Versatile coordination behaviour of Ph2AsCH2AsPh2 with Ru(II)

Treatment of ‘RuCl₃ · 3H₂O’ with Ph₂AsCH₂AsPh₂ (dpam) in hot EtOH gives either trans-[RuCl₂(dpam-As,As′)(dpam-As)₂] (1), or cis-[RuCl₂(dpam-As,As′)₂] (2), depending on the mole ratio. On exposure to light, solutions of 2 isomerise to trans-[RuCl₂(dpam-As,As′)₂] (3). Treatment of [RuCl₂(PPh₃)₃] with two equivalents of dpam in CH₂Cl₂ gave a mixture of two products, from which trans-[RuCl₂(PPh₃) (dpam-As,As′)(dpam-As)] (4) was isolated by recrystallisation. The crystal structures of 1-4 are reported. Complexes 1-3 in CH₂Cl₂ undergo electrochemical oxidation to Ru(III), and the Ru(III) form of 2 undergoes isomerisation on the voltammetric timescale to the Ru(III) form of 3.     

Syntheses and structures of vinyl and aryl derivatives of carbonyl halide iron complexes

cis,trans-Fe(CO)₂(PMe₃)₂(p-Y-C₆H₄)X [X=Br, Y=H (4a), MeO (4b), Cl (4c), F (4d), Me (4e); X=I, Y=H (5); X=Cl, Y=H (6)] and cis,trans-Fe(CO)₂(PMe₃)₂(σ-CHCH₂)X [X=Br (7); X=I (8); X=Cl (9)] are prepared by reacting dihalide complexes cis,trans,cis- Fe(CO)₂(PMe₃)₂X₂ [X=Br (1), X=I (2), X=Cl (3)] with Grignard reagents p-Y-C₆H₄-MgBr (Y=H, OMe, Cl, F, Me) or CH₂CH-MgBr and with lithium reagents PhLi, CH₂CH-Li. With both reagents, the reaction proceeds following two parallel pathways: one is the metallation reaction which yields alkyl derivatives, the other affords 17 electron complexes [Fe(CO)₂(PMe₃)₂X] via monoelectron reductive elimination. The influence of the halides and organometallic reagents on the yield of the metallation reaction is discussed. The solution structure of the complexes is assigned on the basis of IR and ¹H, ¹³C, ¹⁹F, ³¹P NMR spectra. The solid state structure of complexes 4a, 5 and 6 is determined by single crystal X-ray diffractometric methods.     

Synthesis of ruthenium(II) monosubstituted squarates: 1. Procedural considerations

Attempted syntheses of ruthenium(II) monosubstituted squarate complexes in acetonitrile using cis-[RuCl₂(dmso)₄] and anisole-, methoxy-, methyl- and diphenylamino-squarate ligands, respectively, resulted in the formation in each case of the monomer cis, fac-Ru(CH₃CN)Cl₂(dmso)₃ (1) with the ruthenium atom in a distorted octahedral environment. A second crop of crystals harvested from the reaction with the methoxysquarate ligand was identified as the oxalato-bridged dimer [{cis-(CH₃CN)(Cl)(dmso)₂Ru}₂(μ-C₂O₄)] (2). When cis-[RuCl₂(dmso)₄] and methylsquarate were reacted in aqueous solution instead of acetonitrile, the dimer [{fac-(Cl)(dmso)₃Ru}₂(μ-C₂O₄)] (3) was produced. The dimers 2 and 3 are formed from oxidation/ring opening of the methoxy- and methyl-squarate ligands, respectively. Use of the salts of these ligands instead of their non-ionised forms under different reaction conditions, afforded [Na] fac-[RuCl₃(dmso)₃] (4) and [(C₄H₉)₄N]₂[(C₄O₄)(C₄H₂O₄)₂] (7), respectively, which were shown to be products of competing reactions. The information acquired from these failed attempts has provided the basis for the development of a strategy to overcome these problems and lead to a successful synthetic route to ruthenium(II) monosubstituted squarates.     

