Mechanism of reversible alkyne coupling at zirconocene: ancillary ligand effects

The mechanism of reversible alkyne coupling at zirconium was investigated by examination of the kinetics of zirconacyclopentadiene cleavage to produce free alkynes. The zirconacyclopentadiene rings studied possess trimethylsilyl substituents in the alpha-positions, and the ancillary Cp2, Me2C(eta(5)-C5H4)2, and CpCp* (Cp* = eta(5)-C5Me5) bis(cyclopentadienyl) ligand sets were employed. Fragmentation of the zirconacyclopentadiene ring in Cp2Zr[2,5-(Me3Si)2-3,4-Ph2C4] with PMe3, to produce Cp2Zr(eta(2)-PhC[triple bond]CSiMe3)(PMe3) and free PhC[triple bond]CSiMe3, is first-order in initial zirconacycle concentration and zero-order in incoming phosphine (k(obs) = 1.4(2) x 10(-5) s(-1) at 22 degrees C), and the activation parameters determined by an Eyring analysis (DeltaH(double dagger) = 28(2) kcal mol(-1) and DeltaS(double dagger) = 14(4) eu) are consistent with a dissociative mechanism. The analogous reaction of the ansa-bridged complex Me2C(eta(5)-C5H4)2Zr[2,5-(Me3Si)2-3,4-Ph2C4] is 100 times faster than that for the corresponding Cp2 complex, while the corresponding CpCp* complex reacts 20 times slower than the Cp2 derivative. These rates appear to be largely influenced by the steric properties of the ancillary ligands.     

Aluminacyclopropene: syntheses, characterization, and reactivity toward terminal alkynes

Reactions of LAl with ethyne, mono- and disubstituted alkynes, and diyne to aluminacyclopropene LAl[eta2-C2(R1)(R2)] ((L = HC[(CMe)(NAr)]2, Ar = 2,6-iPr2C6H3); R1 = R2 = H, (1); R1 = H, R2 = Ph, (2); R1 = R2 = Me, (3); R1 = SiMe3, R2 = C[triple bond]CSiMe3, (4)) are reported. Compounds 1 and 2 were obtained in equimolar quantities of the starting materials at low temperature. The amount of C2H2 was controlled by removing an excess of C2H2 in the range from -78 to -50 degrees C. Compound 4 can be alternatively prepared by the substitution reaction of LAl[eta2-C2(SiMe3)2] with Me3SiC[triple bond]CC[triple bond]CSiMe3 or by the reductive coupling reaction of LAlI2 with potassium in the presence of Me3SiC[triple bond]CC[triple bond]CSiMe3. The reaction of LAl with excess C2H2 and PhC[triple bond]CH (<1:2) afforded the respective alkenylalkynylaluminum compounds LAl(CH=CH2)(C[triple bond]CH) (5) and LAl(CH=CHPh)(C[triple bond]CPh) (6). The reaction of LAl(eta2-C2Ph2) with C2H2 and PhC[triple bond]CH yielded LAl(CPh=CHPh)(C[triple bond]CH) (7) and LAl(CPh=CHPh)(C[triple bond]CPh) (8), respectively. Rationally, the formation of 5 (or 6) may proceed through the corresponding precursor 1 (or 2). The theoretical studies based on DFT calculations show that an interaction between the Al(I) center and the C[triple bond]C unit needs almost no activation energy. Within the AlC2 ring the computational Al-C bond order of ca. 1 suggests an Al-C sigma bond and therefore less pi electron delocalization over the AlC2 ring. The computed Al-eta2-C2 bond dissociation energies (155-82.6 kJ/mol) indicate a remarkable reactivity of aluminacyclopropene species. Finally, the 1H NMR spectroscopy monitored reaction of LAl(eta2-C2Ph2) and PhC[triple bond]CH in toluene-d8 may reveal an acetylenic hydrogen migration process.     

Generation and coupling of [Mn(dmpe)2(C triple bond CR)(C triple bond C)]* radicals producing redox-active C4-bridged rigid-rod complexes

