Bis(cyclopentadienyl) compounds of zirconium with various ligands

Russian Chemical Bulletin -     

Synthesis and characterization of chromocenes containing bulky cyclopentadienyl ligands

Two equivalents of K[Cp′] (Cp′=C₅(i-Pr)₃H₂, C₅(i-Pr)₄H, C₅(t-Bu)₂H₃) react with CrCl₂ in THF to give the corresponding chromocenes, Cp′₂Cr, in good yield. Despite the presence of bulky substituents on the rings that could affect their properties, the complexes are extremely air- and moisture-sensitive, and possess a low-spin ground state. The low-spin paramagnetic nature of each chromocene was confirmed by magnetic susceptibility measurements. The solid-state structure of [C₅(i-Pr)₃H₂]₂Cr was obtained using single crystal X-ray analysis. It displays rigorously parallel rings, with an average Cr–C(ring) distance of 2.17(1)Å; the chromium resides on a crystallographically imposed inversion center. The orientation of the isopropyl groups minimizes unfavorable steric interactions between the rings.     

Effect of bulky ligands on one-dimensional platinum compounds

Summary Diaminedithiocyanatoplatinum(II) complexes react with iodine in ethanolic suspension to yield diamagnetic compounds of empirical formula Pt(diamine)(SCN)₂I, which exhibit properties characteristic of one-dimensional materials. Incorporation of bulky substituents in the diamine ligand does not prevent the extended z-axis interaction responsible for these properties, in contrast to the effect of large ligands upon cooperative phenomena in Magnus' Green Salt analogues.Reprintsof this article are not available.The phase cooperative phenomena refers to magnetic and electronic properties that arise form the interaction between neihbouring metal in the solid state.     

Titanium(IV) complexes containing mono‐cyclopentadienyl and bulky trityloxy mixed ligands: synthesis and polymerization activity

Eight new R¹CpTiCl₂(OC(C₆H₄R²)Ph₂) complexes were synthesized by the reaction of R¹CpTiCl₃ with Ph₂(R²C₆H₄)COH (R²C₆H₄ = phenyl or o‐methyl‐phenyl) in the presence of Et₃N in good yield and characterized by ¹H NMR, elemental analysis, IR and mass spectrometry. A suitable single crystal of complex 2 (R¹: CH₃, R²: H) was obtained and the structure determined by X‐ray diffraction. When activated by methylaluminoxane (MAO), all complexes were active for the polymerization of ethylene and styrene. The effect of variation in temperature, catalyst concentration and MAO/catalyst molar ratio was also studied. Complex 5 (R¹: n‐C₄H₉, R²: H) showed a moderate conversion (37.4%) for the polymerization of methyl methacrylate. Copyright © 2005 John Wiley & Sons, Ltd.     

Hafnium cyclopentadienyl compounds containing various chelate ligands in the molecule

Conclusions Some previously unknown hafnium cyclopentadienyl compounds, containing various chelate ligands in the molecule, were synthesized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2359–2361, October, 1973.     

Cyclooctatetraenide-based single-ion magnets featuring bulky cyclopentadienyl ligand

We report a family of organometallic rare-earth complexes with the general formula (COT)M(Cp^ttt) (where (COT)²⁻ = cyclooctatetraenide, (Cp^ttt)⁻ = 1,2,4-tri(tert-butyl)cyclopentadienide, M = Y(iii), Nd(iii), Dy(iii) and Er(iii)). Similarly to the prototypical Er(iii) analog featuring pentamethylcyclopentadienyl ligand (Cp*)⁻, (COT)Er(Cp^ttt) behaves as a single-ion magnet. However, the introduction of the sterically demanding (Cp^ttt)⁻ imposes geometric constraints that lead to a simplified magnetic relaxation behavior compared to the (Cp*)⁻ containing complexes. Consequently, (COT)Er(Cp^ttt) can be viewed as a model representative of this organometallic single-ion magnet architecture. In addition, we demonstrate that the increased steric profile associated with the (Cp^ttt)⁻ ligand permits preparation, structural characterization and interrogation of magnetic properties of the early-lanthanide complex, (COT)Nd(Cp^ttt). Such a mononuclear derivative could not be obtained when a (Cp*)⁻ ligand was employed, a testament to larger ionic radius of this early lanthanide ion.

