Hydrogen exchange of rhenium(VII) heptahydridobis(triphenylphosphine) with water, aniline, methanol, and itself

The hydride ligands of ReH₇(PPh₃)₂ undergo fast hydrogen exchange with water at room temperature while exchanging with the hydrogen atoms of aromatic solvent molecules at a slower rate. The amount of time required for isotopomer peaks to appear in the ¹H NMR hydride resonance of ReH₇(PPh₃)₂ was used to distinguish fast hydrogen exchange from slow hydrogen exchange. The room temperature ¹H NMR T₁ values of adventitious water resonances were used to distinguish two rhenium heptahydride compounds that participate in fast hydrogen exchange with water, ReH₇(PPh₃)₂ and ReH₇(AsPh₃)₂, from one compound that does not participate, ReH₇(PCy₃)₂. Fast hydrogen exchange between ReH₇(PPh₃)₂ and water is greatly slowed or stopped when the compound is dissolved in a solution that contains DMSO. The compound ReH₆D(PPh₃)₂, an isotopomer of ReH₇(PPh₃)₂ that was prepared in situ, exhibited an isotopomer shift in its ³¹P-{¹H} NMR spectrum as well as D-P coupling when measured in the solvent anisole. In a solvent system containing deuteroaniline, nearly all of the hydride ligands were exchanged with deuterium, from aniline, in less than 2 h. Hydrogen exchange between the hydride ligands of ReH₇(PPh₃)₂ and deuteroaniline was found to be reversible upon the addition of normal aniline. The distribution of hydrogen isotopes in the rhenium coordination spheres reflected the overall composition of the exchangeable hydrogen isotopes present in the bulk sample. In a deuteromethanol-containing solvent system, the exchange of hydride ligands between separate ReH₇(PPh₃)₂ isotopomers was evident. The presumed hydrogen exchange intermediate, [ReH₆(H₂)(PPh₃)₂]⁺, may be responsible for the evident exchange of hydride ligands and may also be important to the thermal loss of dihydrogen from ReH₇(PPh₃)₂.     

Synthesis and structural characterization of zwitterionic oxorhenium(V) complexes with 2-hydroxypyridine

[ReOX₃(PPh₃)₂] complexes (X = Cl and Br) react with equivalent amounts of 2-hydroxypyridine (Hhp) under formation of the mono-substituted, zwitterionic complexes mer-[ReOCl₃(Hhp)(PPh₃)] (1) and mer-[ReOBr₃(Hhp)(PPh₃)] (2). Crystal structure determinations of 1 · CH₂Cl₂ and 2 revealed the Cl and Br ligands adopt a mer arrangement. The Hhp ligands coordinate neutral and monodentate via their exocyclic oxygen atoms in axial positions, trans to the oxo groups. The distorted octahedral coordination sphere of the rhenium(V) complexes is completed by the phosphorus atom of the remaining PPh₃ ligand.     

Novel p-tolylimido rhenium(V) complexes incorporating quinoline-2-carboxylate ion - Synthesis, X-ray studies, spectroscopic characterization and DFT calculations

Novel p-tolylimido rhenium(V) complexes trans-[Re(p-NC₆H₄CH₃)X₂(quin-2-COO)(PPh₃)] and cis-[Re(p-NC₆H₄CH₃)X₂(quin-2-COO)(PPh₃)]·MeCN have been obtained in the reactions of [Re(p-NC₆H₄CH₃)X₃(PPh₃)₂] (X = Cl, Br) with quinoline-2-carboxylic acid. The compounds were identified by elemental analysis IR, UV-Vis spectroscopy and X-ray crystallography. The electronic structures of trans- and cis-halide isomers of [Re(p-NC₆H₄CH₃)Cl₂(quin-2-COO)(PPh₃)] have been calculated with the density functional theory (DFT) method. Additional information about binding in the compounds [Re(p-NC₆H₄CH₃)Cl₂(quin-2-COO)(PPh₃)] with cis- and trans-halide arrangement has been obtained by NBO analysis. The electronic spectra of trans and cis isomers of [Re(p-NC₆H₄CH₃)Cl₂(quin-2-COO)(PPh₃)] were investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.     

