Use of the tetrahydroborate ligand as "gate-keeper" and protected hydride ligand: preparation and study of alkyl hydride and acyl hydride complexes of ruthenium(II)

Complex 3, [Ru(eta2-BH4)(CO)(Et)L2] (L = PMe2Ph) can be converted by nucleophiles L' {a, PMe2Ph; b, P(OMe)3; c, Me3CNC; d, CO} to alkyl and acyl complexes [Ru(eta1-BH4)(CO)(Et)L2L'] (4a), [Ru(eta2-BH4)(COEt)L2L'] (5a-d), and [Ru(eta1-BH4)(COEt)L2L'2] (7d and isomers 7c and 10c). Deprotection can then be achieved under conditions mild enough to allow study of the resulting alkyl hydride complexes [Ru(CO)(Et)HL2L'] (1a, 1b) and acyl hydride complexes [Ru(COEt)HL2L'2] (8c, 8d) prior to elimination of ethane and propanal respectively, with formation of ruthenium(0) complexes [Ru(CO)L2L'2] (6a, 6b, 6d). With Me3CNC, however, the final product is (depending on the solvent used) [Ru(CNCMe3)2{C(H)NCMe3}(COEt)L2] (9c) or [Ru(CNCMe3)3(COEt)L2]+ (11c). Successive treatment of [Ru(eta2-BH4)(CO)HL2], , with ethene and then CO yields propanal, but turning this into a catalytic cycle is hindered by the greater readiness of to yield propanal non-catalytically (reacting with CO) than catalytically (reacting with H2).     

Functionalization of aminophosphanes: synthesis and X-ray crystal structure of novel dilithium and trilithium complexes containing silicon-fused heteronuclear SiN2PLi five-membered rings

A first structurally characterized primary aminophosphane (Ar 2PNH 2 ( 2); Ar = 2,4,6- iPr 3C 6H 2) that is a stable solid at room temperature without decomposition by self-condensation is reported. Reactions of N-phosphanyllithium amide ( tBu 2PNHLi ( 3)) with Me 2SiCl 2 and MeSiCl 3 in Et 2O result in the formation of Me 2Si(NHP tBu 2) 2 ( 4) and MeSi(NHP tBu 2) 3 ( 5), respectively. Subsequent treatment of 4 and 5 with 2 and 3 equiv of nBuLi gave the dilithium ( 6) and trilithium ( 7) complexes, respectively. Further treatment of 5 with 3 equiv of AlMe 3 yielded the trialuminum complex MeSi[N(AlMe 2)P tBu 2] 3 ( 8). These three complexes were investigated by microanalysis and multinuclear NMR spectroscopy. The dilithium complex [Me 2Si(NLiP tBu 2) 2.3THF] ( 6) and the trilithium complex [MeSi(NLiP tBu 2) 3.3Et 2O] ( 7) were further characterized by single-crystal X-ray structural analysis.     

Monovalent iron in a sulfur-rich environment

A series of low-coordinate, paramagnetic iron complexes in a tris(thioether) ligand environment have been prepared. Reduction of ferrous {[PhTt(tBu)]FeCl}2 [1; PhTt(tBu) = phenyltris((tert-butylthio)methyl)borate] with KC8 in the presence of PR3(R = Me or Et) yields the high-spin, monovalent iron phosphine complexes [PhTt(tBu)]Fe(PR3) (2). These complexes provide entry into other low-valent derivatives via ligand substitution. Carbonylation led to smooth formation of the low-spin dicarbonyl [PhTt(tBu)]Fe(CO)2 (3). Alternatively, replacement of PR 3 with diphenylacetylene produced the high-spin alkyne complex [PhTt(tBu)]Fe(PhCCPh) (4). Lastly, 2 equiv of adamantyl azide undergoes a 3 + 2 cycloaddition at 2, yielding high-spin dialkyltetraazadiene complex 5.     

