Diolefin Complexes Research Articles

Protonation of Group 9 Metal (Co, Rh, Ir) Coordinated Bicyclo-[2.2.1]-hepta-2,5-diene and Bicyclo[2.2.2]octa-2,5-diene complexes: Facile Activation of Carbon-Carbon Bond in Bicyclo-[2.2.1]hepta-2,5-diene via M-H or M-H-C interactions

The activation of C-C bond in coordinated M (η4 bicyclo [2.2.1]-hepta-diene) or 2,5-NBD via protonation for 3d,4d and 5d transition metals have been examined. Monoprotonation of the diolefin complexes [M(η5C5R5)(η4- NBD] (R = H, CH3) M = Co, Rh,with CF3COOH or CF3SO3H forms transient agostic metal hydrides (M-H-C) at -80°C. Similar reaction with HPF6 (60% aq), the Ir analogues give terminal hydrides [IrH(η5-C5Me4R)(η4-2,5-NBD)]+PF6 (R=Me, or Et) as isolable solids at room temperature. All these hydride complexes coordinated to NBD subsequently undergo ligand migration to give stable η2-vinyl η3cyclopentenyl cations [M(η5C5R5) (C7H9)]+ (M=Co Rh, Ir). Protonation of the cobalt and rhodium coordinated bicyclo-[2.2.2]-octa 2,5- diene gives unstable M-H-C ground state structures at -80°C, which decompose upon warming to room temp. Protonation reactions of the 2,5-BCOD complexes of Ir also give terminal hydrides [IrH(η5-C5Me5)(η4-2,5-BCOD)]+PF6 as solids. Thermolysis of [IrH(η5-C5Me5)(η4-2,5-BCOD)]+PF6 did not give the expected, isomerized or C-C bond activated product, probably because 2,5-BCOD is less strained than 2,5-NBD. Coupling constant [JCH] and stretching frequency [ν M-H] data indicate the electron density donation from the methyl groups in the Cp ring favors agostic structures. The C-C bond activation in the coordinated norbornadiene, via hydride migration is slower for the terminal hydride, M-H (M= Ir) compared to agostic hydrides for (M=Co, Rh) compounds. The vinyl cyclopentenyl cations of Rh,Ir undergo further isomerization in CF3COOH to give corresponding η6-toluene cations [M(η5-C5R5)(η6-C6H5CH3)]+ At 50 °C in vacuo the salt [(η5C5Me5)Ir(H)(η4nbd]+PF6 forms a neutral tetramethylfulvenyliridium (1) complex η5C5Me4=CH2)Ir(η4NBD) by C-H activation of a methyl group in the C5Me5 ring.

C–C coupling of CH activated polar vinyl monomers by a pentaruthenium cluster complex

Reactions of Ru5(CO)15(μ5-C), 1 with the polar vinyl monomers (PVM), methyl acrylate, vinyl acetate and N,N-dimethylacrylamide proceed by cluster opening additions accompanied by CH activation in the vinyl group of the PVM to yield olefin-activated complexes such as Ru5(μ5-C)(CO)14[η2-OCO(Me)CHCH](μ-H), 2, Ru5(μ5-C)(CO)14[η2-(MeCO2)CCH2](μ-H), 3 and Ru5(μ5-C)(CO)14[η2-OC(NMe2)CHCH](μ-H), 6. In this work we have investigated the nature of the addition and coupling/cross-coupling of a second PVM to the CH activated PVM in the complexes 2, 3, and 6. The products consist of C–C coupled diolefin complexes that have been transformed into η3-allyl ligands by shifts of the hydrogen atoms in the C–C coupled ligands. Nine new complexes of Ru5(μ5-C)(CO)13[η3-1-anti, 3-anti-(MeO)CO–C3H3-η1-OC(OMe)CH2](μ-H), 8; Ru5(μ5-C)(CO)13[η3-1-anti, 3-syn-(MeO2C)CH2C3H3–CH2-η1-OC(OMe)](μ-H), 9; Ru5(μ5-C)(CO)12[μ-η3-OC(OMe)CHCH][η2-CHCHCO2Me](μ-H), 10; Ru5(μ5-C)(CO)13[η3-1-syn, 3-anti-(MeO2C)C3H3-η1-OC(OMe)CH2](μ-H), 11; Ru5(μ5-C)(CO)13[η3-1-syn, 3-anti-Me2NCO–C3H3-η1-O=CNMe2CH2](μ-H), 12; Ru5(μ5-C)(CO)13[η3-1-anti, 3-syn-(Me2N)C(=O)–C3H3–CH2-η1-OC(NMe2)](μ-H), 13; Ru5(μ5-C)(CO)12[μ-η3-OC(NMe2)CHCH][η2-CHCHCO2Me](μ-H), 14; Ru5(μ5-C)(CO)13[η3-1-anti, 3-syn-MeO2CCH2C3H3-η1-OC(NMe2)](μ-H), 15, and Ru5(μ5-C)(CO)12[μ-η2-(MeO2C)CHCH][η3-CH2CHOC(=O)Me)](μ-H), 16 have been obtained and structurally characterized. Three of these complexes (10, 14 and 16) contain uncoupled olefin ligands.