Application of steric control principles allows for simplification of the magnetic behavior of an iconic single-ion magnet architecture as well as the preparation of its previously inaccessible representative.     

Multiple bonding in heavier element compounds stabilized by bulky terphenyl ligands

This paper summarizes recent developments involving the preparation and reactivity of molecular species stabilized by terphenyl ligands that feature new bonding environments. Highlights include the synthesis and characterization of dimetallenes and dimetallynes, ArEEAr [E=heavy group 13 (triel) or group 14 (tetrel) element, Ar=terphenyl ligand] and, more recently, the synthesis of a stable chromium(I) dimer, ArCrCrAr, that displays a 5-fold bonding interaction between the chromium centers.     

An infrared and NMR study of the structure of cyclopentadienyl compounds of gold(I)

Cyclopentadienyl- and methylcyclopentadienyl-(triphenylphosphine)gold(I) and cyclpentadienyl(triethylphosphine)gold(I) have been characterized by infrared and variable temperature proton magnetic resonance spectroscopy. The compounds are suggested to have monohapo (i.e. σ-bonded) rings, in contrast with the analogous copper(I) derivatives.     

Dimolybdenum cyclopentadienyl complexes with bridging chalcogenophosphinidene ligands

The reactions of the phosphinidene-bridged complex [Mo(2)Cp(2)(μ-PH)(η(6)-HMes*)(CO)(2)] (1), the arylphosphinidene complexes [Mo(2)Cp(2)(μ-κ(1):κ(1),η(6)-PMes*)(CO)(2)] (2), [Mo(2)Cp(2)(μ-κ(1):κ(1),η(4)-PMes*)(CO)(3)] (3), [Mo(2)Cp(2)(μ-κ(1):κ(1),η(4)-PMes*)(CO)(2)(CN(t)Bu)] (4), and the cyclopentadienylidene-phosphinidene complex [Mo(2)Cp(μ-κ(1):κ(1),η(5)-PC(5)H(4))(η(6)-HMes*)(CO)(2)] (5) toward different sources of chalcogen atoms were investigated (Mes* = 2,4,6-C(6)H(2)(t)Bu(3); Cp = η(5)-C(5)H(5)). The bare elements were appropriate sources in all cases except for oxygen, in which case dimethyldioxirane gave the best results. Complex 1 reacted with the mentioned chalcogen sources at low temperature, to give the corresponding chalcogenophosphinidene derivatives [Mo(2)Cp(2){μ-κ(2)(P,Z):κ(1)(P)-ZPH}(η(6)-HMes*)(CO)(2)] (Z = O, S, Se, Te; P-Se = 2.199(2) ?). The arylphosphinidene complex 2 was the least reactive substrate and gave only chalcogenophosphinidene derivatives [Mo(2)Cp(2)(μ-κ(2)(P,Z):κ(1)(P),η(6)-ZPMes*)(CO)(2)] for Z = O and S (P-O = 1.565(2) ?), along with small amounts of the dithiophosphorane complex [Mo(2)Cp(2)(μ-κ(2)(P,S):κ(1)(S'),η(6)-S(2)PMes*)(CO)(2)], in the reaction with sulfur. The η(4)-complexes 3 and 4 reacted with sulfur and gray selenium to give the corresponding derivatives [Mo(2)Cp(2)(μ-κ(2)(P,Z):κ(1)(P),η(4)-ZPMes*)(CO)(2)L] (L = CO, CN(t)Bu), obtained respectively as syn (Z = Se; P-Se = 2.190(1) ? for L = CO) or a mixture of syn and anti isomers (Z = S; P-S = 2.034(1)-2.043(1) ?), with these diastereoisomers differing in the relative positioning of the chalcogen atom and the terminal ligand at the metallocene fragment, relative to the Mo(2)P plane. The cyclopentadienylidene compound 5 reacted with all chalcogens, and gave with good yields the chalcogenophosphinidene derivatives [Mo(2)Cp(μ-κ(2)(P,Z):κ(1)(P),η(5)-ZPC(5)H(4))(η(6)-HMes*)(CO)(2)] (Z = S, Se, Te), these displaying in solution equilibrium mixtures of the corresponding cis and trans isomers differing in the relative positioning of the cyclopentadienylic rings with respect to the MoPZ plane in each case. The sulfur derivative reacted with excess sulfur to give the dithiophosphorane complex [Mo(2)Cp(μ-κ(2)(P,S):κ(1)(S'),η(5)-S(2)PC(5)H(4))(η(6)-HMes*)(CO)(2)] (P-S = 2.023(4) and 2.027(4) ?). The structural and spectroscopic data for all chalcogenophosphinidene complexes suggested the presence of a significant π(P-Z) bonding interaction within the corresponding MoPZ rings, also supported by Density Functional Theory calculations on the thiophosphinidene complex syn-[Mo(2)Cp(2)(μ-κ(2)(P,S):κ(1)(P),η(4)-SPMes*)(CO)(3)].     

