Heterobimetallic chloro bridgedcomplexes of (η:η−C10H16)-ruthenium(IV) with palladium(II), platinum(II), rhodium(III), iridium(III), copper(I) and rhodium(I)

Metathesis of [(η³:η³−C₁₀H₁₆)Ru(Cl) (μ−Cl)]₂ (1) with [R₃P) (Cl)M(μ-Cl)]₂ (M = Pd, Pt), [Me₂NCH₂C₆H₄Pd(μ-Cl)]₂ and [(OC)₂Rh(μ-Cl)]₂ affords the heterobimetallic chloro bridged complexes (η³:η³-C₁₀H₁₆) (Cl)Ru(μ-Cl)₂M(PR₃)(Cl) (M = Pd, Pt), (η³:η³-C₁₀H₁₆) (Cl)Ru(μ-Cl)₂PdC₆H₄CH₂NMe₂ and (η³:η³-C₁₀H₁₆) (Cl)Ru(μ-Cl)₂Rh(CO)₂, respectively. Complex 1 reacts with [Cp^*M(Cl) (μ-Cl)]₂ (M = Rh, Ir), [p-cymene Ru(Cl) (μ-Cl]₂ and [(Cy₃P)Cu(μ-Cl)]₂ to give an equilibrium of the heterobimetallic complexes and of educts. The structures of (η³:η³-C₁₀H₁₆)Ru(μ-Cl)₂Pd(PR₃) (Cl) (R = Et, Bu) and of one diastereoisomer of (η³:η³-C₁₀H₁₆)Ru(μ-Cl)₂IrCp^*(Cl) were determined by X-ray diffraction.     

Synthesis and properties of the dichloro [tetramethyl (trifluoromethyl)cyclopentadienyl]ruthenium dimer: X-ray structure of [M2(η-C5Me4CF3)2Cl2(μ-Cl)2] (M=Ru, Rh)

The reaction of RuCl₃(H₂O), with C₅Me₄CF₃J in refluxing EtOH gives [Ru₂(η⁵-C₅Me₁CF₂)₂ (μ-Cl₂] (20 in 44% yield. Dimer 2 antiferromagnetic (−2J=200 cm¹). The crystal structures of 2 (rhombohedral system, R3 space group, Z=9, R=0.0589) and [Rh₂(η⁵-C₅Me₄CF₃(₂Cl₂(μ-Cl)₂] (3) (rhombohedral system. space group, Z = 9, R = 0.0641) were solved; both complexes have dimeric structures with a trans arrangement of the η⁵-C₅Me₄CF₄ rings. Comparison of the geometry of 2 and 3 with those of the corresponding η⁵-C₅Me₅ complexes shows that lowering the ring symmetry causes significant distortion of the M₂(μ-Cl)₂ moiety. The analysis of the MCl₃ fragment conformations in 2 and 3 and in the η⁵-C₅ME₅ analogues shows that they are correlated with the M---M distances. The Cl atoms are displaced by Br on reaction of 2 with KBr in MeOH to give the diamagnetic dimer [Ru₂(η⁵-C₅Me₄CF₃)₂Br₂ (μ-Br₂] (4). Complex 2 reacts with O₂ in CH₂Cl₂ solution at ambient temperature to form a mixture of isomeric η⁶-fulvene dimers [Ru₂(η⁶-C₅Me₃CF₃ = CH₂)₂Cl₂(μ-Cl)₂] (5). Reactions of 5 with CO and allyl chloride give Ru(η⁵-C₅Me₃CF₃CH₂Cl)(CO)₂Cl (6) and Ru(η⁵-C₅Me₃CF₃CF₃CH₂Cl)(η³-C₃H₅)Cl₂ (7) respectively.     

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.     

Chelated alkyl halide manganese complexes (η:η-C5H4CH2CH2X)Mn(CO)2 from photolysis of (η-C5H4CH2CH2X)Mn(CO)3

Manganese tricarbonyl complexes (η⁵-C₅H₄CH₂CH₂Br)Mn(CO)₃ (3) and (η⁵-C₅H₄CH₂CH₂I)Mn(CO)₃ (4), with an alkyl halide side chain attached to the cyclopentadienyl ligand, were synthesized as possible precursors to chelated alkyl halide manganese complexes. Photolysis of 3 or 4 in toluene, hexane or acetone-d₆ resulted in CO dissociation and intramolecular coordination of the alkyl halide to manganese to produce (η⁵:η¹-C₅H₄CH₂CH₂Br)Mn(CO)₂ (5) and (η⁵:η¹-C₅H₄CH₂CH₂I)Mn(CO)₂ (6). Low temperature NMR and IR spectroscopy established the structures of 5 and 6. Photolysis of 3 in a glass matrix at 91 K demonstrated CO release from manganese. Low temperature NMR spectroscopy established that the coordinated alkyl halide complexes are stable to approximately −20°C.     

The structure of (η-C6H5Cl)Cr(CO)2PPh3

In a synthetic route that varies from the standard procedure requiring irradiation, the (η⁶-C₆H₅Cl)Cr(CO)₂PPh₃ complex is obtained upon reacting (η⁶-C₆H₅Cl)Cr(CO)₃ with tetrakis(triphenylphosphine)palladium(0), CuI, and trimethylsilylphenylacetylene in triethylamine. The X-ray crystal structure of the yellow–orange crystals of (η⁶-C₆H₅Cl)Cr(CO)₂PPh₃ allows structural comparisons to related (arene)Cr(CO)₂PR₃ complexes.     

On the reduction behaviour of 2-methoxyethyl and 2-methylthioethyl substituted zirconocene dichlorides: crystal structure of (η,σ-C5Me4CH2CH2S)2Zr

A reduction of previously reported 2-methoxyethyl and 2-methylthioethyl functionalized zirconocenedichlorides (η⁵-C₅Me₄CH₂CH₂EMe)(η⁵-C₅Me₅)(ZrCl₂ (E = O, S) and (η⁵-C₅Me₄CH₂CH₂EMe)(η⁵-C₅Me₄CH₂CH₂E′Me)ZrCl₂ (E = O, S; E′ = O, S) with Mg/Hg in THF leads unexpectedly to the products of O---Me and S---Me bond cleavage (η⁵,σ-C₅Me₄CH₂CH₂E)(η⁵-C₅Me₅)ZrMe (E = O, S), (η⁵,σ-C₅Me₄CH₂CH₂E)(η⁵-C₅Me₄CH₂CH₂E′Me)ZrMe (E = O, S; E′ = O), and (η⁵,σ-C₅Me₄CH₂CH₂S)₂Zr respectively. The crystal structure of (η⁵,σ-C₅Me₄CH₂CH₂S)₂Zr was established by X-ray analysis. At that same time the reduction of (ηsu5-C_{5Me4CH2CH2EMe)(η⁵-C5Me5)ZrCl2 (E> = O, S)} under 1 atm of CO gives either only the dicarbonyl derivative (η⁵-C₅Me₄CH₂CH₂EMe) (η⁵-C₆Me₅)Zr(CO)₂ (E = O) or a complex mixture of products (E = S).     

