Regioselective coupling of pentafluorophenyl substituted alkynes: mechanistic insight into the zirconocene coupling of alkynes and a facile route to conjugated polymers bearing electron-withdrawing pentafluorophenyl substituents

The reaction of Cp(2)ZrCl(2) with 2 equiv of BuLi at -78 degrees C, followed by the addition of an unsymmetrical tetra- or pentafluorophenyl substituted alkyne R(1)C[triple bond]CAr(f) (R(1), Ar(f) = (CH(2))(4)Me, p-C(6)F(4)H; Me, p-C(6)F(4)H; Ph, C(6)F(5)), resulted in regioselective couplings of these alkynes to zirconacyclopentadienes in which the Ar(f) substituents preferentially adopt the 3,4-positions (beta beta) of the zirconacyclopentadiene ring. With Cp(2)Zr(py)(Me(3)SiC[triple bond]CSiMe(3)) as the zirconocene reagent, the couplings could be carried out at room temperature; however, at higher temperatures significant quantities of the 2,4-fluoroaryl substituted (alpha beta) isomers were also formed. None of the conditions employed produced the 2,5-fluoroaryl substituted (alpha alpha) isomers. These fluoroaryl-substituted zirconacyclopentadienes were readily converted to butadienes via reactions with acids. The zirconacyclopentadiene Cp(2)ZrC(4)-2,5-Ph(2)-3,4-(C(6)F(5))(2), which resulted from the coupling of PhC[triple bond]C(C(6)F(5)), was converted to the corresponding thiophene by reaction with S(2)Cl(2), and to an arene by reaction with MeO(2)CC[triple bond]CCO(2)Me/CuCl. Mechanistic studies on zirconocene couplings of (p-CF(3)C(6)H(4))C[triple bond]C(p-MeC(6)H(4)) indicate that the observed regioselectivities are determined by an electronic factor that controls the orientation of at least one of the two alkynes as they are coupled. Additionally, these studies suggest an unsymmetrical transition state for the zirconocene coupling of alkynes, and this is supported by DFT calculations. The reaction of [(C(6)F(5))C[triple bond]CCH(2)](2)CH(2) with Cp(2)Zr(py)(Me(3)SiC[triple bond]CSiMe(3)) resulted in a zirconacyclopentadiene in which the pentafluorophenyl substituents have been forced into the 2,5-positions (alpha alpha). Zirconocene coupling of the diyne (C(6)F(5))C[triple bond]C-1,4-C(6)H(4)-C[triple bond]C(C(6)F(5)) provided a route to conjugated polymers bearing electron-withdrawing pentafluorophenyl groups.     

Different C-C coupling reactions of permethyltitanocene and permethylzirconocene with disubstituted 1,3-butadiynes

Herein we describe different C-C coupling reactions of permethyltitanocene and -zirconocene with disubstituted 1,3-butadiynes. The outcomes of these reactions vary depending on the metals and the diyne substituents. The reduction of [Cp2*MCl2] (Cp* = C5Me5; M = Ti, Zr) with Mg in the presence of disubstituted butadiynes RC triple bond C-C triple bond CR' is suitable for the synthesis of different C-C coupling products of the diyne and the permethylmetallocenes, and provides a new method for the generation of functionalized pentamethyl-cyclopentadienyl derivatives. For M = Zr and R = R' = tBu, the reaction gives, by a twofold activation of one pentamethylcyclopentadienyl ligand, the complex [Cp*Zr[-C(=C=CHtBu)-CHtBu-CH2-eta5-C5Me3-CH2-]] (3), containing a fulvene ligand that is coupled to the modified substrate (allenic subunit). When using the analogous permethyltitanocene fragment "Cp2*Ti", the reaction depends strongly on the substituents R and R'. The coupling product of the butadiyne with two methyl groups of one of the pentamethylcyclopentadienyl ring systems, [Cp*Ti[eta5-C5Me3-(CH2-CHR-eta2-C2-CHR'-CH2)]], is obtained with R = R' = tBu (4) and R = tBu, R' = SiMe3 (5). In these complexes one pentamethylcyclopentadienyl ligand is annellated to an eight-membered ring with a C-C triple bond, which is coordinated to the titanium center. A different activation of both pentamethylcyclopentadienyl ligands is observed for R = R' = Me, resulting in the complex [[eta5-C5Me4(CH2)-]Ti[-C(=CHMe)-C(=CHMe)-CH2-eta5-C5Me4]] (6), which displays a fulvene as well as a butadienyl-substituted pentamethylcyclopentadienyl ligand. The influence exerted by the size of the metal is illustrated in the reaction of [Cp2*ZrCl2] with MeC triple bond C-C triple bond CMe. Here the five-membered metallacyclocumulene complex [Cp2*Zr(eta4-1,2,3,4-MeC4Me)] (7) is obtained. The reaction paths found for R = R' = Me are identical to those formerly described for R = R' = Ph.     

