Insertion Reactions of [ReH(CO)5–n(PMe3)n] Complexes (n = 2–4) with aldehydes,CO2, and activated acetylenes

The complexes of the type [ReH(CO)_5–n(PMe₃)_n] (n = 4, 3) were reacted with aldehydes, CO₂, and RC?CCOOMe (R = H, Me) to establish a phosphine-substitutional effect on the reactivity of the Re–H bond. In the series 1–3 , benzaldehyde showed conversion with only 3 to afford a (benzyloxy)carbonyltetrakis(trimethylphosphine)rhenium complex 4 . Pyridine-2-carbaldehyde allowed reaction with all hydrides 1–3 . With 1 and 2 , the same dicarbonyl[(pyridin-2-yl)methoxy-O, N]bis(trimethylphosphine)rhenium 5b was formed with the intermediacy of a [(pyridin-2-yl)methoxy-O]-ligated species and extrusion of CO or PMe₃, respectively. The analogous conversion of 3 afforded the carbonyl[(pyridin-2-yl)methoxy-O,N]tris(trimethylphosphine)rhenium ( 1 ) 7b . While 1 did not react with CO₂, 2 and 3 yielded under relatively mild conditions the formato-ligated [Re(HCO₂)(CO)(L)(PMe₃)₃] species ( 8 (L = CO) and 9 (L = PMe₃)). Methyl propiolate and methyl butynoate were transformed, in the presence of 1 , to [Re{C(CO₂Me)?CHR}(CO)₃(PMe₃)₂] systems ( 10a (R = H), and 10b (R = Me)), with prevailing α-metallation and trans-insertion stereochemistry. Similarly, HC≡CCO₂Me afforded with 2 and 3 , the α-metallation products [Re{C(CO₂Me)?CH₂}(CO)(L)(PMe₃)₃] 11 (L = CO) and 12 (L = PMe₃). The methyl butyonate insertion into 2 resulted in formation of a mixture of the (Z)- and (E)-isomers of [Re{C(CO₂Me)?CHMe} (CO)₂(PMe₃)₃] ( 13a , b ). In the case of the conversion of 3 with MeC?CCO₂Me, a Re–H cis-addition product [Re{(E)-C(CO₂Me)?CHMe}(CO)(PMe₃)₄] ( 14 ) was selectively obtained. Complex 11 was characterized by an X-ray crystal-structure analysis.     

Organic Reactions upon Dimetalated Olefins. Reactions of the Olefinic Group in the Dirhenlum Complex (OC)4Re[E-HC?C(CO2Me)CS2]Re(CO)4 with Amines

The reaction of (OC)₄Re[μ-E-HC? C(CO₂Me)CS₂]Re(CO)₄, 1 with EtNH₂ yielded two new complexes: Re(CO)₄[C(H)? C(CO₂Me)C(NHEt)? S], 2 , (52%) and Re(CO)₃(NH₂Et)[C(H)? C(CO₂Me)C(NHEt)=S], 3a (24%) by competitive attack of the EtNH₂ at the dithiocarboxylate grouping and at the hydrogen substituted olefinic carbon atom in 1 . In both cases there is a loss of one of the rhenium groupings. The reaction of the sulfurized and oxygenated derivatives of 1, (OC)₄Re[EC(H)C(CO₂Me)CS₂]Re(CO)₄, 4a (E=S), 4b (E=O) with EtNH₂ yielded Re(CO)₄[C(H)=C(CO₂Me)C(NHEt)=S], 5a , the parent carbonyl of 3a , by exclusive attack of the amine at the hydrogen substituted olefinic carbon atom. The reaction of (OC)₄Re[μ-SC(S)C(CO₂Me)C(H)S]Re(CO)₄, 6a (an isomer of 4a ) with EtNH₂ produced a similar result. The reaction of 4a with Et₂NH yielded Re(CO)₄[μ-S₂C=C(CO₂Me)C=NEt₂], 5b an N-ethyl substituted derivative of 5a . These results indicate that the addition of certain heteroatoms can have a directing effect upon the reactivity of these compounds with amines. Compounds 2 and 5a were characterized by single crystal x-ray diffraction analyses. Crystal Data: For 2 : space group = P1, a = 10.782(1) Å, b = 14.721(2) Å, c = 9.940(2) Å, a = 91.57(1)°, β = 93.61(1)°, γ = 70.774(9)°, Z = 4, 4516 reflections, R = 0.047 and for 5a : space group = P2₁/n, a = 11.389(2) Å, b = 9.660(2) Å, c = 14.756(3) Å, β = 103.36(2)°, Z = 4, 1601 reflections, R = 0.022.     

