Syntheses, crystal structures and DFT studies of [Me3EM(CO)5] (E = Sb, Bi; M = Cr, W), cis-[(Me3Sb)2Mo(CO)4], and [Bu3BiFe(CO)4]

Syntheses of [Me₃SbM(CO)₅] [M = Cr (1), W (2)], [Me₃BiM(CO)₅] [M = Cr (3), W (4)], cis-[(Me₃Sb)₂Mo(CO)₄] (5), [^tBu₃BiFe(CO)₄] (6), crystal structures of 1-6 and DFT studies of 1-4 are reported.     

Group 12 metal aryl selenolates. Crystal and molecular structure of [2-(Et2NCH2)C6H4]2Se2 and [2-(Me2NCH2)C6H4Se]2M (M = Zn, Cd)

Diorganodiselenide [2-(Et₂NCH₂)C₆H₄]₂Se₂ (1) was obtained by hydrolysis/oxidation of the corresponding [2-(Et₂NCH₂)C₆H₄]SeLi derivative. The treatment of [2-(Et₂NCH₂)C₆H₄]₂Se₂ with elemental sodium in THF resulted in [2-(Et₂NCH₂)C₆H₄]SeNa (2). Reactions between alkali metal selenolates [2-(R₂NCH₂)C₆H₄]SeM′ (R = Me, Et; M′ = Li, Na) and MCl₂ (M = Zn, Cd) in a 2:1 molar ratio resulted in the [2-(R₂NCH₂)C₆H₄Se]₂M species [R = Me, M = Zn (3), Cd (4); R = Et, M = Zn (5), Cd (6)]. The new compounds were characterized by multinuclear NMR (¹H, ¹³C, ⁷⁷Se, ¹¹³Cd) and mass spectrometry. The crystal and molecular structures of 1, 3 and 4 revealed monomeric species stabilized by N → Se (for 1) and N → M (for 3 and 4) intramolecular interactions.     

Liquid crystal behaviour of ionic allylpalladium complexes containing 2-pyrazolylpyridine as bidentate N,N′-ligand

Two types of Pd-complexes containing the new N,N′-ligands 2-[3-(4-alkyloxyphenyl)pyrazol-1-yl]pyridine (pz^Rpy; R = C₆H₄OC_nH_2n+1, n = 6 (hp), 10 (dp), 12 (ddp), 14 (tdp), 16 (hdp), 18 (odp)) (1-6), namely c-[Pd(Cl)₂(pz^Rpy)] (7-10) and c-[Pd(η³-C₃H₅)(pz^Rpy)]BF₄ (11-16), have been synthesised and characterised by different spectroscopic techniques. Those members of the second type containing the largest chains (R = ddp 13, tdp 14, hdp 15, odp 16) have been found to have liquid crystal properties showing smectic A mesophases. By contrast, neither the free ligands pz^Rpy nor their related c-[Pd(Cl)₂(pz^Rpy)] complexes exhibited mesomorphism. The new synthesised metallomesogens are mononuclear complexes with an unsymmetrical molecular shape as deduced from the X-ray structures of c-[Pd(η³-C₃H₅)(pz^Rpy)]BF₄ (R = hp, 11; dp, 12). Both compounds, which are isostructural, show a distorted square-planar environment on the palladium centres defined by the allyl and the bidentate pz^Rpy ligands. The crystal structure reveals that both the counteranion and the pz^Rpy ligand function as a source of hydrogen-bonding and intermolecular π?π contacts resulting in a ²D supramolecular assembly.     

Steric and electronic effects in stabilizing allyl-palladium complexes of “P-N-P” ligands, X2PN(Me)PX2 (X = OC6H5 or OC6H3Me2-2,6)

