Synthesis and reactivity of η-tetramethylcyclopentadienyl-propenyl rhenium complexes: Molecular structure of [(η:η-C5Me4CH2CHCH2)Re(CO)2]

The fulvene complexes [(η⁶-C₅Me₄CH₂)Re(CO)₂(R)] (1a, RI; 1b, RC₆F₅) react at the exocyclic methylene carbon with a vinylmagnesium bromide solution to produce the anionic species [(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₂(R)]⁻. Protonation with HCl at 0 °C produces the hydride complexes [trans-(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₂(R)(H)] (2a, RI; 2b, RC₆F₅). Thermolysis of an hexane solution of the iodo-hydride (2a) under a CO atmosphere yields the complex [(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₃] (3) and [Re(CO)₅I] as by-product. Thermolysis of 2b produced three new products, mainly the chelated complex [(η⁵:η²-C₅Me₄CH₂CHCH₂)Re(CO)₂] (4) and complex 3, with a non-coordinated olefin group, in moderated yield, and traces of [Re(CO)₅(C₆F₅)]. Thermolysis of an hexane solution of 2 in presence of an excess of PMe₃, afforded the phosphine derivative [(η⁵-C₅Me₄CH₂CHCH₂)Re(CO)₂(PMe₃)] (5). All the complexes were characterized by IR, ¹H, ¹³C and ³¹P NMR spectroscopies and mass spectrometry. The molecular structure of 4 has also been determined. The molecule exhibits a formal three-legged piano-stool structure, with two CO groups, and the third position corresponding to the η²-coordination of the propenyl side arm of the η⁵-C₅Me₄ ring.     

From alkenylphosphane aminoallenylidene ruthenium(II) complexes to highly unsaturated ruthenaphosphabicycloheptene complexes

The alkenylaminoallenylidene complex [Ru(η⁵-C₉H₇){CCC(NEt₂)[C(Me)CPh₂]}{κ(P)-Ph₂PCH₂CHCH₂}(PPh₃)][PF₆] (2) has been prepared by the reaction of the allenylidene [Ru(η⁵-C₉H₇)(CCCPh₂){κ(P)-Ph₂PCH₂CHCH₂}(PPh₃)][PF₆] (1) with the ynamine MeCCNEt₂. The reaction proceeds regio- and stereoselectively, and the insertion of the ynamine takes place exclusively at the C_βC_γ bond of the unsaturated chain. The secondary allenylidene [Ru(η⁵-C₉H₇){CCC(H)[C(Me)CPh₂]}{κ(P)-Ph₂PCH₂CHCH₂}(PPh₃)][PF₆] (3) is obtained, in a one-pot synthesis, from the reaction of aminoallenylidene 2 with LiBHEt₃ and subsequent treatment with silica. Moreover, the addition of an excess of NaBH₄ to a solution of the complex 2 in THF at room temperature gives exclusively the alkynyl complex [Ru(η⁵-C₉H₇){CCCH₂[C(Me)CPh₂]}{κ(P)-Ph₂PCH₂CHCH₂}(PPh₃)] (5). The heating of a solution of allenylidene derivative 3 in THF at reflux gives regio- and diastereoselectively the cyclobutylidene complex [Ru(η⁵-C₉H₇) (PPh₃)][PF₆](4) through an intramolecular cycloaddition of the CC allyl and the C_αC_β bonds in the allenylidene complex 3. The structure of complex 4 has been determined by single crystal X-ray diffraction analysis.     

