d0 Metal Olefin Complexes. Synthesis, Structures, and Dynamic Properties of (C5R5)2Zr(OCMe2CH2CH2CHCH2)+ Complexes: Models for the Elusive (C5R5)2Zr(R)(Olefin)+ Intermediates in Metallocene-Based Olefin Polymerization Catalysis

Alkyne and Alkene Complexes of a d0 Zirconocene Aryl Cation

The generation and properties of nonchelated Zr-aryl-alkyne and Zr-aryl-alkene complexes that are stabilized by the presence of beta-Si-substituents in the alkyne and alkene ligands and fluorination of the aryl ligand are described. Reaction of [Cp'2Zr(OtBu)(ClCD2Cl)][B(C6F5)4] (1, Cp' = C5H4Me) with alkyne and alkene substrates (L) generates Cp'2Zr(OtBu)(L)+ adducts (L = HCCCH2SiMe3 (2); H2C=CHCH2SiMe3 (3); HCCMe (4); H2C=CHCH2CMe3 (5)). Equilibrium constants for substrate binding (Keq = [Zr-L][1]-1[L]-1; CD2Cl2, -89 degrees C) are much larger for the beta-Si-substituted compounds 2 (1.0(2) x 105 M-1) and 3 (1.7(4) x 103 M-1) than for hydrocarbon analogues 4 (3.6(7) x 102 M-1) and 5 (1.9(1) M-1), which is ascribed to beta-Si stabilization of the partial positive charge on Cint of the bound substrate. [Cp2Zr(C6F5)][B(C6F5)4] (7, Cp = C5H5) was generated by the reaction of Cp2Zr(C6F5)Me with [Ph3C][B(C6F5)4] in C6D5Cl. Reaction of 7 with alkyne and alkene substrates (L) generates Cp2Zr(C6F5)(L)+ adducts (L = HCCCH2SiMe3 (8); H2C=CHCH2SiMe3 (10)). No insertion of the substrate into the Zr-C6F5 bond is observed in 8 (at -38 degrees C) or 10 (up to 22 degrees C). The allyltrimethylsilane ligand in 10 undergoes nondissociative alkene face exchange ("alkene flipping", i.e., exchange of the Cp2Zr(C6F5)+ unit between the two alkene enantiofaces without alkene dissociation), with a first-order rate constant kflip = 23(1) s-1 (C6D5Cl, -38 degrees C). 10 also undergoes slower reversible decomplexation of the alkene (kdissoc = 5.0(8) s-1; C6D5Cl, -38 degrees C).

Alkyl–η2-alkene niobocene and tantalocene complexes with the allyldimethylsilyl–η5-cyclopentadienyl ligand: synthesis, NMR studies and DFT calculations

Group 5 metal complexes [M(eta5-C5H5)[eta5-C5H4SiMe2(CH2-eta]2-CH=CH2)]X] (M = Nb, X = Me, CH2Ph, CH2SiMe3; M = Ta, X = Me, CH2Ph) and [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2-eta2-CH=CH2)]X] (X = Cl, Me, CH2Ph, CH2SiMe3) containing a chelating alkene ligand tethered to a cyclopentadienyl ring have been synthesized in high yields by reduction with Na/Hg (X = Cl) and alkylation with reductive elimination (X = alkyl) of the corresponding metal(iv) dichlorides [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]Cl2] (Cp = C5H5, M = Nb, Ta, Cp = C5Me5, M = Ta). These chloro- and alkyl-alkene coordinated complexes react with CO and isocyanides [CNtBu, CN(2,6-Me2C6H3)] to give the ligand-substituted metal(III) compounds [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]XL] (X = Cl, Me, CH2Ph, CH2SiMe3). Reaction of the chloro-alkene tantalum complex with LiNHtBu results in formation of the imido hydride derivative [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2CH=CH2)]H(NtBu)]. NMR studies for all of the new compounds and DFT calculations for the alkene-coordinated metal complexes are compared with those known for related group 4 metal cations.