The chemistry of η³-allyl palladium complexes of the diphosphazane ligands, X₂PN(Me)PX₂ [X = OC₆H₅ (1) or OC₆H₃Me₂-2,6 (2)] has been investigated.The reactions of the phenoxy derivative, (PhO)₂PN(Me)P(OPh)₂ with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = H or Me; R′ = H, R″ = Me) give exclusively the palladium dimer, [Pd₂{μ-(PhO)₂PN(Me)P(OPh)₂}₂Cl₂] (3); however, the analogous reaction with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = Ph) gives the palladium dimer and the allyl palladium complex [Pd(η³-1,3-R′,R″-C₃H₃)(1)](PF₆) (R′ = R″ = Ph) (4). On the other hand, the 2,6-dimethylphenoxy substituted derivative 2 reacts with (allyl) palladium chloro dimers to give stable allyl palladium complexes, [Pd(η³-1,3-R′,R″-C₃H₃)(2)](PF₆) [R′ = R″ = H (5), Me (7) or Ph (8); R′ = H, R″ = Me (6)].Detailed NMR studies reveal that the complexes 6 and 7 exist as a mixture of isomers in solution; the relatively less favourable isomer, anti-[Pd(η³-1-Me-C₃H₄)(2)](PF₆) (6b) and syn/anti-[Pd(η³-1,3-Me₂-C₃H₃)(2)](PF₆) (7b) are present to the extent of 25% and 40%, respectively. This result can be explained on the basis of the steric congestion around the donor phosphorus atoms in 2. The structures of four complexes (4, 5, 7a and 8) have been determined by X-ray crystallography; only one isomer is observed in the solid state in each case.     

Chiral “P-N-P” ligands, (C20H12O2)PN(R)PY2 [R = CHMe2, Y = C6H5, OC6H5, OC6H4-4-Me, OC6H4-4-OMe or OC6H4-4-Bu] and their allyl palladium complexes

Chiral “P-N-P” ligands, (C₂₀H₁₂O₂)PN(R)PY₂ [R = CHMe₂, Y = C₆H₅ (1), OC₆H₅ (2), OC₆H₄-4-Me (3), OC₆H₄-4-OMe (4) or OC₆H₄-4-^tBu (5)] bearing the axially chiral 1,1′-binaphthyl-2,2′-dioxy moiety have been synthesised. Palladium allyl chemistry of two of these chiral ligands (1 and 2) has been investigated. The structures of isomeric η³-allyl palladium complexes, (R′ = Me or Ph; Y = C₆H₅ or OC₆H₅) have been elucidated by high field two-dimensional NMR spectroscopy. The solid state structure of [Pd(η³-1,3-Ph₂-C₃H₃){κ²-(racemic)-(C₂₀H₁₂O₂)PN(CHMe₂)PPh₂}](PF₆) has been determined by X-ray crystallography. Preliminary investigations show that the diphosphazanes, 1 and 2 function as efficient auxiliary ligands for catalytic allylic alkylation but give rise to only moderate levels of enantiomeric excess.     

Crystal structure and spectral characterization of hexanuclear oxo titanium(IV) clusters: [Ti6O6(OSi(CH3)3)6(OOCR)6] (R = Bu,CH2Bu,C(CH3)2Et)

Hexanuclear oxo titanium(IV) siloxo carboxylate complexes with the general formula [Ti₆O₆(OSi(CH₃)₃)₆(OOCR)₆] (R = Bu^t (1), CH₂Bu^t (2), C(CH₃)₂Et (3)) were synthesized in quantitative yield, by the reaction of Ti(OSiMe₃)₄ with the appropriate organic acid. Crystal structure determination revealed that molecules of 1–3 are composed of [Ti₆-(μ₃-O)₆] cores stabilized by six syn–syn carboxylato bridges and six terminal siloxide ligands. Each metal atom is surrounded by six oxo atoms, capping the triangular faces of the distorted octahedron. Spectral characterization (IR, NMR) of 1–3 revealed a significant non-equivalence of the carboxylate group interactions, resulting from the asymmetry of the Ti-μ-OOC bonds of the syn–syn bridges. The thermal stability of the studied compounds was determined from TGA/DTA analysis.     