Tungsten(VI) complexes with aminobis(phenolato) [O,N,O] donor ligands

The reaction between trisdiolatotungsten(VI) complex [W(eg)(3)] (1) (eg = 1,2-ethanediolato dianion) and phenolic ligand precursor methylamino-N,N-bis(2-methylene-4,6-dimethylphenol) (H(2)L(Me)) or methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol) (H(2)L(tBu)) affords monomeric oxotungsten complex [WO(eg)(L(Me))] (2) or [WO(eg)(L(tBu))] (3), respectively. These complexes react further with chlorinating reagents, which leads to the displacement of ethanediolato ligands from the complex units and formation of cis and trans isomers of the corresponding dichloro complexes [WOCl(2)(L(Me))] (4) and [WOCl(2)(L(tBu))] (5), respectively. Identical dichloro complexes were also prepared by the reaction between the above-mentioned phenolic ligand precursors and [WOCl(4)]. Molecular structures of 3, cis-4, trans-4, and cis-5 were verified by X-ray crystallography. Complexes 2-5 can be activated by Et(2)AlCl to catalyze ring-opening metathesis polymerization of norbornene.     

Facile synthesis of fluoroalkenes by palladium-catalyzed reductive defluorination of allylic gem-difluorides

Chemo- and stereoselective synthesis of fluoroalkenes was achieved in excellent yields via Pd-catalyzed C-F bond activation. In this transformation, Et3N plays a crucial role to produce reactive hydride species such as Ph(EtO)SiH2 and Ph(EtO)2SiH by promoting dehydrogenative coupling. The reaction proceeds efficiently at 50 degrees C with a variety of substrates and is also useful for the synthesis of fluoroalkene peptidomimetics.     

End-group-confined chain walking within a group 4 living polyolefin and well-defined cationic zirconium alkyl complexes for modeling this behavior

Living polymers derived from the polymerization of 1-butene using the cationic zirconium initiator, {Cp*ZrMe[N(Et)C(Me)-N(tBu)]}[B(C6F5)4] (Cp* = eta5-C5Me5) (1), have been shown to undergo end-group-confined chain walking that is competitive with direct beta-hydride elimination and chain release at -10 degrees C. The well-defined complexes, {Cp*Zr(iBu)[N(Et)C(Me)N(tBu)]}[B(C6F5)4] (2) and {Cp*Zr(2-ethylbutyl)[N(Et)C(Me)N(tBu)]}[B(C6F5)4] (3), were prepared, and each was found to possess a strong beta-hydrogen agostic interaction that is absent in the living polymer. The isotopically single- and double-labeled derivatives, {Cp*Zr(2-d-2-methylpropyl)[N(Et)C(Me)N(tBu)]}[B(C6F5)4] (2') and {Cp*Zr(1-13C-2-d-2-methylpropyl)[N(Et)C(Me)N(tBu)]}[B(C6F5)4] (2' '), were also prepared and found to undergo isotopic label scrambling at 0 degrees C. For 2' ', the observation that after scrambling each deuterium label is located on a 13C-labeled carbon atom is consistent with the Busico mechanism for chain-end epimerization rather than the Resconi mechanism. Decomposition of 3 yielded olefinic products also consistent with chain walking prior to beta-hydride elimination and chain release. Finally, the unexpected decrease in stability of the living polymer relative to that of the model complexes reveals the importance of subtle differences in steric and electronic factors in controlling beta-hydride elimination and chain release.     

