Bent Sandwich Structure Research Articles

Bis(methylborole) sandwich compounds of the first row transition metals

Bis(borole)nickel derivatives (η5-C4H4BR)2Ni, isoelectronic with the corresponding ferrocenes (η5-C5H4R)2Fe, have been synthesized and characterized structurally by X-ray crystallography as sandwich compounds with parallel borole rings. The geometries, energetics, and preferred spin states of the complete series of bis(methylborole)metal sandwich compounds (C4H4BCH3)2M of the first row transition metals (M=Ti to Ni) have now been investigated by density functional theory. The late transition metal derivatives (η5-C4H4BCH3)2M energetically prefer metallocene-like sandwich structures having parallel pentahapto borole rings with singlet, doublet, triplet, quartet, and quintet spin states for M=Ni, Co, Fe, Mn, and Cr, respectively. However, the early transition metal (η5-C4H4BCH3)2M derivatives energetically prefer bent sandwich structures having ∼30° dihedral angles between the pentahapto borole rings with singlet, doublet, and triplet spin states for M=Ti, V, and Cr, respectively. For (η5-C4H4BCH3)2Cr the closeness in energy (within ∼1kcal/mol) of the parallel quintet and bent triplet structures suggests interesting magnetic properties. The titanium and vanadium derivatives are predicted to form marginally stable [(C4H4BCH3)2M]2 dimers (M=Ti, V) with the two halves linked by a metal–metal bond as well as two bridging borole carbon atoms through agostic hydrogen atoms.

Synthesis and characterisation of alkaline earth bis(diphenylphosphano)metallocene complexes and heterobimetallic alkaline earth metal/platinum(ii) complexes [Ae(thf)x(η5-C5H4PPh2)2Pt(Me)2] (Ae = Ca, Sr, Ba)

A series of alkaline earth metallocene complexes carrying the diphenylphosphanocyclopentadienyl ligand, [Ae(L)(x)(η(5)-C(5)H(4)PPh(2))(2)] (Ae = Ca, L = thf, x = 1 (6a); Ae = Ca, L = dme, x = 1 (6b); Ae = Sr, L = thf, x = 1 (7); Ae = Ba, L = thf, x = 1 (8a); Ae = Ba, L = dme, x = 2 (8b)), were prepared by redox transmetallation/protolysis from the free metals, diphenylmercury and diphenylphosphanocyclopentadiene. These complexes were characterised using multinuclear NMR spectroscopy and two by single crystal X-ray diffraction. [Ca(dme)(η(5)-C(5)H(4)PPh(2))(2)] (6b) is a discrete neutral monomeric eight coordinate molecule in which the phosphorus atoms are not coordinated to the calcium ion and the larger barium analogue, ten-coordinate [Ba(dme)(2)(η(5)-C(5)H(4)PPh(2))(2)] (8b), has an extremely bent sandwich structure due to the two dme ligands attached to the metal. Bimetallic complexes, [Ae(thf)(x)(η(5)-C(5)H(4)PPh(2))(2)Pt(Me)(2)].(solv) (Ae = Ca, L = thf, x = 2, solv = 1.5thf (9); Ae = Sr, L = thf, x = 3, solv = 1.5thf (10); Ae = Ba, L = thf, x = 3, solv = thf (11)) were obtained by reaction of the homometallic complexes with [Pt(cod)(Me)(2)]. The crystal structures of [Ca(thf)(2)(η(5)-C(5)H(4)PPh(2))(2)Pt(Me)(2)].1.5thf (9), [Sr(thf)(3)(η(5)-C(5)H(4)PPh(2))(2)Pt(Me)(2)].1.5thf (10) and [Ba(thf)(3)(η(5)-C(5)H(4)PPh(2))(2)Pt(Me)(2)].thf (11) show the eight (calcium) and nine coordinate (strontium and barium) fragments acting as a chelating metalloligand attached to the square planar platinum through the phosphorus donor atoms. The solution chemistry of these bimetallic complexes has been investigated by NMR spectroscopy, electro-spray ionisation mass spectrometry and conductivity experiments which indicate that the bimetallic compounds persist in solution.