The symmetric d(5) trans-bis-alkynyl complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(2)] (R = Me, 1 a; Et, 1 b; Ph, 1 c) (dmpe = 1,2-bis(dimethylphosphino)ethane) have been prepared by the reaction of [Mn(dmpe)(2)Br(2)] with two equivalents of the corresponding acetylide LiC triple bond CSiR(3). The reactions of species 1 with [Cp(2)Fe][PF(6)] yield the corresponding d(4) complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(2)][PF(6)] (R = Me, 2 a; Et, 2 b; Ph, 2 c). These complexes react with NBu(4)F (TBAF) at -10 degrees C to give the desilylated parent acetylide compound [Mn(dmpe)(2)(C triple bond CH)(2)][PF(6)] (6), which is stable only in solution at below 0 degrees C. The asymmetrically substituted trans-bis-alkynyl complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(C triple bond CH)][PF(6)] (R = Me, 7 a; Et, 7 b) related to 6 have been prepared by the reaction of the vinylidene compounds [Mn(dmpe)(2)(C triple bond CSiR(3))(C=CH(2))] (R = Me, 5 a; Et, 5 b) with two equivalents of [Cp(2)Fe][PF(6)] and one equivalent of quinuclidine. The conversion of [Mn(C(5)H(4)Me)(dmpe)I] with Me(3)SiC triple bond CSnMe(3) and dmpe afforded the trans-iodide-alkynyl d(5) complex [Mn(dmpe)(2)(C triple bond CSiMe(3))I] (9). Complex 9 proved to be unstable with regard to ligand disproportionation reactions and could therefore not be oxidized to a unique Mn(III) product, which prevented its further use in acetylide coupling reactions. Compounds 2 react at room temperature with one equivalent of TBAF to form the mixed-valent species [[Mn(dmpe)(2)(C triple bond CH)](2)(micro-C(4))][PF(6)] (11) by C-C coupling of [Mn(dmpe)(2)(C triple bond CH)(C triple bond C*)] radicals generated by deprotonation of 6. In a similar way, the mixed-valent complex [[Mn(dmpe)(2)(C triple bond CSiMe(3))](2)(micro-C(4))][PF(6)] [12](+) is obtained by the reaction of 7 a with one equivalent of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The relatively long-lived radical intermediate [Mn(dmpe)(2)(C triple bond CH)(C triple bond C*)] could be trapped as the Mn(I) complex [Mn(dmpe)(2)(C triple bond CH)(triple bond C-CO(2))] (14) by addition of an excess of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) to the reaction mixtures of species 2 and TBAF. The neutral dinuclear Mn(II)/Mn(II) compounds [[Mn(dmpe)(2)(C triple bond CR(3))](2)(micro-C(4))] (R = H, 11; R = SiMe(3), 12) are produced by the reduction of [11](+) and [12](+), respectively, with [FeCp(C(6)Me(6))]. [11](+) and [12](+) can also be oxidized with [Cp(2)Fe][PF(6)] to produce the dicationic Mn(III)/Mn(III) species [[Mn(dmpe)(2)(C triple bond CR(3))](2)(micro-C(4))][PF(6)](2) (R = H, [11](2+); R = SiMe(3), [12](2+)). Both redox processes are fully reversible. The dinuclear compounds have been characterized by NMR, IR, UV/Vis, and Raman spectroscopies, CV, and magnetic susceptibilities, as well as elemental analyses. X-ray diffraction studies have been performed on complexes 4 b, 7 b, 9, [12](+), [12](2+), and 14.     

Synthesis, characterization, and activity in ethylene polymerization of silica supported cationic cyclopentadienyl zirconium complexes

Cp*ZrMe3 reacts with silica pretreated at 800 degrees C, SiO(2-(800)) through two pathways: (a) protolysis of a Zr-Me group by surface silanols and (b) transfer of a methyl group to the surface by opening of strained siloxane bridges, in a relative proportion of ca. 9/1, respectively, affording a well-defined surface species [([triple bond]SiO)ZrCp*(Me)2], 3, but with two different local environments 3a, [([triple bond]SiO)ZrCp*(Me)2][[triple bond]Si-O-Si[triple bond]], and the other with 3b, [structure: see text]. The reaction of the species 3 with B(C6F5)3 is controlled by this local environment and gives three surface species [([triple bond]SiO)ZrCp*(Me)](+)[MeB(C6F5)3]- [[triple bond]Si-O-Si[triple bond]], 4a (20%), [([triple bond]SiO)ZrCp*(Me)](+)[(Me)B(C6F5)3]- [[triple bond]Si-Me], 4b (10%), and [([triple bond]SiO)2ZrCp*](+)[(Me)B(C6F5)(3)](-)[[triple bond]Si-O-Si[triple bond]], 5 (70%). On the contrary, the reaction of Cp*Zr(Me)3, Cp2Zr(Me)2 with [[triple bond]SiO-B(C6F5)3](-)[HNEt2Ph]+, 6, leads to a unique species [([triple bond]SiO)B(C6F5)3](-)[Cp*Zr(Me)2.NEt2Ph]+, 7, and [([triple bond]SiO)ZrCp2](+)[(Me)B(C6F5)3]-, 9 respectively. The complexes 4 and 7 are active catalysts in ethylene polymerization at room temperature, 93 and 67 kg PE mol Zr1- atm(-1) bar(-1), respectively, indicating that covalently bounded Zr catalyst 4 is slightly more active than the "floating" cationic catalyst 7.     