New and versatile routes to zirconium imido dichloride compounds

Reactions of zirconium dialkyl- or bis(amido)-dichloride complexes "[Zr(CH2SiMe3)2Cl2(Et2O)2]" or [Zr(NMe2)2Cl2(THF)2] with primary alkyl and aryl amines are described. Reaction of "[Zr(CH2SiMe3)2Cl2(Et2O)2]" with RNH2 in THF afforded dimeric [Zr2(mu-NR)2Cl4(THF)4](R=2,6-C6H3iPr2 (1), 2,6-C6H3Me2 (2) or Ph (3)), [Zr2(mu-NR)2Cl4(THF)3](R=tBu (5), iPr (6), CH2Ph (7)), or the "ate" complex [Zr2(mu-NC6F5)2Cl6(THF)2{Li(THF)3}2](4, the LiCl coming from the in situ prepared "[Zr(CH2SiMe3)2Cl2(Et2O)2]"). With [Zr(NMe2)2Cl2(THF)2] the compounds [Zr2(mu-NR)2Cl4(L)x(L')y](R=2,6-C6H3iPr2 (8), 2,6-C6H3Me2 (9), Ph (10) or C6F5 (11); (L)x(L')y=(NHMe2)3(THF), (NHMe2)2(THF)2 or undefined), [Zr2(mu-NtBu)2Cl4(NHMe2)3] (12) and insoluble [Zr(NR)Cl2(NHMe2)]x(R=iPr (13) or CH2Ph (14)) were obtained. Attempts to form monomeric terminal imido compounds by reaction of or with an excess of pyridine led, respectively, to the corresponding dimeric adducts [Zr2(mu-2,6-C6H3Me2)2Cl4(py)4] (15) and [Zr2(mu-NtBu)2Cl4(py)3] (16). The X-ray structures of 1, 2, 4, 8, 12 and 15 have been determined.     

The effects of light lanthanoid elements (La, Ce, Nd) on (Ar)CF-Ln coordination and C-F activation in N,N-dialkyl-N'-2,3,5,6-tetrafluorophenylethane-1,2-diaminate complexes

A new class of homoleptic organoamido rare earth complexes [Ln(L(Me) or L(Et))(3)] (Ln = La, Ce, Nd; L(Me/Et) = p-HC(6)F(4)N(CH(2))(2)NMe(2)/Et(2)) exhibiting (Ar)CF-Ln interactions has been isolated from redox-transmetallation/protolysis (RTP) reactions between the free metals, Hg(C(6)F(5))(2) and L(Me/Et)H in tetrahydrofuran, together with low yields of [Ln(L(Me))(2)F](3) (Ln = La, Ce) or [Nd(L(Et))(2)F](2) species, resulting from C-F activation reactions. The structures of the homoleptic complexes have eight-coordinate Ln metals with two tridentate (N,N',F) amide ligands including (Ar)CF-Ln bonds and either a bidentate (N,F) ligand (Ln = La, Ce, Nd; L(Et)) or a bidentate (N,N') ligand (Ln = Nd; L(Me)), in an unusual case of linkage variation. All (Ar)CF-Ln bond lengths are shorter than or similar to the corresponding Ln-NMe(2)/Et(2) bond lengths. In [Ln(L(Me))(2)F](3) (Ln = La, Ce) complexes, there is a six-membered ring framework with alternating F and Ln atoms and the metal atoms are eight-coordinate with two tridentate (N,N',F) L(Me) ligands, whilst [Nd(L(Et))(2)F](2) is a fluoride-bridged dimer.     

Octahedral non-heme oxo and non-oxo Fe(IV) complexes: an experimental/theoretical comparison

Electron-transfer series are described for three ferric complexes of the pentadentate ligand 4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane-1-acetate (Me(3)cyclam-acetate) with axial chloride, fluoride, and azide ligands. These complexes can all be reduced coulometrically to their Fe(II) analogs and oxidized reversibly to the corresponding Fe(IV) species. The Fe(II), Fe(III), and Fe(IV) species have been studied spectroscopically and their UV-vis, M?ssbauer, EPR, and IR spectra are presented. The fluoro species [(Me(3)cyclam-acetate)FeF](n+) (n = 0, 1, 2) have been studied computationally using density functional theory (DFT), and the electronic structure of the Fe(IV) dication [(Me(3)cyclam-acetate)FeF](2+) is compared with that of the isoelectronic Fe(IV) oxo cation [(Me(3)cyclam-acetate)FeO](+); the different properties of the two species are mainly due to the significantly covalent Fe=O pi bonds in the latter.     

Detection of platinum dihydride bisphosphine complexes and studies of their reactivity through para-hydrogen-enhanced NMR methods

In-situ NMR studies on the reactions of Pt{CH2 = CHSi(Me)2}2O)(PCy3) with phosphines, HSiEt3 and--hydrogen or Pt(L)(L')(Me)(2) alone enable the detection of cis-Pt(L)(L')(H)2 [L = PCy3 and L' = PCy2H, PPh3 or PCy3] which then undergo hydride site interchange and H2 reductive elimination on the NMR timescale.     