Misdirected π-donor ligands: (η-C5H5)2Zr(Cl) (SR) with sterically more demanding R groups have lower rotational barriers

Rotational barriers about the M-S bonds of 16-electron bent metallocene monothiolates (η⁵-C₅H₅)₂Zr(Cl) (SR) (R = −CH₃, −CH₂CH₃, −CH(CH₃)₂, −C(CH₃)₃) (1a–d) have been measured by dynamic ¹H NMR methods: 32, 33, 35 and 26 kJ mol⁻¹, respectively. The ground-state orientation about the Zr-S bonds of 1 that maximizes Spπ → Mdπ bonding (Cl-Zr-S-R ≈ 90°) also maximizes CpR steric interaction, whereas the rotational transition-state orientation (Cl-Zr-S-R ≈ 0°) is one that minimizes Spπ → Mdπ bonding and maximizes ClR steric interaction. Deviation from a ground-state orientation that is ideal for Spπ → Mdπ bonding might be expected as the size of the R group and CpR steric interaction increases. Thus, the aberrant trend for the R = −C(CH₃)₃ derivative could be attributed to a ground-state steric effect where the sterically demanding −C(CH₃)₃ group forces an unfavorable (misdirected) orientation for Mdπ-Spπ bonding, but a favorable orientation with respect to CpR and ClR steric interactions. However, the solid-state structures of (η⁵-C₅H₅)₂Zr(SR)₂ (R = −CH₃, −CH₂CH₃, −CH(CH₃)₂, −C(CH₃)₃) (2a–d) exhibit regular variation of their metric parameters as evidenced by their Zr-S-C bond angles of 108, 109, 113, and 124° and S-Zr-S′ bond angles of 97, 99, 100 and 106°, respectively. Neither the S′-Zr-S-R torsion angles nor the dihedral angles that describe the relationship between the S/Zr/S′ and Cp(centroid)/Zr/Cp′ (centroid) planes (both indicators of the relative orientation of the Zr dπ acceptor orbital and the thiolate S pπ donor orbital) reflect the steric demand of the R group. Thus, the size of the R group imposes a measured effect on the geometry of 2 and the tert-butyl group is not extraordinary. Although the enthalpic and entropic effects could not be deconvoluted for rotation about the Zr-S bond of 1 in the present study, literature precedents suggest that both enthalpic and entropic effects may play a role in determining the irregular trend that is observed.     

Organometallic chemistry of diphosphazanes. Rhodium(I) complexes of RN(PX2)2 (R = C6H5; X = OC6H5, OC6H4Br−p, R = CH3; X = OC6H5)

Reactions of [Rh(COD)Cl]₂ with the ligand RN(PX₂)₂ (1: R = C₆H₅; X = OC₆H₅) give mono- or disubstituted complexes of the type [Rh₂(COD)Cl₂{ν²−C₆H₅N(P(OC₆H₅)₂)₂}] or [RhCl{ν²−C₆H₅ N(P(OC₆H₅)₂)₂ }]₂ depending on the reaction conditions. Reaction of 1 with [Rh(CO)₂Cl]₂ gives the symmetric binuclear complex, [Rh(CO)Cl{μ−C₆H₅N(P(OC₆H₅)₂)₂} ₂, whereas the same reaction with 2 (R = CH₃; X = OC₆H₅) leads to the formation of an asymmetric complex of the type [Rh(CO)(μ−CO)Cl{μ−CH₃N(P(OC₆H₅)₂)₂}₂ containing both terminal and bridging CO groups. Interestingly the reaction of 3 (R = C₆H₅, X = OC₆H₄Br−p with either [Rh(COD)Cl]₂ or [Rh(CO)₂Cl]₂ leads only to the formation of the chlorine bridged binuclear complex, [RhCl{ν²−C₆H₅N(P(OC₆H₄Br−p)₂)₂}]₂. The structural elucidation of the complexes was carried out by elemental analyses, IR and ³¹P NMR spectroscopic data.     