Preparation, structures and some reactions of novel diynyl complexes of iron and ruthenium

Reactions between HC triple bond CC triple bond CSiMe3 and several ruthenium halide precursors have given the complexes Ru(C triple bond CC triple bond CSiMe3)(L2)Cp'[Cp'= Cp, L = CO (1), PPh3 (2); Cp' = Cp*, L2= dppe (3)]. Proto-desilylation of 2 and 3 have given unsubstituted buta-1,3-diyn-1-yl complexes Ru(C triple bond CC triple bond CH)(L2)Cp'[Cp'= Cp, L = PPh3 (5); Cp'= Cp*, L2 = dppe (6)]. Replacement of H in 5 or 6 with Au(PR3) groups was achieved in reactions with AuCl(PR3) in the presence of KN(SiMe3)2 to give Ru(C triple bond CC triple bond CAu(PR3)](L2)Cp'[Cp' = Cp, L = PPh3, R = Ph (7); Cp' = Cp*, L2= dppe, R = Ph (8), tol (9)]. The asymmetrically end-capped [Cp(Ph3P)2Ru]C triple bond CC triple bond C[Ru(dppe)Cp*] (10) was obtained from Ru(C triple bond CC triple bond CH)(dppe)Cp* and RuCl(PPh3)2Cp. Single-crystal X-ray structural determinations of and are reported, with a comparative determination of the structure of Fe(C triple bond CC triple bond CSiMe3)(dppe)Cp* (4), and those of a fifth polymorph of [Ru(PPh3)2Cp]2(mu-C triple bond CC triple bond C) (12), and [Ru(dppe)Cp]2(mu-C triple bond CC triple bond C) (13).     

Selective C-C bond formation between alkynes mediated by the [RuCp(PR)(3)](+) fragment leading to allyl,butadienyl, and allenyl carbene complexes--an experimental and theoretical study

The reaction of alkynes with [RuCp(PR(3))(CH(3)CN)(2)]PF(6) (R=Me, Ph, Cy) affords, depending on the structure of the alkyne and the substituent of the phosphine ligand, allyl carbene or butadienyl carbene complexes. These reactions involve the migration of the phosphine ligand or a facile 1,2 hydrogen shift. Both reactions proceed via a metallacyclopentatriene complex. If no alpha C[bond]H bonds are accessible, allyl carbenes are formed, while in the presence of alpha C[bond]H bonds butadienyl carbenes are typically obtained. With diphenylacetylene, on the other hand, a cyclobutadiene complex is formed. A different reaction pathway is encountered with HC[triple bond]CSiMe(3), ethynylferrocene (HC[triple bond]CFc), and ethynylruthenocene (HC[triple bond]CRc). Whereas the reaction of [RuCp(PR(3))(CH(3)CN)(2)]PF(6) (R=Ph and Cy) with HC[triple bond]CSiMe(3) affords a vinylidene complex, with HC[triple bond]CFc and HC[triple bond]CRc this reaction does not stop at the vinylidene stage but subsequent cycloaddition yields allenyl carbene complexes. This latter C[bond]C bond formation is effected by strong electronic coupling of the metallocene moiety with the conjugated allenyl carbene unit, which facilitates transient vinylidene formation with subsequent alkyne insertion into the Ru[double bond]C bond. The vinylidene intermediate appears only in the presence of bulky substituents of the phosphine coligand. For the small R=Me, head-to-tail coupling between two alkyne molecules involving phosphine migration is preferred, giving the more usual allyl carbene complexes. X-ray structures of representative complexes are presented. A reasonable mechanism for the formation of both allyl and allenyl carbenes has been established by means of DFT calculations. During the formation of allyl and allenyl carbenes, metallacyclopentatriene and vinylidene complexes, respectively, are crucial intermediates.     

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.     

Efficient, high-yield route to long, functionalized p-phenylene oligomers containing perfluorinated segments, and their cyclodimerizations by zirconocene coupling

Linear oligophenylene diynes containing 6, 9, and 12 phenylene rings were synthesized in high yields using the nucleophilic aromatic substitution (S(N)Ar) of perfluoroarenes by aryllithium reagents as the key carbon-carbon bond-forming reaction. This reaction was demonstrated to proceed readily at low temperatures with sterically hindered substrates and in the presence of base-sensitive silylalkynyl groups. Diynes synthesized by this methodology were readily zirconocene-coupled into large dimeric macrocycles using the zirconocene reagent Cp(2)Zr(py)(Me(3)SiC triple bond CSiMe(3)).     

Synthetic and computational studies of the palladium(iv) system Pd(alkyl)(aryl)(alkynyl)(bidentate)(triflate) exhibiting selectivity in C-C reductive elimination

