Aggregation of donor base stabilized 2-thienyllithium in a single crystal and in solution: distances from X-ray diffraction and the nuclear Overhauser effect

Various 2-thienyllithium derivatives were investigated in the solid state by X-ray diffraction and in solution by 2D NMR experiments. The determined structures of [(Et(2)O)Li(C(4)H(3)S)](4) (1), [(THF)(2)Li(C(4)H(3)S)](2) (2), [(DME)Li(C(4)H(3)S)](2) (3), [(TMEDA)Li(C(4)H(3)S)](2) (4), and [(PMDETA)Li(C(4)H(3)S)] (5) (DME = 1,2-dimethoxyethane, TMEDA = N,N,N',N'-tetramethylethylene-1,2-diamine, and PMDETA = N,N,N',N",N"-pentamethyldiethylenetriamine) were solved in nondonating toluene and provide firm ground for diffusion-ordered NMR spectroscopy as well as heteronuclear Overhauser enhancement NMR spectroscopy. The distance relation of nuclear Overhauser effects with a factor of r(-6) is employed to gain further insight into the aggregation degree of 1-5 in solution. Comparison of the slope provided by the linear region of the buildup curves and of the ∑r(-6) calculated distances from the crystal structures offers a handle to judge the structure retention versus conversion in solution. The structures of 3-5 are maintained in toluene solution. The data of 2, however, indicate a partial dissociation or a rapid exchange between the vertices of a tetrameric core and free THF molecules. Auxiliary exchange spectroscopy investigations showed that the signals of the nitrogen donor base containing compounds 4 and 5 exchange with the signals of nonlithiated thiophene. This is explained by exchange of the deuterium by a hydrogen atom via lithiation of toluene molecules.     

(MeLi)4(dem)1.5]infinity] and [(thf)3Li3M3[(NtBu)3S--how to reduce aggregation of parent methyllithium

Organolithium compounds play the leading role among the organometallic reagents in synthesis and in industrial processes. Up to date industrial application of methyllithium is limited because it is only soluble in diethyl ether, which amplifies various hazards in large-scale processes. However, most reactions require polar solvents like diethyl ether or THF to disassemble parent organolithium oligomers. If classical bidentate donor solvents like TMEDA (TMEDA= N,N,N',N'tetramethyl-1,2-ethanediamine) or DME (DME=1,2-dimethoxyethane) are added to methyllithium, tetrameric units are linked to form polymeric arrays that suffer from reduced reactivity and/or solubility. In this paper we present two different approaches to tune methyllithium aggregation. In [[(MeLi)4(dem)1,5)infinity] (1; DEM = EtOCH2OEt, diethoxymethane) a polymeric architecture is maintained that forms microporous soluble aggregates as a result of the rigid bite of the methylene-bridged bidentate donor base DEM. Wide channels of 720 pm in diameter in the structure maintain full solubility as they are coated with lipophilic ethyl groups and filled with solvent. In compound 1 the long-range Li3CH3...Li interactions found in solid [[(MeLi)4]infinity] are maintained. A different approach was successful in the disassembly of the tetrameric architecture of [((MeLi)4]infinity]. In the reaction of dilithium triazasulfite both the parent [(MeLi)4] tetramer and the [[Li2[(NtBu)3S]]2] dimer disintegrate and recombine to give an MeLi monomer stabilized in the adduct complex [(thf)3Li3Me-[(NtBu)3S]] (2). One side of the Li3 triangle, often found in organolithium chemistry, is shielded by the tripodal triazasulfite, while the other face is mu3-capped by the methanide anion. This Li3 structural motif is also present in organolithium tetramers and hexamers. All single-crystal structures have been confirmed through solid-state NMR experiments to be the same as in the bulk powder material.     

Allylpalladium dimers with metals connected by binucleating dithiooxamidates in two different coordination modes: solution behavior and solid-state structure