Pyridylpyrrolides as alternatives to cyclometalated phenylpyridine ligands: synthesis and characterization of luminescent zinc and boron pyridylpyrrolide complexes

The synthesis, structure, and properties of six luminescent pyridylpyrrolide complexes and the first structural characterization of pyridylpyrrolide metal complexes are reported. A series of new zinc complexes, bis(pyridylpyrrolyl)zinc, (R2PyrPy)2Zn (R = Me, Et, iPr, tBu, and Ph), that vary in their substituents on the pyrrole ring (Me, Et, iPr, tBu, and Ph), were prepared. Pyrrole substitution produced small structural changes in the complexes and affected the fluorescence properties very little. The zinc complexes were found to be luminescent, emitting at 495 nm (Phi = 0.32, 0.32 0.31, 0.19 and 0.57, respectively). A boron analog, (Me2PyrPy)BF2, was prepared and was found to share the luminescent properties with the zinc complexes, emitting at 505 nm (Phi = 0.22), but not their water-sensitivity. A total of four crystal structures are reported, tBu2PyrPyH, (Me2PyrPy)2Zn, (tBu2PyrPy)2Zn, and (Me2PyrPy)BF2. tBu2PyrPyH crystallizes as a doubly hydrogen bonded dimer with non-coplanar pyridine and pyrrole rings. The solid-state structures of (Me2PyrPy)2Zn and (tBu2PyrPy)2Zn revealed that despite the large change in steric bulk, the two compounds have very similar structures. The structure of (Me2PyrPy)BF2 showed changes that are expected with the interaction between a smaller atom (B as compared to Zn). Molecular orbital calculations were performed on Me2PyrPyH, (Me2PyrPy)BF2, and (Me2PyrPy)2Zn using Gaussian 98 methods. It was found that the main transition (HOMO-LUMO) for all three molecules is a pi-->pi* transition and that in the inorganic complexes, the metal atom (zinc or boron) present has very little effect on transition, evidence that the optical properties are largely ligand based and that the B or Zn atom's main effect is lowering of the LUMO relative energy.     

The binding ability of iron bonded to porphodimethene: structural, magnetic, and electronic relationship to iron porphyrin complexes

The availability of the parent compound, meso-hexaethylporphodimetheneiron(II), [(Et6N4)Fe] (2), of this report results from a novel synthetic methodology that makes [Et6N4Li2] (1) easily available. The major focus is on how the axial positions, which are the key reactive sites in metalloporphyrins, and the electronic configuration of the metal can be affected by the breakdown of the aromaticity of the porphyrin skeleton and by the nonplanar conformation of the ligand. DFT calculations indicate a 3B1(dz2)1(dyz)1 ground state for 2 versus the 3A2(dxz)1(dyz)1 ground state in the porphyrin analogue. The intermediate-spin state (S = 1) of 2 changed drastically upon addition of one or two axial ligands, as hexacoordination is preferred by iron(II). The hexacoordinate complexes [(Et6N4)Fe(L)(L')] (L = L' = THF, 3; L = L' = Py, 4; L = PhNO, L' = Py, 14) have been isolated and structurally characterized. Strong-field ligands lead to a low-spin diamagnetic state for iron(II), namely for complexes 4-7, 9, and 14, whereas 3 is a typical d6 high-spin complex, as is the pentacoordinate [(Et6N4)Fe(CN)]Bu4N (8). The structural analysis showed common features for 6, 7, 9, and 14: i) a small displacement of the metal from the N4 plane, and ii) an N4 cavity, larger than that in the corresponding porphyrins, affecting the Fe-N bond lengths. The 1H NMR spectrum is quite diagnostic of the two-fold symmetry in the diamagnetic hexacoordinate complexes, revealing either a D2h or a C2v symmetry. The CO stretching frequency (1951 cm(-1)) in complex 6 probes the good electron density at the metal. The one-electron oxidation of 2 led to pentacoordinate iron(III) derivatives [(Et6N4)Fe(Cl)] (10), [(Et6N4)2Fe2(mu-O)] (11), and [(Et6N4)2Fe2(mu-p-OC6H4-O)] (12). Complex 10 is a typical high-spin iron(III) (5.85muB at 298 K), while 11 and 12 behave as antiferromagnetic coupled iron(III) (J = -9.4cm(-1), 12, and J = -115cm(-1), 11). In complexes 10, 11, and 12 iron is sitting in a quite distorted square pyramidal geometry, in which the ligand displays a very distorted roof conformation with different degrees of ruffling. Distinctive structural and magnetic features have been found for the nitrosyl derivative [(Et6N4)Fe-NO], which has a low-spin state (S = 1/2) and the following structural parameters: Fe-N-O, 147.3(2) degrees; Fe-N, 1.708(2) A; N-O, 1.172(3) A. A comparative structural, magnetic, and theoretical analysis of the compounds listed above has been made with the analogous porphyrin derivatives. The detailed structural investigation has been mapped through the X-ray analysis of 2, 7, 8, 9, 11, 13, and 14.     

