Experimental observation of spin delocalisation onto the aryl-alkynyl ligand in the complexes [Mo(C≡CAr)(Ph2PCH2CH2PPh2)(η-C7H7)]+ (Ar = C6H5, C6H4-4-F; C7H7 = cycloheptatrienyl): an EPR and ENDOR investigation

The paramagnetic aryl-alkynyl complexes [Mo(C≡CAr)(dppe)(η-C(7)H(7))](+) (dppe = Ph(2)PCH(2)CH(2)PPh(2); Ar = C(6)H(5), [1](+); C(6)D(5), [2](+); C(6)H(4)-4-F, [3](+); C(6)H(4)-4-Me, [5](+)) and [Mo(C≡CBu(t))(dppe)(η-C(7)H(7))](+) [4](+), have been investigated in a combined EPR and ENDOR study. Direct experimental evidence for the delocalisation of unpaired spin density over the framework of an aryl-alkynyl ligand has been obtained. The X-band solution EPR spectrum of the 4-fluoro derivative, [3](+), exhibits resolved hyperfine coupling to the remote para position of the aryl group [a(iso)((19)F) = 4.5 MHz, (1.6 G)] in addition to couplings attributable to (95/97)Mo, (31)P and (1)H of the C(7)H(7) ring. A full analysis of the (1)H ENDOR spectra is restricted by the low g anisotropy of the system which prevents the use of orientation selection. However, inter-comparison of the (1)H cw-ENDOR frozen solution spectra of [1](+), [2](+), [4](+) and [5](+), combined with spectral simulation informed by calculated values derived from DFT investigations, has facilitated estimation of the experimental a(iso)((1)H) hyperfine couplings of [1](+) including the ortho, ±3.7 MHz (±1.3 G) and para, ±3.9 MHz (±1.4 G) positions of the C(6)H(5) substituent of the aryl-alkynyl ligand.     

Rapid binding and activation of small molecules by [MoH4(Ph2PCH2CH2PPh2)2] in the presence of HBF4 · OEt2. Crystal structure of the product obtained with phenylacetylene trans-[MoF(η2-PhCCH)(Ph2PCH2CH2PPh2)2]BF4

In the presence of HBF₄ · OEt₂, [MoH₄(Ph₂PCH₂CH₂PPh₂)₂] exhibits a remarkably rapid and diverse range of reactions with a variety of small molecules. The crystal structure of the product obtained in the presence of phenylacetylene, trans-[MoF(η²-PhCCH)(Ph₂PCH₂CH₂PPh₂)₂]BF₄ is reported.     

The formation of alkyne and alkynyl complexes by reaction of 1-alkynes with trans-[M(N2)2(PH2PCH2CH2PPh2)2] (M  Mo OR W) and with [Mo(Ph2PCH2PPh2)3]: X-ray structure of trans-[Mo(CCPh)2(PH2PCH2CH2PPh2)2]

Reaction of RCCH (R  Ph, CO₂Meor CO₂Et) with trans-[M(N₂)₂(dppe)₂] (M  Mo or W; dppe  Ph₂PCH₂CH₂PPh₂) or [Mo(dppm)₃] (dppm  Ph₂PCH₂PPh₂) gives the alkyne complexes [M(RCCH)₂(diphos)₂] (diphos  dppe, M  Mo, R = Ph; dihpos  dppm, M  Mo, R  Ph or CO₂Me) and the alkynyl complexes trans-[M(cCR)₂(dppe)₂], [MH₂(CCR)₂ (dppe)₂] (M  Mo or W. R  Ph, CO₂Me or CO₂Et) and cis-[WH(CCCO₂Me)(dppe)₂]: the X-ray structure of trans-[Mo(CCPh)₂(dppe)₂] is reported.     

(η5-C5H5)(Ph2PCH2CH2PPH2)RuCH2+ AsF6−. Spectral Characterization and measurement of the barrier to methylene rotation

The electrophilic methylene complex (η⁵-C₅H₅)(Ph₂PCH₂CH₂PPh₂)RuCH₂⁺ (1) has been characterized by ¹³C and variable-temperature ¹H NMR spectroscopy and exhibits a vertical orientation of the methylene group with a barrier for rotation about the rutheniumcarbon double bond of 10.9 kcal/mol.     

Synthesis and crystal structure of [MoH3(CCBut)(Ph2PCH2CH2PPh2)2], a trihydrido-alkynyl complex

Reaction of Bu^tCCH with trans-[Mo(N₂)₂(dppe)₂] (dppe = Ph₂PCH₂CH₂PPh₂) gives [MoH₃(CCBu^t)(dppe)₂], whose X-ray structure is reported.     