Chemistry of Fischer-type rhenacyclobutadiene complexes. II. Reactions with alkynes and sulfonium ylides, and rearrangements induced by nitriles and pyridine

Further investigations into the chemistry of the rhenacyclobutadiene complexes (CO)₄Re(η²-C(R)C(CO₂Me)C(X)) (1: R=Me, X=OEt (1a), O(CH₂)₃CCH (1b), NEt₂ (1c); R=CHEt₂, X=OEt (1d); R=Ph, X=OEt (1e)) are reported. Reactions of 1 with alkynes at reflux temperature of toluene and at ambient temperature either under photochemical conditions or in the presence of PdO yield ring-substituted η⁵-cyclopentadienylrhenium tricarbonyl complexes, 2. The symmetrical alkynes R^′CCR^′ (R^′=Ph, Me, CO₂Me) afford the pentasubstituted complexes (η⁵-C₅(Me)(CO₂Me)(OEt)(Ph)(Ph))Re(CO)₃ (2d), (η⁵-C₅(Me)(CO₂Me)(OEt)(Me)(Me))Re(CO)₃ (2e), (η⁵-C₅(Me)(CO₂Me)(OEt)(CO₂Me)(CO₂Me))Re(CO)₃ (2f), and (η⁵-C₅(Me)(CO₂Me)(NEt₂)(CO₂Me)(CO₂Me))Re(CO)₃ (2i) on reaction with the appropriate 1, whereas the unsymmetrical alkynes R^′CCR″ (R^′=Ph; R″=H, Me) give either only one, (η⁵-C₅(Me)(CO₂Me)(OEt)(Ph)H)Re(CO)₃ (2a)), or both, (η⁵-C₅(Me)(CO₂Me) (OEt)(Ph)(Me))Re(CO)₃ (2b) and (η⁵-C₅(Me)(CO₂Me)(OEt)(Me)(Ph))Re(CO)₃ (2c), (η⁵-C₅(Ph)(CO₂Me)(OEt)(Ph)H)Re(CO)₃ (2g) and (η⁵-C₅(Ph)(CO₂Me)(OEt)(H)(Ph))Re(CO)₃ (2h), of the possible products of [3 + 2] cycloaddition of alkyne to η²-C(R)C(CO₂Me)C(X). Thermolysis of (CO)₄Re(η²-C(Me)C(CO₂Me)C(O(CH₂)₃CCH)) (1b) containing a pendant alkynyl group proceeds to (η⁵-C₅(Me)(CO₂Me)(O(CH₂)₃)H)Re(CO)₃ (2j), a η⁵-cyclopentadienyl-dihydropyran fused-ring product. Competition experiments showed that each of PhCCH and MeO₂CCCCO₂Me reacts faster than PhCCPh with 1a. The results with unsymmetrical alkynes are rationalized by steric properties of substituents at the CC and ReC bonds and by a preference of ReC(Me) over ReC(OEt) to undergo alkyne insertion. A mechanism is proposed that involves substitution of a trans CO by alkyne in 1, insertion of alkyne into ReC bond to give a rhenabenzene intermediate, and collapse of the latter to 2. Complexes 1a and 1d undergo rearrangement in MeCN at reflux temperature to give rhenafuran-like products, (CO)₄Re(κ²-OC(OMe)C(CHCR₂)C(OEt)) (R=H (3a) or Et (3b)). The reaction of 1d also proceeds in EtCN, PhCN, and t-BuCN at comparable temperature, but is slower (especially in t-BuCN) than in MeCN. In pyridine at reflux temperature, 1a undergoes a similar rearrangement, with CO substitution, to give (CO)₃(py)Re(κ²-OC(OMe)C(CHCEt₂)C(OEt)) (4). A mechanism is proposed for these reactions. The sulfonium ylides Me₂SCHC(O)Ph and Me₂SC(CN)₂ (Me₂SCRR^′) react with 1a in acetonitrile at reflux temperature by nucleophilic addition of the ylide to the ReC(Me) carbon, loss of Me₂S, and rearrangement to a rhenafuran-type structure to yield (CO)₄Re(κ²-OC(OMe)C(C(Me)CRR^′)C(OEt)) (R=H, R^′=C(O)Ph (5a); R=R^′CN (5b)). All new compounds were characterized by a combination of elemental analysis, mass spectrometry, and IR and NMR spectroscopy.     

Synthesis and Characterization of Rhenabenzyne Complexes

Reactions of [ReH₅(PMe₂Ph)₃] with alkynols HC≡CC(OH)(R)C≡CSiMe₃ (R=tBu, iPr, 1‐adamantyl) in the presence of HCl give the vinylcarbyne complexes [Re{≡CCH?C(R)C≡CSiMe₃}Cl₂(PMe₂Ph)₃], which react with tBuMgCl to give [Re{≡CCH?C(R)C≡CSiMe₃}HCl(PMe₂Ph)₃]. Treatment of [Re{≡CCH?C(R)C≡CSiMe₃}HCl(PMe₂Ph)₃] with nBu₄NF gives [Re{≡CCH?C(R)C≡CH}HCl(PMe₂Ph)₃], which first isomerizes to the bicyclic complexes [Re{CH?CH? C(R)?CCH?}Cl(PMe₂Ph)₃], and then to the rhenabenzynes [Re{≡CCH?C(R)CH?CH}Cl(PMe₂Ph)₃]. The NMR spectroscopic and structural data as well as the aromatic stabilization energy (ASE) and nucleus‐independent chemical‐shift (NICS) values suggest that these rhenabenzynes have aromatic character.     

