysis of organometallic titanium, zirconium and hafnium (IV) compounds can give M(III) radicals. The formation of the active Ti metal centre is easier than in the case of the corresponding Zr and Hf metal compounds.     

New complexes of zirconium(IV) and hafnium(IV) with heteroscorpionate ligands and the hydrolysis of such complexes to give a zirconium cluster

A series of zirconium and hafnium heteroscorpionate complexes have been prepared by the reaction of MCl4 (M = Zr, Hf) with the compounds [[Li(bdmpza)(H2O)](4)] [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate], [[Li(bdmpzdta)(H2O)](4)] [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate], and (Hbdmpze) [bdmpze = 2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide] (the latter with the prior addition of Bu(n)Li). Under the appropriate experimental conditions, mononuclear complexes, namely, [MCl3(kappa3-bdmpzx)] [x = a, M = Zr (1), Hf (2); x = dta, M = Zr (3), Hf (4); x = e, M = Zr (5), Hf (6)], and dinuclear complexes, namely, [[MCl2(mu-OH)(kappa3-bdmpzx)]2] [x = a, M = Zr (7), Hf (8); x = dta, M = Zr (9); x = e, M = Zr (10)], were isolated. A family of alkoxide-containing complexes of the general formula [ZrCl2(kappa3-bdmpzx)(OR)] [x = a, R = Me (11), Et (12), iPr (13), tBu (14); x = dta, R = Me (15), Et (16), iPr (17), tBu (18); x = e, R = Me (19), Et (20), (i)Pr (21), (t)Bu (22)] was also prepared. Complexes 11-14 underwent an interesting hydrolysis process to give the cluster complex [Zr6(mu3-OH)8(OH)8(kappa2-bdmpza)8] (23). The structures of these complexes have been determined by spectroscopic methods, and the X-ray crystal structures of 7, 8, and 23 were also established.     

Addition and metathesis reactions of zirconium and hafnium imido complexes

The zirconium and hafnium imido metalloporphyrin complexes (TTP)M = NArtPr (TTP = meso-5,10,15,20-tetra-p-tolylporphyrinato dianion; M = Zr (1), Hf; AriPr = 2,6-diisopropylphenyl) were used to mediate addition reactions of carbonyl species and metathesis of nitroso compounds. The imido complexes react in a stepwise manner in the presence of 2 equiv of pinacolone to form the enediolate products (TTP)M[OC(tBu)CHC(tBu)(Me)O] (M = Zr (2), Hf (3)), with elimination of H2NAriPr. The bis(mu-oxo) complex [(TTP)ZrO]2 (4) is formed upon reaction of (TTP)Zr = NAriPr with PhNO. Treatment of compound 4 with water or treatment of compound 2 with acetone produced the (mu-oxo)bis(mu-hydroxo)-bridged dimer [(TTP)Zr]2(mu-O)(mu-OH)2 (5). Compounds 2, 4, and 5 were structurally characterized by single-crystal X-ray diffraction.     

Chemistry of 2,2,6,6,-tetramethyl-3,5-heptanedione (Hthd) modification of zirconium and hafnium propoxide precursors

The modification of different zirconium propoxide and hafnium propoxide precursors with 2,2,6,6,-tetramethyl-3,5-heptanedione (Hthd) was investigated by characterization of the isolated modified species. The complexes [Zr(OnPr)3(thd)](2), [Zr(OnPr)(OiPr)2(thd)]2, Zr(OiPr)(thd)3, [Hf(OnPr)3(thd)]2, and Hf(OiPr)(thd)3 were isolated and characterized. The structure of the n-propoxide analogue of Zr(OiPr)(thd)3 could not be refined, but its existence was clearly demonstrated by XRD and 1H NMR. The modification of the propoxide precursors involves mono- and trisubstituted intermediate compounds and does not involve a disubstituted compound; thus, the commercial product that is claimed to be "Zr(OiPr)2(thd)2" and is most commonly used for the MOCVD preparation of ZrO2 does not exist. No evidence was found for the presence of such a compound in either zirconium- or hafnium-based systems. Formation of the dimeric hydroxo-di-thd-substituted complex, [Hf(OH)(OiPr)(thd)2]2, which could be isolated only for hafnium-based systems, occurs on microhydrolysis. All heteroleptic intermediates are eventually transformed to the thermodynamically stable Zr(thd)4 or Hf(thd)4) The compounds obtained from isopropoxide precursors showed a higher stability than those with n-propoxide ligands or a combination of both types. In addition, it is important to note that residual alcohol facilitates the transformation and strongly enhances its rate. The unusually low solubility and volatility of MIV(thd)4 has been shown to be due to close packing and strong van der Waals interactions in the crystal structures of these compounds.     

