Lothar Stahl

Bicyclic and tricyclic bis(amido)cyclodiphosph(III)azane compounds of main group elements

Abstract The coordination chemistry of bis(amido)cyclodiphosph(III)azanes as dinegative chelating N -donor ligands for main-group elements is reviewed. The subject is introduced by way of an overview of convenient syntheses for bis(amino)cyclodiphosph(III)azanes and a discussion of their structures, followed by classifications of the ligands and their compounds by structure type. Detailed descriptions of syntheses and structures of bicyclic and tricyclic main-group bis(amido)cyclodiphosph(III)azane compounds, organized by groups, constitute the main part of the discussion. A summary of structural trends and potential applications concludes the review.

Pentadienyl Complexes of the Group 4 Transition Metals

Publisher Summary This chapter focuses on the advances made in the pentadienyl chemistry of three elements—namely, titanium, zirconium, and hafnium. As group 4 transition metals, these elements generate a rich coupling chemistry, and as their metallocenes also they have proven to be remarkably unique. The chapter describes some of the most commonly used pentadienyl ligands as illustrated in a chart. In general, a numbering scheme is utilized in which the dienyl termini are defined as C1 and C5, with C2–C4 appearing between C1 and C5. Formally, any charge delocalized over the dienyl fragment can be shared by C1, C3, and C5, leaving C2 and C4 uncharged. The metals themselves play a further role by promoting coupling reactions between unsaturated organic molecules and pentadienyl ligands, much as had already been observed for early metal diene complexes. A number of open and half-open titanocenes, zirconocenes, and hafnocenes have been reported to yield catalysts for the hydrogenation of unsaturated polymers such as polybutadiene. The hydrogenations are carried out in solution phase, and generally are very efficient (84–89%). In addition, the chapter discusses reactions in which pentadienyl ligands are altered, as may occur via a coupling reaction, and applications of metal pentadienyl compounds in materials and catalytic processes.

Reactions of cyclic bis(amino)germylenes and -stannylenes with [CpFe(CO)2]2 and CpFe(CO)2Me (Cp = .eta.5-C5H5) : syntheses and single-crystal x-ray structures of four new insertion compounds

The interaction of El(NtBu)2SiMe2, El = Ge, Sn with CpFe(CO)2Me in toluene has yielded CpFe(CO)2[El(NtBu)2SiMe2]Me, El = Ge (2) and El = Sn (3), respectively. Both compounds have been characterized by NMR, IR, MS, elemental analysis, and single crystal X-ray methods. Compound 2 crystallizes in the monoclinic system, space group P21/m, Z = 2, a = 9.330(6) A°, b = 12.552(9) A°, c = 9.939(7) A°, s = 105.01(2)°, V = 1124(1) A°3. The isostructural 3 forms orthorhombic crystals of space group Pnma, Z = 4, a = 17.871(9) A°, b = 12.998(7) A°, c = 9.838(5) A°, V = 2285(2) A°3. The refinement of 2 with 1431 unique, observed (I > 2s(I)) reflections led to final agreement indices of R = 0.043, Rw = 0.048. The structure of 3 was refined to R = 0.027 (Rw = 0.027) by using 1397 unique and observed (I > 2s(I)) reflections. Treatment of [CpFe-(CO)2]2 with 2 equiv. of El(NtBu)2SiMe2 under identical reaction conditions afforded [CpFe(CO)2]2Ge(NtBu)2SiMe 2, 4, for the cyclic germylene, whereas in the case of the tin homolog the tetranuclear complex {[CpFe(CO)2Sn(NtBu)2SiMe2] 2·C7H8}, 5, was isolated. Complete characterizations (NMR, IR, MS, EA, single crystal X-ray determination) were carried out on both compounds. The solid state structure of 5 contains one of the longest (2.992(2) A°) unbridged tin-tin bonds known to date. The trinuclear compound 4 is triclinic, space group P1, Z = 2. Its lattice parameters are: a = 9.549(5) A°, b = 10.102(5) A°, c = 16.438(8) A°, a = 81.98(4)°, s = 74.00(3)°, ? = 62.80(3)°, V = 1355(1) A°3. Refinement of this structure using 3100 unique, observed (I > 2s(I)) data led to agreement indices of R = 0.023 and Rw = 0.023. The tetranuclear 5 crystallizes as a toluene solvate. Crystal data: monoclinic, space group P21/n, Z = 2, a = 10.547(7) A°, b = 19.944(11) A°, c = 11.366(7) A°, s = 92.36(5)°. Of 3024 collected data 2724 were considered unique and observed (I > 3s(I)) and used in the refinement. Final agreement indices are R = 0.031, Rw = 0.033.