Synthetic routes to methyl(aryl)alkynylpalladium(iv) motifs are presented, together with studies of selectivity in carbon-carbon coupling by reductive elimination from Pd(IV) centres. The iodonium reagents IPh(C[triple bond, length as m-dash]CR)(OTf) (R = SiMe(3), Bu(t), OTf = O(3)SCF(3)) oxidise Pd(II)Me(p-Tol)(L(2)) (1-3) [L(2) = 1,2-bis(dimethylphosphino)ethane (dmpe) (1), 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3)] in acetone-d(6) or toluene-d(9) at -80 °C to form complexes Pd(IV)(OTf)Me(p-Tol)(C[triple bond, length as m-dash]CR)(L(2)) [R = SiMe(3), L(2) = dmpe (4), bpy (5), phen (6); R = Bu(t), L(2) = dmpe (7), bpy (8), phen (9)] which reductively eliminate predominantly (>90%) p-Tol-C[triple bond, length as m-dash]CR above ～-50 °C. NMR spectra show that isomeric mixtures are present for the Pd(IV) complexes: three for dmpe complexes (4, 7), and two for bpy and phen complexes (5, 6, 8, 9), with reversible reduction in the number of isomers to two occurring between -80 °C and -60 °C observed for the dmpe complex 4 in toluene-d(8). Kinetic data for reductive elimination from Pd(IV)(OTf)Me(p-Tol)(C[triple bond, length as m-dash]CSiMe(3))(dmpe) (4) yield similar activation parameters in acetone-d(6) (66 ± 2 kJ mol(-1), ΔH(?) 64 ± 2 kJ mol(-1), ΔS(?)-67 ± 2 J K(-1) mol(-1)) and toluene-d(8) (E(a) 68 ± 3 kJ mol(-1), ΔH(?) 66 ± 3 kJ mol(-1), ΔS(?)-74 ± 3 J K(-1) mol(-1)). The reaction rate in acetone-d(6) is unaffected by addition of sodium triflate, indicative of reductive elimination without prior dissociation of triflate. DFT computational studies at the B97-D level show that the energy difference between the three isomers of 4 is small (12.6 kJ mol(-1)), and is similar to the energy difference encompassing the six potential transition state structures from these isomers leading to three feasible C-C coupling products (13.0 kJ mol(-1)). The calculations are supportive of reductive elimination occurring directly from two of the three NMR observed isomers of 4, involving lower activation energies to form p-TolC[triple bond, length as m-dash]CSiMe(3) and earlier transition states than for other products, and involving coupling of carbon atoms with higher s character of σ-bonds (sp(2) for p-Tol, sp for C[triple bond, length as m-dash]C-SiMe(3)) to form the product with the strongest C-C bond energy of the potential coupling products. Reductive elimination occurs predominantly from the isomer with Me(3)SiC[triple bond, length as m-dash]C trans to OTf. Crystal structure analyses are presented for Pd(II)Me(p-Tol)(dmpe) (1), Pd(II)Me(p-Tol)(bpy) (2), and the acetonyl complex Pd(II)Me(CH(2)COMe)(bpy) (11).     

Luminescent hepta- and tetradecanuclear complexes of 5,5'-diethynyl-2,2'-bipyridine capped with triangular trinuclear Cu3/Ag3 cluster units

Heteroheptanuclear ReM6 (M = Cu 2, Ag 3) complexes of 5,5-diethynyl-2,2'-bipyridine were prepared by the reaction of [M2(mu-dppm)2(MeCN)2]2+ (dppm = bis(diphenylphosphino)methane) with the precursor compound Re(Me3SiC[triple bond]CbpyC[triple bond]CSiMe3)(CO)3Cl in the presence of potassium fluoride by fluoride-catalyzed desilylation. When [Cu2(mu-dppm)2(MeCN)2]2+ reacts directly with Me3SiC[triple bond]CbpyC[triple bond]CSiMe3, a binuclear CuI complex [Cu2(mu-dppm)2(SiMe3C[triple bond]CbpyC[triple bond]CSiMe3)2]2+ (4) was isolated. Further addition of [Cu2(mu-dppm)2(MeCN)2]2+ into a THF-MeOH (3:1, v/v) solution of 4 in the presence of potassium fluoride induced isolation of a tetradecanuclear CuI14 complex [Cu14(mu-dppm)14(C[triple bond]CbpyC[triple bond]C)2]10+, which is composed of a binuclear Cu2(mu-dppm)2 and four triangular trinuclear Cu3 units. Both heteroheptanuclear ReIMI6 and tetradecanuclear CuI14 complexes display luminescence in both solid states and dichloromethane solutions at room temperature with emissive lifetimes in the range of microseconds. The dual emissive feature for the ReM6 and CuI14 complexes is ascribed tentatively to originate from both MLCT [d(Re/Cu) -->pi* (bpy)] and LMCT (acetylide --> M3) transitions. .     

Catalytic coupling of terminal alkynes with isonitriles promoted by organoactinide complexes

The coupling reaction of terminal alkynes and tert-butylisonitrile to yield substituted alpha,beta-acetylenic aldimines is catalyzed by the organoactinide neutral complexes Cp*2AnMe2 (Cp* = C5Me5, An = Th, U) and the cationic complex [(Et2N)3U][BPh4]. The reaction proceeds by a 1,1-insertion of the isonitrile into the metal-acetylide bond. Additional insertion products can be obtained by altering the catalyst and the reactant ratios. A plausible mechanism for the catalytic reaction is presented, in addition to the crystal structure of Cp*2UMe2     

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.     