Sulfur-bridged early-late heterobimetallics synthesized by incorporation of titanium,vanadium, and molybdenum into bis(hydrosulfido) templates of group 9 metals

Reactions of the bis(hydrosulfido) complexes [Cp*Rh(SH)(2)(PMe(3))] (1a; Cp* = eta(5)-C(5)Me(5)) with [CpTiCl(3)] (Cp = eta(5)-C(5)H(5)) and [TiCl(4)(thf)(2)] in the presence of triethylamine led to the formation of the sulfido-bridged titanium-rhodium complexes [Cp*Rh(PMe(3))(micro(2)-S)(2)TiClCp] (2a) and [Cp*Rh(PMe(3))(micro2-S)(2)TiCl(2)] (3a), respectively. Complex 3a and its iridium analogue 3b were further converted into the bis(acetylacetonato) complexes [Cp*M(PMe(3))(micro(2)-S)(2)Ti(acac)(2)] (4a, M = Rh; 4b, M = Ir) upon treatment with acetylacetone. The hydrosulfido complexes 1a and [Cp*Ir(SH)(2)(PMe(3))] (1b) also reacted with [VCl(3)(thf)(3)] and [Mo(CO)(4)(nbd)] (nbd = 2,5-norbornadiene) to afford the cationic sulfido-bridged VM2 complexes [(Cp*M(PMe(3))(micro2-S)(2))2V](+) (5a(+), M = Rh; 5b(+), M = Ir) and the hydrosulfido-bridged MoM complexes [Cp*M(PMe(3))(micro2-SH)(2)Mo(CO)(4)] (6a, M = Rh; 6b, M = Ir), respectively.     

Mono(sulfido)-bridged mixed-valence nitrosyl complex: protonation and oxidative addition of iodine across the Ir(II)-Ir(0) bond

Treatment of [Cp*IrH(SH)(PMe3)] (Cp* = eta5-C5Me5) with [IrCl2(NO)(PPh3)2] in the presence of triethylamine yielded the sulfido-bridged Ir(II)Ir0 complex [Cp*Ir(PMe3)(mu-S)Ir(NO)(PPh3)], which further reacted with I2 and triflic acid to give the diiodo complex [Cp*Ir(PMe3)(mu-I)(mu-S)IrI(NO)(PPh3)] and the hydrido complex [Cp*Ir(PMe3)(mu-H)(mu-S)Ir(NO)(PPh3)][OSO2CF3], respectively.     

Terminal stibinidene ligands. Generation of CpCp*Hf=Sb(dmp) and trapping reactions with PMe3 and 2-butyne

Treating CpCp*HfMe(OTf) (1) with LiSbH(dmp) results in formation of CpCp*HfMe(SbHdmp), which undergoes alpha-abstraction to liberate methane and generate CpCp*Hf=Sb(dmp), which is thermally unstable but can be trapped with PMe(3) or 2-butyne to give CpCp*Hf(PMe(3))=Sb(dmp) (2) and CpCp*Hf[eta(2)-Sb,C:Sb(dmp)C(Me)=C(Me)] (3), respectively.     