The dimerization of diphenyl(cyclopentadienyl)phosphine ligands by Diels-Alder addition

Reaction of diphenyl(cyclopentadienyl)phosphine, 1, with [PdCl₂(PhCN)₂], [PtCl₂(SMe₂)₂] or [M(CO)₄(norbornadiene)], where M = Mo or W, gave the complexes [PdCl₂{(Ph₂P)₂C₁₀H₁₀}], [PtCl₂{(Ph₂P)₂C₁₀H₁₀}] or [M(CO)₄{(Ph₂P)₂C₁₀H₁₀}] respectively, in which the ligand underwent dimerization by Diels-Alder addition. The reaction occurs in a very selective way and this is rationalized in terms of a template effect, in which two ligands 1 in mutually cis positions undergo the Diels-Alder reaction. In contrast, the complex [Fe(CO)₄(Ph₂PC₅H₅)] is stable to Diels-Alder addition. The structures of the complexes were deduced by ¹H, ¹³C and ³¹P NMR spectroscopy. The major product contains a six-membered chelate ring while a minor product, formed in the palladium and platinum systems only, contains a five-membered chelate ring.     

Phenylphosphatrioxa-adamantanes: bulky, robust, electron-poor ligands that give very efficient rhodium(I) hydroformylation catalysts

The cage phosphines 1,3,5,7-tetramethyl-6-phenyl-2,4,8-trioxa-6-phosphaadamantane (1a) and 1,3,5,7-tetraethyl-6-phenyl-2,4,8,trioxa-6-phosphaadamantane (1b) have been made by the acid catalysed addition of PhPH(2) to the appropriate beta-diketones; the acid used (HCl, H(3)PO(4) or H(2)SO(4)) and its concentration affect the rate and selectivity of these condensation reactions. Phosphines 1a and 1b react with [PdCl(2)(NCPh)(2)] to form complexes trans-[PdCl(2)(1a)(2)](2a) and trans-[PdCl(2)(1b)(2)](2b) as mixtures of rac and meso diastereoisomers. The platinum(II) chemistry is more complicated and when 1a or 1b is added to [PtCl(2)(cod)], equilibrium mixtures of trans-[PtCl(2)L(2)] and [Pt(2)Cl(4)L(2)](L = or ) are formed in CH(2)Cl(2) solution. Meso/rac mixtures of trans-[MCl(CO)(1a)(2)] M = Ir (6a) or Rh (7a) are formed upon treatment of MCl(3).nH(2)O with an excess of 1a and the anionic cobalt complex [NHEt(3)][CoCl(3)(1a)](9) was isolated from the product formed by CoCl(2).6H(2)O and 1a. The nu(CO) values from the IR spectra of 6a and 7a suggest that 1a resembles a phosphonite in its bonding to Rh and Ir. Crystal structures of meso-2a, meso-2b, rac-6a and 9 are reported and in each case a small intracage C-P-C angle of ca. 94 degrees is observed; this may partly explain the bonding characteristics of ligands 1a and 1b. The cone angles for 1a and 1b are similar and large (ca. 200 degrees). Rhodium complexes of ligands 1a and 1b are hydroformylation catalysts with similarly high activity to catalysts derived from phosphites. The catalysts derived from 1a and 1b gave unusually low linear selectivity in the hydroformylation of hexenes. This feature has been further exploited in quaternary-selective hydroformylations of unsaturated esters; catalysts derived from 1a give better yields and regioselectivities than any previously reported catalyst.     