Olefin versus sulfur coordination of benzo[b]thiophene (BT) in Cp(CO)2Re(η:η-μ2-BT)Cr(CO)3

Reactions of Cr(CO)₃(η⁶-BT), in which the Cr is π-coordinated to the benzene ring of benzo[b]thiophene (BT), with Cp′(CO)₂Re(THF), where Cp′ = η⁵-C₅H₅ or η⁵-C₅Me₅, give the products Cp′(CO)₂Re(η²:η⁶-μ₂-BT)Cr(CO)₃ in which the Cr remains coordinated to the benzene ring and Re is bound to the C(2)=C(3) double bond. An X-ray diffraction study of Cp(CO)₂Re(η²:η⁶-μ₂-BT)Cr(CO)₃ (3) provides details of the geometry. This structure contrasts with that of the Cp′(CO)₂Re(BT) complexes that exist as mixtures of isomers in which the BT is coordinated to the Re through either the double bond (2,3-η²) or the sulfur (η¹(S)). Thus, the electron-withdrawing Cr(CO)₃ group in 3 stabilizes the 2,3-η² mode of BT coordination to the Cp′(CO)₂Re fragment. Implications of these results for catalytic hydrodesulfurization of BT are discussed. Crystal data for 3: triclinic, space group

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The preparation, characterisation and low temperature X-ray structure of Ru6(η-μ4-CO)2(CO)13(η6-C6Me6)

The new organometallic cluster (η²-μ₄-CO)₂(CO)₁₃(η⁶-C₆Me₆) has been prepared by the thermolysis of Ru₃(CO)₁₂ with hexamethylbenzene in octane and characterised by a single crystal X-ray diffraction study. It is isostructural with the known cluster Ru₆(η²-μ₄-CO)₂(CO)₁₃(η⁶-C₆H₃Me₃) and the metal core constitutnts the same tetrahedral Ru₄ unit with two edge-bridging Ru atoms. The mesitylene derivative has been shown to undergo rearrangement to afford the octahedral carbido cluster Ru₆C(CO)₁₄(η⁶-C₆H₃Me₃), but this conversion is not observed for the new hexamethylbenzene derivative.     

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.     

Reactivity, variable temperature solution H NMR studies and MO calculations of dimolybdenum allenylidene complexes of the type [(η-C5H5)2Mo2(CO)4(μ,η(4e)-C=C=CR1R2)]

The reactivity, towards nucleophiles and electrophiles, of dimolybdenum allenylidene complexes of the type [Cp₂Mo₂(CO)₄(μ,η²(4e)-C=C=CR1R2)] (Cp=η⁵-C₅H₅) has been investigated. The nucleophilic attacks occur at the C_γ carbon atom, while electrophiles affec the C atom. Variable temperature solution ¹H NMR studies show a dynamic behavior of these complexes consisting of an equilibrium between two enantiomers with a symmetrical [Cp₂Mo₂(CO)₄(μ-σ,σ(2e)-C=C=CR1R2)] transition state. Extended Hückel MO calculations have been carried out on the model [Cp₂Mo₂(CO)₄(μ,η²-C=C=CH₂]. The calculated charges of the allenylidene carbon atoms suggest that the electrophilic attacks are under charge control, while the nucleophilic attacks are rather under orbital control.     

Synthesis and characterization of SrCu2(O2CR)3(bdmap)3 and Bi2(O2CCH3)4(bdmap)2(H2O) (R = CH3, CF3; bdmap = 1,3-bis(dimethylamino)-2-propanolato)

New mixed metal complexes SrCu₂(O₂CR)₃(bdmap)₃ (R = CF₃ (1a), CH₃ (1b)) and a new dinuclear bismuth complex Bi₂(O₂CCH₃)₄(bdmap)₂(H₂O) (2) have been synthesized. Their crystal structures have been determined by single-crystal X-ray diffraction analyses. Thermal decomposition behaviors of these complexes have been examined by TGA and X-ray powder diffraction analyses. While compound 1a decomposes to SrF₂ and CuO at about 380°C, compound 1b decomposes to the corresponding oxides above 800°C. Compound 2 decomposes cleanly to Bi₂O₃ at 330°C. The magnetism of 1a was examined by the measurement of susceptibility from 5–300 K. Theoretical fitting for the susceptibility data revealed that 1a is an antiferromagnetically coupled system with g = 2.012(7), −2J = 34.0(8) cm⁻¹. Crystal data for 1a: C₂₇H₅₁N₆O₉F₉Cu₂Sr/THF, monoclinic space group P2₁/m, A = 10.708(6), B = 15.20(1), C = 15.404(7) Å, β = 107.94(4)°, V = 2386(2) ų, Z = 2; for 1b: C₂₇H₆₀N₆O₉Cu₂Sr/THF, orthorhombic space group Pbcn, A = 19.164(9), B = 26.829(8), C = 17.240(9) Å, V = 8864(5) ų, Z = 8; for 2: C₂₂H₄₈O₁₁N₄Bi₂, monoclinic space group P2₁/c, A = 17.614(9), B = 10.741(3), C = 18.910(7) Å, β = 109.99(3)°, V = 3362(2) ų, Z = 4.     