Tethered olefin studies of alkene versus tetraphenylborate coordination and lanthanide olefin interactions in metallocenes

The tethered olefin cyclopentadienyl ligand, [(C(5)Me(4))SiMe(2)(CH(2)CH=CH(2))](-), forms unsolvated metallocenes, [(C(5)Me(4))SiMe(2)(CH(2)CH=CH(2))](2)Ln (Ln = Sm, 1; Eu, 2; Yb, 3), from [(C(5)Me(4))SiMe(2)(CH(2)CH=CH(2))]K and LnI(2)(THF)(2) in good yield. Each complex in the solid state has both tethered olefins oriented toward the Ln metal center with the Ln-C(terminal alkene carbon) distances 0.2-0.3 A shorter than the Ln-C(internal alkene carbon) distances. The olefinic C-C bond distances in 2 and 3, 1.328(4) and 1.328(5) A, respectively, are normal. Like its permethyl analogue, (C(5)Me(5))(2)Sm(THF)(2), complex 1 reductively couples CO(2) to form the oxalate-bridged dimer [[(C(5)Me(4))SiMe(2)(CH(2)CH=CH(2))](2)Sm](2)(mu-eta(2):eta(2)-O(2)CCO(2)), 4, in which the tethered olefins are noninteracting substituents. Complex 1 reacts with AgBPh(4) to form an unsolvated cation that has the option of coordinating [BPh(4)](-) or a pendant olefin, a competition common in olefin polymerization catalysis. The structure of [[(C(5)Me(4))SiMe(2)(CH(2)CH=CH(2))](2)Sm][BPh(4)], 5, shows that both pendant olefins are located near samarium rather than the [BPh(4)](-) counterion.

Reaction of vinyl chloride with late transition metal olefin polymerization catalysts

The reactions of vinyl chloride (VC) with representative late metal, single-site olefin dimerization and polymerization catalysts have been investigated. VC coordinates more weakly than ethylene or propylene to the simple catalyst (Me(2)bipy)PdMe(+) (Me(2)bipy = 4,4'-Me(2)-2,2'-bipyridine). Insertion rates of (Me(2)bipy)Pd(Me)(olefin)(+) species vary in the order VC > ethylene > propylene. The VC complexes (Me(2)bipy)Pd(Me)(VC)(+) and (alpha-diimine)Pd(Me)(VC)(+) (alpha-diimine = (2,6-(i)Pr(2)[bond]C(6)H(3))N[double bond]CMeCMe[double bond]N(2,6-(i)Pr(2)[bond]C(6)H(3))) undergo net 1,2 VC insertion and beta-Cl elimination to yield Pd[bond]Cl species and propylene. Analogous chemistry occurs for (pyridine-bisimine)MCl(2)/MAO catalysts (M = Fe, Co; pyridine-bisimine = 2,6-[(2,6-(i)Pr(2)[bond]C(6)H(3))N[double bond]CMe](2)-pyridine) and for neutral (sal)Ni(Ph)PPh(3) and (P[bond]O)Ni(Ph)PPh(3) catalysts (sal = 2-[C(H)[double bond]N(2,6-(i)Pr(2)-C(6)H(3))]-6-Ph-phenoxide; P[bond]O = [Ph(2)PC(SO(3)Na)[double bond]C(p-tol)O]), although the initial metal alkyl VC adducts were not detected in these cases. These results show that the L(n)MCH(2)CHClR species formed by VC insertion into the active species of late metal olefin polymerization catalysts undergo rapid beta-Cl elimination which precludes VC polymerization. Termination of chain growth by beta-Cl elimination is the most significant obstacle to metal-catalyzed insertion polymerization of VC.