Mono(cycloheptatrienyl) Tantalum Chemistry: Synthesis and Characterization of New Tantalum Halide, Hydride, and Alkyl Species

The new tantalum(II) complex (eta (6)-C 7H 8)TaCl 2(PMe 3) 2 ( 1) was synthesized by the reduction of TaCl 5 with n-butyllithium in the presence of PMe 3 and cycloheptatriene. Compound 1 adopts a four-legged piano stool structure in which the tantalum center is bound to a eta (6)-cycloheptatriene ring in addition to two chlorides and two phosphine ligands in a transoid arrangement. Treatment of 1 with methyllithium results in a loss of the equivalents of HCl and formation of the eta (7)-cycloheptatrienyl complex (eta (7)-C 7H 7)TaCl(PMe 3) 2 ( 2), whereas treatment of 1 with sodium or sodium borohydride affords small amounts of the eta (5)-cycloheptadienyl complex (eta (5)-C 7H 9)TaCl 2(PMe 3) 2 ( 3). Compound 2 adopts a three-legged piano stool structure; the eta (7)-C 7H 7 ring is fully aromatic and planar. The molecular structure of 3 is similar to that of 1, except for the eta (5) binding mode of the seven-membered ring. Treatment of the previously described sandwich compound (C 5Me 5)Ta(C 7H 7) with allyl bromide affords the tantalum(V) product (C 5Me 5)Ta(C 7H 7)Br ( 4), which reacts with LiAlH 4 to give the tantalum(V) hydride (C 5Me 5)Ta(C 7H 7)H ( 5). Compound 4 also reacts with alkylating agents to generate the methyl, allyl, and cyclopropyl complexes (C 5Me 5)Ta(C 7H 7)Me ( 6), (C 5Me 5)Ta(C 7H 7)(eta (1)-CH 2CHCH 2) ( 7), and (C 5Me 5)Ta(C 7H 7)(c-C 3H 5) ( 8). Compounds 4- 8 all adopt bent sandwich structures in which the dihedral angle between the two carbocyclic rings is 34.9 degrees for the bromo compound 4, 26.6 degrees for the hydride 5, 33.1 degrees for the methyl compound 6, 34.2 degrees for the allyl compound 7, and 37.5 degrees for the cyclopropyl compound 8. (1)H and (13)C NMR data are reported for the diamagnetic compounds.

Molecular structure of decamethylgermanocene in the solid state

The low temperature X-ray structure analysis of decamethylgermanocene reveals two independent molecules in the unit cell, both of which have a bent sandwich structure with angles between the planes of the two C 5Me 5 rings of 31.26(0.09)° and 31.55(0.10)°, respectively. The perpendicular germanium to ring distances are 220 pm, corresponding to Ge–C bond lengths ranging from 240 to 266 pm.

Strukturen von polaren Bariumorganylen: Synthese und Struktur von Pyridinund Kronenether-Addukten des Bis(indenyl)bariums

The synthesis and structure of six bis(fluorenyl)barium complexes is reported. Bis(fluorenyl)barium (1) was synthesized from barium bis(hexamethyldisilazide) and fluorene. Tetrahydrofuran, dimethoxyethane, and pyridine containing complexes (1a, 1b, 2, and 3a) could be synthesized by crystallizing 1 from THF, DME, or pyridine. The X-ray structures of all crystalline compounds reveal a bent-sandwich structure with Ba–C distances between 303.3 and 322.2 pm to the five-membered rings of the fluorenyl ligands and a ring centroid–Ba distance of 288.2 to 289.0 pm. The ring centroid–Ba–ring centroid angles are 134.8 to 137.0°. Three THF (1a, 1b), two DME (2), or three pyridine molecules (3a) complete the coordination sphere of the barium atom. Two crown ether complexes (4a and 5a) of bis(fluorenyl)barium were synthesized by reacting 1 with the crown ethers 18-crown-6 and dibenzo-18-crown-6. From pyridine as solvent the following two compounds could be obtained in single crystals: [Ba(C13H9)(18-crown-6)(pyridine)]+[C13H9]−·pyridine (4a) and [Ba(C13H9)(dibenzo-18-crown-6)(pyridine)]+[C13H9]−·2 pyridine (5a). The structures of 4a and 5a could be determined by X-ray diffraction, too. The complexes 4a and 5a have a salt-like structure with a complex [Ba(C13H9)(18-crown-6)(pyridine)]+-cation and a free fluorenide anion.