Substituted lithiumtrimethylsiloxysilanides LiSiRR′(OSiMe3) - Investigations of their synthesis, stability and reactivity

The reactions of the trimethylsiloxychlorosilanes (Me₃SiO)RR′SiCl (1a-h: R′ = Ph, 1a: R = H, 1b: R = Me, 1c: R = Et, 1d: R = ⁱPr, 1e: R = ^tBu, 1f: R = Ph, 1g: R = 2,4,6-Me₃C₆H₂ (Mes), 1h: R = 2,4,6-(Me₂CH)₃C₆H₂ (Tip); 1i: R = R′ = Mes) with lithium metal in tetrahydrofuran (THF) at −78 °C and in a mixture of THF/diethyl ether/n-pentane in a volume ratio 4:1:1 at −110 °C lead to mixtures of numerous compounds. Dependent on the substituents silyllithium derivatives (Me₃SiO)RR′SiLi (2b-i), Me₃SiO(RR′Si)₂Li (3a-g), Me₃SiRR′SiLi (4a-h), (LiO)RR′SiLi (12e, 12g-i), trisiloxanes (Me₃SiO)₂SiRR′ (5a-i) and trimethylsiloxydisilanes (6f^∗, 6h^∗, 6i^∗) are formed. All silyllithium compounds were trapped with Me₃SiCl or HMe₂SiCl resulting in the following products: (Me₃SiO)RR′SiSiMe₂R″ (6b-i: R″ = Me, 7c-i: R″ = H), Me₃SiO(RR′Si)₂SiMe₂R″ (8a-g: R″ = Me, 9a-g: R″ = H), Me₃SiRR′SiSiMe₂R″ (10a-h: R″ = Me, 11a-h: R″ = H) and (HMe₂SiO)RR′SiSiMe₂H (13e, 13g-i). The stability of trimethylsiloxysilyllithiums 2 depends on the substituents and on the temperature. (Me₃SiO)Mes₂SiLi (2i) is the most stable compound due to the high steric shielding of the silicon centre. The trimethylsiloxysilyllithiums 2a-g undergo partially self-condensation to afford the corresponding trimethylsiloxydisilanyllithiums Me₃SiO(RR′Si)₂Li (3a-g). (Me₃)Si-O bond cleavage was observed for 2e and 2g-i. The relatively stable trimethylsiloxysilyllithiums 2f, 2g and 2i react with n-butyllithium under nucleophilic butylation to give the n-butyl-substituted silyllithiums ⁿBuRR′SiLi (15g, 15f, 15i), which were trapped with Me₃SiCl. By reaction of 2g and 2i with 2,3-dimethylbuta-1,3-diene the corresponding 1,1-diarylsilacyclopentenes 17g and 17i are obtained.X-ray studies of 17g revealed a folded silacyclopentene ring with the silicon atom located 0.5 Å above the mean plane formed by the four carbon ring atoms.     

Spectroscopic and structural characterization of cationic N-(2-aminoethyl)aziridine-N,N′ chelate complexes of the d-metals Rh(III) and Ir(III)

The syntheses of the compounds [M(Cp^∗)(aeaz)(az)](OTf)₂ (4, 5) (M = Rh(III), Ir(III); aeaz = C₂H₄NC₂H₄NH₂, az = C₂H₄NH (3)) containing cationic N-(2-aminoethyl)aziridine-N,N′ chelate complexes are described. The bis-aziridine complexes [MCl(Cp^∗)(az)₂]Cl (M = Rh (1), M = Ir (2)) react with an excess of the aziridine (az) in the presence of AgO₃SCF₃ (=AgOTf) via AgCl precipitation and az addition followed by a metal-mediated coupling reaction, to give the compounds [M(Cp^∗)(aeaz)(az)](OTf)₂ (4, 5). The new aeaz ligand is formally the dimerisation product of az. Using the same reaction conditions with the analogous, but weaker Lewis acidic ruthenium(II) complex [RuCl(C₆Me₆)(az)₂]Cl (6) an anion exchange reaction yielding [RuCl(C₆Me₆)(az)₂]OTf (8) is observed. After purification, all compounds are fully characterized using IR, FAB-MS, ¹H and ¹³C NMR spectroscopy. The single crystal X-ray structure analysis reveals a distorted octahedral geometry for all complexes.     