Structures and reactivity of Zr(IV) chlorobenzene complexes

The synthesis, structures, and unusual reactivity of (C5R5)2ZrR'(ClPh)+ chlorobenzene complexes are described. The reaction of (C5R5)2ZrR'2 with [Ph3C][B(C6F5)4] in C6D5Cl affords [(C5R5)2ZrR'(ClC6D5)][B(C6F5)4] chlorobenzene complexes (1-d5, R' = CH2Ph and (C5R5)2 = (C5H5)2; 2a-d-d5, R' = Me and (C5R5)2 = rac-(1,2-ethylene(bis)indenyl) (2a), (C5H5)2 (2b), (C5H4Me)2 (2c), (C5Me5)2 (2d, C5Me5 = Cp*)). Complexes 1 and 2b,c are thermally robust but are converted to [{(C5R5)2Zr(mu-Cl)}2][B(C6F5)4]2 (4b,c) by a photochemical process in ClPh solution. In contrast, 2d undergoes facile thermal ortho-C-H activation to yield [Cp*2Zr(eta2-C,Cl-2-Cl-C6H4)][B(C6F5)4] (5), which slowly rearranges to [(eta4,eta1-C5Me5C6H4)Cp*ZrCl][B(C6F5)4] (6) via beta-Cl elimination and benzyne insertion into a Zr-CCp* bond. The higher thermal reactivity of 2d versus that of 1 and 2b,c is attributed to steric crowding associated with the Cp* ligands of 2d, which forces a ClPh ortho-hydrogen close to the Zr-Me group.     

Trapping reactions of an intermediate containing a tungsten-phosphorus triple bond with alkynes

The thermolysis of the phosphinidene complex [Cp*P[W(CO)5]2] (1) in toluene in the presence of tBuC(triple bond)CMe leads to the four-membered ring complexes [[[eta2-C(Me)C(tBu)]Cp*(CO)W(mu3-P)[W(CO)3]][eta4:eta1:eta1-P[W(CO)5]WCp*(CO)C(Me)C(tBu)]] (4) as the major product and [[W[Cp*(CO)2]W(CO)2WCp*(CO)[eta1:eta1-C(Me)C(tBu)]](mu,eta3:eta2:eta1-P2[W(CO)5]] (5). The reaction of 1 with PhC(triple bond)CPh leads to [[W(Co)2[eta2-C(Ph)C(Ph)]][(eta4:eta1-P(W(CO)5]W[Cp*(CO)2)C(Ph)C(Ph)]] (6). The products 4 and 6 can be regarded as the formal cycloaddition products of the phosphido complex intermediate [Cp*(CO)2W(triple bond)P --> W(CO)5] (B), formed by Cp* migration within the phosphinidene complex 1. Furthermore, the reaction of 1 with PhC(triple bond)CPh gives the minor product [[[eta2:eta1-C(Ph)C(Ph)]2[W(CO)4]2][mu,eta1:eta1-P[C(Me)[C(Me)]3C(Me)][C(Ph)](C(Ph)]] (7) as a result of a 1,3-dipolaric cycloaddition of the alkyne into a phosphaallylic subunit of the Cp*P moiety of 1. Compounds 4-7 have been characterized by means of their spectroscopic data as well as by single-crystal X-ray structure analysis.     

Syntheses and structures of mono-, di- and tetranuclear rhodium or iridium complexes of thiacalix[4]arene derivatives

The reactions of [Cp*MCl2]2(Cp*=eta5-C5Me5, M = Rh, Ir) with thiacalix[4]arene (TC4A(OH)4) and tetramercaptothiacalix[4]arene (TC4A(SH)4) gave the mononuclear complexes [(Cp*M){eta3-TC4A(OH)2(O)2}] and the dinuclear complexes [(Cp*M)2{eta3eta3-TC4A(S)4}] respectively, while the analogous reactions with dimercaptothiacalix[4]arene (TC4A(OH)2(SH)2) produced the tetranuclear complexes [(Cp*M)2(Cp*MCl2)2-{eta3eta3eta1eta1-TC4A(O)2(S)2}].     