Synthesis and intramolecular and interionic structural characterization of half-sandwich (arene)ruthenium(II) derivatives of bis(pyrazolyl)alkanes

Arene ruthenium(II) complexes containing bis(pyrazolyl)methane ligands have been prepared by reacting the ligands L' (L' in general; specifically L(1) = H(2)C(pz)(2), L(2) = H(2)C(pz(Me2))(2), L(3) = H(2)C(pz(4Me))(2), L(4) = Me(2)C(pz)(2) and L(5) = Et(2)C(pz)(2) where pz = pyrazole) with [(arene)RuCl(mu-Cl)](2) dimers (arene = p-cymene or benzene). When the reaction was carried out in methanol solution, complexes of the type [(arene)Ru(L')Cl]Cl were obtained. When L(1), L(2), L(3), and L(5) ligands reacted with excess [(arene)RuCl(mu-Cl)](2), [(arene)Ru(L')Cl][(arene)RuCl(3)] species have been obtained, whereas by using the L(4) ligand under the same reaction conditions the unexpected [(p-cymene)Ru(pzH)(2)Cl]Cl complex was recovered. The reaction of 1 equiv of [(p-cymene)Ru(L')Cl]Cl and of [(p-cymene)Ru(pzH)(2)Cl]Cl with 1 equiv of AgX (X = O(3)SCF(3) or BF(4)) in methanol afforded the complexes [(p-cymene)Ru(L')Cl](O(3)SCF(3)) (L' = L(1) or L(2)) and [(p-cymene)Ru(pzH)(2)Cl]BF(4), respectively. [(p-cymene)Ru(L(1))(H(2)O)][PF(6)](2) formed when [(p-cymene)Ru(L(1))Cl]Cl reacts with an excess of AgPF(6). The solid-state structures of the three complexes, [(p-cymene)Ru{H(2)C(pz)(2)}Cl]Cl, [(p-cymene)Ru{H(2)Cpz(4Me))(2)}Cl]Cl, and [(p-cymene)Ru{H(2)C(pz)(2)}Cl](O(3)SCF(3)), were determined by X-ray crystallographic studies. The interionic structure of [(p-cymene)Ru(L(1))Cl](O(3)SCF(3)) and [(p-cymene)Ru(L')Cl][(p-cymene)RuCl(3)] (L' = L(1) or L(2)) was investigated through an integrated experimental approach based on NOE and pulsed field gradient spin-echo (PGSE) NMR experiments in CD(2)Cl(2) as a function of the concentration. PGSE NMR measurements indicate the predominance of ion pairs in solution. NOE measurements suggest that (O(3)SCF(3))(-) approaches the cation orienting itself toward the CH(2) moiety of the L(1) (H(2)C(pz)(2)) ligand as found in the solid state. Selected Ru species have been preliminarily investigated as catalysts toward styrene oxidation by dihydrogen peroxide, [(p-cymene)Ru(L(1))(H(2)O)][PF(6)](2) being the most active species.     

