Strategy for the resolution of a chiral dearomatization agent:[TpRe(CO)(1-methylimidazole)] coordination of alpha-pinene (Tp = hydridotris(pyrazolyl)borate)

A methodology for resolving TpRe(CO)(1-methylimidazole)(eta(2)-benzene) has been developed utilizing (R)-alpha-pinene. Each enantiomer of the [TpRe(CO)(MeIm)] system can be obtained with the enantiomer ratio (er) = 97:3 by taking advantage of differing rates of pinene substitution for the two diastereomers of TpRe(CO)(MeIm)(eta(2)-(R)-alpha-pinene).     

Dihapto coordination of carboxylic acid derivatives with an asymmetric rhenium pi-base: a new mechanism for amide isomerization?

The asymmetric pi basic metal fragment [TpRe(CO)(MeIm)] (Tp = hydridotris(pyrazolyl)borate, MeIm = 1-methylimidazole) forms thermally stable complexes with ethyl acetate, acetic anhydride, N-methylsuccinimide, N-acetylpyrrole, and N-methylmaleimide in which the metal binds a carbonyl group in a pi fashion. In all cases a single diastereomer is observed, indicating that one enantioface of the carbonyl is selectively coordinated. X-ray and NMR data for the compound TpRe(CO)(MeIm)(eta(2)-N-methylsuccinimide) indicate that metal coordination effectively removes the pi interaction between the bound carbonyl and the nitrogen of the succinimide ring.     

Stereoselective tandem 1,4-addition reactions for benzenes: a comparison of Os(II), Re(I), and W(0) systems

The arene ligand in the complex TpRe(CO)(MeIm)(eta2-benzene) (Tp = hydridotris(pyrazolyl)borate; MeIm = N-methylimidazole) undergoes tandem electrophile/nucleophile 1,4-addition reactions. Subsequent oxidative demetalation affords cis-3,6-disubstituted 1,4-cyclohexadienes (46-84%). Common organic electrophiles such as acetals and Michael acceptors were successfully added to the bound benzene to generate eta3-benzenium complexes, which then were treated with a silyl ketene acetal, silyl vinyl ether, phenyllithium, or malonate ester to afford 1,4-dialkylated dihydrobenzene complexes. The d6 transition metal analogues TpW(NO)(PMe3)(eta2-benzene) and [Os(NH3)5(eta2-benzene)]2+ also undergo 1,4-dialkylation reactions, and the relative ability of all three metals to activate arenes is compared.     

Transition metal-stabilized arenium cations: protonation of arenes dihapto-coordinated to pi-basic metal fragments

A series of metal complexes was synthesized in which arenes were dihapto-coordinated to pi-basic metal fragments having the general form [TpM(pi-acid)(L)], where Tp = hydridotris(pyrazolyl)borate, M = rhenium, molybdenum, or tungsten, pi-acid = CO or NO(+), and L = 1-methylimidazole, 1-butylimidazole, pyridine, or trimethylphosphine. The arene complexes were shown to be significantly more basic than the analogous pentaammineosmium(II) arene complexes and were protonated by moderate acids to give remarkably stable eta(2) and eta(3) arenium cation complexes. A crystal structure of [TpRe(CO)(MeIm)(5,6-eta(2)-2H-anisolium)](OTf) confirmed the eta(2) coordination of the anisolium ligand, but suggests a weak long-range interaction between the metal and C1 of the anisolium.     

Interfacial and intrafacial linkage isomerizations of rhenium complexes with aromatic molecules

The mechanisms for the interconversion of facial diastereomers of a variety of TpRe(CO)(L)(eta(2)-L(Ar)) complexes [L = (t)BuNC, pyridine (py), PMe(3), or 1-methylimidazole (MeIm); L(Ar) = benzene, anisole, naphthalene, 1-methylpyrrole, furan, or thiophene; Tp = hydridotris(pyrazolyl)borate] have been investigated by (1)H NMR spin saturation experiments. In addition, the rates and free energies of activation for these processes were calculated from spin saturation experiments and T(1) measurements. The operative mechanisms for interconversion of the pi diastereomers were found to be nondissociative, undergoing either an interfacial or intrafacial linkage isomerization. A comparison of the kinetic parameters for isomerization of related eta(2)-olefin complexes of the [TpRe(CO)(PMe(3))] and [CpRe(NO)(PPh(3))](+) fragments is also presented.     