(N-pyrrolyl)B(C6F5)2--a new organometallic Lewis acid for the generation of group 4 metallocene cation complexes

Treatment of the (C6F5)2BF x OEt2 (3) complex with N-pyrrolyl lithium gives bis(pentafluorophenyl)(N-pyrrolyl)borane (2), a strong organometallic Lewis acid, which was characterized by X-ray diffraction (B-N bond length: 1.401(5) A). It exhibits a columnar superstructure in the crystal and contains pi-stacks of pyrrolyl units. Compound 2 readily abstracts alkyl anions from a variety of alkyl Group 4 metallocene-type complexes and leads to the clean formation of the respective metallocene ions or ion pairs. For example, the treatment of Cp3ZrCH3 (9) with 2 transfers a methyl anion to yield the ion pair [Cp3Zr]+[(C4H4N)B(CH3)(C6F5)2]- (12). The X-ray crystal structure analysis of 12 shows a close contact between zirconium and the pyrrolyl-beta-carbon (2.641(2) A). The borane 2 adds to (butadiene)zirconocene (13) to yield the betaine system [Cp2Zr]+[(C4H6)B- (NC4H4)(C6F)2]- (15). Complex 15 contains a distorted eta3-allyl moiety inside the metallacyclic framework and it features an internal Zr+...(pyrrolyl)B- ion pair interaction with a Zr...pyrrolyl-alphacarbon separation of 2.723(3) A (determined by X-ray diffraction). From the dynamic NMR spectra of 15 the bond strength of the internal ion pair interaction was estimated to be deltaGdiss (223 K) approximately = to15 kcalmol(-1). Treatment of dimethylzirconocene (16) with 2 yields the metallocene borate salt [Cp2ZrCH3]+[(C4H4N)B(CH3)(C6F5)2]- (17), which is an active catalyst for the polymerization of ethene.     

Regioselective synthesis of indenols via nickel-catalyzed carbocyclization reaction

2-Halophenyl ketones 1a-e (1a, o-IC(6)H(4)COCH(3)) undergo carbocyclization with alkyl propiolates (2a, CH(3)(CH(2))(4)C[triple bond]CCO(2)CH(3); 2b, TMSC[triple bond]CCO(2)Et 2c, CH(3)C[triple bond]CCO(2)CH(3); 2d, CH(3)OCH(2)C[triple bond]CCO(2)CH(3); 2e, CH(3)(CH(2))(3)C[triple bond]CCO(2)CH(3); 2f, PhC[triple bond]CCO(2)CH(3); and 2g, (CH(3))(3)C[triple bond]CCO(2)CH(3)) in the presence of Ni(dppe)Br(2) and zinc powder in acetonitrile at 80 degrees C to afford the corresponding indenol derivatives 3a-m with remarkable regioselectivity in good to excellent yields. The nickel-catalyzed carbocyclization reaction was successfully extended to other simple disubstituted alkynes. Thus, the reaction of 2-halophenyl ketones 1a-e with disubstituted alkynes (2h, PhC[triple bond]CPh; 2i, CH(3)C(6)H(4)C[triple bond]CC(6)H(4)CH(3); 2j, CH(3)CH(2)C[triple bond]CCH(2)CH(3); 2k, PhC[triple bond]CCH(3); 2l, TMSC[triple bond]CCH(3); and 2m, PhC[triple bond]C(CH(2))(3)CH(3)) proceeded smoothly to afford the corresponding indenols 4a-t in good to excellent yields. For unsymmetrical alkynes 2k-m, the carbocyclization gave two regioisomers with regioselectivities ranging from 1:2 to 1:12 depending on the substituents on the alkyne and on the aromatic ring of halophenyl ketone. A possible mechanism for this nickel-catalyzed carbocyclization reaction is also proposed.     

Synthetic and structural studies on C-ethynyl- and C-bromo-carboranes

A high-yield preparation of the C-monoethynyl para-carborane, 1-Me(3)SiC[triple bond]C-1,12-C2B10H11, from C-monocopper para-carborane and 1-bromo-2-(trimethylsilyl)ethyne, BrC[triple bond]CSiMe(3) is reported. The low-yield preparation of 1,12-(Me3SiC[triple bond]C)2-1,12-C2B10H10 from the C,C'-dicopper para-carborane derivative with 1-bromo-2-(trimethylsilyl)ethyne, BrC[triple bond]CSiMe3, has been re-investigated and other products were identified including the C-monoethynyl-carborane 1-Me3SiC[triple bond]C-1,12-C2B10H11 and two-cage assemblies generated from cage-cage couplings. The contrast in the yields of the monoethynyl and diethynyl products is due to the highly unfavourable coupling process between 1-RC[triple bond]C-12-Cu-1,12-C2B10H10 and the bromoalkyne. The ethynyl group at the cage carbon C(1) strongly influences the chemical reactivity of the cage carbon at C(12)-the first example of the "antipodal effect" affecting the syntheses of para-carborane derivatives. New two-step preparations of 1-ethynyl- and 1,12-bis(ethynyl)-para-carboranes have been developed using a more readily prepared bromoethyne, 1-bromo-3-methyl-1-butyn-3-ol, BrC[triple bond]CCMe2OH. The molecular structures of the two C-monoethynyl-carboranes, 1-RC[triple bond]C-1,12-C2B10H11 (R = H and Me3Si), were experimentally determined using gas-phase electron diffraction (GED). For R = H (R(G) = 0.053) a model with C(5v) symmetry refined to give a C[triple bond]C bond distance of 1.233(5) A. For R = Me3Si (R(G) = 0.048) a model with C(s) symmetry refined to give a C[triple bond]C bond distance of 1.227(5) A. Molecular structures of 1,12-Br2-1,12-C2B10H10, 1-HC[triple bond]C-12-Br-1,12-C2B10H10 and 1,12-(Me(3)SiC[triple bond]C)2-1,12-C2B10H10 were determined by X-ray crystallography. Substituents at the cage carbon atoms on the C2B10 cage skeleton in 1-X-12-Y-1,12-C2B10H10 derivatives invariably lengthen the cage C-B bonds. However, the subtle substituent effects on the tropical B-B bond lengths in these compounds are more complex. The molecular structures of the ethynyl-ortho-carborane, 1-HC[triple bond]C-1,2-C2B10H11 and the ethene, trans-Me3SiBrC=CSiMe3Br are also reported.     

