“…253,254 While a mixture of [(SiO) 2 Ta III H] (188) and [( SiO) 2 Ta V (H) 3 ] ( 189) is observed experimentally, 255 5). 256 [W] s −H (193) also gives a higher percentage of C 3 products (Table 5), similar to [Ta] s −H (192) 62 The catalyst support (silica−alumina, silica) plays an important role in dictating the catalyst's activity for hydrogenolysis. An exemplary study is in Ti−H catalyzed hydrogenolysis of a low-molecular weight paraffin wax (C 20 -C 50 ) at 180 °C.…”
Section: β-Alkyl Elimination By Solid-supported and Homogeneous Catal...mentioning
confidence: 73%
“…However, the ratio of incorporation of 7-methylenebicyclo[4.1.0]heptane into the copolymer is very low. This is particularly evident with catalyst 155 , which has the smallest propensity to incorporate 7-methylenebicyclo[4.1.0]heptane relative to ethylene …”
Section: Ring-opening Polymerization (Rop) Of Strained
Cycloalkanes V...mentioning
confidence: 99%
“…This is particularly evident with catalyst 155, which has the smallest propensity to incorporate 7-methylenebicyclo[4.1.0]heptane relative to ethylene. 192 In contrast to the previous examples, metallocene catalysts 25−27 and 152−159 do not polymerize 2-phenyl-1-methylenecyclopropane (Scheme 56). However, catalysts 26, 155, 156, and [Cp* 2 YH] 2 (160) are capable of copolymerizing 2phenyl-1-methylenecyclopropane and ethylene.…”
Section: β-Alkyl Elimination From Organoruthenium Complexesmentioning
This review describes organometallic compounds and materials that are capable of mediating a rarely encountered but fundamentally important reaction: β-alkyl elimination at the metal-Cα-Cβ-R moiety, in which an alkyl group attached to the Cβ atom is transferred to the metal or to a coordinated substrate. The objectives of this review are to provide a cohesive fundamental understanding of β-alkyl-elimination reactions and to highlight its applications in olefin polymerization, alkane hydrogenolysis, depolymerization of branched polymers, ring-opening polymerization of cycloalkanes, and other useful organic reactions. To provide a coherent understanding of the β-alkyl elimination reaction, special attention is given to conditions and strategies used to facilitate β-alkyl-elimination/transfer events in metal-catalyzed olefin polymerization, which provide the well-studied examples.
“…253,254 While a mixture of [(SiO) 2 Ta III H] (188) and [( SiO) 2 Ta V (H) 3 ] ( 189) is observed experimentally, 255 5). 256 [W] s −H (193) also gives a higher percentage of C 3 products (Table 5), similar to [Ta] s −H (192) 62 The catalyst support (silica−alumina, silica) plays an important role in dictating the catalyst's activity for hydrogenolysis. An exemplary study is in Ti−H catalyzed hydrogenolysis of a low-molecular weight paraffin wax (C 20 -C 50 ) at 180 °C.…”
Section: β-Alkyl Elimination By Solid-supported and Homogeneous Catal...mentioning
confidence: 73%
“…However, the ratio of incorporation of 7-methylenebicyclo[4.1.0]heptane into the copolymer is very low. This is particularly evident with catalyst 155 , which has the smallest propensity to incorporate 7-methylenebicyclo[4.1.0]heptane relative to ethylene …”
Section: Ring-opening Polymerization (Rop) Of Strained
Cycloalkanes V...mentioning
confidence: 99%
“…This is particularly evident with catalyst 155, which has the smallest propensity to incorporate 7-methylenebicyclo[4.1.0]heptane relative to ethylene. 192 In contrast to the previous examples, metallocene catalysts 25−27 and 152−159 do not polymerize 2-phenyl-1-methylenecyclopropane (Scheme 56). However, catalysts 26, 155, 156, and [Cp* 2 YH] 2 (160) are capable of copolymerizing 2phenyl-1-methylenecyclopropane and ethylene.…”
Section: β-Alkyl Elimination From Organoruthenium Complexesmentioning
This review describes organometallic compounds and materials that are capable of mediating a rarely encountered but fundamentally important reaction: β-alkyl elimination at the metal-Cα-Cβ-R moiety, in which an alkyl group attached to the Cβ atom is transferred to the metal or to a coordinated substrate. The objectives of this review are to provide a cohesive fundamental understanding of β-alkyl-elimination reactions and to highlight its applications in olefin polymerization, alkane hydrogenolysis, depolymerization of branched polymers, ring-opening polymerization of cycloalkanes, and other useful organic reactions. To provide a coherent understanding of the β-alkyl elimination reaction, special attention is given to conditions and strategies used to facilitate β-alkyl-elimination/transfer events in metal-catalyzed olefin polymerization, which provide the well-studied examples.