Coordination of alkenes and alkynes to a cationic d(0) zirconocene alkoxide complex

This paper describes the synthesis of base-free (C5R5)2Zr(OtBu)+ cations, the direct observation of nonchelated alkene and alkyne adducts of these cations, and studies of the thermodynamic and dynamic properties of these novel species. Reaction of %@mt;sys@%Cp%@/xs;55;%lnwidth@%'%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%2%@sbx@%%@/hd@%ZrMe%@sb@%2%@sbx@%%@mx@% (Cp' = C5H4Me) with tert-butyl alcohol followed by [Ph3C][B(C6F5)4] in benzene yields [%@mt;sys@%Cp%@/xs;55;%lnwidth@%'%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%2%@sbx@%%@/hd@%Zr%@/hd@%%@fn;(;vis;full;auto@%O%@ital@%%@ex@%t%@rsf@%%@exx@%%@/hd@%Bu%@fnx;);vis;full@%%@/hd@%%@mx@% ][B(C6F5)4] (1), which exists as %@mt;sys@%Cp%@/xs;55;%lnwidth@%'%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%2%@sbx@%%@/hd@%Zr%@/hd@%%@fn;(;vis;full;auto@%O%@ital@%%@ex@%t%@rsf@%%@exx@%%@/hd@%Bu%@fnx;);vis;full@%%@/hd@%%@fn;(;vis;full;auto@%ClR%@fnx;);vis;full@%%@ex@%+%@exx@%%@mx@% solvent adducts in C6D5Cl and CD2Cl2 solutions. Addition of ligands L (L = ethylene, propylene, propyne, 2-butyne, CO, phenylacetylene, allene, 1-hexene, cis-2-butene) to 1 in CD2Cl2 at -89 degrees C results in reversible formation of %@mt;sys@%Cp%@/xs;55;%lnwidth@%'%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%2%@sbx@%%@/hd@%Zr%@/hd@%%@fn;(;vis;full;auto@%O%@ital@%%@ex@%t%@rsf@%%@exx@%%@/hd@%Bu%@fnx;);vis;full@%%@/hd@%%@fn;(;vis;full;auto@%L%@fnx;);vis;full@%%@ex@%+%@exx@%%@mx@% adducts. NMR data for %@mt;sys@%Cp%@/xs;55;%lnwidth@%'%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%2%@sbx@%%@/hd@%Zr%@/hd@%%@fn;(;vis;full;auto@%O%@ital@%%@ex@%t%@rsf@%%@exx@%%@/hd@%Bu%@fnx;);vis;full@%%@/hd@%%@fn;(;vis;full;auto@%H%@sb@%2%@sbx@%C=%@/bd@%CHMe%@fnx;);vis;full@%%@ex@%+%@exx@%%@mx@% (4) indicate that the propylene coordinates unsymmetrically and is polarized with positive charge buildup at Cint. Equilibrium constants, defined by Keq = [Zr-L][1]-1[L]-1, vary in the order CO > propyne > 2-butyne > phenylacetylene > ethylene > allene > propylene > 1-hexene > cis-2-butene > vinyl chloride. Loss of L from %@mt;sys@%Cp%@/xs;55;%lnwidth@%'%@/xs;63;(%lnwidth-x55)@%%@mh;-x63@%%@sb@%2%@sbx@%%@/hd@%Zr%@/hd@%%@fn;(;vis;full;auto@%O%@ital@%%@ex@%t%@rsf@%%@exx@%%@/hd@%Bu%@fnx;);vis;full@%%@/hd@%%@fn;(;vis;full;auto@%L%@fnx;);vis;full@%%@ex@%+%@exx@%%@mx@% to give 1 appears to proceed via associative displacement by CD2Cl2 in most cases.