The crystal and molecular structures of dioxo mo(VI) complexes of tripodal,tetradentate N,S-donor ligands

The crystal and molecular structures of the complexes MoO₂((SCH₂CH₂)₂NCH₂CH₂SCH₃), I and MoO₂((SCH₂CH₂)₂NCH₂CH₂N(CH₃)₂), II, have been determined from X-ray intensity data collected by counter methods. Compound I crystallizes in two forms, Ia and Ib. In form Ia the space group is P2₁/n with cell parameters a = 7.235(2), b = 7.717(2), c = 24.527(6) Å, β = 119.86(2)°, V = 1188(1) ų, Z = 4. In form Ib the space group is P2₁/c with cell parameters a = 14.945(5), b = 11.925(5), c = 14.878(4) Å, β = 114.51(2)°, V = 2413(3) ų, Z = 8. The molecules of I in Ia and Ib are very similar having an octahedral structure with cis oxo groups, trans thiolates (cis to both oxo groups) and N and thioether sulfur atoms trans to oxo groups. Average ditances are MoO = 1.70, MoS (thiolate) = 2.40, MoN = 2.40 and MoS (thioether) = 2.79 Å. Molecule II crystallizes in space group P2₁2₁2₁ with a = 7.188(1), b = 22.708(8), c = 7.746(2) Å, V = 1246(1) ų and Z = 4. The coordination about Mo is octahedral with cis oxo groups, trans thiolates and N atoms trans to oxo. Distances in the first coordination sphere are MoO = 1.705(2), 1.699(2), MoS = 2.420(1), 2.409(1) and MoN = 2.372(2), 2.510(2) Å. The conformational features of the complexes are discussed. Complex I displays MoO and MoS distances which are very similar to those found by EXAFS in sulfite oxidase. This similarity is discussed.     

Synthesis of dimethylcobalt(III) complexes containing trimethylphosphine and 2-formyl-phenolato- or 2-formyl-enolato(O:O) ligands

Substituted salicylaldehydes [C₆HR¹R²R³(CHO)(OH)] react with CoMe₃(PMe₃)₃ to afford 6-coordinate (cis-dimethyl)(2-formyl-phenolato)trans-bis(trimethylphosphine)cobalt(III) compounds Co[C₆HR¹R²R³(CHO)(O)Me₂](PMe₃)₂ (1: R¹ = H; R² = Me; R³ = tert-Bu; 2: R¹, R² = C₆H₄; R³ = H). Accordingly, substituted enolated malonic dialdehydes (CHO-CR⁴CR⁵-OH) react with CoMe₃(PMe₃)₃ to afford 6-coordinate (cis-dimethyl)(2-formyl-enolato)trans-bis(trimethylphosphine)cobalt(III) compounds Co[(CHO-CR⁴CR⁵-O)(Me)₂](PMe₃)₂ (3: R⁴, R⁵ = (CH₂)₂C₆H₄; 4: R⁴ = R⁵ = C₆H₅). In the molecular structure of 4, the cobalt atom is centred in an octahedral coordination geometry brought about by a six-membered chelate ring (O:O-ligand), cis-dimethyl and trans-trimethylphosphine groups. A reaction mechanism is suggested.     