Cycloaddition reactions of dihapto-coordinated furans

Complexes of the type [TpRe(CO)(L)(eta(2)-furan)], where Tp = hydridotris(pyrazolyl)borate and L = PMe(3) (1) or (t)BuNC (2), undergo dipolar cycloadditions with TCNE (tetracyanoethylene) to afford 7-oxabicycloheptene complexes 3 and 4, respectively. The corresponding 2-methylfuran complexes (5 and 7) for these L ligands give similar methyloxabicycloheptene complexes (6 and 8), with a diastereomer ratio >20:1 for 8. For L = N-methylimidazole (MeIm, 9), TCNE oxidizes the complex, but cycloadditions can be achieved with DMAD (dimethyl acetylenedicarboxylate) as the electrophile. Three complexes are observed: one in which DMAD undergoes a cycloaddition with the carbonyl ylide form of the complex (10C), and two complexes that are coordination diastereomers where DMAD has undergone a formal [2+2] cycloaddition with the uncoordinated double bond of the 4,5-eta(2)-furan ligand (10B and 10A). With the imidazole complex of 2-methylfuran (11), only the [2+2] products (12B and 12A) are observed. In the case of the 2,5-dimethylfuran complex (L = MeIm, 13), which is formed as a single coordination diastereomer, only one [2+2] product is observed (14), the structure of which was confirmed by X-ray crystallography. Oxidative decomplexation of 14 results in liberation of the free oxabicyclo[3.2.0]heptadiene 15, which can be thermally converted to the corresponding oxepin 16 in 70% yield.     

Ligand-modulated stereo- and regioselective tandem addition reactions of rhenium-bound naphthalene

A series of complexes of the form TpRe(CO)(L)(eta(2)-naphthalene) (Tp = hydridotris(pyrazolyl)borate) undergoes tandem electrophile/nucleophile addition reactions with a high degree of regiocontrol depending on the auxiliary ligand, L. When L = PMe(3), the reaction of the eta(2)-naphthalene complex with triflic acid followed by a silyl ketene acetal favors the 1,4-addition product, whereas when L = pyridine, N,N-dimethylaminopyridine, N-methylimidazole, or NH(3) the 1,2-addition product is favored. These reactions proceed with excellent stereocontrol: both electrophile (H(+), D(+)) and nucleophile (silyl ketene acetal) add anti to the face of metal coordination, and a single coordination diastereomer can be isolated for each reaction. One-electron oxidation of the Re complex affords the corresponding free dihydronaphthalene in good yield.     

Subtle reactivity patterns of non-heteroatom-substituted manganese alkynyl carbene complexes in the presence of phosphorus probes