Water-soluble platinum nanoparticles stabilized by sulfonated N-heterocyclic carbenes: influence of the synthetic approach.

The synthesis of metal nanoparticles (NPs) under controlled conditions in water remains a challenge in nanochemistry. Two different approaches to obtain platinum NPs, which involve the treatment of aqueous solutions of preformed sulfonated (NHC)Pt(ii) dimethyl complexes with carbon monoxide, and of (NHC)Pt(0) diolefin complexes with dihydrogen (NHC = N-heterocyclic carbene), are disclosed here. The resulting NPs were found to be highly stable in water under air for an indefinite time period. Coordination of the NHC ligands to the platinum surface via the carbenic carbon was monitored by solid-state NMR spectroscopy, and the presence of a platinum-carbon bond was unambiguously evidenced by the determination of a 13C-195Pt coupling constant (1106 and 1050 Hz for NPs containing 13C labeled-NHC ligands and prepared under CO and H2, respectively). The coordination of CO to the (NHC)Pt(ii) precursors prior to formation of the NPs was confirmed by NMR spectroscopy. When using a disulfonated NHC ligand, a second coordination sphere containing bis(NHC)Pt(ii) complexes is described. Under CO, the formation of NPs was found to be slower than in a previously reported thermal method (Angew. Chem., Int. Ed., 2014, 53, 13220-13224), but led to NPs of similar sizes, whereas under H2, the synthesis of platinum NPs progressed even more slowly and produced larger NPs. In addition to the influence of the synthetic approach, the present study highlights the importance of ligand design for NP stabilization.

Cobalt(I) Olefin Complexes: Precursors for Metal-Organic Chemical Vapor Deposition of High Purity Cobalt Metal Thin Films.

We report the synthesis and characterization of a family of organometallic cobalt(I) metal precursors based around cyclopentadienyl and diene ligands. The molecular structures of the complexes cyclopentadienyl-cobalt(I) diolefin complexes are described, as determined by single-crystal X-ray diffraction analysis. Thermogravimetric analysis and thermal stability studies of the complexes highlighted the isoprene, dimethyl butadiene, and cyclohexadiene derivatives [(C5H5)Co(η(4)-CH2CHC(Me)CH2)] (1), [(C5H5)Co(η(4)-CH2C(Me)C(Me)CH2)] (2), and [(C5H5)Co(η(4)-C6H8)] (4) as possible cobalt metal organic chemical vapor deposition (MOCVD) precursors. Atmospheric pressure MOCVD was employed using precursor 1, to synthesize thin films of metallic cobalt on silicon substrates under an atmosphere (760 torr) of hydrogen (H2). Analysis of the thin films deposited at substrate temperatures of 325, 350, 375, and 400 °C, respectively, by scanning electron microscopy and atomic force microscopy reveal temperature-dependent growth features. Films grown at these temperatures are continuous, pinhole-free, and can be seen to be composed of hexagonal particles clearly visible in the electron micrograph. Powder X-ray diffraction and X-ray photoelectron spectroscopy all show the films to be highly crystalline, high-purity metallic cobalt. Raman spectroscopy was unable to detect the presence of cobalt silicides at the substrate/thin film interface.