The unexpected reactions of [RuCl3(2mqn)NO] (H2mqn=2-methyl-8-quinolinol) with 2-chloro-8-quinolinol (H2cqn) and of [RuCl(2cqn)(2mqn)NO] on photoirradiation

The reaction of [RuCl₃(2mqn)NO]⁻ (H2mqn=2-methyl-8-quinolinol) with 2-chloro-8-quinolinol (H2cqn) afforded cis-1 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2cqn is trans to the NO) (complex 1), cis-1 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2mqn is trans to the NO) (complex 2) and a 1:1 mixture of cis-2 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2mqn is trans to the NO) and cis-2 [RuCl(2cqn)(2mqn)NO] (the oxygen of 2cqn is trans to the NO) (complex 3). The reaction was compared with that of [RuCl₃(2mqn)NO]⁻ with 8-quinolinol (Hqn) or 5-chloro-8-quinolinol (H5cqn). Photoirradiation reaction of complex 1 at room temperature in deaerated CH₂Cl₂ in the presence of NO gave trans-[RuCl(2cqn)(2mqn)NO] (the Cl is trans to the NO) and complex 2 with recovery of complex 1. The reaction was contrasted with that of cis-1 [RuCl(qn)(2mqn)NO] or cis-1 [RuCl(5cqn)(2mqn)NO]. The crystal structure of complex 1 was determined by X-ray diffraction. The reactions were examined under consideration of atomic charge of the phenolato oxygen in 8-quinolinol and its derivatives calculated at the restricted Hartree-Fock/6-311G** level.     

Stabilization of dimethyliron(II) and methylcobalt(I) complexes bearing a hemilabile 2-benzoylpyridine ligand in octahedral and square-pyramidal coordination

Octahedral cis-Fe(CH₃)₂{2-(benzoyl)pyridyl-N,O}(PMe₃)₂ (1), square-pyramidal Co(CH₃){2-(benzoyl)pyridyl-N,O}(PMe₃)₂ (2), and triangular-planar Ni{2-(benzoyl)pyridyl-η²-C,O}(PMe₃)₂ (3) have been synthesized by reaction of 2-benzoylpyridine with thermally labile Fe(CH₃)₂(PMe₃)₄ and Co(CH₃)(PMe₃)₄ complexes. With Ni(CH₃)₂(PMe₃)₃, reductive elimination of ethane is observed when a η²-C,O-coordination is constituted. The complexes were investigated by NMR spectroscopic methods and the molecular structures of 1 and 2 were determined by X-ray crystallography.     

Synthesis and characterization of ruthenium(II) complexes bearing the bis(2-pyridylmethyl)amine ligand

The reaction of [Ru(CO)₂Cl₂]_n with bis(2-pyridylmethyl)amine (bpma) in refluxing ethanol followed by anion exchange yields two products: cis,fac-[Ru(bpma)(CO)₂Cl]PF₆ (1a, 71%) and trans,fac-[Ru(bpma)(CO)₂Cl]PF₆ (1b, 29%). Reaction of 1a with AgBF₄ in acetone, followed by acetonitrile and then anion exchange gave cis,fac-[Ru(bpma)(CO)₂(CH₃CN)](PF₆)₂ (2a). In the same way, 1b afforded trans,fac-[Ru(bpma)(CO)₂(CH₃CN)](PF₆)₂ (2b). Reaction of depolymerized [Ru(CO)₂Cl₂]_n with bpma in ethanol at room temperature afforded cis,cis-[Ru(η²-bpma)(CO)₂Cl₂] (3). In refluxing ethanol, 3 was converted to cis,fac-[Ru(bpma)(CO)₂Cl]Cl (1a-Cl). Heating 3 in chlorobenzene afforded 1b-Cl, exclusively; heating 3 in ethylene glycol gave mainly 1a-Cl. Heating 1a-Cl in ethanol resulted in no isomerization, but heating in chlorobenzene gave a mixture of 3 and 1b-Cl. Anion exchange for PF₆ with 1a-Cl and 1b-Cl afforded 1a and 1b, respectively, whereas anion exchange for BPh₄ afforded 1a-BPh₄. Compounds 1a, 1b, 2a and 3 have been structurally characterized.     