The non-heteroatom-substituted manganese alkynyl carbene complexes (eta5-MeC5H4)(CO)2Mn=C(R)C[triple bond]CR'(3; 3a: R = R'= Ph, 3b: R = Ph, R'= Tol, 3c: R = Tol, R'= Ph) have been synthesised in high yields upon treatment of the corresponding carbyne complexes [eta5-MeC5H4)(CO)2Mn[triple bond]CR][BPh4]([2][BPh4]) with the appropriate alkynyllithium reagents LiC[triple bond]CR' (R'= Ph, Tol). The use of tetraphenylborate as counter anion associated with the cationic carbyne complexes has been decisive. The X-ray structures of (eta5-MeC5H4)(CO)2Mn=C(Tol)C[triple bond]CPh (3c), and its precursor [(eta5-MeC5H4)(CO)2Mn=CTol][BPh4]([2b](BPh4]) are reported. The reactivity of complexes toward phosphines has been investigated. In the presence of PPh3, complexes act as a Michael acceptor to afford the zwitterionic sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh3)R' (5) resulting from nucleophilic attack by the phosphine on the remote alkynyl carbon atom. Complexes 5 exhibit a dynamic process in solution, which has been rationalized in terms of a fast [NMR time-scale] rotation of the allene substituents around the allene axis; metrical features within the X-ray structure of (eta5-MeC5H4)(CO)2MnC(Ph)=C=C(PPh3)Tol (5b) support the proposal. In the presence of PMe3, complexes undergo a nucleophilic attack on the carbene carbon atom to give zwitterionic sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PMe3)C[triple bond]CR' (6). Complexes 6 readily isomerise in solution to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R')=C=C(PMe3)R (7) through a 1,3 shift of the [(eta5-MeC5H4)(CO)2Mn] fragment. The nucleophilic attack of PPh2Me on 3 is not selective and leads to a mixture of the sigma-propargylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)(PPh(2)Me)C[triple bond]CR' (9) and the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R)=C=C(PPh(2)Me)R' (10). Like complexes 6, complexes 9 readily isomerize to give the sigma-allenylphosphonium complexes (eta5-MeC5H4)(CO)2MnC(R')=C=C(PPh2Me)R'). Upon gentle heating, complexes 7, and mixtures of 10 and 10' cyclise to give the sigma-dihydrophospholium complexes (eta5-MeC5H4)(CO)2MnC=C(R')PMe2CH2CH(R)(8), and mixtures of complexes (eta5-MeC5H4)(CO)2MnC=C(Ph)PPh2CH2CH(Tol)(11) and (eta5-MeC5H4)(CO)2MnC=C(Tol)PMe2CH2CH(Ph)(11'), respectively. The reactions of complexes 3 with secondary phosphines HPR(1)(2)(R1= Ph, Cy) give a mixture of the eta2-allene complexes (eta5-MeC5H4)(CO)2Mn[eta2-{R(1)(2)PC(R)=C=C(R')H}](12), and the regioisomeric eta4-vinylketene complexes [eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R)=CHC(R')=C=O}](13) and (eta5-MeC5H4)(CO)Mn[eta4-{R(1)(2)PC(R')=CHC(R)=C=O}](13'). The solid-state structure of (eta5-MeC5H4)(CO)2Mn[eta2-{Ph2PC(Ph)=C=C(Tol)H}](12b) and (eta5-MeC5H4)(CO)Mn[eta4-{Cy2PC(Ph)=CHC(Ph)=C=O}](13d) are reported. Finally, a mechanism that may account for the formation of the species 12, 13, and 13' is proposed.     

Diastereo- and enantioselective dearomatization of rhenium-bound naphthalenes

Dihapto-coordinated naphthalene complexes of the form TpRe(CO)(L)(eta(2)-naphthalene) (L = PMe(3), pyridine, or 1-methylimidazole) undergo electrophilic addition with dimethoxymethane and with various Michael acceptors to generate 1H-naphthalenium species. These naphthalenium complexes undergo intra- or intermolecular nucleophilic addition reactions with stabilized enolates, silyl ketene acetals, or enols to form the corresponding dihydronaphthalene complexes. Oxidative decomplexation generates the free dihydronaphthalene. When a resolved form of the rhenium dearomatization agent is used, these reactions can be performed enantioselectively. DFT calculations provide a useful guide in explaining the observed stereochemistry. Depending on reaction conditions, a Michael-Michael ring-closure sequence (MIMIRC) or a net [2 + 4] cycloaddition with the bound naphthalene is also observed, and the corresponding tricyclic molecules can be removed from the metal in high yield.     

Comparison of M[bond]S, M[bond]O, and M[bond](eta 2-SO) structures and bond dissociation energies in d6 (CO)5M(SO2)nq complexes using density functional theory

Density functional theory studies of the series of isomeric d(6) (pentacarbonyl)metal complexes (CO)(5)M(eta(1)-SO(2))(nq), (CO)(5)M(eta(1)-OSO)(nq)(), and (CO)(5)M(eta(2)-SO(2))(nq) (M = Ti-Hf, nq = 2-; M = V-Ta, nq = 1-; M = Cr -W, nq = 0; M = Mn-Re, nq = 1+; M = Fe-Os, nq = 2+) provide accurate structural modeling and quantitative prediction of the relative stabilities of the isomers. The eta(1)-S-bound complexes display planar SO(2) moieties that adopt staggered orientations with respect to the carbonyl ligands, in keeping with experimental observations. The OSO chain in the eta(1)-O-bound complexes generally adopts the u-shape with a staggered orientation. The dianions (CO)(5)(Ti-Hf)(eta(1)-OSO)(2-) differ in that the OSO chain adopts the eclipsed z-shape orientation. The eta(2)-SO(2) complexes exhibit a facial interaction and are stable only for anionic and neutral complexes, supporting the view that this motif involves substantial M --> SO(2) pi-back-bonding. The relative stabilities of the isomers generally follow u-shaped trends both across a row and down a family. This fits with qualitative ideas that the bond dissociation energies (BDEs) for the (CO)(5)M(SO(2))(nq) complexes track competition between relative hardness/softness of the metal fragment and its capacity for pi-back-bonding. Quantitatively, examination of BDEs by bond energy decomposition approaches suggests that electrostatic considerations dominate bonding for the eta(1)-SO(2) complexes and covalent effects dominate for the eta(2)-SO(2) species, while both are important for eta(1)-OSO complexes.     

