Ruthenium agostic (phosphinoaryl)borane complexes: multinuclear solid-state and solution NMR, X-ray, and DFT studies

The reactivity of the (o-phosphinophenyl)(amino)borane compound HB(N(i)Pr(2))C(6)H(4)(o-PPh(2)) prepared from Li(C(6)H(4))PPh(2) and HBCl(N(i)Pr(2)) toward the bis(dihydrogen) complex RuH(2)(H(2))(2)(PCy(3))(2) (1) was studied by a combination of DFT, X-ray, and multinuclear NMR techniques including solid-state NMR, a technique rarely employed in organometallic chemistry. The study showed that the complex RuH(2){HB(N(i)Pr(2))C(6)H(4)(o-PPh(2))}(PCy(3))(2) (3), isolated in excellent yield as yellow crystals and characterized by X-ray diffraction, led in solution to PCy(3) dissociation and formation of an unsaturated 16-electron complex RuH(2){HB(N(i)Pr(2))C(6)H(4)(o-PPh(2))}(PCy(3)) (4), with a hydride trans to a vacant site. In both cases, the (phosphinoaryl)(amino)borane acts as a bifunctional ligand through the phosphine moiety and a Ru-H-B interaction, thus featuring an agostic interaction.     

sigma-Borane and dihydroborate complexes of ruthenium

Room temperature reaction of the bis(dihydrogen) complex RuH(2)(H(2))(2)(PCy(3))(2) (1) with excess pinacol borane (HBpin) generates the novel complex RuH[(mu-H)(2)Bpin](sigma-HBpin)(PCy(3))(2) (2) by loss of dihydrogen. Complex 2 was characterized spectroscopically and by X-ray crystallography. It contains two pinacolborane moieties coordinated in a different fashion, one as a dihydroborate (B-H distances : 1.58(3) and 1.47(3) A) and the other as a sigma-borane (B-H distance: 1.35(3) A). In addition, reaction of 1 with one equiv of HBpin yields total conversion to a new complex tentatively formulated as RuH[(mu-H)(2)Bpin](H(2))(PCy(3))(2) (3) on the basis of NMR data. In the presence of excess HBpin, 3 is converted to 2. Furthermore, under an atmosphere of dihydrogen, a C(7)D(8) solution of 2 rapidly converts to 3 and finally regenerates 1 over a much longer period. Thus, complex 3 is an intermediate in the formation of 2 from 1. In these processes the borane is eliminated as HBpin later hydrolyzed to BpinOBpin. Selective hydroboration of ethylene (3 bar) into C(2)H(5)Bpin is achieved using 1 or 2 as catalyst precursors in toluene, whereas in THF, competitive formation of the vinylborane C(2)H(3)Bpin (56% under 20 bar of C(2)H(4)) can be favored.     

Synthesis, neutron structure, and reactivity of the bis(dihydrogen) complex RuH2(eta(2)-H2)2(PCyp3)2 stabilized by two tricyclopentylphosphines

Treatment of Ru(eta4-C8H12)(eta6-C8H10) with 3 bar H2 in the presence of 2 equiv of tricyclopentylphosphine (PCyp3) in pentane resulted in the isolation of the new bis(dihydrogen) complex RuH2(eta2-H2)2(PCyp3)2 (2), characterized by NMR and single-crystal X-ray and neutron diffraction. The single-crystal neutron diffraction study is the first carried out for a bis(dihydrogen) complex. The coordination geometry around the metal center is a distorted octahedron defined by the two phosphines in a trans configuration (making an angle of 168.9(1) degrees ), two cis dihydrogen ligands, and two hydrides trans to them, defining the equatorial plane. The H-H bond distances (0.825(8) and 0.835(8) A) are characteristic of two "unstretched" dihydrogen ligands. H/D exchange between the Ru-H and the C-D bonds of deuterated benzene is observed within 1 h, leading to the formation of various isotopomers RuHxD6-x(PCyp3)2 (with x = 0-6). 2 is a catalyst precursor for ethylene coupling (20 bar, 293 K) to a functionalized arene (Murai reaction). We found a 90% conversion of acetophenone to 2-ethylacetophenone within 35 min, whereas 10 h was needed in the same conditions using the analogous tricyclohexylphosphine complex, RuH2(eta2-H2)2(PCy3)2, the best catalyst precursor, at room temperature, prior to this work.     

