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The chemical shifts of the diastereotopic hydrogens of the ethyl group of the cyclopropane ring-opening product of conjugate addition of LiCu(CH3)2 to cyclopropyl enone 1 were computed. Comparison of computed and observed 1H NMR chemical shifts of the diastereotopic hydrogens of the ethyl group of 2 established the stereochemistry of the ring-opening product as 2d-b. This provides evidence that the reaction proceeds by conjugate addition of the cuprate to the enone, followed by ring-opening of the cyclopropylmethyl copper species and reductive elimination.

The bis(trimethylsilyl)-substituted hydroxycyclopentadienyl ruthenium hydride [2,5-(SiMe(3))(2)-3,4-(CH(2)OCH(2))(η(5)-C(4)COH)]Ru(CO)(2)H (10) is an efficient catalyst for hydrogenation of aldehydes and ketones. Because 10 transfers hydrogen rapidly to aldehydes and ketones and because it does not form an inactive bridging hydride during reaction, hydrogenation of aldehydes and ketones can be performed at room temperature under relatively low hydrogen pressure (3 atm); this is a significant improvement compared with previously developed Shvo type catalysts. Kinetic and (2)H NMR spectroscopic studies of the stoichiometric reduction of aldehydes and ketones by 10 established a two-step process for the hydrogen transfer: (1) rapid and reversible hydrogen bond formation between OH of 10 and the oxygen of the aldehyde or ketone, (2) followed by slow transfer of both proton and hydride from 10 to the aldehyde or ketone. The stoichiometric and catalytic activities of complex 10 are compared to those of other Shvo type ruthenium hydrides and related iron hydrides.

The reaction of the dienone ruthenium dicarbonyl dimer {[2,5-Ph-3,4-Tol(η5-C4CO)]Ru(CO)2}2 (7) with propargyl alcohol at room temperature gave a high yield of β-ruthenium-enal (E)-[2,5-Ph-3,4-Tol(η5-C4COH)]Ru(CO)2(CH═CHCHO) (8E), which was characterized spectroscopically and by X-ray crystallography. Reaction of 7 with pent-2-yn-1-ol led to the kinetic formation of the E-isomer (E)-[2,5-Ph-3,4-Tol(η5-C4COH)]Ru(CO)2[C(CH2CH3)═CHCHO] (10E-Et), which isomerized to an equilibrium mixture of Z- and E-isomers upon heating. The intramolecular nature of the 1,2-hydrogen shifts involved in these reactions was established by the absence of crossover products in the reaction of 7 with a mixture of PhC≡CCH2OH and PhC≡CCD2OH. A primary deuterium isotope effect (kH/kD ≈ 11) was seen on the product-forming step in the reaction of 7 with PhC≡CCHDOH. The reaction of PhC≡CCH3 with 7 produced the alkyne complex [2,5-Ph2-3,4-Tol2(η5-C4COH)]Ru(CO)2(η2-PhC≡CCH3) (14). The key step in the mechanism of the reaction of 7 with pro...

The boron-substituted hydroxycycylopentadienyl ruthenium hydride [2,5-Ph2-3,4-Tol2(η5-C4COBpin)Ru(CO)2H] (Bpin = 4,4,5,5-tetramethyl-1,3,2-dioxaborolane) 5 was synthesized by the addition of pinacolborane to ruthenium dimer [2,5-Ph2-3,4-Tol2(η5-C4CO)Ru(CO)2]2 4. Complex 5 reacts with aldehydes both stoichiometrically and catalytically, providing hydroboration products under mild reaction conditions. A Hammett correlation plot of para-substituted benzaldehydes provided a ρ value of +0.91. Catalytic hydroboration of aryl imines provided high yields of the corresponding amines. The hydroboration of aryl ketones, however, required strongly electron-withdrawing substituents to induce hydroboration in reasonable reaction times.

PMe(3) adds selectively to the central carbon of the η(3)- propargyl complex [C(5)Me(5)(CO)(2)Re(η(3)-CH(2)C≡CCMe(3))][BF(4)] (1-t-Bu) to form the metallacyclobutene [C(5)Me(5)(CO)(2)Re(CH(2)C(PMe(3))=CCMe(3))][BF(4)] (7). The rate of rearrangement of the metallacyclobutene 7 to η(2)-alkyne complex [C(5)Me(5)(CO)(2)Re(η(2)-Me(3)PCH(2)C≡CCMe(3))][BF(4)] (8) is is independent of phosphine concentration, consistent with a dissociative mechanism proceeding via η(3)-propargyl complex 1-t-Bu. The rate of this rearrangement is 480 times slower than the rate of exchange of PMe(3) with the labeled metallacyclobutene 7-d(9). This rate ratio provides an indirect measurement of the regioselectivity for addition of PMe(3) to the central carbon of η(3)-propargyl complex 1-t-Bu to give 7 compared to addition to a terminal carbon to give 8. The addition of PPh(3) to 1-t-Bu gives the metallacyclobutene [C(5)Me(5)(CO)(2)Re(CH(2)C(PPh(3))=CCMe(3))][BF(4)] (11). Low temperature (1)H NMR spectra provide evidence for an equilibrium between metallacyclobutene 11 and η(3)-propargyl complex 1-t-Bu (K(eq) ≈ 44 M(-1) at -46 °C and ΔG° (0 °C) = -1.2 ± 0.2 kcal mol(-1)).

The PPh3-substituted hydroxycyclopentadienyl ruthenium hydride [2,5-Ph2-3,4-Tol2(η5-C4COH)]Ru(CO)(PPh3)H (1) stoichiometrically reduces aldehydes and ketones in the presence of a pyridine trap to produce alcohols and the ruthenium pyridine complex 5, with a rate law that is dependent only on [aldehyde] and [1]. The observation of deuterium kinetic isotope effects on substitution of the acidic and hydridic protons of 1 are consistent with concerted transfer of hydrogen to aldehydes during reduction. 1 catalytically hydrogenates aldehydes under mild temperature and pressure conditions. While the Shvo catalyst 2 shows little activity under these conditions, it surpasses 1 at elevated temperatures and pressures. 1 shows high chemoselectivity for catalytic hydrogenation of aldehydes over ketones, while 2 is much less selective.

The phosphine-substituted hydroxycyclopentadienyl ruthenium hydride [2,5-Ph2-3,4-Tol2(η5-C4COH)]Ru(CO)(PPh3)H (8) displayed behavior significantly different from that of the dicarbonyl analogue, including the failure to form an unreactive diruthenium complex analogous to the Shvo catalyst 5. Complex 8 shows no apparent reduction of aldehydes in the absence of a trap but exchanges deuterium between the hydride of 8-RuDOD and the aldehydic hydrogen of p-tolualdehyde. This provides evidence that aldehyde reduction by 8 occurs but is reversible. 8 catalyzes the hydrogenation of benzaldehyde under mild temperature and pressure conditions. A rate law of −d[RCHO]/dt = k[RCHO][8][H2]0 was obtained.