A series of allylpalladium dimers having metals connected by binucleating dialkyldithiooxamidate [N(R)SC-CS(R)N](2-) [R = methyl, ethyl, isopropyl, benzyl, isoamyl, (S)-1-(1-phenyl)ethyl, meso-(1-phenyl)ethyl, and rac-(1-phenyl)ethyl] were prepared by reacting the monochelate [(η(3)-allyl)Pd(N(R)SC-CS(R)NH κ-S,S Pd)] with [(η(3)-allyl)PdCl](2) in chloroform. At low temperature (20 °C), the bimetallic complexes [(η(3)-allyl)Pd](2)(μ-dialkyldithiooxamidate κ-N,N' Pd, κ-S,S' Pd') (kinetic compounds) are formed in a short reaction time (10 min). At a higher temperature (50 °C) and a longer reaction time (24 h), the corresponding bimetallic isomers [(η(3)-allyl)Pd](2)(μ-dialkyldithiooxamidate κ-N,S Pd, κ-N',S' Pd') (thermodynamic compounds) are obtained. Both kinetic and thermodynamic compounds can exist as endo or exo isomers, depending on the reciprocal orientation of the allyl cuspids. Both endo and exo isomers are only detectable in solution when the alkyl substituents are chiral alkyl groups. Moreover, diffractometric modeling agrees with the presence of both isomers in the solid state even when the alkyl substituent is an achiral alkyl group. In a chloroform solution, endo and exo isomers undergo isomeric conversion owing to the apparent allyl rotation that follows the Pd-N bond rupture in the (η(3)-allyl)Pd(N^N) frame of kinetic compounds or in the (η(3)-allyl)Pd(N^S) frame of thermodynamic compounds. The dithiooxamidate [N(R)SC-CS(R)N](2-), when engaged in a κ-N,S Pd, κ-N',S' Pd' coordination mode, behaves as a hybrid hemilabile binucleating ligand. At room temperature and in a chloroform solution, the kinetic compounds rearrange into the thermodynamically more stable isomers in about 3 or 4 days. The higher stability of the thermodynamic species was evaluated by means of computational studies in accordance with the maximum hardness principle. Finally, the crystal structures of [(η(3)-allyl)Pd](2)(μ-diethyldithiooxamidate κ-N,S Pd, κ-N',S' Pd'), [(η(3)-allyl)Pd](2)(μ-meso-(1-phenyl)ethyldithiooxamidate κ-N,S Pd, κ-N',S' Pd'), and [(η(3)-allyl)Pd](2)(μ-rac-(1-phenyl)ethyldithiooxamidate κ-N,N' Pd, κ-S,S' Pd') are reported.     

Homoleptic, heteroleptic and mixed-valent thallium and indium complexes of multidentate chalcogen-centred PCP-bridged ligands

The metathetical reaction of [Li(TMEDA)][HC(PPh(2)Se)(2)] ([Li(TMEDA)]1) with TlOEt in a 1:1 molar ratio afforded a homoleptic Tl(I) complex as an adduct with LiOEt, Tl[HC(PPh(2)Se)(2)]·LiOEt (7), which undergoes selenium-proton exchange upon mild heating (60 °C) to give the mixed-valent Tl(I)/Tl(III) complex {[Tl][Tl{(Se)C(PPh(2)Se)(2)}(2)]}(∞) (8). Treatment of TlOEt with [Li(TMEDA)](2)[(SPh(2)P)(2)CE'E'C(PPh(2)S)(2)] (3b, E' = S; 3c, E' = Se) in a 2:1 molar ratio produced the binuclear Tl(i)/Tl(i) complexes Tl(2)[(SPh(2)P)(2)CE'E'C(PPh(2)S)(2)] (9b, E' = S; 9c, E' = Se), respectively. Selenium-proton exchange also occurred upon addition of [Li(TMEDA)]1 to InCl(3) to yield the heteroleptic complex (TMEDA)InCl[(Se)C(PPh(2)Se)(2)] (10a). Other examples of this class of In(III) complex, (TMEDA)InCl[(E')C(PPh(2)E)(2)] (10b, E = E' = S; 10c, E = S, E' = Se) were obtained via metathesis of InCl(3) with [Li(TMEDA)](2)[(E')C(PPh(2)E)(2)] (2b, E = E' = S; 2c, E = S, E' = Se, respectively). All new compounds have been characterized in solution by (1)H and (31)P NMR spectroscopy and the solid-state structures have been determined for 8, 9c and 10a-c by single-crystal X-ray crystallography. Complex 8 is comprised of Tl(+) ions that are weakly coordinated to octahedral [Tl{(Se)C(PPh(2)Se)(2)}(2)](-) anions to give a one-dimensional polymer. The complex 9c is comprised of two four-coordinate Tl(+) ions that are each S,S',S',Se bonded to the hexadentate [(SPh(2)P)(2)CSeSeC(PPh(2)S)(2)](2-) ligand in which d(Se-Se) = 2.531(2) ?. The six-coordinate In(III) centres in the distorted octahedral complexes 10a-c are connected to a tridentate [(E')C(PPh(2)E)(2)](2-) dianion, a chloride ion and a neutral bidentate TMEDA ligand.     

