Approaches to prepare perfluoroalkyl and pentafluorophenyl copper couples for cross-coupling reactions with organohalogen compounds.

The reactions of iodoperfluoroalkanes CnF2n+1I (n = 2, 3, 4) and n-BuLi at low temperatures give NMR spectroscopic evidence for LiCnF2n+1 which were converted into LiCu(CnF2n+1)2 derivatives upon treatment with 0.5 mol copper(i) bromide, CuBr. An alternative route to obtain perfluoroorgano copper couples, Cu(Rf)2Ag (Rf = n-C3F7, n-C4F9, C6F5) was achieved from the reactions of the corresponding perfluoroorgano silver(i) reagents, AgRf, and elemental copper through redox transmetallations. The composition of the resulting reactive intermediates was investigated by means of (19)F NMR spectroscopy and ESI mass spectrometry. Perfluoro-n-propyl and perfluoro-n-butyl copper-silver reagents prepared by the oxidative transmetallation route exhibited good properties in C-C bond formation reactions with acid chlorides even under moderate conditions. Substitution of bromine directly bound to aromatics for perfluoroalkyl groups was achieved at elevated temperatures, while success in halide substitution reactions using lithium copper couples remained poor.

Single-source precursors for alloyed gold-silver nanocrystals - a molecular metallurgy approach.

Multiple silver(I)-aurates(I) have been prepared by salt metathesis reactions that act as efficient single-source precursors to colloidal gold silver alloys with the highest possible atom economy in the chemical synthesis of nanostructures. The CF3 group present on the Au cation acts as an in situ reducing agent and can be converted into CO ligands by simple hydrolysis. This ligand-mediated activation and subsequent decomposition of metal-organic precursors impose a molecular control over the nucleation process, producing homogeneously alloyed (Ag-Au) nanoparticles with an atomic Au:Ag ratio of 1:1. The concept also works for the Au-Cu system and acts as a pointer to replace Au (Ag) with less expensive (Cu) metals.

Ligand-modulated chemical and structural implications in four-, five-, and six-fold coordinated aluminum heteroaryl alkenolates.

Synthesis and characterization (gas phase, solution, and solid-state) of a series of four-, five- and six-fold coordinated heteroaryl-alkenolato aluminum complexes were performed to demonstrate the delicate interplay of structural and chemical influences of ligands in the design of new precursors for chemical vapor deposition. We are investigating the properties of heteroaryl alkenols as O^N chelating ligands [where O^N is 3,3,3-trifluoro(pyridin-2-yl)propen-2-ol (H-PyTFP), 3,3,3-trifluoro(1,3-benzimidazol-2-yl)propen-2-ol (H-BITFP), 3,3,3-trifluoro(dimethyl-1,3-oxazol-2-yl)propen-2-ol (H-DMOTFP), 3,3,3-trifluoro(1,3-benzoxazol-2-yl)propen-2-ol (H-BOTFP), 3,3,3-trifluoro(1,3-benzthiazol-2-yl)propen-2-ol (H-BTTFP), and 3,3,3-trifluoro(dimethyl-1,3-thiazol-2-yl)propen-2-ol (H-DMTTFP)] to prepare volatile and air-stable compounds. All three methyl groups in highly reactive AlMe3 could be replaced by H-PyTFP, H-BITFP, H-DMOTFP, and H-BOTFP yielding octahedral complexes of the type Al(O^N)3; under similar conditions H-BTTFP and H-DMTTFP produced heteroleptic MeAl(O^N)2 compounds with five-fold coordinated aluminum centers. Various attempts to obtain tris-alkenolato derivatives by choosing higher temperatures and prolonged reaction times were not successful. The reaction of H-PyTFP with [Al(O(t)Bu)3]2 produced the dimeric heteroleptic [Al(PyTFP)(O(t)Bu)2]2 complex with Al atoms present in both octahedral (Oh) and tetrahedral (Td) coordination in a single molecular unit. The introduction of the chelating ligand H-PyTFP in the dimeric framework of [Al(O(t)Bu)3]2 enhanced the stability against hydrolyses significantly. The tendency of Al(III) centers to preferably coordinate in Td or Oh environment was elucidated by hydrolysis studies of monomeric Al(PyTFP)3, Al(BOTFP)3, and MeAl(BTTFP)2 that produced hydroxo-bridged dimers to retain the octahedral environment for Al atoms. Surprisingly, hydrolysis of monomeric MeAl(DMTTFP)2 yielded an oxo-bridged dimer with two five-fold coordinated aluminum centers. The structural features of all new complexes were investigated in solution, vapor, and solid state by multinuclear NMR spectroscopy, EI-MS spectrometry, and single-crystal X-ray diffraction analyses, respectively.