Further reactions of some bis(vinylidene)diruthenium complexes

Whereas {Ru(dppm)Cp*}₂(μ-CCCC) (2) is the only product formed by deprotonation of [{Ru(dppm)Cp*}₂{μ(CCHCHC)}]⁺ with dbu, a mixture of 2 with Ru{CCCHCH(PPh₂)₂[RuCp*]}(dppm)Cp* (3) and {Cp*Ru(PPh₂CHCCH-)}₂ (4) is obtained with KOBu^t. A similar reaction with [{Ru(dppm)Cp*}₂{μ(CCMeCMeC)}]⁺ (5) gave Ru{CCCMeCH(PPh₂)₂[RuCp*]}(dppm)Cp* (6). X-ray structures of 4, 5 and 6 confirm the presence of the 1-ruthena-2,4-diphosphabicyclo[1.1.1]pentane moiety, which is likely formed by an intramolecular attack of the deprotonated dppm ligand on C(1) of the vinylidene ligand. Protonation of {Ru(dppe)Cp*}₂(μ-CCCC) (8-Ru) regenerates its precursor [{Ru(dppe)Cp*}₂{μ(CCHCHC)}]²⁺ (7-Ru). Ready oxidation of the bis(vinylidene) complex affords the cationic carbonyl [Ru(CO)(dppe)Cp*]PF₆ (9) (X-ray structure).     

Ferrole-type compounds containing thiophenic or thiepinic rings in the 3,4-positions of the metallacycle

The new ferrole Fe₂(CO)₆[μ-η²,η⁴-(Fc)CC{C(H)C(R)S}CC(SiMe₃)] [R = SiMe₃ (1) and R = Fc (2)] and ruthenoles Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC{SC(Fc)C(H)}CC(Fc)] 3 and Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC(SCCFc)C(H)C(Fc)] 4, have been obtained from the reactions of M₃(CO)₁₂ (M = Fe, Ru) and FcCCSCCSiMe₃ through S-C bond activations and C-C coupling reactions. Thermolysis of Ru₂(CO)₆[μ₃-η²,η⁴,η³-(Me₃Si)CC{SC(Fc)C(SCCSiMe₃}Ru(CO)₃}CC(Fc)] alone and in the presence of HCCFc, yielded the compounds Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC{SC(Fc)C(SCCSiMe₃)}CC(Fc)] 5 and Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC{SC(Fc)C(SCCSiMe₃)C(H)C(Fc)}CC(Fc)] 6, respectively. The crystal structures of the compounds 1, 3, 4 and 6 are reported.     

Synthesis and MMA polymerization of chiral ansa-zirconocene ester enolate complexes with C2- and Cs-ligation

A series of chiral ansa-zirconocene ester enolate complexes incorporating C₂- or C_s-symmetric ligands, including neutral rac-(EBI)ZrCl[OC(OⁱPr)CMe₂] (1), rac-(EBI)Zr(OTf)[OC(OⁱPr)CMe₂] (2), rac-(EBI)Zr(OTf)[OC(OMe)C(Me)CH₂C(Me₂)C(OⁱPr)O] (3), [Me₂C(Cp)(Flu)]ZrMe[OC(OⁱPr)CMe₂] (4), and cationic [Me₂C(Cp)(Flu)]Zr⁺(THF)[OC(OⁱPr)CMe₂][MeB(C₆F₅)₃]⁻ (5), have been synthesized. Within the neutral C₂-ligated zirconocene ester enolate series, the chloride derivative 1 is inactive toward any methyl methacrylate (MMA) additions, the methyl derivative rac-(EBI)ZrMe[OC(OⁱPr)CMe₂] adds cleanly only 1 equiv. of MMA, and the triflate derivative 2 can add either 1 equiv. of MMA to form the single-MMA-addition product 3 or multiple equivalents of MMA to form P(MMA). Unlike the C_s-ligated methyl cation [Me₂C(Cp)(Flu)ZrMe]⁺, which is inactive for MMA polymerization under various conditions, the C_s-ligated ester enolate cation 5 is moderately active for polymerization of MMA and N,N-dimethylacrylamide at ambient temperature; the resulting P(MMA) has a high molecular weight of M_n = 388 000 Da but a low syndiotacticity of [rr] = 64%, and the polymerization conforms to a chain-end control mechanism.     