Main group multiple C-H/N-H bond activation of a diamine and isolation of a molecular dilithium zincate hydride: experimental and DFT evidence for alkali metal-zinc synergistic effects

The surprising transformation of the saturated diamine (iPr)NHCH(2)CH(2)NH(iPr) to the unsaturated diazaethene [(iPr)NCH═CHN(iPr)](2-) via the synergic mixture nBuM, (tBu)(2)Zn and TMEDA (where M = Li, Na; TMEDA = N,N,N',N'-tetramethylethylenediamine) has been investigated by multinuclear NMR spectroscopic studies and DFT calculations. Several pertinent intermediary and related compounds (TMEDA)Li[(iPr)NCH(2)CH(2)NH(iPr)]Zn(tBu)(2) (3), (TMEDA)Li[(iPr)NCH(2)CH(2)CH(2)N(iPr)]Zn(tBu) (5), {(THF)Li[(iPr)NCH(2)CH(2)N(iPr)]Zn(tBu)}(2) (6), and {(TMEDA)Na[(iPr)NCH(2)CH(2)N(iPr)]Zn(tBu)}(2) (11), characterized by single-crystal X-ray diffraction, are discussed in relation to their role in the formation of (TMEDA)M[(iPr)NCH═CHN(iPr)]Zn(tBu) (M = Li, 1; Na, 10). In addition, the dilithio zincate molecular hydride [(TMEDA)Li](2)[(iPr)NCH(2)CH(2)N(iPr)]Zn(tBu)H 7 has been synthesized from the reaction of (TMEDA)Li[(iPr)NCH(2)CH(2)NH(iPr)]Zn(tBu)(2)3 with nBuLi(TMEDA) and also characterized by both X-ray crystallographic and NMR spectroscopic studies. The retention of the Li-H bond of 7 in solution was confirmed by (7)Li-(1)H HSQC experiments. Also, the (7)Li NMR spectrum of 7 in C(6)D(6) solution allowed for the rare observation of a scalar (1)J(Li-H) coupling constant of 13.3 Hz. Possible mechanisms for the transformation from diamine to diazaethene, a process involving the formal breakage of four bonds, have been determined computationally using density functional theory. The dominant mechanism, starting from (TMEDA)Li[(iPr)NCH(2)CH(2)N(iPr)]Zn(tBu) (4), involves the formation of a hydride intermediate and leads directly to the observed diazaethene product. In addition the existence of 7 in equilibrium with 4 through the dynamic association and dissociation of a (TMEDA)LiH ligand, also provides a secondary mechanism for the formation of the diazaethene. The two reaction pathways (i.e., starting from 4 or 7) are quite distinct and provide excellent examples in which the two distinct metals in the system are able to interact synergically to catalyze this otherwise challenging transformation.     

Co-complexes of ortho-dilithiated thiophenol or 2-trimethylsilylthiophenol with lithiated TMEDA molecules: synthesis, crystal structures and theoretical studies (TMEDA = N,N,N',N'-tetramethylethylenediamine)

When an excess of nBuLi was used in the ortho-dilithiation of thiophenol or 2-trimethylsilylthiophenol in the presence of TMEDA (TMEDA = N,N,N',N'-tetramethylethylenediamine), deprotonation of TMEDA occurred and crystals of [Li3{(2-S-C6H4)(CH2MeNCH2CH2NMe2)(TMEDA)}]2 (1) or [Li4{(2-S-3-SiMe3-C6H3)(CH2MeNCH2CH2NMe2)2(TMEDA)}] (2) were obtained. Molecular orbital calculations on gas-phase 1 and 2 at the DFT B3LYP/6-31G(d) level reproduce the experimental structures fairly well. In spite of the short Li...Li distances, total electron density representations do not support the existence of Li...Li interactions.     