Syntheses and Structures of Cationic and Neutral, Homo- and Heteroleptic tert-Butoxides of the Group 4 Metals

The utility of tri-tert-butoxystannate as a chelating tridentate ligand for group 4 metals was investigated. The highly Lewis acidic metals degraded the stannate ion in a series of tert-butoxide abstraction steps to produce a variety of group 4 tert-butoxides. A total of 1 equiv of NaSn(O(t)Bu)(3) reacted with cis-MCl(4)(THF)(2) [M = Zr (1), Hf (2)] in THF solutions to furnish the salts fac-{[M(O(t)Bu)(3)(THF)(3)](SnCl(3))}, which are separated ion pairs featuring weakly coordinating trichlorostannate ions. Neutral complexes, namely, [M(O(t)Bu)(2)Cl(2)(THF)(2)] [M = Zr (3), Hf (4)], were isolated when 2/3 equiv of sodium stannate was used in these reactions. Titanium tetrachloride formed analogues neither of 1 and 2 nor of 3 and 4, but Ti(O(t)Bu)(3)Cl reacted with silver triflate to give [Ti(O(t)Bu)(2)(OTf)(2)(THF)(2)] (5). Anion exchange of triflate for trichlorostannate transformed 1 to the contact ion pair fac-[Zr(O(t)Bu)(3)OTf(THF)(2)] (6). A total of 2 equiv of NaSn(O(t)Bu)(3) reacted with cis-MCl(4)(THF)(2) to give the complexes fac-[Sn(mu-O(t)Bu)(3)M(O(t)Bu)(3)] [M = Zr (7), Hf (8)]. Tri-tert-butoxystannate may be used as a selective alkoxylating agent for group 4 metals, and it can be transferred to these metals intact if their Lewis acidity is appropriately attenuated as in fac-{[M(O(t)Bu)(3)(THF)(3)](SnCl(3))}. Single-crystal X-ray studies revealed distorted octahedral coordination geometries for all compounds (1-8), with 1, 2, 7, and 8 being crystallographically C(3) symmetric.

Synthetic, structural and PE spectroscopic studies on bis(pentadienyl) compounds of iron, ruthenium and osmium. The role of the heavy metal

Abstract The syntheses of bis(2,3,4-trimethylpentadienyl)iron and bis(2,4-dimethylpentadienyl)osmium are reported, as well as their variable temperature NMR behaviour and a single-crystal X-ray diffraction study for the latter compound. All data indicate that these complexes adopt a gauche -eclipsed conformation in the ground state. Photoelectron spectra have also been obtained for these complexes, and suggest that the radical cations of bis(pentadienyl)iron complexes differ significantly from their ruthenium and osmium counterparts.

Vapor-phase and solution-phase UV spectroscopic studies of η5-pentadienyl derivatives of iron and ruthenium

Abstract The electronic absorption spectra of the ‘half-open metallocenes’, (Cp)(C 7 H 11 )Fe, (Cp)(C 7 H 11 )Ru, (Cp*)(C 7 H 11 )Ru (Cp= η 5 -cyclopentadienyl, Cp*= η 5 -pentamethylcyclopentadienyl, C 7 H 11 = η 5 -2,4-dimethylpentadienyl), and ‘open metallocenes’, (C 7 H 11 ) 2 Fe, (C 7 H 11 ) 2 Ru, have been measured in the vapor phase and in n -pentane solution and have been compared with the spectrum of the ‘closed ferrocene’ (Cp)(Cp*)Fe. The vapor-phase spectrum of (Cp)(Cp*)Fe reveals two sharp absorption bands arising from the 3d z 2→R4s and 3d z 2→R4d transitions. These bands are absent in the solution spectrum. Similarly, the spectra of iron and ruthenium η 5 -pentadienyl complexes show absorption features which disappear on going from the vapor to the solution phase. These features were interpreted as being due to Rydberg excitations originating at the metal d z 2 orbital. The estimated term values indicate that Rydberg bands in the spectra of ‘half-open metallocenes’ and ‘open metallocenes’ most likely correspond to transitions from the molecular orbital responsible for the first ionization peak in the photoelectron spectra to the lowest Rydberg s, p, and d levels. Gaussian analysis shows that Rydberg bands are successively broadened on going from the ‘closed ferrocene’ to ‘half-open metallocenes’ and then to ‘open metallocenes’. This broadening can be interpreted as a result of an increase in mixing of the metal d z 2 orbital with ligand functions in this group of compounds.

