Binuclear Complexes Cp Research Articles

Influence of electron-donating ability of ligand and pH value on MLCT properties of cyanido-bridged complexes

In this work, one mononuclear complex CH3CNFeII(eq-Py4PzMe2) (1) and two binuclear complexes Cp(dppe)MIICNFeII(eq-Py4PzMe2) (M = Ru 2, Fe 3; Cp = cyclopentadiene, dppe = 1,2-bis(diphenylphosphino)ethane, eq-Py4PzMe2 = 2-(1-(6-(1,1-di(pyridin-2-yl)ethyl)pyridin-2-yl)-1-(pyridin-2-yl)ethyl)pyrazine) were synthesized. Combined with the TDDFT calculations, the metal-to-ligand charge transfer (MLCT) properties of all the compounds were investigated. The results show that for the mononuclear complex, the MLCT originates from FeII to the pyrazine (Pz) component of the eq-Py4PzMe2 ligand. After the substitution of CH3CN in complex 1 by the half-sandwich fragment Cp(dppe)MIICN, the binuclear complexes 2 and 3 exhibit the MLCT transition from the neighboring FeII atom to the Pz component of the eq-Py4PzMe2 together with some contributions from the remote MII. With the increase of the electron-donating ability from CH3CN, Cp(dppe)RuIICN to Cp(dppe)FeIICN, the MLCT transition energy decreases. Furthermore, with the decrease of pH value, all the MLCT absorption bands are significantly redshifted by 160 nm or more, and the extent of these red shifts increases from complex 1 to 2, to 3.

EPR Spectroscopy Study of the Radical Cation Cluster (η⁵-C₅H₅)(CO)₅ReFePt(μ₃-C=CHPh)(η²-Ph₂P(CH₂)₂PPh₂)

The chemical oxidation of the cluster CpReFePt(μ3-C=CHPh)(CO)5(dppe) (Cp = η5-C5H5, dppe = η2- Ph2P(CH2)2PPh2) resulted in a radical cation [CpReFePt(μ3-C=CHPh)(CO)5(dppe)]+• that is sufficiently stable only at low temperature. An electronic structure of the radical cation was studied by EPR and following parameters were obtained by comparison of the experimental and model spectrum: gx = 2.070 gy = 2.0295 gz = 1.997; Ax(31P) = 17 Ay(31P) = 49 Az(31P) = 35 (Gs);Ax(195Pt) = 62 Ay(195Pt) = 45 Az(195Pt) = 105 (Gs). An unpaired electron is seen to be mainly concentrated on the iron atom (85-90%) and partially on the platinum atom (10-15%). Further transformation of the radical cation led to the formation of the binuclear complex Cp(CO)2RePt(μ-C=CHPh)(dppe) and the Fe-carbonyl fragment

Hexatriynediyl Chain Spanning Two Cp*(dppe)M Termini (M = Fe, Ru): Evidence for the Dependence of Electronic and Magnetic Couplings on the Relative Orientation of the Termini

The binuclear complexes Cp*(dppe)FeC≡CC≡CC≡CM(dppe)Cp* (6, M = Fe; 8, M = Ru) were obtained in good yield by treatment of the iron chloro complex Cp*(dppe)Fe–Cl (5) in the presence of KF with the bis(silylated) hexatriyne Me3SiC≡CC≡CC≡CSiMe3 and the ruthenium complex Cp*(dppe)RuC≡CC≡CC≡CSiMe3 (7), respectively. The oxidized species 6(PF6)n (n = 1, 2) and 8(PF6) were obtained in ca. 80% yield by treatment of the parent neutral compounds with 1 or 2 equiv of [Cp2Fe](PF6) in THF or dichloromethane at −78 °C. The CV of these compounds show three reversible waves with a separation larger than 0.5 V. The salts 6(PF6)n (n = 1, 2), and 8(PF6) were characterized by XRD. Quantum chemistry calculations performed at the DFT level on the oxidized species show a strong contribution of the −C6– spacer to the delocalization of the spin density. IR spectra analyzed with the support of TD-DFT calculations are consistent with the delocalization of the odd electron on the fast IR time scale for the two mixed-valence complexe...