Synthesis, NMR characterisation and X-ray structures of mixed chalcogenido PNP ligands containing tellurium: crystal structures of SeiPr2PNP(H)iPr2 and [NaN(EPiPr2)2]infinity (E = Se, Te)

Reaction of HN(PiPr2)2 with one equivalent of selenium in hexane at room temperature yields the monoselenide as the P-H tautomer Se=PiPr2-N=P(H)iPr2 (2b). Deprotonation of 2b with n butyllithium in the presence of TMEDA at -78 degrees C followed by addition of tellurium produces the air-sensitive, mixed chalcogenido complex [(TMEDA)Li(SePiPr2)(TePiPr2)N] (8Li) in >97% purity after recrystallisation. Similarly, deprotonation of Te=PiPr2-N=P(H)iPr2 (2c), followed by addition of sulfur, gives the sulfur analogue [(TMEDA)Li(SPiPr2)(TePiPr2)N] (7Li) in >99% purity. The symmetrical complexes [(TMEDA)Li(SePiPr2)2N] (4Li) and [(TMEDA)Li(TePiPr2)2N] (5Li) are produced by similar methods. Compounds 2b, 4Li, 5Li, 7Li and 8Li were characterised in solution by multinuclear (1H, 31P, 77Se and 125Te) NMR spectroscopy and their solid-state structures were determined by X-ray crystallography. The X-ray crystal structures of the polymeric chains [NaN(EPiPr2)2]infinity (4Na, E = Se and 5Na, E = Te) are also reported.     

Anionic polymerization of 1,3‐cyclohexadiene with alkyllithium/amine system in an aromatic hydrocarbon solvent: Predominant formation of 1,2‐addition product

Steric hindrance of the amine strongly affected the formation of the dominant 1,2‐addition product from the anionic polymerization of 1,3‐cyclohexadiene (1,3‐CHD) initiated by the alkyllithium (RLi)/amine system in an aromatic hydrocarbon solvent. 1,2‐Cyclohexadiene (1,2‐CHD)/1,4‐cyclohexadiene (1,4‐CHD) unit molar ratios from 85/15 to 93/7 were obtained using an RLi/N,N,N′,N′‐tetramethylethylenediamine (TMEDA) system in toluene. The C? Li bonds of poly(1,3‐cyclohexadienyl)lithium (PCHDLi)/TMEDA complex in toluene appeared to be strongly polarized with small steric hindrance. Intermolecular forces contributing to the aggregation were strong for high‐molecular‐weight poly(1,3‐cyclohexadiene) (PCHD) consisting of almost all 1,2‐CHD units. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6604–6611, 2008     

Synthesis and structural characterization of silanethiolato complexes having tert-butyldimethylsilyl and trimethylsilyl groups

Treatment of cyclotrisilathiane (Me2SiS)3 with 3 equiv. of RLi (R = Me, But) in hexane-Et2O afforded the lithium silanethiolates LiSSiMe2R, and the tmeda adduct [(tmeda)LiSSiMe2But]2 1 (tmeda =N,N,N',N'-tetramethylethylenediamine) was isolated in the case of R = But. Reaction of Fe(CH3CN)2(CF3SO3)2, CoCl2, and [Cu(CH3CN)4](PF6) with 1 gave rise to the silanethiolato complexes M(SSiMe2But)2(tmeda)(M = Fe 2, Co 3), and [Cu(SSiMe2But)]4 4, respectively. Complexes (C5H5)2Ti(SSiMe2R)2(R = Me 5, But 6) and Ni(SSiMe2R)2(dppe)[R = Me 7, But 8; dppe = 1,2-bis(diphenylphosphino)ethane] were prepared from treatments of (C5H5)2TiCl2 and NiCl2(dppe) with the corresponding lithium silanethiolates. Complex 7 readily reacted with (C5H5)TiCl3 to produce the Ti-Ni heterobimetallic compound (C5H5)TiCl(mu-S)2Ni(dppe) 9, in which silicon-sulfur bond cleavage took place. Characterization of all compounds through spectroscopic techniques and elemental analyses are also described. X-Ray structural data for compounds 1 and 3-9 are reported.     