Syntheses and structures of doubly tucked-in titanocene complexes with tetramethyl(aryl)cyclopentadienyl ligands

Titanocene–bis(trimethylsilyl)ethyne complexes [Ti(η⁵-C₅Me₄R)₂(η²-Me₃SiCCSiMe₃)], where R=benzyl (Bz, 1a), phenyl (Ph, 1b) and p-fluorophenyl (FPh, 1c), thermolyse at 150–160°C to give products of double C---H activation [Ti(η⁵-C₅Me₄Bz){η³:η⁴-C₅Me₃(CH₂)(CHPh)}] (2a), [Ti(η⁵-C₅Me₄Bz){η³:η⁴-C₅Me₂Bz(CH₂)₂}] (2a′), [Ti(η⁵-C₅Me₄Ph){η³:η⁴-C₅Me₂Ph(CH₂)₂}] (2b), and [Ti(η⁵-C₅Me₄FPh){η³:η⁴-C₅Me₂FPh(CH₂)₂}] (2c). In the presence of 2,2,7,7-tetramethylocta-3,5-diyne (TMOD) the thermolysis affords analogous doubly tucked-in compounds bearing one η³:η⁴-allyldiene and one η⁵-C₅Me₄R ligand having TMOD attached by its C-3 and C-6 carbon atoms to the vicinal methylene groups adjacent to the substituent R (R=Bz (3a), Ph (3b), and FPh (3c)). Compound 3a is smoothly converted into air-stable titanocene dichloride [TiCl₂{η⁵-C₅Me₂Bz(CH₂CH(t-Bu)CH=CHCH(t-Bu)CH₂)}(η⁵-C₅Me₄Bz)] (4a) by a reaction with hydrogen chloride. Yields in both series of doubly tucked-in complexes decrease in the order of substituents: BzPh>FPh. Crystal structures of 1c, 2a, 2b, and 3b have been determined.     

Rhenium(I) compounds bound by tripodal ligands of pyridine and N-methylimidazole

The reaction of Re(CO)(5)Br with tris(2-pyridyl)methanol (tpmOH) leads to unexpectedly complex chemistry with three new compounds forming instead of a single product. In compound 1, the tpmOH ligand binds to the metal in the N,N',N'-mode; 2 has tpmO(-) bound in the N,N',O-mode; while 3 is a dimer with the tpmO(-) ligand utilizing each of the four donor atoms to bridge the two metal centers. The analogous methyl ether ligands, tris(2-pyridyl)methoxymethane (tpmOMe) or tris[2-(l-methylimidazolyl)]methoxymethane (timmOMe), each yielded a single product, 4 and 5, respectively, bound in the N,N',N'-mode, and are new leads for potential radiotherapeutic agents. All compounds have been structurally characterized.     

Synthesis and structures of binuclear half-sandwich cobalt (III) ortho-carboranedithiolato complexes with silyl-bridged bis(cyclopentadienyl) ligands

Five binuclear half-sandwich cobalt complexes, [(η⁵-C₅H₄)Co(CO)I₂]₂SiMe₂ (3), [(η⁵-C₅H₄)Co(S₂C₂B₁₀H₁₀)]₂SiMe₂ (4), [(η⁵-C₅H₄)]₂Co₂(μ₂-S₂C₂B₁₀H₁₀)SiMe₂ (5), [(η⁵-C₅H₃)CoI₂](μ-I)[(η⁵-C₅H₃)Co(CO)I](SiMe₂)₂ (8), [(η⁵-C₅H₃)Co(S₂C₂B₁₀H₁₀)]₂(SiMe₂)₂ (9), were successfully synthesized in moderate yield by the reactions of corresponding ligands, (C₅H₅)₂SiMe₂ (1) and (C₅H₄)₂(SiMe₂)₂ (6), respectively. The molecular structures of 3, 5, 6, 8 and 9 was determined by X-ray crystallographic analysis, which distinctly depict various molecular structures containing the Cp rings and the metal centers with halide or 1,2-dicarba-closo-dodecaborane-1,2-dithiolato ligands. For the (η⁵-C₅H₄)₂SiMe₂ complexes, coordination of the fragments CpCo favors a exo conformation. With the rigid structure of the di-bridged ligand (C₅H₄)₂(SiMe₂)₂, only cis isomers of the corresponding (η⁵-C₅H₃)₂(Si₂Me₂)₂ complexes are formed. All the complexes have been well characterized by elemental analysis, NMR and IR spectra.     