Chemical and electrochemical reduction of polyarene manganese tricarbonyl cations: hapticity changes and generation of syn- and anti-facial bimetallic eta4,eta6-naphthalene complexes

(Eta6-naphthalene)Mn(CO)(3)(+) is reduced reversibly by two electrons in CH(2)Cl(2) to afford (eta4-naphthalene)Mn(CO)(3)(-). The chemical and electrochemical reductions of this and analogous complexes containing polycyclic aromatic hydrocarbons (PAH) coordinated to Mn(CO)(3)(+) indicate that the second electron addition is thermodynamically easier but kinetically slower than the first addition. Density functional theory calculations suggest that most of the bending or folding of the naphthalene ring that accompanies the eta6 --> eta4 hapticity change occurs when the second electron is added. As an alternative to further reduction, the 19-electron radicals (eta6-PAH)Mn(CO)(3) can undergo catalytic CO substitution when phosphite nucleophiles are present. Chemical reduction of (eta6-naphthalene)Mn(CO)(3)(+) and analogues with one equivalent of cobaltocene affords a syn-facial bimetallic complex (eta4,eta6-naphthalene)Mn(2)(CO)(5), which contains a Mn-Mn bond. Catalytic oxidative activation under CO reversibly converts this complex to the zwitterionic syn-facial bimetallic (eta4,eta6-naphthalene)Mn(2)(CO)(6), in which the Mn-Mn bond is cleaved and the naphthalene ring is bent by 45 degrees . Controlled reduction experiments at variable temperatures indicate that the bimetallic (eta4,eta6-naphthalene)Mn(2)(CO)(5) originates from the reaction of (eta4-naphthalene)Mn(CO)(3)(-) acting as a nucleophile to displace the arene from (eta6-naphthalene)Mn(CO)(3)(+). Heteronuclear syn-facial and anti-facial bimetallics are formed by the reduction of mixtures of (eta6-naphthalene)Mn(CO)(3)(+) and other complexes containing a fused polycyclic ring, e.g., (eta5-indenyl)Fe(CO)(3)(+) and (eta6-naphthalene)FeCp(+). The great ease with which naphthalene-type manganese tricarbonyl complexes undergo an eta6 --> eta4 hapticity change is the basis for the formation of both the homo- and heteronuclear bimetallics, for the observed two-electron reduction, and for the far greater reactivity of (eta6-PAH)Mn(CO)(3)(+) complexes in comparison to monocyclic arene analogues.     

Organometallic building blocks with amino-substituted cyclopentadienyl and boratabenzene ligands for the synthesis of heterometallic complexes and clusters