Molecular Co(II) and Co(III) heteroarylalkenolates as efficient precursors for chemical vapor deposition of Co3O4 nanowires.

Two new cobalt precursors, Co(II)(PyCHCOCF3)2(DMAP)2 (1) and Co(III)(PyCHCOCF3)3 (2), based on Co(II) and Co(III) centers were synthesized using a redox active ligand system. The different chemical configurations of 1 and 2 and differential valence states of cobalt were confirmed by crystal structure determination and comprehensive analytical studies. Whereas 1 could not be studied by NMR due to the paramagnetic nature of the central atom, 2 was unambiguously characterized by multinuclear 1D and 2D NMR experiments in solution. Both compounds are efficient precursors for catalyst-free growth of Co3O4 nanowires on Si and Al2O3 substrates by a chemical vapor deposition process. The different valence states of cobalt species influenced their chemical decomposition pathways in the gas phase; for instance, 1 was partially oxidized (Co(2+) → Co(3+)), and 2 underwent reduction (Co(3+) → Co(2+)) to form pure cobaltite in both cases that verified the metal-ligand redox interplay. Co3O4 nanowires with nanometric diameters (50-100 nm) were obtained irrespective of the chosen cobalt precursor. Investigations on the humidity sensing behavior of CVD deposits demonstrated their potential as promising sensor materials.

Octakis(tert-butoxo)dicerium(IV) [Ce2(O(t)Bu)8]: synthesis, characterization, decomposition, and reactivity.

An advanced synthesis for the homometallic derivative [Ce2(O(t)Bu)8] (1) starting from [Ce(O(t)Bu)2{N(SiMe3)2}2] was developed. Structural characterization of a cerium(IV) complex and its decomposition products confirmed the coexistence of both ether elimination and Ce-O bond cleavage processes, which lead to the formation of [Ce3O(O(t)Bu)10] and [Ce3(O(t)Bu)11] (2) derivatives, respectively. Variable-temperature NMR spectroscopy under strict exclusion of moisture enabled insight into the decomposition processes in noncoordinating solvents and at elevated temperature. In addition, structural analysis of the heterovalent 2 and of two new complexes of the general formula [Ce2(O(t)Bu)8(L)] [L = HO(t)Bu (3), OCPh2 (4)] is described.

Heterobi- and trimetallic cerium(IV) tert-butoxides with mono-, di-, and trivalent metals (M = K(I), Ge(II), Sn(II), Pb(II), Al(III), Fe(III)).

The reaction of Cerium Ammonium Nitrate (CAN) with varying amounts of KO(t)Bu produced homometallic Ce(O(t)Bu)4(NC5H5)2 (1) and the heterometallic derivative KCe2(O(t)Bu)10 (3) characterized by X-ray diffraction and NMR spectroscopy. The oxo-alkoxide cluster Ce3O(O(t)Bu)9 (2) was obtained from a solution of cerium(IV) tetrakis(tert-butoxide) in n-heptane under stringent precautions to avoid any adventitious hydrolysis. Lewis acid-base reactions of in situ generated Ce(O(t)Bu)4(THF)2 (THF = tetrahydrofuran) with bi- and trivalent metal alkoxides [M(O(t)Bu)x]n (M = Ge, Sn; x = 2; n = 2; M = Pb, x = 2; n = 3; M = Al, Fe; x = 3; n = 2) resulted in volatile products of the general formula MCe(O(t)Bu)(4+x) (M = Al (4), Fe (5); x = 3; M = Ge (8), Sn (9), Pb (10); x = 2) in high yields. By dissolving 4 and 5 in pyridine the solvent adducts MCe(O(t)Bu)7(NC5H5) (M = Al (6), Fe (7)) were formed, whereas 8 and 9 reacted with Mo(CO)6 in boiling toluene to yield the termetallic complexes (CO)5MoM(µ2-O(t)Bu)3Ce(O(t)Bu)3 (M = Ge (11), Sn (12)). The new compounds were characterized by comprehensive spectral studies, mass spectroscopy, and single crystal X-ray diffraction analysis.

[(CF3)4Au2(C5H5N)2]--a new alkyl gold(II) derivative with a very short Au-Au bond.

A new gold(II) species [(CF(3))(4)Au(2)(C(5)H(5)N)(2)] with a very short unsupported Au-Au bond (250.62(9) pm) was generated by photo irradiation of a silver aurate, [Ag(Py)(2)][Au(CF(3))(2)], unambiguously characterized by (19)F and (109)Ag NMR studies.

