The synthesis and reactions of A-ring aromatic steroid complexes of manganese tricarbonyl

Treatment of the A-ring aromatic steroids estrone 3-methyl ether and β-estradiol 3, 17-dimethyl ether with Mn(CO)₅⁺BF₄⁻ in CH₂Cl₂ yields the corresponding [(steroid)Mn(CO)₃]BF₄ salts 1 and 2 as mixtures of and β isomers. The X-ray structure of [(estrone 3-methyl ether)Mn(CO)₃]BF₄ · CH₂Cl₂ (1) having the Mn(CO)₃ moiety on the side of the steroid is reported: space group P2₁ with a=10.3958(9), b=10.9020(6), c=12.6848(9) Å, β=111.857(6)°, Z=2, V=1334.3(2) ų, _calc=.481 cm⁻³, R=0.0508, and wR=0.0635. The molecule has the traditional ‘piano stool’ structure with a planar arene ring and linear Mn---C---O linkages. The nucleophiles NaBH₄ and LiCH₂C(O)CMe₃ add to [(β-estradiol 3,17-dimethyl ether)Mn(CO)₃]BF₄ (2) in high yield to give the corresponding - and β-cyclohexadienyl manganese tricarbonyl complexes (3). The nucleophiles add meta to the arene -OMe substituent and exo to the metal. The and β isomers of 3 were separated by fractional crystallization and the X-ray structure of the β isomer with an exo-CH₂C(O)CMe₃ substituent is reported (complex 4): space group P2₁2₁2₁ with a=7.5154(8), b=15.160(2), c=25.230(3) Å, Z=4, V=2874.4(5) ų, _calc=1.244 g cm⁻³, R=0.0529 and wR2=0.1176. The molecule 4 has a planar set of dienyl carbon atoms with the saturated C(1) carbon being 0.592 Å out of the plane away from the metal. The results suggest that the manganese-mediated functionalization of aromatic steroids is a viable synthetic procedure with a range of nucleophiles of varying strengths.     

Hetero-polynuclear complexes containing bridging diphenylphosphino-alkenes and -alkynes. The crystal structure of an Rh2{μ−ν:ν−P(Ph2) (CH2)3C≡CR}Co2 complex

The phosphinoalkenes Ph₂P(CH₂)_nCH=CH₂ (n= 1, 2, 3) and phosphinoalkynes Ph₂P(CH₂)_n C≡CR (R = H, N = 2, 3; R = CH₃, N = 1) have been prepared and reacted with the dirhodium complex (η−C₅H₅)₂Rh₂(μ−CO) (μ−η²−CF₃C₂CF₃). Six new complexes of the type (ν−C₅H₅)₂(Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃)L, where L is a P-coordinated phosphinoalkene, or phosphinoalkyne have been isolated and fully characterized; the carbonyl and phosphine ligands are predominantly trans on the Rh---Rh bond, but there is spectroscopic evidence that a small amount of the cis-isomer is formed also. Treatment of the dirhodium-phosphinoalkene complexes with (η−CH₃C₅H₄)Mn(CO)₂thf resulted in coordination of the manganese to the alkene function. The Rh₂---Mn complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂P(CH₂)₃CH=CH₂} (η−CH₃C₅H₄)Mn(CO)₂] was fully characterized. Simi treatment of the dirhodium-phosphinoalkyne complexes with Co₂(CO)₈ resulted in the coordination of Co₂(CO)₆ to the alkyne function. The Rh₂---Co₂ complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂PCH₂C≡CCH₃}Co₂(CO)₂], C₃₇H₂₅Co₂F₆O₇PRh₂, was fully characteriz spectroscopically, and the molecular structure of this complex was determined by a single crystal X-ray diffraction study. It is triclinic, space group (C_i¹, No. 2) with a = 18.454(6), B = 11.418(3), C = 10.124(3) Å, = 112.16(2), β = 102.34(3), γ = 91.62(3)°, Z = 2. Conventional R on |F| was 0.052 fo observed (I > 3σ(I)) reflections. The Rh₂ and Co₂ parts of the molecule are distinct, the carbonyl and phosphine are mutually trans on the Rh---Rh bond, and the orientations of the alkynes are parallel for Rh₂ and perpendicular for Co₂. Attempts to induce Rh₂Co₂ cluster formation were unsuccessful.     

