Competing C-F activation pathways in the reaction of Pt(0) with fluoropyridines: phosphine-assistance versus oxidative addition

A survey of computed mechanisms for C-F bond activation at the 4-position of pentafluoropyridine by the model zero-valent bis-phosphine complex, [Pt(PH3)(PH2Me)], reveals three quite distinct pathways leading to square-planar Pt(II) products. Direct oxidative addition leads to cis-[Pt(F)(4-C5NF4)(PH3)(PH2Me)] via a conventional 3-center transition state. This process competes with two different phosphine-assisted mechanisms in which C-F activation involves fluorine transfer to a phosphorus center via novel 4-center transition states. The more accessible of the two phosphine-assisted processes involves concerted transfer of an alkyl group from phosphorus to the metal to give a platinum(alkyl)(fluorophosphine), trans-[Pt(Me)(4-C5NF4)(PH3)(PH2F)], analogues of which have been observed experimentally. The second phosphine-assisted pathway sees fluorine transfer to one of the phosphine ligands with formation of a metastable metallophosphorane intermediate from which either alkyl or fluorine transfer to the metal is possible. Both Pt-fluoride and Pt(alkyl)(fluorophosphine) products are therefore accessible via this route. Our calculations highlight the central role of metallophosphorane species, either as intermediates or transition states, in aromatic C-F bond activation. In addition, the similar computed barriers for all three processes suggest that Pt-fluoride species should be accessible. This is confirmed experimentally by the reaction of [Pt(PR3)2] species (R = isopropyl (iPr), cyclohexyl (Cy), and cyclopentyl (Cyp)) with 2,3,5-trifluoro-4-(trifluoromethyl)pyridine to give cis-[Pt(F){2-C5NHF2(CF3)}(PR3)2]. These species subsequently convert to the trans-isomers, either thermally or photochemically. The crystal structure of cis-[Pt(F){2-C5NHF2(CF3)}(P iPr3)2] shows planar coordination at Pt with r(F-Pt) = 2.029(3) A and P(1)-Pt-P(2) = 109.10(3) degrees. The crystal structure of trans-[Pt(F){2-C5NHF2(CF3)}(PCyp3)2] shows standard square-planar coordination at Pt with r(F-Pt) = 2.040(19) A.     

Electronic and medium effects on the rate of arene C [bond] H activation by cationic Ir(III) complexes

A detailed mechanistic study of arene C [bond] H activation in CH(2)Cl(2) solution by Cp(L)IrMe(X) [L = PMe(3), P(OMe)(3); X = OTf, (CH(2)Cl(2))BAr(f); (BAr(f) = B[3,5-C(6)H(3)(CF(3))(2)](4))(-)] is presented. It was determined that triflate dissociation in Cp(L)IrMe(OTf), to generate tight and/or solvent-separated ion pairs containing a cationic iridium complex, precedes C [bond] H activation. Consistent with the ion-pair hypothesis, the rate of arene activation by Cp(L)IrMe(OTf) is unaffected by added external triflate salts, but the rate is strongly dependent upon the medium. Thus the reactivity of Cp(PMe(3))IrMe(OTf) can be increased by almost 3 orders of magnitude by addition of (n-Hex)(4)NBAr(f), presumably because the added BAr(f) anion exchanges with the OTf anion in the initially formed ion pair, transiently forming a cation/borate ion pair in solution (special salt effect). In contrast, addition of (n-Hex)(4)NBAr(f) to [CpPMe(3)Ir(Me)CH(2)Cl(2)][BAr(f)] does not affect the rate of benzene activation; here there is no initial covalent/ionic pre-equilibrium that can be perturbed with added (n-Hex)(4)NBAr(f). An analysis of the reaction between Cp(PMe(3))IrMe(OTf) and various substituted arenes demonstrated that electron-donating substituents on the arene increase the rate of the C [bond] H activation reaction. The rate of C(6)H(6) activation by [Cp(PMe(3))Ir(Me)CH(2)Cl(2)][BAr(f)] is substantially faster than [Cp(P(OMe)(3))Ir(Me)CH(2)Cl(2)][BAr(f)]. Density functional theory computations suggest that this is due to a less favorable pre-equilibrium for dissociation of the dichloromethane ligand in the trimethyl phosphite complex, rather than to a large electronic effect on the C [bond] H oxidative addition transition state. Because of these combined effects, the overall rate of arene activation is increased by electron-donating substituents on both the substrate and the iridium complex.     