A comparative study of the reactivity of isolobal rhenium and molybdenum carbonylmetallates containing a borole, in [Re(eta5-C4H4BPh)(CO)3]- (2), a boratanaphthalene, in [Mo(eta5-2,4-MeC9H6BMe)(CO)3]- (4a) and [Mo(eta5-2,4-MeC9H6BNi-Pr2)(CO)3]- (4b), a boratabenzene, in [Mo(eta5-3,5-Me2C5H3BNi-Pr2)(CO)3]- (6) or a dimethylaminocyclopentadienyl ligand, in [Mo(eta5-C5H4NMe2)(CO)3]- (7), toward palladium(II), gold(I), mercury(II) and platinum(II) complexes has allowed an evaluation of the role of these pi-bonded ligands on the structures and unprecedented coordination modes observed in the resulting metal-metal bonded, heterometallic complexes. The new metallate 6 was reacted with [AuCl(PPh3)], and with 1 or 2 equiv. HgCl2, which afforded the new heterodinuclear complexes [Au{Mo(eta5-3,5-Me2C5H3BNi-Pr2)(CO)3}(PPh3)] (Mo-Au) (10) and [Hg{Mo(eta5-3,5-Me2C5H3BNi-Pr2)(CO)3}Cl] (Hg-Mo) (11) and the heterometallic chain complex [Hg{Mo(eta5-3,5-Me2C5H3BNi-Pr2)(CO)3}2] (Mo-Hg-Mo) (12), respectively. Reactions of the new metallate 7 with HgCl2, trans-[PtCl2(CNt-Bu)2] and trans-[PtCl2(NCPh)2] yielded the heterodinuclear complex [Hg{Mo(eta5-C5H4NMe2)(CO)3}Cl] (Mo-Hg) (15), the heterotrinuclear chain complexes trans-[Pt{Mo(eta5-C5H4NMe2)(CO)3}2(CNt-Bu)2] (Mo-Pt-Mo) (16) and trans-[Pt{Mo(eta5-C5H4NMe2)(CO)3}2(NCPh)2] (Mo-Pt-Mo) (17), the mononuclear complex [Mo(eta5-C5H4NMe2)(CO)3Cl] (18), the lozenge-type cluster [Mo2Pt2(eta5-C5H4NMe2)2(CO)8] (19) and the heterodinuclear complex [[upper bond 1 start]Pt{Mo(eta5-C5H4N[upper bond 1 end]Me2)(CO)3}(NCPh)Cl](Mo-Pt) (20), respectively. The complexes 11, 16, 17.2THF, 18 and 20 have been structurally characterized by X-ray diffraction and 20 differs from all other compounds in that the dimethylaminocyclopentadienyl ligand forms a bridge between the metals.     

Structural isomers of aryl-substituted eta(3)-propargyl complexes: eta(2)-1-Metalla(methylene)cyclopropene and eta(3)-benzyl complexes

Hydride abstraction from C(5)Me(5)(CO)(2)Re(eta(2)-PhC triple bond CCH(2)Ph) (1) gave a 3:1 mixture of eta(3)-propargyl complex [C(5)Me(5)(CO)(2)Re(eta(3)-PhCH-C triple bond CPh)][BF(4)] (5) and eta(2)-1-metalla(methylene)cyclopropene complex [C(5)Me(5)(CO)(2)Re(eta(2)-PhC-C=CHPh)][BF(4)] (6). Observation of the eta(2)-isomer requires 1,3-diaryl substitution and is favored by electron-donating substituents on the C(3)-aryl ring. Interconversion of eta(3)-propargyl and eta(2)-1-metalla(methylene)cyclopropene complexes is very rapid and results in coalescence of Cp (1)H NMR resonances at about -50 degrees C. Protonation of the alkynyl carbene complex C(5)Me(5)(CO)(2)Re=C(Ph)C triple bond CPh (22) gave a third isomer, the eta(3)-benzyl complex [C(5)Me(5)(CO)(2)Re[eta(3)(alpha,1,2)-endo,syn-C(6)H(5)CH(C triple bond CC(6)H(5))]][BF(4)] (23) along with small amounts of the isomeric complexes 5 and 6. While 5 and 6 are in rapid equilibrium, there is no equilibration of the eta(3)-benzyl isomer 23 with 5 and 6.     

eta1:eta2-Alkynyl-bridged W-Si complexes: formation, structure, and reaction with acetone

Reactions of (eta5-C5Me4R)(CO)2(MeCN)WMe (R = Me, Et) with HPh2SiCCtBu gave the novel alkynyl-bridged W-Si complexes, (eta5-C5Me4R)(CO)2W(mu-eta1:eta2-CCtBu)(SiPh2) (R = Me, Et), whose alkynyl ligands bridge the tungsten and silicon atoms in an eta1:eta2-coordination mode. The structures of these complexes were fully characterized, including X-ray crystallography. Treatment of (eta5-C5Me5)(CO)2W(mu-eta1:eta2-CCtBu)(SiPh2) with acetone resulted in acetone insertion into the silicon-alkynyl linkage followed by intramolecular C-H activation of the tBu group to give the chelate-type alkyl-alkene complex, (eta5-C5Me5)(CO)2W(eta1:eta2-CH2CMe2C=CHSiPh2OCMe2).     