Alkoxigermanate(II), -stannate(II) und -plumbate(II) zweiwertiger Metallionen, I [1] / Alkoxigermanates(II), -stannates(II) and -plumbates(II) of Two-Valent Metal Ions, I [1]

Bis(tri-tert-butoxigermanates), -stannates and -plumbates of Mg (1a), Ca (1b, 2b, 3b), Sr (1c, 2c, 3c), Ba (1d, 2d, 3d), Cd (le, 2e, 3e), Eu (1f, 2f, 3f) and Pb (1g, 2g, 3g) have been synthesized by various procedures from starting materials such as sodium tri-tert-butoxigermanate (5) and -plumbate (6) and other analogous compounds. While in 1 g and 2g the lead atom is situated in the middle of the molecule, it can also occupy two different coordination sites as in Pb(OtBu)3Pb(OtBu)3Pb (3g) and in Ge(OtBu)3Pb(OtBu)3Pb (7). X-ray structure investigations on 1a, 1b, 1e, 1f, 1g, 2b, 2e, 2g, 3c, 3d and 3g reveal that all these molecules have a common ElO3MO3El cage unit. This cage unit can be visualized as two ElO3M trigonal bipyramids sharing the central metal M. Consequently in all structures the central element M is sixfold coordinated by oxygen while the outer metals (El) have three oxygen neighbours. The oxygen atoms are further bonded to tert-butyl-groups, which surround the whole ElO3MO3El frame. Four different structure types have been found to exist: a monoclinic type α (1a), an orthorhombic type β (1b, le, 2b, 2e), a rhombohedral type γ (1f, 1g, 3c, 3d, 3g) and a monoclinic type δ (2g). In the β-structure type the molecules are found to exist as three different isomers, depending on the arrangement of the alkoxy groups in a right- or left-handed manner within the El(OtBu)3 groups (RR, SS and RS). Solution equilibria between these isomers are observed by NMR. In the case of 1e a more detailed picture of this intramolecular motion, attributed to the inversion of the trigonal-pyramidally coordinated oxygen atoms, can be given. CP-MAS-NMR-spectra as well as solution spectra have been obtained for le (13C, 113Cd), 2e (13C, 113Cd, 119Sn), 2g (119Sn, 207Pb), 3g (13C). While δ113Cd values of 2e in solution and in the solid are comparable (92.8 vs 73.7 ppm), the 2J(119Sn/113Cd) values rise from 39 Hz to 295 Hz. Detailed comparison of bond lengths and angles in the different derivatives shows that the “softness” of the El(OtBu)3 groups (or the ability of the groups to accommodate a metal atom with respect to its size) follows the order Sn(OtBu)3 < Ge(OtBu)3 < Pb(OtBu)3. From these findings it can be explained, why the lead derivative 2g shows stereochemical activity of the lone pair, while 1g and 3g do not show this effect at room temperature. All compounds except the lead derivatives 1g, 2g, 3g and 7 are colourless.

Synthesis and characterization of the triethylphosphine adduct of bis(2,4-dimethylpentadienyl)tungsten, [W(2,4-C7H11)2(PEt3)], a complex with one η5-U and one η5-S pentadienyl ligand

Abstract The reaction of [WCl4(PEt3)2] with 4 equiv. of the 2,4-dimethylpentadienyl anion leads to the spontaneous reduction of the W(IV) complex by two of the dienyl anions, along with incorporation of the other two anions in the resulting W(II) complex [W(2,4-C7H11)2(PEt3)] (2,4-C7H11=2,4-dimethylpentadienyl). Spectroscopic data reveal a low symmetry structure, presumed to be analogous to that found for the molybdenum analogue, in which one dienyl ligand was bound in the usual η5-U conformation, the other in the uncommon η5-S (sickle) conformation. This has been confirmed through a single crystal X-ray diffraction study.

Bis(tert-butylamido)- and bis(arylamido)cyclodiphosph(III)azane complexes of Ti, V, Zr and Hf: ligand substituent effects and coordination number

Syntheses and structures of [{(ButNP)2(ButN)2}MCl2], M = Zr, Hf, [{(ButNP)2(ArN)2}TiCl2], Ar = Ph, m-Tol, p-Tol, and of [{(ButNP)2(PhN)2}VCl·THF], are reported. In the solid-state these compounds are seco-heterocubic metal complexes featuring one η3-coordinated bis(amido)cyclodiphosphazane ligand. When ZrCl4 and HfCl4 are treated with {(ButNP)2(PhNLi·THF)2}, however, the diligand complexes [{(ButNP)2(PhN)2}2M], M = Zr, Hf are isolated.

Syntheses and single-crystal X-ray structures of[(ButNP)2(ButN)2]MCl2 (M = Zr, Hf): the first transition-metalbis(alkylamido)cyclodiphosphazane complexes

The interaction of [(Bu t NP){Bu t NLi(thf)} 2 ] with ZrCl 4 and HfCl 4 produces the remarkably stable monomeric [(Bu t NP) 2 (Bu t N) 2 ]MCl 2 (M = Zr, Hf) complexes.