Photoinduced Fe-Cp bond cleavage and insertion reactions of strained silicon- and sulphur-bridged [1]ferrocenophanes in the presence of transition-metal carbonyls

The photochemical reactions of the moderately strained sila[1]ferrocenophane [Fe(eta-C(5)H(4))(2)SiPh(2)] (1) and the highly strained thia[1]ferrocenophane [Fe(eta-C(5)H(4))(2)S] (8) with transition-metal carbonyls ([Fe(CO)(5)], [Fe(2)(CO)(9)] and [Co(2)(CO)(8)]) have been studied. The use of metal carbonyls has allowed the products of photochemically induced Fe-cyclopentadienyl (Cp) bond cleavage reactions in the [1]ferrocenophanes to be trapped as stable, characterisable products. During the course of these studies the synthesis of 8 from [Fe(eta-C(5)H(4)Li)(2)TMEDA] (TMEDA=N,N,N',N'-tetramethylethylenediamine) and S(SO(2)Ph)(2) has been significantly improved by a change of reaction solvent and temperature. Photochemical reaction of 1 with excess [Fe(CO)(5)] in THF gave the dinuclear complex [Fe(2)(CO)(2)(mu-CO)(2)(eta-C(5)H(4))(2)SiPh(2)] (9). The analogous photolytic reaction of 8 with [Fe(CO)(5)] in THF gave cyclic dimer [Fe(eta-C(5)H(4))(2)S](2) (10) and [Fe(2)(CO)(2)(mu-CO)(2)(eta-C(5)H(4))(2)S] (11), with the former being the major product. Photolysis of 1 with [Co(2)(CO)(8)] afforded the remarkable tetrametallic dimer [(CO)(2)Co(eta-C(5)H(4))SiPh(2)(eta-C(5)H(4))Fe(CO)(2)](2) (13). The corresponding photochemical reaction of 8 with [Co(2)(CO)(8)] gave a trimetallic insertion product in high conversion, [Co(CO)(4)(CO)(2)Fe(eta-C(5)H(4))S(eta-C(5)H(4))Co(CO)(2)] (14). These reactivity studies show that UV light promotes Fe-Cp bond cleavage reactions of both of the [1]ferrocenophanes 1 and 8. We have found that, whereas the less strained sila[1]ferrocenophane 1 requires photoactivation for Fe-Cp bond insertions to occur, the highly strained thia[1]ferrocenophane 8 undergoes both irradiative and non-irradiative insertions, although the latter occur at a slower rate. Our results suggest that such photoinduced bond cleavage reactions may be general and applicable to other related strained organometallic rings with pi-hydrocarbon ligands.     

Low-valent chemistry of cobalt amide. Synthesis and structural characterization of cobalt(II) amido, aryloxide, and thiolate compounds

The binuclear cobalt(II) amide complex [(CoL2)2-(TMEDA)] (1) [L = N(Si(t)BuMe2)(2-C5H3N-6-Me); TMEDA = Me2NCH2CH2NMe2] has been synthesized by the reaction of anhydrous CoCl2 with 2 equiv of [Li(L)(TMEDA)]. X-ray crystallography revealed that complex 1 consists of two [CoL2] units linked by one TMEDA ligand molecule, which binds in an unusual N,N'-bridging mode. Protolysis of 1 with the bulky phenol Ar(Me)OH (Ar(Me) = 2,6-(t)Bu2-4-MeC6H2) and thiophenol ArSH (Ar = 2,4,6-(t)Bu3C6H2) gives the neutral monomeric cobalt(II) bis(aryloxide) [Co(OAr(Me))2(TMEDA)] (2) and dithiolate [Co(SAr)2(TMEDA)] (3), respectively. Complexes 1-3 have been characterized by mass spectrometry, microanalysis, magnetic moment, and melting-point measurements, in addition to X-ray crystallography.     

Synthesis and characterisation of new bimetallic alkali metal-magnesium mixed diisopropylamide-acetylides: structural variations in bimetallic lithium- and sodium-heteroleptic magnesiates

The reactivity of the Br?nsted basic mixed-metal tris-amide compounds of empirical formula [MMg(N(i)Pr2)3] [where M = Li (1), Na (2)] towards phenylacetylene (HC[triple bond, length as m-dash]CPh) has been investigated and has led to the synthesis of a series of mixed-metal acetylido-amido-magnesiates. Thus, 1 and 2 molar equivalents of the alkyne with [MMg(N(i)Pr2)3] produce heteroanionic bis(amido)-mono(acetylido) [LiMg(N(i)Pr2)2(C[triple bond, length as m-dash]CPh)]2 (3) and mono(amido)-bis(acetylido) [(TMEDA) x Na(C[triple bond, length as m-dash]CPh)2Mg(N(i)Pr2)](2) (4) (TMEDA = N,N,N',N'-tetramethylethylenediamine) respectively. X-Ray crystallographic studies reveal that the new compounds adopt a different structural motif. Complex can be defined as an inverse crown structure, having a cationic eight-atom [(NaNMgN)2]2+ ring which hosts in its core two acetylido ligands. On the other hand, adopts a tetranuclear NaMgMgNa near-linear chain arrangement, held together by acetylido and amido bridges. The metal coordination geometries in both structures are distorted tetrahedral, and the sodium cations at the end of the mixed-metal chain carry terminal chelating TMEDA ligands. 1H and 13C NMR spectral data recorded in C6D6 solutions are also reported for and , and are consistent with the solid-state structures being retained in solution.     