Ligand substitution reactions of the [ReX6] (X = Cl, Br) anions. Synthesis and crystal structure of novel oxalato complexes of rhenium(IV)

The reaction of K₂[ReX₆] (X = Cl, Br) with oxalic acid and triethylamine in dimethylformamide solution yields the substituted complexes [ReX₄(ox)]²⁻ and cis-[ReX₂(ox)₂]²⁻, which can be obtained separately depending on the amount of added amine. The crystal structures of (PPh₄)₂[ReBr₄(ox)], cis-(PPh₄)₂[ReBr₂(ox)₂] and cis-(AsPh₄)₂[ReCl₂(ox)₂] have been determined by single-crystal X-ray diffraction. The anionic complexes are octahedral with only slight distortions. The direct isolation of the pure complexes as well as the formation of only the cis isomers - without the presence of trans isomers and/or [Re(ox)₃]²⁻ - is probably due to the kinetic inertness of Re(IV)-X bonds, which increases with the number of oxalato ligands bound to the metal ion.     

New acylhydridorhodium(III) complexes containing terdentate PNN ligands from the reaction of diolefinic rhodium(I) complexes with o-(diphenylphosphino)benzaldehyde in the presence of chelating amino ligands

[{Rh(cod)Cl}₂] (cod=1,5-cyclooctadiene) reacts with o-(diphenylphosphino)benzaldehyde (PPh₂(o-C₆H₄CHO)) (Rh:P=1:1) in the presence of aromatic diamines or 8-aminoquinoline (NN) to give acylhydride [Rh(Cl)(H){PPh₂(o-C₆H₄CO)}(NN)] species. The oxidative addition of PPh₂(o-C₆H₄CHO) in the presence of (NN) and PPh₃ gives cationic species [Rh(H){PPh₂(o-C₆H₄CO)} (PPh₃)(NN)]⁺ containing mutually trans phosphorus atoms. When (NN)=8-aminoquinoline, a mixture of two isomers is obtained. These isomers differ in the nitrogen cis to the hydride, amino or quinolinic. By using Rh:PPh₂(o-C₆H₄CHO)=1:2 stoichiometric ratios, oxidative addition of one PPh₂(o-C₆H₄CHO) and P-coordination of another PPh₂(o-C₆H₄CHO) occurs. The aldehyde group undergoes then a condensation reaction with the coordinated amine to afford new PNN terdentate ligands, phosphine-amino-imine when (NN)=diamine or phosphine-diimine when (NN)=8-aminoquinoline. These reactions give selectively the corresponding complexes [Rh(H){PPh₂(o-C₆H₄CO)}(PNN)]⁺ containing trans phosphorus atoms and the hydride cis to the new imino group. X-ray diffraction studies of the PNN complexes are reported.     

Reactions of the fac-[Re(CO)3] and [ReO] moieties with substituted benzothiazoles

The reaction of 2-(2-aminophenyl)benzothiazole (Habt) with [Re(CO)₅Br] led to the isolation of the rhenium(I) complex fac-[Re(Habt)(CO)₃Br] (1). With trans-[ReOCl₃(PPh₃)₂], the ligand Habt decomposed to form the oxofree rhenium(V) complex [Re(itp)₂Cl(PPh₃)] (2) (itp = 2-amidophenylthiolate). From the reaction of trans-[ReOBr₃(PPh₃)₂] with 2-(2-hydroxyphenyl)benzothiazole (Hhpd) the complex [Re^VOBr₂(hpd)(PPh₃)] (3) was obtained. Complexes 1-3 are stable and lipophilic. ¹H NMR and infrared assignments, as well as the X-ray crystal structures, of the complexes are reported.     

Reactivity of [MO] (M = Tc, Re) core towards 2-mercapto-1,3-azole ligands. Formation of a new organometallic complex of Re(IV) and X-ray crystal structures