Syntheses and characterization of the W(II) and W(III) N2 complexes, [WCl2(PMe3)3]2N2 and [WCl3(PMe3)2]2N2

Refluxing WCl₄(PMe₃)₃ under a nitrogen atmosphere in the presence of two equivalents of sodium amalgam leads to a reduction to the W(II) complex [cis,mer-WCl₂(PMe₃)₃]₂N₂ (1), which can be converted to [mer,trans-WCl₃(PMe₃)₂]₂N₂ (2) via appropriate oxidation/chlorination. Structural data have been obtained for both complexes, and demonstrate significantly increased steric crowding in 1 due to PMe₃/PMe₃ interactions. The N-N bond distances in the two compounds are similar, at 1.279(4) and 1.243(18) Å, respectively.     

Mechanism of toxicity of platinum(II) compounds in repair-deficient strains of Escherichia coli

The survival of wild-type and repair-deficient Escherichia coli treated with cis-Pt(NH₃)₂Cl₂, trans-Pt(NH₃)₂Cl₂ and [Pt(dien)Cl]Cl (dien = H₂NCH₂CH₂NHCH₂CH₂NH₂) was inversely correlated with the ability of these compounds to inhibit DNA synthesis in different bacterial strains. The relative amounts of these 3 compounds covalently bound to DNA immediately after treatment with the same dose were, respectively, 1:?2:1, their relative abilities to inhibit DNA synthesis were 6:1:0 and their relative toxicities toward the wild-type and uvrA strains were 3–5:1:0. More repair synthesis, as measured by density-gradient centrifugation techniques, was observed in wild-type bacteria after treatment with the cis than with the trans isomer whereas no repair synthesis was detected after exposure to [Pt(dien)Cl]Cl.These results are consistent with the hypothesis that cis-Pt(NH₃)Cl₂ binds to DNA and inhibits DNA synthesis thereby killing the cell. The lower toxicity of this compound toward wild-type bacteria compared with repair-deficient strains is in part a consequence of DNA repair. trans-Pt(NH₃)₂Cl₂ and [Pt(dien)Cl]Cl are less toxic than the cis isomer; this lesser toxicity is not a consequence of low levels of DNA binding or enhanced repair of the lesions but appears to reflect a weaker inhibition of DNA synthesis by these Pt-DNA adducts.     

Transition metal complexes with sulfur ligands. XIX. Mono- and bis-alkylation of [Ru(II)L1L2dttd] complexes controlled by the ligands L as well as the charge of the resulting compounds (dttd2−=2,3:8,9-dibenzo-1,4,7,10-tetrathiadecane(−2), L1L2PPh3; L1L2PMe3; L1PPh3, L2PMe3)

The alkylation of the thiolato-S atoms of the dttd- ligand in [RuL₁L₂dttd] complexes was investigated (L₁L₂PPh₃; L₁L₂PMe₃; L₁PPh₃, L₂PMe₃; dttd²⁻=2,3:8,9-dibenzo-1,4,7,10-tetrathiadecane(−2)). The substitution lability of the phosphine ligands L₁ and L₂ determines whether one or both of the thiolato-S atoms are alkylated when [RuL₁L₂dttd] is reacted with alkylhalides. [Ru(PPh₃)₂dttd], in which one PPh₃ is substitution labile, is doubly alkylated on reaction with CH₃I yielding [Ru(PPh₃)I(Me₂-dttd)]I (Me₂-dttd=1,10-dimethyl-2,3:8,9-dibenzo-1,4,7,10-tetrathiadecane). Reaction of the substitution inert phosphine complexes [Ru(PMe₃)₂dttd] and [Ru(PPh₃)(PMe₃)dttd] with CH₃I yields the monoalkylated derivatives [Ru(PMe₃)₂(Me-dttd)]I and [Ru(PPh₃)(PMe₃)(Me- dttd)]I, respectively. Analogously, ethyl as well as bromine derivatives can be obtained. The cation in [Ru(PPh₃)X(Me₂-dttd)]X (XI, Br) proves to be substitution inert under ordinary conditions; the anion X can be exchanged for other singly charged anions via [Ru(PPh₃)X(Me₂dttd)]₂SO₄. In concentrated H₂SO₄, [Ru(PPh₃)Br(Me₂-dttd)]Br could be reacted to give [Ru(Br₂)(Me₂dttd)]. All compounds were characterized spectroscopically as well as by elemental analyses. The structure of [Ru(PPh₃)I(Me₂- dttd)]I was determined by X-ray structure analysis.[Ru(PPh₃)I(Me₂-dttd)]I (1) crystallizes from CH₂Cl₂ as 1·3CH₂Cl₂ in the monoclinic space group P2₁/c with the following unit cell dimensions: a= 20.103(0.03), b=11.148(0.009), c=26.985(0.03) Å; β=130.71(0.07)°, V=4584(3) ų and Z=4. The structure refinement stopped at R₁=8.86 and R₂= 10.44% because of disorder of the CH₂Cl₂ solvate molecules. In the cation of 1 Ru is coordinated pseudo-octahedrally by I-, P- and four thioether-S atoms.     