Synthesis of one dimensional tin selenides in supercritical amines

Three new crystalline tin selenide salts have been prepared from the reactions of [PPh₄]₂[Sn(Se₄₃] in supercritical solvents. The starting material pyrolyzes in supercritical acetonitrile to form [PPh₄]₄[Sn₆Se₂₁] (I), and it also reacts with SnSe in supercritical ammonia leading to a mixture of [PPh₄]₄[Sn₃Se₁₁]₂ (II). and [PPh₄]₂[Sn(Se₄)(Se₆)₂] (III). All three compounds have been characterized by single crystal X-ray diffraction. Crystallographic data: for I, C₉₆H₉₀P₄Se₂₁Sn₆, space group triclinic, P-1, A = 18.763(3), B = 24.600(4), C = 13.137(1) Å, = 102.63(1), β = 93.66(1), γ = 108.72(1)°, V = 5544(1) ų, Z = 2, R = 0.0350, R_W = 0.0317: for II, C₉₆H₈₀P₄Se₂₂Sn₆, space group monoclinic P2₁/c, A = 31.500(4), B = 16.572(3), C = 22.352(3) Å, β = 103.53(1)°, V = 11344(3) ų, Z = 4, R = 0.0771, R_W = 0.0664: for III, C₄₈H₄₀P₂Se₁₆Sn, space group monoclinic, C2/c, A = 25.381(2), B = 13.934(4), C = 19.465(3) Å, β = 121.587(8)°, V = 5867(2) ų, Z = 4, R = 0.0807, R_W = 0.0650. One of the compounds, [PPh₄]₂[Sn(Se₄(Se₆₂], is a molecular cluster while the other two complexes [PPh₄]₄[Sn₃Se₁₁]₂ and [PPh₄]₄[Sn₆Se₂₁], are one dimensional tin selenide chains. The structures of the two chains are related and consits of tetrahedral and distorted trigonal bipyramidal tin(IV) centers bridged by Se²⁻, Se₂²⁻ and Se₃²⁻ chains.     

Reactions of agostic manganese complexes with molecular hydrogen

Reactions between manganese agostic species having (Mn---C---H) interactions and molecular hydrogen have been investigated. Treatment of the bridging agostic cyclooctenylmanganese tricarbonyl, 3, and butenylmanganese tricarbonyl, 5, with hydrogen in benzene results in the formation of the cyclohexadienylmanganese tricarbonyl compound 4. This suggests that the hydrogen molecule is highly reactive toward organometallic manganese complexes containing an agostic C---H bond. In these reactions (η²-H₂) bonded species are plausible intermediates but these are not detected by NMR. The results indicate that the suggested intermediates in the reactions may be useful as hydrogenation catalysts and as precursors to prepare new manganese compounds which may not be accessible by other pathways.     

The synthesis, fluctionality and structural characterization of ReMo3H4(CO)12

The reaction of ReH₉²⁻ with Mo(diglyme)(CO)₃ leads to the formation of the mixed metal cluster trianion, ReMo₃H₄(CO)₁₂³⁻. This species has been characterized analytically, spectroscopically and through X-ray diffraction analysis. A pseudo-tetrahedral arrangement of M(CO)₃ fragments is adopted, such that each set of three carbonyl ligands eclipses the adjacent three tetrahedral edges, an apparent result of the location of the hydride ligands on the tetrahedral faces. Variable temperature NMR studies revealed a fluctional process for some of the carbonyl ligands, but not for the hydrides. Crystal data for [Me₄N]₃[ReMo₃H₄(CO)₁₂]·THF; space group P2₁/n, a = 12.157(2), B = 21.480(4), C = 15.964(3) Å, β = 98.26(1)°, Z = 4, R = 0.067 and R_w = 0.076.     