The tolyl analogue of Shvo's hydroxycyclopentadienyl ruthenium hydride (4) efficiently transfers a hydride and proton to benzaldehyde or acetophenone to produce an alcohol. This reduction can be performed in toluene, methylene chloride, and THF. Reduction of benzaldehyde in toluene and methylene chloride occurs approximately 300 times faster than in THF at 0 °C. Reduction of acetophenone occurs between 75 and 150 times slower than benzaldehyde at 0 °C in each respective solvent. Despite the differences in rate, mechanistic studies have provided evidence for a similar concerted transfer of acidic and hydridic hydrogens in each solvent. Addition of water to THF led to further rate decrease coupled with an increase in the OH/D kinetic isotope effect and a decrease in the RuH/D kinetic isotope effect. Addition of excess alcohol to toluene or methylene chloride results in the significant retardation of the rate of reduction. The slower rate in THF and in the presence of alcohol is attributed to the stabilization of the ground state of ruthenium hydride 4 by hydrogen bonding and the additional energy required to break these bonds prior to carbonyl reduction.Key words: ruthenium hydrogenation catalysis, hydrogenation mechanism, kinetic isotope effects, ligand–metal bifunctional catalysis.

At high temperatures in toluene, [2,5-Ph(2)-3,4-Tol(2)(eta(5)-C(4)COH)]Ru(CO)(2)H (3) undergoes hydrogen elimination in the presence of PPh(3) to produce the ruthenium phosphine complex [2,5-Ph(2)-3,4-Tol(2)-(eta(4)-C(4)CO)]Ru(PPh(3))(CO)(2) (6). In the absence of alcohols, the lack of RuH/OD exchange, a rate law first order in Ru and zero order in phosphine, and kinetic deuterium isotope effects all point to a mechanism involving irreversible formation of a transient dihydrogen ruthenium complex B, loss of H(2) to give unsaturated ruthenium complex A, and trapping by PPh(3) to give 6. DFT calculations showed that a mechanism involving direct transfer of a hydrogen from the CpOH group to form B had too high a barrier to be considered. DFT calculations also indicated that an alcohol or the CpOH group of 3 could provide a low energy pathway for formation of B. PGSE NMR measurements established that 3 is a hydrogen-bonded dimer in toluene, and the first-order kinetics indicate that two molecules of 3 are also involved in the transition state for hydrogen transfer to form B, which is the rate-limiting step. In the presence of ethanol, hydrogen loss from 3 is accelerated and RuD/OH exchange occurs 250 times faster than in its absence. Calculations indicate that the transition state for dihydrogen complex formation involves an ethanol bridge between the acidic CpOH and hydridic RuH of 3; the alcohol facilitates proton transfer and accelerates the reversible formation of dihydrogen complex B. In the presence of EtOH, the rate-limiting step shifts to the loss of hydrogen from B.

Hydroxycyclopentadienyl ruthenium hydride 5 efficiently reduces imines below room temperature. Better donor substituents on nitrogen give rise to faster rates and a shift of the rate-determining step from hydrogen transfer to amine coordination. Reduction of electron-deficient N-benzilidenepentafluoroaniline (8) at 11 degrees C resulted in free amine and kinetic isotope effects of k(OH)/k(OD) = 1.61 +/- 0.08, k(RuH)/k(RuD) = 2.05 +/- 0.08, and k(RuHOH)/k(RuDOD) = 3.32 +/- 0.14, indicative of rate-limiting concerted hydrogen transfer, a mechanism analogous to that proposed for aldehyde and ketone reduction. Reduction of electron-rich N-alkyl-substituted imine, N-isopropyl-(4-methyl)benzilidene amine (9), was accompanied by facile imine isomerization and scrambling of deuterium labels from reduction with 5-RuDOH into the N-alkyl substituent of both the amine complex and into the recovered imine. Inverse equilibrium isotope effects were observed in the reduction of N-benzilidene-tert-butylamine (11) at -48 degrees C (k(OH)/k(OD) = 0.89 +/- 0.06, k(RuH)/k(RuD) = 0.64 +/- 0.05, and k(RuHOH)/k(RuDOD) = 0.56 +/- 0.05). These results are consistent with a mechanism involving reversible hydrogen transfer followed by rate-limiting amine coordination.

Thermal rearrangements of η2-(o-ethynylbenzoyl)-Re complexes 2 produced isobenzofuryl-Re carbene complexes 3. This reaction might proceed via nucleophilic attack of the carbonyl oxygen on the Re-bo...

Deuterioformylation of styrene catalyzed by [(2S,4S)-BDPP]Pt(SnCl(3))Cl at 39 degrees C gave 3-phenylpropanal (3) and 2-phenylpropanal (2) (n:i = 1.8, 71% ee (S)-2) with deuterium only beta to the aldehyde carbonyl and in the formyl group. Small amounts of deuterium were also found in the internal (2.8%), cis terminal (1.4%), and trans terminal (1.3%) vinyl positions of the recovered styrene. Deuterioformylation of styrene at 98 degrees C gave 3- (3) and 2-phenylpropanal (2) (n:i = 2.3, 10% ee (R)-2) with deuterium both alpha and beta to the aldehyde carbonyl and in the formyl group. Deuterium was also found in the internal (20%), cis terminal (12%), and trans terminal (12%) vinyl positions of the recovered styrene. These deuterioformylation results establish that platinum hydride addition to styrene is largely irreversible at 39 degrees C but reversible at 98 degrees C. Hydroformylation of (E)- and (Z)-beta-deuteriostyrene at 40 degrees C, followed by oxidation of the aldehydes to acids, and subsequent derivitization to the (S)-mandelate esters confirmed that 84% of 2-phenylpropanal (2) arises from platinum hydride addition to the si-face of styrene, while 73% of 3-phenylpropanal (3) arises from platinum hydride addition to the re-face of styrene. At 100 degrees C, the effect of variable H(2) and CO pressure on n:i, % ee, and TOF of hydroformylation of styrene was investigated. The results are consistent with enantioselectivity not being fully determined until the final hydrogenolysis of a platinum acyl intermediate.