Chemistry of vinylidene complexes

The reaction of Cp(CO)2Mn=C=CHPh(1) with Pd(PPh3)4 followed by the replacement of the PPh3 ligands by diphosphines Ph2P(CH2)2PPh2 (dppe) or Ph2P(CH2)3PPh2 (dppp) (where dppe is bis(diphenylphosphino)ethane and dppp is 1,3-bis(diphenylphosphino)propane) afforded the binuclear complexes Cp(CO)2MnPd(μ-C=CHPh)(dppe) (2a) and Cp(CO)2MnPd(μ-C=CHPh)(dppp) (2b), respectively. The reactions of2a and2b with Fe2(CO)9 gave the trinuclear complex CpMnFe2(μ3-C=CHPh(CO)3 (3). Competitive transmetallation took the second pathway to yield clusters containing the PdFe3 and PdFe2 cores. Complex3 was also formed in the thermal reaction of compound1 with Fe2(CO)9. Complex3 was studied by IR spectroscopy,1H and13C NMR spectroscopy, mass-spectrometry, and X-ray diffraction analysis.

Metal alkyl complexes as models for catalytic intermediates

Many catalytic reactions, whether homogeneous or heterogeneous, involving hydrocarbons and transition metals are believed to go through transition metal alkyl intermediates. Transition metal alkyl complexes, which can be isolated, fully characterized and their properties investigated, can be used as models for metal alkyl intermediates in catalytic reactions and thus give us information regarding the behaviour of the catalytic intermediates. In this paper we describe the results of some of our work on metal alkyl complexes of the types RMn(CO) 5 (R = alkyl group) and CpM(CO) 2R (Cp = η 5-C 5H 5, M = Fe, Ru or Os) as well as the binuclear complexes Cp(CO) 2Ru(CH 2) 2Ru(CO) 2Cp. These results may give us a better understanding of catalytic reactions.

Cp★Mo-halide chemistry. Rapid halide scrambling during the conproportionation of Cp 2★Mo 2Y 4 (Y  Cl, Br, I) and Cp★MoX 4(X  Cl, Br): A paramagnetic 1H NMR study

The reaction of the d 1 four-legged piano-stool complexes Cp★MoX 4 (X  Cl, Br) with the d 3-d 3 binuclear complexes Cp 2★Mo 2Y 4 (Y  Cl, Br, I) results in electron transfer and formation of the salts [Cp 2★Mo 2Y 2] +[Cp★MoX 4] −. Solutions of [Cp 2★Mo 2I 4] +[Cp★MoX 4] − (X  Cl, Br) are stable indefinitely in chlorocarbon solvents. However, for the Cp 2★Mo 2Y 4 /Cp★MoX 4 (Y, X  Cl, Br) systems, conversion to the complexes Cp 2★Mo 2Y 6- n X n is observed together with halide exchange reactions between the cation and the anion. The formation of Cp 2★Mo 2 Y 6- n X n and the halide exchange are postulated to proceed via a common associative intermediate. The rate of formation of Cp 2★Mo 2Y 6- n X n depends mostly on the Lewis acidity of the cation Cp 2 ★Mo 2Y 4 +, which varies in the order [Cp 2★Mo 2Cl 4] +å[Cp 2★Mo 2Br 4] +å [Cp 2★Mo 2I 4] +, and has little dependence on the nature of X.

Chalkogen-Verbrückte Derivate des Pentamethylcyclopentadienylrhenium-Halbsandwich-Fragments (Cp★Re): Bildung und Molekülstruktur der Selenkomplexe Cp★ 2Re 2(μ-Se 4) 2 und Cp★ 2Re 2O 2(μ-Se) 2

Starting from the halfsandwich compound Cp★Re(O)Cl 2, the chalcogen-bridged binuclear complexes Cp★ 2Re 2(μ-E 4) 2 (E  S, Se), Cp★ 2Re 2O 2(μ-E)(μ-E 2)(E  S, Se) and Cp★ 2Re 2O 2(μ-E) 2 (E  Se, Te) have been prepared by reaction with oligochalcogenides and subsequent chalcogen abstraction using tertiary phosphanes, PR 3. The molecular structures in the crystalline state of three selenium compounds have been determined by X-ray structure analyses; in contrast to the oxo complexes, the oxygen-free compounds Cp★ 2Re 2(μ-E 4) are distinguished by a strong intramolecular ReRe interaction ( d(ReRe) 2.692 (1)Å in Cp★ 2Re 2(μ-Se 4) 2, d(Re … Re) 4.32 Å and 3.77 Å in Cp★ 2Re 2O 2(μ-Se) (μ-Se 2) and Cp★ 2Re 2O 2(μ-Se) 2, respectively). The reactions of Cp★Re(O)Cl 2 with either Na 2S 4 or (NEt 4) 2Se 6 lead initially to the mononuclear cyclo-tetrachalcogenide compounds Cp★Re(O)(E 4) (E  S, Se), which can then be converted into the binuclear complexes. However, Cp★ 2Re 2O 2(μ-Te) 2 was directly formed in the reaction between Cp★Re(O)Cl 2 and (N nBu 4) 2Te 5.