Homogeneous CO hydrogenation and transfer hydrogenation catalyzed by ruthenium(II) complexes containing optically active Ph2PCH(Ph)CH(Me)NH2 and 1,2-C5H8(PPh2)2 ligands

Combination of (1S,2S)-cyclopentanediylbis(diphenylphosphine) with [Ru(η⁴-C₈H₁₂){η³-(CH₂)₂CMe}₂] afforded the chelate complex [Ru{η³-(CH₂)₂CMe}₂{(1S,2S)-C₅H₈(PPh₂)₂}] (1), which gave (OC-6-13)-[RuCl₂{(1S,2S)-C₅H₈(PPh₂)₂}{(1S,2S)-Ph₂PCH(Ph)CH(Me)NH₂}] (2) upon reaction with methanolic HCl in acetone, followed by the addition of the β-aminophosphine in DMF. The (P ∩ N)₂-chelated complexes (OC-6-13)-[RuCl₂{(1S,2S)-Ph₂PCH(Ph)CH(Me)NH₂}₂] (3) and (OC-6-13)-[RuCl₂{(1R,2S)-Ph₂PCH(Ph)CH(Me)NH₂}₂] (4) resulted from RuCl₃ · 3H₂O and the P,N ligands under reducing conditions. The crystal structures of 3 and 4 were determined by single-crystal X-ray diffraction. Following activation by KOBu-t in isopropanol, compounds 2–4 catalyzed the enantioselective transfer hydrogenation of acetophenone with i-PrOH as the hydrogen source as well as the direct hydrogenation of the ketone by H₂ in low to moderate e.e. (up to 67%).     

Coordination chemistry of higher oxidation states. Part 21. Platinum-195 NMR studies of platinum(II) and platinum(IV) complexes of bi- and multi-dentate phosphorus,arsenic and sulphur ligands

195-Platinum NMR spectra are reported for a series of complexes of bidentate ligands [Pt(LL)X₄] (X=Cl, Br; LL=diphosphine, diarsine, dithioether, diselenoether), [Pt(Me₂PCH₂CH₂PMe₂)₂X₂]X₂, [Pt(o-C₆H₄(AsMe₂)₂)₂X₂]X₂, and for the Pt(II) analogues. The trends in chemical shifts δ(Pt) and ¹J(PtP), ¹J(PtSe) coupling constants are discussed, and used to establish the nature of the solution species obtained by oxidation of Pt(II) complexes of some multidentate phosphorus and arsenic ligands. The [Pt(LL)I₄] materials are shown to exist as [Pt^II(LL)I₂] in dimethylsulphoxide solution, but [Pt(o-C₆H₄(AsMe₂)₂)₂I₂]²⁺ is a genuine Pt(IV) iodo-complex.     