Sandwich Complexes of the Heavier Alkaline Earth Metals Containing η5-β-Diketiminato Ligand Sets

Treatment of N-tert-butyl-4-(tert-butylimino)-2-penten-2-amine (LtBuH) with 0.5 equiv of M(N(SiMe3)2)2(THF)2 (M = Ca, Sr, Ba) in toluene at ambient temperature afforded Ca(η5-LtBu)2 (98%), Sr(η5-LtBu)2 (93%), and Ba(η5-LtBu)2 (93%). Crystal structure determinations of these complexes revealed bent sandwich structures in which the β-diketiminato ligands are coordinated in a η5-fashion to the metal centers. Similar treatment of N-isopropyl-4-(isopropylimino)-2-penten-2-amine (LiPrH) with 0.5 equiv of M(N(SiMe3)2)2(THF)2 led to the isolation of Ca(η2-LiPr)2 (72%), Sr(η5-LiPr)2 (80%), and a novel dinuclear barium complex [(η5-LiPr)Ba(μ-η5:η5-LiPr)(μ-η1:η1-LiPr)Ba(η5-LiPr)] (39%). Structural assignments for these complexes were based on spectral and analytical data as well as X-ray crystallography. [(η5-LiPr)Ba(μ-η5:η5-LiPr)(μ-η1:η1-LiPr)Ba(η5-LiPr)] exhibits three different bonding modes for the β-diketiminato ligands, including η5, μ-η1:η1, and μ-η5:η5. Variable-temperature NMR studies suggest that the dinuclear structure of [(η5-LiPr)Ba(μ-η5:η5-LiPr)(μ-η1:η1-LiPr)Ba(η5-LiPr)] persists in solution.

Synthesis, Structures, and Reactivity of Mono- and Bis(ferrocenyl)-Substituted Group 14 Metallocenes

New mono- and bis(ferrocenyl)-substituted germanocenes and stannocenes have been synthesized in good yield by the reaction between group 14 dichlorides (Cl2Ge·dioxane, Cl2Sn) and the lithium salts of the corresponding mono- and bis(cyclopentadienyl)-substituted ferrocenes. The X-ray crystal structure analyses of germanocenes 3a and 4a reveal a bent sandwich structure with an angle between the cyclopentadienyl planes of 45.4° and 40.9° for 3a and 4a, respectively. Mass spectrometry and electrochemical studies show the stabilization of the generated transient cations by ferrocenyl groups, particularly in the germanium series. Their reactions with electrophilic reagents such as catechol and cycloaddition with o-quinone also are reported and show, in the latter case, an increase of the specific reactivity of the dimethylcyclopentadienyl moiety.

Crown compounds for anions. Sandwich complex of cyclic trimeric perfluoro-o-phenylenemercury with [B12H11SCN]2– anion

The reaction of cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4Hg)3 (1) with the polyhedral [B12H11SCN]2– anion in THF at 20 °C affords the {[(o-C6F4Hg)3](B12H11SCN)}2– (4) and {[(o-C6F4Hg)3]2(B12H11SCN)}2– (5) complexes. Complex 5 was isolated as the tetrabutylammonium salt. X-ray diffraction analysis showed that this complex has a bent-sandwich structure in which the [B12H11SCN]2– anion is located between the planes of two molecules 1 and is coordinated to both these molecules through B—H—Hg bridges and S—Hg bonds. The stability constants of complexes 4 and 5 in THF (20 °C), which were determined from the IR spectroscopic data, are 16 L mol–1 and 992 L2 mol–2, respectively.