Imidazole-2-thiol derivatives H₂L^1-3 (H₂L¹ = 1H-benzoimidazole-2-thiol, H₂L² = 5-methyl-1H-benzoimidazole-2-thiol, and H₂L³ = 1H-imidazole-2-thiol) act as neutral monodentate ligands in a number of technetium and rhenium complexes. Disubstituted M(V) (M = Tc, Re) complexes of the type [AsPh₄]{[MOCl₂(H₂Lⁿ)₂(H₂O)]Cl₂} are formed when [MOCl₄]⁻ react with H₂L^1-3 in 1:2 stoichiometric ratio. Single crystal X-ray structure determinations were carried out on [AsPh₄]{[TcOCl₂(H₂L¹)₂(H₂O)]Cl₂}. The coordination sphere is pseudo-octahedral in which the sulfur atoms of two ligands sit in the equatorial plane and a water molecule is in trans to the TcO multiple bond. All the complexes react with an excess of the corresponding ligand to form tetrasubstituted cationic species {[MO(H₂Lⁿ)₄]Cl₃}. These complexes can be also isolated by reaction of [MOCl₄]⁻ with an excess of ligand. No complex is obtained with benzothiazole-2-thiol (HL⁴) and benzoxazole-2-thiol (HL⁵). Ligand exchange reactions of [ReOCl₃(PPh₃)₂] with HL^4,5 have also been investigated. Treating the oxo-precursor with HL⁴ no product is isolated, while with HL⁵ the chelate oxo-compound [ReOCl₂(L⁵)(PPh₃)] is formed as two isomers. An interesting organometallic complex of Re(IV) [ReCl₃(L^5∗)(PPh₃)₂] is obtained when a slight excess of HL⁵ reacts with [ReOCl₃(PPh₃)₂] in refluxing benzene solution and in air. Geometry about the Re atom is approximately octahedral in which the equatorial plane contains three Cl atoms and the carbon atom of the benzoxazole ligand anion, the apical positions are occupied by two PPh₃. The reaction with O-ethyl S-hydrogen p-tolyl carbonothioimidate HL⁶ which contains the same heteroatoms of HL⁵ does not form an organometallic species, but forms the chelate oxo-Re(V) complex [ReOCl₂(L⁶)(PPh₃)]. The solid-state structure has been authenticated by X-ray crystallography.     

Hydrido iridium(III) complexes of azoaromatic ligands. Isolation, structure and studies of their physicochemical properties

Reactions of 2-(arylazo)pyridine (L^a-c) with [IrCl₃(PPh₃)₂] in two different solvents, viz. ethanol and toluene are reported. In refluxing toluene two new isomeric (mer and fac geometries) iridium complexes, having molecular formula [IrCl₃(PPh₃)(L)] (1 and 2) have been isolated. The reaction in refluxing ethanol yielded two new hydrido complexes of molecular formula [IrHCl₂(PPh₃)(L)] (3) and [IrHCl(PPh₃)₂(L)]Cl (4) along with the compound 2. All the complexes have been thoroughly characterized by NMR, UV-Vis spectroscopy, cyclic voltammetry and X-ray crystallographic analysis. The ¹H NMR spectra of the hydrido complexes 3 and 4 showed a doublet and a triplet signals at δ −20.43 and −14.82 respectively due to coupling with magnetically equivalent phosphorous nuclei. Strong trans influence of the π-acceptor ligands guided the X-ray structural parameters; bonds trans to the these ligands are unusually long. Similar elongation effect was also noted for the bonds trans to the coordinated hydrido ligand. UV-Vis-NIR spectrum consisted of multiple transitions in the UV and visible regions. Cyclic voltammetry of each of these complexes has exhibited a reductive response between −0.25 and −0.55 V, which has been assigned to azo-ligand reduction. The compound 3, however, showed a quasireversible oxidative wave near 1.45 V, due to Ir^III/Ir^IV couple.     