Platinum Diolefin Complexes – Synthesis, Structures, and Cytotoxicity

AbstractThe synthesis, spectroscopy, structures and chemical reactivity of platinum(II) diolefin complexescis‐[(∥∧∥)PtCl2],cis‐[(∥∧∥)PtCl(R)] andcis‐[(∥∧∥)Pt(R)2] [∥∧∥ = chelate diolefin ligand: 1,5‐cyclooctadiene (COD), 1,5‐dimethylocta‐1,5‐diene (Me2COD), norbornadiene (NBD), 1,5‐hexadiene (HEX), 3‐allyloxypropene (All2O, diallyl ether), diallylamine (All2NH); R = Me, Bn, C6F5, C6F4H‐4 (or ‐5), or C≡C(4‐Me)Ph] have been explored. The relative exchange rates of thecis‐[(∥∧∥)PtCl2] complexes towards the diimine ligand diisopropyl‐1,4‐diazabutadiene (iPr‐DAB) increased along the series COD < Me2COD < NBD < HEX < All2O by a factor of 4. The presumably dimeric complex [(All2NH)PtCl2]2undergoes a unique rearrangement process in dimethyl sulfoxide (DMSO) solution to yield the dimeric piperazine complex [PtCl(dmso)(C6H10N)]2, which has been characterised by single‐crystal XRD. For selected platinum complexes, cytotoxic effects in HT‐29 colon carcinoma and MCF‐7 breast cancer cell lines were evaluated. For comparison, the dicationic complexes [(COD)Pt(Bn)(L)][PF6]2with the very labile coligandsN‐methyl‐4,4′‐bipyridinium (MQ+) andN‐methyl‐1,4‐pyrazinium (Mpz+) were added to the study. Although the hexadiene complexes [(HEX)Pt(C6F4H‐4)2] and [(HEX)Pt(C6F4H‐5)2] show strong cytotoxicity, the introduction of labile diolefin ligands or the labile cationic MQ+or Mpz+coligands does not generally lead to markedly increased cytotoxicity.

New pentacoordinated rhodium species as unexpected products during the in situ generation of dimeric diphosphine-rhodium neutral catalysts.

Dimeric rhodium complexes of the type [Rh(PP)(μ2 -Cl)]2 (PP=diphosphine) are often used as precatalysts and are generated "in situ" from the corresponding diolefin complexes by exchange of the diene with the desired diphosphine. Herein, we report that the "in situ" procedure also leads to unexpected monomeric pentacoordinated neutral complexes of the type [RhCl(PP)(diolefin)], for the first time herein characterized by NMR spectroscopy and X-ray crystallography for the ligands 1,4-bis(diphenylphosphino)propane (DPPP), 1,4-bis(diphenylphosphino)butane (DPPB), and 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (BINAP). The pentacoordinated complexes are in equilibrium with the dimeric target compound [Rh(PP)(μ2 -Cl)]2 . The equilibrium is influenced by the rhodium-diolefin precursor, the solvent and the temperature. Based on the results of NMR and UV/Vis spectroscopic analysis (kinetics) it could be shown that the pentacoordinated complex [RhCl(PP)(diolefin)] may arise both from the "in situ"-generated neutral complex [Rh(PP)(μ2 -Cl)] by reaction with the free diolefin and, more surprisingly, directly from [Rh(diolefin)(μ2 -Cl)]2 and the diphosphine.

Cationic rhodium(I)–diolefin complexes containing an optically active C2-symmetric bis(sulfoximine) ligand: Synthesis and catalytic activity

A series of cationic rhodium(I) complexes [Rh(diene)(N^N)][BF 4] (diene = 1,5-cyclooctadiene (cod), norbornadiene (nbd), tetrafluorobenzobarralene (tfb)), containing the optically pure bis(sulfoximine) ligand 1,2-bis( S-methyl- S-phenylsulfonimidoyl)benzene, have been synthesized and fully characterized. The structure of the R, R enantiomer of the ligand, and that of its cyclooctadiene–Rh(I) complex, were confirmed by means of single-crystal X-ray diffraction techniques. Studies on the catalytic activity of these complexes in acetophenone hydrosilylation and dimethyl itaconate hydrogenation are also reported.

