Some additional aspects of versatile starting compounds for cationic organoiron complexes: molecular structure of the aqua complex [(η-C5Me4Et)Fe(CO)2(OH2)]BF4 and solution behavior of the THF complex [(η---C5R5)Fe(CO)2(THF)]BF4

The structures of the versatile starting compounds for organoiron complexes, the cationic aqua complex [(η⁵-C₅Me₄Et)Fe(CO)₂(OH₂)]BF₄ (1b) and the halide complexes (η⁵-C₅Me₅)Fe(CO)₂-I (2a), (η⁵-C₅Me₄Et)Fe(CO)₂-I (2b) and (η⁵-C₅Me₄Et)Fe(CO)₂-Cl (3b), are characterized by X-ray crystallography. Complex 1b [Fe---O: 2.022(8) Å and 2.043(9) Å, two independent molecules] is the first structurally characterized example of organoiron aqua complexes. Details of the synthetic procedures for the above complexes and the labile cationic THF complexes [η⁵-C₅R₅)Fe(CO)₂(THF)]BF₄ (4) are disclosed, and the dissociation equilibrium of 4 is confirmed by means of variable temperature ¹H-NMR as well as saturation transfer experiment.     

The lively chemistry of the di-μ-methylene-bis(pentamethylcyclopentadienyl-rhodium) complexes, analogues of surface reactions in heterogeneous catalysis

The chemistry of the di-μ-methylene-bis(pentamethylcyclopentadienyl-rhodium) complexes is reviewed. The complex [{(η⁵-C₅Me₅)RhCl₂}₂] (1a) reacted with MeLi to give, after oxidative work-up, blood-red cis-[{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(Me)₂], 2. This has the two rhodiums in the +4 oxidation state (d⁵), and linked by a metal-metal bond (2.620 Å). Trans-2 was formed on isomerisation of cis-2 in the presence of Lewis acids, or by direct reaction of 1a with Al₂Me₆, followed by dehydrogenation with acetone. The Rh-methyls in [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(Me)₂] were readily replaced under acidic conditions (HX) to give [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(X)₂] (X = Cl, Br or I); these latter complexes reacted with a variety of RMgX to give [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(R)₂] (R = alkyl, Ph, vinyl, etc.). Trans-2 also reacted with HBF₄ in the presence of L to give first [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(Me)(L)]⁺ and then [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(L)₂]²⁺ (L = MeCN, CO, etc.). The {(η⁵-C₅Me₅)Rh(μ-CH₂)}₂ core is rather kinetically inert and also forms a variety of complexes with oxy-ligands, both cis-, e.g. [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(μ-OAc)]⁺ and trans-, such as [(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(H₂O)₂]²⁺. The complexes [{(η⁵-C₅Me₅)Rh(μ-CH₂)}₂(R)L]⁺ (R = Me or aryl) in the presence of CO, or [{(η⁵-C₄Me₅)Rh(μ-CH₂)}₂(R)₂] (R = Me, Ph or CO₂Me) in the presence of mild oxidants, readily yield the C---C---C coupled products RCH=CH₂. The mechanisms of these couplings have been elucidated by detailed labelling studies: they are more complex than expected, but allow direct analogies to be drawn to C---C couplints that occur during Fischer-Tropsch reactions on rhodium surfaces.     

The crystal structure of (η-C6Me6)Ti[(μ-Cl)2(AlClEt)]2 and the catalytic activity of the (C6Me6)TiAl2Cl8−xEtx(x = 0---4) complexes towards butadiene

The composition of (C₆Me₆)TiAl₂Cl_8−xEt_x complexes in (C₆Me₆)TiAl₂Cl₈ + n Et₃Al (n = 0.5-6) systems was studied by UV-Vis spectroscopy and the X-ray crystal structure of one of them, (η⁶-C₆Me₆)Ti[(μ-Cl)₂(AlClEt)]₂ (IIa-2), has been determined. The complex crystallizes in the orthorhombic space group Pna2₁ with Z = 4 and lattice parameters a 15.634(3), b 11.355(2), c 14.417(2) Å. The ethyl groups of IIa-2 reside in outer positions of aluminate ligands farther away from the C₆Me₆ ligand. The other part of the complex does not differ remarkably from structures of other (arene)Ti^II complexes. Negligible activity of (C₆Me₆)TiAl₂Cl₈ towards the butadiene cyclotrimerization is considerably increased by addition of 2.5–3.0 equivalents of Et₃Al. As follows from UV-Vis spectra, such systems contain mainly the (C₆Me₆)TiAl₂Cl₅Et₃ complex. It is suggested that the introduction of three Et substituents destabilizes the Ti-(η⁶-C₆Me₆) bond so that the replacement of hexamethylbenzene by butadiene in the first step of a catalytic cycle becomes more feasible.     