Antiferromagnetic complexes with metalmetal bonds: XXIV. Bi- and trinuclear cyclopentadienyl clusters of chromium with nitrene bridges

An antiferromagnetic trinuclear cluster Cp 3Cr 3(μ-NPh) 3(μ 3-NPh) (I) has been obtained by refluxing of chromocene with azobenzene in toluene. Chromatography of the cluster on Al 2O 3 (with MeOH as an eluent) leads to its oxidation into the diamagnetic ionic cluster Cp 3Cr 3(μ-NPh) 3(μ 3-NPh) + OH −·MeOH (II) (CrCr 2.530(3)-2.561(3) Å). The same cation (CrCr 2.544-2.575 Å) may be isolated with Co(CO) 4 − (III) as the outer anion if I is oxidized by cobalt carbonyl. III has been studied by means of X-ray structural analysis (space group C2/ c, a  31.860(6), b  16.246(3), c  24.178(5) Å, β  138.211(1)°, V  8338.94 Å 3, Z  8). Bond lengths (CrCr) in II are 2.544-2.575 Å. The dimeric complex Cp 2Cr 2(OCMe 3) 2(μ-NPh) 2 (V), with a chromiumchromium bond length of 2.627 Å and the Cp ligands located in trans position relative to the CrCr bond, has been obtained by reaction of the binuclear complex Cp 2Cr 2(OCMe 3) 2 with azobenzene. It is antiferromagnetic (–2 J  146 cm −1) and does not interact with Co 2(CO) 8; however, it may readily be oxidized by oxygen to form Cp 2Cr 2(O) 2(μ-NPh) 2 (VI) (space group P2 1/ c, a  6.723(1), b  16.303(4), c  9.220(3) Å, β  96.43(2)°, V  1004.2 Å 3, Z  2). Calculations of electronic structures of V and VI have been performed by the extended Hückel method. It has been shown that in VI there is, along with the existence of a CrCr bond (2.532 Å), an antiferromagnetic interaction (−2 J  600 cm −1) between Cr V ions (electronic configuration d 1). This has been explained by there being only a small gap between the CrCr σ- and the non-bonding vacant δ-orbitals.

Antiferromagnetic complexes with the metalmetal bond: XVI. Synthesis and molecular structure of binuclear dihalogenide cyclopentadienly-t-butylate chromium(III) complexes

Reactions of (CpCrOR) 2 (I) (R = CME 3) with CH 2X 2 in toluene and benzene at room temperature yield the binuclear complexes Cp 2Cr 2(μ-OR) 2X 2 (X = Cl (II); Br (III); I (IV)) with the X ligands in the cis-position with respect to the CPCrCrCp moiety. The X-ray structural study of complexes II–Iv showed that the CrX distances (2.28(1), 2.29(1); 2.478(2); 2.716(2)m 2.711(2) Å in II–IV) are markedly shortened compared with the sums of the corresponding covalent radii, owing to additional XCr π-bonding which involves the half-filled orbitals of the Cr atoms. This shortening is accompanied by the elongation of the CrCr bonds from 2.635 Å in I up to 2.917(7), 2.971(2) and 2.967(2) Å in II–IV and the weakening of the antiferromagnetic exchange interactions (−2 J = 150, 168 and 148 cm−1 for II–IV respectively as compared with −2 J = 246 cm−1 for I). The similarity between the ligand environment of the chromium atom in I and the vanadium atom in Cp 2V is described.