Catalytic Aerobic Dehydrogenative Coupling of Primary Alcohols and Water to Acids Promoted by a Rhodium(I) Amido N‐Heterocyclic Carbene Complex

AbstractThe amino diolefin complex [Rh(trop2NH)(TMIY)]+(OTf)− (OTf−=CF3SO3−; trop=5‐H‐dibenzo[a,d]cyclohepten‐5yl), incorporating N‐heterocyclic carbene ligand 1,3,4,5‐tetramethylimidazole‐2‐ylidene (TMIY), has been prepared. The structure is determined by single‐crystal X‐ray diffraction, which shows a butterfly structure with the NH and TMIY groups in the apical and the two olefinic binding sites in the equatorial position of a trigonal bipyramid with one vacant site in the equatorial plane. This complex can be deprotonated to give the amide [Rh(trop2N)(TMIY)], which cleaves H2 heterolytically across the RhN bond to give the amino hydride [RhH(trop2NH)(TMIY)]. In dimethylsulfoxide (DMSO), both the amide and amino hydride complexes are active as catalysts in the dehydrogenative coupling (DHC) of various primary alcohols with water to give the corresponding acids under aerobic conditions. O2 serves as hydrogen acceptor. One O atom is converted into water while the other is transferred to DMSO as oxygen acceptor, to yield Me2SO2. Hence, the net reaction RCH2OH+2 O2+2 DMSO→RCOOH+2 Me2SO2+H2O is catalyzed by the butterfly‐shaped rhodium amide complexes.

BINAP: rhodium–diolefin complexes in asymmetric hydrogenation

The complexes [Rh(( S)-BINAP)(COD)]BF 4 1, [Rh(( S)-BINAP)(NBD)]BF 4 2, [Rh(( R)-BINAP)(COD)]OTf 3, [Rh(( R)-BINAP)(NBD)]OTf 4, and [Rh(( R)-BINAP)(COD)]BArF 5 were synthesized, and 1–4 were analyzed by single crystal X-ray crystallography. The transformation of these precatalysts into hydrogenation-active species was investigated as well as the hydrogenation of prochiral olefins. In particular, this series of transformations was investigated with regard to solvent and counterions.

Synthesis of Tetranuclear Rhodium and Iridium Complexes Directed by 6-Mercaptopyridin-2-ol: Electrochemical Behavior, Chemical Oxidation, and Coordination Chemistry

The new ligand 6-mercapto-2(1H)-pyridone (H(2)PySO) has been prepared in good yield by reaction of 6-chloro-pyridin-2-ol with NaSH. Reaction of the salt K(2)PySO, generated in situ, with the appropriate complex [M(mu-Cl)(diolefin)](2) affords the tetranuclear complexes [M(4)(mu-PySO)(2)(diolefin)(4)] [M = Rh, diolefin = 1,5-cyclooctadiene (cod) (1), tetrafluorobenzobarralene (tfbb) (2); M = Ir, diolefin = cod (3)]. The molecular structure of complex 1 has been determined by X-ray diffraction methods. The tetranuclear structure is supported by two S,N,O-tridentate ligands exhibiting a 1kappaO, 2kappaN, 3:4kappa(2)S coordination mode. Carbonylation of the rhodium diolefin complexes at atmospheric pressure gives [Rh(4)(mu-PySO)(2)(CO)(8)] (4). The carbonylation of 1 is partially reversible, and the mixed-ligand complex [Rh(4)(mu-PySO)(2)(cod)(2)(CO)(4)] (5) has been obtained as a single isomer. The reaction of 4 with triphenylphosphine gives the compound [Rh(4)(mu-PySO)(2)(CO)(4)(PPh(3))(4)] (6) which also exists as a single isomer of C(2) symmetry. The diolefin complexes are redox active and exhibit two one-electron oxidations at a platinum disk electrode in dichloromethane separated by approximately 0.5 V at potentials accessible by chemical oxidants. The tetranuclear complexes were selectively oxidized to the 63-electron mixed-valence cationic complexes [M(4)(mu-PySO)(2)(diolefin)(4)](+) (1a(+), 2(+), and 3(+)) by using AgCF(3)SO(3) as oxidant and isolated as the triflate salts. Alternatively, the oxidation with [Cp(2)Fe]PF(6) gives [Rh(4)(mu-PySO)(2)(cod)(4)][PF(6)] (1b(+)). The parameters obtained from the simulation of the electron paramagnetic resonance spectra of the oxidized species strongly suggest that the unpaired electron is delocalized over only two metal atoms in the complexes.