Complexes of hybrid ligands. Synthesis of mixed-ligand,phosphino-alkoxide complexes of Pd2+: the crystal and molecular structure of the complex Ph2 PCH2C(CF3 )2OPdCl(PPh2Me)

The hybrid, bidentate, diarylphosphino-alkoxide ligand PPh₂CH₂C(CF₃)₂O⁻, L¹, gives the Pd²⁺ bis- complex Pd(L¹)₂, from which the chloride-bridged dinuclear complex [(L¹)Pd(μ-Cl)₂Pd(L¹)] is made by reaction with PdCl₂(PhCN)₂. Cleavage of the dinuclear complex with monodentate ligands L² then gives Pd(L¹)Cl(L²) (L² =PPh₃, PPh₂Me, PPhMe₂, PMe₃, SMe₂, or pyridine); NMR data show that PR₃ is cis to the phosphine site in L¹ in these complexes, but SMe₂ or pyridine are probably trans.A complete crystal and molecular structural determination has been made for cis-Pd(L¹)Cl(PPh₂Me). Crystals are monoclinic, space group P2₁/c, a = 10.821(1), b = 14.600(1), c = 18.674(2) Å, β = 101.25(1)°, V = 2893 ų, Z = 4. Least-squares refinement on F of 361 variables using 3977 observations converged at a conventional agreement factor R = 0.025. The complex is square-planar, with the two phosphines cis; the 5-membered chelate ring is in a dissymmetric envelope conformation. The PdP bonds differ in length, with that to the unidentate phosphine, 2.259(1) Å, being significantly longer than that to the phosphine on the chelating ligand, 2.231(1) Å.     

Structure and reactivity of [Ru(2,3-Medpp)2Cl2]

The structure and reactivity of the complex [Ru(2,3-Medpp)₂Cl₂](PF₆)₂ (2,3-Medpp⁺=2-[2-(1-methylpyridiniumyl)]-3-(2-pyridyl)pyrazine) was investigated by X-ray diffraction (XRD), ¹H NMR, redox, and UV-Vis absorption measurements. X-ray analysis shows that crystals obtained from an acetonitrile-toluene solution contain the trans-Cl₂, trans-pyrazine isomeric form, while ¹H NMR and redox measurements on the main product of the synthetic workup indicate the presence of the trans-Cl₂, cis-pyrazine isomer. In the dark at 70 °C, the complex [Ru(2,3-Medpp)₂Cl₂]²⁺ reacts slowly in acetonitrile isomerizing to the cis-[Ru(2,3-Medpp)₂(CH₃CN)Cl]³⁺ species. Under ambient light in the presence of excess AgNO₃ the cis-[Ru(2,3-Medpp)₂(CH₃CN)₂]⁴⁺ species is obtained.     

Unexpected formation and structure elucidation of mer-[RuCl3(TMSO)(bpy)] derived from [H(TMSO)][trans-RuCl4(TMSO)2] under mild condition

Treatment of [H(TMSO)][trans-RuCl₄(TMSO)₂] (1) with 2,2′-bipyridine (bpy) in ethanol at room temperature resulted an unknown mer-[RuCl₃(TMSO)(bpy)] (3) and a known cis-[RuCl₂(TMSO)₄] (4) (TMSO =  tetramethylene sulfoxide) complexes. The 3 was obtained by the substitution with bpy in mer-[RuCl₃(TMSO)₃] (2), whereas 4 was obtained by one-electron reduction of 2, suggesting that 2 is a precursor for both 3 and 4. The structure of 3 was determined by single crystal X-ray diffraction. The reaction is a new synthetic procedure for 3 and/or 3 and 4 in mild reaction conditions from the anionic complex 1. It involves simultaneous substitution and redox reaction. This is the first known example of precisely characterized Ru(III)-chloride-TMSO-bpy-complex derived from anionic [H(TMSO)][trans-RuCl₄(TMSO)₂] at room temperature.     