Chiroptical properties of heterotrimetallic ‘wing-tip’ butterflies; synthesis and crystal structure of (μ-H)Ru2Fe2PdC(CO)12 (η-ß-C10H15)

HRu₂Fe₂PdC(CO)₁₂ (η³-ß-C₁₀H₁₅) cluster was prepared in the reaction of (Et₄N) [HFe₂Ru₂C(CO)₁₂] with [Pd(η³-ß-C₁₀H₁₅)Cl]₂. X-ray structural study of HRu₂Fe₂PdC(CO)₁₂ (η³-ß-C₁₀H₁₅) (where ß-C₁₀H₁₅ is ß-pinenyl) revealed a wing-tip butterfly geometry of the metal core and (1R, 2S, 3S, 5R) absolute configuration for both crystallography independent molecules in the crystal. Chiroptical properties of this cluster are compared with other clusters containing a Pd(η³-ß-C₁₀H₁₅) fragment and discussed.     

Kinetics and mechanisms of ligand substitution reactions of molybdenum SO2 complexes. Synthesis and X-ray structure of trans-Mo(CO)2 (dmpe) (PPh3) (SO2)

Kinetic results are reported for intramolecular PPh₃ substitution reactions of Mo(CO)₂(η¹-L)(PPh₃)₂(SO₂) to form Mo(CO)₂(η²-L)(PPh₃)(SO₂) (L = DMPE = (Me)₂PC₂H₄P(Me)₂ and dppe=Ph₂PC₂H₄PPh₂) in THF solvent, and for intermolecular SO₂ substitutions in Mo(CO)₃(η²-L)(η²-SO₂) (L = 2,2′-bipyridine, dppe) with phosphorus ligands in CH₂Cl₂ solvent. Activation parameters for intramolecular PPh₃ substitution reactions: ΔH^≠ values are 12.3 kcal/mol for dmpe and 16.7 kcal/mol for dppe; ΔS^≠ values are −30.3 cal/mol K for dmpe and −16.4 cal/mol K for dppe. These results are consistent with an intramolecular associative mechanism. Substitutions of SO₂ in MO(CO)₃(η²-L)(η²-SO₂) complexes proceed by both dissociative and associative mechanisms. The facile associative pathways for the reactions are discussed in terms of the ability of SO₂ to accept a pair of electrons from the metal, with its bonding transformations of η²-SO₂ to η¹-pyramidal SO₂, maintaining a stable 18-e count for the complex in its reaction transition state. The structure of Mo(CO)₂(dmpe)(PPh₃)(SO₂) was determined crystallographically: P2₁/c, A=9.311(1), B = 16.344(2), C = 18.830(2) Å, ß=91.04(1)°, V=2865.1(7) ų, Z=4, R(F)=3.49%.     

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.     