Site-differentiated hexanuclear rhenium(III) cyanide clusters [Re(6)Se(8)(PEt(3))(n)()(CN)(6)(-)(n)()](n)()(-)(4) (n = 4, 5) and kinetics of solvate ligand exchange on the cubic [Re(6)Se(8)](2+) Core

The site-differentiated, cyanide-substituted hexanuclear rhenium(III) selenide clusters cis- and trans-[Re(6)Se(8)(PEt(3))(4)(CN)(2)] and [Re(6)Se(8)(PEt(3))(5)(CN)](+) have been prepared from heterogeneous reactions of the corresponding iodo clusters with AgCN in refluxing chloroform. Isolated yields are 68%, 46%, and 64% for cis-[Re(6)Se(8)(PEt(3))(4)(CN)(2)], trans-[Re(6)Se(8)(PEt(3))(4)(CN)(2)], and [Re(6)Se(8)(PEt(3))(5)(CN)](+), respectively. The new compounds are air- and water-stable and are characterized by X-ray diffraction crystallography, (31)P NMR and IR spectroscopies, and FAB mass spectrometry. In related work, the solvent exchange rates of two site-differentiated monosolvate clusters, [Re(6)Se(8)(PEt(3))(5)(MeCN)](SbF(6))(2) and [Re(6)Se(8)(PEt(3))(5)(Me(2)SO)](SbF(6))(2), in neat solvents were measured by (1)H NMR. These clusters are substitutionally inert; k approximately 10(-)(5)-10(-)(6) s(-)(1) at 318 K. Activation parameters indicate a dissociative ligand exchange mechanism; DeltaH() values obtained from least-squares fitting of temperature-dependent kinetics data exceed RT by a factor of ca. 50 over the temperature range studied. These results demonstrate that the substitutional lability encountered in a previous study of cluster photophysics (Gray, T. G.; Rudzinski, C. M.; Nocera, D. G.; Holm, R. H. Inorg. Chem. 1999, 38, 5932) cannot result from ground-state thermal reactions.     

The synthesis, characterisation and reactivity of 2-phosphanylethylcyclopentadienyl complexes of cobalt, rhodium and iridium

2-Phosphanylethylcyclopentadienyl lithium compounds, Li[C(5)R'(4)(CH(2))(2)PR(2)] (R = Et, R' = H or Me, R = Ph, R' = Me), have been prepared from the reaction of spirohydrocarbons C(5)R'(4)(C(2)H(4)) with LiPR(2). C(5)Et(4)HSiMe(2)CH(2)PMe(2), was prepared from reaction of Li[C(5)Et(4)] with Me(2)SiCl(2) followed by Me(2)PCH(2)Li. The lithium salts were reacted with [RhCl(CO)(2)](2), [IrCl(CO)(3)] or [Co(2)(CO)(8)] to give [M(C(5)R'(4)(CH(2))(2)PR(2))(CO)] (M = Rh, R = Et, R' = H or Me, R = Ph, R' = Me; M = Ir or Co, R = Et, R' = Me), which have been fully characterised, in many cases crystallographically as monomers with coordination of the phosphorus atom and the cyclopentadienyl ring. The values of nu(CO) for these complexes are usually lower than those for the analogous complexes without the bridge between the cyclopentadienyl ring and the phosphine, the exception being [Rh(Cp'(CH(2))(2)PEt(2))(CO)] (Cp' = C(5)Me(4)), the most electron rich of the complexes. [Rh(C(5)Et(4)SiMe(2)CH(2)PMe(2))(CO)] may be a dimer. [Co(2)(CO)(8)] reacts with C(5)H(5)(CH(2))(2)PEt(2) or C(5)Et(4)HSiMe(2)CH(2)PMe(2) (L) to give binuclear complexes of the form [Co(2)(CO)(6)L(2)] with almost linear PCoCoP skeletons. [Rh(Cp'(CH(2))(2)PEt(2))(CO)] and [Rh(Cp'(CH(2))(2)PPh(2))(CO)] are active for methanol carbonylation at 150 degrees C and 27 bar CO, with the rate using [Rh(Cp'(CH(2))(2)PPh(2))(CO)] (0.81 mol dm(-3) h(-1)) being higher than that for [RhI(2)(CO)(2)](-) (0.64 mol dm(-3) h(-1)). The most electron rich complex, [Rh(Cp'(CH(2))(2)PEt(2))(CO)] (0.38 mol dm(-3) h(-1)) gave a comparable rate to [Cp*Rh(PEt(3))(CO)] (0.30 mol dm(-3) h(-1)), which was unstable towards oxidation of the phosphine. [Rh(Cp'(CH(2))(2)PEt(2))I(2)], which is inactive for methanol carbonylation, was isolated after the methanol carbonylation reaction using [Rh(Cp'(CH(2))(2)PEt(2))(CO)]. Neither of [M(Cp'(CH(2))(2)PEt(2))(CO)] (M = Co or Ir) was active for methanol carbonylation under these conditions, nor under many other conditions investigated, except that [Ir(Cp'(CH(2))(2)PEt(2))(CO)] showed some activity at higher temperature (190 degrees C), probably as a result of degradation to [IrI(2)(CO)(2)](-). [M(Cp'(CH(2))(2)PEt(2))(CO)] react with MeI to give [M(Cp'(CH(2))(2)PEt(2))(C(O)Me)I] (M = Co or Rh) or [Ir(Cp'(CH(2))(2)PEt(2))Me(CO)]I. The rates of oxidative addition of MeI to [Rh(C(5)H(4)(CH(2))(2)PEt(2))(CO)] and [Rh(Cp'(CH(2))(2)PPh(2))(CO)] are 62 and 1770 times faster than to [Cp*Rh(CO)(2)]. Methyl migration is slower, however. High pressure NMR studies show that [Co(Cp'(CH(2))(2)PEt(2))(CO)] and [Cp*Rh(PEt(3))(CO)] are unstable towards phosphine oxidation and/or quaternisation under methanol carbonylation conditions, but that [Rh(Cp'(CH(2))(2)PEt(2))(CO)] does not exhibit phosphine degradation, eventually producing inactive [Rh(Cp'(CH(2))(2)PEt(2))I(2)] at least under conditions of poor gas mixing. The observation of [Rh(Cp'(CH(2))(2)PEt(2))(C(O)Me)I] under methanol carbonylation conditions suggests that the rhodium centre has become so electron rich that reductive elimination of ethanoyl iodide has become rate determining for methanol carbonylation. In addition to the high electron density at rhodium.     