Synthesis, structural characterization and reactivity of new tin bridged ansa-bis(cyclopentadiene) compounds: X-ray crystal structures of Me2Sn(C5Me4R-1)2 (R = H, SiMe3)

The organo-tin compounds, Me₂Sn(C₅H₄R-1)₂ (R = Me (1), Prⁱ (2), Bu^t (3), SiMe₃ (4)) and Me₂Sn(C₅Me₄R-1)₂ (R = H (5), SiMe₃ (6)), were prepared by the reaction of Me₂SnCl₂ with the lithium or sodium derivative of the corresponding cyclopentadiene. Compounds 1-6 have been characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ¹¹⁹Sn). In addition the molecular structures of 5 and 6 were determined by single crystal X-ray diffraction studies. The transmetalation reaction of 1-6 with ZrCl₄ or [NbCl₄(THF)₂] gave the corresponding metallocene complexes in high yields.     

Uranyl(VI) complexes of [O,N,O,N′]-type diaminobis(phenolate) ligands: Syntheses,structures and extraction studies

The syntheses and crystal structures of four new uranyl complexes with [O,N,O,N′]-type ligands are described. The reaction between uranyl nitrate hexahydrate and the phenolic ligand [(N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-N′,N′-dimethylethylenediamine)], H₂L1 in a 1:2 molar ratio (M to L), yields a uranyl complex with the formula [UO₂(HL1)(NO₃)] · CH₃CN (1). In the presence of a base (triethylamine, one mole per ligand mole) with the same molar ratio, the uranyl complex [UO₂(HL1)₂] (2) is formed. The reaction between uranyl nitrate hexahydrate and the ligand [(N,N-bis(2-hydroxy-3,5-di-t-butylbenzyl)-N′,N′-dimethylethylenediamine)], H₂L2, yields a uranyl complex with the formula [UO₂(HL2)(NO₃)] · 2CH₃CN (3) and the ligand [N-(2-pyridylmethyl)-N,N-bis(2-hydroxy-3,5-dimethylbenzyl)amine], H₂L3, in the presence of a base yields a uranyl complex with the formula [UO₂(HL3)₂] · 2CH₃CN (4). The molecular structures of 1–4 were verified by X-ray crystallography. The complexes 1–4 are zwitter ions with a neutral net charge. Compounds 1 and 3 are rare neutral mononuclear [UO₂(HLn)(NO₃)] complexes with the nitrate bonded in η²-fashion to the uranyl ion. Furthermore, the ability of the ligands H₂L1–H₂L4 to extract the uranyl ion from water to dichloromethane, and the selectivity of extraction with ligands H₂L1, H₃L5 (N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-3-amino-1-propanol), H₂L6 · HCl (N,N-bis(2-hydroxy-5-tert-butyl-3-methylbenzyl)-1-aminobutane · HCl) and H₃L7 · HCl (N,N-bis(2-hydroxy-5-tert-butyl-3-methylbenzyl)-6-amino-1-hexanol · HCl) under varied chemical conditions were studied. As a result, the most efficient and selective ligand for uranyl ion extraction proved to be H₃L7 · HCl.     

Reactions of Mo(II)-tetraphosphine complex [MoCl2{meso-o-C6H4(PPhCH2CH2PPh2)2}] with a series of small molecules

Reactions of Mo(II)-tetraphosphine complex [MoCl₂(κ⁴-P4)] (2; P4 = meso-o-C₆H₄(PPhCH₂CH₂PPh₂)₂) with a series of small molecules have been investigated. Thus, treatment of 2 with alkynes RCCR′ (R = Ph, R′ = H; R = p-tolyl, R′ = H; R = Me, R′ = Ph) in benzene or toluene gave neutral mono(alkyne) complexes [MoCl₂(RCCR′)(κ³-P4)] containing tridentate P4 ligand, which were converted to cationic complexes [MoCl(RCCR′)(κ⁴-P4)]Cl having tetradentate P4 ligand upon dissolution into CDCl₃ or CD₂Cl₂. The latter complexes were available directly from the reactions of 2 with the alkynes in CH₂Cl₂. On the other hand, treatment of 2 with 1 equiv. of XyNC (Xy = 2,6-Me₂C₆H₃) afforded a seven-coordinate mono(isocyanide) complex [MoCl₂(XyNC)(κ⁴-P4)] (7), which reacted further with XyNC to give a cationic bis(isocyanide) complex [MoCl(XyNC)₂(κ⁴-P4)]Cl (8). From the reaction of 2 with CO, a mono(carbonyl) complex [MoCl₂(CO)(κ⁴-P4)] (9) was obtained as a sole isolable product. Reaction of 9 with XyNC afforded [MoCl(CO)(XyNC)(κ⁴-P4)]Cl (10a) having a pentagonal-bipyramidal geometry with axial CO and XyNC ligands, whereas that of 7 with CO resulted in the formation of a mixture of 10a and its isomer 10b containing axial CO and Cl ligands. Structures of 7 and 9 as well as [MoCl(XyNC)₂(κ⁴-P4)][PF₆](8′) and [MoCl(CO)(XyNC)(κ⁴-P4)][PF₆] (10a′) derived by the anion metathesis from 8 and 10a, respectively, were determined in detail by the X-ray crystallography.     