The reaction of (Z)-HDC=CHCH(OCH(3))C(6)H(5) (1) with Cp(2)Zr(D)Cl followed by BF(3).OEt(2) gave phenylcyclopropanes 3a and 3b, both having cis deuterium. This stereochemical outcome requires inversion of configuration at the carbon bound to zirconium and is consistent with a "W-shaped" transition state structure for cyclopropane formation. In a Kulinkovich hydroxycyclopropanation, trans-3-deutero-1-methyl-cis-2-phenyl-1-cyclopropanol (5) was formed stereospecifically from Ti(O-i-Pr)(4), ethyl acetate, EtMgBr, and trans-beta-deuterostyrene. This stereochemistry requires retention of configuration at the carbon bound to titanium and is consistent with frontside attack of the carbon-titanium bond on a carbonyl group coordinated to titanium. In a de Meijere cyclopropylamine synthesis, a 3:1 mixture of N,N-dimethyl-N-(trans-3-deutero-trans-2-phenylcyclopropyl)amine (6a) and N,N-dimethyl-N-(cis-3-deutero-cis-2-phenylcyclopropyl)amine (6b) was formed from Ti(O-i-Pr)(4), DMF, Grignard reagents, and trans-beta-deuterostyrene. This stereochemistry requires inversion of configuration at the carbon bound to titanium and is consistent with a W-shaped transition structure for ring closure.

Trifluoroacetoxycarbene complexes generated from reaction of stable manganese acyl complexes with trifluoroacetic anhydride are convenient alternatives to thermally sensitive manganese carbyne complexes in reactions with diynes that lead eventually to free cyclic enediynes. In situ reaction of these trifluoroacetoxycarbene complexes with alkynyl copper intermediates generated from diynes, CuBr, and NEt(i-Pr)2 led to the isolation of cyclic enediynes via intermediate linked alkynylcarbene complexes and manganese enediyne complexes.

Cyclic cis-enediynes are readily prepared by a two-step one-pot procedure. The first step is the copper-catalyzed addition of α,ω-diynes to manganese carbyne complexes to give intermediate bis(alkynylcarbene) complexes that rearrange to enediyne complexes below room temperature. In the second step, the free enediyne is released from manganese by photolysis, copper-catalyzed air oxidation, or stoichiometric Cu(II) oxidation. These new procedures have been applied to a variety of five-, six-, and seven-membered-ring cyclic enediynes containing a range of ether, ester, and ketone functional groups.

Dimerization of the alkynylcarbene complex (C5H4Me)(CO)2MnC(Tol)CCTol (10) occurred at 65 °C to give a mixture of E- and Z-enediyne complexes [(C5H4Me)(OC)2Mn]2[η2,η2-TolCC(Tol)CC(Tol)CCTol] (13). Thermolysis of alkynye complexes 10 at higher (100 °C) temperature led to the formation of manganese-free E- and Z-enediynes TolCC(Tol)CC(Tol)CCTol (14-E and 14-Z). Attempted synthesis of the tethered bis-(alkynylcarbene) complex Cp(OC)2MnC(Ph)CCCH2CH2CH2CCC(Ph)Mn(CO)2Cp led instead to the cyclic enediyne complex [Cp(OC)2Mn]2[η2,η2-PhCCC(CH2CH2CH2)CCCPh] (19), from which the metal-free enediyne 1,2-bis(phenylethynyl)cyclopentene (20) was released by thermolysis at 90 °C.

CO substitution of the indenyl alkyne complex (η5-C9H7)(CO)2Re(η2-MeC⋮CMe) (3) to form (η5-C9H7)Re(CO)3 (8) is much faster than that of either the indenyl alkene complex (η5-C9H7)(CO)2Re(η2-cis-MeHCCHMe) (2) or the cyclopentadienyl alkyne complex (η5-C5H5)(CO)2Re(η2-MeC⋮CMe) (5). The acceleration of the reaction of 3 with CO is proposed to involve cooperativity between slippage of the indenyl ring from an η5 6e-donor to an η3 4e-donor and shifting of the alkyne ligand from a 2e- to a 4e-donor as CO associates with the rhenium complex. The rate of reaction of 3 with CO showed a linear dependence on CO pressure between 1 and 10 atm, consistent with CO-promoted indenyl ring slippage. At very high CO pressure, 3 is rapidly converted to (η1-C9H7)(CO)4Re(η2-MeC⋮CMe) (12). Upon release of CO pressure, 12 reverts to a 12:1 mixture of starting material 3 and CO substitution product 8 at a rate that is inversely dependent on CO pressure. When the reaction of 13CO with 3 was carried to about 50% conversion, extensiv...

Yttrium alkyl complexes Cp* 2 YR react with CH bonds of alkenes to form either yttrium allyl complexes or yttrium vinyl complexes. Less substituted alkenes react faster, consistent with prior alkene coordination. The selectivity of the reaction of Cp* 2 YR with CH bonds is allylic CH 3 ≫vinyl CH≫allylic CH 2 . Propene is readily metallated by Cp* 2 YR giving the η 3 -allyl complex Cp* 2 Y(η 3 -CH 2 ⋯ CH  CH 2 ) which does not react further with propene. This explains why Cp* 2 YR (R=alkyl, H) complexes make poor propene polymerization catalysts.

Reaction of N-phenyl-2,5-dimethyl-3,4-diphenylcyclopenta-2,4-dienimine (6) with Ru3CO12 formed two isomers of {[2,5-Me2-3,4-Ph2(η5-C4CNHPh)]Ru(CO)(μ-CO)}2 (8-trans and 8-cis). Photolysis of 8 under a H2 atmosphere led to the formation of the aminocyclopentadienyl ruthenium hydride [2,5-Me2-3,4-Ph2(η5-C4CNHPh)]Ru(CO)2H (9-H). 9-H reduced benzaldehyde slowly at 75 °C to give benzyl alcohol and 8. Protonation of 9-H with triflic acid produced {[2,5-Me2-3,4-Ph2(η5-C4CNH2Ph)]Ru(CO)2H}OTf (11-H), which reacted rapidly with benzaldehyde at −80 °C to give benzyl alcohol and [2,5-Me2-3,4-Ph2(η5-C4CNHPh)]Ru(CO)2OTf (9-OTf). Reaction of 9-OTf with H2 and base led to the re-formation of 9-H. These reactions provide the transformations required for a catalytic cycle for hydrogenation of aldehydes.