Kinetics of nucleophilic attack on coordinated organic moieties Part 29. Mechanism of addition of tertiary phosphines and phosphites to the tropylium ring of [M(CO)3(η-C7H7] (M = Cr, Mo, W) cations

Kinetic studies of the addition of a wide range of tertiary phosphines and phosphites to the tropylium ring of the cation [Cr(CO)₃(η⁷-C₇H₇]⁺ (1) reveal the two-term raw, k_obs = k₁[PR₃] + k₋₁. This is consistent with the reversible equilibrium process (i) which is also confirmed from IR and ¹H NMR studies. In the case of the highly basic nucleophiles PBu₃ⁿ and PEt₂Ph, the rate is dominated by the k₁ term and the equilibrium lies far to the right.

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The first-order rate constants k₁, for addition to the tropylium ring decrease markedly down the series PBu₃ⁿ>PEt₂Ph>P(4-MeOC₆H₄)₃>P(4-MeC₆H₄)₃>P(C₆H_{11 3}>PPh₂(4-MeC₆H₄)>PPh₃>P(2-CNC₂H₄)₃>P(OBuⁿ)₃ (overall variation 10⁴). This reactivity order parallels the decreasing electron availability at the phosphorus centres, as confirmed by the linear correlation between log k₁ and the Tolman Σ_χ values for the nucleophiles. Excellent Hammett and Brønsted correlations are also observed for ring addition by a range of P(4-XC₆H₄)₃ nucleophiles. The Brønsted slope, , of 0.7 conirms the major importance of basicity in determining nucleophilicity towards cation 1. Kinetic studies of the related additions of PBu₃ⁿ to the cations [M(CO)₃(η⁷-C₇H₇]⁺ (M = Mo, W) reveal the rate law, Rate = k₁[M][PBu₃ⁿ, and show only a small dependence of k₁ on the nature of metal (Cr>WMo; 2:1.1:1). These data, together with the associated activation parameters, support a mechanism involving direct addition (k₁) of the phosphorus nucleophiles to the tropylium ring, and are inconsistent with initial rate-determining attack at the metal centre.     

Reactions of the haloalcohols HO(CH2)nCl (n = 2, 3) with platinum(II) - alkynyl and -alkyne complexes. X-ray crystal structure of trans-[Pt(Me) {C(OCH2CH2Cl) (CH2Ph)} (PPh3)2] [BF4]

The chloro complexes trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄, react with 1-alkynes HC---C---R in the presence of NEt₃ to afford the corresponding acetylide derivatives trans-[Pt(Me) (C---C---R) (PPh₃)₂] (R = p-tolyl (1), Ph (2), C(CH₃)₃ (3)). These complexes, with the exception of the t-butylacetylide complex, react with the chloroalcohols HO(CH₂)_nCl (n = 2, 3) in the presence of 1 equiv. of HBF₄ to afford the alkyl(chloroalkoxy)carbene complexes trans-[Pt(Me) {C[O(CH₂)_nCl](CH₂R) } (PPh₃)₂][BF₄] (R = p-tolyl, N = 2 (4), N = 3 (5); R=Ph, N = 2 (6)). A similar reaction of the bis(acetylide) complex trans-[Pt(C---C---Ph)₂(PMe₂Ph)₂] with 2 equiv. HBF₄ and 3-chloro-1-propanol affords trans-[Pt(C---CPh) {C(OCH₂CH₂CH₂Cl)(CH₂Ph) } (PMe₂Ph)₂][BF₄] (7). T alkyl(chloroalkoxy)-carbene complex trans-[Pt(Me) {C(OCH₂CH₂Cl)(CH₂Ph) } (PPh₃)₂][BF₄] (8) is formed by reaction of trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄ in HOCH₂CH₂Cl, with phenylacetylene in the presence of 1 equiv. of n-BuLi. The reaction of the dimer [Pt(Cl)(μ-Cl)(PMe₂Ph)]₂ with p-tolylacetylene and 3-chloro-1-propanol yields cis-[PtCl₂{C(OCH₂CH₂CH₂Cl)(CH₂C₆H₄-p-Me}(PMe₂Ph)] (9). The X-ray molecular structure of (8) has been determined. It crystallizes in the orthorhombic system, space group Pna2₁, with a = 11.785(2), B = 29.418(4), C = 15.409(3) Å, V = 4889(1) ų and Z = 4. The carbene ligand is perpendicular to the Pt(II) coordination plane; the PtC(carbene) bond distance is 2.01(1) Å and the short C(carbene)-O bond distance of 1.30(1) Å suggests extensive electronic delocalization within the Pt---C(carbene)---O moietry.     