Reaction of vinyl chloride with group 4 metal olefin polymerization catalysts

The reactions of three types of group 4 metal olefin polymerization catalysts, (C(5)R(5))(2)ZrX(2)/activator, (C(5)Me(5))TiX(3)/MAO (MAO = methylalumoxane), and (C(5)Me(4)SiMe(2)N(t)Bu)MX(2)/activator (M = Ti, Zr), with vinyl chloride (VC) and VC/propylene mixtures have been investigated. Two general pathways are observed: (i) radical polymerization of VC initiated by radicals derived from the catalyst and (ii) net 1,2 VC insertion into L(n)MR(+) species followed by beta-Cl elimination. rac-(EBI)ZrMe(mu-Me)B(C(6)F(5))(3) (EBI = 1,2-ethylenebis(indenyl)) reacts with 2 equiv of VC to yield oligopropylene, rac-(EBI)ZrCl(2), and B(C(6)F(5))(3). This reaction proceeds by net 1,2 VC insertion into rac-(EBI)ZrMe(+) followed by fast beta-Cl elimination to yield [rac-(EBI)ZrCl][MeB(C(6)F(5))(3)] and propylene. Methylation of rac-(EBI)ZrCl(+) by MeB(C(6)F(5))(3)(-) enables a second VC insertion/beta-Cl elimination to occur. The evolved propylene is oligomerized by rac-(EBI)ZrR(+) as it is formed. At high Al/Zr ratios, rac-(EBI)ZrMe(2)/MAO catalytically converts VC to oligopropylene by 1,2 VC insertion into rac-(EBI)ZrMe(+), beta-Cl elimination, and realkylation of rac-(EBI)ZrCl(+) by MAO; this process is stoichiometric in Al-Me groups. The evolved propylene is oligomerized by rac-(EBI)ZrR(+). Oligopropylene end group analysis shows that the predominant chain transfer mechanism is VC insertion/beta-Cl elimination/realkylation. In the presence of trace levels of O(2), rac-(EBI)ZrMe(2)/MAO polymerizes VC to poly(vinyl chloride) (PVC) by a radical mechanism initiated by radicals generated by autoxidation of Zr-R and/or Al-R species. CpTiX(3)/MAO (Cp = C(5)Me(5); X = OMe, Cl) initiates radical polymerization of VC in CH(2)Cl(2) solvent at low Al/Ti ratios under anaerobic conditions; in this case, the source of initiating radicals is unknown. Radical VC polymerization can be identified by the presence of terminal and internal allylic chloride units and other "radical defects" in the PVC which arise from the characteristic chemistry of PCH(2)CHCl(*) macroradicals. However, this test must be used with caution, since the defect units can be consumed by postpolymerization reactions with MAO. (C(5)Me(4)SiMe(2)N(t)Bu)MMe(2)/[Ph(3)C]][B(C(6)F(5))(4)] catalysts (M = Ti, Zr) react with VC by net 1,2 insertion/beta-Cl elimination, yielding [(C(5)Me(4)SiMe(2)N(t)Bu)MCl][B(C(6)F(5))(4)] species which can be trapped as (C(5)Me(4)SiMe(2)N(t)Bu)MCl(2) by addition of a chloride source. The reaction of rac-(EBI)ZrMe(2)/MAO or [(C(5)Me(4)SiMe(2)N(t)Bu)ZrMe][B(C(6)F(5))(4)] with propylene/VC mixtures yields polypropylene containing both allylic and vinylidene unsaturated chain ends rather than strictly vinylidene chain ends, as observed in propylene homopolymerization. These results show that the VC insertion of L(n)M(CH(2)CHMe)(n)R(+) species is also followed by beta-Cl elimination, which terminates chain growth and precludes propylene/VC copolymerization. Termination of chain growth by beta-Cl elimination is the most significant obstacle to metal-catalyzed insertion polymerization/copolymerization of VC.

Chiral Ansa metallocenes with Cp ring-fused to thiophenes and pyrroles: syntheses, crystal structures, and isotactic polypropylene catalysts