Borabenzene Derivatives. 30. Bis(1-methylboratabenzene) Compounds of Germanium, Tin, and Lead. First Structural Characterization of Facial Bonding of a Boratabenzene to a p-Element and the Structures of Pb(C5H5BMe)2 and Its 2,2‘-Bipyridine Adduct,1

Bis(1-methylboratabenzene)lead, Pb(C5H5BMe)2 (1), was synthesized by the reaction of Li(C5H5BMe) with PbCl2 as a low-melting (mp 60 °C) thermochromic yellow crystalline solid (63%). The lighter homologues Sn(C5H5BMe)2 (2) and Ge(C5H5BMe)2 (3) were obtained from 1-methyl-2-(trimethylstannyl)-1,2-dihydroborinine, 2-(Me3Sn)C5H5BMe, and SnCl2 and GeI2, respectively, as colorless liquids (70%). The plumbocene analogue 1 possesses a monomeric bent-sandwich structure with a bending angle of 135.2(3)°. Compound 1 forms addition compounds with nitrogen bases such as 1·TMEDA (6) and 1·bipy (7). Adduct 7 has a bent-sandwich structure with the 2,2‘-bipyridine ligand in the pseudoequatorial plane; the bending angle is 139.1(5)°.

{[(7-C2B10H12)(6-C2B10H12)U][K2(thf)5]}2]: A Metallacarborane Containing the Novel 7-C2B10H124 Ligand

The tetranion ligand η7-C2B10H124− has been observed for the first time in 1, which was obtained from the reaction of o-C2B10H12 with excess K metal followed by treatment with UCl4. As shown in the picture (without K cations and coordinated THF molecules), 1 is a centrosymmetric dimer with a bent sandwich structure.

{[(η7 -C2 B10 H12 )(η6 -C2 B10 H12 )U][K2 (thf)5 ]}2 ]: A Metallacarborane Containing the Novel η7 -C2 B10 H124- Ligand.

The tetranion ligand η7 -C2 B10 H124- has been observed for the first time in 1, which was obtained from the reaction of o-C2 B10 H12 with excess K metal followed by treatment with UCl4 . As shown in the picture (without K cations and coordinated THF molecules), 1 is a centrosymmetric dimer with a bent sandwich structure.

Synthesis and Structure of Cp*2TiH, Cp*2TiH2Li(tmed), and [Cp*2TiOLi(THF)]2

The solid-state crystal structure of the d1 hydride Cp*2TiH shows that it has a bent sandwich structure with an open Cp*(centroid)−Ti−Cp*(centroid) angle of 150°. The crystal structure contains two molecules in the asymmetric unit, and the hydridic hydrogen atom is located and refined with isotropic thermal parameters to a Ti−H distance of 1.69(5) and 1.84(4) A in each independent molecule; the average Ti−H distance is 1.76 A. In each molecule, the Ti−H vector lies on the idealized C2 axis of the bent metallocene. The addition of n-BuLi and Me2NCH2CH2NMe2 (tmed) in hexane to Cp*2TiH or the addition of [Li(tmed)]2C10H8 to Cp*2TiCl gives the anionic dihydride Cp*2Ti(μ-H)2Li(tmed). The hydride atoms are not located in the X-ray diffraction experiment, but electron paramagnetic resonance spectra show coupling to two equivalent hydrogen nuclei, AHiso = 9.6 G. In addition, coupling to 7Li, confirmed by the preparation of the 6Li isotopomer, shows that the unpaired electron couples with each hydridic hydrogen an...

New Metallacarborane Chemistry: Molybdenum and Tungsten Carbonyl Multidecker Sandwiches. Cluster Dimers Linked via Metal-Metal Bonds(1).