Chemistry of Fischer-type rhenacyclobutadiene complexes. I. Deprotonation, addition/substitution of nucleophilic reagents at α-carbon, and insertion of heteroatoms into rhenium-carbon bonds

The rhenacyclobutadienes (CO)₄Re(η²- C(R)C(CO₂Me)C(OR^′)) (2) undergo a number of reactions that mirror those of Fischer alkoxycarbene complexes. Thus, (CO)₄Re(η²-C(Me)C(CO₂Me)C(OEt)) (2a) can be deprotonated by LDA, Na[OBu-t], or Na[CH(CO₂Me)₂] to give the ylide-like conjugate base [(CO)₄Re(η²-C(CH₂)C(CO₂Me)C(OEt)]⁻ (3), which was isolated as PPN(3). Li(3) undergoes deuteriation with DCl/D₂O and alkylation with Et₃OPF₆ at ReCCH₂, with the latter reaction affording (CO)₄Re(η²-C(CH₂Et)C(CO₂Me)C(OEt)) (4). Repetition of the sequence deprotonation-ethylation on 4 generates (CO)₄Re(η²-C(CHEt₂)C(CO₂Me)C(OEt)) (5). The nature of the alkoxy substituent in 2 can be varied by use of the rhenacyclobutenones Na[(CO)₄Re(η²-C(R)C(CO₂Me)C(O))] (Na(1)) in conjunction with AcCl and R^′OH to produce a series of new complexes (R=Ph, R^′=Et (2b); R=Me, R^′=CH₂CHCH₂ (2c), (CH₂)₃CCH (2d), Me (2e)). Aminolysis of 2a with the primary and secondary amines PhNH₂, HO(CH₂)₂NH, p-TolNH₂, and Et₂NH yields the aminorhenacyclobutadiene complexes (CO)₄Re(η²-C(Me)C(CO₂Me)C(NHR^′ or NR^′₂)) (R₂^′=Et₂ (6a); R^′=Ph (6b), (CH₂)₂OH (6c), p-Tol (6d)). These complexes display lesser carbene-like character than their alkoxy counterparts 2, as evidenced by ¹H and ¹³C NMR spectroscopic properties and lack of reactivity toward LDA by 6a. Reactions of each 2a and 6a with PPhMe₂ at low temperature afford (CO)₄Re(η²-C(Me)(PPhMe₂)C(CO₂Me)C(OEt)) (7) and (CO)₃(PPhMe₂)Re(η²-C(Me)C(CO₂Me)C(NEt₂)) (9), respectively, further in agreement with the more carbenoid nature of 2a than 6a. 7 undergoes conversion to (CO)₃(PPhMe₂)Re(η²-C(Me)C(CO₂Me)C(OEt)) (8) upon heating. 2a reacts with each of (NH₄)₂[Ce(NO₃)₆], DMSO, EtNO₂/Et₃N, and Me₃NO under various conditions to afford one or both of the oxygen atom insertion products into the ReC bonds, (CO)₄Re(κ²-OC(Me)C(CO₂Me)C(OEt)) (10) and (CO)₄Re(κ²-C(Me)C(CO₂Me)C(OEt)O) (11). In contrast, no reaction occurred between 2a and S₈ on heating. However, 6a was converted to the NH insertion product (CO)₄Re(κ²-NHC(Me)C(CO₂Me)C(NEt₂)) (12) by the action of H₂NNH₂ · H₂O at 0 °C. All new compounds were characterized by a combination of elemental analysis, mass spectrometry, and IR and NMR spectroscopy.     

Stabilization of a Silaaldehyde by its η2 Coordination to Tungsten

Treatment of pyridine‐stabilized silylene complexes [(η⁵‐C₅Me₄R)(CO)₂(H)W?SiH(py)(Tsi)] (R=Me, Et; py=pyridine; Tsi=C(SiMe₃)₃) with an N‐heterocyclic carbene ^MeIⁱPr (1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene) caused deprotonation to afford anionic silylene complexes [(η⁵‐C₅Me₄R)(CO)₂W?SiH(Tsi)][H^MeIⁱPr] (R=Me ( 1‐Me ); R=Et ( 1‐Et )). Subsequent oxidation of 1‐Me and 1‐Et with pyridine‐N‐oxide (1 equiv) gave anionic η²‐silaaldehydetungsten complexes [(η⁵‐C₅Me₄R)(CO)₂W{η²‐O?SiH(Tsi)}][H^MeIⁱPr] (R=Me ( 2‐Me ); R=Et ( 2‐Et )). The formation of an unprecedented W‐Si‐O three‐membered ring was confirmed by X‐ray crystal structure analysis.     