Synthesis and structure of the iron-substituted silylacetylene [(η-C5H5)Fe(CO)2SiMe2C]2 and its cobalt hexacarbonyl derivative [(η-C5H5)Fe(CO)2SiMe2C]2 · Co2(CO)6

A transition metal-substituted silylacetylene [(η⁵-C₅H₅)Fe(CO)₂SiMe₂C]₂, [FpMe₂SiC]₂ (I) was synthesized and characterized spectroscopically and structurally. I crystallized in the monoclinic space group P2₁/n, A = 13.011(3) Å B = 12.912(3) Å, C = 13.175(5) Å, β = 94.95(2). The acetylene linkage is reactive toward Co₂(CO)₈ to form I. Co₂(CO)₆ (II) which was also characterized spectroscopically and by single crystal X-ray diffraction. II crystallized in the orthorhombic space group Pbca, A = 17.64(2) Å, B = 14.225(10) Å, C = 24.49(2) Å.     

The stereochemistry at silicon of an iron to cyclopentadienyl ligand silyl group migration in (η-C5H5)Fe(CO)2SiR3

The silyl group migration observed upon treating (R)(+)-(η⁵-C₅H₅)Fe(CO)₂-SiMePh(1-Np) with n-BuLi occurs with retention of configuration at silicon. The anion resulting from the migration, (η⁵-C₅H₄SiMePh(1-Np))Fe(CO)₂Li, is alkylated with MeI to give (R)-(−)-(η⁵-C₅H₄SiMePh(1-Np))Fe(CO)₂Me (II). Compound II is independently prepared from (η⁵-C₅H₅)Fe(CO)₂Me. A concerted mechanism for the migration involving frontside nucleophilic attack at silicon is suggested.     

Photochemical synthesis and structural characterization of (η-C5Me5)3Mo3(CO)4(μ2-H)(μ3-O): an unprecedented 46-electron trimolybdenum cluster containing a localized monoprotonated Mo---Mo double bond

Irradiation of the 30-electron Mo₂(η⁵-C₅Me₅)₂(CO)₄ and Re₂(CO)₁₀ in toluene solution (containing H₂O) afforded (in 1–2% yields) a novel triangular metal cluster, (η⁵-C₅Me₅)₃Mo₃(CO)₄(η₂-H)(η₃-O) (1), which was characterized by a single-crystal X-ray diffraction study. Compound 1, of pseudo C_s-m symmetry, has a triangulo-Mo₃(η₃-O) core with composite Mo---H---Mo and Mo---Mo electron-pair bonds along one unusually short edge (2.660(1) Å) and Mo--- electron-pair bonds along the other two edges (2.916(1) and 2.917(1) Å). The edge-bridged hydride ligand, which displays a characteristic high-field proton NMR resonance at δ −17.79 ppm, was not found from the crystallographic determination but was located via a quantitative potential-energy-minimization method. This procedure unambiguously established that the optimized hydrogen position, which corresponds to a distinct coordination site with identical Mo---H distances of 1.85 Å, is the only one that can be sterically occupied by a metal-bound hydride ligand. This 46-electron species is the first electron-deficient trimolybdenum cluster containing a monoprotonated Mo---Mo double bond; its existence is attributed to ligand overcrowding due to the bulky pentamethylcyclopentadienyl rings. Black (η⁵- C₅Me₅)₃Mo₃(CO)₄(η₂-H)(η₃-O) · 1/2THF crystallizes with two formula species in a triclinic unit cell of P1 symmetry with a 8.603(4), b 11.115(4), c 19.412(11) Å, 80.69(4)°, β 101.10(4)°, and γ 98.88(3)° at −40° C. Least-squares refinement (RAELS with 221 variables) of one independent Mo₃ molecule and a centrosymmetrically-disordered THF molecule converged at R₁(F) 5.62%, R₂(F 6.88% for 8460 independent diffractometry data (I₀ ρ 3σ(I₀ collected at −40° C with Mo-K radiation     

Highly stereoselective reduction of methyl ketone complexes of the chiral Lewis acid [(η-C5H5)Re(NO)(PPh3)] by K(s-C4H9)3BH; synthesis of optically active secondary alcohols and derivatives

Reaction of optically active ketone complexes (+)-(R)-[(η⁵-C₅H₅)Re(NO)-(PPh₃)(η¹-O=C(R)(CH₃)]⁺ BF₄⁻ (R = CH₂CH₃, CH(CH₃)₂m C(CH₃)₃, C₆H₅) with K(s-C₄H₉)₃BH gives alkoxide complexes (+)-(RS)-(η⁵-C₅H₅)Re(NO)(PPh₃)-(OCH(R)CH₃) (73–90%) in 80–98% de. The alkoxide ligand is then converted to Mosher esters (93–99%) of 79–98% de.     