Insertion of heteroallenes into the rhenium-hydride bond

Dithioformato [Re{η²-SC(H)S}(NO)P₃]BPh₄ (1), thioformamido [Re{η²-RNC(H)S}(NO)P₃]BPh₄ (2) (R = Et, p-tolyl), formamido [Re{η²-PhNC(H)O}(NO)P₃]BPh₄ (3) and formamidinato [Re{η²-p-tolylNC(H)Np-tolyl}(NO)P₃]BPh₄ (4) (P = PPh₂OEt) complexes were prepared by allowing the hydride ReH₂(NO)P₃ to react first with triflic acid and then with the appropriate heteroallene CS₂, RNCS, PhNCO and p-tolylNCNp-tolyl. Treatment of the ReH₂(NO)L(PPh₃)₂ [L = P(OEt)₃, PPh(OEt)₂] and ReH₂(NO)(PPh₃)₃ hydrides first with triflic acid and then with isothiocyanate RNCS (R = Et, p-tolyl) gave the [Re{η²-RNC(H)S}(NO){P(OEt)₃}(PPh₃)₂]BPh₄ (5, 6) and [Re(η²-RNC(H)S)(NO)(PPh₃)₃]BPh₄ (7) derivatives. Depending on the nature of the phosphite, instead, the reaction of ReH₂(NO)L(PPh₃)₂ and ReH₂(NO)(PPh₃)₃ hydrides first with CF₃SO₃H and then with isocyanate R1NCO (R1 = Ph, p-tolyl) gave the chelate [Re{η²-R1NC(H)O}(NO){P(OEt)₃}(PPh₃)₂]BPh₄ (8) and [Re{η²-R1NC(H)O}(NO)(PPh₃)₃]BPh₄(10) complexes with P(OEt)₃ or PPh₃, while the η¹-coordinate [Re{η¹-RNC(H)S}(NO){PPh(OEt)₂}₂(PPh₃)₂]BPh₄ (9) derivative was obtained with the PPh(OEt)₂ phosphite ligand. η¹-Coordinate dithioformato [Re{η¹-SC(H)S}(NO){PPh(OEt)₂}₂(PPh₃)₂]BPh₄ (11) and formato [Re{η¹-OC(H)O}(NO){PPh(OEt)₂}₂(PPh₃)₂]BPh₄ (12) complexes, as well as the formamidinato [Re{η²-p-tolylNC(H)Np-tolyl}(NO){P(OEt)₃}(PPh₃)₂]BPh₄ (13) derivative were also prepared.     

Rhodium(III) cis-dihydrido complexes with 3,6-bis(2′-pyridyl)pyridazine (dppn) and bidiazines. Crystal and molecular structure of [Rh(H)2(dppn)(PPh3)2]PF6· CH2Cl2

The acetone complex [Rh(H)₂(acetone)₂(PPh₃)₂]- PF₆ reacts with bidiazines and 3,6-bis(2′-pyridyl)- pyridazine (dppn) giving the air stable cis-dihydrido rhodium(III) [Rh(H)₂(L)(PPh₃)₂]PF₆ complexes. The structure of the dichloromethane solvate of [Rh(H)₂(dppn)(PPh₃)₂]PF₆ has been determined by X-ray crystal structure analysis. Crystals are monoclinic, space group P2₁/a, with a = 18.629(6), b = 15.339(5), c = 17.146(5) Å, β = 101.02(3)° and Z = 4. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by block-matrix least-squares to R = 0.076 for 6225 observed reflections. In the structure discrete [Rh(H)₂(dppn)(PPh₃)₂]⁺ cationic complexes, PF₆⁻ anions and dichloromethane solvent molecules are present. The Rh atom is octahedrally surrounded by two cis hydride ligands and by two cis nitrogen atoms from a dppn molecule acting as a bidentate chelating ligand through two neighbouring pyridyl and pyridazinyl nitrogen atoms. Two P atoms from PPh₃, ligands in trans apical positions complete to octahedral the coordination of Rh.     

Synthesis and characterisation of adducts of [Pt2(μ-S)2(PPh3)4] with organo-palladium and platinum-hydride substrates

The reactions of [Pt₂(μ-S)₂(PPh₃)₄] towards a range of palladium(II) complexes containing organometallic ligands (cyclopalladated N-donor ligands, η³-allyl, phenyl) have been explored, leading to the formation of a series of cationic, trinuclear sulfido-bridged aggregates containing {Pt₂PdS₂} cores. [Pt₂(μ-S)₂(PPh₃)₄] also reacts with the platinum(II) hydride complex trans-[PtHCl(PPh₃)₂] giving the adduct [Pt₂(μ-S)₂(PPh₃)₄PtH(PPh₃)]⁺. X-ray crystal structure determinations on the complexes [Pt₂(μ-S)₂(PPh₃)₄PdPh(PPh₃)]PF₆ and [Pt₂(μ-S)₂(PPh₃)₄PtH(PPh₃)]PF₆ are reported, and show the expected bis μ₃-sulfido aggregates with three square-planar metal centres.     