Hydride abstraction from C(5)Me(5)(CO)(2)Re(eta(2)-PhC triple bond CCH(2)Ph) (1) gave a 3:1 mixture of eta(3)-propargyl complex [C(5)Me(5)(CO)(2)Re(eta(3)-PhCH-C triple bond CPh)][BF(4)] (5) and eta(2)-1-metalla(methylene)cyclopropene complex [C(5)Me(5)(CO)(2)Re(eta(2)-PhC-C=CHPh)][BF(4)] (6). Observation of the eta(2)-isomer requires 1,3-diaryl substitution and is favored by electron-donating substituents on the C(3)-aryl ring. Interconversion of eta(3)-propargyl and eta(2)-1-metalla(methylene)cyclopropene complexes is very rapid and results in coalescence of Cp (1)H NMR resonances at about -50 degrees C. Protonation of the alkynyl carbene complex C(5)Me(5)(CO)(2)Re=C(Ph)C triple bond CPh (22) gave a third isomer, the eta(3)-benzyl complex [C(5)Me(5)(CO)(2)Re[eta(3)(alpha,1,2)-endo,syn-C(6)H(5)CH(C triple bond CC(6)H(5))]][BF(4)] (23) along with small amounts of the isomeric complexes 5 and 6. While 5 and 6 are in rapid equilibrium, there is no equilibration of the eta(3)-benzyl isomer 23 with 5 and 6.

Protonation of η 2 -enyne rhenium complex C 5 Me 5 (CO) 2 Re(η 2 -3,4- trans -PhCCCHCHPh) ( 24 ) occurred at the coordinated alkyne to produce 1-metallacyclopropene complex C 5 Me 5 (CO) 2 Re[η 2 - trans -(PhHCCH)CCHPh] + BF 4 − ( 26 ), instead of protonation at the non-coordinated alkene to produce an η 3 -propargyl complex. Protonation of the alkene coordinated η 2 -enyne rhenium complex C 5 Me 5 (CO) 2 Re(η 2 -1,2- cis -PhHCCHCCPh] ( 25 ) occurred at the non-coordinated alkyne to produce exo -alkylidene η 3 -allyl complex C 5 Me 5 (CO) 2 Re(η 3 - exo , anti -CHPhCHCCHPh) + BF 4 − ( 27 ), instead of protonation at the coordinated alkene to produce an η 3 -propargyl complex. Protonation of η 2 -diyne complex C 5 Me 5 (CO) 2 Re(η 2 -CH 3 CCCCCH 3 ) ( 32 ) at −78 °C produced the rhenium hydride complex trans -C 5 Me 5 (CO) 2 ReH(η 2 -CH 3 CCCCCH 3 ) + BF 4 − ( 33 ), which was converted to exo -alkylidene η 3 -propargyl complexes C 5 Me 5 (CO) 2 Re[η 3 -(CH 3 CH)CCCCH 3 ] + BF 4 − ( 34a and 34b ) at 0 °C.

The reaction of [2,3,4,5-Ph4(η4-C4CO)]Ru(CO)3 (5a) with Na2CO3 in aqueous acetone followed by low-temperature treatment with NH4Cl was reported to give the material A, which was formulated as the isopropyl alcohol complex [2,3,4,5-Ph4(η4-C4CO)](CO)2Ru(HOCHMe2) (3a). Reinvestigation of this reaction indicates that A is instead the isopropylamine complex [2,3,4,5-Ph4(η4-C4CO)](CO)2Ru(H2NCHMe2) (4a). The formation of 4a is proposed to occur by formation of the imine of acetone followed by reduction of the imine by the (hydroxycyclopentadienyl)ruthenium hydride [2,3,4,5-Ph4(η5-C4COH)]Ru(CO)2H (2a) formed in the reaction of 5a with Na2CO3 in aqueous acetone and subsequent acidification with aqueous NH4Cl.

The reaction of Cp* 2 Zr(CH 3 ) 2 ( 1 ) with [(C 6 H 5 ) 3 C][B(C 6 F 5 ) 4 ] in CD 2 Cl 2 at −78 °C proceeds with the unexpected formation of [Cp* 2 Zr(CH 3 )η-C 6 H 5 C(C 6 H 5 ) 2 CH 3 ][B(C 6 F 5 ) 4 ] ( 2 ). Evidence for the coordination of one of the phenyl rings to zirconium comes from 1 H- and 13 C-NMR chemical shifts and from nOe experiments showing spin saturation transfer from the Cp* methyl protons to the protons of the bound phenyl ring. No chemical exchange between the bound and free phenyl rings is observed up to 0 °C, where decomposition to intractable products occurs. Attempts to disfavor coordination of the arene ring by employing a more sterically protective isobutyl substituent in Cp* 2 Zr(CH 3 )CH 2 CH(CH 3 ) 2 ( 7 ) led to rapid, quantitative β-hydride elimination producing isobutylene and [Cp* 2 Zr(H)η-C 6 H 5 C(C 6 H 5 ) 2 CH 3 ][B(C 6 F 5 ) 4 ] ( 8 ) even at temperatures as low as −135 °C. Addition of propylene to cold solutions of the trityl-coordinated complexes resulted in very rapid formation of polypropylene. This polymerization resulted in no observable changes in the NMR spectra of the zirconium complexes in solution, implying a very rapid rate of propagation following a much slower first monomer insertion.

The dissociation of the dimer (Cp* 2 YH) 2 (2) to the Cp* 2 YH monomer is an important process in reactions of 2 with alkenes. The rate of dissociation of 2 was measured by NMR line-broadening techniques (14 s - 1 at 0 °C, ΔG = 14.5 kcal mol- 1 , ΔH = 14.9(8) kcal mol - 1 , and ΔS = 3(2) eu). A full range of dissociative and associative mechanisms for reaction of alkenes with 2 was found. For the most crowded and least reactive alkenes studied, 2-butene and 2-methylpropene, reaction with 2 occurred slower than dissociation of dimer 2; kinetic studies established reversible dissociation of 2 to monomeric Cp* 2 YH followed by competitive trapping by alkene and recombination to regenerate 2. Kinetic studies of the less crowded alkene 3-methyl-1-butene are consistent with rate-limiting dissociation of dimer 2 followed by efficient trapping of the intermediate Cp* 2 YH by alkene. The least crowded terminal alkenes such as 1-hexene reacted with 2 at a rate faster than dimer dissociation; kinetic studies established a two-component rate law involving a second-order term for direct attack of alkene on the dimer and a first-order term involving rate-determining dimer dissociation followed by rapid alkene reaction with monomeric Cp* 2 YH. The reactions of terminal alkenes with 2 initially gave mixtures of single- and double-alkene-insertion products but no triple-insertion products. The initially formed n-alkyl yttrium complex reacts with terminal alkenes at a rate similar to the reaction of yttrium hydride dimer 2 with terminal alkenes. The more crowded β-alkyl yttrium double-insertion product is much less reactive toward terminal alkenes.