Substituted cyclopentadienyl ligands—10. Intramolecular steric interactions in [(η-C5H3(SiMe3)2)Mo(CO)2(L)I]

Reaction of C₅H₄(SiMe₃)₂ with Mo(CO)₆ yielded [(η⁵-C₅H₃(SiMe₃)₂)Mo(CO)₃]₂, which on addition of iodine gave [(η⁵-C₅H₃(SiMe₃)₂Mo(CO)₃I]. Carbonyl displacement by a range of ligands: [L = P(OMe)₃, P(OPrⁱ)₃,P(O-o-tol)₃, PMe₃, PMe₂Ph, PMePh₂, PPh₃, P(m-tol)₃] gave the new complexes [(η⁵-C₅H₃(SiMe₃)₂ MO(CO)₂(L)I]. For all the trans isomer was the dominant, if not exclusive, isomer formed in the reaction. An NOE spectral analysis of [(η⁵-C₅H₃(SiMe₃)₂)Mo(CO)₂(L)I] L = PMe₂Ph, P(OMe)₃] revealed that the L group resided on the sterically uncongested side of the cyclopentadienyl ligand and that the ligand did not access the congested side of the molecule. Quantification of this phenomenon [L = P(OMe)₃] was achieved by means of the vertex angle of overlap methodology. This methodology revealed a steric preference with the trans isomer (less congestion of CO than I with an SiMe₃ group) being the more stable isomer for L = P(OMe)₃.     

Photochemical reactions of the isostructural 17- and 18-electron complexes (η-C5H5)M(Me)PPh3 (M=Co, Ni)

The photochemical reactions of the title complexes were studied in air-free benzene solution. In both cases photolysis leads to the production of complexes of the formula (η⁵-C₅H₅)M(PPh₃)₂. Both reactions are the result of the initial loss of a methyl radical from the excited state. The primary photoproduct, (η⁵-C₅H₅)MPPh₃ (M=CO, Ni), then scavenges neutral ligands from the solution to yield, in the case of PPh₃, (η⁵-C₅H₅)M(PPh₃)₂. In the absence of uncoordinated ligand in the reaction solution, the cobalt derivative reacts with the starting material to yield (η⁵-C₅H₅)Co(PPh₃)₂, a methyl radical and (η⁵-C₅H₅)Co(solvent)_n.     

The chemistry of compounds of the type Ru(η---C5Me4Et)(CO)2X (X=Cl, Br or I)

The title compounds react with unidentate ligands, L, containing either phosphorus or arsenic donor atoms to yield the corresponding compounds of the type Ru(η⁵---C₅Me₄Et)(CO)LX; with didentate phosphorus donor ligands the major species formed is the bridged complex {Ru(η⁵---C₅Me₄Et)(CO)X}₂{Ph₂P(CH₂)_nPPh ₂} n = 1, X = Br; n = 2, X = Cl). In contrast, unidentate ligands containing nitrogen donor atoms such as pyridine did not react with Ru(η⁵---C₅Me₄Et)(CO)₂Cl although reaction with 1,10-phenanthroline or diethylenetriamine yielded the ionic products [Ru(η⁵---C₅Me₄Et)(CO)L]⁺Cl⁻ (L = phen or (NH₂CH₂CH₂)₂NH). Reaction of Ru(η⁵---C₅Me₄Et)(CO)₂Br with AgOAc yielded the corresponding acetato complex Ru(η⁵---C₅Me₄Et)(CO)₂0Ac. Ru(η⁵--- C₅Me₄Et)(CO)₂X reacts with AgY (Y = BF₄ or PF₆) in either acetone or dichloromethane to give the useful solvent intermediates [Ru(η⁵---C₅Me₄Et)(CO)₂(solvent)]⁺Y⁻, which readily react with ligands L to yield ionic derivatives of the type [Ru(η⁵---C₅Me₄Et)(CO)₂L]⁺Y⁻ (where L = CO, NCMe, py, C₂H₄ or MeO₂CCCCO₂Me).     