Fixation of Metallo Nitrile Ylides and Metallo Nitrile Imines as Ligands in Transition Metal Complexes [1]

1,3‐Dipoles of the type metallo nitrile ylide and metallo nitrile imine were prepared by mono‐α‐deprotonation of CH‐acidic {[W(CO)₅CHCH₂PPh₃]PF₆, M(CO)₅CNCH₂CO₂R (M = Cr, W; R = Me, Et), [Pt(Cl)(CNCH₂CO₂Et)(PPh₃)₂]BF₄} and NH‐acidic isocyanide complexes (Cr(CO)₅CNNH₂) and were stabilized by coordination to a second transition metal complex fragment {Cr(CO)₅, [M(CO)₅]⁺ (M = Mn, Re), [FeCp(CO)₂]⁺, [Pt(Cl)(PR₃)₂]⁺ (R = Et, Ph)}. All dinuclear products 1 – 7 , 10 , and 11 are neutral species except [(Ph₃P)₂(Cl)Pt{μ₂‐CNCH(CO₂Et)}Pt(Cl)(PPh₃)₂]BF₄ ( 8 ). Complex (OC)₅W{μ₂‐CNCH(CO₂Et)}Pt(Cl)(PEt₃)₂ ( 5b ) was characterized by X‐ray diffraction. Twofold deprotonation/platination to give (OC)₅Cr{μ₃‐CNC(Ph)}[Pt(Cl)(PPh₃)₂]₂ ( 9 ) was achieved in the case of Cr(CO)₅CNCH₂Ph.     

Zur Reaktion von Diphenoxyphosphorylchlorid mit N,N-disubstituierten Harnstoffen – Bildung von phosphorylierten Biuret-Verbindungen

Reaction of Diphenoxyphosphorylchloride with N,N-disubstituted Ureas – Formation of Phosphorylated Biuret Compounds N′,N′-disubstituted N-diphenoxyphosphorylureas, (PhO)₂P(O)? NH? CO? NR¹R² (R¹ = R² = Et, 1 ; n-Pr, 2 ; n-Bu, 3 ; i-Bu, 4 ; R¹ = Me and R² = Ph, 5 ) as well as phosphorylated biuret compounds, (PhO)₂P(O)? NH? CO? NH? CO? NR¹R² are obtained in the reaction of diphenoxyphosphorylchloride with N,N-disubstituted ureas and triethylamine. The biuret derivatives are formed via (PhO)₂P(O)NCO. Their yield rises if the reaction is carried out without amine. The X-ray crystal structure analysis of (PhO)₂P(O)? NH? CO? NH? CO? NPr₂, 8 , shows that dimers exist in the crystal with intermolecular as well as intramolecular hydrogen bonds. The framework formed by atoms P? N1? C1(O4)? N2? C2(O5)? N3(C3)C6 is planar. The existence of a rotation barrier along the bond C2–N3 was detected by NMR spectroscopy.     

Darstellung und oxidative Derivatisierung von Dialkylthiophosphiten

Preparation and Oxidative Derivatisation of Phosphonothionic Esters The kind of the amine used influences decisively course and rate of the reaction of trialkyl phosphites, (RO)₃P (R = Me, Et, Ph) with H₂S in the presence of different amines (Et₃N, Et₂NH, Et₂NPh, pyridine). Phosphonothionic esters, (RO)₂P(S)H (R = Me, Et, Bu), are obtained in over 80% yield by using pyridine as base and an alkali alcoholate as catalyst. The oxidative derivatisation of phosphonothionic esters by means of CCI₄ and protic (4-nitrophenol, 2,4,5-trichlorophenol, ammonia, piperidine, phenylhydrazine) or anionic nucleophiles (F^?, NCS^?, NCO^?, CN^?, N₃^?) (Atherton-Todd reaction) yields thiophosphoric acid derivatives (RO)₂P(S)Nuc (R = Me, Et, Bu: Nuc = 4-nitrophenoxy, PhNHNH; R = Me, Et: Nuc = 2,4,5-trichlorophenoxy, F, NCS, N₃; R = Me: NH₂, C₅H₁₀N; R = Et: Nuc = CI, CN) and in some cases the dealkylated products (RO)P(Nuc)SO^? (R = Me; Nuc = CI, F, NCS, CN). The phosphazenes (EtO)₂P(S)? N = PPh₃ and (MeO)₂P(S)? N ? P(OEt)₃, up to now unknown in literature, were obtained by treating thiophosphoryl azides with PPh₃ or P(OEt)₃, resp.     

1,1‐Ethylboration of alkyn‐1‐yl‐chloro(methyl)silanes: alkenes with chloro(methyl)silyl and diethylboryl groups in cis positions

The 1,1‐ethylboration of alkyn‐1‐yl‐chloro(methyl)silanes, Me₂Si(Cl)? C?C? R ( 1 ) and Me(H)Si(Cl)? C?C? R ( 2 ) [R = Bu ( 2a ), CH₂NMe₂ ( 2b )] requires harsh reaction conditions (up to 20 days in boiling triethylborane), and leads to alkenes in which the boryl and silyl groups occupy cis ((E)‐isomers: 3a , 3b , 5a , 5b ) or trans positions ((Z)‐isomers in smaller quantities: 4b and 6b ). The alkenes are destabilized in the presence of SiH(Cl) and CH₂NMe₂ units ( 5b , 6b ). NMR data indicate hyper‐coordinated silicon by intramolecular N? Si coordination in 3b and 5b , by which, at the same time, weak Si? Cl? B bridges are favoured. Copyright © 2005 John Wiley & Sons, Ltd.     