Electronic and steric effects on molecular dihydrogen activation in [CpOsH4(L)]+ (L = PPh3, AsPh3, and PCy3)

Single-crystal neutron diffraction, inelastic neutron scattering, and density functional calculations provide experimental and theoretical analyses of the nature of the osmium-bound, "elongated" dihydrogen ligands in [Cp*OsH(4)(L)][BF(4)] complexes (L = PPh(3), AsPh(3), or PCy(3)). The PPh(3) and AsPh(3) complexes clearly contain one dihydrogen ligand and two terminal hydrides; the H(2) ligand is transoid to the Lewis base, and the H-H vector connecting the central two hydrogen atoms lies parallel to the Ct-Os-L plane (Ct = centroid of Cp* ring). In contrast, in the PCy(3) complex the H-H vector is perpendicular to the Ct-Os-L plane. Not only the orientation of the central two hydrogen atoms but also the H-H bond length between them depends significantly on the nature of L: the H...H distance determined from neutron diffraction is 1.01(1) and 1.08(1) A for L = PPh(3) and AsPh(3), respectively, but 1.31(3) A for L = PCy(3). Density functional calculations show that there is a delicate balance of electronic and steric influences created by the L ligand that change the molecular geometry (steric interactions between the Cp* and L groups most importantly change the Ct-Os-L angle), changing the relative energy of the Os 5d orbitals, which in turn govern the H-H distance, preferred H-H orientation, and rotational dynamics of the elongated dihydrogen ligand. The geometry of the dihydrogen ligand is further tuned by interactions with the BF(4)(-) counterion. The rotational barrier of the bound H(2) ligand in [Cp*OsH(4)(PPh(3))](+), determined experimentally (3.1 kcal mol(-)(1)) from inelastic neutron scattering experiments, is in reasonable agreement with the B3LYP calculated H(2) rotational barrier (2.5 kcal mol(-)(1)).     

Ruthenium hydride complexes of the hindered phosphine ligand tris(3-diisopropylphosphinopropyl)phosphine

The synthesis and characterization of the novel hindered tripodal phosphine ligand P(CH(2)CH(2)CH(2)P(i)Pr(2))(3) (P(3)P(3)(iPr)) (1) are reported, along with the synthesis and characterization of ruthenium chloro and hydrido complexes of 1. Complexes [RuCl(P(3)P(3)(i)Pr)][BPh(4)] (2[BPh(4)]), RuH(2)(P(3)P(3)(i)Pr) (3), and [Ru(H(2))(H)(P(3)P(3)(iPr))][BPh(4)] (4[BPh(4)]) were characterized by crystallography. Complex 2 is fluxional in solution, and low-temperature NMR spectroscopy of the complex correlates well with two dynamic processes, an exchange between stereoisomers and a faster turnstile-type exchange within one of the stereoisomers.     

Dihydrogen complexes of rhodium: [RhH2(H2)x (PR3)2]+ (R = Cy, iPr; x = 1, 2)

Addition of H2 (4 atm at 298 K) to [Rh(nbd)(PR3)2][BAr(F)4] [R = Cy, iPr] affords Rh(III) dihydride/dihydrogen complexes. For R = Cy, complex 1a results, which has been shown by low-temperature NMR experiments to be the bis-dihydrogen/bis-hydride complex [Rh(H)2(eta2-H2)2(PCy3)2][BAr(F)4]. An X-ray diffraction study on 1a confirmed the {Rh(PCy3)2} core structure, but due to a poor data set, the hydrogen ligands were not located. DFT calculations at the B3LYP/DZVP level support the formulation as a Rh(III) dihydride/dihydrogen complex with cis hydride ligands. For R = iPr, the equivalent species, [Rh(H)2(eta2-H2)2(P iPr3)2][BAr(F)4] 2a, is formed, along with another complex that was spectroscopically identified as the mono-dihydrogen, bis-hydride solvent complex [Rh(H)2(eta2-H2)(CD2Cl2)(P iPr3)2][BAr(F)4] 2b. The analogous complex with PCy3 ligands, [Rh(H)2(eta2-H2)(CD2Cl2)(PCy3)2][BAr(F)4] 1b, can be observed by reducing the H2 pressure to 2 atm (at 298 K). Under vacuum, the dihydrogen ligands are lost in these complexes to form the spectroscopically characterized species, tentatively identified as the bis hydrides [Rh(H)2(L)2(PR3)2][BAr(F)4] (1c R = Cy; 2c R = iPr; L = CD2Cl2 or agostic interaction). Exposure of 1c or 2c to a H2 atmosphere regenerates the dihydrogen/bis-hydride complexes, while adding acetonitrile affords the bis-hydride MeCN adduct complexes [Rh(H)2(NCMe)2(PR3)2][BAr(F)4]. The dihydrogen complexes lose [HPR3][BAr(F)4] at or just above ambient temperature, suggested to be by heterolytic splitting of coordinated H2, to ultimately afford the dicationic cluster compounds of the type [Rh6(PR3)6(mu-H)12][BAr(F)4]2 in moderate yield.     