Examination of the coordination sphere of Al(III) in trifluoromethyl-heteroarylalkenolato complex ions by gas-phase IRMPD spectroscopy and computational modelling.

A series of aluminium complex ions with trifluoromethyl-heteroarylalkenolato (TMHA) ligands are studied by gas-phase infrared multiphoton-dissociation (IRMPD) spectroscopy and computational modelling. The selected series of aluminium TMHA complex ions are promising species for the initial study of intrinsic binding characteristics of Al(III) cations in the gas phase as corresponding molecular ions. They are readily available for examination by (+) and (-) electrospray ionization mass spectrometry (ESI-MS) by spraying of [Al(3+)⋅(L(-))(3)] solutions. The complex ions under investigation contain trivalent Al(3+) cations with two chelating anionic enolate ligands, [Al(3+)⋅(L(-))(2)](+), providing insights in the nature of the heteroatom-Al bonds. Additionally, the structure of a deprotonated benzimidazole ligand, L(-,) and an anionic complex ion of Al(III) with two doubly deprotonated benzimidazole ligands, [Al(3+)⋅(L(2-))(2)](-), are examined by (-)ESI-IRMPD spectroscopy. Experimental and computational results are highly consistent and allow a reliable identification of the ion structures. In all complex ions examined the planar TMHA ligands are oriented perpendicular to each other around the metal ion, leading to a tetrahedral coordination sphere in which aluminium interacts with the enolate oxygen and heteroaryl nitrogen atoms available in each of the bidentate ligands.

Novel air-stable and volatile bis(pyridylalkenolato)palladium(II) and -platinum(II) derivatives.

Six novel homoleptic palladium(II) and platinum(II) complexes of donor-substituted alkenol ligands [PyCHC(R)OH; Py = pyridine, R = CH(3), CF(3), C(2)F(5), C(3)F(7)] of the general formula M[PyCHC(R)O](2) (M = Pd, Pt) were synthesized by reacting the deprotonated ligands with PdCl(2) and K(2)PtCl(4), respectively. Molecular structures, revealed by single-crystal X-ray diffraction analyses, showed a square-planar arrangement of ligands around palladium and platinum centers, with the pyridine-ring nitrogen atoms situated in a mutually trans position. The monomeric nature of the compounds in the solution state was confirmed by multinuclear ((1)H, (13)C, and (19)F) NMR spectroscopy. Thermal decomposition profiles recorded under a nitrogen atmosphere suggested their potential as volatile precursors to palladium and platinum materials. The volatility was increased upon elongation of the perfluoroalkyl chain, which suppressed the intermolecular interactions, as is evident in crystal packings. The volatility of these compounds was attributed to bidentate chelation of the alkenol units and cooperativity among the electron-back-donating nitrogen atom and interplay of electron-withdrawing C(x)F(y) groups, resulting in an effective steric shielding of the metal atoms.

New iso-propoxides, tert-butoxides and neo-pentoxides of niobium(V): synthesis, structure, characterization and stabilization by trifluoroheteroarylalkenolates and pyridine ligands.

The synthesis and characterization of nine new heteroleptic alkoxides of niobium is described. Metathesis reactions of Nb(2)Cl(10) with (t)BuCH(2)OH and pyridine (py) or 4-dimethylaminopyridine (DMAP) affords monomeric octahedral complexes Nb(OCH(2)(t)Bu)(5)py (1) and Nb(OCH(2)(t)Bu)(5)DMAP (2), respectively, in high yields (>60%). The same reaction with (t)BuOH resulted in a chloro functionalized alkoxide Nb(O(t)Bu)(4)pyCl (3) and could not be pushed to complete removal of remaining Cl(-) ligand. The introduction of a chelating bidental ligand 3,3,3-trifluoro-1-(pyridine-2-yl)propen-2-ol (2-PyCHCOHCF(3)) (4'') in the dimeric framework of Nb(2)(O(i)Pr)(10) (4') produced a heteroleptic, monomeric niobium complex Nb(O(i)Pr)(4)(2-PyCHCOCF(3)) (4) with significantly enhanced stability and volatility. As a comparison to (4), five different heteroaryl systems (5-9) with the same side chain have been synthesized and examined in order to understand the influence upon physio-chemical properties. All the new compounds (1-9) have been characterized by microanalysis, variable temperature multinuclear NMR spectroscopy, mass spectrometry, thermal analysis and single crystal X-ray diffraction studies ((3), (4) and (9)). The molecular structure of (3) revealed mononuclear species with Nb atoms present in the distorted octahedral environment of four (t)BuO, one chloride and one pyridine ligand. Compounds (4) and (9) consisting of four (i)PrO and a trifluoroheteroarylenolate exhibited a stronger distortion in the molecular geometry due to the rigidity of chelating ß-alkenolate moiety.