Synthesis of η-allyl-Pd complexes and subsequent formation of N-heterocycles via the reaction of a cyclometallated compound with conjugated dienes

The Pd---C bond of the cyclopalladated derivative of dimethylaminomethylferrocene (1) is fairly reactive to insertion of conjugated dienes such as 1,3-butadiene, isoprene, 2,3-dimethylbutadiene or 1,3-cyclohexadiene. This reaction affords organopalladium complexes containing an η³-allyl-Pd moiety where the NMe₂ unit of the starting material is still intramolecularly coordinated to Pd. These complexes are stable in solution but in MeOH in the presence of PPh₃, reductive elimination of Pd is observed. This occurs whilst a nucleophilic intramolecular addition of the NMe₂ group to the allylic fragment takes place, affording six-, seven- or eight-membered heterocyclic compounds. The importance of the steric effects of the substituents on the butenyl chain upon the course of the reaction has been investigated.     

The coordination chemistry of cationic main group clusters: syntheses and structures of [Fe3(Se2)2(CO)10] and [Fe4(Se2)3(CO)12]

The reactions of the polysulfur and selenium cationic clusters S₈²⁺ and Se₈²⁺ with various iron carbonyls were investigated. Several new chalcogen containing iron carbonyl cluster cations were isolated, depending on the nature of the counteranion. In the presence of SbF₆⁻ as a counterion, the cluster [Fe₃(E₂)₂(CO)₁₀] [SbF₆]₂·SO₂ (E = S, Se) could be isolated from the reaction of E₈²⁺ and excess iron carbonyl. The cluster is a picnic-basket shaped molecule of two iron centers linked by two Se₂ groups, with the whole fragment capped by an Fe(CO)₄ group. Crystallographic data for C₁₀O₁₂Fe₃Se₄Sb₂F₁₂S (I): space group monoclinic P2₁/c, A = 11.810(9), b = 24.023(6), c = 10.853(7) Å, β = 107.15(5)°, V = 2942(3) ų, Z = 4, R = 0.0426, R_w = 0.0503. When Sb₂F₁₁⁻ is present as the counterion, or Se₄[Sb₂F₁₁]₂ is used as the cluster cation source, a different cluster can be isolated, which has the formula [Fe₄(Se₂)₃(CO)₁₂] [SbF₆]₂·3SO₂. The dication contains two Fe₂Se₂ fragments bridged by an Se₂ group. Crystallographic data for C₁₂O₁₈Fe₄Se₆Sb₂F₁₂S₃ (III): space group triclinic , b = 18.400(9), C = 10.253(4) Å, = 93.10(4), β = 103.74(3), γ = 93.98(3)°, V = 1995(1) ų, Z = 2, R = 0.0328, R_w = 0.0325. The CO stretches in the IR spectrum all show a large shift to higher wavenumbers, suggesting almost no τ backbonding from the metals. This also correlates with the observed bond distances. All the compounds are extremely sensitive to air and water, and readily lose SO₂ when removed from the solvent. Thus all the crystals were handled at −100°C. The clusters seem to be either insoluble or unstable in all solvents investigated.     

Steric control in the formation of Co2(CO)6-alkyne complexes from Group 14 tetraalkynes and their reactions with acid

A series of tetrakis(trimethylsilylethyne) derivatives of Group 14 metals (2–4) was prepared. Co₂(CO)₆ complexes 5–10 were synthesised by the reaction of 2–4 with Co₂(CO)₈. From the silyl and germyl based compounds 2 and 3, either one or two alkynes could be complexed with Co₂(CO)₆. In contrast, the tin derived compound 4 could accommodate up to four Co₂(CO)₆ complexes. The longest wavelength UV-Vis absorbances of the silicon and germanium-based complexes were consistent with multiple, non-conjugated Co₂(CO)₆ chromophores. The tetrakis Co₂(CO)₆ complex 10, however, absorbs at a much longer wavelength suggesting conjugation of Co₂(CO)₆ complexes through the tin. The reactivity towards protonolysis of the uncomplexed alkynes 2–4 is a consequence of the hyperconjugative stabilisation of the intermediate β-vinyl cation (the β-effect): Sn(CCSiMe₃)₃>SnOTf(CCSiMe₃)₂>SiMe₃>Ge(CCSiMe₃)₃. The reactivity of the Co₂(CO)₆ complexes, however, was quite different from the reactions of 2–4 and from analogous all-carbon systems. Treatment of 5–10 with strong acid led neither to protiodemetallation of the complexed or non-complexed alkynes but to decomplexation of the cobalt. Similarly, ligand metathesis reactions between 10 and Ph₂SiCl₂ were not observed. The normal reactivity of silylalkynes towards electrophiles, which was expected to be enhanced by the presence of the cobalt complex, was diminished by the particular steric environment of the molecules under examination (5–10). As a result, the favoured reaction under these conditions was decomplexation of the cobalt.     