The bis(allyldimethylsilylmethyl)bis(cyclopentadienyl)zirconium complex Cp2Zr[CH2Si(CH3)2CH2CHCH2]2 (5) reacted rapidly with [(C6H5)2(CH3)NH][B(C6F5)4] in CD2Cl2 at −78 °C to form the cationic zirconium−alkyl−alkene complex Cp2Zr[η1,η2-CH2Si(CH3)2CH2CHCH2][B(C6F5)4] (6). Low-temperature 1H and 13C NMR spectroscopy established the coordination of the tethered alkene to the d0 metal center. Line shape analysis of the coalescence of the diastereotopic Cp ligand resonances allowed measurement of the alkene dissociation energy barrier [ΔG⧧(−28 °C) = 12.7 ± 0.8 kcal mol-1].

Thermolysis of the alkynylcarbene complex Cp*(CO)2ReC(Ph)13C⋮13CTol (5) at 120 °C resulted in rapid equilibration (t1/2 = 33 min) to a 1:1 mixture of 5 and Cp*(CO)2Re13C(Tol)13C⋮CPh (7) via a [1,3]-rhenium shift. Extended thermolysis of this mixture provided the CH insertion products {η5:η2-[C5(CH3)4CH213CH(Tol)13C⋮CPh]}Re(CO)2 (8) and {η5:η2-[C5(CH3)4CH2CH(Ph)13C⋮13CTol]}Re(CO)2 (9). Thermolysis of the symmetrically substituted alkynylcarbene complex Cp*(CO)2ReC(Ph)C⋮CPh (6) produced the CH insertion product {η5:η2-[C5(CH3)4CH2CH(Ph)C⋮CPh]}Re(CO)2 (10). The CH insertion of Cp*(CO)2ReC(Ph)C⋮CC6D5 (6-HD) was monitored at low conversion before complete equilibration with Cp*(CO)2ReC(C6D5)C⋮CPh (6-DH) occurred. An excess of {η5:η2-[C5(CH3)4CH2CH(C6D5)C⋮CPh]}Re(CO)2 (13-HD) over {η5:η2-[C5(CH3)4CH2CH(Ph)C⋮CC6D5]}Re(CO)2 (13-DH) provides evidence for site-selective CH insertion of the remote alkyne carbon into the CH bond of a Cp* methyl group.

Addition of excess HCO2H to {2,5-Ph2-3,4-Tol2(η5-C4CO)]Ru(CO)2}2 (6) at -20°C led to the formation of [2,5-Ph2-3,4-Tol2(η5-C4COH)]Ru(CO)2(η1-OCHO) (5), a proposed intermediate in catalytic transfer hydrogenations developed by Shvo. Hydroxycyclopentadienyl formate 5 undergoes rapid reversible dissociation of HCO2H at –20°C, and undergoes decarboxylation at 1°C to form a 1:10 mixture of {[2,5-Ph2-3,4-Tol2(η5-C4CO)]2H}Ru2(CO)4(µ-H) (3):[2,5-Ph2-3,4-Tol2(η5-C4COH)Ru(CO)2H] (4). 5 does not reduce PhCHO below the temperature at which 5 is converted to hydride 4. The catalytic production of benzyl alcohol from 5 and PhCHO in the presence of excess HCO2H is not accelerated by higher concentrations of PhCHO, indicating that 5 does not directly reduce PhCHO. Formate complex 5 is the precursor of hydride 4 which transfers hydrogen to PhCHO. A crucial role for the CpOH proton in the decarboxylation of 5 was indicated by the much slower decarboxylation of the methoxycyclopentadienyl analog [2,5-Ph2-3,4-Tol2(η5-C4COCH3)]Ru(CO)2(η1-OCHO) (7). A mechanism for decarboxylation of 5 is proposed which involves reversible dissociation of formic acid to form the unsaturated dienone dicarbonyl ruthenium intermediate C, followed by simultaneous transfer of hydride to ruthenium from the formic acid carbon and of proton to the carbonyl of C from the formic acid OH group.Key words: Shvo catalyst, ruthenium formate, decarboxylation.

Addition of PPh 2 CH 3 to the alkynyl carbene complex Cp(CO) 2 ReC(Tol)(CCPh) ( 1a ) led to formation of the dihydrophospholium complex Cp(CO) 2 Re[CC(Ph)PPh 2 CH 2 CH(Tol)] ( 4 ). When the reaction was monitored by low temperature NMR spectroscopy, initial phosphine addition to the carbene carbon atom of 1a to give σ-propargyl complex Cp(CO) 2 ReC(PPh 2 CH 3 )(Tol)CCPh ( 5 ) was observed at −78°C. Upon warming to −20°C, 5 rearranged to the σ-allenyl complex Cp(CO) 2 Re(Tol)CCC(Ph)(PPh 2 CH 3 ) ( 6 ) via phosphine dissociation and readdition. Upon further warming to room temperature, 6 rearranged to 4 . A protonation-deprotonation mechanism for the conversion of 6 to 4 is supported by the observation that reaction of 6 with DOTf produces the cationic allene complex Cp(CO) 2 Re[η 2 -2,3-(Tol)DCCC(Ph)(PPh 2 CH 3 )]OTf ( 11 - d ), which is converted to 4 - d upon treatment with KO- t -Bu. The reaction of 1a with Ph 2 PCHCH 2 led to the formation of the cyclopropane Cp(CO) 2 Re[CC(Ph)PPh 2 CHCH 2 C(Tol)] ( 8 ).

The β-allyl zirconacyclobutane complex Cp*2Zr[CH2CH(CH2CHCH2)CH2] (7) reacted rapidly with B(C6F5)3 in CD2Cl2 at −78 °C to form the zwitterionic d0 zirconium(IV) chelate complex Cp*2Zr[η1,η2-CH2CH[CH2B(C6F5)3]CH2CHCH2] (2a and 2b). Low-temperature 1H, 13C, TOCSY1D, and NOESY1D NMR spectroscopy of 2 established the bonding of the tethered alkene to the d0 metal center. A dynamic NMR study of the interconversion of 2a and 2b allowed measurement of the alkene dissociation energy (ΔG⧧ = 10.5 (2a to 2b) and 10.3 (2b to 2a) kcal mol-1), but the complex decomposed before the barrier for site epimerization at the zirconium center could be determined. Reaction of 7 with [(C6H5)2(CH3)NH][B(C6F5)4] led to the formation of two isomeric d0 zirconium(IV)−alkyl−alkene chelates Cp*2Zr[η1,η2-CH2CH(CH3)CH2CHCH2][B(C6F5)4] (8a and 8b). This more thermally stable zirconium−alkyl−alkene complex allowed the measurement of barriers associated with decomplexation of the alkene (ΔG⧧ =10.7 and 11.1 kcal mol-1) and site epimerizati...