Divalent dirhodium imido complexes: formation, structure, and alkyne cycloaddition reactivity

Dirhodium amido complexes [(Cp*Rh)2(mu2-NHPh)(mu2-X)] (X = NHPh (2), Cl (3), OMe (4); Cp* = eta5-C5Me5) were prepared by chloride displacement of [Cp*Rh(mu2-Cl)]2 (1) and have been used as precursors to a dirhodium imido species [Cp*Rh(mu2-NPh)RhCp*]. The imido species can be trapped by PMe3 to give the adduct [Cp*Rh(mu2-NPh)Rh(PMe3)Cp*] (5) and undergoes a formal [2 + 2] cycloaddition reaction with unactivated alkynes to give the azametallacycles [Cp*Rh(mu2-eta2:eta3-R1CCR2NPh)RhCp*] (R1 = R2 = Ph (6a), R1 = H, R2 = t-Bu (6b), R1 = H, R2 = p-tol (6c)). Isolation of a relevant unsaturated imido complex [Cp*Rh(mu2-NAr)RhCp*] (7) was achieved by the use of a sterically hindered LiNHAr (Ar = 2,6-diisopropylphenyl) reagent in a metathesis reaction with 1. X-ray structures of 2, 6a, 7 and the terminal isocyanide adduct [Cp*Rh(mu2-NAr)Rh(t-BuNC)Cp*] (8) are reported.     

End-group-confined chain walking within a group 4 living polyolefin and well-defined cationic zirconium alkyl complexes for modeling this behavior

Living polymers derived from the polymerization of 1-butene using the cationic zirconium initiator, {Cp*ZrMe[N(Et)C(Me)-N(tBu)]}[B(C6F5)4] (Cp* = eta5-C5Me5) (1), have been shown to undergo end-group-confined chain walking that is competitive with direct beta-hydride elimination and chain release at -10 degrees C. The well-defined complexes, {Cp*Zr(iBu)[N(Et)C(Me)N(tBu)]}[B(C6F5)4] (2) and {Cp*Zr(2-ethylbutyl)[N(Et)C(Me)N(tBu)]}[B(C6F5)4] (3), were prepared, and each was found to possess a strong beta-hydrogen agostic interaction that is absent in the living polymer. The isotopically single- and double-labeled derivatives, {Cp*Zr(2-d-2-methylpropyl)[N(Et)C(Me)N(tBu)]}[B(C6F5)4] (2') and {Cp*Zr(1-13C-2-d-2-methylpropyl)[N(Et)C(Me)N(tBu)]}[B(C6F5)4] (2' '), were also prepared and found to undergo isotopic label scrambling at 0 degrees C. For 2' ', the observation that after scrambling each deuterium label is located on a 13C-labeled carbon atom is consistent with the Busico mechanism for chain-end epimerization rather than the Resconi mechanism. Decomposition of 3 yielded olefinic products also consistent with chain walking prior to beta-hydride elimination and chain release. Finally, the unexpected decrease in stability of the living polymer relative to that of the model complexes reveals the importance of subtle differences in steric and electronic factors in controlling beta-hydride elimination and chain release.     

Kinetics and mechanism of N2 hydrogenation in bis(cyclopentadienyl) zirconium complexes and dinitrogen functionalization by 1,2-addition of a saturated C-H bond

The rates of hydrogenation of the N2 ligand in the side-on bound dinitrogen compounds, [(eta(5)-C5Me4H)2Zr]2(mu2,eta(2),eta(2)-N2) and [(eta(5)-C5Me5)(eta(5)-C5H2-1,2-Me2-4-R)Zr]2(mu2,eta(2),eta(2)-N2) (R = Me, Ph), to afford the corresponding hydrido zirconocene diazenido complexes have been measured by electronic spectroscopy. Determination of the rate law for the hydrogenation of [(eta(5)-C5Me5)(eta(5)-C5H2-1,2,4-Me3)Zr]2(mu2,eta(2),eta(2)-N2) establishes an overall second-order reaction, first order with respect to each reagent. These data, in combination with a normal, primary kinetic isotope effect of 2.2(1) for H2 versus D2 addition, establish the first H2 addition as the rate-determining step in N2 hydrogenation. Kinetic isotope effects of similar direction and magnitude have also been measured for hydrogenation (deuteration) of the two other zirconocene dinitrogen complexes. Measuring the rate constants for the hydrogenation of [(eta(5)-C5Me5)(eta(5)-C5H2-1,2,4-Me3)Zr]2(mu2,eta(2),eta(2)-N2) over a 40 degrees C temperature range provided activation parameters of deltaH(double dagger) = 8.4(8) kcal/mol and deltaS(double dagger) = -33(4) eu. The entropy of activation is consistent with an ordered four-centered transition structure, where H2 undergoes formal 1,2-addition to a zirconium-nitrogen bond with considerable multiple bond character. Support for this hypothesis stems from the observation of N2 functionalization by C-H activation of a cyclopentadienyl methyl substituent in the mixed ring dinitrogen complexes, [(eta(5)-C5Me5)(eta(5)-C5H2-1,2-Me2-4-R)Zr]2(mu2,eta(2),eta(2)-N2) (R = Me, Ph), to afford cyclometalated zirconocene diazenido derivatives.     