Improved solubility of β-cyclodextrin inclusion complexes by using liquid ammonia as a solvent and the possibility of asymmetric reduction

Dramatic improvement in the poor solubility of β-cyclodextrin (β-CD) and its inclusion complexes in water was achieved by using liquid ammonia (liq. NH₃) instead of water as the solvent. Asymmetric NaBH₄ reduction of the carbonyl groups of the inclusion complexes in liq. NH₃ was examined in a homogeneous condition to give the corresponding alcohols with moderate chirality.     

Mechanistic details for metathetical exchange between XCO (X = O and RN) and the tin(II) dimer, {Sn[N(SiMe3)2] (μ-OBu)}2

Metathetical exchange between carbon dioxide and the tin(II) dimer, {Sn[N(SiMe₃)₂](μ-OBu¹)}₂ (3) has been observed to cleanly produce the two new heteroleptic tin(II) dimers, Sn[N(SiMe₃)₂](μ-OBu^t)₂Sn(OSiMe₃) (6) and [Sn(OSiMe₃)](μ-OBu^t)]₂ (7]). In addition, reaction of 3 with I equiv, of tert-butylisocyanate (8), at 25°C, quantitatively provides 6, and with 2 equiv., quantitatively provides 7. Likewise 6 reacts with 1 equiv, of 8 to quantitatively provide 7. The mechanism for these latter processes has been investigated by low temperature ¹H NMR spectroscopy which reveals that metathetical exchange does not involve the tri-coordinate tin(II) centers of the dimeric structures, but rather, it occurs, in each case, via the transient monomeric tin(II) species, Sn[N(SiMe₃)₂](μ-OBu^t) (4), that undergoes metathesis to produce, initially the open dimer intermediate, Sn(OCNBu^t)(OSiMe₃)(μ-OBu^t)Sn(OBu^t) (OSiMe₃) (12), that is observed at −10°C. Subsequent redistribution reactions then generate the final products that are observed. Together, these mechanistic details provide additional support for the ‘monomeric tin(II)’ hypothesis proposed earlier for metathetical exchange between XCO and Sn[N (SiMe₃)₂]₂ (1).     

Notch3 is dispensable for thymocyte β-selection and Notch1-induced T cell leukemogenesis

Notch1 (N1) signaling induced by intrathymic Delta-like (DL) ligands is required for T cell lineage commitment as well as self-renewal during “β-selection” of TCRβ⁺ CD4⁻CD8⁻ double negative 3 (DN3) T cell progenitors. However, over-expression of the N1 intracellular domain (ICN1) renders N1 activation ligand-independent and drives leukemic transformation during β-selection. DN3 progenitors also express Notch3 (N3) mRNA, and over-expression of ligand-independent mutant N3 (ICN3) influences β-selection and drives T cell leukemogenesis. However, the importance of ligand-activated N3 in promoting β-selection and ICN1-induced T cell leukemogenesis has not been examined. To address these questions we generated mice lacking functional N3. We confirmed that DN3 progenitors express N3 protein using a N3-specific antibody. Surprisingly however, N3-deficient DN3 thymocytes were not defective in generating DP thymocytes under steady state conditions or in more stringent competition assays. To determine if N3 co-operates with N1 to regulate β-selection, we generated N1;N3 compound mutants. However, N3 deficiency did not exacerbate the competitive defect of N1^+/− DN3 progenitors, demonstrating that N3 does not compensate for limiting N1 during T cell development. Finally, N3 deficiency did not attenuate T cell leukemogenesis induced by conditional expression of ICN1 in DN3 thymocytes. Importantly, we showed that in contrast to N1, N3 has a low binding affinity for DL4, the most abundant intrathymic DL ligand. Thus, despite the profound effects of ectopic ligand-independent N3 activation on T cell development and leukemogenesis, physiologically activated N3 is dispensable for both processes, likely because N3 interacts poorly with intrathymic DL4.     

Preparation of η-1,3-dienyl, η-1,2-dienyl and η-cyclobutenone complexes via reactions of transition-metal carbonyl containing anions with allenic electrophiles

The preparation and reaction chemistry of 1,3- and 1,2-diene and related complexes derived from metal carbonyl containing anions and allenic electrophiles are addressed. The preparation of some CpFe(CO)₂ η¹-diene complexes and their conversion into CpFe(CO) η³-diene complexes is presented followed by reactions of CpMo(CO)₃⁻, CpW(CO)₃⁻ and CpMo(CO)₂PR₃⁻ anions with allenic electrophiles which produce metal complexed cyclobutenones (via CO and alkene insertions from the initially formed product) and 1,2-diene complexes, respectively. Lastly, the reactions of PPh₃(CO)₃Co⁻ anions with allenic electrophiles are outlined which result in several different coordination geometries depending on the reaction conditions used.     

Cis- and trans-titanium complexes with doubly silyl-bridged dicyclopentadienyl ligands: molecular structure of [(TiCl)2(μ-O){(SiMe2)2(η-C5H3)2}]2(μ-O)2

The reaction of TiCl₄ with Li₂[(SiMe₂)₂(η⁵-C₅H₃)₂] in toluene at room temperature afforded a mixture of cis- and trans-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] in a molar ratio of 1/2 after recrystallization. The complex trans-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] was hydrolyzed immediately by the addition of water to THF solutions to give trans-[(TiCl₂)₂(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}] as a solid insoluble in all organic solvents, whereas hydrolysis of cis-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] under different conditions led to the dinuclear μ-oxo complex cis-[(TiCl₂)₂)(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}] and two oxo complexes of the same stoichiometry [(TiCl)₂(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}]₂(μ-O)₂ as crystalline solids. Alkylation of cis- and trans-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] with MgCIMe led respectively to the partially alkylated cis-[(TiMe₂Cl)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] and the totally alkylated trans-[(TiMe₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] compounds. The crystal and molecular structure of the tetranuclear oxo complex [(TiCl)₂(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}]₂(μ-O)₂ was determined by X-ray diffraction.     

Generation and spectroscopic characterization of new 18+δ electron complexes. Relationship between the stability of 18+δ electron organometallic complexes and their ligand reduction potentials

The relationship between the electrochemical reduction potential of a ligand and the ability of that ligand to form a kinetically inert 18+δ complex in a reaction with a 17-electron radical was investigated. (18+δ complexes are 19-electron adducts in which the unpaired electron is primarily located on a ligand orbital.) To probe the relationship, a series of 18+δ complexes was generated by irradiating the Cp′₂Mo₂(CO)₆, Cp₂Fe₂(CO)₄ and Co₂(CO)₈ dimers in the presence of a series of bidentate phosphorus ligands. (Irradiation of the dimers formed 17-electron metal radicals by photolysis of the metal-metal bonds.) These experiments showed that bidentate phosphorus ligands with reduction potentials more positive than −1 volt (versus SCE) formed long-lived 18+δ complexes (in THF or CH₂Cl₂ solutions at 23 °C), while ligands with potentials more negative than −1 V formed reactive 18+δ complexes. The inability to detect 18+δ complexes in the latter case is attributed to kinetic factors: the 18+δ complexes are powerful reductants and they readily initiate a chain disproportionation of the dimers by electron transfer. Analogous experiments with bidentate nitrogen ligands did not produce any detectable 18+δ complexes. In this case, the undetectability of the 18+δ complexes is probably thermodynamic in origin: the hard nitrogen ligands and soft metal centers form adducts that are unstable with respect to metal-nitrogen bond cleavage. 18+δ complexes are the subject of increasing interest, especially as models for their more reactive 19-electron-complex counterparts. These results provide some guidelines for the design of 18+δ complexes that can be synthesized, isolated and characterized for such studies.     

Reactions of benzocyclobutene chromium complexes with carbon, nitrogen and oxygen nucleophiles: nucleophilic addition and unexpected proximal ring opening reactions

Tricarbonyl(η⁶-1-oxobenzocyclobutene)chromium(0) (1) can be transformed to tricarbonyl(η⁶-1-endo-hydroxybenzocyclobutene) chromium(0) derivatives with substituents R (R=CH₃, CH=CH₂, (CH₂)₄CH=CH₂, (CH₂)₄OSi(Me)₂tBu) at Cl on the exo face of the complex. The relative configuration is proven by an X-ray crystal structure analysis of the trimethylsilyl ether 8 (C₁₆H₁₈CrO₄Si: a=8.693(1), b=9.490(1), c=11.063(1) Å, =97.51(1), β=110.32(1), γ=95.38(1)°, triclinic, space group P (No.2), R=0.037, R_w=0.052 for 4609 observed reflections. Attempts directed at an intramolecular cycloaddition of the ortho-quinodimethane complex derived from 17 by anion promoted ring opening unexpectedly resulted in the formation of 12 as the product of an opening of the proximal bond of the anellated ring located between the hydroxy group and the coordinated aromatic ring in 16. The fact that the intermolecular cycloaddition reaction for 16 is possible in the presence of a dienophile is taken as evidence for an equilibrium between the alcoholate 17 and the two ring opened products 16 and 18. The proximal ring opening of 6 is not observed when the free organic ligand 21 is used as the educt. Ketone complexes 1 and 25 undergo proximal ring opening reaction when treated with alcoholate or primary amines.     

Reactivity of {(Ph3P)Pt[μ-η-H---SiH(Ar)]}2 (Ar=2-isopropyl-6-methylphenyl) with phosphines. X-ray crystal structure of trans-{(dppe)Pt[μ-SiH(Ar)]}2

The dinuclear Pt---Si complex {(Ph₃P)Pt{μ-η²-H---SiH(IMP)]}₂ (trans-1a–cis-1b=3:1; IMP=2-isopropyl-6-methylphenyl) reacted with basic phosphines such as 1,2-bis(diphenylphosphino)ethane (dppe) and dimethylphenylphosphine (PMe₂Ph) to afford different dinuclear Pt---Si complexes with loss of H₂, {(P)₂Pt[μ-SiH(IMP)]}₂ [P=dppe, trans-2a (major), cis-2b (trace); PMe₂Ph, 3 (trans only)]. Complexes 2 and 3 were characterized by multinuclear NMR spectroscopy and X-ray crystallography (2a). In contrast, the reaction of 1a,b with the sterically demanding tricyclohexylphosphine (PCy₃) afforded {(Cy₃P)Pt{μ-η²-H---SiH(IMP)]}₂ (trans-4a–cis-4b 2:1) analogous to 1a,b where the central Pt₂Si₂(μ-H)₂ core remains intact but the PPh₃ ligands have been replaced by PCy₃. Complexes 4a and 4b was characterized by multinuclear NMR and IR spectroscopies.     

π-Arene complexes.: Part 12. Synthesis of chromiumtricarbonyl complexes of quinoline and N-methylindoles and selected metallation reactions

The lithiation of indole, using a slight excess of n-butyl lithium in THF, followed by methylation and reaction with [Cr(CO)₆] in refluxing dibutyl ether, resulted in the formation of [Cr(η⁶-N-methylindole)(CO)₃] (1a) and [Cr(η⁶-N-methyl-2-methylindole)(CO)₃] (1b). In contrast, lithiation of quinoline in THF, silylation and the subsequent reaction with [Cr(CO)₆] under similar reaction conditions, afforded [Cr(η⁶-N-trimethylsilyl-2-butyl-1,2-dihydroquinoline)(CO)₃] (2) and [Cr(η⁶-{2-butyl-1,2,3,4-tetrahydroquinoline})(CO)₃] (3). The formation of [Cr(η⁶-2,2′-bis{N-methylindolyl})(CO)₃] (4) implied lithiation at the 2-position of 1a. However, metallation at the 7-position was also indicated during the same reaction. In the presence of [Mn(CO)₅Br], product 4 and the transmetallation product [Cr(η⁶-{7-(N-methylindolyl)Mn(CO)₅})(CO)₃] (5) were isolated. Reaction with titanocene dichloride gave [Cr(η⁶-{2-(N-methylindolyl)TiCp₂Cl})(CO)₃] (6), which slowly converted into [TiCp₂{Cr(η⁶-2-(N-methylindolyl)(CO)₃}₂] (7).     