Imine-assisted C-F bond activation by electron-rich iron complexes supported by trimethylphosphine

C-F bond activation of ortho-fluorinated benzalimines 2,6-F(2)C(6)R1R2R3-CH=N-R (1-3) using the electron-rich complex Fe(PMe(3))(4) is reported. With the assistance of the imine group as the anchoring group, bis-chelated iron(II) complexes (C(6)FR1R2R3-CH=N-R)(2)Fe(PMe(3))(2) (4-6) were formed. The reaction of 2,6-difluorobenzylidenenaphthalen-1-amine 2,6-F(2)C(6)H(3)-CH=N-C(10)H(7) (9) with Fe(PMe(3))(4) affords [CNC]-pincer iron(II) complex (C(6)H(3)F-CH=N-C(10)H(6))Fe(PMe(3))(3) (10) through both C-F and C-H bond activation and π-(C=N) coordinate iron(0) complex (C(6)H(3)F-CH=N-C(10)H(7))(2)Fe(PMe(3))(2) (11) with C,C-coupling, while a similar reaction with perfluorobenzylidenenaphthalen-1-amine C(6)F(5)-CH=N-C(10)H(7) (14) gave rise to only [CNC]-pincer iron(II) complex (C(6)F(4)-CH=N-C(10)H(6))Fe(PMe(3))(3) (15). The proposed formation mechanisms of these complexes are discussed. The structures of complexes 5, 6, 10 and 11 were confirmed by X-ray single crystal diffraction.     

The F/Ph rearrangement reaction of [(Ph3P)3RhF], the fluoride congener of Wilkinson's catalyst

The fluoride congener of Wilkinson's catalyst, [(Ph(3)P)(3)RhF] (1), has been synthesized and fully characterized. Unlike Wilkinson's catalyst, 1 easily activates the inert C-Cl bond of ArCl (Ar = Ph, p-tolyl) under mild conditions (3 h at 80 degrees C) to produce trans-[(Ph(3)P)(2)Rh(Ph(2)PF)(Cl)] (2) and ArPh as a result of C-Cl, Rh-F, and P-C bond cleavage and C-C, Rh-Cl, and P-F bond formation. In benzene (2-3 h at 80 degrees C), 1 decomposes to a 1:1 mixture of trans-[(Ph(3)P)(2)Rh(Ph(2)PF)(F)] (3) and the cyclometalated complex [(Ph(3)P)(2)Rh(Ph(2)PC(6)H(4))] (4). Both the chloroarene activation and the thermal decomposition reactions have been shown to occur via the facile and reversible F/Ph rearrangement reaction of 1 to cis-[(Ph(3)P)(2)Rh(Ph)(Ph(2)PF)] (5), which has been isolated and fully characterized. Kinetic studies of the F/Ph rearrangement, an intramolecular process not influenced by extra phosphine, have led to the determination of E(a) = 22.7 +/- 1.2 kcal mol(-)(1), DeltaH(++) = 22.0 +/- 1.2 kcal mol(-)(1), and DeltaS(++) = -10.0 +/- 3.7 eu. Theoretical studies of F/Ph exchange with the [(PH(3))(2)(PH(2)Ph)RhF] model system pointed to two possible mechanisms: (i) Ph transfer to Rh followed by F transfer to P (formally oxidative addition followed by reductive elimination, pathway 1) and (ii) F transfer to produce a metallophosphorane with subsequent Ph transfer to Rh (pathway 2). Although pathway 1 cannot be ruled out completely, the metallophosphorane mechanism finds more support from both our own and previously reported observations. Possible involvement of metallophosphorane intermediates in various P-F, P-O, and P-C bond-forming reactions at a metal center is discussed.     