Hypervalence in germanium compounds containing the tetracylic moiety {S(C6H3S)2O}Ge via O···Ge transannular interactions: A structural study

Treatment of R_nGeCl_4−n with {S(C₆H₃SH)₂O} (1) afforded the stable phenoxathiin-4,6-dithiolate compounds [{S(C₆H₃S)₂O}GeR₂] [n = 2; R = Et (2), Ph (3)] and [{S(C₆H₃S)₂O}GeRCl] [n = 1; R = Et (4), Ph (5)]. Treatment of GeCl₄ with 1 in benzene afforded the dichloro compound [{S(C₆H₃S)₂O}GeCl₂] (8) at 7 °C. Bromo compounds [{S(C₆H₃S)₂O}GeRBr] [R = Et (6), Ph (7)] and [{S(C₆H₃S)₂O}GeBr₂] (9) were synthesized by halogen exchange from the appropriate chloro derivative using KBr/HBr. X-ray structure determinations of diorganyl dithiolate compounds 2 and 3 revealed that germanium atom is contained in a boat–chair-shaped eight-membered central ring and displays a tetrahedral geometry. In contrast, compounds 4–6 display a boat–boat-shaped central ring with a significant intramolecular transannular O···Ge interaction. The geometry of the pentacoordinate Ge atom in these last complexes may be described as distorted trigonal bipyramidal with a 62–65% distortion displacement.     

Synthesis and structures of bimetallic silicon-containing imido alkylidene complexes of tungsten (R′O)2(ArN)WCH-SiR2-CHW(NAr)(OR′)2 (R = Me, Ph) and (R′O)2(ArN)WCH-SiMe2SiMe2-CHW(NAr)(OR′)2

Bimetallic alkylidene complexes of tungsten (R′O)₂(ArN)WCH-SiR₂-CHW(NAr)(OR′)₂ (R = Me (1), Ph (2)) and (R′O)₂(ArN)WCH-SiMe₂SiMe₂-CHW(NAr)(OR′)₂ (3) (Ar = ; R′ = CMe₂CF₃) have been prepared by the reactions of divinyl silicon reagents R₂Si(CHCH₂)₂ with known alkylidene compounds R′′-CHMo(NAr)(OR′)₂. (R′′ = Bu^t, PhMe₂C) Complexes 1-3 were structurally characterized. Ring opening metathesis polymerization (ROMP) of cyclooctene using compounds 1-3 as initiators led to the formation of high molecular weight polyoctenamers with predominant trans-units content in the case of 1 and 3 and predominant cis-units content in the case of 2.     

Complexes derived from the general copper(II)/maleamic acid/N,N′,N′′-chelate reaction systems: Synthetic,reactivity, structural and spectroscopic studies