Synthesis and investigation of [Cp(PMe(3))Rh(H)(H(2))](+) and its partially deuterated and tritiated isotopomers: evidence for a hydride/dihydrogen structure

Hydrogenolysis of [Cp(PMe(3))Rh(Me)(CH(2)Cl(2))](+)BAr'(4)(-) (4, Ar' = 3,5-C(6)H(3)(CF(3))(2)) in dichloromethane afforded the nonclassical polyhydride complex [Cp*PMe(3))Rh(H)(H(2))](+)BAr'(4)(-) (1), which exhibits a single hydride resonance at all accessible temperatures in the (1)H NMR spectrum. Exposure of solutions of 1 to D(2) or T(2) gas resulted in partial isotopic substitution in the hydride sites. Formulation of 1 as a hydride/dihydrogen complex was based upon T(1) (T(1)(min) = 23 ms at 150 K, 500 MHz), J(H-D) (ca. 10 Hz), and J(H-T) (ca. 70 Hz) measurements. The barrier (Delta G(++)) to exchange of hydride with dihydrogen sites was determined to be less than ca. 5 kcal/mol. Protonation of Cp(PMe(3))Rh(H)(2) (2) using H(OEt(2))(2)BAr'(4) resulted in binuclear species [(Cp(PMe(3))Rh(H))(2)(mu-H)](+)BAr'(4)(-) (3), which is formed in a reaction involving 1 as an intermediate. Complex 3 contains two terminal hydrides and one bridging hydride ligand which exchange with a barrier of 9.1 kcal/mol as observed by (1)H NMR spectroscopy. Additionally, the structures of 3 and 4, determined by X-ray diffraction, are reported.     

Influence of media and homoconjugate pairing on transition metal hydride protonation. An IR and DFT study on proton transfer to CpRuH(CO)(PCy3)

The interaction of the ruthenium hydride complex CpRuH(CO)(PCy(3)) (1) with proton donors HOR of different strength was studied in hexane and compared with data in dichloromethane. The formation of dihydrogen-bonded complexes (2) and ion pairs stabilized by hydrogen bonds between the dihydrogen ligand and the anion (3) was observed. Kinetics of the interconversion from 2 to 3 was followed at different (CF(3))(3)COH concentrations between 200 and 240 K. The activation enthalpy and entropy values for proton transfer from the dihydrogen-bonded complex 2 to the (eta(2)-H(2))-complex 3 (DeltaH() = 11.0 +/- 0.5 kcal/mol and DeltaS() = -19 +/- 3 eu) were obtained for the first time. The results of the DFT study of the proton transfer process, taking CF(3)COOH and (CF(3))(3)COH as a proton donors and introducing solvent effects in the calculation with the PCM method, are presented. The role of homoconjugate pairs [ROHOR](-) in the protonation is analyzed by means of the inclusion of an additional ROH molecule in the calculations. The formation of the free cationic complex [CpRu(CO)(PCy(3))(eta(2)-H(2))](+) is driven by the formation of the homoconjugated anionic complex [ROHOR](-). Solvent polarity plays a significant role stabilizing the charged species formed in the process. The theoretical study also accounts for the dihydrogen release and production of CpRu(OR)(CO)(PCy(3)), observed at temperatures above 250 K.     