Syntheses, crystal structures, and polymerization data for new isospecific metallocenes (heterocenes) having cyclopentenyl ligands b-fused to substituted thiophenes (Tp) and pyrroles (Pyr) are reported. The C2- and C1-symmetric heterocenes are dimethylsilyl bridged, have methyl groups adjacent to the bridgehead carbon atoms, and have aryl substituents protruding in the front. rac-Me2Si(2,5-Me2-3-Ph-6-Cp[b]Tp)2ZrCl2/MAO (MAO = methyl alumoxanes) is the most active metallocene catalyst for polypropylene reported to date. rac-Me2Si(2,5-Me2-3-Ph-6-Cp[b]Tp)2ZrCl2 and rac-Me2Si(2,5-Me2-1-Ph-4-Cp[b]Pyr)2ZrCl2 have the same structure, and the former is 6 times more active, produces half the total enantiofacial errors, and is 3.5 times less regiospecific in propylene polymerizations at the same conditions. rac-Me2Si(2-Me-4-Ph-1-Ind)2ZrCl2/MAO is 3.5 times lower in activity than rac-Me2Si(2,5-Me2-3-Ph-6-Cp[b]Tp)2ZrCl2 catalyst, and while the former is the more stereospecific and the less regiospecific, the sum of these two enantioface errors is the same for both species. Fine-tuning the heterocene sterics by changing selected hydrogen atoms on the ligands to methyl groups influenced their catalyst activities, stereospecificites, regiospecificites, and isotactic polypropylene (IPP) Mw. Thus, both substituting a hydrogen atom adjacent to the phenyl ring with a methyl group on an azapentalenyl ligand system and replacing one and then two hydrogens on the phenyl ring with methyls on thiopentalenyl ligands provided increased polymer Tm and Mw with increasing ligand bulk. Polymer molecular weights are sensitive to and inversely proportional to MAO concentration, and the catalyst activities increase when hydrogen is added for molecular weight control. The polymer Tm values with the thiopentalenyls as TIBAL/[Ph3C][B(C6F5)4] systems were higher than with MAO as catalyst activator. A racemic C1, pseudo-meso complex with a hybrid dimethylsilyl-bridged 2-Me-4-Ph-1-Ind/2,5-Me2-4-Ph-1-Cp[b]Pyr ligand produced the first sample of IPP with all the steric pentad intensities fitting the enantiomorphic site control model. Speculative mechanistic considerations are offered regarding electronic effects of the heteroatoms and steric effects of the ligand structures, the preferred phenyl torsion angles, and anion effects.

Solution structures and dynamic properties of chelated d(0) metal olefin complexes [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(OCMe(2)CH(2)CH(2)CH=CH(2))(+) (R = H, Me): Models for the [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(R')(olefin)(+) intermediates in "constrained geometry" catalysts

To model the Ti-olefin interaction in the putative [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(R')(olefin)(+) intermediates in "constrained geometry" Ti-catalyzed olefin polymerization, chelated alkoxide olefin complexes [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(OCMe(2)CH(2)CH(2)CH=CH(2))(+) have been investigated. The reaction of [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]TiMe(2) (1a,b; R = H, Me) with HOCMe(2)CH(2)CH(2)CH=CH(2) yields mixtures of [eta(5)-C(5)R(4)SiMe(2)NH(t)Bu]TiMe(2)(OCMe(2)CH(2)CH(2)CH=CH(2)) (2a,b) and [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]TiMe(OCMe(2)CH(2)CH(2)CH=CH(2)) (3a,b). The reaction of 2a/3a and 2b/3b mixtures with B(C(6)F(5))(3) yields the chelated olefin complexes [[eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(OCMe(2)CH(2)CH(2)CH=CH(2))][MeB(C(6)F(5))(3)] (4a,b; 71 and 89% NMR yield). The reaction of 2b/3b with [Ph(3)C][B(C(6)F(5))(4)] yields [[eta(5): eta(1)-C(5)Me(4)SiMe(2)N(t)Bu]Ti(OCMe(2)CH(2)CH(2)CH=CH(2))][B(C(6)F(5))(4)] (5b, 88% NMR yield). NMR studies establish that 4a,b and 5b exist as mixtures of diastereomers (isomer ratios: 4a/4a', 62/38; 4b/4b', 75/25; 5b/5b', 75/25), which differ in the enantioface of the olefin that is coordinated. NMR data for these d(0) metal olefin complexes show that the olefin coordinates to Ti in an unsymmetrical fashion primarily through C(term) such that the C=C pi bond is polarized with positive charge buildup on C(int). Dynamic NMR studies show that 4b/4b' undergoes olefin face exchange by a dissociative mechanism which is accompanied by fast inversion of configuration at Ti ("O-shift") in the olefin-dissociated intermediate. The activation parameters for the conversion of 4b to 4b' (i.e., 4b/4b' face exchange) are: DeltaH = 17.2(8) kcal/mol; DeltaS = 8(1) eu. 4a/4a' also undergoes olefin face exchange but with a lower barrier (DeltaH = 12.2(9) kcal/mol; DeltaS = -2(3) eu), for the conversion of 4a to 4a'.