Further chemistry of ruthenium butatrienylidene complexes

Several complexes have been obtained from reactions carried out in early attempts to prepare the diynyl complexes Ru(CCCCR)(dppe)Cp* (R = H, SiMe₃). These have been identified crystallographically as the acyl complex Ru{CCC(O)Me}(dppe)Cp* (3), the cationic imido complex [Ru{CCC(NH₂)Me}(dppe)Cp*]PF₆ (4), the binuclear butenynylallenylidene [{Ru(dppe)Cp*}₂{μ-CCC(OMe)CHCMeCC}]PF₆ (5), and the bis(ethynyl)cyclobutenylidene [{Ru(dppe)Cp*}₂{μ-CCC₄H₂(SiMe₃)CC}]PF₆ (6). NMR studies of 5 have revealed the existence of two isomers. Plausible routes for their formation from the putative butatrienylidene intermediate [Ru(CCCCH₂)(dppe)Cp*]⁺ (A) are discussed.     

Assembly and incorporation of a CO2Me group into a bridging vinyliminium ligand in a diiron complex

The diiron complex [Fe₂{μ-к¹(O):η¹(C):η³(C)-C(N(Me)(Xyl))C(H)C(Me)C(O)OMe}(μ-CO)(Cp)₂] (2) has been obtained from the diiron bridging vinyliminium [Fe₂{μ-η¹:η³-C(Me)C(H)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)₂][SO₃CF₃] (1; Xyl = 2,5-C₆H₃Me₂) upon treatment with NaH in the presence of CH₂CCMe₂, followed by chromatography on alumina with MeOH as eluent. The reaction consists in the incorporation of a methylcarboxylate unit, assembled from CO and MeO⁻, into the bridging vinyliminium ligand. The resulting complex 2 exhibits a C₄ fragment bridging the two iron centres through the carbonyl oxygen atom and the allylidene moiety.The X-ray molecular structure of 2 has been determined.     

Dimerisation and reactivity of HCCCCFc at ruthenium centres

In contrast to the simple diynyl complexes formed in reactions between HCCCCFc and MCl(dppe)Cp∗; (M = Fe, Ru), an analogous reaction with RuCl(PPh₃)₂Cp∗; in the presence of KPF₆ and dbu resulted in dimerisation of the diyne at the Ru centre to afford a mixture of [Ru{η¹,η²-C(CCFc)C(L)CHCCCHFc}(PPh₃)Cp∗]PF₆ (L = dbu 1, PPh₃2). Similar reactions with RuCl(PR₃)₂L gave [Ru{η¹,η²-C(CCFc)C(dbu)CHCCCHFc}(PR₃)L]PF₆ (L = Cp, R = Ph 3, m-tol 4; L = η⁵-C₉H₇, R = Ph 5). The reaction between 3 and I₂, followed by crystallization of the paramagnetic product from MeOH, afforded the dicationic [Ru{C(CCFc)C(dbu)CHC(OMe)C(OMe)CHFc}(PPh₃)Cp](I₃)₂6. The molecular structures of 2·2CH₂Cl₂ and 6.S (S = 2CH₂Cl₂, C₆H₆) were determined by single-crystal XRD studies.     

Synthesis, characterization and solid state structures of thiosemicarbazone palladacycles: Influence of hydrogen bonding in the molecular arrangement

Treatment of the thiosemicarbazones 4-FC₆H₄C(Me)NN(H)C(S)NHR, (R = Me, a; Ph, b) and 2-ClC₆H₄C(Me)NN(H)C(S)NHR (R = Ph, c) with lithium tetrachloropalladate(II) in methanol or palladium(II) acetate in acetic acid gave the tetranuclear cyclometallated complex [Pd{4-FC₆H₃C(Me)NNC(S)NHR}]₄ (1a, 1b) and [Pd{2-ClC₆H₃C(Me)NNC(S)NHPh}]₄ (1c). Reaction of these tetramers with the diphosphines dppe, t-dppe, dppp or dppb in a 1:2 molar ratio gave the dinuclear cyclometallated complexes [(Pd{4-FC₆H₃C(Me)NNC(S)NHR})₂(μ-Ph₂P(CH₂)_nPPh₂)], (n = 2, 2a, 2b; 3, 4a, 4b; 4, 5a, 5b), [(Pd{4-FC₆H₃C(Me)NNC(S)NHPh})₂(μ-Ph₂PCHCHPPh₂)], (3a, 3b) and [(Pd{2-ClC₆H₃C(Me)NNC(S)NHR})₂(μ-Ph₂P(CH₂)_nPPh₂)], (n = 2, 2c, 2d; 3, 4c, 4d; 4, 5c, 5d), [(Pd{2-ClC₆H₃C(Me)NNC(S)NHPh})₂(μ-PPh₂CHCHPPh₂)], (3c, 3d). The X-ray crystal structure of the ligand b and the complexes 3c, 4a and 4d were determined. The structures of complexes 4a and 4d show that the different disposition of the chain cyclometallated of the thiosemicarbazones (in the same orientation or in the opposite one) is due to the different H bonds produced.     