Dynamics of a cis-dihydrogen/hydride complex of iridium

Insertion of CS2 into one of the Ir-H bonds of [Ir(H)5(PCy3)2] takes place to afford the dihydrido dithioformate complex cis-[Ir(H)2(eta2-S2CH)(PCy3)2] accompanied by the elimination of H2. Protonation of the dithioformate complex using HBF4.Et2O gives cis-[Ir(H)(eta2-H2)(eta2-S2CH)(PCy3)2][BF4] wherein the H atom undergoes site exchange between the dihydrogen and the hydride ligands. The dynamics was found to be so extremely rapid with respect to the NMR time scale that the barrier to exchange could not be measured. Partial deuteration of the hydride ligands resulted in a J(H,D) of 6.5 and 7.7 Hz for the H2D and the HD2 isotopomers of cis-[Ir(H)(eta2-H2)(eta2-S2CH)(PCy3)2][BF4], respectively. The H-H distance (d(HH)) for this complex has been calculated to be 1.05 A, which can be categorized under the class of elongated dihydrogen complexes. The cis-[Ir(H)(eta2-H2)(eta2-S2CH)(PCy3)2][BF4] complex undergoes substitution of the bound H2 moiety with CH(3)CN and CO resulting in new hydride derivatives, cis-[Ir(H)(L)(eta2-S2CH)(PCy3)2][BF4] (L = CH3CN, CO). Reaction of cis-[Ir(H)2(eta2-S2CH)(PCy3)2] with electrophilic reagents such as MeOTf and Me3SiOTf afforded a new hydride aquo complex cis-[Ir(H)(H2O)(eta2-S2CH)(PCy3)2][OTf] via the elimination of CH4 and Me3SiH, respectively, followed by the binding of a water molecule (present in trace quantities in the solvent) to the iridium center. The X-ray crystal structures of cis-[Ir(H)2(eta2-S2CH)(PCy3)2] and cis-[Ir(H)(H2O)(eta2-S2CH)(PCy3)2][OTf] have been determined.     

Competition between NH.HIr Intramolecular Proton-Hydride Interactions and NH.FBF(3)(-) or NH.O Intermolecular Hydrogen Bonds Involving [IrH(2-thiazolidinethione)(4)(PCy(3))](BF(4))(2) and Related Complexes

The reaction of IrH(5)(PCy(3))(2) in acetone with 2 equiv of HBF(4) results in the formation of the air-stable complex [Ir(H)(2)(PCy(3))(2)(acetone)(2)]BF(4), 1. The reaction of 1 with an excess of 2-thiazolidinethione or 2-benzothiazolethione in the presence of 2 equiv of HBF(4) gives the complexes [Ir(H)(PCy(3))(L)(4)](BF(4))(2) (2a, L = 2-thiazolidinethione; 2b, L = 2-benzothiazolethione). Complex 2a has an intramolecular NH.H(Ir).HN interaction both in the crystalline solid as determined by X-ray diffraction and in a CD(2)Cl(2) solution as determined by the T(1) method. The d(HH) were determined to be 2.2 +/- 0.1 ? in the solid state and 1.9 +/- 0.1 ? in solution. The NH.H(Ir).HN interactions and NH.F.HN hydrogen bonds which involve FBF(3)(-) form a four-member ring in a butterfly conformation. The nOe effect of the hydride on the NH proton is around 10%. A crystal of 2a is in the triclinic space group P&onemacr; with a = 11.426(3), b = 11.922(3), c = 19.734(4) ?, alpha = 87.05(1) degrees, beta = 88.23(1) degrees, gamma = 75.50(1) degrees, V = 2599(1) ?(3), and Z = 2 at T = 173 K; full-matrix least-squares refinement on F(2) was performed for 10 198 independent reflections; R[F(2)>2sigma(F(2))] = 0.0480, R(w)(F(2)) = 0.099. The formation of the NH.HIr proton-hydride interaction is as favorable as the formation of intermolecular hydrogen bonds NH.FBF(3)(-) or NH.O hydrogen bonds with OPPh(3) or H(2)O in CD(2)Cl(2). A similar NH.HIr interaction also has been observed in the complexes [Ir(H)(2)(PCy(3))(2)(L)(2)]BF(4) (3a, L = 2-thiazolidinethione; 3b, L = 2-benzothiazolethione) but not in the complexes with L = NH(2)NH(2) (3c) and L = NH(3) (3d). Both the NH and IrH protons are deuterated when a solution of 2 or 3 in C(6)D(6) is exposed to 1 atm of D(2) gas or D(2)O.     

Preparation of hydrido(vinylidene)ruthenium(II) complexes and a one-pot synthesis of Grubbs-type ruthenium carbenes