Replacement of terminal and bridging oxo groups by phenylimido groups in (η-C5H5)OMo(μ-O)2OMo(η-C5H5) giving (η-C5H5)(NPh)Mo(μ-NPh)2Mo(NPh)(η-C5H5)

The treatment of (η-C₅H₅)OMo(μ-O)₂MoO(η-C₅H₅) with excess phenylisocyanate at reflux in tetrahydrofuran yields the arylimido-substituted complex (η-C₅H₅)(NPh)Mo(η-NPh)₂Mo(NPh)(η-C₅H₅), which has been characterized by elemental analysis, and mass, IR and ¹H NMR spectra.     

Self-recognition by the iron chiral auxiliary [(η5-C5H5)Fe(CO)(PPh3] in the formation of (RR,SS)-[(η5-C5H5)FE(CO)(PPh3)COCH2]2CH2

Complete self-recognition of chirality is observed in the Michael addition of the enolate derived from R,S-[η⁵-C₅H₅Fe(CO)(PPh₃-COCH₃] to the acryloyl complex R,S-[(η⁵-C₅H₅Fe(CO)(PPh₃)-COCHCH₂)] to generate exclusively the single diastereoisomer of the glutaroyl complex RR,SS-[(η⁵-C₅H₅)Fe(CO)(PPh₃)COCH₂]₂CH₂.     

Optically active [(η-C5H5)Ru{(R)-Ph2PCH(CH3)CH2PPh2}(Olefin)]PF6 complexes: Influence of the stereogenic metal atom on the enantioface selection

The synthesis and characterization of optically active olefinic complexes of the type [(η-C₅H₅)Ru{Ph₂PCH(CH₃)CH₂PPh₂}(CH₂CHR″)]PF₆ (R″  H, CH₃, C₆H₅, COOCH₃), in which the metal is a stereogenic center, are reported. The enantioface discrimination of the prochiral olefin is influenced by the chiral ligand and by the stereogenic metal atom. The chiral center at the metal appears to be optically labile. The rates of the epimerization at the metal and of the olefin enantioface depend on the structure of the coordinated olefin.     

Electrochemical and Theoretical Investigations of the Role of the Appended Base on the Reduction of Protons by [Fe(2) (CO)(4) (κ(2) -PNP(R) )(μ-S(CH(2) )(3) S] (PNP(R) ={Ph(2) PCH(2) }(2) NR, R=Me, Ph)

The behavior of [Fe(2) (CO)(4) (κ(2) -PNP(R) )(μ-pdt)] (PNP(R) =(Ph(2) PCH(2) )(2) NR, R=Me (1), Ph (2); pdt=S(CH(2) )(3) S) in the presence of acids is investigated experimentally and theoretically (using density functional theory) in order to determine the mechanisms of the proton reduction steps supported by these complexes, and to assess the role of the PNP(R) appended base in these processes for different redox states of the metal centers. The nature of the R substituent of the nitrogen base does not substantially affect the course of the protonation of the neutral complex by CF(3) SO(3) H or CH(3) SO(3) H; the cation with a bridging hydride ligand, 1?μH(+) (R=Me) or 2?μH(+) (R=Ph) is obtained rapidly. Only 1?μH(+) can be protonated at the nitrogen atom of the PNP chelate by HBF(4) ?Et(2) O or CF(3) SO(3) H, which results in a positive shift of the proton reduction by approximately 0.15?V. The theoretical study demonstrates that in this process, dihydrogen can be released from a η(2) -H(2) species in the Fe(I) Fe(II) state. When R=Ph, the bridging hydride cation 2?μH(+) cannot be protonated at the amine function by HBF(4) ?Et(2) O or CF(3) SO(3) H, and protonation at the N atom of the one-electron reduced analogue is also less favored than that of a S atom of the partially de-coordinated dithiolate bridge. In this situation, proton reduction occurs at the potential of the bridging hydride cation, 2?μH(+) . The rate constants of the overall proton reduction processes are small for both complexes 1 and 2 (k(obs) ≈4-7?s(-1) ) because of the slow intramolecular proton migration and H(2) release steps identified by the theoretical study.     

Conformational analysis and x-ray crystal structure of [(η5-C5H5)Fe(CO)(PPh3)CH2CH3]

The complex [(η⁵-C₅H₅)Fe(CO)(PPh₃)CH₂CH₃] is shown by ¹H NMR spectroscopy and an X-ray crystal structure analysis to adopt a single conformation with the methyl group residing between the cyclopentadienyl and carbon monoxide ligands.     