Proton reduction catalysis by manganese vinylidene and allenylidene complexes

The present paper reports the unprecedented observation of a catalytic electrochemical proton reduction based on metallocumulene complexes. Manganese phenylvinylidene (η⁵-C₅H₅)(CO)(PPh₃)MnCC(H)Ph (1) and diphenylallenylidene (η⁵-C₅H₅)(CO)₂MnCCCPh₂ (3) are shown to catalyze the reduction of protons from HBF₄ into dihydrogen in CH₂Cl₂ or CH₃CN media at −1.60 and −0.84 V (in CH₃CN) vs. Fc, respectively. The working potential for 3 (−0.84 V vs. Fc in CH₃CN) is the lowest reported to date for protonic acids reduction in non-aqueous media. The similar catalytic cycles disclosed here include the protonation of 1, 3 into the carbyne cations [(η⁵-C₅H₅)(CO)(PPh₃)MnC-CH₂Ph]BF₄ ([2]BF₄), [(η⁵-C₅H₅)(CO)₂MnC-CHCPh₂]BF₄ ([4]BF₄) followed by their reduction to the corresponding 19-electron radicals 2, 4, respectively. Both carbyne radicals undergo a rapid homolytic cleavage of the C_β-H bond generating an H-radical producing molecular hydrogen with concomitant recovery of the neutral metallocumulenes thereby completing a catalytic cycle.     

A ruthenium(II) allenylidene complex with a 4,5-diazafluorene functional group: A new building-block for organometallic molecular assemblies

The synthesis of the new ruthenium(II) allenylidene complex [ClRu(dppe)₂CCC₁₁H₆N₂][OTf] (4) (dppe = 1,2-bis(diphenylphosphino)ethane) terminated with a 4,5-diazafluorene ligand is reported. Further coordination of that metal allenylidene to ruthenium and rhenium moieties leads to the bimetallic adducts [ClRu(dppe)₂CCC₁₁H₆N₂{Ru(bpy)₂}][B(C₆F₅)₄]₃ (5a), [ClRu(dppe)₂CCC₁₁H₆N₂{Ru(^tBu-bpy)₂}][PF₆]₃ (5b) and [ClRu(dppe)₂CCC₁₁H₆N₂{Re(CO)₃Cl}][OTf] (6). Their optical and electrochemical properties show that the allenylidene moiety is an attractive molecular clip for the access to larger original redox-active homo/heteronuclear multi-component supramolecular assemblies. The X-ray crystal structure of the allenylidene metal building block is also described.     

Bis(amino)allenylidene complexes by displacement of the MeO group in methoxy allenylidene complexes of chromium and tungsten. Synthesis, DFT calculations and solid-state structures of new bis(amino)allenylidene complexes