Synthesis and luminescence spectroscopy of a series of [eta(5)-CpFe(CO)2] complexes containing 1,12-dicarba-closo-dodecaboranyl and -ylene ligands

Three new cyclopentadienyliron dicarbonyl compounds, 1-[eta(5)-CpFe(CO)(2)]-1,12-C(2)B(10)H(11), 1-[[eta(5)-CpFe(CO)(2)]-1,12-C(2)B(10)H(10)-12-yl](2)Hg, and 1,12-[eta(5)-CpFe(CO)(2)](2)-1,12-C(2)B(10)H(10), composed of 1,12-dicarba-closo-dodecaborane as a ligand precursor were synthesized and found to be luminescent. The uncoordinated 1,12-C(2)B(10)H(12) bridging ligand precursor is luminescent with a band maximum at 25180 cm(-1), while the iron complexes luminesce at lower energies in the range 13120-14210 cm(-1). The lowest energy excited electronic state in the iron complexes is assigned to a ligand field transition of the iron chromophore. Cyclic voltammetry of 1,12-[eta(5)-CpFe(CO)(2)](2)-1,12-C(2)B(10)H(10) displays two discrete one-electron oxidations, and the luminescence maximum is red shifted from that observed in 1-[eta(5)-CpFe(CO)(2)]-1,12-C(2)B(10)H(11). Both of these observations suggest that the iron-centered chromophores are weakly coupled. In contrast, the 1-[[eta(5)-CpFe(CO)(2)]-1,12-C(2)B(10)H(10)-12-yl](2)Hg complex is uncoupled as is evident from the single oxidation process observed with cyclic voltammetry. The extinction coefficient of 1,12-[eta(5)-CpFe(CO)(2)](2)-1,12-C(2)B(10)H(10) is six times that of 1-[eta(5)-CpFe(CO)(2)]-1,12-C(2)B(10)H(11), while the extinction coefficient of 1-[[eta(5)-CpFe(CO)(2)]-1,12-C(2)B(10)H(10)-12-yl](2)Hg is only twice that of 1-[eta(5)-CpFe(CO)(2)]-1,12-C(2)B(10)H(11). These spectroscopic properties are explained in terms of two coupled antiparallel transition dipole moments.     

Synthesis, characterization, and structure of cyclopenta[c]thiophenes and their manganese complexes

1,3-Diaryl-4H-cyclopenta[c]thiophenes are efficiently prepared from 1,2-diaroylcyclopentadienes by use of Lawesson's reagent. eta5-Cyclopenta[c]thienyl complexes, [Mn(eta5-SC7H3-1,3-R2)(CO)3] (R = Me, Ph), are prepared in high yield by ligand substitution reactions of [MnBr(CO)5] with [SnMe3(SC7H3-1,3-R2)]. Alternatively, thiation with P4S10/NaHCO3 converts [Mn{eta5-1,2-C5H3(COR)2)(CO)3] to [Mn(eta5-SC7H3-1,3-R2)(CO)3] (R = Ph, 4-tolyl, 4-MeOC6H4, benzo[2,3-b]thienyl). The molecular structures of complexes with R = Me, Ph show planar eta5-cyclopenta[c]thienyl ligands, with the manganese atom slightly displaced away from the ring-fusion bond.     

Re(2)(CO)(10)-promoted S-binding, C-S bond cleavage, and hydrogenation of benzothiophenes: organometallic models for the hydrodesulfurization of thiophenes

In hydrodesulfurization model reactions of dinuclear metal complexes with thiophenes, we observe that ultraviolet photolysis of Re(2)(CO)(10) and benzothiophenes (BT) in hexanes solution produces the ring-opened BT complexes Re(2)(CO)(7)(mu-BT) (1a-d) (BT = benzothiophene (BT) 1a, 2-methylbenzothiophene (2-MeBT) 1b, 3-methylbenzothiophene (3-MeBT) 1c, and 3,5-dimethylbenzothiophene (3,5-Me(2)BT) 1d). The eta(1)(S)-bound BT complexes Re(2)(CO)(9)(eta(1)(S)-BT) (2a-d), prepared from Re(2)(CO)(9)(THF) and BT, are readily converted into 1a-d in good yields (40-60%) during UV photolysis in hexanes solution, which suggests that the eta(1)(S)-bound complexes 2a-d are precursors to 1a-d in the reactions of Re(2)(CO)(10) with BT. Irradiation of Re(2)(CO)(10) and 3,5-Me(2)BT with UV light in decane solution under an atmosphere of H(2) produces complex 1d and the partially hydrogenated BT complex Re(2)(CO)(7)(mu-3,5-Me(2)BT-H)(eta-H) (3d). Reactions of 1a with phosphines yield further ring-opened BT-Re complexes of the types Re(2)(CO)(7)(PMe(3))(3)(mu-BT) (4) and Re(2)(CO)(7)(PR(3))(2)(mu-BT) (R = Me (5), (i)Pr (6), Cy (7), and bis(diethylphosphino)ethane (8)). Structures of 1d, 2c, 3d, and 6, which demonstrate various bonding modes of benzothiophene and its C-S cleaved derivatives to two metal centers, were determined by X-ray crystallographic studies.     