Reactions of transition metal acetylides: VI. Some addition reactions of substituted styrenes with Ru(C2R)(L)2(η-C5H5) (R = Me OR Ph; L2 = (CO,PPh3), (PPh3)2 OR (dppe)). X-ray crystal structure of Ru{C[C(CN)2]CPhCH(C6H4NO2-4)}(dppe)(η-C5H5) · 0.5CH2Cl2

Further studies of the reactions between ruthenium σ-acetylide complexes and electrophilic olefins CHArC(CN)(X) (Ar = C₆H₄NO₂-4, Ph; X = CN; Ar = C₆H₄NO₂-4, X = CO₂Et) have shown the formation of allylic, butadienyl, and in one case, cyclobutenyl complexes. The direction of addition is such that the =C(CN)(X) group becomes attached to the α-carbon of the acetylide. This is confirmed by the X-ray structure of Ru{C[C(CN)₂]CPhCH(C₆H₄NO₂-4)}(dppe)(η-C₅H₅) · 0.5CH₂Cl₂, cr with cell dimensions a 28.81(1), b 9.661(2), c 30.782(8) Å, β 95.02 (3)°, and Z = 8. The structure was refined by a least-squares procedure with the use of 4291 statistically significant reflections [I > 2.5σ(I)] to R 0.075 and R_w 0.076.     

Stereo- and regio-specific CC bond formation via the coupling of electrophilic and nucleophilic organotransition-metal complexes: The x-ray crystal structure of [Ru(CO)2(PPh3)(η2,η3-C8H8R)][PF6]·0.5CH2Cl2 (R = CH2C(Me)CH2)

The coupling of [Ru(CO)₂L(η⁴-cot)] (L = CO or PPh₃, cot = cyclooctatetraene) with [Fe(CO)₃(η⁵-cyclohexadienyl)]⁺ or [Fe{P(OMe)₃}(NO)₂(η³-allyl)]⁺ yields respectively the dimetallic species [Ru(CO)₂L(η²,η³-C₈H₈{Fe(CO)₃(η⁴-C₆H₇)}] (3) and the allyl-substituted derivative [Ru(CO)₂L(η⁵-C₈H₈CH₂C(Me)CH₂)][PF₆] (5) whose X-ray structure is reported; paramagnetic [Co(η-C₅H₅)₂] and [Ru(CO)₃(η⁵-cyclohexadienyl)]⁺ give diamagnetic [Ru(CO)₃(η⁴-C₆H₇C₅H₆(o-C₅H₅)] (8) via CC bond formation and one-electron reduction.     

Synthesis of a Mo–Ru/Carbon Nanocomposite Using (η-C7H7)(OC)2MoRu(CO)2(η-C5H5) as a Single-Source Molecular Precursor

Degradation of a (-C₇H₇)(OC)₂MoRu(CO)₂(-C₅H₅)/carbon powder composite under appropriate thermal conditions affords a nanocomposite containing crystalline nanoclusters of Mo–Ru alloy highly dispersed on the carbon support. The alloy nanoparticles have an average diameter of 2.2 nm and crystallize as a fully disordered fcc lattice having a cell constant of 4.09 Å. When tested as an cathode catalyst in a direct methanol fuel cell, this nanocomposite shows significant methanol tolerance but affords current production too low to be of practical importance.     

Enantioselective synthesis: Catalysis of the aldol reaction by neutral gold(I)-chiral ferrocenylphosphine complexes. Crystal structure of the complex [{(η5-C5H4PPh2)(η5-C5H3(PPh2)CH(Me)N(Me)CH2CH2NMe2)Fe}2(AuCl)3] · Et2O

The chiral aminoferrocenylphosphine [(η⁵-C₅H₄PPh₂)(η⁵-C₅H₃(PPh₂)CH(CH₃)-N(CH₃)CH₂CH₂N(CH₃)₂)Fe] (1) reacts with (H₃C)₂SAuCl to give neutral gold(I) complexes that are active catalysts for the enantioselective coupling of isocyanoacetate esters with aldehydes, forming dihydrooxazoles. The structure of the trimeric complex [(rac-1)₂(AuCl)₃] · Et₂O has been determined by X-ray diffraction.     

The insertion of cycloheptatriene and cyclohepta-1,3-diene into the RuH bond of RuHCl(PPh3)3 to give Ru(η5-C7H9)Cl(PPh3)2 and Ru(η3-C7H11)Cl(PPh3)2

RuHCl(PPh₃)₃ reacts quantitatively with cycloheptatriene in CH₂Cl₂ at 35°C in 15 min to give Ru(η⁵-C₇H₉)Cl(PPh₃)₂ and PPh₃. The major isomer adopts a conformation with inequivalent phosphorus ligands and no plane of symmetry through the C₇H₉ ligand, but rapid intramolecular scrambling with δG³ = 10.6 kcal mol⁻¹ results in an averaged ¹H, ¹³C, and ³¹P NMR spectrum at room temperature. RuHCl(PPh₃)₃ reacts with cyclohepta-1,3-diene to give initially Ru(η³-C₇H₁₁)Cl(PPh₃)₂, but in a subsequent reaction this is dehydrogenated to give Ru(η⁵-C₇H₉)Cl(PPh₃)₂.     