Pentacarbonyl dimethylamino(methoxy)allenylidene tungsten, [(CO)₅WCCC(OMe)NMe₂] (1b), reacts with one equivalent of primary amines, H₂NR, by selectively replacing the methoxy group to give dimethylamino(amino)allenylidene complexes, [(CO)₅WCCC(NHR)NMe₂]. When the amine is used in excess both terminal groups, OMe as well as NMe₂, are replaced by the primary amino group giving [(CO)₅WCCC(NHR)₂ ]. The NHR substituent in these complexes may be modified by deprotonation with LDA followed by alkylation. The replacement of the methoxy group in 1b by a secondary amino group, NR₂, can be achieved by a stepwise process. Addition of Li[NR₂] to the C_γ atom of 1b affords an alkynyl tungstate. Subsequent OMe⁻ elimination induced by TMS-Cl/SiO₂ yields the allenylidene complexes [(CO)₅WCCC(NR₂)NMe₂]. When bidentate diamines are used instead of monoamines both substituents, OMe and NMe₂, are replaced and allenylidene complexes are formed in which C_γ constitutes part of a 5-, 6-, or 7-membered heterocycle. The reaction of [(CO)₅CrCCC(OMe)NMe₂] (1a) with diethylene triamine affords an allenylidene complex with a heterocyclic endgroup carrying a dangling CH₂CH₂NH₂ substituent. All reactions follow a strict regioselective attack of the nucleophile at C_γ and proceed with good to excellent yields. The addition of N-H to the C_αC_β bond is not observed. By applying either one of these routes nearly any substitution pattern in bis(amino)allenylidene complex can be realized.     

Synthesis of ruthenium phenylindenylidene, carbyne, allenylidene and vinylmethylidene complexes from (PPh3)3−4RuCl2: A mechanistic and structural investigation

The reaction of (Ph₃P)₃RuCl₂ with 1,1-diphenyl-2-propyn-1-ol was investigated in various solvents. The reaction in thf under reflux is reported to produce the (PPh₃)₂Cl₂Ru(3-phenylindenylidene) complex (3) which has undergone rearrangement of the allenylidene C₃-spine. We have improved the reliability of the reported synthesis by adding acetyl chloride which converts the formed water of the reaction and thus increases the acidity of the reaction solution. Without the additive, we observed the exclusive formation of an intermediate of the transformation and identified it as dinuclear (PPh₃)₂ClRu(μ-Cl)₃(PPh₃)₂RuCCCPh₂ complex (5). The reaction of (Ph₃P)₃₋₄RuCl₂ with 1,1-diphenyl-2-propyn-1-ol in CH₂Cl₂ or C₂H₄Cl₂ under reflux in the presence of excess conc. aqueous HCl afforded the new, neutral (PPh₃)₂Cl₃RuC-CHCPh₂ carbyne complex (7), an HCl adduct of previously elusive (PPh₃)₂Cl₂RuCCCPh₂ complex 6 in high yields. In contrast to the formation of complex 3, the reaction in a non-coordinating solvent did not afford the rearrangement of the allenylidene C₃-spine. Complex 7 was converted into complex 3 in thf under reflux under loss of a molecule HCl. Complex 7 was converted with triethylamine under loss of HCl to complex 6. Pentacoordinate complex 6 was crystallized in the presence of O-donor ligands (EtOH, MeOH and H₂O) to give hexacoordinate (PPh₃)₂Cl₂(ROH)RuCCCPh₂ (R = H, CH₃, C₂H₅) complexes (9)-(11) with the O-donor coordinating in trans-position to the allenylidene moiety. The reaction of complex 7 with 2 equiv. of 4-(N,N-dimethylamino)pyridine (DMAP) gave hexacoordinate (PPh₃)₂Cl₂(DMAP)RuCCCPh₂complex (12) with one molecule DMAP also coordinating in trans-position to the allenylidene group. Methanol and acetic acid in the absence of strong bases afforded the Fischer-carbene complexes (PPh₃)₂Cl₂RuC(OCH₃)-CHCPh₂ (14) and (PPh₃)₂Cl₂RuC(OAc)-CHCPh₂ (15) where the nucleophile added to the α-carbon atom. The structures of complexes 5, 7, 9-11, 14, and 15 were solved via X-ray crystallography.     