Thermal and photochemical substitution reactions of CpRe(PPh3)2H2 and CpRe(PPh3)H4. Catalytic insertion of ethylene into the C-H bond of benzene

The thermal and photochemical reactions of CpRe(PPh₃)₂H₄ and CpRe(PPh₃)H₄ (Cp = η⁵-C₅H₅) with PMe₃, P(p-tolyl)₃, PMe₂Ph, DMPE, DPPE, DPPM, CO, 2,6-xylylisocyanide and ethylene have been examined. While CpRe(PPh₃)₂H₂ is thermally inert, it will undergo photochemical substitution of one or two PPh₃ ligands. With ethylene, substitution is followed by insertion of the olefin into the C-H bond of benzene, giving ethylbenzene. CpRe(PPh₃)H₄ undergoes thermal loss of PPh₃, which leads to substituted products of the type CpRe(L) H₄. Photochemically, reductive elimination of dihydrogen occurs preferentially. The complex trans-CpRe(DMPE)H₂ was structurally characterized, crystallizing in the monoclinic space group P2₁/n (No. 14) with a = 6.249(6), b = 16.671(8), c = 13.867(7) Å, β = 92.11(6)°, V = 1443.7(2.9) Å and Z = 4. The complex trans-CpRe(PMe₂Ph)₂H₂ was structurally characterized, crystallizing in the monoclinic space group P2₁/n (No. 14) with a = 7.467(3), b = 23.874(14), c = 11.798(6) Å, β = 100.16(4)°, V = 2070.2(3.4) ų and Z = 4.     

Reactions of tungsten phosphonium carbyne complexes with aryloxide nucleophiles to form aryloxycarbyne and η-ketenyl complexes

Tungsten phosphoranylideneketene complexes of the type Tp′(CO)(p-OC₆H₄R)W(η²-(C,C)---O=CC---PR′₂Ph) (R=NO₂, R′=Me (6a); R=NO₂, R′=Ph (6b); R=CN, R′=Me (7a); R=CN, R′=Ph (7b); R=Cl, R′=Ph (8b)) have been synthesized from phosphonium carbyne precursors in a reaction that reflects coupling of carbonyl and carbyne ligands. In addition to these products, aryloxycarbyne complexes Tp′(CO)₂WCO(p-C₆H₄NO₂) (9a), Tp′(CO)₂WCO(p-C₆H₄CN) (9b), and Tp′(CO)₂WCO(p-C₆H₄Cl) (9c)) have been prepared via substitution of the phosphonium carbyne phosphine with an aryloxide nucleophile. The product ratio of substitution at the carbyne carbon to carbonyl–carbyne coupling can be tuned by variation of the aryloxide para-substituent. Aryloxy carbyne complexes are the favored products with stronger nucleophiles, while weaker nucleophiles result in a mixture of aryloxy carbyne complexes and η²-ketenyl coupled complexes. Formation of η²-ketenyl complexes is favored for the least nucleophilic aryloxides. Ketenyl complexes 6a and 6b were methylated at the ketenyl oxygen to form cationic alkyne complexes [Tp′(CO)(p-OC₆H₄NO₂)W(η²-(C,C)---CH₃OCCPR₂Ph)][OTf] (R=Me (10a), R=Ph (10b)). The structures of η²-ketenyl complexes 6a and 7b and the structure of cationic alkyne complex 10a were determined by X-ray crystallography.