On the P‐Coordinating Limit of NHC–Phosphenium Cations toward RhI Centers

Two types of imidazoliophosphane with additional electron‐withdrawing substituents, such as alkoxy or imidazolio groups, are experimentally described and theoretically studied. Diethyl N,N′‐2,4,6‐methyl(phenyl)imidazoliophosphonite is shown to retain a P‐coordinating ability toward a {RhCl(cod)} (cod=cycloocta‐1,5‐diene) center, thus competing with the cleavage of the labile C? P bond. Derivatives of N,N′‐phenylene‐bridged diimidazolylphenylphosphane were isolated in good yield. Whereas the dicationic phosphane proved to be inert in the presence of [{RhCl(cod)}₂], the monocationic counterpart was shown to retain the P‐coordinating ability toward a {RhCl(cod)} center, thus competing with the N‐coordinating ability of the nonmethylated imidazolyl substituent. The ethyl phosphinite version of the dication, thus possessing an extremely electron‐poor P^III center, was also characterized. According to the difference between the calculated homolytic and heterolytic dissociation energies, the N₂C???P bond of imidazoliophosphanes with aryl, amino, or alkoxy substituents on the P atom is shown to be of dative nature. The P‐coordinating properties of imidazoliophosphanes with various combinations of phenyl or ethoxy substituents on the P atom and those of six diimidazolophosphane derivatives with zero, one, or two methylium substituents on the N atom, were analyzed by comparison of the corresponding HOMOs and LUMOs and by calculation of the IR C?O stretching frequencies of their [RhCl(CO)₂] complexes. Comparison of the ν_CO values allows the family of the electron‐poor Im⁺PRR′ (Im=imidazolyl) potential ligands to be ranked in the following order versus (R,R′): P(OEt)₃<(Ph,Ph)<(Ph,OEt)<(OEt,OEt)<PF₃<(Ph,Im)<(Ph,Im⁺)<(OEt,Im⁺). The (Ph,Im) representative is therefore the least electron‐donating phosphane for which coordinating behavior toward a Rh^I center has been experimentally evidenced to date. Ultimate applications in catalysis could be envisaged.     

Alkoxy-1,3,5-triazapentadien(e/ato) copper(II) complexes: template formation and applications for the preparation of pyrimidines and as catalysts for oxidation of alcohols to carbonyl products

Template combination of copper acetate (Cu(AcO)₂?H₂O) with sodium dicyanamide (NaN(C≡N)₂, 2 equiv) or cyanoguanidine (N≡CNHC(=NH)NH₂, 2 equiv) and an alcohol ROH (used also as solvent) leads to the neutral copper(II)–(2,4‐alkoxy‐1,3,5‐triazapentadienato) complexes [Cu{NH?C(OR)NC(OR)?NH}₂] (R=Me ( 1 ), Et ( 2 ), nPr ( 3 ), iPr ( 4 ), CH₂CH₂OCH₃ ( 5 )) or cationic copper(II)–(2‐alkoxy‐4‐amino‐1,3,5‐triazapentadiene) complexes [Cu{NH?C(OR)NHC(NH₂)?NH}₂](AcO)₂ (R=Me ( 6 ), Et ( 7 ), nPr ( 8 ), nBu ( 9 ), CH₂CH₂OCH₃ ( 10 )), respectively. Several intermediates of this reaction were isolated and a pathway was proposed. The deprotonation of 6 – 10 with NaOH allows their transformation to the corresponding neutral triazapentadienates [Cu{NH?C(OR)NC(NH₂)?NH}₂] 11 – 15 . Reaction of 11 , 12 or 15 with acetyl acetone (MeC(?O)CH₂C(?O)Me) leads to liberation of the corresponding pyrimidines NC(Me)CHC(Me)NC NHC(?NH)OR, whereas the same treatment of the cationic complexes 6 , 7 or 10 allows the corresponding metal‐free triazapentadiene salts {NH₂C(OR)?NC(NH₂)?NH₂}(OAc) to be isolated. The alkoxy‐1,3,5‐triazapentadiene/ato copper(II) complexes have been applied as efficient catalysts for the TEMPO radical‐mediated mild aerobic oxidation of alcohols to the corresponding aldehydes (molar yields of aldehydes of up to 100 % with >99 % selectivity) and for the solvent‐free microwave‐assisted synthesis of ketones from secondary alcohols with tert‐butylhydroperoxide as oxidant (yields of up to 97 %, turnover numbers of up to 485 and turnover frequencies of up to 1170 h^?1).     

Aromatic Osmacyclopropenefuran Bicycles and Their Relevance for the Metal‐Mediated Hydration of Functionalized Allenes

The aromatic osmacyclopropenefuran bicycles [OsTp{κ³‐C¹,C²,O‐(C¹H₂C²CHC(OEt)O)}(PⁱPr₃)]BF₄ (Tp=hydridotris(1‐pyrazolyl)borate) and [OsH{κ³‐C¹,C²,O‐(C¹H₂C²CHC(OEt)O)}(CO)(PⁱPr₃)₂]BF₄, with the metal fragment in a common vertex between the fused three‐ and five‐membered rings, have been prepared via the π‐allene intermediates [OsTp(η²‐CH₂=CCHCO₂Et)(OCMe₂)(PⁱPr₃)]BF₄ and [OsH(η²‐CH₂=CCHCO₂Et)(CO)(OH₂)(PⁱPr₃)₂]BF₄, and their aromaticity analyzed by DFT calculations. The bicycle containing the [OsH(CO)(PⁱPr₃)₂]⁺ metal fragment is a key intermediate in the [OsH(CO)(OH₂)₂(PⁱPr₃)₂]BF₄‐catalyzed regioselective anti‐Markovnikov hydration of ethyl buta‐2,3‐dienoate to ethyl 4‐hydroxycrotonate.     