Treatment of the hydrido(dihydrogen) compound [RuHCl(H2)(PCy3)2] 1 with alkynes RC[triple bond, length as m-dash]CH (R=H, Ph) afforded the hydrido(vinylidene) complexes [RuHCl(=C=CHR)(PCy3)2] 2, 3 which react with HCl or [HPCy3]Cl to give the corresponding Grubbs-type ruthenium carbenes [RuCl2(=CHCH2R)(PCy3)2] 4, 5. The reaction of 2 (R=H) with DCl, or D2O in the presence of chloride sources, led to the formation of [RuCl2(=CHCH2D)(PCy3)2] 4-d1. Based on these observations, a one-pot synthesis of compounds 4 and 5 was developed using RuCl3.3H2O as the starting material. The hydrido(vinylidene) derivative 2 reacted with CF3CO2H and HCN at low temperatures to yield the carbene complexes [RuCl(X)(=CHCH3)(PCy3)2] 6, 7, of which 7 (X=CN) was characterized crystallographically. Salt metathesis of 2 with CF3CO2K and KI led to the formation of [RuH(X)(=C=CH2)(PCy3)2] 8, 9. The bis(trifluoracetato) and the diiodo compounds [RuX2(=CHCH3)(PCy3)2] 10, 11 as well as the new phosphine P(thp)3 12 (thp=4-tetrahydropyranyl) and the corresponding complex [RuCl2(=CHCH3){P(thp)3}2] 14 were also prepared. The catalytic activity of the ruthenium carbenes 4-7, 10, 11 and 14 in the olefin cross-metathesis of cyclopentene and allyl alcohol was investigated.     

Theoretical study of Pt(PR3)(2)(AlCl3) (R = H, Me, Ph, or Cy) including an unsupported bond between transition metal and non-transition metal elements: geometry, bond strength, and prediction

The molecular structure and the binding energy of Pt(PR(3))(2)(AlCl(3)) (R = H, Me, Ph, or Cy) were investigated by DFT, MP2 to MP4(SDTQ), and CCSD(T) methods. The optimized structure of Pt(PCy(3))(2)(AlCl(3)) (Cy = cyclohexyl) by the DFT method with M06-2X and LC-BLYP functionals agrees well with the experimental one. The MP4(SDTQ) and CCSD(T) methods present similar binding energies (BE) of Pt(PH(3))(2)(AlCl(3)), indicating that these methods provide reliable BE value. The DFT(M06-2X)-calculated BE value is close to the MP4(SDTQ) and CCSD(T)-calculated values, while the other functionals present BE values considerably different from the MP4(SDTQ) and CCSD(T)-calculated values. All computational methods employed here indicate that the BE values of Pt(PMe(3))(2)(AlCl(3)) and Pt(PPh(3))(2)(AlCl(3)) are considerably larger than those of the ethylene analogues. The coordinate bond of AlCl(3) with Pt(PR(3))(2) is characterized to be the σ charge transfer (CT) from Pt to AlCl(3). This complex has a T-shaped structure unlike the well-known Y-shaped structure of Pt(PMe(3))(2)(C(2)H(4)), although both are three-coordinate Pt(0) complex. This T-shaped structure results from important participation of the Pt d(σ) orbital in the σ-CT; because the Pt d(σ) orbital energy becomes lower as the P-Pt-P angle decreases, the T-shaped structure is more favorable for the σ-CT than is the Y-shaped structure. [Co(alcn)(2)(AlCl(3))](-) (alcn = acetylacetoneiminate) is theoretically predicted here as a good candidate for the metal complex, which has an unsupported M-Al bond because its binding energy is calculated to be much larger than that of Pt(PCy(3))(2)(AlCl(3)).     

Intramolecular Hydrogen Site Exchange in an HRu(SiHPh(2)) Moiety

RuH(Ph)(CO)L(2) (L = P(t)Bu(2)Me) reacts with SiH(2)Ph(2) to give first benzene and RuH(SiHPh(2))(CO)L(2), and then RuH(3)(SiHPh(2))(CO)L(2) and Ru(H)(2)(CO)L(2), the trihydride being formed by a dehydrogenative silane coupling reaction when excess SiH(2)Ph(2) is present. Variable-temperature spin saturation transfer experiments reveal exchange between H(a) and H(b) in RuH(a)(SiH(b)Ph(2))(CO)L(2); this occurs both by an intramolecular mechanism and (when SiH(2)Ph(2) is present) by a mechanism dependent on SiH(2)Ph(2) concentration. Spin saturation transfer also reveals exchange between all three of the above complexes via addition/loss of SiH(2)Ph(2) or H(2).     