Catalytic P--H activation by Ti and Zr catalysts

Catalytic dehydrocoupling of phosphines was investigated using the anionic zirconocene trihydride salts [Cp*2Zr(mu-H)3Li]3 (1 a) or [Cp*2Zr(mu-H)3K(thf)4] (1 b), and the metallocycles [CpTi(NPtBu3)(CH2)4] (6) and [Cp*M(NPtBu3)(CH2)4] (M=Ti 20, Zr 21) as catalyst precursors. Dehydrocoupling of primary phosphines RPH2 (R=Ph, C6H2Me3, Cy, C10H7) gave both dehydrocoupled dimers RP(H)P(H)R or cyclic oligophosphines (RP)n (n=4, 5) while reaction of tBu3C6H2PH2 gave the phosphaindoline tBu2(Me2CCH2)C6H2PH 9. Stoichiometric reactions of these catalyst precursors with primary phosphines afforded [Cp*2Zr((PR)2)H][K(thf)4] (R=Ph 2, Cy 3, C6H2Me3 4), [Cp*2Zr((PPh)3)H][K(thf)4] (5), [CpTi(NPtBu3)(PPh)3] (7) and [CpTi(NPtBu3)(mu-PHPh)]2 (8), while reaction of 6 with (C6H2tBu3)PH2 in the presence of PMe3 afforded [CpTi(NPtBu3)(PMe3)(P(C6H2tBu3)] (10). The secondary phosphines Ph2PH and (PhHPCH2)2CH2 also undergo dehydrocoupling affording (Ph2P)2 and (PhPCH2)2CH2. The bisphosphines (CH2PH2)2 and C6H4(PH2)2 are dehydrocoupled to give (PCH2CH2PH)2)(12) and (C6H4P(PH))2 (13) while prolonged reaction of 13 gave (C6H4P2)(8) (14). The analogous bisphosphine Me2C6H4(PH)2 (17) was prepared and dehydrocoupling catalysis afforded (Me2C6H2P(PH))2 (18) and subsequently [(Me2C6H2P2)2(mu-Me2C6H2P2)]2 (19). Stoichiometric reactions with these bisphosphines gave [Cp*2Zr(H)(PH)2C6-H4][Li(thf)4] (22), [CpTi(NPtBu3)(PH)2C6H4]2 (23) and [Cp*Ti(NPtBu3)(PH)2C6H4] (24). Mechanistic implications are discussed.     

Carbon-carbon bond activation of R-CN (R = Me, Ar, iPr, tBu) using a cationic Rh(III) complex

Addition of 1.0 equiv of Ph3SiH to [Cp*(PMe3)Rh(Me)(CH2Cl2)]+BAr'4- (1) resulted in release of methane and quantitative formation of [Cp*(PMe3)Rh(SiPh3)(CH2Cl2)]+BAr'4- (2). Subsequent addition of 1.0 equiv of MeCN to 2 caused immediate displacement of dichloromethane to form the eta1-nitrile adduct [Cp*(PMe3)Rh(SiPh3)(NCMe)]+BAr'4- (3). Upon standing at room-temperature overnight, complex 3 converted quantitatively to another product which has been characterized as the C-C activation product, [Cp*(PMe3)Rh(Me)(CNSiPh3)]+BAr'4- (5). Addition of other nitrile substrates (R-CN, R = Ph, (4-CF3)Ph, (4-MeO)Ph, iPr, tBu) to 2 also resulted in C-C activation of the R-CN bond to form [Cp*(PMe3)Rh(R)(CNSiPh3)]+BAr'4-. Evidence for an eta2-iminoacyl intermediate complex, [Cp*(PMe3)Rh(eta2-C(R)=N(SiPh3)]+BAr'4-, is also presented.     