“…In addition, this unique reactivity has been additionally harnessed as a ring-opening step in chain propagation and has provided functionalized polyolefins with backbone exo-methylene groups . The organolanthanide and zirconocenium-mediated alkyl shift-based ring-opening mechanisms for methylenecycloalkanes have been well-established by 13 C labeling copolymerization experiments of methylenecyclobutane (MCB) and ethylene (eqs 21 and 22),72a in which the C2−C3/C2−C5 bond is exclusively cleaved (eq 21) rather than the C3−C4/C4−C5 bond (eq 22). 6 Proposed Catalytic Pathways for Organolanthanide-Catalyzed Intermolecular Hydroamination of 2-Phenylmethylenecyclopropane…”
Organolanthanide complexes of the type Cp'(2)LnCH(SiMe(3))(2) (Cp' = eta(5)-Me(5)C(5); Ln = La, Nd, Sm, Lu) and Me(2)SiCp' '(2)LnCH(SiMe(3))(2) (Cp' ' = eta(5)-Me(4)C(5); Ln = Nd, Sm, Lu) serve as efficient precatalysts for the regioselective intermolecular hydroamination of alkynes R'Ctbd1;CMe (R' = SiMe(3), C(6)H(5), Me), alkenes RCH=CH(2) (R = SiMe(3), CH(3)CH(2)CH(2)), butadiene, vinylarenes ArCH=CH(2) (Ar = phenyl, 4-methylbenzene, naphthyl, 4-fluorobenzene, 4-(trifluoromethyl)benzene, 4-methoxybenzene, 4-(dimethylamino)benzene, 4-(methylthio)benzene), di- and trivinylarenes, and methylenecyclopropanes with primary amines R' 'NH(2) (R' ' = n-propyl, n-butyl, isobutyl, phenyl, 4-methylphenyl, 4-(dimethylamino)phenyl) to yield the corresponding amines and imines. For R = SiMe(3), R = CH(2)=CH lanthanide-mediated intermolecular hydroamination regioselectively generates the anti-Markovnikov addition products (Me(3)SiCH(2)CH(2)NHR' ', (E)-CH(3)CH=CHCH(2)NHR' '). However, for R = CH(3)CH(2)CH(2), the Markovnikov addition product is observed (CH(3)CH(2)CH(2)CHNHR' 'CH(3)). For internal alkynes, it appears that these regioselective transformations occur under significant stereoelectronic control, and for R' = SiMe(3), rearrangement of the product enamines occurs via tautomerization to imines, followed by a 1,3-trimethylsilyl group shift to stable N-SiMe(3)-bonded CH(2)=CMeN(SiMe(3))R' ' structures. For vinylarenes, intermolecular hydroamination with n-propylamine affords the anti-Markovnikov addition product beta-phenylethylamine. In addition, hydroamination of divinylarenes provides a concise synthesis of tetrahydroisoquinoline structures via coupled intermolecular hydroamination/subsequent intramolecular cyclohydroamination sequences. Intermolecular hydroamination of methylenecyclopropane proceeds via highly regioselective exo-methylene C=C insertion into Ln-N bonds, followed by regioselective cyclopropane ring opening to afford the corresponding imine. For the Me(2)SiCp' '(2)Nd-catalyzed reaction of Me(3)SiCtbd1;CMe and H(2)NCH(2)CH(2)CH(2)CH(3), DeltaH() = 17.2 (1.1) kcal mol(-)(1) and DeltaS() = -25.9 (9.7) eu, while the reaction kinetics are zero-order in [amine] and first-order in both [catalyst] and [alkyne]. For the same substrate pair, catalytic turnover frequencies under identical conditions decrease in the order Me(2)SiCp' '(2)NdCH(SiMe(3))(2) > Me(2)SiCp' '(2)SmCH(SiMe(3))(2) > Me(2)SiCp' '(2)LuCH(SiMe(3))(2) > Cp'(2)SmCH(SiMe(3))(2), in accord with documented steric requirements for the insertion of olefinic functionalities into lanthanide-alkyl and -heteroatom sigma-bonds. Kinetic and mechanistic evidence argues that the turnover-limiting step is intermolecular C=C/Ctbd1;C bond insertion into the Ln-N bond followed by rapid protonolysis of the resulting Ln-C bond.
“…In particular, we were interested in learning how substitution at the methylenecyclopropane skeletal positions 2 and 3 might influence the polymerization pathway. We report here our observations on the single-site polymerization and ethylene copolymerization characteristics of 2-phenyl-1-methylenecyclopropane ( A ) and 7-methylenebicyclo[4.1.0]heptane ( B ) . It will be seen here that while d 0 /f n metallocene catalysts are curiously ineffective in homopolymerizations of A , a variety of catalysts are competent to effect random copolymerization of A with ethylene to produce the new polymer C .…”
The mono- and disubstituted methylenecyclopropane derivatives 2-phenyl-1-methylenecyclopropane (A) and 7-methylenebicyclo[4.1.0]heptane (B) have been successfully implemented in ring-opening Ziegler polymerization. Homogeneous ethylene + 2-phenyl-1-methylenecyclopropane (A) random copolymerizations are mediated efficiently by the single-site catalysts Cp*2ZrMe+B(C6F5)4
-, [Cp*2LuH]2, [Cp*2SmH]2, and [Cp*2YH]2 (Cp* = C5Me5)
to produce a copolymer (C) with A enchained in a ring-opened fashion. Single-site coordinative
polymerization of 7-methylenebicyclo[4.1.0]heptane (B) proceeds via either ring-opened or
ring-unopened pathways. In the presence of Cp*2ZrMe+ MeB(C6F5)3
- at 0 °C, B undergoes
polymerization to afford the insoluble, ring-unopened homopolymer D, which was characterized by CPMAS NMR, DSC, elemental analysis, FTIR, TGA, and XRD. The melting point of
polymer D lies above its decomposition temperature (>300 °C). Random copolymerizations
of B and ethylene mediated by Cp*2ZrMe+MeB(C6F5)3
- at room temperature result in polymer
E, a polyethylene capped by a ring-opened B fragment. The formation of B-capped polymer
E is a consequence of a new chain transfer mechanism, as evidenced by a linear relationship
between M
n and [B]-1. The rate constant for insertion of ethylene is ∼25× greater than the
rate constant for insertion of monomer B into the metal−alkyl bond. Random copolymers
(F) of ring-opened B and ethylene are produced when the catalysts Me2Si(Me4C5)(tBuN)ZrMe2, Me2Si(Me4C5)(tBuN)TiMe2 (activated by either (C6H5)3C+ B(C6F5)4
- or B(C6F5)3), and
[Cp*2LuH]2 are employed.
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