This article reports the synthesis, characterization, and chemistry of the first molybdenum and tungsten complexes bearing small carborane ligands, including novel M-M-linked dicluster species. The reaction of the nido-2,3-Et(2)C(2)B(4)H(4)(2)(-) dianion with (RCN)(3)M(CO)(3) reagents (M = Mo, W; R = Me, Et) gave the (Et(2)C(2)B(4)H(4))M(CO)(3)(2)(-) anions, which were isolated as lithium (12-crown-4) salts 1b (M = Mo) and 2b (M = W). Treatment of 1b and 2b with Ph(4)PX (X = Cl, Br, I) followed by triflic acid afforded the dimeric products [(Et(2)C(2)B(4)H(4))Mo(CO)(2)](2)(&mgr;-X)(2) (X = Cl (3a), Br (3b), I (3c)) and the corresponding tungsten dimers 4a-c, all of which are red or orange air-stable crystalline solids. X-ray crystallography on 3b revealed a geometry without precedent in small metallacarborane dimers, in which two MC(2)B(4) pentagonal pyramidal clusters are linked via an intercluster metal-metal bond. From NMR and other spectroscopic evidence, the remaining dimeric products 3a, 3c, and 4a-c are proposed to have structures similar to 3b. Decapitation of 3b with HCl/EtOAc in THF gave red solid [(Et(2)C(2)B(3)H(5))Mo(CO)(2)](2)(&mgr;-Br)(2) (5), which is proposed to have two open planar C(2)B(3) end rings and, hence, is a potential building block for linear polymers via deprotonation and metal-ion-stacking reactions. Compound 3b was also generated in a different reaction, involving the nido-Et(2)C(2)B(4)H(5)(-) anion and [Mo(CO)(4)Br](2)[&mgr;-Br](2) which also produced the bis(carboranyl)molybdenum complex (Et(2)C(2)B(4)H(4))(2)Mo(CO)(2) (6), a nearly colorless solid for which a bent sandwich structure is postulated. The reaction of the nido-cobaltacarborane anion CpCo(Et(2)C(2)B(3)H(4))(-) with [Mo(CO)(4)Cl](2)[&mgr;-Cl](2) in toluene gave two isolable products, red CpCo(Et(2)C(2)B(3)H(3))Mo(CO)(4) (7) and dark red [CpCo(Et(2)C(2)B(3)H(3))](2)Mo(CO)(2) (8), which have, respectively, triple-decker and bent-tetradecker sandwich structures based on X-ray crystallographic structure determinations. The reaction of CpCo(Et(2)C(2)B(3)H(4))(-) with [Mo(CO)(4)Br](2)[&mgr;-Br](2) in toluene gave 8 and a known fused-cluster complex Cp(2)Co(2)(Et(4)C(4)B(6)H(6)) (9). Treatment of the CpCo(Et(2)C(2)B(3)H(4))(-) anion with [W(CO)(4)Br](2)[&mgr;-Br](2) afforded red crystalline CpCo(Et(2)C(2)B(3)H(3))W(CO)(4) (10), which on reaction with PhLi followed by Me(3)OBF(4) gave 11, a B(5)-benzyl derivative of 10. X-ray diffraction analyses established triple-decker sandwich structures for both compounds. The new products were characterized by multinuclear NMR, IR, UV-vis, and mass spectroscopy, and elemental analysis, supplemented by electrochemical data on 3b, 8, and 11.

Borabenzene Derivatives. 26.1 Syntheses of 1-Methylboratabenzene Complexes of Titanium, Zirconium, and Hafnium. Structures of TiCl3(C5H5BMe), TiCl2Cp(C5H5BMe), ZrCl2(C5H5BMe)2, and ZrCl2Cp*(C5H5BMe)

The complexes TiCl3(C5H5BMe) (6a), [MCl3(C5H5BMe)]x (6b, M = Zr; 6c, M = Hf), and MCl2(C5H5BMe)2 (7b, M = Zr; 7c, M = Hf) are obtained from the tetrachlorides MCl4 (M = Ti, Zr, Hf) and Li(C5H5BMe) (3), 2-(Me3Si)C5H5BMe (4), or 2-(Me3Sn)C5H5BMe (5) in excellent yields. The complexes MCl2Cp(C5H5BMe) (8a, M = Ti; 8b, M = Zr) and MCl2Cp*(C5H5BMe) (9b, M = Zr; 9c, M = Hf) are made similarly from the corresponding cyclopentadienyl precursors MCl3Cp (M = Ti, Zr) and MCl3Cp* (M = Zr, Hf). The redox potentials are shifted by 0.35−0.41 V to more anodic values than those for the corresponding Cp complexes. Molecule 6a shows a piano-stool-type structure, while 7b, 8a, and 9b possess typical bent sandwich structures.

Molecular mechanics calculations on carboranes and metallocarboranes

A new approach has been developed within the framework of the MM3 force field which allows us to calculate the molecular conformations of organometallic molecules containing 7-vertex carborane and metallocarborane residues. A carborane cage in the molecular mechanics approximation is treated as a superimposition of a 5-membered ring and apical (cap) groups. Chemical bonds between these fragments are described by a Hill-like potential. The fitting of the force field parameters was based on the results of ab initio calculations of geometry and energy-distance dependences of several simple 7-vertex carborane molecules: 2,4-C 2B 5H 7, 2,3-C 2B 5H 7, l-(SiH 2)-2,3-C 2B 4H 6 and 1-Mg-2, 3-C 2B 4H 6. The elaborated force field was applied in calculations of conformational features of a series of sandwich metallocarboranes of the [RR′C 2B 4H 2] 2M type. It was shown that the bent sandwich structure of the Sn derivative is due to nonbonded interligand interactions, as in the case of the metallocenes.