Synthesis and reactivity of the monomeric late-transition-metal parent amido complex [Ir(Cp*)(PMe3)(Ph)(NH2)

The late-transition-metal parent amido compound [Ir(Cp*)(PMe3)(Ph)(NH2)] (2) has been synthesized by deprotonation of the corresponding ammine complex [Ir(Cp*)(PMe3)(Ph)(NH3)][OTf] (6) with KN(SiMe3)2. An X-ray structure determination has ascertained its monomeric nature. Proton-transfer studies indicate that 2 can successfully deprotonate p-nitrophenylacetonitrile, aniline, and phenol. Crystallographic analysis has revealed that the ion pair [Ir(Cp*)(PMe3)(Ph)(NH3)][OPh] (8) exists as a hydrogen-bonded dimer in the solid state. Reactions of 2 with isocyanates and carbodiimides lead to overall insertion of the heterocumulenes into the N--H bond of the Ir-bonded amido group, demonstrating the ability of 2 to act as an efficient nucleophile. Intriguing reactivity is observed when amide 2 reacts with CO or 2,6-dimethylphenyl isocyanide. eta4-Tetramethylfulvene complexes [Ir(eta4-C5Me4CH2)(PMe3)(Ph)(L)] (L=CO (15), CNC6H3-2,6-(CH3)2 (16)) are formed in solution through displacement of the amido group by the incoming ligand followed by deprotonation of a methyl group on the Cp* ring and liberation of ammonia. Conclusive evidence for the presence of the Ir-bonded eta4-tetramethylfulvene moiety in the solid state has been provided by an X-ray diffraction study of complex 16.     

Purity testing of organometallic catalysts by packed capillary supercritical fluid chromatography

A packed capillary column supercritical fluid chromatography system with flame ionization detection has been used for purity testing of candidates for homogeneous catalysis such as methyl tricarbonyl pentamethylcyclopentadienyl tungsten [Cp*W(CO)3Me], methyl tricarbonyl cyclopentadienyl tungsten [CpW(CO)3Me], tetramethyl pentamethylcyclopentadienyl iridium (Cp*IrMe4), trimethyl (1,4,7-trimethyl-1,4,7-triazocyclononane) rhodium (CnRhMe3), trimethylphosphine hydride dicarbonyl cyclopentadienyl molybdenum [eta5-CpMoH(CO)2PMe3] and triphenylphosphine hydride dicarbonyl cyclopentadienyl molybdenum [eta5-CpMoH(CO)2PPh3]. A mass limit of detection of 240 pg was found for eta5-CpMoH(CO)2PMe3 when using a 60-nl injection volume and pure CO2 as mobile phase on a 5 microm Kromasil C18 column. The stability of the catalysts in solution has been examined. After 24 h more than 70% of eta5-CpMoH(CO)2PMe3 and 50% of eta5-CpMoH(CO)2PPh3 had decomposed. Due to the instability of the compounds the purity testing had to take place rapidly after sample dissolution.     

Strain-controlled, photochemically, or thermally promoted haptotropic shifts of cyclopentadienyl ligands in group 8 metallocenophanes