Synthesis and Structural Characterization of New Rhodium‐Tin Heterodimetallic Complexes

AbstractReaction of the triamidostannates(II) MeSi{SiMe2N(p‐tol)}3SnLi(OEt2) (1a) and MeSi{SiMe2N(3,5‐xyl)}3SnLi(OEt2) (1b) with 1/2 molar equiv. of [RhCl(diolefin)]2 (diolefin = COD, NBD) and phosphanes, phosphites or isonitriles (“L”) gave the square‐planar complexes [MeSi{SiMe2NAryl}3SnRh(L)(diolefin)] (Aryl = 3,5‐xyl, p‐tol) in which thestannates are directly bonded to rhodium through Rh–Sn bonds. In contrast, the analogous transformation of 1b with 1/2 equiv. of [RhCl(C2H4)2]2 and PiPr3 in toluene did not lead to a square‐planar bisethylene complex [MeSi{SiMe2N(3,5‐xyl)}3SnRh(C2H4)2(PiPr3)] but the brown 18e π‐arene complex [MeSi{SiMe2N(3,5‐xyl)}3SnRh(PiPr3)(η6‐toluene)] (6). Equilibria of the square planar diolefin complexes with π‐arene systems such as 6 were observed upon their dissolution in toluene.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Rhodium‐Complex‐Catalyzed Asymmetric Hydrogenation: Transformation of Precatalysts into Active Species

The use of diolefin-containing rhodium precatalysts leads to induction periods in asymmetric hydrogenation of prochiral olefins. Consequently, the reaction rate increases in the beginning. The induction period is caused by the fact that some of the catalyst is blocked by the diolefin and thus not available for hydrogenation of the prochiral olefin. Therefore, the maximum reaction rate cannot be reached initially. Due to the relatively slow hydrogenation of cyclooctadiene (cod) the share of active catalysts increases at first, and this leads to typical induction periods. The aim of this work is to quantify the hydrogenation of the diolefins cyclooctadiene (cod) and norborna-2,5-diene (nbd) for cationic complexes of the type [Rh(ligand)(diolefin)]BF(4) for the ligands Binap (1,1'-binaphthalene-2,2'-diylbis(phenylphosphine)), Me-Duphos (1,2-bis(2,5-dimethylphospholano)benzene, and Catasium in the solvents methanol, THF, and propylene carbonate. Furthermore, an approach is presented to determine the desired rate constant and the resulting respective pre-hydrogenation time from stoichiometric hydrogenations of the diolefin complexes via UV/Vis spectroscopy. This method is especially useful for very slow diolefin hydrogenations (e.g., cod hydrogenation with the ligands Me-Duphos, Et-Duphos (1,2-bis(2,5-diethylphospholano)benzene), and dppe (1,2-bis(diphenylphosphino)ethane).

Peripheral SH-functionalisation of carbosilane dendrimers including the synthesis of the model compound dimethylbis(propanethiol)silane and their interaction with rhodium complexes