Dititanium complexes of preorganized binucleating bis(amidinates)

Four different dianionic bis(amidinate) ligands ((iPr)L(DBF)(2)(-), (tBu,Et)L(DBF)(2)(-), (iPr)L(Xan)(2)(-), (tBu,Et)L(Xan)(2)(-)) featuring rigid dibenzofuran (DBF) and 9,9-dimethylxanthene (Xan) backbones have been used to prepare several new dititanium complexes. Reaction of the free-base bis(amidines) (LH(2)) with 2 equiv of Ti(NMe(2))(4) forms the hexaamido derivatives (iPr)L(DBF)Ti(2)(NMe(2))(6) (1), (tBu,Et)L(DBF)Ti(2)(NMe(2))(6) (2), (iPr)L(Xan)Ti(2)(NMe(2))(6) (3), and (tBu,Et)L(Xan)Ti(2)(NMe(2))(6) (4) in good yields. Compound 4, which features an unsymmetrically substituted bis(amidinate) ligand, was isolated as an 8:1 mixture of rotational diastereomers with C(2) and C(s)() symmetry, respectively. The two diastereomers interconvert upon heating, and at equilibrium the C(2) isomer is preferred thermodynamically by 0.2 kcal/mol. Compound 3 reacts with excess Me(3)SiCl in toluene to form the mixed amido-chloride derivative (iPr)L(Xan)Ti(2)(NMe(2))(2)Cl(4) (5) in low-moderate yield. Alternatively, 5 is also prepared by reaction of (iPr)L(Xan)H(2) with 2 equiv of Ti(NMe(2))(2)Cl(2) in good yield. Compound 3 reacts with CO(2) to form the red carbamate derivative (iPr)L(Xan)Ti(2)(NMe(2))(4)(O(2)CNMe(2))(2) (6) in moderate yield. Infrared data for 6 indicates bidentate coordination of the carbamate ligands. Metathesis reaction of (iPr)L(Xan)Li(2) with 2 equiv of CpTiCl(3) affords (iPr)L(Xan)Ti(2)Cp(2)Cl(4) (7) in moderate yield. Reduction of 7 with 1% Na amalgam in toluene solution affords the paramagnetic dititanium(III) complex (iPr)L(Xan)Ti(2)Cp(2)Cl(2) (8) in good yield. Structural studies reveal that 8 features two bridging chloride ligands. Reaction of the free-base bis(amidines) with 2 equiv of CpTiMe(3) forms the red sigma-alkyl derivatives (iPr)L(DBF)Ti(2)Cp(2)Me(4) (9), (tBu,Et)L(DBF)Ti(2)Cp(2)Me(4) (10), and (iPr)L(Xan)Ti(2)Cp(2)Me(4) (11) in good yields. Structural data are presented for compounds 4, 5, 8, and 9.     

Synthesis, reactivity, spectroscopic characterization, X-ray structures, PGSE, and NOE NMR studies of (eta5-C5Me5)-rhodium and -iridium derivatives containing bis(pyrazolyl)alkane ligands

Rhodium(III) and iridium(III) complexes containing bis(pyrazolyl)methane ligands (pz = pyrazole, L' in general; specifically, L1 = H2C(pz)2, L2 = H2C(pzMe2)2, L3 = H2C(pz4Me)2, L4 = Me2C(pz)2), have been prepared in a study exploring the reactivity of these ligands toward [Cp*MCl(mu-Cl)]2 dimers (M = Rh, Ir; Cp* = pentamethylcyclopentadienyl). When the reaction was carried out in acetone solution, complexes of the type [Cp*M(L')Cl]Cl were obtained. However, when L1 and L2 ligands have been employed with excess [Cp*MCl(mu-Cl)]2, the formation of [Cp*M(L')Cl][Cp*MCl3] species has been observed. PGSE NMR measurements have been carried out for these complexes, in which the counterion is a cyclopentadienyl metal complex, in CD2Cl2 as a function of the concentration. The hydrodynamic radius (rH) and, consequently, the hydrodynamic volume (VH) of all the species have been determined from the measured translational self-diffusion coefficients (Dt), indicating the predominance of ion pairs in solution. NOE measurements and X-ray single-crystal studies suggest that the [Cp*MCl3]- approaches the cation, orienting the three Cl-legs of the "piano-stool" toward the CH2 moieties of the bis(pyrazolyl)methane ligands. The reaction of 1 equiv of [Cp*M(L')Cl]Cl or [Cp*M(L')Cl][Cp*MCl3] with 1 equiv of AgX (X = ClO4 or CF3SO3) in CH2Cl2 allows the generation of [Cp*M(L')Cl]X, whereas the reaction of 1 equiv of [Cp*M(L')Cl] with 2 equiv of AgX yields the dicationic complexes [Cp*M(L')(H2O)][X]2, where single water molecules are directly bonded to the metal atoms. The solid-state structures of a number of complexes were confirmed by X-ray crystallographic studies. The reaction of [Cp*Ir(L')(H2O)][X]2 with ammonium formate in water or acetone solution allows the generation of the hydride species [Cp*Ir(L')H][X].     