Antiferromagnetic complexes with a metal—metal bond: XI. Synthesis and structure of the pentanuclear cyclopentadienyl-t-butylthiolate-sulphidechromium cluster [Cp 2Cr 2(μ 2-SCME 3)(μ 3-S) 2] 2Cr with a “bow-tie” frame

The reaction of the binuclear complex Cp 2Cr 2(SCMe 3) 2S (I) with C 6H 6Cr(CO) 3 in a benzene/heptane ( 1 2 ) mixture under UV irradiation yields black crystals of the cluster [Cp 2Cr 2(SCMe 3)S 2] 2Cr (II), which, according to X-ray data, contains a pentanuclear “bow-tie” frame with a central Cr II atom, the angle between the Cr 3 triangle planes being 90°. The bonds between the central and peripheral chromium atoms are oridinary (2.933(1) and 2.889(1) Å), while two pairs of Cr II atoms are double-bonded (CrCr 2.655(1) Å). Above and below each Cr 3 triangle is a μ 3-sulphide bridge (average Cr (centr.)S 2.333(3), average Cr (periph.)S 2.305(3) Å). Moreover, the peripheral Cr III atoms are bonded in pairs with a μ 2-SCMe 3 bridge (average CrS 2.358(4) Å), and every Cr III atom is coordinated by a π-cyclopentadienyl ligand (average CrC 2.26(1) Å, average CC 1.43(2) Å).

The catalytic system [(C 5H 5) 2TiCl] 2/LiAlH 4 in aromatic solvents : I. Formation of titanocene hydride complexes; an ESR study

The reaction between (Cp 2TiCl) 2 and LiAlH 4 in aromatic solvents yields a stable complex compound which probably consists of linear, polynuclear form of Cp 2TiAlH 4 bearing Cp 2TiH side groups. It is characterized by a broad ESR single line Δ H 3.5.–4.5 mT at g = 1.990–1.991. The binuclear complexes Cp 2TiH 2AlCl 2 (I), Cp 2TiH 2Al(Cl)H (II) and Cp 2TiH 2AlH 2 (III) are successive formed as minor components. The ESR spectrum of II, consisting of 13 lines (α A1 0.78 mT, a H(bridge) 0.39 mT), and that of a new form of III (IIIb, a A1 0.36 mT, a H(bridge) 0.40 mT) were observed for the first time. Complexes, I II and IIIb show a superhyperfine splitting at low temperatures. Changes of the multiplicity of this splitting revealed that a H(outer) is close to that of cyclopentadienyl-hydrogen atoms 0.056–0.058 mT. All these hydrides have an electronic absorption band ( dd) at λ max 550 nm, ε ∼ 130 (1 cm mol −1).

ChemInform Abstract: NITROSYLATION OF DICYCLOPENTADIENYLDI(μ‐TERT‐BUTYLTHIOLATO)(μ‐SULFIDO)DICHROMIUM GIVING TERT‐BUTYLSULFANIC GROUP. MOLECULAR STRUCTURES OF THE BINUCLEAR COMPLEX CP(NO)CR(μ‐SCME3)(μ‐S‐SCME3)CR(NO)CP AND MONOMER CPCR(NO)2(ONO)

AbstractAls Nitrosylprodukte der Titelverbindung (I) werden der Dichrom‐Komplex (II) und der monomere Komplex (III) isoliert.

Nitrosylation of dicyclopentadienyldi(μ-tert-butylthiolato)(μ-sulfido)dichromium giving tert-butylsulfanic group. Molecular structures of the binuclear complex Cp(NO)(NO)Cp and monomer CpCr(NO)2(ONO)

Reaction of CpCp (I) with NO in THF led to the binuclear complex Cp(NO)(NO)Cp (II) and monomer CpCr(NO)2(ONO) (III). The X-ray study demonstrates that the complex II has an ordinary CrCr bond (2.906(3) A) supported by the bridged SCMe3 (CrS 2.295(4) A) and (SSCMe3 (CrS 2.296(4) A), (SS 2.076(4) A) groups. In the monomeric complex III the Cr atom is surrounded by π-C5H5 (CrC 2.24(3) A), two terminal NO groups (CrN 1.71(1) A) and terminal ONO group (CrO 1.982(4) A, ONO 115(2)°).