Perfluoroalkyl(dithiocarbamato) tellurium(II) compounds.

[NMe(4)][R(f)Te(SC(S)NR(2))(2)] derivatives are selectively formed by the oxidation of [NMe(4)]TeR(f) (R(f) = CF(3), C(2)F(5)) with [R(2)NC(S)S](2) (NR(2) = NEt(2), NBz(2), N(CH(2))(4)) in almost quantitative yields. An alternative route to obtain the dithiocarbamato complex anions offer reactions of Te[SC(S)NR(2)](2) (NR(2) = NEt(2), NBz(2)) with equimolar amounts of Me(3)SiR(f) and [NMe(4)]F. Some of the derivatives were recrystallized with bulky cations in order to determine the crystal structures. Structural elucidation by diffraction methods exhibit the structural feature of a distorted pentagonal planar environment (resembling "butterflies") around the tellurium centres. The carbamato tellurates can be transferred easily into the neutral derivatives, R(f)TeSC(S)NR(2), upon treatment with Ag[BF(4)]. In solution they equilibrate with Te(2)(R(f))(2) and [R(2)NC(S)S](2) and finally are transformed into Te(R(f))(2), Te[SC(S)NR(2)](2), and Te[SC(S)NR(2)](4), respectively. All compounds are fully characterized by NMR spectroscopic methods ((1)H, (13)C, (19)F, (125)Te). Additionally, synthesis and characterization of the hitherto unknown derivative [NMe(4)]TeC(2)F(5) are described.

A fluent transition from triiodide, I3-, to tris(trifluoromethyltellurate)(1-), [(TeCF3)3]- --a structural study.

A complete series of compounds with the anions [(TeCF3)(3-x)I(x)]- (x = 0-2) had been prepared and characterised in the solid state and by NMR spectroscopic methods. Dynamic behaviour in solution can be assumed for [(TeCF3)3]- and [(TeCF3)2I]-, while in the solid state all three bis(triphenylphosphoranyliden)ammonium (PNP) salts resemble structures found in triiodides. The molecular structures of [PNP][(TeCF3)(3-x)I(x)]- (x = 0-2) are discussed in comparison with [PNP]I3, I2, and Te2(CF3)2. On this basis, the structures of the [(TeCF3)3]- and [(TeCF3)I2]- ions are comparable to symmetric I3- ions, while the [(TeCF3)2I]- ion resembles an asymmetric I3- unit.

How trimethyl(trifluoromethyl)silane reacts with itself in the presence of naked fluoride--a one-pot synthesis of bis([15]crown-5)cesium 1,1,1,3,5,5,5-heptafluoro-2,4-bis(trifluoromethyl)pentenide.

Reactions of trimethyl(trifluoromethyl)silane in the presence of "naked" fluoride proceed up to a temperature of +5 degrees C mainly with formation of [Me3Si(CF3)2]-. A further rise of temperature up to about 20 degrees C gives evidence for the formation of a salt with the 1,1,1,2,3,6,6,6-octafluoro-2,4,4,5,5-pentakis(trifluoromethyl)hexan-3-ide anion. This intermediate decomposes at room temperature into the 1,1,1,3,5,5,5-heptafluoro-2,4-bis(trifluoromethyl)pentenide anion. The bis([15]crown-5)cesium salt, [Cs([15]crown-5)2][(CF3)2CCFC(CF3)2] has been characterized unambiguously as the stable final product of this reaction sequence. Thermal decomposition of this salt opens a convenient nontoxic route to obtain 1,1,3,3-tetrakis(trifluoromethyl)allene, (F3C)2C=C=C(CF3)2.

Alkynylxenon(II) fluorides.

Alkynylxenon(II) fluorides, RCC(triple bond)XeF, have been prepared from the reactions of the corresponding trimethyl(alkynyl)silanes, Me3(-)SiC(triple bond)CR, and XeF2 in the presence of [NMe4F in common organic solvents at low temperature. The existence of the linear unit C(triple bond)C-Xe-F was proved for PhC(triple bond)CXeF by the 19F-13C NMR correlation method using the HMBC pulse sequence.