Anionic Snieckus-Fries rearrangement: solvent effects and role of mixed aggregates

Lithiated aryl carbamates (ArLi) bearing methoxy or fluoro substituents in the meta position are generated from lithium diisopropylamide (LDA) in THF, n-BuOMe, Me2NEt, dimethoxyethane (DME), N,N,N',N'-tetramethylethylenediamine (TMEDA), N,N,N',N'-tetramethylcyclohexanediamine (TMCDA), and hexamethylphosphoramide (HMPA). The aryllithiums are shown with (6)Li, (13)C, and (15)N NMR spectroscopies to be monomers, ArLi-LDA mixed dimers, and ArLi-LDA mixed trimers, depending on the choice of solvent. Subsequent Snieckus-Fries rearrangements afford ArOLi-LDA mixed dimers and trimers of the resulting phenolates. Rate studies of the rearrangement implicate mechanisms based on monomers, mixed dimers, and mixed trimers.     

Mixed guanidinato/alkylimido/azido tungsten(VI) complexes: synthesis and structural characterization

A series of structurally characterized new examples of pentacoordinated heteroleptic tungsten(VI)-guanidinates complexes are described. Starting out from [WCl(2)(Nt-Bu)(2)py(2)] (1) (py = pyridine) and the guanidinato transfer reagents (TMEDA)Li[(Ni-Pr)(2)CNi-Pr(2)] (2a) (TMEDA = N,N,N',N'-tetramethylethylendiamine) and [Li(NC(NMe(2))(2))](x) (2b), the title compounds [WCl(Nt-Bu)(2)[(Ni-Pr)(2)CNi-Pr(2)]] (3) and [W(Nt-Bu)(2)Cl{NC(NMe(2))(2)]](2) (6) were selectively formed by the elimination of one mole equivalent of lithium chloride. The isopropyl-substituted guanidinato ligand [(Ni-Pr)(2)CNi-Pr(2)} of monomeric 3 is N(1),N(3)-bonded to the tungsten center. The introduction of the sterically less-demanding tetramethyl guanidinato ligand [NC(NMe(2))(2)] expectedly leads to dimeric 6 exhibiting a planar W(2)N(2) ring with the guanidinato group bridging the two tungsten centers via the deprotonated imino N-atom. The remaining chloro ligand of 3 is labile and can be substituted by sterically less-crowded groups such as dimethylamido or azido that yield the presumably monomeric compounds 4 and 5, respectively. A similar treatment of 6 with sodium azide yields the dimeric azido derivative 7. Reacting [WCl(2)(Nt-Bu)(2)py(2)] directly with an excess of sodium azide leads to the dimeric bis-azide species [[W(Nt-Bu)(2)(N(3))(mu(2)-N(3))py](2)]. The new compounds were fully characterized by single-crystal X-ray diffractometry (except 2, 4, and 5), NMR, IR, and mass-spectroscopy as well as elemental analysis. Compound 5, [W(N(3))(Nt-Bu)(2)[(Ni-Pr)(2)CNi-Pr(2)]], can be sublimed at 80 degrees C, 1 Pa.     

Novel nucleophilic reactivity of disulfido ligands coordinated parallel to M-M (M = Rh, Ir) bonds