Cyclopentadienyl (Cp) ligands in moderately strained [1]- and [2]ferrocenophanes [Fe{(eta5-C5H4)2(ERx)y}: Fe{(eta5-C5H4)2SiMe2} (1), Fe{(eta5-C5H4)CH2}2 (10)] and highly strained [2]ruthenocenophanes [Ru{(eta5-C5H4)CR2}2 {R = H (15), Me (16)}] are susceptible to partial substitution by P donors and form mixed-hapticity metallocycles-[M(L2){(eta5-C5H4)(ERx)y(eta1-C5H4)}]: [Fe(dppe){(eta5-C5H4)SiMe2(eta1-C5H4)}] (5), [Fe(dmpe){(eta5-C5H4)SiMe2(eta1-C5H4)}] (6), [Fe(dmpe){(eta5-C5H4)(CH2)2(eta1-C5H4)}] (11), [Ru(dmpe){(eta5-C5H4)(CH2)2(eta1-C5H4)}] (17), [Ru(dmpe){(eta5-C5H4)(CMe2)2(eta1-C5H4)}] (18), and [Ru(PMe3)2{(eta5-C5H4)(CH2)2(eta1-C5H4)}] (19)-through haptotropic reduction of one eta5-, pi-bound Cp to eta1, sigma-coordination. These reactions are strain-controlled, as highly ring-tilted [2]ruthenocenophanes 15 and 16 [tilt angles (alpha) approximately 29-31 degrees ] react without irradiation to form thermodynamically stable products, while moderately strained [n]ferrocenophanes 1 and 10 (alpha approximately 19-22 degrees ) require photoactivation. The iron-containing photoproducts 5 and 11 are metastable and thermally retroconvert to their strained precursors and free phosphines at 70 degrees C. In contrast, the unprecedented ring-opening polymerization (ROP) of the essentially ring-strain-free adduct 6 to afford poly(ferrocenyldimethylsilane) [Fe(eta5-C5H4)2SiMe2]n (Mw approximately 5000 Da) was initiated by the thermal liberation of small amounts of P donor. Unlike reactions with bidentate analogues, monodentate phosphines promoted photolytic ROP of ferrocenophanes 1 and 10. MALDI-TOF analysis suggested a cyclic structure for the soluble poly(ferrocenyldimethylsilane), 8-cyclic, produced from 1 in this manner. While the polymer likewise produced from 10 was insoluble, the initiation step in the ROP process was modeled by isolation of a tris(phosphine)-substituted ring-opened ferrocenophane [Fe(PMe3)3{(eta5-C5H4)(CH2)2(C5H5)}][OCH2CH3] (13[OCH2CH3]) generated by irradiation of 10 and PMe3 in a protic solvent (EtOH). Studies of the cation 13 revealed that the Fe center reacts with a Cp- anion with loss of the phosphines to form [Fe(eta5-C5H5){(eta5-C5H4)(CH2)2(C5H5)}] (14) under conditions identical to those of the ROP experiments, confirming the likelihood of "back-biting" reactions to yield cyclic structures or macrocondensation to produce longer chains.     

Unusual reactivity of tris(pyrazolyl)borate zirconium benzyl complexes

The synthesis and reactivity of [Tp*Zr(CH2Ph)2][B(C6F5)4] (2, Tp* = HB(3,5-Me2pz)3, pz = pyrazolyl) have been explored to probe the possible role of Tp'MR2+ species in group 4 metal Tp'MCl3/MAO olefin polymerization catalysts (Tp' = generic tris(pyrazolyl)borate). The reaction of Tp*Zr(CH2Ph)3 (1) with [Ph3C][B(C6F5)4] in CD2Cl2 at -60 degrees C yields 2. 2 rearranges rapidly to [{(PhCH2)(H)B(mu-Me2pz)2}Zr(eta2-Me2pz)(CH2Ph)][B(C6F5)4] (3) at 0 degrees C. Both 2 and 3 are highly active for ethylene polymerization and alkyne insertion. Reaction of 2 with excess 2-butyne yields the double insertion product [Tp*Zr(CH2Ph)(CMe=CMeCMe=CMeCH2Ph)][B(C6F5)4] (4). Reaction of 3 with excess 2-butyne yields [{(PhCH2)(H)B(mu-Me2pz)2}Zr(Cp*)(eta2-Me2pz)][B(C6F5)4] (6, Cp* = C5Me5) via three successive 2-butyne insertions, intramolecular insertion, chain walking, and beta-Cp* elimination.     

A non-classical hydrogen bond in the molybdenum arene complex [eta 6-C6H5C6H3(Ph)OH]Mo(PMe3)3: evidence that hydrogen bonding facilitates oxidative addition of the O-H bond

Mo(PMe3)6 reacts with 2,6-Ph2C6H3OH to give the eta 6-arene complex [eta 6-C6H5C6H3(Ph)OH]Mo(PMe3)3 which exhibits a non-classical Mo...H-OAr hydrogen bond; DFT calculations indicate that the hydrogen bonding interaction facilitates oxidative addition of the O-H bond to give [eta 6,eta 1-C6H5C6H3(Ph)O]Mo(PMe3)2H.     