Synthesis, structure and properties of di- and mononuclear ruthenium(III) complexes with N-(benzoyl)-N′-(salicylidene)hydrazine and its derivatives

The reactions of [Ru(PPh₃)₃Cl₂], N-(benzoyl)-N′-(5-R-salicylidene)hydrazines (H₂bhsR, R = H, OCH₃, Cl, Br and NO₂) and triethylamine (1:1:2 mole ratio) in methanol afford mononuclear ruthenium(III) complexes having the general formula trans-[Ru(bhsR)(PPh₃)₂Cl]. In the case of R = H, a dinuclear ruthenium(III) complex of formula [Ru₂(μ-OCH₃)₂(bhsH)₂(PPh₃)₂] has been isolated as a minor product. The complexes are characterized by elemental analysis, magnetic, spectroscopic and electrochemical measurements. The crystal structures of the dinuclear complex and two mononuclear complexes have been determined. In the dinuclear complex, each metal centre is in distorted octahedral NO₄P coordination sphere constituted by the two bridging methoxide groups, one PPh₃ molecule and the meridionally spanning phenolate-O, imine-N and amide-O donor bhsH²⁻. The terminal PPh₃ ligands are trans to each other. In the mononuclear complexes, bhsR²⁻ and the chlorine atom form an NO₂Cl square-plane around the metal centre and the P-atoms of the two PPh₃ molecules occupy the remaining two axial sites to complete a distorted octahedral NO₂ClP₂ coordination sphere. All the complexes display ligand-to-metal charge transfer bands in the visible region of the electronic spectra. The cryomagnetic measurements reveal the antiferromagnetic character of the diruthenium(III) complex. The low-spin mononuclear ruthenium(III) complexes as well as the diruthenium(III) complex display rhombic EPR spectra in frozen solutions. All the complexes are redox active in CH₂Cl₂ solutions. Two successive metal centred oxidations at 0.69 and 1.20 V (versus Ag/AgCl) are observed for the dinuclear complex. The mononuclear complexes display a metal centred reduction in the potential range −0.53 to −0.27 V. The trend in these potential values reflects the polar effect of the substituents on the salicylidene moiety of the tridentate ligand.     

The naphthylamine palladium(II) template induced E-Z isomerism of exocyclic vinyl group in five-membered P-N chelates: detailed spectroscopic studies

The exocyclic CC bond E-Z isomerism of chelating Ph₂PC(CHPh)-CHNAr in organopalladium complexes containing orthometallated [(S)-1-(dimethylamino)ethyl]naphthalene is reported. In dilute solutions of non-coordinating CH₂Cl₂ or CHCl₃, all the original E-isomers, in which the CHPh phenyl rings are located trans to PPh₂ moieties were partly converted to their Z-isomers. The isomerism was found to be dependent on temperature, concentration and solvent. At higher temperature, the Z-isomers were transformed completely back to their original E-isomers. Removal of the chiral auxiliaries of the E-Z mixtures by concentrated HCl, gave only the dichloro complexes of the E-isomers. The E-Z isomerization processes were well established by detailed spectroscopic studies, including ³¹P NMR, ¹H NMR and 2D ¹H-¹H ROESY NMR studies. It is noteworthy that the dichloro complexes and free P-N ligands did not show such isomerization processes, indicating that the isomerization processes were triggered by the orthopalladated naphthylamine moiety.     

Ruthenium PCP–bis(phosphinite) pincer complexes

The reactions of [RuHCl(CO)(PPh₃)₃] with resorcinol bis(phosphinite) pincer ligands lead to complexes of the general formula [RuCl(PCP)(CO)(PPh₃)]; the crystal structure of one example has been determined. The structures of the bulky resorcinol 2-methyl-4,6-di-tert-butyl resorcinol and its mono-diisopropylphosphinite derivative were also determined. Reactions of [RuCl₂(PPh₃)₃] with resorcinol bis(phosphinite) ligands yield complexes of the type [RuCl(PCP)(PPh₃)], while the reaction of C₆H-2-Me-4,6-^tBu₂-1,3-(OPPh₂) with [RuHCl(CO)(PPh₃)₃] provides a PCP–pincer complex in which the ligand has undergone 2-methyl C–H activation.     