C-F activation of fluorinated arenes using NHC-stabilized nickel(0) complexes: selectivity and mechanistic investigations

The reaction of [Ni2((i)Pr2Im)4(COD)] 1a or [Ni((i)Pr2Im)2(eta(2)-C2H4)] 1b with different fluorinated arenes is reported. These reactions occur with a high chemo- and regioselectivity. In the case of polyfluorinated aromatics of the type C6F5X such as hexafluorobenzene (X = F) octafluorotoluene (X = CF3), trimethyl(pentafluorophenyl)silane (X = SiMe3), or decafluorobiphenyl (X = C6F5) the C-F activation regioselectively takes place at the C-F bond in the para position to the X group to afford the complexes trans-[Ni((i)Pr2Im)2(F)(C6F5)]2, trans-[Ni((i)Pr2Im)2(F)(4-(CF3)C6F4)] 3, trans-[Ni((i)Pr2Im)2(F)(4-(C6F5)C6F4)] 4, and trans-[Ni((i)Pr2Im)2(F)(4-(SiMe3)C6F4)] 5. Complex 5 was structurally characterized by X-ray diffraction. The reaction of 1a with partially fluorinated aromatic substrates C6H(x)F(y) leads to the products of a C-F activation trans-[Ni((i)Pr2Im)2(F)(2-C6FH4)] 7, trans-[Ni((i)Pr2Im)2(F)(3,5-C6F2H3)] 8, trans-[Ni((i)Pr2Im)2(F)(2,3-C6F2H3)] 9a and trans-[Ni((i)Pr2Im)2(F)(2,6-C6F2H3)] 9b, trans-[Ni((i)Pr2Im)2(F)(2,5-C6F2H3)] 10, and trans-[Ni((i)Pr2Im)2(F)(2,3,5,6-C6F4H)] 11. The reaction of 1a with octafluoronaphthalene yields exclusively trans-[Ni((i)Pr2Im)2(F)(1,3,4,5,6,7,8-C10F7)] 6a, the product of an insertion into the C-F bond in the 2-position, whereas for the reaction of 1b with octafluoronaphthalene the two isomers trans-[Ni((i)Pr2Im)2(F)(1,3,4,5,6,7,8-C10F7)] 6a and trans-[Ni((i)Pr2Im)2(F)(2,3,4,5,6,7,8-C10F7)] 6b are formed in a ratio of 11:1. The reaction of 1a or of 1b with pentafluoropyridine at low temperatures affords trans-[Ni((i)Pr2Im)2(F)(4-C5NF4)] 12a as the sole product, whereas the reaction of 1b performed at room temperature leads to the generation of trans-[Ni((i)Pr2Im)2(F)(4-C5NF4)] 12a and trans-[Ni((i)Pr2Im)2(F)(2-C5NF4)] 12b in a ratio of approximately 1:2. The detection of intermediates as well as kinetic studies gives some insight into the mechanistic details for the activation of an aromatic carbon-fluorine bond at the {Ni((i)Pr2Im)2} complex fragment. The intermediates of the reaction of 1b with hexafluorobenzene and octafluoronaphthalene, [Ni((i)Pr2Im)2(eta(2)-C6F6)] 13 and [Ni((i)Pr2Im)2(eta(2)-C10F8)] 14, have been detected in solution. They convert into the C-F activation products. Complex 14 was structurally characterized by X-ray diffraction. The rates for the loss of 14 at different temperatures for the C-F activation of the coordinated naphthalene are first order and the estimated activation enthalpy Delta H(double dagger) for this process was determined to be Delta H(double dagger) = 116 +/- 8 kJ mol(-1) (Delta S(double dagger) = 37 +/- 25 J K(-1) mol(-1)). Furthermore, density functional theory calculations on the reaction of 1a with hexafluorobenzene, octafluoronaphthalene, octafluorotoluene, 1,2,4-trifluorobenzene, and 1,2,3-trifluorobenzene are presented.     