Treatment of the allyl-containing compounds Me2Si(CH2CHCH2)2 and MeSi(CH2CHCH2)3 with thioacetic acid in the presence of AIBN gave Me2Si[(CH2)3SC(O)CH3]2 and MeSi[(CH2)3SC(O)CH3]3, respectively, which were reduced with LiAlH4 to the dithiols Me2Si[(CH2)3SH]2(3) and MeSi[(CH2)3SH]3(4). This protocol was applied to the first and second generations of the doubly and triply-branched carbosilane allyl dendrimers, Si[(CH2)3SiMe(CH2CHCH2)2]4(G(1)allyl-8), Si[(CH2)3SiMe{(CH2)3SiMe(CH2CHCH2)2}2]4(G(2)allyl-16), Si[(CH2)3Si(CH2CHCH2)3]4(G(1)allyl-12), and Si[(CH2)3Si{(CH2)3Si(CH2CHCH2)3}3]4(G(2)allyl-36) to give the corresponding SH functionalised surface dendrimers Si[(CH2)3SiMe(CH2CH2CH2SH)2]4(G(1)SH-8), G(2)SH-16, G(1)SH-12, and G(2)SH-36. Reactions of 3 with [M(acac)(diolefin)](M = Rh, Ir; diolefin = 1,5-cyclooctadiene, 2,5-norbornadiene) gave the compounds of the type [M2(mu-Me2Si[(CH2)3S]2)(diolefin)2]n. These diolefin complexes are octanuclear (n= 4) in solution while the complex [Rh2(mu-Me2Si[(CH2)3S]2)(cod)2]n(5) is tetranuclear in the solid state. The structure of 5, solved by X-ray diffraction methods, consists of a 20-membered metallomacrocycle formed by two dimethylbis(propylthiolate)silane moieties bridging four fragments Rh(cod) in a mu2 fashion through the sulfur atoms. Treatment of [Rh(acac)(CO)2] with 3 gave [Rh2(mu-Me2Si[(CH2)3S]2)(CO)4]n, which is a mixture of tetra (n= 2) and octanuclear (n= 4) complexes in a 2 : 1 ratio in solution, while the related complex [Rh2(mu-Me2Si[(CH2)3S]2)(CO)2(PPh3)2]2 is tetranuclear. Reactions of [Rh(acac)(L-L)](L-L = cod, (CO)2, (CO)(PPh3)) with 4 and the dendrimers G(1)SH-8, G(2)SH-16, and G(1)SH-12, gave microcrystalline solids of formulae [Rh3(MeSi[(CH2)3S]3)(L-L)3]n, [Si[(CH2)3SiMe{(CH2)3SRh(cod)}2]4]n([G(1)Rh(cod)-8]n), [Si[(CH2)3Si{(CH2)3SRh(cod)}3]4]n([G(1)Rh(cod)-12]n), etc., which presumably are tridimensional coordination polymers.

Coordinatively unsaturated molybdenum complexes with chelating cycloheptatrienyl-phosphane ligands and their use in transition metal catalysis

The synthesis of the tetrahydroborate complex [(2-iPr2PC6H4-η7-C7H6)Mo(η2-BH4)(P–Mo)] 3 containing the linked cycloheptatrienyl-phosphane ligand [2-(diisopropylphosphanyl)phenyl]cycloheptatrienyl is described, which provides the possibility to generate the 14-electron complex [(2-iPr2PC6H4-η7-C7H6)Mo(P–Mo)]+ (4) on treatment with dimethylanilinium salts such as [HNMe2Ph][BPh4]. Generation of (4)BPh4 in the presence of 2,6-dimethylphenyl isocyanide, 2,5-norbornadiene or phenylacetylene affords the diisocyanide complex (5a)BPh4, the diolefin complex (5b)BPh4 and the alkyne complex (6)BPh4, respectively. The latter complex can be used for the catalytic oligomerization of phenylacetylene affording predominantly the cyclotrimers 1,3,5- and 1,2,4-triphenylbenzene.

A stable chiral diolefin complex of CuI with predetermined configuration at the metal centre

A derivative of (S,S)-bis(pinene)bipyridine, which contains two terminal olefin groups, forms a mononuclear complex with CuI; X-ray crystallography shows the predetermination of configuration around the metal centre.

Rhodium/iridium-titanium azaheterometallocubanes.