Reaction of trans-[(MCp)(2)(mu-CH(2))(2)Cl(2)] (M = Rh, Ir; Cp = eta(5)-C(5)Me(5)) with Li(2)S(2) afforded the disulfido complexes [(MCp)(2)(mu-CH(2))(2)(mu-S(2)-S:S')] which were easily oxidized by O(2) to give the oxygenated complexes [(MCp)(2)(mu-CH(2))(2)(mu-SSO(2)-S:S')]. Although [(RhCp)(2)(mu-CH(2))(2)(mu-S(2)-S:S')] gave a complicated mixture when reacted with CH(2)Cl(2) or CHCl(3), [(IrCp)(2)(mu-CH(2))(2)(mu-S(2)-S:S')] reacted with both CH(2)Cl(2) and CHCl(3) to give the dithioformato complex [(IrCp)(2)(mu-CH(2))(2)(mu-S(2)CH-S:S')]Cl and the cyclotetrasulfido complex [((IrCp)(2)(mu-CH(2))(2))(2)(mu-S(4)-S:S':S":S"')]Cl(2). The oxygenated complexes [(RhCp)(2)(mu-CH(2))(2)(mu-SSO(2)-S:S')] reacted with hydrocarbyl halides to afford bridging hydrocarbyl thiolato complexes accompanied by the generation of SO(2) gas. These complexes have been characterized by NMR spectroscopy, ESI-MS, and X-ray diffraction.     

NMR studies of structure and reorganization dynamics of an [6Li]-allylic lithium compound complexed to [14N,15N]-N,N,N',N'-tetramethylethylenediamine: inversion and ligand lithium exchange

Proton, 13C, 6Li, and 15N NMR line-shape studies of exo,exo-1-trimethylsilyl-3-(dimethylethylsilyl)allyllithium-6Li complexed to [14N,15N]-N,N,N',N'-tetramethylethylenediamine (TMEDA) 2 as a function of temperature and of added diamine reveal the dynamics of three fast equilibrium reorganization processes. These are (with DeltaH values in kilocalories per mole and DeltaS values in entropic units): mutual exchange of lithium between two 2 molecules (6.3, -21), exchange of TMEDA between its free and complexed states (5.0 and -22), and first-order transfer of complexed ligand between the allyl faces (7.0 and -20). Intermediates that are dimeric in TMEDA are proposed for the first two of these reorganization processes.     

Synthetic and structural investigations of alkali metal diamine bis(phenolate) complexes

Two lithium and one sodium diamine bis(phenolate) complexes have been prepared and characterised by X-ray crystallography and NMR spectroscopy. Two parent diamine bis(phenol) ligands were utilised in the study (1-H2 and 2-H2). Dimeric (1-Li2)(2) was prepared by treating 1-H2 with two molar equivalents of n-butyllithium in hydrocarbon solvent. It adopts a ladder-like structure in the solid state, which appears to deaggregate in C6D6 solution. The monomeric (hence, dinuclear) TMEDA-solvated species [2-Li(2).(TMEDA)] has two chemically unique Li atoms in the solid state and is prepared by reacting 2-H2 with two molar equivalents of n-butyllithium in hydrocarbon solvent, in the presence of N,N,N',N'-tetramethylethylenediamine (TMEDA). Finally, the dimeric sodium-based [2-Na(2) x (OEt2](2) was prepared by reacting 1-H2 with two molar equivalents of freshly prepared n-butylsodium in a hydrocarbon-diethyl ether medium. The complex adopts a Na4O4) cuboidal structure in the solid state, which appears to remain intact in C6D6 solution.     

Synthesis and structures of monomeric magnesium, calcium, strontium, and barium amides involving the N,N-(2,4,6-trimethylphenyl)(trimethylsilyl)amido ligand

An extended family of aryl-substituted alkaline earth metal silylamides M{N(2,4,6-Me3C6H2)(SiMe3)}donor(n) was prepared using alkane elimination (Mg), salt elimination (Ca, Sr, Ba), and direct metalation (Sr, Ba). Three different donors, THF, TMEDA (TMEDA = N,N,N',N'-tetramethylethylenediamine), and PMDTA (PMDTA = N,N,N',N',N'-pentamethyldiethylenetriamine) were employed to study their influence on the coordination chemistry of the target compounds, producing monomeric species with the composition M{N(2,4,6-Me3C6H2)(SiMe3)}2(THF)2 (M = Mg, Ca, Sr, Ba), M{N(2,4,6-Me3C6H2)(SiMe3)}2TMEDA (M = Ca, Ba), and M{N(2,4,6-Me3C6H2)(SiMe3)}2PMDTA (M = Sr, Ba). For the heavier metal analogues, varying degrees of agostic interactions are completing the coordination sphere of the metals. Compounds were characterized using IR and NMR spectroscopy in addition to X-ray crystallography.     