Photoluminescent copper(I) complexes with amido-triazolato ligands

A series of heteroleptic copper(I) complexes incorporating amido-triazole and diphosphine ligands, [Cu(I)(N-phenyl-2-(1-phenyl-1H-1,2,3-triazol-4-yl)aniline)(dppb)] (1), [Cu(I)(N-(4-methylphenyl)-2-(1-phenyl-1H-1,2,3-triazol-4-yl)aniline)(dppb)] (2), [Cu(I)(N-(4-methoxyphenyl)-2-(1-phenyl-1H-1,2,3-triazol-4-yl)aniline)(dppb)] (3), [Cu(I)(N-(4-chlorophenyl)-2-(1-phenyl-1H-1,2,3-triazol-4-yl)aniline)(dppb)] (4), [Cu(I)(2,6-dimethyl-N-[2-(1-phenyl-1H-1,2,3-triazol-4-yl)phenyl]aniline)(dppb)] (5), [Cu(I)(2,6-dimethyl-N-[2-(1-benzyl-1H-1,2,3-triazol-4-yl)phenyl]aniline)(dppb)] (6), (dppb = 1,2-bis(diphenylphosphino)benzene), have been prepared. The complexes adopt a distorted tetrahedral geometry in the solid state with the amido-triazole ligand forming a six-member ring with the Cu(I) ion. The complexes exhibit long-lived photoluminescence with colors ranging from yellow to red-orange in the solid state, in frozen glass at 77 K, and in fluid solution with modest quantum yields of up to 0.022. Electrochemically, complexes 1-4 show irreversible oxidation waves while 5 and 6 are characterized by quasi-reversible oxidations as determined by cyclic voltammetry. For 1-4, the emission energy and oxidation potential are found to vary linearly with the Hammett parameter σ(p) of the substituent in the para position of the amido ligand, while in 5 and 6, large differences in emission are observed because of the nature of N3 substitution in the triazole ring. Density functional theory calculations have been performed on the singlet ground states (S(o)) of all complexes at the BP86/6-31G(d) level to assist in assignment of the excited states. On the basis of both experimental and computational results, we have assigned the excited states as intraligand + metal-to-ligand charge transfer (3)(ILCT+MLCT) or ligand-to-ligand charge transfer mixed with MLCT (3)(MLCT +LLCT) in these complexes.     

Zirconium and titanium complexes with side-chain functionalized cyclopentadienyl ligands

The present review summarizes the results of studies of Zr and Ti complexes based on chelating side-chain functionalized cyclopentadienyl ligands, which were synthesized by the author of the present review and co-workers. The coordination ability of the functional groups is considered. Dynamic processes that occur in half-sandwich complexes in solutions were studied by NMR spectroscopy. Emphasis is given to the reduction reactions of side-chain functionalized zirconocene dichlorides, as well as to the structures and properties of the reaction products depending on the nature of the heteroatomic substituent.     

A general and convenient method of synthesizing dihydridoplatinum(II) complexes with bulky phosphine ligands

Platinum(II) dihydrides containing bulky phosphine ligands, trans-PtH₂L₂ (L = PCy₃, P-i-Pr₃, P-n-Bu-t-Bu₂, PMe-t-Bu₂), have been prepared conveniently and in excellent yield from the reaction of the corresponding peroxycarbonato complexes with NaBH₄. A similar reduction of the dioxygen platinum(II) complexes also affords the dihydrides but less readily. All these dihydrides react with highly activated acetylenes to form the trans-hydridovinyl complexes.     

Synthesis of cationic metallocyclophanes with arene and cyclopentadienyl ligands

Previously unknown bridged cationic complexes (metallocyclophanes) with arene and cyclopentadienyl ligands have been obtained by ligand exchange in trifluoroacetic acid: