Platinum(II) complexes containing 2-(alkenyl)pyridines

The ligands 2-(allyl)pyridine(APy), and 2-(1-methallyl)pyridine (1-MAPy) react with [Pt₂X₄(PEt₃)₂] (X = Cl or Br), in acetone solution to give complexes of the type [PtX(PEt₃)L] [PtX₃(PEt₃)], (L = APy or 1-MAPy), which contain a bidentate 2-(alkenyl)pyridine, whereas the same reaction in benzene solution gives trans-[PtBr₂(PEt₃)L], (L = APy or 1-MAPy), which contains a monodentate 2-(alkenyl)pyridine; ¹H NMR spectra indicate that both types of product undergo olefin exchange in solution. The same reaction with 2-(3-methallyl)-pyridine [2-(2-butenyl)pyridine] (3-MAPy), 2-(3,3-dimethylallyl)pyridine [2-(3-methyl-2-butenyl)pyridine] (3,3-DMAPy), and 2-(3-butenyl)pyridine (BPy), in either acetone or benzene solution, gives only trans-[PtBr₂(PEt₃)L]. The reaction of trans-[PtBr₂(PEt₃)L] (L = APy or 3-MAPy) with AgClO₄ gives [PtBr(PEt₃)L]ClO₄. Complexes of the type [PtCl₂L], which contain bidentate 2-(alkenyl)pyridines, result on reaction of L = APy, 3-MAPy, 3,3-DMAPy, BPy, MBPy with [Pt₂Cl₄(C₂H₄)₂].     

Solvent induced ionisation of η-allydicarbonylmolybdenum(II) complexes

[MoCl(η-C₃H₅)(CO)₂(MeCN)₂] dissolved in aprotic solvents is extensively ionised to [Mo(η-C₃H₅)(CO)₂(MeCN)₃]⁺[Mo₂Cl₃(η-C₃H₅)₂(CO)₄]^- with the liberation of free acetonitrile. The corresponding bromo- complex shows similar but less pronounced ionisation in (CD₃)₂CO, whereas the iodo-complex retains its molecular structure.     

The reactions of hydrosilanes with trifluoropropene and pentafluorostyrene catalyzed by ruthenium, rhodium and palladium complexes

The reactions of hydrosilanes with trifluoropropene (TFP) and pentafluorostyrene (PFS) catalyzed by Ru₃(CO)₁₂ or RhCl(PPh₃)₃ give β-R_f-vinylsilane (1) and/or β-R_f-ethylsilane (2) (R_f = perfluorocarbon group). The 1/2 ratio is highly dependent on the nature of hydrosilane used. The ruthenium catalyst favors the formation of 1 compared with the rhodium catalyst. Neither -R_f-vinylsilane nor -R_f-ethyl-silane was formed at all. Possible mechanisms which can accommodate characteristic features of these reactions are discussed. The hydrosilylation of TFP with dichloro-methylsilane catalyzed by PdCl₂(PhCN)₂/2PPh₃ gives the -adduct (9a) exclusively, and this is transformed to the corresponding dialkoxysilanes, silane diol, oligosilane diols and cyclic oligosiloxanes.     

Carbonyl complexes of molybdenum and tungsten with sulfur donors: V. Reactions of carbonyl complexes of molybdenum(0) with uninegative (X,Y)-donor ligands (X,Y = S,N, O)

The reactions of the zerovalent carbonyl complexes Mo(CO)₆ and Mo(CO)₄(bipy) with a series of uninegative bidentate (X,Y)-donor ligands (X,Y = xanthates, dithiocarbamates, o-aminophenoxide, o-aminothiophenoxide, 2-picolinate and thioacetate) lead to new anionic tetracarbonyl complex anions [Mo⁰(X,Y)(CO)₄]^?. These anions, which can be isolated as their tetraphenylphosphonium salts, contain the (X,Y)-ligand as a bidentate group. In the case of (X,Y) = monothioacetate the decarbonylated species [PPh₄][Mo^II(TA)₃] is formed. The reacions of the new complexes with allyl bromide and methyl iodide are described.     

Cobaloxime(II)-initiated coupling of α,α,α-trihalomethylbenzenes

Bis(dimethylglyoximato) complexes of cobalt(II), cobaloxime(II), under mild conditions initiate coupling of α,α,α-trihalomethylbenzenes to form PhCX₂CX₂Ph (X  Cl), PhCXCXPh (X  Cl, Br) and mixtures of halocobaloxime products. Stoichiometry, product distribution, and control experiments suggest that coupling may result from the decomposition of a highly unstable haloalkylcobaloxime intermediate, Co(dmgH)₂(PhCX₂)(S(CH₃)₂). A general mechanism for the formation of this intermediate and its decomposition to the observed products is presented.     

Polarographic behaviour of π-allylic complexes of transition metals : II. π-allyltricarbonylcobalt and some phosphinic derivatives

The polarographic reduction in acetonitrile (ACN) of π-C₃H₅Co(CO)₃ and of the phosphinic derivatives π-C₃H₅Co(CO)₂L [L = P(OC₆H₅)₃, P(OCH₂)₃CC₂H₅, P(C₆H₅)₃, P(OC₂H₅)₃, P-n-Bu₃, P(C₆H₁₁)₃] is reported and the reduction mechanism is discussed. The dependence of the E_{$\text{1}\text{2}$} of thecomplexes on the properties of the ligands is analysed, and a linear plot of E_{$\text{1}\text{2}$} vs. ΔHNP of the ligands is observed. The pseudo first-order rate constants for the reduction of the complexes with NaBH₄ in ACN are reported.     

Stabilization of platinum(II) hydrides by tri-t-butylarsine; facile syntheses of stable trans-PtH2[As(t-Bu)3]2 and trans-PtHX[As(t-Bu)3]2 complexes

trans-PtH₂[As(t-Bu)₃]₂ was prepared in very good yield by afacile reaction of K₂PtC1₄ with As(t-Bu)₃ in alkaline ethanol. Treatment of trans-PtH₂[As(t-Bu)₃]₂ with CF₃CO₂H or HCI afforded trans-PtH(O₂CCF₃)[As(t-Bu)₃]₂ or trans-PtHCl[As(t-Bu)₃]₂. respectively, in almost quantitative yield.     

Reaction of ethylene with the unsaturated cluster complex H2Os3 (CO)10

Treatment of H₂Os₃(CO)₁₀ with excess ethylene forms ethane and a hydridovinyl cluster complex HOs₃(CO)₁₀(CHCH₂), which rearranges in refluxing octane to the vinylidene complex H₂Os₃(CO)₉(CCH₂).     

Transition metal promoted reactions of unsaturated hydrocarbons : III. Insertion of 1,2-dienes into allylic palladium bonds

Addition of strained olefins, based on norbornene, norbornadiene,benzonorbornadiene or bicyclo [2.2.2] octene skeletons to π-allylic(hexafluoroacetylacetonato) palladium(II) complexes [(π-All)Pd(Hfacac)], gives “enyl” products derived from “insertion” of the olefin into the least substituted terminal allylicpalladium bond. The reaction involves an initial rapid and reversible formation of (gs-allyl)(π-olefin)Pd(Hfacac). The rate-determining step involves migration of a σ-allylic carbon atom from Pd to the coordinated olefin in a concerted cis—exo addition of Pd---C across the double bond. Remote electronegative substituents on the olefin do not affect the coordinative ability of the olefin towards Pd. They do however inhibit the migration of the σ-allylic ligand to the coordinated olefin. This observation is interpreted in terms of a small degree of polarization of the π-olefin—Pd bond in the transition state for the σ-allyl migration.     

195Pt, 119Sn and 31P NMR studies of alkyl,aryl and acyl trichlorostannate complexes of platinum(II). The crystal structure of trans-[Pt(SnCl3)(COC6H5)(PEt3)2]

¹⁹⁵Pt, ¹¹⁹Sn and ³¹P NMR characteristics of the complexes trans-[Pt(SnCl₃)(carbon ligand)(PEt₃)₂] (1a-1e) are reported, (carbon ligand = CH₃ (1a), CH₂Ph (1b), COPh (1c), C₆Cl₅ (1d), C₆Cl₄Y (e); Y = meta- and para-NO₂, CF₃, Br, H, CH₃, OCH₃, or Pt(SnCl₃)(PEt₃)₂. The values of ¹J(¹⁹⁵Pt, ¹¹⁹Sn) vary from 2376 to 11895 Hz with the COPh ligand having the smallest and the C₆Cl₅ ligand the largest value, making a total range for this coupling constant, when the dimer syn-trans-[PtCl(SnCl₃)(PEt₃)]₂ is included, of ca. 33000 Hz. In the meta- and para-substituted phenyl complexes ¹J(¹⁹⁵Pt, ¹¹⁹Sn) (a) is greater for electron-withdrawing substituents, (b) varies more for the meta-substituted derivatives (5634 to 7906 Hz) than for the para analogues (6088 to 7644 Hz) and (c) has the lowest values when the Pt(SnCl₃)(PEt₃)₂ group is the meta- or para-substituent. The direction of the change in ¹J(¹⁹⁵Pt, ¹¹⁹Sn) is opposite to that found for ¹J(¹⁹⁵Pt, ¹¹⁹P). For the aryl complexes linear correlations are observed between δ(¹¹⁹Sn), ¹J(¹⁹⁵Pt, ¹¹⁹Sn), ¹J(¹⁹⁵Pt, ³¹P), ¹J(¹¹⁹Sn, ³¹P) and the Hammett substituent constant σⁿ. δ(¹¹⁹Sn) and ¹J(¹⁹⁵Pt, ¹¹⁹Sn) are related linearly to v(Pt-H) in the complexes trans-[PtH(C₆H₄Y)(PEt₃)₂]; δ(¹¹⁹Sn) and δ(¹H) (hydride) are also linearly related. Based on ¹J(¹⁹⁵Pt, ¹¹⁹Sn), the acyl ligand is suggested to have a very large NMR trans influence. The differences in the NMR parameters for (1a-e) are rationalized in terms of differing σ- and π-bonding abilities of the carbon ligands.The structure of 1c has been determined by crystallographic methods. The complex has a slightly distorted square planar geometry with trans-PEt₃ ligands. Relevant bond lengths (Å) and bond angles (°) are: PtSn, 2.634(1), PtP, 2.324(4) and 2.329(4), PtC, 2.05(1); PPtP, 170.7(6), SnPtC, 173.0(3), SnPtP, 92.1(1), 91.7(1), PPtC, 88.8(4) and 88.3(4). The PtSn bond separation is the longest yet observed for square-planar platinum trichlorostannate complexes, and would be consistent with a large crystallographic trans influence of the benzoyl ligand. The PtSn bond separation is shown to correlate with ¹J(¹⁹⁵Pt, ¹¹⁹Sn).     

Carbon-13 NMR spectra of chromium pentacarbonyl carbenoid complexes

The carbon-13 NMR spectra of six carbenoid complexes of the type (OC)₅Cr-(CXX′) have been recorded. The carbenoid carbon atoms are all markedly deshielded (chemical shifts vs. TMS in the range ?271 to ?360). With only one minor inversion of uncertain significance, the chemical shifts correlate well with the expected ability of the X and X′ groups to engage in dative π bonding to the carbenoid carbon atom. The longitudinal relaxation times for both carbenoid and carbonyl carbon atoms in (OC)₅Cr[C(CH₃)(OC₂H₅)] are 1 – 2 sec. The chemical shift difference for carbonyl carbon atoms cis and trans to the carbenoid ligand is essentially invariant in the six compounds.     

ortho-Effects on carbon monoxide insertion in benzyl-molybdenum complexes

The formation of phosphine-substituted acylmolybdenums [(η⁵-C₅H₅)-(CO)₂(PPh₃)Mo(COR)], from reactions between substituted benzylmolybdenum complexes and triphenylphosphine in acetonitrile, is enhanced by the presence of a single bulky substituent in the ortho-position. However di-substitution (for i-Pr, Cl and OMe) causes a pronounced lowering of reactivity. The results are interpreted in terms of the steric demands of the reaction.     

Niobium and tantalum mesityl complexes and the role of the mesityl ligand in α- and γ-hydrogen abstraction reactions

The Ta and Nb complexes M(Mes)_nX_5?n (Mes = Mesityl; XCl or Br; n = 1, 2 or 3) and several derivatives can be prepared in high yield. They are considerably more stable than their phenyl analogues. 1H NMR data indicate that a mesityl ligand most likely occupies an equatorial site in a trigonal bipyramidal molecule but cannot rotate freely because its ortho methyl groups cannot pass by the axial chloride ligands. TaMes(CH₂CMe₃)X3 reacts with PMe₃ ( L) to give the known alkylidene complexes, Ta(CHCMe₃)L2X3, but TaMes(CH₃)X₃ reacts with PMe₃ to give the benzylidene complexes, Ta(CHC₆H₃Me₂)L₂X₃ (by γ-abstraction from the mesityl ligand), instead of the hoped for analogous methylene complex.     

The preparation and structure of μ-iodobis(h5-cyclopentadienyldicarbonyliron) fluoroborate

The identity and structure of a compound which arises frequently in the generation of (h⁵-C₅H₅)Fe(CO)₂⁺ ion from (h⁵-C₅H₅)Fe(CO)₂I and AgBF₄ have been determined. The substance was shown to be {[h⁵-C₅H₅)Fe(CO)₂]₂I}BF_4s a compound already known from the work of Fischer and Moser. It consists of a BF₄^? anion and a cation formed by two (h⁵-C₅H₅)Fe(CO)₂, groups having the expected shape and dimensions, united by a bridging iodine atom. The FeI bonds have an average lenght of 2.588 » and the FeIFe angle is 110.8(1)°. The FeFe distance of 4.26 » is consistent with the expectation that there should be no metalmetal bond. Presumably the large FeIFe angle results from a compromise between the tendency of I to maximize p character in its bonding orbitals and the necessity of niminizing non-bonded contact between the (h⁵-C₅H₅)Fe(CO)₂ groups. Crystallographic data are: space group, P2/a; unit cell dimensions, a=15.605(2)», b=9.607(2)», c=12.373(2)», β=104.86(1)°, V=1792.9(6)»³; d_ealc=2.10 g/cm³ for Z=4; d_obs=2.08±0.02 g/cm³. Refinement using 1595 independent reflections with F_o²>3σ(F_o² was terminated at residuals of R₁=0.076 and R₂=0.114.     

Cationic iron complexes containing the η2-Butatriene ligand

Cationic iron complexes of the type Fp(alkene)⁺ (Fp =η⁵-C₅ H₅ (CO)₂ Fe) containing an unsubstitutedη²-butatriene ligand are synthesized and characterized by spectroscopic and analytical data.     

The preparation,properties and crystal structure of bis(η5-cyclopentadienyldicarbonyliron)dimethylgermyl]oxide, [(η5-C5H5)(CO)2FeGe(CH3)2]2O

One of the main products of oxidation of (η⁵-C₅-H₅)₂Fe₂(CO)₃Ge(CH₃)₂ by air has been shown to be [(η⁵-C₅H₅)(CO)₂FeGe(CH₃)₂]₂O. The infrared, NMR and mass spectra are consistent with this formula and the detailed structure has been established by X-ray crystallography. In polar solvents the NMR suggests the existence of major and minor conformers interconverting only slowly on the NMR time scale at ≈ 25°. The X-ray diffraction study has shown the compound to consist of two (η⁵-C₅H₅)(CO)₂FeGe(CH₃)₂ moieties joined by a bridging oxygen atom. Two rotational isomers are present in the unit cell in a disordered fashion. Some pertinent average distances and angles are: FeGe, 2.372 Å; GeO, 1.785 Å; GeOGe′, 134°. The compound crystallizes in the monoclinic system, space group P2₁/n, with a 8.056(2), b 12.506(2), c 22.631(3) Å, β 98.01(1)°, d_calc 1.692 g cm^?3. Counter data were collected using Mo-K_α radiation. The 1780 reflections above background were used in least-squares refinement which converged at R₁ = 0.051 and R₂ = 0.068.     

Studies of organosulfur compounds : X. Preparation of some trimethylmetal(IVb) esters of dithio acids and their spectral properties

Some trimethylmetal(IVb) esters of dithio acids have been prepared by treatment of the secondary or tertiary amine salts of dithio acids with chlorotrimethylsilane, -germane, or -tin, and their IR, UV and NMR spectra recorded.     

Cyclometallation. Palladium 2-arylpyridine complexes

A number of new cyclometallated compounds of palladium with 2-arylpyridines have been synthesized and characterized. Palladium acetate has been proven to be a more useful starting material than Li₂PdCl₄, since the resulting acetato-bridged dimers, [Pd(OAc)(2-arylpyridine)]₂, unlike the chloro-bridged dimers, are conveniently soluble in common organic solvents. The effect of varying substituents on the aryl nucleus supports the concept that after initial N-complexation, the 2-position of the aryl nucleus undergoes electrophilic attack by the palladium atom. Detailed NMR studies of the soluble acetato compounds showed that the 6-heteroaryl and “ortho” to the Pd-C bond protons in the complexes are shifted (≈0.75 and 0.5 ppm, respectively) upfield from the ligand position. These shielding effects are believed to be due primarily to through-space interactions of overlying aromatic rings and secondarily to through-bond (Pd-to-ligand) effects. Both acetato- and chloro-bridged dimers will react with certain ligands to give mononuclear species containing the intact cyclometallated ligand.