Reaction of [M(eta3-allyl)(eta2-amidinato)(CO)2(pyridine)] complexes (M = Mo, W) with bidentate ligands: nitrogen donor vs. phosphorus donor

The reactivity of amidinato complexes of molybdenum and tungsten bearing pyridine as a labile ligand, [M(eta(3)-allyl)(eta(2)-amidinato)(CO)(2)(pyridine)](M = Mo; 1-Mo, M = W; 1-W), toward bidentate ligands such as 1,10-phenanthroline (phen) and 1,2-bis(diphenylphosphino)ethane (dppe) was investigated. The reaction of 1 with phen at ambient temperature resulted in the formation of monodentate amidinato complexes, [M(eta(3)-allyl)(eta(1)-amidinato)(CO)(2)(eta(2)-phen)](M = Mo; 2-Mo, M = W; 2-W), which has pseudo-octahedral geometry with the amidinato ligand coordinated to the metal in an eta(1)-fashion. The phen ligand was located coplanar with two CO ligands and the eta(1)-amidinato ligand was positioned trans to the eta(3)-allyl ligand. In solution, both complexes 2-Mo and 2-W showed fluxionality, and complex 2-Mo afforded allylamidine (3) on heating in solution. In the reaction of 1 with dppe at ambient temperature, the simple substitution reaction took place to give dppe-bridged binuclear complexes [{M(eta(3)-allyl)(eta(2)-amidinato)(CO)(2)}(2)(mu-dppe)](M = Mo; 5-Mo, M = W; 5-W), whereas mononuclear monocarbonyl complexes [M(eta(3)-allyl)(eta(2)-amidinato)(CO)(eta(2)-dppe)](M = Mo; 6-Mo, M = W; 6-W) were obtained under acetonitrile- or toluene-refluxing conditions. Mononuclear complex 6 was also obtained by the reaction of binuclear complex 5 with 0.5 equivalents of dppe under refluxing in acetonitrile or in toluene. The X-ray analyses and variable-temperature (31)P NMR spectroscopy of complex 6 indicated the existence of the rotational isomers of the eta(3)-allyl ligand, i.e., endo and exo forms, with respect to the carbonyl ligand. The different reactivity of complex 1 toward phen and dppe seems to have come from the difference in the pi-acceptability of each bidentate ligand.     

Phosphaallyl complexes of Ru(II) derived from dicyclohexylvinylphosphine (DCVP)

The complexes [(eta5-RC5H4)Ru(CH3CN)3]PF6(R = H, CH3) react with DCVP (DCVP = Cy2PCH=CH2) at room temperature to produce the phosphaallyl complexes [(eta5-C5H5)Ru(eta1-DCVP)(eta3-DCVP)]PF6 and [(eta5-MeC5H4)Ru(eta1-DCVP)(eta3-DCVP)]PF6. Both compounds react with a variety of two-electron donor ligands displacing the coordinated vinyl moiety. In contrast, we failed to prepare the phosphaallyl complexes [(eta5-C5Me5)Ru(eta1-DCVP)(eta3-DCVP)]PF6, [(eta5-MeC5H4)Ru(CO)(eta3-DCVP)]PF6 and [(eta5-C5Me5)Ru(CO)(eta3-DPVP)]PF6(DPVP = Ph2PCH=CH2).The compounds [(eta5-MeC5H4)Ru(CO)(CH3CN)(DPVP)]PF6 and [(eta5-C5Me5)Ru(CO)(CH3CN)(DPVP)]PF6 react with DMPP (3,4-dimethyl-1-phenylphosphole) to undergo [4 + 2] Diels-Alder cycloaddition reactions at elevated temperature. Attempts at ruthenium catalyzed hydration of phenylacetylene produced neither acetophenone nor phenylacetaldehyde but rather dimers and trimers of phenylacetylene. The structures of the complexes described herein have been deduced from elemental analyses, infrared spectroscopy, 1H, 13C{1H}, 31P{1H} NMR spectroscopy and in several cases by X-ray crystallography.     