Alkene dissociation from the yttrium chelate Cp*2Y[η1,η2-CH2CH2CH2CHCH2] (7-on) became slow enough below −100 °C to be measured by dynamic 1H NMR spectroscopy [ΔG⧧(−110 °C) = 7.5 kcal mol-1, ΔH⧧ = 9.3 kcal mol-1]. Coalescence of the Cp* resonances of Cp*2Y[η1,η2-CH2CH2CH(CH3)CHCH2] (8-on) requires alkene dissociation plus inversion at yttrium and occurred substantially slower than simple alkene dissociation [ΔG⧧(−72 °C) = 9.6 kcal mol-1, ΔH⧧ = 10.8 kcal mol-1]. The binding energy of a disubstituted alkene to a d0 yttrium center was determined to be ΔH° = 2.6 kcal mol-1 by direct observation of the equilibrium between Cp*2Y(η1,η2-CH2CH2CH2C(CH3)CH2) (6-on) and Cp*2Y(η1-CH2CH2CH2C(CH3)CH2) (6-off). The significantly greater ΔH⧧ of alkene dissociation compared with ΔH° of alkene binding can be attributed either to stabilization of the dissociated yttrium alkyl by a β-agostic interaction or to destabilization of the transition state leading to alkene dissociation by increased strain in the chelate tether. Bin...

Electronic effects on rhodium-catalyzed hydroformylation of 1-hexene with electronically dissymmetric DIPHOS derivatives [3,5-(CF3)2C6H3]2PCH2CH2PPh2 = [DIPHOS−(3,5-CF3,H)] (1), [2-(CF3)C6H4]2PCH2CH2PPh2 = [DIPHOS−(2-CF3,H)] (2), [3,5-(CF3)2C6H3]2PCH2CH2P[2-(CH3)C6H4]2 = [DIPHOS−(3,5-CF3,2-CH3)] (3), and [2-(CF3)C6H4]2PCH2CH2P[2-(CH3)C6H4]2 = [DIPHOS−(2-CF3,2-CH3)] (4) were investigated. Two apical−equatorial chelate isomers were observed for model (diphosphine)Ir(CO)2H complexes of dissymmetric diphosphines 1−4. In each case, the equatorial phosphine of the major isomer (96−60%) had electron-withdrawing aryl substituents. These dissymmetric DIPHOS derivatives were used to test the hypothesis that an electron-withdrawing substituent on an equatorial phosphine increases the hydroformylation n:i ratio while an electron-withdrawing substituent on an apical phosphine decreases the n:i ratio. In agreement with the predictions of this hypothesis, hydroformylation with the dissymmetric diphosphine ligand DIPHOS−...

Protonation of the rhenium η2-alkyne complex C5Me5(CO)2Re(η2-MeC⋮CMe) (4) with HBF4 at room temperature produced the η3-allyl complex C5Me5(CO)2Re(η3-exo,anti-MeHC−CH−CH2)+BF4- (5). The protonation of 4 at −78 °C occurred at rhenium to give the rhenium alkyne hydride complex C5Me5(CO)2ReH(η2-MeC⋮CMe)+BF4- (6). At −16 °C, net proton migration from rhenium to the alkyne ligand of 6 occurred to produce the 1-metallacyclopropene complex C5Me5(CO)2Re(η2-CMeCHMe)+BF4- (7), which then rearranged to form the η3-allyl complex 5. The degenerate rearrangement of 7 by hydride migration between the two metallacyclopropene carbons was demonstrated by deuterium labeling. Protonation of the rhenium η2-alkyne complex C5Me5(CO)2Re(η2-PhC⋮CPh) (10) with HBF4 at −78 °C initially produced the rhenium alkyne hydride complex C5Me5(CO)2ReH(η2-PhC⋮CPh)+BF4- (11), which was observed spectroscopically. Upon warming to room temperature, 11 was converted to the stable 1-metallacyclopropene complex C5Me5(CO)2Re(η2-CPhCHPh)+BF4- (12), ...

The rhenium dimer complex Cp*(CO)2ReRe(CO)2Cp* (1) (Cp*=C5Me5) reacted in THF with diethyl fumarate in a fragmentation reaction to form Cp*Re(CO)3 (3) and Cp*Re(CO)(η2-(E)-EtO2CCHCHCO2Et)(THF) (6). Reaction of 6 with CO resulted in substitution of the THF ligand with CO to form the alkene complex Cp*Re(CO)2(η2-(E)-EtO2CCHCHCO2Et) (7). Variable temperature 1H-NMR spectroscopy of 7 showed that rotation of the alkene ligand is slow below −50°C.

Manganese tricarbonyl complexes ( η 5 -C 5 H 4 CH 2 CH 2 Br)Mn(CO) 3 ( 3 ) and ( η 5 -C 5 H 4 CH 2 CH 2 I)Mn(CO) 3 ( 4 ), with an alkyl halide side chain attached to the cyclopentadienyl ligand, were synthesized as possible precursors to chelated alkyl halide manganese complexes. Photolysis of 3 or 4 in toluene, hexane or acetone-d 6 resulted in CO dissociation and intramolecular coordination of the alkyl halide to manganese to produce ( η 5 : η 1 -C 5 H 4 CH 2 CH 2 Br)Mn(CO) 2 ( 5 ) and ( η 5 : η 1 -C 5 H 4 CH 2 CH 2 I)Mn(CO) 2 ( 6 ). Low temperature NMR and IR spectroscopy established the structures of 5 and 6 . Photolysis of 3 in a glass matrix at 91 K demonstrated CO release from manganese. Low temperature NMR spectroscopy established that the coordinated alkyl halide complexes are stable to approximately −20°C.

The alkyne complexes C{sub 5}Me{sub 5}(CO){sub 2}Re({eta}{sup 2}-MeC{triple_bond}CMe) (1) and C{sub 5}H{sub 5}(CO){sub 2}Re({eta}{sup 2}-MeC{triple_bond}CMe) (6) underwent acid-catalyzed isomerization by way of 1-metallacyclopropene intermediates to form the allene complexes C{sub 5}Me{sub 5}(CO){sub 2}Re({eta}{sup 2}-2,3-MeHC{double_bond}C{double_bond}CH{sub 2}) (5) and C{sub 5}H{sub 5}(CO){sub 2}Re({eta}{sup 2}-2,3-MeHC{double_bond}C{double_bond}CH{sub 2}) (7). Stoichiometric reaction of 1 with CF{sub 3}CO{sub 2}H initially produced the kinetic addition product C{sub 5}Me{sub 5}(CO){sub 2}Re[{eta}{sup 2}-(Z)-MeHC{double_bond}CMeO{sub 2}CCF{sub 3}] (8-Z), which slowly isomerized to the thermodynamically more stable E isomer 8-E. The reaction of 6 with CF{sub 3}CO{sub 2}H at {minus}73 C produced only C{sub 5}H{sub 5}(CO){sub 2}Re[{eta}{sup 2}-(E)-MeHC{double_bond}CMeO{sub 2}CCF{sub 3}] (9-E), which isomerized at -60 C to a 80:20 equilibrium mixture of 9-E and 9-Z. Treatment of 9-E and 9-Z with base led to formation of allene complex 7. The rate of this elimination was independent of base concentration. Labeling studies showed that the 1-metallacyclopropene intermediate C{sub 5}H{sub 5}(CO){sub 2}({eta}{sup 2}-CMeCHMe){sup +}CF{sub 3}CO{sub 2}{sup {minus}} (12-CF{sub 3}CO{sub 2}) undergoes a number of important reactions which include, in order of decreasing relative rates: (1) addition of trifluoroacetate to give enol trifluoroacetate complexes, (2) deprotonation to give complexed allenes, (3) degenerate 1,2-hydride migrations, (4) hydride migrations to give {eta}{sup 3}-allyl complexes, and (5) deprotonation tomore » give complexed alkynes.« less