Triosmium compounds containing the oxametallacycle [Os(CO)3{C(R)CHC(O)CHC(H)C5H4FeC5H5}] moiety. Synthesis and electrochemical studies

The compounds [Os₃(CO)₁₀{μ,η³-(SCH₂CH₂SCCHC(O)CHCH(C₅H₄)Fe (C₅H₅)}] (2), [Os₃(CO)₉{μ,η³-(SCH₂CH₂SCCHC(O)CHCH(C₅H₄)Fe(C₅H₅)}] (3) and [Os₃(CO)₈{μ₃,η²-{CCHC(O)CHCH(C₅H₄)Fe(C₅H₅)}(SCH₂CH₂S)}] (4) have been obtained by rupture of S-C bonds in the ketene dithioacetal [C₅H₅FeC₅H₄CHCHC(O)CHC(SCH₂CH₂S)], in their reaction with the activated cluster [Os₃(CO)₁₀(NCMe)₂]. The presence of an oxametallacycle in these derivatives has been confirmed by an X-ray diffraction analysis. The electrochemical study has indicated the ability of these compounds to modify the electrode surfaces.     

Crystal structures of amarine and isoamarine and copper(I) coordination chemistry with their allylation products

The crystal structures of amarine (1) and isoamarine (2), important intermediates in the preparation of 1,2-diphenyl-diaminoethane, were successfully determined. Their allylation products, 1,3-diallyl amarine (1)(CH₂CHCH₂)₂Br (3) and isoamarine bromide (2)(CH₂CHCH₂)₂Br (4) [the crystal structures of (1)(CH₂CHCH₂)₂PF₆(3-Br + PF₆) and (2)(CH₂CHCH₂)₂PF₆ (4-Br + PF₆) are also successfully determined to confirm allylation products], react with CuBr to afford (1)₂(CH₂CHCH₂)₄(Cu₂Br₄) (5) and (2)(CH₂CHCH₂)₂(Cu₂Br₃) (6), respectively. Crystal structures of 5 and 6 reveal that 5 is an anion discrete complex without olefin moiety coordination, and 6 has a 1D infinite chain with olefin moiety coordination as a bridging spacer. The fluorescent emission spectra of 5 (λ_emax = 570 nm) and 6 (λ_emax = 642 nm) were measured, and display a significant difference that can be used for solid state fluorescent sensing them.     

Additions and intramolecular migrations of nucleophiles in cationic diruthenium μ-allenyl complexes

The diruthenium μ-allenyl complex [Ru₂(CO)(NCMe)(μ-CO){μ-η¹:η²-C(H)CC(Me)(Ph)}(Cp)₂][BF₄], 3b, reacts with halide anions to yield the neutral derivatives [Ru₂(CO)₂(X){μ-η¹:η²-C(H)CC(Me)(Ph)}(Cp)₂] [X = Cl, 4b; X = Br, 4c; X = I, 4d]. Complex 4b undergoes isomerization to the unprecedented bridging vinyl-chlorocarbene species [Ru₂(CO)(μ-CO){μ-η¹:η³- C(Cl)C(H)C(Me)(Ph)}(Cp)₂], 10, upon filtration of a CH₂Cl₂ solution through an alumina column.Complex 3b reacts with an excess of NaBH₄ to give five products: the allene complex [Ru₂(CO)₂{μ-η²:η²- CH₂CC(Me)(Ph)}(Cp)₂], 5; the hydride species trans-[Ru₂(CO)₂(μ-H){μ-η¹:η²-CHCC(Me)(Ph)}(Cp)₂], 6, and cis-[Ru₂(CO)₂(μ-H){μ-η¹:η²-CHCC(Me)(Ph)}(Cp)₂], 8; the vinyl-alkylidene [Ru₂(CO)(μ-CO){μ-η¹:η³- C(H)C(H)C(Me)(Ph)}(Cp)₂], 9; and the cluster [Ru₃(CO)₃(μ-H)₃(Cp)₃], 7.Studies on the thermal stabilities of 5, 6, 8 and 9 have suggested a plausible mechanism for the formation of these complexes and for the synthesis of 10.     