Nitro‐substituted iron(II) tridentate bis(imino)pyridine complexes as high‐temperature catalysts for the production of α‐olefins

A new series of nitro‐substituted bis(imino)pyridine ligands {2,6‐bis[1‐(2‐methyl‐4‐nitrophenylimino)ethyl]pyridine, 2,6‐bis[1‐(4‐nitrophenylimino)ethyl]pyridine, (1‐{6‐[1‐(4‐nitro‐phenylimino)‐ethyl]‐pyridin‐2‐yl}‐ethylidene)‐(2,4,6‐trimethyl‐phenyl)‐amine, and 2,6‐bis[1‐(2‐methyl‐3‐nitrophenylimino)ethyl]pyridine} and their corresponding Fe(II) complexes [{p‐NO₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐ Me? p‐NO₂}FeCl₂ ( 10 ), L₂FeCl₂ ( 11 ), {m‐NO₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? m‐NO₂}FeCl₂ ( 12 ), and {p‐NO₂? Ph? N?C(Me)? Py? C(Me)?N? Mes}FeCl₂ ( 14 )] were synthesized. According to X‐ray analysis, there were shortenings of the axial Fe? N bond lengths (up to 0.014 Å) in para‐nitro‐substituted complex 10 and (up to 0.015 Å) in meta‐nitro‐substituted complex 12 versus the Fe(II) complex without nitro groups [{o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me}FeCl₂ ( 1 )]. Complexes 10 , 12 , and 14 afforded very active catalysts for the production of α‐olefins and were more temperature‐stable and had longer lifetimes than parent non‐nitro‐substituted Fe(II) complex 1 . The reaction between FeCl₂ and a sterically less hindered ligand [p‐NO₂? Ph? N?C(Me)? Py? C(Me)?N? Ph? p‐NO₂] resulted in the formation of octahedral complex 11 . A para‐dialkylamino‐substituted bis(imino)pyridine ligand [p‐NEt₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? p‐NEt₂] and the corresponding Fe(II) complex [{p‐NEt₂? o‐Me? Ph? N?C(Me)? Py? C(Me)?N? Ph? o‐Me? p‐NEt₂}FeCl₂ ( 16 )] were synthesized to evaluate the effect of enhanced electron donation of the ligand on the catalytic performance. According to X‐ray analysis, there was a shortening (up to 0.043 Å) of the axial Fe? N bond lengths in para‐diethylamino‐substituted complex 16 in comparison with parent Fe(II) complex 1 . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2615–2635, 2006     

N,O‐chelate aluminum and zinc complexes: synthesis and catalysis in the ring‐opening polymerization of ε‐caprolactone

Reaction between 2‐(1H‐pyrrol‐1‐yl)benzenamine and 2‐hydroxybenzaldehyde or 3,5‐di‐tert‐butyl‐2‐hydroxybenzaldehyde afforded 2‐(4,5‐dihydropyrrolo[1,2‐a]quinoxalin‐4‐yl)phenol (HOL¹NH, 1a) or 2,4‐di‐tert‐butyl‐6‐(4,5‐dihydropyrrolo[1,2‐a]quinoxalin‐4‐yl)phenol (HOL²NH, 1b). Both 1a and 1b can be converted to 2‐(H‐pyrrolo[1,2‐a]quinoxalin‐4‐yl)phenol (HOL³N, 2a) and 2,4‐di‐tert‐butyl‐6‐(H‐pyrrolo[1,2‐a]quinoxalin‐4‐yl)phenol (HOL⁴N, 2b), respectively, by heating 1a and 1b in toluene. Treatment of 1b with an equivalent of AlEt₃ afforded [Al(Et₂)(OL²NH)] (3). Reaction of 1b with two equivalents of AlR₃ (R = Me, Et) gave dinuclear aluminum complexes [(AlR₂)₂(OL²N)] (R = Me, 4a; R = Et, 4b). Refluxing the toluene solution of 4a and 4b, respectively, generated [Al(R₂)(OL⁴N)] (R = Me, 5a; R = Et, 5b). Complexes 5a and 5b were also obtained either by refluxing a mixture of 1b and two equivalents of AlR₃ (R = Me, Et) in toluene or by treatment of 2b with an equivalent of AlR₃ (R = Me, Et). Reaction of 2a with an equivalent of AlMe₃ afforded [Al(Me₂)(OL³N)] (5c). Treatment of 1b with an equivalent of ZnEt₂ at room temperature gave [Zn(Et)(OL²NH)] (6), while reaction of 1b with 0.5 equivalent of ZnEt₂ at 40 °C afforded [Zn(OL²NH)₂] (7). Reaction of 1b with two equivalents of ZnEt₂ from room temperature to 60 °C yielded [Zn(Et)(OL⁴N)] (8). Compound 8 was also obtained either by reaction between 6 and an equivalent of ZnEt₂ from room temperature to 60 °C or by treatment of 2b with an equivalent of ZnEt₂ at room temperature. Reaction of 2b with 0.5 equivalent of ZnEt₂ at room temperature gave [Zn(OL⁴N)₂] (9), which was also formed by heating the toluene solution of 6. All novel compounds were characterized by NMR spectroscopy and elemental analyses. The structures of complexes 3, 5c and 6 were additionally characterized by single‐crystal X‐ray diffraction techniques. The catalysis of complexes 3, 4a, 5a–c, 6 and 8 toward the ring‐opening polymerization of ε‐caprolactone was evaluated. Copyright © 2008 John Wiley & Sons, Ltd.     