Alcohol addition to acetonitrile activated by the [Re6(mu3-Se)8]2+ cluster core

The addition of methanol and ethanol to the previously reported cluster solvates [Re6(mu3-Se)8(PEt3)5(MeCN)](SbF6)2 and trans-[Re6(mu3-Se)8(PEt3)4(CH3CN)2][SbF6]2 afforded three cluster complexes with imino ester ligands: {Re6(mu3-Se)8(PEt3)5[HN=C(OCH3)(CH3)]}(SbF6)2, {Re6(mu3-Se)8(PEt3)5[HN=C(OCH2CH3)(CH3)]}{SbF6}2, and trans-{Re6(mu3-Se)8(PEt3)4[HN=C(OCH3)(CH3)]2}{SbF6}2. In all cases, predominant formation of the Z isomers was observed.     

Facile insertion and halogen migration reactions of the hexaphosphapentaprismane cage P6C4tBu4 with zerovalent and divalent platinum complexes

The hexaphosphapentaprismane P(6)C(4)(t)Bu(4) undergoes specific insertion of the zerovalent platinum fragment [Pt(PPh(3))(2)] into the unique P-P bond between the 5-membered rings to afford [Pt(PPh(3))(2)P(6)C(4)(t)Bu(4)]. A similar reaction with the Pt(ii) complexes [{PtCl(2)(PMe(3))}(2)] and [PtCl(2)(eta(4)-COD)] results in both insertion and chlorine migration reactions. The complexes [Pt(PPh(3))(2)P(6)C(4)(t)Bu(4)], trans-[PtCl(PMe(3))P(6)C(4)(t)Bu(4)Cl], cis-,trans-[{PtCl(2)(PMe(3))}micro-{P(6)C(4)(t)Bu(4)}{PtCl(2)(PMe(3))}], [{PtClP(6)C(4)(t)Bu(4)Cl}(2)] and cis-[PtClP(6)C(4)(t)Bu(4)Cl(P(6)C(4)(t)Bu(4))] have been structurally characterized by single crystal X-ray diffraction and multinuclear NMR studies.     

Si-H and Si-Si activation at Pt: synthesis and reactivity of neutral and cationic silyl complexes

Reactions of [Pt(PEt(3))(3)] (1) with the silanes HSiPh(3), HSiPh(2)Me and HSi(OEt)(3) led to the products of oxidative addition, cis-[Pt(H)(SiPh(3))(PEt(3))(2)] (2), cis-[Pt(H)(SiPh(2)Me)(PEt(3))(2)] (3), cis-[Pt(H){Si(OEt)(3)}(PEt(3))(2)] (cis-4) and trans-[Pt(H){Si(OEt)(3)}(PEt(3))(2)] (trans-4). The complexes cis-4 and trans-4 can also be generated by hydrogenolysis of (EtO)(3)SiSi(OEt)(3) in the presence of 1. Furthermore, the silyl compounds cis-4 and trans-4 react with B(C(6)F(5))(3) and CH(3)CN by hydride abstraction to give the cationic silyl complex trans-[Pt{Si(OEt)(3)}(NCCH(3))(PEt(3))(2)][HB(C(6)F(5))(3)] (8). In addition, the reactivity of the complexes cis-4, trans-4 and 8 towards alkenes and CO was studied using NMR experiments.     

C-F or C-H bond activation and C-C coupling reactions of fluorinated pyridines at rhodium: synthesis, structure and reactivity of a variety of tetrafluoropyridyl complexes

Reactions of [RhH(PEt3)3] (1) or [RhH(PEt3)4] (2) with pentafluoropyridine or 2,3,5,6-tetrafluoropyridine afford the activation product [Rh(4-C5NF4)(PEt3)3] (3). Treatment of 3 with CO, 13CO or CNtBu effects the formation of trans-[Rh(4-C5NF4)(CO)(PEt3)2] (4a), trans-[Rh(4-C5NF4)(13CO)(PEt3)2] (4b) and trans-[Rh(4-C5NF4)(CNtBu)(PEt3)2] (5). The rhodium(III) compounds trans-[RhI(CH3)(4-C5NF4)(PEt3)2] (6a) and trans-[RhI(13CH3)(4-C5NF4)(PEt3)2] (6b) are accessible on reaction of 3 with CH3I or 13CH3I. In the presence of CO or 13CO these complexes convert into trans-[RhI(CH3)(4-C5NF4)(CO)(PEt3)2] (7a), trans-[RhI(13CH3)(4-C5NF4)(CO)(PEt3)2] (7b) and trans-[RhI(13CH3)(4-C5NF4)(13CO)(PEt3)2] (7c). The trans arrangement of the carbonyl and methyl ligand in 7a-7c has been confirmed by the 13C-13C coupling constant in the 13C NMR spectrum of 7c. A reaction of 4a or 4b with CH3I or 13CH3I yields the acyl compounds trans-[RhI(COCH3)(4-C5NF4)(PEt3)2] (8a) and trans-[RhI(13CO13CH3)(4-C5NF4)(PEt3)2] (8b), respectively. Complex 8a slowly reacts with more CH3I to give [PEt3Me][Rh(I)2(COCH3)(4-C5NF4)(PEt3)](9). On heating a solution of 7a, the complex trans-[RhI(CO)(PEt3)2] (10) and the C-C coupled product 4-methyltetrafluoropyridine (11) have been obtained. Complex 8a also forms 10 at elevated temperatures in the presence of CO together with the new ketone 4-acetyltetrafluoropyridine (12). The structures of the complexes 3, 4a, 5, 6a, 8a and 9 have been determined by X-ray crystallography. 19F-1H HMQC NMR solution spectra of 6a and 8a reveal a close contact of the methyl groups in the phosphine to the methyl or acyl ligand bound at rhodium.     