Synthesis and characterization of Ru(II) and Ru(III) complexes of diphenylphosphinoacetic acid and their interaction with small molecules

Complexes of Ru(II) and Ru(III) with the bidentate ligand diphenylphosphinoacetic acid (POH) are reported. The ligand POH reacts with RuCl₂(PPh₃)₃ in a 1:3 ratio to give a five-coordinate complex of composition Ru(PO)₂(POH) with complete displacement of PPh₃. In a 1:2 ratio however the complex Ru(PO)₂(PPh₃) is formed. The reaction of POH with RuCl₂(DMSO)₄ in a 2:1 ratio afforded a yellow complex of composition HRu(PO)₂Cl(DMSO). In a 3:1 ratio of POH to RuCl₂(DMSO)₄ however, the complex HRu(PO)₃ was obtained. Neutral complexes of the composition Ru(PO)₂Cl(AsPh₃) and Ru(PO)₃ were obtained by the reaction of RuCl₃(AsPh₃)₂·MeOH with POH in 1:2 and 1:3 mole ratios in acetone solution, respectively. A dimeric chloro bridged complex of composition [Ru(PO)₂Cl]₂ was obtained on reaction of RuCl₃3H₂O with POH in methanol. The complexes have been characterized on the basis of elemental analysis ¹H, ¹³C{¹H} and ³¹P{¹H} NMR, EPR and electrochemical studies.The square pyramidal complexes 1 and 2 undergo facile addition reactions with CO, H₂, PPh₃ and DMSO to form octahedral species. The redox potentials Ru^III/Ru^II of the complexes become more positive with an increase in the π-acidity of the ligand coordinated to the metal ion.     

The tungsten-tungsten triple bond. XV. Synthesis,structure and reactivity of 1,2-W2[CH(SiMe3)2]2(NMe2)4: the remarkable inertness of a sterically-encumbered tungsten-amido complex

Addition of 1,2-W₂Cl₂(NMe₂)₄(W≡W) to a toluene slurry of LiCH(SiMe₃)₂(2 equiv) results in the formation of 1,2-W₂[CH(SiMe₃)₂]₂(NMe₂)₄(W≡W) (I) in 79% isolated yield. Compound I has been characterized by ¹H and ¹³C NMR, IR, elemental analysis and single-crystal X-ray diffraction. The molecule exists exclusively in the gauche conformation in solution and in the solid state with WW = 2.320(1) Å. Compound I is very sterically encumbered as evidenced by: (1) large WWC angles, 110°, at the disyl ligand; (2) skewing of the NC₂ planes of the NMe₂ ligands off the WW vector; (3) anomalously large barriers to WNM₂ bond rotation in solution; (4) the inertness of I towards CO₂ and alcohols. However, compound I reacts with acetic anhydride to form 1,2-W₂[CH(SiMe₃)₂]₂(O₂CMe)₄(W≡W) (II) in 31% isolated yield. Compound II has been characterized by ¹H and ¹³C NMR, IR, and elemental analysis. The mechanistic implications of these studies with regard to alcoholysis and CO₂ insertion reactions of other 1,2-W₂R₂(NMe₂)₄ compounds are discussed. Crystal data for 1,2-W₂[CH(SiMe₃)₂]₂(NMe₂)₄ at −140°C: space group P2₁/n, a = 12.555(3), b = 18.699(5), c = 15.214(4) Å, β = 95.24(1)° and Z = 4.     