Zur Reaktivität des Ferriophosphaalkens (Z)‐[Cp*(CO)2FeP=C(tBu)NMe2] gegenüber Propiolsäureestern HC≡C‐CO2R (R=Me,Et) und Acetylendicarbonsäureestern RO2C‐C≡C‐CO2R (R=Me,Et, tBu)

On the Reactivity of the Ferriophosphaalkene (Z)‐[Cp*(CO)₂Fe‐P=C(tBu)NMe₂] towards Propiolates HC≡C‐CO₂R (R=Me, Et) and Acetylene Dicarboxylates RO ₂C‐C≡C‐CO₂R (R=Me, Et, tBu) The reaction of equimolar amounts of (Z)‐[Cp*(CO)₂Fe‐P=C(tBu)NMe₂] 3 and methyl‐ and ethyl‐propiolate ( 2a, b ) or of 3 and dialkyl acetylene dicarboxylates 1a (R=Me), 1b (Et), 1c (tBu) afforded the five‐membered metallaheterocycles [Cp*(CO) =C(tBu)NMe₂] ( 4a, b ) and [Cp*(CO) =C(tBu)NMe₂] ( 5a—c ). The molecular structures of 4b and 5a were elucidated by single crystal X‐ray analyses. Moreover, the reactivity of 4b towards ethereal HBF₄ was investigated.     

Synthesis, characterization, and structural studies of multimetallic ferrocenyl carbene complexes of group VII transition metals

Fischer carbene complexes of the group VII transition metals (Mn and Re) containing at least two or three different transition metal substituents, all in electronic contact with the carbene carbon atom, were synthesized. The structural features and their relevance to bonding in the carbene multimetal compounds were investigated, as they represent indicators of possible reactivity sites in polymetallic carbene assemblies. For complexes of the type [ML(x){C(OR)R'}] (ML(x) = MnCp(CO)(2) or Re(2)(CO)(9)), ferrocenyl (Fc) was chosen as the R' substituent, while the OR substituent was systematically varied between an ethoxy or a titanoxy group, to yield the complexes 1a (ML(x) = MnCp(CO)(2), R = Et, R' = Fc), 2a (ML(x) = MnCp(CO)(2), R = TiCp(2)Cl, R' = Fc), 3a (ML(x) = Re(2)(CO)(9), R = Et, R' = Fc), and 4a (ML(x) = Re(2)(CO)(9), R = TiCp(2)Cl, R' = Fc). Direct lithiation of the ferrocene with n-BuLi/TMEDA at elevated temperatures, followed by the Fischer method of carbene preparation, resulted in formation of the novel biscarbene complexes with bridging ferrocen-1,1'-diyl (Fc') substituents [{π-Fe(C(5)H(4))(2)-C,C'}{C(OEt)ML(x)}(2)] (1b, ML(x) = MnCp(CO)(2); 3b, ML(x) = Re(2)(CO)(9)) or the unusual bimetallacyclic bridged biscarbene complexes [{π-TiCp(2)O(2)-O,O'}{π-Fe(C(5)H(4))(2)-C,C'}{CML(x)}(2)] (2b, ML(x) = MnCp(CO)(2); 4b, ML(x) = Re(2)(CO)(9)). The target compounds that were isolated displayed a variety of different geometric isomers and conformations. The greater reactivity of the binary dirhenium acylates in solution, compared to that of the cyclopentadienyl manganese acylate, resulted in a complex reaction mixture. Although the stabilization of hydroxycarbene or hydrido-acyl intermediates of dirhenium carbonyls could not be achieved, their existence in solution was confirmed by the isolation of [(π-H)(2)-(Re(CO)(4){C(O)Fc})(2)] (8), the unique dichloro-bridged biscarbene complex fac-[(π-Cl)(2)-(Re(CO)(3){C(OEt)Fc})(2)] (6), the known hydrido complex [Re(3)(CO)(14)H] (5), the acyl complex [Re(CO)(5){C(O)Fc}] (7), and the aldehyde-functionalized eq-[Re(2)(CO)(9){C(OTiCp(2)Cl)(Fc'CHO)}] (9).     