Ethynyl[2.2]paracyclophanes and 4-isocyano[2.2]paracyclophane as ligands in organometallic chemistry

An alternative synthesis of (±)-4-ethynyl[2.2]paracyclophane (PCPCCH) (5) and 4,16-diethynyl[2.2]paracyclophane (6) via the Corey-Fuchs reaction has been developed. The olefinic intermediate 4-dibromovinyl[2.2]paracyclophane (3) has been isolated and structurally characterized. The racemic terminal alkyne 5 was employed as starting material for assembling of a luminescent extended π-conjugated system containing a thiophene unit and for a catalytic bis-silylation reaction yielding the olefinic dithioether Z-PhSCH₂Me₂SiC(H)C(PCP)SiMe₂CH₂SPh (9). The dimetallatetrahedran [Co₂(CO)₆(μ-η²-PCP-CCH)] (10) has been prepared and its crystal structure determined by an X-ray diffraction analysis. Alkyne 5 has also been used for the preparation of the Pt(0) complex [Pt(PPh₃)₂(PCPCCH)] (11) and the heterodinuclear dimetallacyclopentenone [(OC)₂Fe{μC(O)C(PCP)C(H)}(μ-dppm)Pt(PPh₃)] (12). The synthesis and reactivity of 4-isocyano[2.2]paracyclophane (15) towards heterobimetallic iron-platinum and palladium-platinum complexes is also presented. Opening of the dative iron → platinum bond of [(OC)₄Fe(μ-dppm)PtCl₂] (16) occurred upon addition of 15 to a CH₂Cl₂ solution of 16 leading to [(OC)₄Fe{μ-dppm}PtCl₂(CNPCP)] (17). Treatment of [ClPd(μ-dppm)₂PtCl] (18) with isocyanide 15 in a 1:1 ratio affords the A-frame compound [ClPd(μ-dppm)₂(μ-CNPCP)PtCl] (19), resulting from formal insertion of 15 into the Pd-Pt bond. Addition of 2 equiv. of 15-18 leads to the ionic A-frame compound [ClPd(μ-dppm)₂(μ-CNPCP)Pt(CNPCP)]Cl (20).     

Remarkable Lewis acid effects on polymerization of functionalized alkenes by metallocene and lithium ester enolates

Drastic effects of Lewis acids E(C₆F₅)₃ (E = Al, B) on polymerization of functionalized alkenes such as methyl methacrylate (MMA) and N,N-dimethyl acrylamide (DMAA) mediated by metallocene and lithium ester enolates, Cp₂Zr[OC(OⁱPr)CMe₂]₂ (1) and Me₂CC(OⁱPr)OLi, are documented as well as elucidated. In the case of metallocene bis(ester enolate) 1, when combined with 2 equiv. of Al(C₆F₅)₃, it effects highly active ion-pairing polymerization of MMA and DMAA; the living nature of this polymerization system allows for the synthesis of well-defined diblock and triblock copolymers of MMA with longer-chain alkyl methacrylates. In sharp contrast, the 1/2B(C₆F₅)₃ combination exhibits low to negligible polymerization activity due to the formation of ineffective adduct Cp₂Zr[OC(OⁱPr)CMe₂]⁺[OC(OⁱPr)CMe₂B(C₆F₅)₃]⁻ (2). Such a profound Al vs. B Lewis acid effect has also been observed for the lithium ester enolate; while the Me₂CC(OⁱPr)OLi/2Al(C₆F₅)₃ system is highly active for MMA polymerization, the seemingly analogous Me₂CC(OⁱPr)OLi/2B(C₆F₅)₃ system is inactive. Structure analyses of the resulting lithium enolaluminate and enolborate adducts, Li⁺[Me₂CC(OⁱPr)OAl(C₆F₅)₃]⁻ (3) and Li⁺[Me₂CC(OⁱPr)OB(C₆F₅)₃]⁻ (4), coupled with polymerization studies, show that the remarkable differences observed for Al vs. B are due to the inability of the lithium enolborate/borane pair to effect the bimolecular, activated-monomer anionic polymerization as does the lithium enolaluminate/alane pair.