Optical activity of dimolybdenum complex induced by chiral,chelating diamine ligand; syntheses and structures of [Mo2(O2CCF3)2(S,S-dach)2(CH3CN)2][BF4]2 and [Mo2(O2CCF3)2(R,R-dach)2(CH3CN)2][BF4]2 (dach=1,2-diaminocyclohexane)

The first structurally characterized, quadruply bonded complexes containing chiral diamine ligands, [Mo₂(O₂CCF₃)₂(S,S-dach)₂(CH₃CN)₂][BF₄]₂ (1), and [Mo₂(O₂CCF₃)₂(R,R-dach)₂(CH₃CN)₂][BF₄]₂ (2); (dach=1,2-diaminocyclohexane) were prepared by reactions of [Mo₂(O₂CCF₃)₂(CH₃CN)₆][BF₄]₂ with S,S-dach and R,R-dach, respectively, in CH₃CN. Their UV–Vis and circular dichroism (CD) spectra have been recorded and their structures determined by X-ray crystallography. Crystals of complexes 1 and 2 conform to the space groups P2 with two independent half molecules in the asymmetric unit. The two molecules have a similar structure consisting of a Mo₂ unit bridged by two cis-trifluoroacetate ligands and chelated by two dach ligands. Two acetonitrile molecules are coordinated to the Mo centers along the MoMo bond. The absorption wavelength at 507 nm for both 1 and 2 can be assigned to δ_xy→δ_xy* transitions. The solution CD spectra of these two complexes show two prominent bands at 525 and 385 nm and form mirror images of each other. The solid CD spectra of complexes 1 and 2 show marked red-shift in the absorption energies as compared with those measured in solution. The one-electron static coupling mechanism was invoked to explain the CD spectra for these complexes and the second lowest energy bands were assigned to be δ_xy→δ_x²−y² transitions.     

Synthesis and spectroscopic properties of CpRuCl(R-DAB(4e)) and CpRuCo(CO)3(R-DAB(6e)). Part XVII. X-ray structure determination of CpRuCo(CO)3(t-Bu-DAB(6e))

CpRuCl(PPh₃)₂ reacted with excess R-DAB in refluxing toluene to give CpRuCl(R-DAB(4e)) (1a: R = i-Pr; 1b: R = t-Bu; 1c: R = neo-Pent; 1d: R =p-Tol). ¹H NMR and ¹³C NMR spectroscopic data indicated that in these complexes the R-DAB ligand is bonded in a chelating 4e coordination mode.Reaction of 1a and 1b with one equivalent of [Co(CO)₄]⁻ afforded CpRuCo(CO)₃(R-DAB(6e)) (2a: R = i-Pr; 2b: R = t-Bu). The structure of 2b was determined by a single crystal X-ray structure determination. Crystals of 2b are monoclinic, space group P2₁/n, with four molecules in a unit cell of dimensions: a = 16.812(4), b = 12.233(3), c = 9.938(3) Å and β = 105.47(3)°. The structure was solved via the heavy atom method and refined to R = 0.060 and R_w = 0.065 for the 3706 observed reflections. The molecule contains a RuCo bond of 2.660(3) Å and a cyclopentadienyl group that is η⁵-coordinated to ruthenium [RuC(cyclopentadienyl) = 2.208(3) Å (mean)]. Two carbonyls are terminally coordinated to cobalt (CoC(1) = 1.746(7) and CoC(2) = 1.715(6) Å) while the third is slightly asymmetrically bridging the RuCo bond (RuC(3) = 2.025(6) and CoC(3) = 1.912(6) Å). The RuC(3)O(3) and CoC(3)O(3) angles are 138.4(5)° and 136.5(5)°, respectively. The t-Bu-DAB ligand is in the bridging 6e coordination mode: σ-N coordinated to Ru (RuN(2) = 2.125(4) Å), μ₂-N′ bridging the RuCo bond and η²-CN coordinated to Co (RuN(1) = 2.113(5), CoN(1) = 1.941(4) and CoC(4) = 2.084(5) Å). The η²-CN′ bonded imine group has a bond length of 1.394(7) Å indicating substantial π-backbonding from Co into the anti-bonding orbital of this CN bond.¹H NMR spectroscopy indicated that 2a and 2b are fluxional on the NMR time scale. The fluxionality of 6e bonded R-DAB ligands is rarely observed and may be explained by the reversible interchange of the σ-N and η²-CN′ coordinated imine parts of the R-DAB ligand.