Spectrophotometric characteristics of dissociation of Zr and Hf complexes with Methylthymol Blue

Two modifications of the spectrophotometric method for determination of the stability constants of ML and ML(2) complexes are derived and used for determination of the stability constants of Zr and Hf complexes with Methylthymol Blue. The dependence of the degree of dissociation of the complexes on the Zr and Hf concentrations is discussed.     

Zirconium and hafnium (1-pyridinio)imido complexes: functionalized terminal hydrazinediido analogues

Reaction of the diamidozirconium complex [Zr(N2(TBS)Npy)(NMe2)2] (1) (N2(TBS)Npy = CH3C(C5H4N)(CH2NSiMe2tBu)2) or the diamidohafnium complex [Hf(N2(TBS)Npy)(NMe2)2] (2) with one molar equiv. of 1-aminopyridinium triflate in the presence of one equiv. of pyridine gave the corresponding (1-pyridinio)imido complexes [Zr(N2(TBS)Npy)(=N-NC5H5)(OTf)(py)] (3) and [Hf(N2(TBS)Npy)(=N-NC5H5)(OTf)(py)] (4). These were converted to the acetylide complexes [Zr(N2(TBS)Npy)(=N-NC5H5)(CCPh)(py)] (5) and [Hf(N2(TBS)Npy)(=N-NC5H5)(CCPh)(py)] (6) by reaction with lithium phenylacetylide and substitution of the triflato ligand. Upon reaction of 3 and 4 with one molar equivalent of R-NC (R = tBu, Cy, 2,6-xyl), N-N bond cleavage in the (1-pyridinio)imido unit took place and the respective carbodiimido complexes [M(N2(TBS)Npy](N=C=NR)(OTf)(py)] (7-12) were formed instantaneously. A similar type of reaction with CO gave the isocyanato complex [Zr(N2(TBS)Npy](NCO)(OTf)(py)] (13). Finally, the abstraction of the pyridine ligand in compounds 3 and 4 with B(C6F5)3 led to the formation of the triflato-bridged dinuclear complexes [Zr(N2(TBS)Npy)(=N-NC5H5)(OTf)]2 (14) and [Hf(N2(TBS)Npy)(=N-NC5H5)(OTf)]2 (15).     

Synthesis and catalysis of di- and tetranuclear metal sandwich-type silicotungstates [(gamma-SiW10O36)2M2(mu-OH)2]10- and [(gamma-SiW10O36)2M4(mu4-O)(mu-OH)6]8- (M = Zr or Hf)