Synthesis,characterization, and biological activity of platinum II,III, and IV pivaloamidine complexes

Imino ligands have proven to be able to activate the trans geometry of platinum(II) complexes towards antitumor activity. These ligands, like aromatic N-donor heterocycles, have a planar shape but, different from the latter, have still an H atom on the coordinating nitrogen which can be involved in H-bond formation. Three classes of imino ligands have been extensively investigated: iminoethers (HN=C(R)OR′), ketimines (HN=CRR′), and amidines (HN=C(R)NR′R″). The promising efficacy of the platinum compounds with amidines (activity comparable to that of cisplatin for cis complexes and much greater than that of transplatin for trans complexes) prompted us to extend the investigation to amidine complexes with a bulkier organic residue (R = t-Bu). The tert-butyl group can confer greater affinity for lipophilic environments, thus potentiating the cellular uptake of the compound. In the present study we describe the synthesis and characterization of pivaloamidine complexes of platinum(II), (cis and trans-[PtCl₂(NH₃){Z-HN=C(t-Bu)NH₂}] and cis and trans-[PtCl₂{Z-HN=C(t-Bu)NH₂}₂]), platinum(III) ([Pt₂Cl₄{HN=C(t-Bu)NH}₂(NH₃)₂]), and platinum(IV) (trans-[PtCl₄(NH₃){Z-HN=C(t-Bu)NH₂}] and trans-[PtCl₄{Z-HN=C(t-Bu)NH₂}₂]). The cytotoxicity of all new Pt complexes was tested toward a panel of cultured cancer cell lines, including cisplatin and multidrug resistant variants. In addition, cellular uptake and DNA binding, perturbations of cell cycle progression, induction of apoptosis, and p53 activation were investigated for the most promising compound trans-[PtCl₂(NH₃){Z-HN=C(t-Bu)NH₂}]. Remarkably, the latter complex was able to overcome both acquired and intrinsic cisplatin resistance.     

Studies on the reactions of ruthenium(II) substrates with tridentate (N,N,O) azo ligands

Reactions of 1-{[2-(arylazo)phenyl]iminomethyl}-2-phenol, HL_sal, 1, [where H represents the dissociable protons upon complexation and aryl groups of HL_sal are phenyl for HL¹_sal, p-methylphenyl for HL²_sal, and p-chlorophenyl for HL³_sal], ligands with Ru(H)(CO)(Cl)(PPh₃)₃ afforded complexes of composition [(L_sal)Ru(CO)(Cl)(PPh₃)] and (L_sal)₂Ru where the N,N,O donor tridentate (L_sal)⁻ ligands coordinated the metal centre facially and meridionally, respectively. Stepwise formation of [(L_sal)₂Ru] has been ascertained. Reaction of 1-{[2-(arylazo)phenyl]iminomethyl}-2-napthol, HL_nap, 2, [where H represents the dissociable protons upon complexation and aryl groups of HL_nap are phenyl for HL¹_nap, p-methylphenyl for HL²_nap, and p-chlorophenyl for HL³_nap], ligands with Ru(H)(CO)(Cl)(PPh₃)₃ afforded exclusively the complexes of composition [(L_nap)Ru(CO)(Cl)(PPh₃)], where N,N,O donor tridentate (L_nap)⁻ was facially coordinated. The ligand 1-{[2-(phenylazo)phenyl]aminomethyl}-2-phenol, HL, 3, was prepared by reducing the aldimine function of HL¹_sal. Reaction of HL with Ru(PPh₃)₃Cl₂ afforded new azosalen complex of Ru(III) in concert with regiospecific oxygenation of phenyl ring of HL. All the new ligands were characterized by analytical and spectroscopic techniques. The complexes were characterized by analytical and spectroscopic techniques and subsequently confirmed by the determination of X-ray structures of selected complexes.     

Synthesis and study of Pt(II)-aromatic amines complexes of the types cis- and trans-Pt(amine)2(NO3)2 and cis-Pt(amine)2(R(COO)2)

Complexes of the types cis- and trans-Pt(amine)₂(NO₃)₂ with amines containing a phenyl group were synthesized and studied mainly by IR and multinuclear magnetic resonance spectroscopies. The cis complexes could be synthesized pure only with the amines of the type Ph-R-NH₂ (R = alkyl), while pure trans compounds were synthesized with all the studied amines. In ¹⁹⁵Pt NMR spectroscopy, the dinitrato complexes of the amines Ph-R-NH₂ were observed around −1700 ppm for the cis isomers and at about −1580 for the trans complexes. For the other amines, where a phenyl ring is directly attached to the amino group, the signals were observed at lower fields, −1528 ppm for cis-Pt(PhNH₂)(NO₃)₂ and around −1450 ppm for all the trans isomers. There is a linear relationship between the δ(Pt) of the Pt(amine)₂(NO₃)₂ complexes and the pK_a of the protonated amines. The coupling constants ²J(¹⁹⁵Pt-¹HN) are larger in the cis compounds (ave. 76 Hz) than in the trans isomers (ave. 63 Hz). The complexes cis-Pt(amine)₂(R(COO)₂) with bidentate dicarboxylato ligands were also synthesized and characterized mainly by IR spectroscopy. The compounds apparently decompose in DMF and are too insoluble in other solvents for solution studies.     