The structure and chemistry of tris(pentafluorophenyl)borane protected mononuclear nitridotitanium complexes

Treatment of TiCl(NMe(2))(3) with H(3)N·B(C(6)F(5))(3) results in N-H activation and ligand exchange to yield the structurally characterised salt [TiCl(NMe(2))(2)(NMe(2)H)(2)](+)[Ti[triple bond]NB(C(6)F(5))(3)(Cl)(2)(NMe(2)H)(2)](-). Cation exchange with [Me(4)N]Cl, [Ph(4)P]Cl and [(PhCH(2))Ph(3)P]Cl yields the respective ammonium and phosphonium salts of the [Ti[triple bond]NB(C(6)F(5))(3)(Cl)(2)(NMe(2)H)(2)](-) anion. X-ray crystallography reveals that the essential trigonal bipyramidal geometry and composition of the anion is retained in each of these salts despite some minor variations in the Ti-N-B angle and the nature of the interionic interactions. Electronic investigation by DFT calculations confirmed the Ti-N triple bond character implied by the experimentally determined bond length, with the HOMO and HOMO-1 having Ti-N π-bonding character. The dimethylamine ligands of the anion resist substitution by moderate bases but can be displaced by pyridine to give a pentacoordinate anion. In contrast, addition of 2,2'-bipyridyl gives a neutral octahedral complex. Treatment of the pyridine complex with TlCp results in the formation of a four coordinate anionic cyclopentadienyl complex.     

Coupling reaction of zirconacyclopentadienes with dihalonaphthalenes and dihalopyridines: a new procedure for the preparation of substituted anthracenes, quinolines, and isoquinolines.

Reactions of tetraiodobenzene with zirconacyclopentadienes, which were conveniently prepared from two alkynes (or diynes) and zirconocene complexes, afforded 1,2,3,4-tetrasubstituted diiodonaphthalene derivatives in good isolated yields. These 1,2,3,4-tetrasubstituted diiodonaphthalene derivatives could be converted to 1,2,3,4,5,6,7,8-octasubstituted anthracene derivatives by reaction with a second zirconacyclopentadiene. When the two zirconacyclopentadienes were different, unsymmetrical anthracenes such as 1,2,3,4-tetraethyl-5,6,7,8-tetraphenylanthracene (68% isolated yield) were obtained. On the other hand, treatment of a 2,3-dihalopyridine such as 2-bromo-3-iodopyridine with zirconacyclopentadienes gave 5,6,7,8-tetrasubstituted quinoline derivatives in good to high yields. 3,4-dihalopyridines such as 4-chloro-3-iodopyridine reacted with zirconacyclopentadienes to afford 5,6,7,8-tetrasubstituted isoquinoline derivatives in good to high yields.     

Living photolytic ring-opening polymerization of amino-functionalized [1]ferrocenophanes: synthesis and layer-by-layer self-assembly of well-defined water-soluble polyferrocenylsilane polyelectrolytes