Hydrogen elimination from a hydroxycyclopentadienyl ruthenium(II) hydride: study of hydrogen activation in a ligand-metal bifunctional hydrogenation catalyst

At high temperatures in toluene, [2,5-Ph(2)-3,4-Tol(2)(eta(5)-C(4)COH)]Ru(CO)(2)H (3) undergoes hydrogen elimination in the presence of PPh(3) to produce the ruthenium phosphine complex [2,5-Ph(2)-3,4-Tol(2)-(eta(4)-C(4)CO)]Ru(PPh(3))(CO)(2) (6). In the absence of alcohols, the lack of RuH/OD exchange, a rate law first order in Ru and zero order in phosphine, and kinetic deuterium isotope effects all point to a mechanism involving irreversible formation of a transient dihydrogen ruthenium complex B, loss of H(2) to give unsaturated ruthenium complex A, and trapping by PPh(3) to give 6. DFT calculations showed that a mechanism involving direct transfer of a hydrogen from the CpOH group to form B had too high a barrier to be considered. DFT calculations also indicated that an alcohol or the CpOH group of 3 could provide a low energy pathway for formation of B. PGSE NMR measurements established that 3 is a hydrogen-bonded dimer in toluene, and the first-order kinetics indicate that two molecules of 3 are also involved in the transition state for hydrogen transfer to form B, which is the rate-limiting step. In the presence of ethanol, hydrogen loss from 3 is accelerated and RuD/OH exchange occurs 250 times faster than in its absence. Calculations indicate that the transition state for dihydrogen complex formation involves an ethanol bridge between the acidic CpOH and hydridic RuH of 3; the alcohol facilitates proton transfer and accelerates the reversible formation of dihydrogen complex B. In the presence of EtOH, the rate-limiting step shifts to the loss of hydrogen from B.     

Synthesis, NMR Study, and Reactivity of Isomeric Early-Late Heterobimetallic Dihydrides. X-ray Crystal Structure of (PPh(3))HRu(&mgr;-H)(&mgr;-PMe(2)C(5)Me(4))(2)(&mgr;-Cl)ZrCl

The new isomeric ruthenium/zirconium dihydrides of the formula (PPh(3))HRuH(&mgr;-PMe(2)Cp)(2)ClZrCl (1, 2) (Cp = C(5)Me(4)) have been characterized by elemental analysis and NMR ((1)H, (31)P and (1)H relaxation data). Complex 1, stabilized by Cl and H bridges, has been isolated from the room temperature reaction between RuH(2)(H(2))(PPh(3))(3) and (PMe(2)Cp)(2)ZrCl(2). The X-ray crystallographic study of 1 revealed a bimetallic complex. The six-coordinate Ru atom and the five-coordinate Zr atom are held together by two bifunctional phosphinocyclopentadienyl ligands and by H and Cl bridges. Crystal data for 1: monoclinic space group P2(1)/c, a = 13.901(2) ?, b = 18.205(6) ?, c = 16.633(3) ?, beta = 92.43(1) degrees, V = 4206 ?(3), Z = 4, d(calc) = 1.472 g cm(-)(3), R(F) = 0.056, R(w)(F) = 0.058. Complex 2 with two H bridges and terminal Cl ligands at Ru and Zr has been obtained by an irreversible isomerization of 1 in the presence of HNEt(3)BPh(4). This transformation has been proposed to occur through slow protonation of one of the phosphorus ligands with the five-coordinate Ru center formed by undergoing rapid pseudorotation. Complexes 1 and 2 do not react with H(2), N(2), or 3,3-dimethyl-but-1-ene. Treatment of 1 with 1 equiv of NaHBEt(3) in C(6)D(6) gives a mixture of new trihydrides (PPh(3))HRu(&mgr;-Cl)(&mgr;-H)(&mgr;-PMe(2)Cp)(2)ZrH (3) and (PPh(3))HRu(&mgr;-H)(2)(&mgr;-PMe(2)Cp)(2)ZrCl (4). Complex 3 transforms to 4 upon standing in solution for a period of several days. Under the same conditions, complex 2 leads smoothly to trihydride 4. Both trihydrides are new and have been characterized by (1)H, (31)P NMR, and (1)H NMR relaxation data. Complexes 1 and 4 are fluxional in solution at room temperature, showing hydride exchange between the terminal and bridging positions. The variable-temperature (1)H NMR spectra allowed determinations of the DeltaG() values of 16.4 (313 K, THF-d(8)) and 13.5 kcal/mol (295 K, toluene-d(8)) for the exchange in complexes 1 and 4, respectively. Possible exchange mechanisms have been discussed. Complex 2 is rigid on the NMR time scale.     