Kinetic addition of nucleophiles occurs at the center carbon of η3-propargyl rhenium complexes to produce rhenacyclobutenes. Reaction of P(CH3)3 with C5Me5(CO)2Re[η3-CH2C⋮CC(CH3)3]+BF4- (3a) gave the metallacyclobutene C5Me5(CO)2ReCH2C(PMe3)CC(CH3)3+BF4- (4a), which was characterized by X-ray crystallography. Malonate and acetylide nucleophiles reacted with C5Me5(CO)2Re[η3-CH2C⋮CCH3]+PF6- (3b) to give metallacyclobutene complexes. Pyridine added to the central propargyl carbon of 3b at low temperature to produce the metastable metallacyclobutene C5Me5(CO)2ReCH2C(NC5H5)CCH3+PF6- (14b) which rearranged to the η2-allene complex C5Me5(CO)2Re[η2-H2CCC(NC5H5)CH3]+PF6- (15K) at room temperature. 4-(Dimethylamino)pyridine (DMAP) added to the central carbon of the tert-butyl-substituted η3-propargyl complex 3a below −38 °C to give the rhenacyclobutene complex C5Me5(CO)2ReCH2C(NC5H4NMe2)CC(CH3)3+BF4- (22a) which rearranged to the η2-alkyne complex C5Me5(CO)2Re[η2-(CH3)3CC⋮CCH2NC5H4NMe2]+BF4- (23) at room temperatur...

The electronic effects of electron withdrawing aryl substituents on equatorial and apical diphosphines were investigated. Chelating diphosphines designed to coordinate in diequatorial or in apical−equatorial positions were synthesized, and their effects on the regioselectivity of rhodium catalyzed 1-hexene hydroformylation were observed. Only diequatorial coordination was observed for 2,2‘-bis[(diphenylphosphino)methyl]-1,1‘-biphenyl (BISBI) complexes (BISBI)Ir(CO)2H (8) and [BISBI-(3,5-CF3)]Ir(CO)2H (10), and only apical−equatorial coordination was seen for 1,2-bis(diphenylphosphino)ethane (DIPHOS) complexes (DIPHOS)Ir(CO)2H (14) and [DIPHOS-(3,5-CF3)]Ir(CO)2H (15). For the trans-1,2-bis[(diphenylphosphino)methyl]cyclopropane (T-BDCP) complexes, a mixture of diequatorial and apical−equatorial complexes was seen. For (T-BDCP)Ir(CO)2H (12), 12-ae was favored over 12-ee by 63:37, but for [T-BDCP-(3,5-CF3)]Ir(CO)2H (13) the conformational preference was reversed and a 10:90 ratio of 13-ae:13-ee was seen. The...

Protonation of (Ph3P)2Pt[η2-HC≡CC(CH3)=CH2] (2a) with excess HBF4·Et2O produced the π-allyl complex (Ph3P)2Pt[η3-H2C=CC(CH3)=CH2+BF4− (3a-BF4) instead of a π-propargyl complex. Reaction of excess CF3CO2H with 2a initially produced the analogous π-allyl complex 3a-CF3CO2 which then added CF3CO2H across the vinylidene unit of 3a-CF3CO2 to give the π-allyl complex (Ph3P)2Pt[η3-CH3C(CF3CO2)C(CH3)CH2]+CF3CO2−. Protonation of the platinum diyne complex [(p-CH3-C6H4)3P]2Pt(η2-CH3C≡CC≡CCH3) (7b) with HBF4·Et2O at −73°C initially produced the platinum hydride complex trans-[(p-CH3-C6H4)3P]2PtH(η2-CH3C≡CC≡CCH3)+ BF4− (9), which rearranged to the platinum π-propargyl complex [(p-CH3-C6H4)3P]2Pt[η3(CH3CH=)-CC≡CCH3]+ BF4− (11) at −28°C.

The yttrium hydride dimer (Cp*2YH)2 (2) reacted rapidly with 3,3-dimethyl-1,4-pentadiene in methylcyclohexane-d14 at −78 °C to form the d0 yttrium(III) pentenyl chelate complex Cp*2Y[η1,η2-CH2CH2C(CH3)2CHCH2] (4). Low-temperature 1H, 13C, and 1H NOESY NMR spectroscopy of 4 established bonding of the tethered alkene to the d0 metal center. Quantitative analysis of the NOESY time course using the Conformer Population Analysis method demonstrates that the dominant conformers in solution are interconverting pairs of chelated complexes, one in a twist-boat conformation and the other a chair conformer. No significant contribution by a free alkene conformation is required to explain the spectroscopic data. Addition of THF to pentenyl chelate 4 at −78 °C displaced the alkene and formed the yttrium(III) pentenyl THF adduct Cp*2Y[η1-CH2CH2C(CH3)2CHCH2](THF) (5), in which there is no interaction between the pendant alkene and the d0 metal center. Yttrium hydride dimer 2 also reacted with either 1,4-pentadiene or met...

The isomerization of parallel−perpendicular allyl vinyl ketone complex C5H5(CO)Re(η2,η2-H2CCHCH2COCHCHCH2CMe3) (2) to the diastereomeric perpendicular−parallel complex C5H5(CO)Re(η2,η2-H2CCHCH2COCHCHCH2CMe3) (6) occurred without formation of an unsaturated intermediate trappable by either PMe3 or 13CO. The rearrangement of exo-C5H5(CO)Re[η2,η2-CH2CHCH(CH3)COCHCHCH2CMe3] (8-exo) occurred with retention of stereochemistry at rhenium and with enantioface inversion of both complexed alkenes. The kinetically formed parallel−perpendicular isomer 8-exo rearranged by sequential enantioface inversion of the vinyl π-bond to give parallel−parallel intermediate exo-C5H5(CO)Re[η2,η2-CH2CHCH(CH3)COCHCHCH2CMe3] (12-exo) and then enantioface inversion of the allyl π-bond to form the perpendicular−parallel isomer exo-C5H5(CO)Re[η2,η2-CH2CHCH(CH3)COCHCHCH2CMe3] (9-exo). Enolization of allyl vinyl ketone complexes was observed, but is not required for the isomerization. C−H insertion mechanisms involving a net hydrogen migr...