Characterization of imidazolate-bridged dinuclear and mononuclear hydroperoxo complexes

Dinucleating ligands having two metal-binding sites bridged by an imidazolate moiety, Hbdpi, HMe(2)bdpi, and HMe(4)bdpi (Hbdpi = 4,5-bis(di(2-pyridylmethyl)aminomethyl)imidazole, HMe(2)bdpi = 4,5-bis((6-methyl-2-pyridylmethyl)(2-pyridylmethyl)aminomethyl)imidazole, HMe(4)bdpi = 4,5-bis(di(6-methyl-2-pyridylmethyl)aminomethyl)imidazole), have been designed and synthesized as model ligands for copper-zinc superoxide dismutase (Cu,Zn-SOD). The corresponding mononucleating ligands, MeIm(Py)(2), MeIm(Me)(1), and MeIm(Me)(2) (MeIm(Py)(2) = (1-methyl-4-imidazolylmethyl)bis(2-pyridylmethyl)amine, MeIm(Me)(1) = (1-methyl-4-imidazolylmethyl)(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine, MeIm(Me)(2) = (1-methyl-4-imidazolyl-methyl)bis(6-methyl-2-pyridylmethyl)amine), have also been synthesized for comparison. The imidazolate-bridged Cu(II)-Cu(II) homodinuclear complexes represented as [Cu(2)(bdpi)(CH(3)CN)(2)](ClO(4))(3).CH(3)CN.3H(2)O (1), [Cu(2)(Me(2)bdpi)(CH(3)CN)(2)](ClO(4))(3) (2), [Cu(2)(Me(4)bdpi)(H(2)O)(2)](ClO(4))(3).4H(2)O (3), a Cu(II)-Zn(II) heterodinuclear complex of the type of [CuZn(bdpi)(CH(3)CN)(2)](ClO(4))(3).2CH(3)CN (4), Cu(II) mononuclear complexes of [Cu(MeIm(Py)(2))(CH(3)CN)](ClO(4))(2).CH(3)CN (5), [Cu(MeIm(Me)(1))(CH(3)CN)](ClO(4))(2)( )()(6), and [Cu(MeIm(Me)(2))(CH(3)CN)](ClO(4))(2)( )()(7) have been synthesized and the structures of complexes 5-7 determined by X-ray crystallography. The complexes 1-7 have a pentacoordinate structure at each metal ion with the imidazolate or 1-methylimidazole nitrogen, two pyridine nitrogens, the tertiary amine nitrogen, and a solvent (CH(3)CN or H(2)O) which can be readily replaced by a substrate. The reactions between complexes 1-7 and hydrogen peroxide (H(2)O(2)) in the presence of a base at -80 degrees C yield green solutions which exhibit intense bands at 360-380 nm, consistent with the generation of hydroperoxo Cu(II) species in all cases. The resonance Raman spectra of all hydroperoxo intermediates at -80 degrees C exhibit a strong resonance-enhanced Raman band at 834-851 cm(-1), which shifts to 788-803 cm(-1) (Deltanu = 46 cm(-1)) when (18)O-labeled H(2)O(2) was used, which are assigned to the O-O stretching frequency of a hydroperoxo ion. The resonance Raman spectra of hydroperoxo adducts of complexes 2 and 6 show two Raman bands at 848 (802) and 834 (788), 851 (805), and 835 (789) cm(-1) (in the case of H(2)(18)O(2), Deltanu = 46 cm(-1)), respectively. The ESR spectra of all hydroperoxo complexes are quite close to those of the parent Cu(II) complexes except 6. The spectrum of 6 exhibits a mixture signal of trigonal-bipyramid and square-pyramid which is consistent with the results of resonance Raman spectrum.