The synthetic investigation of the Cu^II/maleamate(−1) ion (HL⁻)/N,N′,N′′-chelate general reaction system has allowed access to compounds [Cu₂(HL)₂(bppy)₂](ClO₄)₂·H₂O (1·H₂O), [Cu(HL)(bppy)(ClO₄)] (2) and [Cu(HL)(terpy)(H₂O)](ClO₄) (4) (bppy = 2,6-bis(pyrazol-1-yl)pyridine, terpy = 2,2′;6′,2′′-terpyridine). In the absence of externally added hydroxides, compound [Cu₂(L′)₂(bppy)₂](ClO₄)₂ (3) was obtained from MeOH solutions; L′⁻ is the monomethyl maleate(−1) ligand which is formed in situ via the Cu^II-assisted HL⁻ → L′⁻ transformation. In the case of tptz-containing (tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine) reaction systems, the Cu^II-assisted hydrolysis of tptz to pyridine-2-carboxamide (L1) afforded complex [Cu(L1)₂(NO₃)₂] (5). The crystal structures of 1–5 are stabilized by intermolecular hydrogen bonding and π–π stacking interactions. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the ligands.     

Reactivity of 2,3-bis(2-pyridyl)pyrazine with [Re2(CO)8(CH3CN)2]: Molecular structures of [Re2(CO)8(C14H10N4)] and [Re2(CO)8(C14H10N4)Re2(CO)8]

The reaction of the labile compound [Re₂(CO)₈(CH₃CN)₂] with 2,3-bis(2-pyridyl)pyrazine in dichloromethane solution at reflux temperature afforded the structural dirhenium isomers [Re₂(CO)₈(C₁₄H₁₀N₄)] (1 and 2), and the complex [Re₂(CO)₈(C₁₄H₁₀N₄)Re₂(CO)₈] (3). In 1, the ligand is σ,σ′-N,N′-coordinated to a Re(CO)₃ fragment through pyridine and pyrazine to form a five-membered chelate ring. A seven-membered ring is obtained for isomer 2 by N-coordination of the 2-pyridyl groups while the pyrazine ring remains uncoordinated. For 2, isomers 2a and 2b are found in a dynamic equilibrium ratio [2a]/[2b]  =  7 in solution, detected by ¹H NMR (−50 °C, CD₃COCD₃), coalescence being observed above room temperature. The ligand in 3 behaves as an 8e-donor bridge bonding two Re(CO)₃ fragments through two (σ,σ′-N,N′) interactions. When the reaction was carried out in refluxing tetrahydrofuran, complex [Re₂(CO)₆(C₁₄H₁₀N₄)₂] (4) was obtained in addition to compounds 1-3. The dinuclear rhenium derivative 4 contains two units of the organic ligand σ,σ′-N,N′-coordinated in a chelate form to each rhenium core. The X-ray crystal structures for 1 and 3 are reported.     

A contribution to 1-azapentadienylmetal chemistry: Si, Sn(II), Fe(II) and Co(II) complexes

Complexes of three related 1-azapentadienyl ligands [N(SiMe₂R¹)C(Bu^t)(CH)₃SiMe₂R]⁻, abbreviated as L (R = Bu^t, R¹ = Me), L′ (R = Me = R¹), and L″ (R = Bu^t = R¹), are described. The crystalline compounds Sn(L)₂ (1), Sn(L′)₂ (2), [Sn(L′)(μ-Cl)]₂ (3) and [Sn(L″)(μ-Cl)]₂ (4) were prepared from SnCl₂ and 2 K(L), 2 K(L′), K(L′) and K(L″), respectively, in thf. Treatment of the appropriate lithium 1-azapentadienyl with Si(Cl)Me₃ yielded the yellow crystalline Me₃Si(L) (5) and the volatile liquid Me₃Si(L′) (6) and Me₃Si(L″) (7), each being an N,N,C-trisilyldieneamine. The red, crystalline Fe(L)₂ (8) and Co(L′)₂ (9) were obtained from thf solutions of FeCl₂ with 2 Li(L)(tmeda) and CoCl₂ with 2 K(L′), respectively. Each of 1-9 gave satisfactory C, H, N analyses; 6 and 7 (GC-MS) and 1, 2, 8 and 9 (MS) showed molecular cations and appropriate fragments (also 3 and 4). The ¹H, ¹³C and ¹¹⁹Sn NMR (1-4) and IR spectra support the assignment of 1-4 as containing Sn-N(SiMe₂R¹)-C(Bu^t)(CH)₃SiMe₂R moieties and 5-7 as N(SiMe₃)(SiMe₂R¹)C(Bu^t)(CH)₃SiMe₂R molecules; for 1-4 this is confirmed by their X-ray structures. The magnetic moments for 8 (5.56 μ_B) and 9 (2.75 μ_B) are remarkably close to the appropriate Fe and Co complex [M{η³-N(SiMe₃)C(Bu^t)C(H)SiMe₃}₂]; hence it is proposed that 8 and 9 have similar metal-centred, centrosymmetric, distorted octahedral structures.     