Zinc complexes of Ttz(R,Me) with O and S donors reveal differences between Tp and Ttz ligands: acid stability and binding to H or an additional metal (Ttz(R,Me) = tris(3-R-5-methyl-1,2,4-triazolyl)borate; R = Ph, tBu)

Alkylzinc complexes, (Ttz(R,Me))ZnR' (R = tBu, Ph; R' = Me, Et), show interesting reactivity with acids, bases and water. With acids (e.g. fluorinated alcohols, phenols, thiophenol, acetylacetone, acetic acid, HCl and triflic acid) zinc complexes of the conjugate base (CB), (Ttz(R,Me))ZnCB, are generated. Thus the B-N bonds in Ttz ligands are acid stable. (Ttz(R,Me))ZnCB complexes were characterized by (1)H, (13)C-NMR, IR, MS, elemental analysis, and, in most cases, single crystal X-ray diffraction. The four coordinate crystal structures included (Ttz(R,Me))Zn(CB) [where R = Ph, CB (conjugate base) = OCH(2)CF(3) (2), OPh (6), SPh (8), p-OC(6)H(4)(NO(2)) (10); R = tBu, CB = OCH(CF(3))(2) (3), OPh (5), SPh (7)*, p-OC(6)H(4)(NO(2)) (9) (* indicates a rearranged Ttz ligand)]. The use of bidentate ligands resulted in structures [(Ttz(Ph,Me))Zn(CB) (CB = acac (12), OAc (14))] in which the coordination geometries are five, and intermediate between four and five, respectively. Interestingly, three forms of (Ttz(Ph,Me))Zn(p-OC(6)H(4)(NO(2))) (10) were analyzed crystallographically including a Zn coordinated water molecule in 10(H(2)O), a coordination polymer in 10(CP), and a p-nitrophenol molecule hydrogen bonded to a triazole ring in 10(Nit). Ttz ligands are flexible since they are capable of providing κ(3) or κ(2) metal binding and intermolecular interactions with either a metal center or H through the four position nitrogen (e.g. in 10(CP) and HTtz(tBu,Me)·H(2)O, respectively). Preliminary kinetic studies on the protonolysis of LZnEt (L = Ttz(tBu,Me), Tp(tBu,Me)) with p-nitrophenol in toluene at 95 °C show that these reactions are zero order in acid and first order in the LZnEt.     

Direct incorporation of a ferric ion in the porphyrinogen core: tetrakis(cyclohexyl)iron porphyrinogen anion with different conformers and its reaction with iodine

Et(4)N[L' 'Fe(III)].3DCM (1) is directly synthesized by adding ferric chloride into a solution of a lithium salt of tetrakis(cyclohexyl)porphyrinogen (L' '). [L' '](4-) is a good chelating ligand for both Fe(III) and Fe(II) ions. It is an avid proton scavenger but not a reducing agent. 1 showed a magnetic moment (mu(eff)) of 4.3 micro(B) in the solid, which changed to 6.0 micro(B) in solution. This change in spin state is common for all iron porphrinogens. 1 showed polymorphism, and with pyridine in the lattice, it changed to Et(4)N[L' 'Fe(III)].DCM(0.5)Py(1.5) (2), possessing two different conformers. Calculation of these conformers at the density functional theory level showed the relative energies of all d orbital changes in three conformers, highlighting the influence of the disposition of a peripheral ligand. Iodine oxidation of 1 yielded [L' '(DeltaDelta)Fe(II)I][I(3).I(2)(+).I(3)(-)] (3) with the introduction of two C(alpha)-C(alpha) bonds with concomitant reduction of Fe(III) to Fe(II). Its mu(eff) (5.4 mu(B)) in the solid changed to 4.8 micro(B) in solution, suggesting a high spin state (S = 2) for Fe(II).     