Facile synthetic routes have been developed that provide access to cationic and anionic water-soluble polyferrocenylsilane (PFS) polyelectrolytes with controlled molecular weight and narrow polydispersity. Living photolytic ring-opening polymerization of amino-functionalized [1]ferrocenophane (fc) monomers [fcSiMe{C[triple chemical bond]CCH(2)N(SiMe(2)CH(2))(2)}] (3), [fcSi{C[triple chemical bond]CCH(2)N(SiMe(2)CH(2))(2)}(2)] (10), [fcSiMe(C[triple chemical bond]CCH(2)NMe(2))] (14), and [fcSiMe(p-C(6)H(4)CH(2)NMe(2))] (20) yielded the corresponding polyferrocenylsilanes [(fcSiMe{C[triple chemical bond]CCH(2)N(SiMe(2)CH(2))(2)})(n)](5), [(fcSi{C[triple chemical bond]CCH(2)N(SiMe(2)CH(2))(2)}(2))(n)] (11), [{fcSiMe(C[triple chemical bond]CCH(2)NMe(2))}(n)] (15), and [{fcSiMe(p-C(6)H(4)CH(2)NMe(2))}(n)] (21) with controlled architectures. Further derivatization of 5, 15, and 21 generated water-soluble polyelectrolytes [(fcSiMe{C[triple chemical bond]CCH(2)N(CH(2)CH(2)CH(2)SO(3)Na)(2)})(n)] (6), [{fcSiMe(C[triple chemical bond]CCH(2)NMe(3)OSO(3)Me)}(n)] (7), and [{fcSiMe(p-C(6)H(4)CH(2)NMe(3)OSO(3)Me)}(n)] (22), respectively. The polyelectrolytes were readily soluble in water and NaCl aqueous solutions, with 6 and 22 exhibiting long-term stability in aqueous media. The PFS materials 6 and 22, have been utilized in the layer-by-layer (LbL) self-assembly of electrostatic superlattices. Our preliminary studies have indicated that films made from controlled low molecular-weight PFSs possess a considerably thinner bilayer thickness and higher refractive index than those made from PFSs that have an uncontrolled high molecular-weight. These results suggest that the structure and optical properties of LbL ultra-thin films can be tuned by varying polyelectrolyte chain length. The water-soluble low molecular weight PFSs are also useful materials for a range of applications including LbL self-assembly in highly confined spaces.     

Insertion reactions of alkynes and organic isocyanides into the palladium-carbon bond of dimetallic Fe-Pd alkoxysilyl complexes

Insertion of MeO(2)C-C[triple bond]C-CO(2)Me (DMAD) into the Pd-C bond of the heterodimetallic complex [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d(dmba-C)] (2) (dppm = Ph(2)PCH(2)PPh(2), dmba-C = metallated dimethylbenzylamine) and [(OC)(3){(MeO)(3)Si}F[upper bond 1 start]e(mu-dppm)P[upper bond 1 end]d(8-mq-C,N)] (3) (8-mq-C,N = cyclometallated 8-methylquinoline) yielded the sigma-alkenyl complexes [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{C(CO(2)Me)=C(CO(2)Me)(o-C(6)H(4)CH(2)NMe(2))}] (7) and [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{C(CO(2)Me)[double bond, length as m-dash]C(CO(2)Me)(CH(2)C(9)H(6)N)}] (8), respectively. The latter afforded the adduct [(OC)(3){(MeO)(3)Si}F[upper bond 1 start]e(mu-dppm)P[upper bond 1 end]d{C(CO(2)Me)=C(CO(2)Me)(CH(2)C(9)H(6)N)}(CNBu(t))] (9) upon reaction with 1 equiv. of Bu(t)NC. The heterodinuclear sigma-butadienyl complexes [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{C(Ph=C(Ph)C(CO(2)Me)=(CO(2)Me)(o-C(6)H(4)CH(2)NMe(2))}] (11) and [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{C(Ph)=C(CO(2)Et)C(Ph)=C(CO(2)Et)(CH(2)C(9)H(6)N)}] (13) have been obtained by reaction of the metallate K[Fe{Si(OMe)(3)}(CO)(3)(dppm-P)] (dppm = Ph(2)PCH(2)PPh(2)) with [P[upper bond 1 start]dCl{C(Ph)=C(Ph)C(CO(2)Me)=C(CO(2)Me)(o-C(6)H(4)CH(2)N[upper bond 1 end]Me(2))}] or [P[upper bond 1 start]dCl{C(Ph)=C(CO(2)Et)C(Ph)=(CO(2)Et)}(CH(2)C(9)H(6)N[upper bond 1 end])], respectively. Monoinsertion of various organic isocyanides RNC into the Pd-C bond of 2 and 3 afforded the corresponding heterometallic iminoacyl complexes. In the case of complexes [(OC)(3){(MeO)(3)Si}F[upper bond 1 start]e(mu-dppm)P[upper bond 1 end][upper bond 1 start]d{C=(NR)(CH(2)C(9)H(6)N[upper bond 1 end])}] (15a R = Ph, 15b R = xylyl), a static six-membered C,N chelate is formed at the Pd centre, in contrast to the situation in [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{C(=NR)(o-C(6)H(4)CH(2)NMe(2))}] (14a R = o-anisyl, 14b R = 2,6-xylyl) where formation of a mu-eta(2)-Si-O bridge is preferred over NMe(2) coordination. The outcome of the reaction of the dimetallic alkyl complex [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]dMe] with RNC depends both on the stoichiometry and the electronic donor properties of the isocyanide employed for the migratory insertion process. In the case of o-anisylisocyanide, the iminoacyl complex [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{C(=N-o-anisyl)Me}] (16) results from the reaction in a 1 : 1 ratio. Addition of three equiv. of o-anisylisocyanide affords the tris(insertion) product [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{[C(=N-o-anisyl)](3)Me}] (18). After addition of a fourth equivalent of o-anisylNC, exclusive formation of the isocyanide adduct [(OC)(3){(MeO)(3)Si}F[upper bond 1 start]e(mu-dppm)P[upper bond 1 end]d{[C(=N-o-anisyl)](3)Me}(CN-o-anisyl)] (19) was spectroscopically evidenced. In the complex [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]d{[C(=N-o-C(6)H(4)COCH(2))](2)Me}] (20), the sigma-bound diazabutadienyl unit is part of a 12-membered organic macrocyle which results from bis(insertion) of 1,2-bis(2-isocyanophenoxy)ethane into the Pd-Me bond of the precursor complex [(OC)(3)F[upper bond 1 start]e{mu-Si(OMe)(2)([lower bond 1 start]OMe)}(mu-dppm)P[lower bond 1 end][upper bond 1 end]dMe]. In contrast, addition of two equivalents of tert-butylisocyanide to a solution of the latter afforded [(OC)(3){(MeO)(3)Si}F[upper bond 1 start]Fe(mu-dppm)P[upper bond 1 end]d{C(=NBu(t))Me}(CNBu(t))] (21) in which both a terminal and an inserted isocyanide ligand are coordinated to the Pd centre. In all cases, there was no evidence for competing CO substitution at the Fe(CO)(3) fragment by RNC. The molecular structures of the insertion products 8 x CH(2)Cl(2) and 16 x CH(2)Cl(2) have been determined by X-ray diffraction.     