H(2) activation and hydride transfer to olefins by al(c(6) f(5) )(3) -based frustrated lewis pairs

Frustrated delivery: Frustrated Lewis pairs derived from tBu(3) P and Al(C(6) F(5) )(3) activate H(2) to give [tBu(3) PH][(μ-H)(Al(C(6) F(5) )(3) )(2) ], which reacts with unactivated olefins to give RAl(C(6) F(5) )(2) (R=Et or Cy) and [tBu(3) PH][Al(C(6) F(5) )(4) ]. The proposed mechanism involves olefin activation by aluminum, which is supported by the isolation of the cyclohexene complex [Al(C(6) F(5) )(3) ?(C(6) H(10) )].     

Carbon-fluorine bond cleavage in the preparation of Osmium(III) and Osmium(IV) fluorothiolate complexes. Fluorine by fluorine NMR-assignment and fluxional processes

Reactions of OsO4 with HSR (R=C6F5, C6F4H-4,) in refluxing ethanol afford [Os(SC6F5)3(SC6F4(SC6F5)-2)] (1) and [Os(SC6F4H-4)3(SC6F3H-4-(SC6F4H-4)-2)] (2), which involve the rupture of C-F bonds. At room temperature, the compound [Os(SC6F5)3(PMe2Ph)2] or [Os(SC6F5)4(PMe2Ph)] reacts with KOH(aq) in acetone, giving rise to [ Os(SC6F5)(SC6F4(SC6F4O-2)-2)(PMe2Ph)2] (3), through a process involving the rupture of two C-F bonds, while the compound [Os(SC6F4H)4(PPh3)] reacts with KOH(aq) in acetone to afford [Os(SC6F4H-4)2(SC6F3H-4-O-2)(PPh3)] (4), which also implies a C-F bond cleavage. Single-crystal X-ray diffraction studies of 1, 2, and 4 indicate that these compounds include five-coordinated metal ions in essentially trigonal-bipyramidal geometries, whereas these studies on the paramagnetic compound 3 show a six-coordinated osmium center in a distorted octahedral geometry. 19F, 1H, 31P{1H}, and COSY 19F-19F NMR studies for the diamagnetic 1, 2, and 4 compounds, including variable-temperature 19F NMR experiments, showed that these molecules are fluxional. Some of the activation parameters for these dynamic processes have been determined.     

Synthesis and characterisation of triselenocarbonate [CSe3]2- complexes

[Pt(CSe3)(PR3)2] (PR3= PMe3, PMe2Ph, PPh3, P(p-tol)3, 1/2 dppp, 1/2 dppf) were all obtained by the reaction of the appropriate metal halide containing complex with carbon diselenide in liquid ammonia. Similar reaction with [Pt(Cl)2(dppe)] gave a mixture of triselenocarbonate and perselenocarbonate complexes. [{Pt(mu-CSe3)(PEt3)}4] was formed when the analogous procedure was carried out using [Pt(Cl)2(PEt3)2]. Further reaction of [Pt(CSe3)(PMe2Ph)2] with [M(CO)6] (M = Cr, W, Mo) yielded bimetallic species of the type [Pt(PMe2Ph)2(CSe3)M(CO)5] (M = Cr, W, Mo). The dimeric triselenocarbonate complexes [M{(CSe3)(eta5-C5Me5)}2] (M = Rh, Ir) and [{M(CSe3)(eta6-p-MeC6H4(i)Pr)}2] (M = Ru, Os) have been synthesised from the appropriate transition metal dimer starting material. The triselenocarbonate ligand is Se,Se' bidentate in the monomeric complexes. In the tetrameric structure the exocyclic selenium atoms link the four platinum centres together.     