The di- and tetranuclear metal sandwich-type silicotungstates of Cs10[(gamma-SiW10O36)2{Zr(H2O)}2(mu-OH)2] x 18 H2O (Zr2, monoclinic, C2/c (No. 15), a = 25.3315(8) A, b = 22.6699(7) A, c = 18.5533(6) A, beta = 123.9000(12) degrees, V = 8843.3(5) A(3), Z = 4), Cs10[(gamma-SiW10O36)2{Hf(H2O)}2(mu-OH)2] x 17 H2O (Hf2, monoclinic, space group C2/c (No. 15), a = 25.3847(16) A, b = 22.6121(14) A, c = 18.8703(11) A, beta = 124.046(3) degrees, V = 8974.9(9) A(3), Z = 4), Cs8[(gamma-SiW10O36)2{Zr(H2O)}4(mu4-O)(mu-OH)6] x 26 H2O (Zr4, tetragonal, P4(1)2(1)2 (No. 92), a = 12.67370(10) A, c = 61.6213(8) A, V = 9897.78(17) A(3), Z = 4), and Cs8[(gamma-SiW10O36)2{Hf(H2O)}4(mu4-O)(mu-OH)6] x 23 H2O (Hf4, tetragonal, P4(1)2(1)2 (No. 92), a = 12.68130(10) A, c = 61.5483(9) A, V = 9897.91(18) A(3), Z = 4) were obtained as single crystals suitable for X-ray crystallographic analyses by the reaction of a dilacunary gamma-Keggin silicotungstate K8[gamma-SiW10O36] with ZrOCl2 x 8 H2O or HfOCl2 x 8 H2O. These dimeric polyoxometalates consisted of two [gamma-SiW10O36](8-) units sandwiching metal-oxygen clusters such as [M2(mu-OH)2](6+) and [M4(mu4-O)(mu-OH)6](8+) (M = Zr or Hf). The dinuclear zirconium and hafnium complexes Zr2 and Hf2 were isostructural. The equatorially placed two metal atoms in Zr2 and Hf2 were linked by two mu-OH ligands and each metal was bound to four oxygen atoms of two [gamma-SiW10O36](8-) units. The tertanuclear zirconium and hafnium complexes Zr4 and Hf4 were isostructural and consisted of the adamantanoid cages with a tetracoordinated oxygen atom in the middle, [M4(mu4-O)(mu-OH)6](8+) (M = Zr or Hf). Each metal atom in Zr4 and Hf4 was linked by three mu-OH ligands and bound to two oxygen atoms of the [gamma-SiW10O36](8-) unit. The tetra-nuclear zirconium and hafnium complexes showed catalytic activity for the intramolecular cyclization of (+)-citronellal to isopulegols without formation of byproducts resulting from etherification and dehydration. A lacunary silicotungstate [gamma-SiW10O34(H2O)2](4-) was inactive, and the isomer ratio of isopulegols in the presence of MOCl2 x 8 H2O (M = Zr or Hf) were much different from that in the presence of tetranuclear complexes, suggesting that the [M4(mu4-O)(mu-OH)6](8+) core incorporated into the POM frameworks acts as an active site for the present cyclization. On the other hand, the reaction hardly proceeded in the presence of dinuclear zirconium and hafnium complexes under the same conditions. The much less activity is possibly explained by the steric repulsion from the POM frameworks in the dinuclear complexes.     

Reactions of d0 group 4 amides with dioxygen. Preparation of unusual oxo aminoxy complexes and theoretical studies of their formation

Reactions of d0 amides M(NMe2)4 (M = Zr, 1; Hf, 2) with O2 have been found to yield unusual trinuclear oxo aminoxide complexes M3(NMe2)6(mu-NMe2)3(mu3-O)(mu3-ONMe2) (M = Zr, 3; Hf, 4) in high yields. Tetramethylhydrazine Me2N-NMe2 was also observed in the reaction mixtures. Crystal structures of 3 and 4 have been determined. Density functional theory calculations have been performed to explore the mechanistic pathways in the reactions of model complexes Zr(NR2)4 (R = H, 5; Me, 1) and [Zr(NR2)4]2 (R = H, 5a; Me, 1a) with triplet O2. Monomeric and dimeric reaction pathways in the formation of the Zr complex 3 are proposed.     

Highly Strained Heterometallacycles of Group 4 Metallocenes with Bis(diphenylphosphino)amide Ligands

A study regarding coordination chemistry of the bis(diphenylphosphino)amide ligand Ph(2) P-N-PPh(2) at Group?4 metallocenes is presented herein. Coordination of N,N-bis(diphenylphosphino)amine (1) to [(Cp(2) TiCl)(2) ] (Cp=η(5) -cyclopentadienyl) generated [Cp(2) Ti(Cl)P(Ph(2) )N(H)PPh(2) ] (2). The heterometallacyclic complex [Cp(2) Ti(κ(2) -P,P-Ph(2) P-N-PPh(2) )] (3?Ti) can be prepared by reaction of 2 with n-butyllithium as well as from the reaction of the known titanocene-alkyne complex [Cp(2) Ti(η(2) -Me(3) SiC(2) SiMe(3) )] with the amine 1. Reactions of the lithium amide [(thf)(3) Li{N(PPh(2) )(2) }] with [Cp(2) MCl(2) ] (M=Zr, Hf) yielded the corresponding zirconocene and hafnocene complexes [Cp(2) M(Cl){κ(2) -N,P-N(PPh(2) )(2) }] (4?Zr and 4?Hf). Reduction of 4?Zr with magnesium gave the highly strained heterometallacycle [Cp(2) Zr(κ(2) -P,P-Ph(2) P-N-PPh(2) )] (3?Zr). Complexes 2, 3?Ti, 4?Hf, and 3?Zr were characterized by X-ray crystallography. The structures and bondings of all complexes were investigated by DFT calculations.     