Cationic hafnium silyl complexes and their enhanced reactivity in sigma-bond metathesis processes with Si-H and C-H bonds

Reaction of the mixed-ring silyl methyl complex CpCp*Hf[Si(SiMe3)3]Me (4) with B(C6F5)3 in bromobenzene-d5 yielded the zwitterionic hafnium silyl complex [CpCpHfSi(SiMe3)3][MeB(C6F5)3] (7), which is stable for at least 12 h in solution. Addition of PhSiH3 to 7 rapidly produced HSi(SiMe3)3, CpCp*HfH(mu-H)B(C6F5)3, and oligomeric silane products. Reactions of CpCp*Hf(SiR3)Me (SiR3 = SitBuPh2, SiHMes2) with B(C6F5)3 rapidly produced HSiR3 in quantitative yield along with unidentified hafnium-containing species. However, reactions of Cp2Hf(SiR3)Me (SiR3 = Si(SiMe3)3 (8), SitBuPh2 (9), SiPh3 (10)) with B(C6F5)3 quantitatively produced the corresponding cationic hafnium silyl complexes 12-14. The complex Cp2Hf(SitBuPh2)(mu-Me)B(C6F5)3 (13) was isolated by crystallization from toluene at -30 degrees C and fully characterized, and its spectroscopic properties and crystal structure are compared to those of its neutral precursor 9. The sigma-bond metathesis reaction of 13 with Mes2SiH2 yielded HSitBuPh2 and the reactive species Cp2Hf(eta(2)-SiHMes2)(mu-Me)B(C6F5)3 (16, benzene-d6), which was also generated by reaction of Cp2Hf(SiMes2H)Me (11) with B(C6F5)3. Spectroscopic data provide evidence for an unusual alpha-agostic Si-H interaction in 16. At room temperature, 16 reacts with benzene to form Cp2Hf(Ph)(mu-Me)B(C6F5)3 (17), and with toluene to give isomers of Cp2Hf(C6H4Me)(mu-Me)B(C6F5)3 (18-20) and Cp2Hf(CH2Ph)(mu-Me)B(C6F5)3 (21). The reaction with benzene is first order in both 16 and benzene. Kinetic data including activation parameters (deltaH = 19(1) kcal/mol; deltaS = -17(3) eu), a large primary isotope effect (kH/kD = 6.9(7)), and the experimentally determined rate law are consistent with a mechanism involving a concerted transition state for C-H bond activation.     

Transition metal complexes of the chelating phosphine borane ligand Ph2PCH2Ph2P.BH3

Chromium and ruthenium complexes of the chelating phosphine borane H(3)B.dppm are reported. Addition of H(3)B.dppm to [Cr(CO)(4)(nbd)](nbd = norbornadiene) affords [Cr(CO)(4)(eta1-H(3)B.dppm)] in which the borane is linked to the metal through a single B-H-Cr interaction. Addition of H(3)B.dppm to [CpRu(PR(3))(NCMe)(2)](+)(Cp =eta5)-C(5)H(5)) results in [CpRu(PR(3))(eta1-H(3)B.dppm)][PF(6)](R = Me, OMe) which also show a single B-H-Ru interaction. Reaction with [CpRu(NCMe)(3)](+) only resulted in a mixture of products. In contrast, with [Cp*Ru(NCMe)(3)](+)(Cp*=eta5)-C(5)Me(5)) a single product is isolated in high yield: [Cp*Ru(eta2-H(3)B.dppm)][PF(6)]. This complex shows two B-H-Ru interactions. Reaction with L = PMe(3) or CO breaks one of these and the complexes [Cp*Ru(L)(eta1-H(3)B.dppm)][PF(6)] are formed in good yield. With L = MeCN an equilibrium is established between [Cp*Ru(eta2-H(3)B.dppm)][PF(6)] and the acetonitrile adduct. [Cp*Ru (eta2-H(3)B.dppm)][PF(6)] can be considered as being "operationally unsaturated", effectively acting as a source of 16-electron [Cp*Ru (eta1-H(3)B.dppm)][PF(6)]. All the new compounds (apart from the CO and MeCN adducts) have been characterised by X-ray crystallography. The solid-state structure of H(3)B.dppm is also reported.