Generation and reactions of ruthenium phosphido complexes [(eta5-C5H5)Ru(PR'3)2(PR2)]: remarkably high phosphorus basicities and applications as ligands for palladium-catalyzed Suzuki cross-coupling reactions

Reactions of [(eta5-C5H5)Ru(PR'3)2(Cl)] with NaBAr(F) [BAr(F)-=B{3,5-[C6H3(CF3)2]}4-; PR'3=PEt3 or 1/2Et2PCH2CH2PEt2) (depe)] and PR2H (R=Ph, a; tBu, b; Cy, c) in C6H5F, or of related cationic Ru(N2) complexes with PR2H in C6H5F, gave the secondary phosphine complexes [(eta5-C5H5)Ru(PR'3)2(PR2H)]+ BAr(F)- (PR'3=PEt3, 3 a-c; 1/2depe, 4 a,b) in 65-91 % yields. Additions of tBuOK (3 a, 4 a; [D6]acetone) or NaN(SiMe3)2 (3 b,c, 4 b; [D8]THF) gave the title complexes [(eta5-C5H5)Ru(PEt3)2(PR2)] (5 a-c) and [(eta5-C5H5)Ru(depe)(PR2)] (6 a,b) in high spectroscopic yields. These complexes were rapidly oxidized in air; with 5 a, [(eta5-C5H5)Ru(PEt3)2{P(=O)Ph2}] was isolated (>99 %). The reaction of 5 a and elemental selenium yielded [(eta5-C5H5)Ru(PEt3)2{P(=Se)Ph2}] (70 %); selenides from 5 c and 6 a were characterized in situ. Competitive deprotonation reactions showed that 5 a is more basic than the rhenium analog [(eta5-C5H5)Re(NO)(PPh3)(PPh2)], and that 6 b is more basic than PtBu3 and P(iPrNCH2CH2)3N. The latter is one of the most basic trivalent phosphorus compounds [pK(a)(acetonitrile) 33.6]. Complexes 5 a-c and 6 b are effective ligands for Pd(OAc)2-catalyzed Suzuki coupling reactions: 6 b gave a catalyst nearly as active as the benchmark organophosphine PtBu3; 5 a, with a less bulky and electron-rich PR2 moiety, gave a less active catalyst. The reaction of 5 a and [(eta3-C3H5)Pd(NCPh)2]+ BF4- gave the bridging phosphido complex [(eta5-C5H5)Ru(PEt3)2(PPh2)Pd(NCPh)(eta3-C3H5)]+ BAr(F)- in approximately 90 % purity. The crystal structure of 4 a is described, as well as substitution reactions of 3 b and 4 b.     

Cluster carbonyls of the [Re6(mu3-Se)8]2+ core

The first [Re(6)(mu(3)-Se)(8)](2+) core-containing cluster carbonyls, [Re(6)(mu(3)-Se)(8)(PEt(3))(5)(CO)][SbF(6)](2) and trans-[Re(6)(mu(3)-Se)(8)(PEt(3))4(CO)(2)][SbF(6)](2), were produced by reacting [Re(6)(mu(3)-Se)(8)(PEt(3))(5)I]I and trans-[Re(6)(mu(3)-Se)8(PEt(3))(4)I2], respectively, with AgSbF(6) in CO-saturated dichloromethane solutions. Spectroscopic and crystallographic studies suggest significant cluster-to-CO back-donation in these novel cluster derivatives and interesting electronic structures. Thermal and photolytic studies of the mono-carbonyl complex revealed its interesting and synthetically useful reactivity in producing new cluster derivatives.     

Carbon-fluorine bond activation coupled with carbon-carbon bond formation at iridium. Confirmation of complete kinetic diastereoselectivity at the new carbon stereocenter by intramolecular trapping using vinyl as the migrating group