Ethyl-substituted (π 5-cyclopentadienyl)-bis(dihaloalanedi-μ-halo)titanium(III) and (η 6-benzene)bis(dihaloalanedi-μ-halo)titanium(II) chloro and bromo complexes

Ethyl-substituted trinuclear complexes CpTiAl 2Cl 8− n Et x ( x = 1-4) were prepared by by the reaction of CpTicl 3 with two equivalents of ethylaluminium compounds. The complexes were characterized by the half-width of their EPR single-line spectra, which decreased from 1.9 mT for x = 1 to 0.85 mT for x = 4, and by the position of their d-d absorption bands. From these data the composition of ethylated titanium complexes formed in the systems CpTiAl 2Cl 8-Et 3− x AlCl x ( x = 0, 1, 2) was determined. In the system C 6H 6 · TiAl 2Cl 8−Et 3− x AlCl x the formation of only the first two members of ethylated arenetitanium(II) series C 6H 6 · TiAl 2Cl 7Et and C 6H 6 · TiAl 2Cl 6Et 2 could be observed. The latter complexes differed from the parent complex in the position of the charge transfer band Ti II → C 6H 6 and, after addition of an equimolar amount of cyclopentadiene, the EPR spectra of corresponding CpTi III trinuclear complexes were observed. In both, Ti III and Ti II series, the stability of the complexes decreased with increasing content of ethyl groups. The properties of CpTi III trinuclear complexes are compared with those of the binuclear complexes Cp 2TiAlCl 4− x Et x ( x = 0, 1, 2). Results for the series of bromo complexes were mostly analogous.

Untersuchungen zur reaktivität von metall-π-komplexen : XXIX. Synthesewege und reaktivität von ( PdPd)- und ( PtPt)-zweikernkomplexen des typs (μ-C 5H 5)(μ-allyl)M 2L 2

The binuclear complexes (Cp)(2-RC 3H 4)M 2L 2 are formed either on reaction of equimolar amounts of CpM(2-RC 3H 4) and L (where L is a tertiary phosphine, phosphite or arsine) or by a “1 + 1” addition of CpM(2-RC 3H 4) and ML 2. The NMR data suggest that in all complexes the cyclopentadienyl and allyl ligands are analogously coordinated to both metal atoms and thus sandwich the LMML unit. CpPd(2-ClC 3H 4) reacts with L to give CpPd(L)Cl and allene. The reaction of CpPd(2-ClC 3H 4) and PdL 2 (L = P(i-Pr) 3) leads, probably via the intermediate (Cp)(Cl)Pd 2L 2, to the unsymmetrical binuclear complex Cp(L)PdPd(L)(2-ClC 3H 4) which isomerizes on heating to give (2-CpC 3H 4)(Cl)Pd 2L 2. The reactions of the ( PdPd)-complexes (Cp)(2-RC 3H 4)Pd 2L 2 with electrophilic and nucleophilic reagents proceed predominantly by cleavage of the metal-to-metal bond. With I 2, HCl and MeI a mixture of mononuclear cyclopentadienylpalladium and allylpalladium complexes is always formed. In the reaction of (Cp)(2-MeC 3H 4)Pd 2L 2 with HBr, however, the formation of binuclear complexes with bromide as bridging ligand occurs. An exchange of L is only observed in the reaction of (Cp)(2-MeC 3H 4)Pd 2L 2 with trimethylphosphine.

Vinylidene complexes of transition metals : IV. The transfer of the phenylvinylidene ligand from manganese to rhenium. the novel binuclear complex Cp 2MnRe(μ-CCHPh)(CO) 4

The novel complex Cp 2MnRe(μ-CCHPh)(CO) 4 (I) containing the bridging phenylvinylidene ligand and MnRe bond was obtained in the reaction of CpMn(CCHPh)(CO) 2 with CpRe(CO) 2·THF. Complex I turns into CpRe(CCHPh)(CO) 2 under normal conditions. This is the first example of the transfer of the vinylidene ligand from one transition metal to another.

Vinylidene complexes of transition metals : III. Derivatives of cyclopentadienyltricarbonyl rhenium with phenylvinylidene ligands. Crystal and molecular structure of Cp(CO) 2Re[CC(Ph)C(Ph)CH 2]Re(CO) 2Cp

The novel complexes CpRe(CCHPh)(CO) 2 and Cp 2Re 2(μ-CCHPh)(CO) 4 containing a terminal and a bridging phenylvinylidene ligand respectively and the binuclear complex Cp(CO) 2Re[CC(Ph)C(Ph)CH 2]Re(CO) 2Cp were obtained in the reaction of CpRe(CO) 3 with PhCCH. According to an X-ray study of the latter complex the unusual bridging ligand is η 1-bonded to one Re atom and η 2-bonded to the other.