Mixed-transition-metal acetylides: synthesis and characterization of complexes with up to six different transition metals connected by carbon-rich bridging units

The synthesis and reaction chemistry of heteromultimetallic transition-metal complexes by linking diverse metal-complex building blocks with multifunctional carbon-rich alkynyl-, benzene-, and bipyridyl-based bridging units is discussed. In context with this background, the preparation of [1-{(eta(2)-dppf)(eta(5)-C(5)H(5))RuC[triple bond]C}-3-{(tBu(2)bpy)(CO)(3)ReC[triple bond]C}-5-(PPh(2))C(6)H(3)] (10) (dppf = 1,1'-bis(diphenylphosphino)ferrocene; tBu(2)bpy = 4,4'-di-tert-butyl-2,2'-bipyridyl; Ph = phenyl) is described; this complex can react further, leading to the successful synthesis of heterometallic complexes of higher nuclearity. Heterotetrametallic transition-metal compounds were formed when 10 was reacted with [{(eta(5)-C(5)Me(5))RhCl(2)}(2)] (18), [(Et(2)S)(2)PtCl(2)] (20) or [(tht)AuC[triple bond]C-bpy] (24) (Me = methyl; Et = ethyl; tht = tetrahydrothiophene; bpy = 2,2'-bipyridyl-5-yl). Complexes [1-{(eta(2)-dppf)(eta(5)-C(5)H(5))RuC[triple bond]C}-3-{(tBu(2)bpy)(CO)(3)ReC[triple bond]C}-5-{PPh(2)RhCl(2)(eta(5)-C(5)Me(5))}C(6)H(3)] (19), [{1-[(eta(2)-dppf)(eta(5)-C(5)H(5))RuC[triple bond]C]-3-[(tBu(2)bpy)(CO)(3)ReC[triple bond]C]-5-(PPh(2))C(6)H(3)}(2)PtCl(2)] (21), and [1-{(eta(2)-dppf)(eta(5)-C(5)H(5))RuC[triple bond]C}-3-{(tBu(2)bpy)(CO)(3)ReC[triple bond]C}-5-{PPh(2)AuC[triple bond]C-bpy}C(6)H(3)] (25) were thereby obtained in good yield. After a prolonged time in solution, complex 25 undergoes a transmetallation reaction to produce [(tBu(2)bpy)(CO)(3)ReC[triple bond]C-bpy] (26). Moreover, the bipyridyl building block in 25 allowed the synthesis of Fe-Ru-Re-Au-Mo- (28) and Fe-Ru-Re-Au-Cu-Ti-based (30) assemblies on addition of [(nbd)Mo(CO)(4)] (27), (nbd = 1,5-norbornadiene), or [{[Ti](mu-sigma,pi-C[triple bond]CSiMe(3))(2)}Cu(N[triple bond]CMe)][PF(6)] (29) ([Ti] = (eta(5)-C(5)H(4)SiMe(3))(2)Ti) to 25. The identities of 5, 6, 8, 10-12, 14-16, 19, 21, 25, 26, 28, and 30 have been confirmed by elemental analysis and IR, (1)H, (13)C{(1)H}, and (31)P{(1)H} NMR spectroscopy. From selected samples ESI-TOF mass spectra were measured. The solid-state structures of 8, 12, 19 and 26 were additionally solved by single-crystal X-ray structure analysis, confirming the structural assignment made from spectroscopy.