Synthesis and characterization of homologous nickel(II) and palladium(II) complexes with biphosphine monoxide ligands Ph2P(CH2)nP(O)Ph2 (n = 1–3) and pTol2P(CH2)P(O)pTol2

A series of cationic nickel complexes [(η³-methally)Ni(PP(O))]SbF₆ (1–4) [PP(O) = Ph₂P(CH₂)P(O)Ph₂ (dppmO) (1), Ph₂P(CH₂)₂P(O)Ph₂ (dppeO) (2), Ph₂P(CH₂)₃P(O)Ph₂ (dpppO) (3), pTol₂P(CH₂)P(O)pTol₂ (dtolpmO) (4)] has been synthesized in good yields by treatment of [(η³-methally)NiBr]₂ with biphosphine monoxides and AgSbF₆. The ligands are coordinated in a bidentate way. Starting from [(η³-all)PdI]₂ the cationic complexes [(η³-all)PP(O))]Y (8–14). [PP(O) = dppmO, dppeO, dpppO, dtolpmO;Y = BF₄, SbF₆, CF₃SO₃, pTolSO₃] were synthesized in good yields. The coordination mode of the ligand is dependent on the backbone and the anion, revealing a monodentate coordination with dppmO for stronger coordinating anions. The intermediates [(η³-all)Pd(I)(PP(O)-κ¹-P)] (5–7) [PP(O) = dppmO (5), dppeO (6), dtolpmO (7)] were isolated and characterized. Neutral methyl complexes [(Cl)(Me)Pd(PP(O))] (15–18). [PP(O) = dppmO (15), dppeO (16), dpppO (17), dtolpmO (18)] can easily be obtained in high yields starting from [(cod)PdCl₂]. For dppmO two different routes are presented. The structure of [(Me)(Cl)Pd{;Ph₂P(CH₂-P(O)Ph₂-κ²-P,O};] · CH₂Cl₂ (15) with the chlorine atom trans to phosphorus was determined by X-ray diffraction.     

Ligand induced P---H bond formation and a comparison of the reactivity of two isomers of the carbonyl hydride [Pt2(μ-PBu2)2(H)(CO)(PBu2H)]CF3SO3

The Pt₂ ^(II) isomeric terminal hydrides [(CO)(H)Pt(μ-PBu^t ₂)₂Pt(PBu^t ₂H)]CF₃SO₃ (1a), and [(CO)Pt(μ-PBu^t ₂)₂Pt(PBu^t ₂H)(H)]CF₃SO₃ (1b), react rapidly with 1 atm of carbon monoxide to give the same mixture of two isomers of the Pt₂ ^(I) dicarbonyl [Pt₂(μ-PBu^t ₂)(CO)₂(PBu^t ₂H)₂]CF₃SO₃ (3-Pt); the solid state structure of the isomer bearing the carbonyl ligands pseudo-trans to the bridging phosphide was solved by X-ray diffraction. A remarkable difference was instead found between the reactivity of 1a and 1b towards carbon disulfide or isoprene. In both cases 1b reacts slowly to afford [Pt₂(μ-PBu^t ₂)(μ,η²,η²-CS₂)(PBu^t ₂H)₂]CF₃SO₃ (4-Pt), and [Pt₂(μ-PBu^t ₂)(μ,η²,η²-isoprene) (PBu^t ₂H)₂]CF₃SO₃ (6-Pt), respectively. In the same experimental conditions, 1a is totally inert. A common mechanism, proceeding through the preassociation of the incoming ligand followed by the P---H bond formation between one of the bridging P atoms and the hydride ligand, has been suggested for these reactions.     

Sn and C NMR study of some trivinyltin(IV) compounds and their complexes

The¹¹⁹Sn and ¹³C NMR spectra of ten trivinyltin(IV) compounds in solutions of non-coordinating (deuteriochloroform, trideuterionitromethane) and coordinating (hexadeuteriodimethyl sulphoxide) solvents have been studied. From δ(¹¹⁹Sn) chemical shifts and ¹J(¹¹⁹Sn,¹³C) coupling constants an evaluation of the coordination number of the central tin atom and the shape of coordination polyhedra around the tin atom has been carried out. Various effects on the δ(¹³C) chemical shifts of both carbon atoms of the vinyl group are also discussed.