Characterization of Nα-Fmoc-protected ureidopeptides by electrospray ionization tandem mass spectrometry (ESI-MS/MS): differentiation of positional isomers

Four pairs of positional isomers of ureidopeptides, FmocNH‐CH(R₁)‐φ(NH‐CO‐NH)‐CH(R₂)‐OY and FmocNH‐CH(R₂)‐φ(NH‐CO‐NH)‐CH(R₁)‐OY (Fmoc = [(9‐fluorenyl methyl)oxy]carbonyl; R₁ = H, alkyl; R₂ = alkyl, H and Y = CH₃/H), have been characterized and differentiated by both positive and negative ion electrospray ionization (ESI) ion‐trap tandem mass spectrometry (MS/MS). The major fragmentation noticed in MS/MS of all these compounds is due to ? N? CH(R)? N? bond cleavage to form the characteristic N‐ and C‐terminus fragment ions. The protonated ureidopeptide acids derived from glycine at the N‐terminus form protonated (9H‐fluoren‐9‐yl)methyl carbamate ion at m/z 240 which is absent for the corresponding esters. Another interesting fragmentation noticed in ureidopeptides derived from glycine at the N‐terminus is an unusual loss of 61 units from an intermediate fragment ion FmocNH = CH₂⁺ (m/z 252). A mechanism involving an ion‐neutral complex and a direct loss of NH₃ and CO₂ is proposed for this process. Whereas ureidopeptides derived from alanine, leucine and phenylalanine at the N‐terminus eliminate CO₂ followed by corresponding imine to form (9H‐fluoren‐9‐yl)methyl cation (C₁₄H₁₁⁺) from FmocNH = CHR⁺. In addition, characteristic immonium ions are also observed. The deprotonated ureidopeptide acids dissociate differently from the protonated ureidopeptides. The [M ? H]^? ions of ureidopeptide acids undergo a McLafferty‐type rearrangement followed by the loss of CO₂ to form an abundant [M ? H ? Fmoc + H]^? which is absent for protonated ureidopeptides. Thus, the present study provides information on mass spectral characterization of ureidopeptides and distinguishes the positional isomers. Copyright © 2010 John Wiley & Sons, Ltd.     

Prediction by 13C NMR of regioselectivity in 1,3‐dipolar cycloadditions of acridin‐9‐yl dipolarophiles

Strong correlation was found between ¹³C NMR chemical shifts of dipolarophilic CH?CH carbons and regioselectivity in 1,3‐dipolar cycloadditions of new acridin‐9‐yl dipolarophiles with stable benzonitrile oxides (BNO). Accordingly, two starting dipolarophiles, (acridin‐9‐yl)‐CH?CH‐R (R = COOCH₃ or Ph), reacted with three BNOs (2,4,6‐trimethoxy, 2,4,6‐trimethyl, and 2,6‐dichloro) to give a mixture of two target isoxazoline regioisomers in which the acridine was bound either to isoxazoline C‐4 carbon (4‐Acr) or C‐5 one (5‐Acr). Methyl 3‐(acridin‐9‐yl)propenoate afforded major 4‐(acridin‐9‐yl)‐isoxazoline‐5‐carboxylates (4‐Acr) and minor 5‐(acridin‐9‐yl)‐4‐carboxylates (5‐Acr). 9‐(2‐Styryl)acridine regiospecifically afforded only 4‐Acr cycloadducts. The ratios of regioisomers were compared with analogous reactions of acridin‐4‐yl dipolarophiles. Regioselectivity was dependent on a polarity of the CH?CH bond, donor effects in BNO, and stabilization by stacking of aromatic substituents in the products. Copyright © 2015 John Wiley & Sons, Ltd.     

Trinuclear Phosphaferroles from Alkylidyne‐Phosphaalkyne Coupling Reactions

Reaction of bisalkylidyne cluster compounds [Fe₃(CO)₉(μ₃‐CR)₂] ( 1a—d ) ( a , R = H; b , R = F; c , R = Cl; d , R = Br) with the phosphaalkyne t‐C₄H₉‐C≡P ( 2 ) yield a single isomer of the phosphaferrole cluster [Fe₃(CO)₈][CR‐C(t‐Bu)‐P‐CR] ( 3a—d ). However, the three isomeric compounds [Fe₃(CO)₈][C(OEt)‐C(t‐Bu)‐P‐C(Me)] ( 5a ), [Fe₃(CO)₈][C(Me)‐C(t‐Bu)‐P‐C(OEt)] ( 5b ), and [Fe₃(CO)₈][C(OEt)‐C(Me)‐C(t‐Bu)‐P] ( 5c ) are obtained in the reaction of [Fe₃(CO)₉(μ₃‐CMe)(μ₃‐C‐OEt)] ( 4 ) with 2 . As the phosphaferroles 3 possess a lone pair of electrons at the phosphorus atom they can act as ligands. [Fe₃(CO)₈][CF‐C(t‐Bu)‐P‐CF]ML_n ( 7a—c ) ( a , ML_n = Cr(CO)₅; b , ML_n = CpMn(CO)₂; c , ML_n = Cp^*Mn(CO)₂) were formed from 3b and L_nM(η²‐C₈H₁₄) ( 6a—c ). The dinuclear cluster [Fe₂(CO)₆][CF‐CF‐C(t‐Bu)‐PH(OMe)] ( 8 ) was obtained from 3b and NiCl₂·6H₂O in methanol. The structures of 3a—d , 5a—c , 7b , and 8 have been elucidated by X‐ray crystal structure determinations.