Reactions of the Tridentate and Tetradentate Amine Ligands di-(2-picolyl)(N-ethyl)amine and 2,5-Bis-(2-pyridylmethyl)-2,5 diazohexane with Technetium Nitrosyl Complexes

The reaction of the Tc(II) nitrosyl complex (Bu₄N)[Tc(NO)Cl₄] with di-(2-picolyl)(NEt)amine in methanol yields the neutral complex [Tc(NO)Cl(py-N(Et)-py)]. The reaction of the Tc(I) nitrosyl complex [Tc(NO)Cl₂(HOMe)(PPh₃)₂] with this tridentate ligand yields cationic [Tc(NO)Cl(py-N(Et)-py)(PPh₃)]Cl. These two complexes have been structurally characterized. The reaction of [Tc(NO)Cl₂(HOMe)(PPh₃)₂] with the tetradentate ligand 1,4-bis-(2-pyridylmethyl)-1,4-diazobutane yields a mixture of products including cationic [Tc(NO)Cl(py-NH-NH-py)]Cl and cationic [Tc(NO)Cl(PPh₃)(py-NH-NH∼py)]Cl, with a pyridyl terminus left dangling.     

Cationic oxorhenium chiral salen complexes for asymmetric hydrosilylation and kinetic resolution of alcohols

High valent transition metal oxo complexes are ubiquitous in catalytic oxidation and oxygen atom transfer reactions, while their application in catalytic reductions is only being realized in the past few years. Reaction of ReOCl₃(PPh₃)₂ with appropriate chiral salen ligands, followed by oxo abstraction with a silylium cation, afforded several cationic oxorhenium(V)-saldach complexes 1-2, including a rare trinuclear rhenium cluster (2), all of which have been fully characterized. These complexes are effective catalysts for hydrosilylation of carbonyl compounds and silane alcoholysis, although the enantioselectivity for both reactions is rather low. An intermediate, featuring a partially reduced saldach ligand (a salen/salan hybrid), was identified in reaction of 1a with Et₃SiH. The reaction mechanism is discussed in light of results from a crossover experiment.     

Voltammetry of half-sandwich manganese group complexes of η-PhC3B7H9 and η-C60Bn2PhH2, two ligands that are cyclopentadienyl mimicks

The potentials of a series of one-electron oxidation and reduction reactions have been determined for manganese group half-sandwich complexes of the tricarbadecaboranyl ligand PhC₃B₇H₉ and the penta-organo fullerene ligand C₆₀Bn₂PhH₂ (Bn = benzyl). The anodic processes were studied in CH₂Cl₂ and the cathodic processes were studied in both CH₂Cl₂ and THF, the supporting electrolyte being [NBu₄][B(C₆F₅)₄]. The manganese complex Mn(CO)₂(PMe₃)(PhC₃B₇H₉) (1) is a member of a three-electron transfer series which includes oxidation to 1⁺ (0.51 V versus ferrocene) and successive reductions to 1⁻ (−1.66 V) and 1²⁻ (−1.77 V). Both the oxidation and reduction of the closely-related complex Mn(CO)₂(PPh₃)(PhC₃B₇H₉) (2) are chemically irreversible under slow-scan cyclic voltammetry conditions. The rhenium complex Re(CO)₂(PPh₃)(PhC₃B₇H₉) (3) oxidizes (E_1/2 = 0.82 V versus ferrocene) to a radical cation which, unlike its cyclopentadienyl analogue, shows no evidence of dimerization. Oxidation of the fullerene-based complex Re(CO)₃(C₆₀Bn₂PhH₂) is more facile than that of its cyclopentadienyl analogue, in contrast to previous findings in this class of metal-fullerene derivatives. An electrochemical ligand factor, E_L, of 0.63 is calculated for the PhC₃B₇H₉ ligand in manganese group half-sandwich complexes.