A convenient synthesis of Fe(CO)2(η-S2CNMe2)2 and Fe(η-S2CNMe2)2 from the monodentate dithiocarbamato derivative, [(η-C5H5)(CO)3W(η-SCSNMe2)] and Fe2(CO)9

A high yield synthesis of the carbonyl dithiocarbamato derivative Fe(CO)₂(η²-S₂CNMe₂)₂ and Fe(η²-S₂CNMe₂)₂ by photolysis with visible light of solutions containing Fe₂(CO)₉ or Fe₃(CO)₁₂ and [(η⁵-C₅H₅)(CO)₃W(η¹-SCSNMe₂)] is reported.     

Bis(η-pentamethylcyclopentadienyl)-and(ηcyclopentadienyl) (η-pentamethylcyclopentadienyl)-platinium dications: Pt(IV) metallocenes

Reaction of [Pt₂(η⁵-C₅Me₅)₂(η-Br)₃]³⁺(Br⁻)₃ with C₅R₅H (R = H,Me) in the presence of AgBF₄ gives the first platinocenium dications, [Pt(η⁵-C₅Me₅)(η⁵-C₅R₅)]²⁺(BF₄⁻ )₂. On electrochemical reduction, [pt(η⁵-C₅Me₅)₂]²⁺ yields [Pt(η⁴-C₅Me₅H)(η²-C₅Me₅)]+ BF₄⁻. kw]Cyclopentadienyl; Metallocenes; Platinum; Electrochemistry     

Structures of propionaldehyde, butyraldehyde, and pivalaldehyde complexes of the chiral rhenium fragment [(η-C5H5)Re(NO)(PPh3)]

The crystal structures of propionaldehyde complex (RS,SR)-(η⁵-C₅H₅)Re(NO)(PPh₃)(η²-O=CHCH₂CH₃)]⁺ PF₆⁻ (1b⁺ PF₆^s−; monoclinic, P2₁/c (No. 14), a = 10.166 (1) Å, b = 18.316(1) Å, c = 14.872(2) Å, β = 100.51(1)°, Z = 4) and butyraldehyde complex (RS,SR)-[(η⁵-C₅H₅)Re(NO)(PPh₃)(η²-O=CHCH₂CH₂CH₃)]⁺ PF₆⁻ (1c⁺PF₆⁻; monoclinic, P2₁/a (No. 14), a = 14.851(1) Å, b = 18.623(3) Å, c = 10.026(2) Å, β = 102.95(1)°, Z = 4) have been determined at 22°C and −125°C, respectively. These exhibit C O bond lengths (1.35(1), 1.338(5) Å) that are intermediate between those of propionaldehyde (1.209(4) Å) and 1-propanol (1.41 Å). Other geometric features are analyzed. Reaction of [(η⁵-C₅H₅)Re(NO)(PPh₃)(ClCH₂Cl)]⁺ BF₄⁻ and pivalaldehyde gives [(η⁵-C₅H₅)Re(NO)(PPh₃)(η²-O=CHC(CH₃)₃)]⁺BF₄⁻ (81%), the spectroscopic properties of which establish a π C O binding mode.     

Synthesis and structural characterization of (μ-H)2RU3(CO)9(μ3-η-C8H12) and (μ-H)RU3(CO)9(μ3-η-C12H19)

The reaction between Ru₃(CO)₁₂ and a cyclic olefin (cis-cyclooctene or trans-cyclododecene) at 100 °C for several hours gives the title compounds (μ-H)₂RU₃(CO)₉(μ₃-η²-C₈H₁₂) (1), and (μ-H)RU₃(CO)₉(μ₃-η³-C₁₂H₁₉) (2), both of which have been characterized by X-ray diffraction studies, IR and NMR spectral measurements and elemental analysis. The prolonged reaction between Ru₃(CO)₁₂ and cis-cyclooctene gives compound HRu₃(CO)₉(C₈H₁₁) (3). Compound 3 has been characterized with IR and NMR spectral analyses. In 1 the cyclooctene ring is linked via a μ₃-η²-alkyne type of bonding to the face of the Ru₃ cluster. It is formally σ-bonded to two of the three Ru atoms and π-bonded to the third Ru. The two hydrides in 1 are bridging Ru---Ru bonds. In 2 the cyclododecene ring is bonded to the Ru₃ face via the μ₃-η³-CCHC linkage. There are two formal σ-bonds from the allyl part to the hydrido-bridged Ru atoms and the η³-allyl linkage to the third Ru atom.     

First examples of η- and η --- η-coordination in triphosphorus analogues of ferrocene. Crystal structure of the iron sandwich complex [Fe(η-C5H5) (η-C2R2P3)W (CO)5] (R = Bu)

Syntheses of the novel sandwich compounds [Fe(η⁵-C₅H₅)(η⁵-C₂R₂P₃)] and [Fe(η⁵-C₅H₅)(η⁵-C₂R₂P₃)W(CO)₅], (R = Bu^t), are described. The mode of attachment of the [W(CO)₅] fragment in the latter compound has been determined by NMR and single crystal X-ray diffraction studies.     