Treatment of [[Ti(eta5-C5Me5)(mu-NH)]3(mu3-N)] (1) with the diolefin complexes [[MCl(cod)]2] (M = Rh, Ir; cod = 1,5-cyclooctadiene) in toluene afforded the ionic complexes [M-(cod)(mu3-NH)3Ti3(eta5-C5Me5)3(mu3-N)]Cl [M = Rh (2), Ir (3)]. Reaction of complexes 2 and 3 with [Ag(BPh4)] in dichloromethane leads to anion metathesis and formation of the analogous ionic derivatives [M(cod)(mu3-NH)3Ti3-(eta5-C5Me5)3(mu3-N)][BPh4] [M = Rh (4), Ir (5)]. An X-ray crystal structure determination for 5 reveals a cube-type core [IrTi3N4] for the cationic fragment, in which 1 coordinates in a tripodal fashion to the iridium atom. Reaction of the diolefin complexes [[MCl(cod))2] (M = Rh, Ir) and [[RhCl(C2H4)2]2] with the lithium derivative [[Li(mu3-NH)2(mu3-N)-Ti3(eta5-C5Me5)3(mu3-N)]2] x C7H8 (6 C7H8) in toluene gave the neutral cube-type complexes [M(cod)(mu-NH)2(mu3-N)Ti3-(eta5-C5Me5)3(mu3-N)] [M = Rh (7), Ir (8)] and [Rh(C2H4)2(mu3-NH)2(mu3-N)Ti3(eta5-C5Me5)3(mu3-N)] (9), respectively. Density functional theory calculations have been carried out on the ionic and neutral azaheterometallocubane complexes to understand their electronic structures.

Deprotonation of Cp2Ti(SH)2 with Mononuclear Rhodium and Iridium Compounds: A New Route to Trinuclear Early−Late Heterobimetallic Complexes

The reaction of Cp2Ti(SH)2 with [M(acac)(diolefin)] (acac = acetylacetonate) yields the complexes [Cp(acac)Ti(μ3-S)2{M(diolefin)}2] (M = Rh, diolefin = 1,5-cyclooctadiene (cod) (1); diolefin = tetrafluorobenzobarrelene (tfbb) (2); M = Ir, diolefin = cod (3)). The formation of the trinuclear heterobimetallic complexes results from a complex reaction involving the deprotonation of the hydrosulfido ligands along with the addition of the late-metal fragment(s), followed by the release of cyclopentadiene and the coordination of acetylacetonate to the titanium center. Similarly, the reaction of Cp2Ti(SH)2 with [M(quinol)(diolefin)] (quinol = 8-oxyquinolinate) gives the complexes [Cp(quinol)Ti(μ3-S)2{M(diolefin)}2] (M = Rh, diolefin = cod (4); tfbb (5); M = Ir, diolefin = cod (6)), which incorporate the 8-oxyquinolinate ligand. The d0−d8 trinuclear early−late heterobimetallic complexes exhibit triangular TiRh2 and TiIr2 cores doubly capped by two μ3-sulfido ligands. Deprotonation of Cp2Ti(SH)2 with the mononuclear carbonyl complexes [M(acac)(CO)2] (M = Rh, Ir) yields the ion-pair complexes [Cp2Ti(acac)][M3(μ3-S)2(CO)6] (M = Rh (7); M = Ir (8)), which result from complete transference of the sulfido ligands to the d8 metal centers. Carbonylation of the diolefin complexes [Cp(acac)Ti(μ3-S)2{M(diolefin)}2] or [Cp(quinol)Ti(μ3-S)2{M(diolefin)}2] yields the compounds [Cp(acac)Ti(μ3-S)2{M(CO)2}2] (M = Rh (9); M = Ir (10)) and [Cp(quinol)Ti(μ3-S)2{M(CO)2}2] (M = Rh (11); M = Ir (12)), respectively. Replacement reactions on the carbonyl complexes with triphenylphosphine give the disubstituted complexes [Cp(acac)Ti(μ3-S)2{M(CO)(PPh3)}2] (M = Rh (13); M = Ir (14)) or [Cp(quinol)Ti(μ3-S)2{M(CO)(PPh3)}2] (M = Rh (15); M = Ir (16)), which are obtained as mixtures of cis and trans isomers. The molecular structures of complexes 1 and 8 have been determined by X-ray diffraction methods.