Linkage and redox isomerism in ruthenium complexes of catecholate, semi-quinone, and o-acylphenolate ligands derived from tri- and tetrahydroxy-9,10-anthracenediones

The complexes Ru(CO)(2)L(2)(PHAQ-2H) (PHAQ = 1,2,4-trihydroxy-9,10-anthracenedione (PUR), 1,2,3- trihydroxy-9,10-anthracenedione (AG), and 1,2,5,8-tetrahydroxy-9,10-anthracenedione (QAL); L = PPh(3), PCy(3), PBu(3)), and Ru(CO)(dppe)(PBu(3))(PHAQ-2H), containing catecholate-type ligands were prepared. The complex Ru(CO)(2)(PBu(3))(2)(AG-2H) crystallizes in the space group P2(1)/n (No. 14 var) with a = 13.317(2), b = 15.628(2), c = 21.076(3) A, beta = 101.660(10) degrees, Z = 4; the crystal structure shows it to contain a 2,3-catecholate ligand. The electrochemistry of these complexes was examined, and the semi-quinone complexes [Ru(CO)(2)L(2)(PHAQ-2H)](1+) and [Ru(CO)(dppe)(PBu(3))(PHAQ-2H)](1+) were generated by chemical oxidation. One example of an o-acylphenolate complex, HRu(CO)(PCy(3))(2)(PUR-H), is also reported.     

Preparation, structure, and ethylene (co)polymerization behavior of Group IV metal complexes with an [OSSO]-carborane ligand

The synthesis of Group IV metal complexes that contain a tetradentate dianionic [OSSO]-carborane ligand [(HOC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2 (B(10)H(10))] (1a) is described. Reactions of TiCl(4) and Ti(OiPr)(4) with the [OSSO]-type ligand 1a afford six-coordinated titanium complex [Ti(OC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2)(B(10)H(10))Cl(2)] (2a) and four-coordinated titanium complex [Ti(OC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2)(B(10)H(10))(OiPr)(2)] (2b), respectively. ZrCl(4) and HfCl(4) were treated with 1a to give six-coordinated zirconium complex [Zr(OC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2)(B(10)H(10))Cl(2) (thf)(2)] (2c) and six-coordinated hafnium complex [Hf(OC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2)(B(10)H(10))Cl(2)] (2d). All the complexes were fully characterized by IR, NMR spectroscopy, and elemental analysis. In addition, X-ray structure analyses were performed on complexes 2a and 2b and reveal the expected different coordination geometry due to steric hindrance effects. Extended X-ray absorption fine structure (EXAFS) spectroscopy was performed on complexes 2c and 2d to describe the coordination chemistry of this ligand around Zr and Hf. Six-coordinated titanium complex 2a showed good activity toward ethylene polymerization as well as toward copolymerization of ethylene with 1-hexene in the presence of methylaluminoxane (MAO) as cocatalyst (up to 1060 kg[mol(Ti)](-1) h(-1) in the case of 10 atm of ethylene pressure).     

Reactions of halofluorocarbons with group 6 complexes M(C(5)H(5))(2)L (M = Mo, W; L = C(2)H(4), CO). Fluoroalkylation at molybdenum and tungsten, and at cyclopentadienyl or ethylene ligands.