Cyclometalated N,N-dimethylbenzylamine ruthenium(II) complexes [Ru(C6HRRR-o-CH2NMe2)(bpy)(RCN)2]PF6 for bioapplications: synthesis, characterization, crystal structures, redox properties, and reactivity toward PQQ-dependent glucose dehydrogenase

Cyclometalated derivatives of ring-substituted N,N-dimethylbenzylamines with controlled redox potentials as potent mediators of bioelectrochemical electron transport are reported. The cycloruthenation of R¹R²R³C₆H₂CH₂NMe₂ (R¹, R², R³ = H, Me, ^tBuO, MeO, NMe₂, F, CF₃, CN, NO₂) by [(η⁶-C₆H₆)RuCl(μ-Cl)]₂ in the presence of NaOH/KPF₆ in acetonitrile or pivalonitrile affords cyclometalated complexes [(η⁶-C₆H₆)Ru(C₆HR¹R²R³-o-CH₂NMe₂)(RCN)]PF₆ [R = Me (1) and R = CMe₃ (2)] in good yields. Reactions of complexes 1 and 2 with 2,2′-bipyridine (bpy) in acetonitrile or pivalonitrile result in dissociation of η⁶-bound benzene and the formation of [Ru(C₆HR¹R²R³-o-CH₂NMe₂)(bpy)(RCN)₂]PF₆ [R = Me (3) and R = CMe₃ (4)]. All new compounds have been fully characterized by mass spectrometry, ¹H/¹³C NMR, and IR spectroscopy. An X-ray crystal structural investigation of complex 1 (R¹/R²/R³ = H/H/H) and two complexes of type 3 (R¹/R²/R³ = MeO/H/H, MeO/MeO/H) has been performed. Acetonitrile ligands of 3 are mutually cis and the σ-bound carbon is trans to one of the bpy nitrogens. Measured by the cyclic voltammetry in MeOH as solvent, the redox potentials of complexes 3 for the Ru^II/III feature cover the range 320-720 mV (versus Ag/AgCl) and correlate linearly with the Hammett constants. Complexes 3 mediate efficiently the electron transport between the active site of PQQ-dependent glucose dehydrogenase (PQQ = pyrroloquinoline quinone) and a glassy carbon electrode. Determined by cyclic voltammetry the second order rate constant for the oxidation of the reduced (by d-glucose) enzyme active site by Ru^III derivative of 3 (R¹/R²/R³ = H) (generated electrochemically) is as high as 4.8 × 10⁷ M⁻¹ s⁻¹ at 25 °C and pH 7.     

Spectroscopic and structural characterization of O,O′-(diphenylphosphineoxide)amidate and acetylacetonate complexes of pentacoordinate nickel(II)

Heteroleptic nickel pentacoordinate complexes with the macrocyclic ligands 2,4,4-trimethyl-1,5,9-triazacyclododec-1-ene (Me₃-mcN₃) or its 9-methyl derivative (Me₄-mcN₃), as ancillary ligands, and O,O′-(diphenylphosphineoxide)amidate ligands, [RC(O)NP(O)Ph₂]^¯ (R = C₆H₆ (1), C₅H₄N (2), C₄H₃S (3)), have been prepared as well as related acetylacetonate derivatives. The complexes have been studied by spectroscopic methods (IR, UV-Vis and ¹H NMR). In acetone solution, the complexes exhibit isotropically shifted ¹H NMR resonances. The full assignment of these resonances has been achieved using one- and two-dimensional ¹H NMR techniques. The single-crystal structures of {(Me₄-mcN₃)Ni[OP(Ph₂)NC(Tf)O]}[PF₆] (9) and {(Me₃-mcN₃)Ni(acac)}[PF₆] (10) have been established by X-ray diffraction.