The iridium(perfluoropropyl)(vinyl) complex CpIr(PMe(3))(n-C(3)F(7))(CH=CH(2)) (5) has been prepared. It has been characterized by X-ray crystallography, and its ground state conformation in solution has been determined by (19)F{(1)H} HOESY NMR studies. It reacts with the weak acid lutidinium iodide to afford the eta(1)-allylic complex CpIr(PMe(3))((Z)-CH(2)CH=CFC(2)F(5))I (6), which has also been characterized crystallographically. The mechanism of C-F bond activation and C-C bond formation leading to 6 has been elucidated in detail by studying the reaction of 5 with lutidinium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate [LutH(+)B(ArF)(4)(-)], containing a weakly coordinating counteranion. The main kinetic product of this reaction, determined by (19)F{(1)H} HOESY studies at -50 degrees C, is the endo-CpIr(PMe(3))(anti-eta(3)-CH(2)CHCFCF(2)CF(3))[B(ArF)(4)] diastereomer 9, along with a small amount of the exo-syn-isomer 8. Isomer 9 rearranges at -20 degrees C to its exo-anti isomer 7, and subsequently to the thermodynamically favored exo-syn-isomer 8, which has been isolated and crystallographically characterized. Complex 8 reacts with iodide to afford complex6. On the basis of the unambiguously defined kinetically controlled stereochemistry of 9 and 8, a detailed mechanism for the C-F activation/C-C coupling reaction is proposed, the principal conclusion of which is that C-F activation is completely diastereoselective.     

Synthesis and structural characterization of the first unsymmetrical diarylpalladium complex trans-Pd(C6F5)(2,4,6-C6F3H2)(PEt3)2, derived from transmetallation between 2,4,6-trifluorophenylboronic acid and trans-Pd(C6F5)I(PEt3)2

The reactions of 2,4,6-trifluorophenylboronic acid with aryl(iodo)palladium(ii) complexes, trans-Pd(C(6)F(5))I(PR(3))(2)(PR(3)= PEt(3), PMe(2)Ph, PMePh(2)) in the presence of Ag(2)O afforded trans-Pd(C(6)F(5))(2,4,6-C(6)F(3)H(2))(PR(3))(2) which are stabilized by fluorine atoms in the ortho positions.     

The synthesis,vibrational spectra,and molecular structure of [Ir(CO)(6)][SbF(6)](3).4HF - the first structurally characterized salt with a tripositive,homoleptic metal carbonyl cation and the first example of a tetrahedral hydrogen-bonded (HF)(4) cluster

The reductive carbonylation of IrF(6) in a dilute solution of SbF(5) in anhydrous HF (1:6 by volume) produces surprisingly at 25 degrees C and 1.5 atm CO the complex salt [Ir(CO)(6)][SbF(6)](3).4HF, while [Ir(CO)(6)][Sb(2)F(11)](3) is obtained in liquid SbF(5) under similar conditions. Vibrational spectra in the CO stretching range for both salts and [Ir(CO)(6)](3+)((solv)) are identical within error limits, and nu(CO)(av) is with 2269 cm(-1) the highest average stretching frequency so far observed for octahedral metal carbonyl cations. A vibrational assignment supported by DFT calculations is presented, and the vibrational fundamentals are compared to those of [Os(CO)(6)](2+). The molecular structure of [Ir(CO)(6)][SbF(6)](3).4HF is determined by single-crystal X-ray diffraction. Crystal data for [Ir(CO)(6)][SbF(6)](3).4HF: rhombohedral, R3c (No. 161), a = 14.630(4) A, c = 18.377(7) A, V = 3406.4(18) A(3), Z = 6, T = 150 K, R(1) = 0.0338 [I > 2sigma (I)], wR(2) = 0.0797). The average Ir-C bond length in the octahedral [Ir(CO)(6)](3+) cation is with 2.029(10) the longest observed for iridium carbonyl derivatives, consistent with the absence of Ir --> CO pi-back-bonding. The four solvate HF molecules form a tetrahedron via long, asymmetric, and partly delocalized hydrogen bonds with F-F edge lengths of 2.857 (3x) and 2.914 (3x) A. There is no precedent for a polyhedral (HF)(n) cluster in the gas, liquid, or solid phase. The four F atoms of the (HF)(4) cluster are coordinated to the C atoms of the six CO ligands of the cation, which again is without precedent. The coordination of one of the F atoms to three C atoms in a iso-tridentate mode with contact distances C-F(8) of 2.641(10) A is most unusual. The observed tight C-F coordination in [Ir(CO)(6)][SbF(6)](3).4HF provides conclusive evidence for the presence of electrophilic carbon in the cation and illustrates how superelectrophilic cations such as [Ir(CO)(6)](3+) are solvent stabilized in the conjugate Br?nsted-Lewis superacid HF-SbF(5).     

Sequential C-F activation and borylation of fluoropyridines via intermediate Rh(I) fluoropyridyl complexes: a multinuclear NMR investigation

The C-F bond activation of fluoropyridines by [Rh(SiPh3)(PMe3)3] afforded Rh(I) fluoropyridyl complexes of the type [Rh(Ar(F))(PMe3)3] with concomitant formation of fluorotriphenylsilane; subsequent treatment with bis-catecholatodiboron yielded fac-[Rh(Bcat)3(PMe3)3] and the free fluoropyridyl boronate esters (Ar(F)Bcat).