Ditropylmolybdenum complexes by the sodium reduction of [Mo(CO)3(η-C7H7)][BF4]. X-Ray crystal structure of the ditropyl complex “Mo(CO)3”2(η6,η′6-C14H14)

Treatment of [Mo(CO)₃(η-C₇H₇)][BF₄] with either sodium amalgam or sodium naphthalide results in a reductive dimerisation to the ditropyl complex “Mo(CO)₃”₂(η₆,η′⁶-C₁₄H₁₄). The results of an X-ray crystallographic study confirm that the hydrogen atoms of the linking carbon atoms are both endo with respect to molybdenum. The reaction of Mo(CO)₆ with ditropyl, C₁₄H₁₄, leads to all three possible isomers of “Mo(CO)₃”²(η⁶,η′⁶-C₁₄-H₁₄). The structure of each is assigned by its ¹H NMR spectrum.     

Reaction of the Binuclear Ruthenium-Platinum Allenyl Complexes (PPh3)2Pt(μ-η1:η2α, β-C(R)=C=CH2)Ru(CO)Cp (R=H, Ph) with (PPh3)AuO3SCF3. The Synthesis and Characterization of a Trimetallic 1:1 Adduct of the Reactants

The reaction of the heterobinuclear metal -allenyl complexes (PPh₃)₂Pt(- ¹: ² _, -C(R)=C=CH₂)Ru(CO)Cp (R=H (1), Ph (2)) with (PPh₃)AuO₃SCF₃ in THF at –78°C to room temperature affords the trimetallic products [(PPh₃)₂Pt( ₂-CO)RuCpAu(PPh₃)( ₃- ¹: ³: ¹-CH₂CCR)]⁺O₃SCF^– ₃ (R=H (3), Ph (4)) in 46 and 55% isolated yield, respectively. The products were characterized by a combination of elemental analysis, FAB mass spectrometry, and IR and ¹H, ¹³C, and ³¹P NMR spectroscopy. The structure of 4 was elucidated by a single-crystal X-ray analysis. The crystal contains discrete trimetallic RuPtAu cations and CF₃SO^– ₃ anions. In the cation, a Pt–Ru bond of 2.7171(6) Å is supported by a semibridging CO and a CH₂CCPh allyl, which is ³-bonded to Ru, and ¹-bonded to each of Pt (through the CPh carbon) and Au (through the central carbon). The Ph₃P–Au–C fragment is close to linear (175.0(2)°), and the coordination environment around Pt is distorted square planar. Complex 3 appears to have the same type of structure as 4 from spectroscopic data.     

Molecular structure of a new palladium-containing vinylidene cluster [η2-Ph2P(CH2)3PPh2]PdFe3(μ4-C=CHPh)(CO)9

The structure of the vinylidene cluster [²-Ph₂P(CH₂)₃PPh₂]PdFe₃(₄-C=CHPh)(CO)₉ was established by X-ray diffraction analysis. The metal core of the molecule has a butterfly shape with the Pd atom occupying a wingtip position. The C(1)=C(2)HPh ligand is -bound to three atoms of the Fe₂Pd triangle through the C(1) atom and is ²-coordinated to the Fe atom located in the second wingtip position via the C(1)=C(2) double bond. The Pd atom is chelated by the diphosphine ligand.     

The mechanism of fluxionality of (1,2,7-η3-2-Me-benzyl)(η5-C5H5)Mo(CO)2

It is shown that (1,2,7-η³-2-Me-benzyl)(η⁵-C₅H₅)Mo(CO)₂ exits in solution as one isomer which is fluxional, probably via (7-η¹-2-Me-benzyl)((η⁵-C₅H₅)Mo(CO)₂, with ΔG^≠₃₇₀ = 23.6 ± 1.0 kcal mol⁻¹. In contrast, (1,2,7-η³-3-Me-benzyl)(η⁵-C₅H₅)Mo(CO)₂ exits as two isomers at −20°C, which undergo interconversion at room temperature with ΔG^≠ 15.7 kcal mol⁻¹. This dynamic process is an allyl rotation. It is probable that there is also a low energy [1,5]-sigmatropic shift.