Mixed hydrazido amido/imido complexes of tantalum, hafnium and zirconium: potential precursors for metal nitride MOCVD

The coordination chemistry of the hydrazine derivatives dimethylhydrazine (Hdmh) and N-trimethylsilyl-N'N'-dimethylhydrazine (Htdmh) at Ta, Zr and Hf was investigated aiming at volatile mixed ligand all-nitrogen coordinated compounds. The hydrazido ligands were introduced either by salt metathesis employing the Li salts of the hydrazines and the tetrachlorides MCl(4) (M = Zr, Hf) or by amine substitution using M(NR(2))(4) (R = Me, Et) and [(t-BuN)Ta(NR(2))(3)]. The new complexes were fully characterised including (1)H/(13)C NMR, mass spectrometry and a study of their thermal behaviour. The crystal structures of [ZrCl(tdmh)(3)] and the all-nitrogen coordinated complex [Ta(N-t-Bu)(NMe(2))(2)(tdmh)] are discussed as well as the structure of the by-product [Li(tdmh)(py)](2). Preliminary MOCVD experiments of the liquid compound [Ta(NEt(2))(2)(N-t-Bu)(tdmh)] were performed and the deposited TaN(Si) films were analysed by RBS and SEM.     

Analysis of FT-IR spectra of dicyclopentadienyl (bis-substituted cyclopentadienyl) dithiocyano of titanium, zirconium and hafnium

The FT-IR spectra of 18 (R-Cp)2M(NCS)2 were measured. The M-Cp, M-NCS (M=Ti, Zr, Hf) and other vibration modes were reasonably assigned. All complexes of (R-Cp)2M(NCS)2 determined in this paper are bonded by N-M, and the absorption of upsilon(s)(M-Cp)(A1) (M=Ti, Zr and Hf) vibration all appear in 365 cm(-1) or so, while upsilon(as)(M-Cp)(B) appear successively around 420, 350 and 320 cm(-1) in order of Ti, Zr and Hf. The influence of the center metal atoms and the substituents on cyclopentadienyl upon the spectra was discussed. It is mainly in far infrared region that center metal atoms influence upon the infrared spectra. The influence of the substituents to cyclopentadienyling upon its vibration is not significant. Only between 1500 and 1480 cm(-1) did a new absorbing peak appear due to the introduction of substituents to activate upsilon(CC) vibration.     

Syntheses and structural systematics of trialkylphosphine complexes of open titanocenes, zirconocenes and hafnocenes

The synthesis and characterization of the open hafnocene, Hf(2,4-C7H11)2(PMe3)(C7H11 = dimethylpentadienyl), is reported. Additionally, a much improved synthetic procedure has been developed for Hf(2,4-C7H11)2(PEt3). Structural data have been obtained for these complexes, and for Ti(2,4-C7H11)2(PEt3) and Zr(2,4-C7H11)2(PMe3), thereby allowing for detailed comparisons between all M(2,4-C7H11)2(PX3) species (M = Ti, Zr, Hf; X = Me, Et). The presence of the coordinated phosphines led in all cases to the adoption of the expected syn-eclipsed geometries, with the phosphines positioned by the open dienyl edges. These phosphine ligands lead to substantial alterations of the bonding patterns in these species, relative to ligand-free complexes. Most notably, the shortest M-C distances involve the central dienyl carbon atoms. Additionally, the data reveal high degrees of steric crowding within these complexes, especially for the weakly bound Ti(2,4-C7H11)2(PEt3), and also demonstrate that significant deformations which have taken place within the dienyl ligands were substantially determined by the relative sizes of the metal centers.     