Displacement of weakly coordinating anions from zirconocene alkyl cations by trialkyl phosphines: A model for olefin coordination in homogeneous Ziegler–Natta catalysis

Displacement of the anion H 3C–B(C 6F 5) 3 − from the zirconocene contact-ion pair [(C 5H 5) 2Zr(CH 3) +⋯( μ-H 3C)–B(C 6F 5) 3 −] by a series of phosphines and formation of a bisphosphine complex by uptake of a second phosphine ligand have been studied by NMR methods in C 6D 6 solutions. Evidence is presented that associated, outer-sphere ion pairs [(C 5H 5) 2Zr(CH 3)(PR 3)] + H 3C–B(C 6F 5) 3 − predominate at zirconocene concentrations up to ca. 2 mM; higher aggregates become apparent at higher zirconocene concentrations. Equilibrium constants for the formation of mono- and bis-PMe 3 complexes have been determined; the latter are found to be highly sensitive to steric perturbations. These data, together with density-functional estimates for reaction enthalpies, lead to the following qualitative conclusions with regard to olefin coordination in zirconocene-based polymerization catalysts: (i) The olefin substrate displaces the borate anion only from a small equilibrium fraction of the zirconocene alkyl cations present; (ii) the predominant fraction of the resulting zirconocene alkyl olefin cation remains in an outer-sphere association with the counteranion; (iii) mutual displacement of olefin and counteranion from the Zr center is slow compared to typical olefin insertions; (iv) uptake of a second olefin under formation of a cationic zirconocene alkyl diolefin complex is rather unlikely even at elevated olefin concentrations.

Dihydrido and Trihydrido Diolefin Complexes Stabilized by the Os(PiPr3)2 Unit: New Examples of Quantum Mechanical Exchange Coupling in Trihydrido Osmium Compounds

The hexahydrido complex OsH6(PiPr3)2 (1) reacts with tetrafluorobenzobarrelene (TFB), 2,5-norbornadiene (NBD), and 1,3-cyclohexadiene to afford OsH2(η4-TFB)(PiPr3)2 (2), OsH2(η4-NBD)(PiPr3)2 (3), and OsH2(η4-cyclohexadiene)(PiPr3)2 (4), respectively. The protonation of 2 and 3 with HBF4 yields [OsH3(η4-TFB)(PiPr3)2]BF4 (5) and [OsH3(η4-NBD)(PiPr3)2]BF4 (6). The 1H NMR spectra of 5 and 6 in the hydrido region at low temperature display AM2X2 spin systems (X = 31P), which are simplified to AM2 spin systems in the 1H{31P} spectra. The values for JAM are temperature dependent, increasing from 13.1 to 35.9 Hz (5) and from 11.0 to 17.7 Hz (6) as temperature is increased from 190 to 230 K and from 180 to 240 K, respectively. The reaction of 4 with HBF4 leads to the cyclohexenyl complex [OsH2(η3-C6H9)(PiPr3)2]BF4 (7), which shows an agostic interaction between the osmium center and one of the two endo-CH bonds adjacent to the π-allyl unit. In solution complex 7 is fluxional. The fluxional process involves the exchange between the relative positions of the hydrido ligands and the endo-CH hydrogen atoms of the cyclohexenyl ligand and, at the same time, the exchange between the CH allyl and the exo-CH hydrogen atoms inside the cyclohexenyl ligand. The structure of 7 in the solid state has been determined by X-ray diffraction. The distribution of ligands around the osmium atom can be described as a piano stool geometry with the agostic hydrogen atom and the midpoints of the carbon−carbon bonds involved in the π-allyl unit forming the three-membered face, while both the hydrido and phosphine ligands lie in the four-membered face.

Optically active transition-metal complexes. III. Synthesis of optically active ( η4-aminodiolefin)tricarbonyl iron complexes. Kinetic resolution of a chiral amine by means of an optically active dienyl iron cation

The synthesis of optically active η 4-(aminodiolefin)tricarbonyl iron complexes by the nucleophilic addition of primary and secondary amines to the optically active tricarbonyl-(1 R)-( η 5-methyl-nopadienyl)iron(1+) cation ( 4) is described. Under either kinetic or thermodynamic control, the reaction leads to ( E, E)-diolefin complexes with generation of a new chiral carbon centre. Racemic ( R/ S)-phenylethylamine was kinetically resolved ( de = 38%) by treatment with 4 at –78°C.