ChemInform Abstract: Main Group Metallocenes: Recent Developments

Synthesis, structure, and chemistry of some trimethylsilylated and permethylated dyclopentadienyl compounds of s- and p-block elements are described. Bent-sandwich structures are found for the magnesium complex ((Me3Si)3C5H2)2Mg, for the calcium compound ((Me3Si)2CsH3)2Ca'THF and for the metallocenes of germanium, tin and lead, (Me5C5)2EI. Half-sandwich structures could be proved for adducts of silylated cyclopenta- dienyllithium compounds with nitrogen- and oxygen- donors, for a new class of boron cations, Me5C5BR +, and for the group 14 cations MesCsEI' (El = Ge,Sn,Pb). - A bent-po- lydecker sandwich is the structural basis of the potassium compound (Me3Si)C5H4KS - De- camethylsilicocene, (MesC5)2Si, the first stable silicon(l1) compound, could be synthesized from a silicon(lV) precursor, (Me5C5)2SiCl2. The properties of this .ii-complex are compa- red with those of the heavier homologues.

Synthetic, X-ray structural and polymerization studies on isopropyltetramethylcyclopentadienyl derivatives of titanium

The reaction of TiCl 3(THF) 3 with one equivalent of isopropyltetramethylcyclopentadienyllithium in THF followed by oxidation with HCl afforded [η 5-(CH 3) 2CHC 5(CH 3) 4]TiCl 3 ( 1) in 66% yield. Treatment of 1 with C 5H 5Tl in refluxing benzene gave [η 5-(CH 3) 2CHC 5(CH 3) 4](η 5-C 5H 5)TiCl 2 ( 2) in 95% yield. Reaction of TiCl 3(THF) 3 with two equivalents of isopropyltetramethylcyclopentadienyllithium in THF followed by oxidation with HCl afforded [η 5-(CH 3) 2CHC 5(CH 3) 4] 2TiCl 2 ( 3) in 73% yield. 3 crystallizes in the monoclinic space group C2/ c with a 17.032(2), b 8.275(2), c 19.078(4) Å, and β 120.83(1)° ( Z = 4). Least-squares refinement leads to a final R (based on F) of 0.038 for 2658 independent reflections. The structure consists of a bent sandwich structure with a CNT-Ti-CNT (CNT = ring centroid) angle of 137.4(1)° and an unusually acute Cl-Ti-Cl bond angle of 88.81(4)°. Ethylene polymerizations by [η 5-(CH 3) 2CHC 5(CH 3) 4](η 5-C 5-H 5)TiCl 2/MAO (MAO = methylalumoxane), [η 5-(CH 3) 2CHC 5(CH 3) 4] 2TiCl 2/MAO, and (η 5-C 5H 5) 2TiCl 2/MAO are compared at 1.3 atm over the temperature range of 0–50°C.

Main-group metallocenes: Recent developments

Abstract

AM1 parameters for zinc

The AM1 semiempirical method has been successfully extended to tin. AM1 heats of formation are slightly better than those obtained by using MNDO, but ionization potential and geometric results have been significantly improved. The AM1 results for organometallic species are especially promising. The correct prediction of the bent sandwich structure for stannocene is indicative of this

Synthesis and thermal average gas phase molecular structures of bis(pentamethylcyclopentadienyl)-strontium and -barium; the first organo-strontium and -barium structures

The thermal average gas phase molecular structures of bis(pentamethylcyclopentadienyl)-strontium, Sr(C5Me5)2, and -barium, Ba(C5Me5)2, are best described as bent sandwich structures where the mean Sr–C and Ba–C bond distances are 275.0(8) and 289.8(17)pm and the ring centroid–metal–ring centroid angles are 149(3)° and 148(6)° respectively.