The molybdenum(II) and tungsten(II) complexes [MCp(2)L] (Cp = eta(5)-cyclopentadienyl; L = C(2)H(4), CO) react with perfluoroalkyl iodides to give a variety of products. The Mo(II) complex [MoCp(2)(C(2)H(4))] reacts with perfluoro-n-butyl iodide or perfluorobenzyl iodide with loss of ethylene to give the first examples of fluoroalkyl complexes of Mo(IV), MoCp(2)(CF(2)CF(2)CF(2)CF(3))I (8) and MoCp(2)(CF(2)C(6)F(5))I (9), one of which (8) has been crystallographically characterized. In contrast, the CO analogue [MoCp(2)(CO)] reacts with perfluorobenzyl iodide without loss of CO to give the crystallographically characterized salt, [MoCp(2)(CF(2)C(6)F(5))(CO)](+)I(-) (10), and the W(II) ethylene precursor [WCp(2)(C(2)H(4))] reacts with perfluorobenzyl iodide without loss of ethylene to afford the salt [WCp(2)(CF(2)C(6)F(5))(C(2)H(4))](+)I(-) (11). These observations demonstrate that the metal-carbon bond is formed first. In further contrast the tungsten precursor [WCp(2)(C(2)H(4))] reacts with perfluoro-n-butyl iodide, perfluoro-iso-propyl iodide, and pentafluorophenyl iodide to give fluoroalkyl- and fluorophenyl-substituted cyclopentadienyl complexes WCp(eta(5)-C(5)H(4)R(F))(H)I (12, R(F) = CF(2)CF(2)CF(2)CF(3); 15, R(F) = CF(CF(3))(2); 16, R(F) = C(6)F(5)); the Mo analogue MoCp(eta(5)-C(5)H(4)R(F))(H)I (14, R(F) = CF(CF(3))(2)) is obtained in similar fashion. The tungsten(IV) hydrido compounds react with iodoform to afford the corresponding diiodides WCp(eta(5)-C(5)H(4)R(F))I(2) (13, R(F) = CF(2)CF(2)CF(2)CF(3); 18, R(F) = CF(CF(3))(2); 19, R(F) = C(6)F(5)), two of which (13 and 19) have been crystallographically characterized. The carbonyl precursors [MCp(2)(CO)] each react with perfluoro-iso-propyl iodide without loss of CO, to afford the exo-fluoroalkylated cyclopentadiene M(II) complexes MCp(eta(4)-C(5)H(5)R(F))(CO)I (21, M = Mo; 22, M = W); the exo-stereochemistry for the fluoroalkyl group is confirmed by an X-ray structural study of 22. The ethylene analogues [MCp(2)(C(2)H(4))] react with perfluoro-tert-butyl iodide to yield the products MCp(2)[(CH(2)CH(2)C(CF(3))(3)]I (25, M = Mo; 26, M = W) resulting from fluoroalkylation at the ethylene ligand. Attempts to provide positive evidence for fluoroalkyl radicals as intermediates in reactions of primary and benzylic substrates were unsuccessful, but trapping experiments with CH(3)OD (to give R(F)D, not R(F)H) indicate that fluoroalkyl anions are the intermediates responsible for ring and ethylene fluoroalkylation in the reactions of secondary and tertiary fluoroalkyl substrates.     

Dimethylaminoborane (H2BNMe2) coordination to late transition metal centers: snapshots of the B-H oxidative addition process

The reaction of cyclodiborazane [Me(2)N-BH(2)](2) with the chloro(dihydrogen) ruthenium complex RuHCl(η(2)-H(2))(P(i)Pr(3))(2) (1) led to the formation of the unsymmetricaly coordinated dimethylaminoborane complex RuHCl(H(2)BNMe(2))(P(i)Pr(3))(2) (2). The dimethylaminoborane coordination (H(2)BNMe(2)) to the ruthenium center in 2 was carefully studied by combining X-ray, multinuclear NMR, and density functional theory (DFT) techniques, and compared with the recently reported osmium analogue which was originally formulated as a σ-B-H borinium complex [OsH(2)Cl(HBNMe(2))(P(i)Pr(3))(2)] (4). All our data are in favor of a bis(σ-B-H) coordination mode at a very activated stage in the case of the ruthenium complex 2, whereas in the osmium complex 4, full oxidative addition is favored leading to a complex better formulated as an osmium(IV) boryl species with an α-agostic B-H interaction. The synthesis and characterization of the symmetrical dihydride complex RuH(2)(H(2)BNMe(2))(P(i)Pr(3))(2) (3) from addition of the lithium dimethylaminoborohydride to 1 is reported for comparison.     

Acrylonitrile polymerization by Cy3PCuMe and (Bipy)2FeEt2

Cy(3)PCuMe (1) undergoes reversible ligand redistribution at low temperature in solution to form the tight ion pair [Cu(PCy(3))(2)][CuMe(2)] (3). The structure of 3 was assigned on the basis of (i) the stoichiometry of the 1 = 3 equilibrium, (ii) the observation of a triplet for the PCy(3) C1 (13)C NMR resonance due to virtual coupling to two (31)P nuclei, and (iii) reverse synthesis of 1 by combining separately generated Cu(PCy(3))(2)(+) and CuMe(2)(-) ions. Complex 1 and [Cu(PCy(3))(2)][PF(6)] (5) coordinate additional PCy(3) to form (Cy(3)P)(2)CuMe and [Cu(PCy(3))(3)][PF(6)], respectively, while 3 does not. Complex 1, free PCy(3), and (bipy)(2)FeEt(2) (2) each initiate the polymerization of acrylonitrile. In each case, the polyacrylonitrile contains branches that are characteristic of an anionic polymerization mechanism. The major initiator in acrylonitrile polymerization by 1 is PCy(3), which is liberated from 1. A transient iron hydride complex is proposed to initiate acrylonitrile polymerization by 2.