Subtle differences between Zr and Hf in early/late heterobimetallic complexes with cobalt

The phosphinoamide-linked Co/Hf complexes ICo(Ph(2)PN(i)Pr)(3)HfCl (4), ICo((i)Pr(2)PNMes)(3)HfCl (5), and ICo((i)Pr(2)PN(i)Pr)(3)HfCl (6) have been synthesized from the corresponding tris(phosphinoamide)HfCl complexes (1-3) for comparison with the recently reported tris(phosphinoamide) Co/Zr complexes. Very minor structural and electronic differences between the Zr and Hf complexes were found when the N-(i)Pr-substituted phosphinoamide ligands [Ph(2)PN(i)Pr](-) and [(i)Pr(2)PN(i)Pr](-) were utilized. The reduction products [(THF)(4)Na-{N(2)-Co(Ph(2)PN(i)Pr)(3)HfCl}(2)]Na(THF)(6) (7) and N(2)-Co((i)Pr(2)PN(i)Pr)(3)Hf (9) are also remarkably similar to the corresponding Zr/Co analogues. In the case of Hf/Co and Zr/Co complexes linked by the N-Mes ligand [(i)Pr(2)PNMes](-) (Mes = 2,4,6-trimethylphenyl), however, more pronounced differences in structure, bonding, and reactivity are observed. While differences associated with 5 are still modest, larger variations are observed when comparing the two-electron reduction product [N(2)-Co((i)Pr(2)PNMes)(3)Hf-X][Na(THF)(5)] (8) with its Zr congener. In addition to structural and spectroscopic differences, vastly different reactivity is observed, with 8 undergoing one-electron oxidation to form ClHf(MesNP(i)Pr(2))(3)CoN(2) (11) in the presence of MeI, while a two-electron oxidative addition process occurs in a similar reaction with the Zr derivative. The activity of 5 toward Kumada coupling was investigated, finding significantly diminished activity in comparison to Co/Zr complexes.     

Fluorinated diarylamido complexes of lithium, zirconium, and hafnium

Deprotonation of N-(2-fluorophenyl)-2,6-diisopropylaniline (H[ (i) PrAr-NF]) with 1 equiv of n-BuLi in toluene at -35 degrees C produced cleanly [ (i) PrAr-NF]Li. Subsequent recrystallization of [ (i) PrAr-NF]Li in diethyl ether generated the bis(ether) adduct [ (i) PrAr-NF]Li(OEt 2) 2. An X-ray study of [ (i) PrAr-NF]Li(OEt 2) 2 showed it to be a four-coordinate species with the coordination of the fluorine atom to the lithium center. The reactions of [ (i) PrAr-NF]Li with MCl 4(THF) 2 (M = Zr, Hf), regardless of the stoichiometry employed, afforded the corresponding dichloride complexes [ (i) PrAr-NF] 2MCl 2 (M = Zr, Hf). Alkylation of [ (i) PrAr-NF] 2MCl 2 with a variety of Grignard reagents generated [ (i) PrAr-NF] 2MR 2 (M = Zr, Hf; R = Me, i-Bu, CH 2Ph). The X-ray structures of [ (i) PrAr-NF] 2ZrCl 2, [ (i) PrAr-NF] 2HfCl 2, [ (i) PrAr-NF] 2ZrMe 2, [ (i) PrAr-NF] 2Zr( i-Bu) 2, and [ (i) PrAr-NF] 2Hf(CH 2Ph) 2 are all indicative of the coordination of the fluorine atoms to these group 4 metals, leading to a C 2-symmetric, distorted octahedral geometry for these molecules.     

Regio‐ and Stereochemistry in Propylene Polymerization Catalyzed with Bis(phenoxy‐imine) Zr and Hf Complexes/MAO Systems

End‐group analyses of the oligo‐ and polypropylenes produced with bis(phenoxy‐imine) Zr and Hf complexes with methylaluminoxane (MAO) indicate that the polymerization is initiated by two consecutive 1,2‐insertions and is terminated by a β‐H transfer following a 2,1‐insertion. Our data indicate that chain propagation occurs with prevailing 1,2‐regiochemistry but with considerable regioerrors, and with virtually no stereoselectivity.

The polymerization of propylene mediated by bis(phenoxy‐imine) Zr and Hf complexes with MAO.