Mechanism of formation of (η-C5H5)2NbH3 from the reaction of (η-C5H5)2NbCl2 with hydridoaluminate reducing agents

The mechanism of the transformation of (η⁵-C₅H₅)₂NbCl₂ to (η⁵-C₅H₅)₂NbH₃ by hydridoaluminate reducing agents has been investigated. Results suggest disproportionation of a niobium(IV) hydrite, leading to the trihydride product and a niobium(III) hydridoaluminate, (η⁵-C₅H₅)₂NbH₂AlR₂, which in turn is converted to the trihydride on hydrolysis. (η⁵-C₅H₅)₂NbH₂AlH₂ has been isolated; deuterium labelling shows that hydrogens exchange between ring and metal-bridging positions in this molecule.     

Synthesis and crystal structure of the novel trimanganese tetrathiolate incomplete cubane: [Mo(η-C5H5)2(H)CO][Mn3(CO)9(μ-SC6H5)4]

An unexpected trimanganese(I) tetrathiolate-bridged complex, [Mn₃(CO)₉(μ-SC₆H₅)₄]⁻, with an incomplete cubane structure, was obtained by thermal reaction of [Mn₂(CO)₁₀] with [Mo(η⁵-C₅H₅)₂(SC₆H₅)₂]. The structure, established by single-crystal X-ray diffraction studies, shows the cation, [Mo(η⁵-C₅H₅)₂(H)CO]⁺, directed towards the vacant site of the cubane structure. Possible routes by which the anion and the cation could be formed are discussed.     

Photochemical reactions of alkynyl iron (II) complexes with carbon disulfide. Insertion of CS2 into an iron-C(sp) bond

The novel alkynyldithiocarboxylate complexes [Fe(η⁵-C₅H₅)(S₂CCCR) (dppm-P)] (3a,b) and [Fe(η₅-C₅H₅)(S₂CCCR)(PPh₃)] (4a,b) were obtained through the insertion of CS₂ into the iron-akynyl bond in the complexes [Fe(η₅-C₅H₅)(CCR)(L)(L′] L, L′ = dppm R = Ph (1a), ^tBu(1b); L = (CO), L′ = (PPh₃) R = Ph (2a), ^tBu (2b). Variable-temperature ³¹P{¹H} NMR studies indicate the presence of two different isomers, [Fe(η⁵-C₅H₅)(η³-S,C,S′---S₂CCCR)(L)(L′)] and [Fe(η⁵-C₅H₅(η²-S,S′-S₂CCCR)(L)(L′)], which rapidly interconvert at room temperature. The synthesis of the precursor complex [Fe(η⁵-C₅H₅)(CC^tBu)(CO)(PPh₃)] is also described.     

Synthesis and X-ray structure of (η-C5H5)2W2Ir2(CO)7(CHCO2Et)2, a tetrahedral heterometal cluster with two different environments for ethylcarboxylatocarbene ligands

The tetrahedral heteronuclear cluster complex (η⁵-C₅H₅)₂W₂Ir₂(CO)₁₀ reacts with N₂CHCO₂R (R = Et, Me) at room temperature to form the dicarbene species (η⁵-C₅H₅)₂W₂Ir₂(CO)₇(CHCO₂R)₂. An X-ray diffraction study (R = Et) shows an intact tetrahedral metal framework with two distinct sites for the CHCO₂Et ligands. The first uses its carbon atom to bridge the Ir---Ir bond; the second uses its carbon atom to bridge an Ir---W bond and, additionally, forms a donor bond from a carbonyl oxygen atom to the second tungsten atom.     

Synthese et etude des complexes [C5H4(CH2)3C5H4]Ti(C5H5)2 presentant un pont entre deux ligands cyclopentadienyles

The complex (di-η⁵-C₅H₄CH₂CH₂CH₂C₅H₄)Ti(η¹-C₅H₅)₂ (I) can be obtained unambiguously starting from the corresponding bridged titanocene dichloride. Attempts to synthesize the isomeric compounds (η⁵-C₅H₅)₂ Ti(di-η¹-C₅H₄-CH₂CH₂CH₂C₅H₄) (I′) by the action of a convenient bridged dianion on (C₅H₅)₂ TiCl₂ afford several compounds, one of them is the complex I. The possibility of interconversion of these complexes by a fluctional process is discussed.