f-Element disiloxanediolates: novel Si-O-based inorganic heterocycles

The preparation and structural characterization of scandium and f-element complexes derived from the disiloxanediolate dianion, [(Ph2SiO)2O]2-, are reported. Reactions of in situ prepared Ln[N(SiMe3)2]3 (Ln = Eu, Sm, Gd) with (Ph2SiOH)2O in different stoichiometries afforded the lanthanide disiloxanediolates [Eu[[(Ph2SiO)2O]Li(Et2O)]3] (1), [[[(Ph2SiO)2O]Li(dme)]2SmCl(dme)] (2), and [[[((Ph2SiO)2O]Li(thf)2]2GdN(SiMe3)2] (3). In situ formed (Ph2SiOLi)2O reacted with anhydrous NdBr3 (molar ratio 3:1) to give polymeric [[Nd[(Ph2SiO)2O]3[mu-Li(thf)]2[mu2LiBrLi(thf)(Et2O)]]n] (4). Treatment of 3 with Ph2Si(OH)2 in the presence of acetonitrile yielded the dilithium trisiloxanediolate derivative [[Ph2Si(OSiPh2O)2][Li(MeCN)]2]2 (5), which according to an X-ray analysis displays an Li4O4 heterocubane structure. The trinuclear scandium complex [[[(Ph2SiO)2O]Sc(acac)2]2Sc(acac)] (6) was obtained by reaction of [(C5Me5)Sc(acac)2] (C5Me5 = eta5-pentamethylcyclopentadienyl) with (Ph2SiOH)2O in a 3:2 molar ratio. Selective formation of the colorless uranium(VI) derivative [U[Ph2Si(OSiPh20)2]2[(Ph2SiO)2O]] (7) was observed when uranocene, U(eta8-C8H8)2, was allowed to react with (Ph2SiOH)2O. An X-ray diffraction study of the solvated derivative [U[Ph2Si(OSiPh2O)2]2[(Ph2SiO)2O]].Et2O.TMEDA (TMEDA= N,N,N',N'-tetramethyl-ethylenediamine) (7a) revealed the presence of both the original [(Ph2SiO)2O]2- dianion as well as the ring-enlarged [Ph2Si(OSiPh2O)2]2- ligand in the same molecule.     

Alkali-metal-mediated manganationII of functionalized arenes and applications of ortho-manganated products in Pd-catalyzed cross-coupling reactions with iodobenzene

Extending the recently introduced concept of "alkali-metal-mediated manganation" to functionalised arenes, the heteroleptic sodium manganate reagent [(tmeda)Na(tmp)(R)Mn(tmp)] (1; TMEDA=N,N,N',N'-tetramethylethylenediamine, TMP=2,2,6,6-tetramethylpiperidide, R=CH2SiMe3) has been treated with anisole or N,N-diisopropylbenzamide in a 1:1 stoichiometry in hexane. These reactions afforded the crystalline products [(tmeda)Na(tmp)(o-C6H4OMe)Mn(tmp)] (2) and [(tmeda)Na(tmp){o-{C(O)N(iPr)2C6H4}Mn(CH2SiMe3] (3), respectively, as determined from X-ray crystallographic studies. On the basis of these products, it can be surmised that reagent 1 has acted, at least partially and ultimately, as an alkyl base in the first reaction liberating the silane Me4Si, but as an amido base in the second reaction liberating the amine TMPH. Both of these paramagnetic products 2 and 3 have contacted ion-pair structures, the key features of which are six-atom, five-element (NaNMnCCO) and seven-atom, five-element (NaNMnCCCO) rings, respectively. Manganates 2 and 3 were successfully cross-coupled with iodobenzene under [PdCl(2)(dppf)] (dppf=1,1'-bis(diphenylphosphino)ferrocene) catalysis to generate unsymmetrical biaryl compounds in yields of 98.0 and 66.2 %, respectively. Emphasizing the importance of alkali-metal mediation in these manganation reactions, the bisalkyl Mn reagent on its own fails to metalate the said benzamide, but instead produces the monomeric, donor-acceptor complex [Mn(R)2{(iPr)2-NC(Ph)(==O)}2] (5), which has also been crystallographically characterised. During one attempt to repeat the synthesis of 2, the butoxide-contaminated complex [{(tmeda)Na(R)(OBu)(o-C6H4OMe)Mn}2] (6) was obtained. In contrast to 2 and 3, due to reduced steric constraints, this complex adopts a dimeric arrangement in the crystal, the centrepiece of which is a twelve atom (NaOCCMnC)2 ring.