A catalytic synthesis of thiosilanes and silthianes: palladium nanoparticle-mediated cross-coupling of silanes with thio phenyl and thio vinyl ethers through selective carbon-sulfur bond activation

Palladium nanoparticles generated in situ from N,N-dimethyl-acetamide (DMA) solutions of PdX(2) (X = Cl(-), OAc(-), OCOCF(3)(-)) or Pd(2)(dba)(3) by reduction with alkyl silanes R(3)SiH (R = Me, Et, i-Pr, t-Bu) are selective catalysts for the cross-coupling of the silanes R(3)SiH with phenyl and vinyl thioethers forming the corresponding thiosilanes and silthianes in high yields and under mild conditions. The method is applicable to phenyl thioglycosides, giving access to thiosilyl glycosides a new class of sugar derivatives.     

From lithium bis(trimethylsilyl)amide with cyanoamine into triazine compounds: synthesis and structures of lithium 6-((trimethylsilyl)amido)-2,4-bis(dimethylamino)[1,3,5]triazines and their manganese and cobalt complexes

Addition reactions of lithium bis(trimethylsilyl)amide with dimethylcyanamide lead to novel lithium salts of 6-((trimethylsilyl)amido)-2,4-bis(dimethylamino)[1,3,5]triazines [LLi(D)](2) (L = NC(NMe(2))NC(NMe(2))NC(NSiMe(3)); D = Me(2)NCN (1), Et(2)O (2)) and to the Mn and Co complexes [LL'M] (L' = N{N(SiMe(3))C(NMe(2))}(2); M = Mn (3), Co (4)); the structures of crystalline 1, 3, and 4 are reported. Their formation involves trimethylsilyl shifts, ring formation, and unusual Me(2)NSiMe(3) elimination.     

Anisole-diphenoxide ligands and their zirconium dichloride and dialkyl complexes

Linear triphenol H3[RO3] (2,6-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-R-phenol; R = Me, tBu) was found to undergo selective mono-deprotonation and mono-O-methylation. Deprotonation of H3[RO3] with 1 equiv of nBuLi resulted in the formation of Li{H2[RO3]}(Et2O)2 (R = Me (1a), tBu (1b)), in which the central phenol unit was lithiated. Treatment of H3[RO3] with methyl p-toluenesulfonate in the presence of K2CO3 in CH3CN gave the corresponding anisol-diphenol H2[RO2O] (2,6-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-R-anisole; R = Me (2a), tBu (2b)). Reaction of H2[RO2O] with 2 equiv of nBuLi gave the dilithiated derivatives Li2[RO2O]. The lithium salts were reacted with ZrCl4 in toluene/THF to obtain the dichloride complex [RO2O]ZrCl2(thf) (R = Me (3a), tBu (3b)). 3b underwent dimerization along with a loss of THF to generate {[tBuO2O]ZrCl2}2 (4), whereas 4 was dissolved in THF to regenerate the monomer 3b. Alkylation of 3 with MeMgBr, PhCH2MgCl, and Me3SiCH2MgCl gave [MeO2O]ZrMe2(thf) (5), [RO2O]Zr(CH2Ph)2 (R = Me (6a), tBu (6b)), and [tBuO2O]Zr(CH2SiMe3)2 (7), respectively. Reaction of 3b with LiBHEt3 produced the hydride-bridged dimer [Li2(thf)4Cl]{[tBuO3]Zr}2(micro-H)3} (8), in which demethylation of the dianionic [tBuO2O] ligand took place to give the trianionic [tBuO3] ligand. The X-ray crystal structures of 1b, 2a, 3a, 4, 6a, and 7 were reported.