The acyl anion complex [(CO)2ReC(O)CH2CH2(η5-C5H4)]-Li+ (7) in which a two-carbon tether links the cyclopentadienyl ring to the acyl carbon was synthesized by attachment of a 2-lithioethyl side chain to the cyclopentadiene ring of CpRe(CO)3 followed by intramolecular attack of the lithium reagent on a carbonyl group. Alkylation of 7 with (CH3)3O+BF4- occurred at oxygen to give the methoxycarbene complex (CO)2ReC(OCH3)CH2CH2(η5-C5H4)(9), which was shown by X-ray crystallography to have significant strain associated with the tethered ring. Protonation of 7 gave a mixture of hydroxycarbene complex (CO)2ReC(OH)CH2CH2(η5-C5H4) (2) and the metal acyl hydride complex trans-(CO)2HReC(O)CH2CH2(η5-C5H4) (3). The unusual observation of the metal acyl hydride is attributed to the two-carbon tether introducing strain into the three-legged piano stool geometry of 2 but leaving the four-legged piano stool geometry of 3 relatively unstrained. In agreement with this hypothesis, no strain was apparent in the X-ray structur...

Cp*(CO)2ReRe(CO)2Cp* (1) reacted with terminal alkynes HC⋮CR (R = H, CH3, C6H5, C(CH3)CH2, OCH2CH3) to produce dimetallacyclopentenones Cp*(CO)2Re(μ-η1,η3-CHCRCO)Re(CO)Cp* (4−8). The reaction of 1 with alkynes having one ester substituent also gave dimetallacyclopentenones. Reaction of 1 with HC⋮CCO2Me gave Cp*(CO)2Re[μ-η1,η3-CHC(CO2CH3)CO]Re(CO)Cp* (9) and with CH3C⋮CCO2Me gave Cp*(CO)2Re[μ-η1,η3-(CO2CH3)CC(CH3)CO]Re(CO)Cp* (10). At low temperature, the η2-propyne complex Cp*(CO)2Re(μ-CO)Re(CO)(HC⋮CCH3)Cp* (12) and Cp*(CO)2Re[μ-η1,η3-C(CH3)CHCO]Re(CO)Cp* (11) were observed as intermediates in the formation of Cp*(CO)2Re[μ-η1,η3-CHC(CH3)CO]Re(CO)Cp* (5). Protonation of dimetallacyclopentenone 2 with CF3CO2H produced [Cp*(CO)2Re(μ-η1,η2-CHCH2)Re(CO)2Cp*]+CF3CO2- (14), a species with a bridging vinyl group. Protonation of the thermodynamically favored regioisomeric dimetallacyclopentenone 5 gave [Cp*(CO)2Re(μ-η1,η2-(E)-CHCHCH3)Re(CO)2Cp*]+CF3CO2- (15). Protonation of kinetically formed regioisomeric dimetal...

The ring-metalated complex (η5-C5H4Li)Re(CO)3 generated by reaction of (η5-C5H5)Re(CO)3 with n-BuLi in THF at −78 °C reacted with additional (η5-C5H5)Re(CO)3 to produce the dirhenium acyl anion (η5...

Cp{sup *}(CO){sub 2}Re=Re(CO){sub 2}Cp{sup *} (1) is a rare example of a dimer of a d{sup 6} 16 electron metal fragment. Here we report that the addition of 2-electron donor ligands to 1 produces a series of tetracarbonyl complexes Cp{sup *}(CO){sub 2}Re({mu}-CO)Re(CO)(L)Cp{sup *} [L=CO (2), PMe{sub 3} (5), CH{sub 3}CN (6), CH{sub 2}=CH{sub 2} (7), CH{sub 3}C=V@CCH{sub 3} (8)] which have interesting stereochemistries and display fascinating fluxional behavior. The observation of a 2-butyne complex is particularly important since such alkyne complexes are likely intermediates in the formation of both dimetallacyclopentenones and dimetallacyclobutenes. The conversion of the 2-butyne adduct 8 to the dimetallacyclopentenone Cp{sup *}(CO){sub 2}Re[{mu}-{eta}{sup 1},{eta}{sup 3}-(CH{sub 3})-C=C(CH{sub 3})CO]Re(CO)Cp{sup *} (9) and the fluxional behavior of 9 that requires a symmetric dimetallacyclobutene or dimetallabicyclobutane intermediate is also presented. 36 refs., 3 figs., 2 tabs.

Hydride abstraction from η2-alkyne rhenium complexes C5Me5(CO)2Re(RC⋮CR‘) (2) with Ph3C+PF6- produces η3-propargyl complexes C5Me5(CO)2Re(η3-CHR‘‘−C⋮CR)+PF6- (3). Successful hydride abstraction to produce η3-propargyl complexes was observed only for internal acetylenes with a methyl or primary alkyl substituent. An unusual regioselectivity for hydride abstraction was observed: CH3CH2 > CH3 ≫ CH(CH3)2. Hydride abstraction from diethylacetylene complex C5Me5(CO)2Re(η2-CH3CH2C⋮CCH2CH3) (2c) produced a single stereoisomer of η3-propargyl complex C5Me5(CO)2Re(η3-CH3CH−C⋮CCH2CH3)+PF6- (3c) in which it is suggested that the methyl group is located in the less crowded position anti to the Cp* group. The regio- and stereoselectivity of hydride abstraction can be explained in terms of transition state A in which the carbon hydrogen bond being cleaved is antiperiplanar with respect to rhenium and the syn propargylic substituent comes into close contact with the Cp* ligand. Protonation of C5Me5(CO)2Re(η2-HC⋮CCH2OH) ...

The reaction of Cp*(CO)2ReRe(CO)2Cp* (1) with dimethyl acetylenedicarboxylate (DMAD) produced the 3,4-dimetallacyclobutene Cp*(CO)2Re(μ-η1,η1-CH3O2CCCCO2CH3)Re(CO)2Cp* (2). Photochemical rearrangement of 2 produced Cp*(CO)2Re(μ-η2,η2-CH3O2CC⋮CCO2CH3)Re(CO)2Cp* (3), in which both Cp*(CO)2Re units are coordinated to the alkyne. Upon heating at 72 °C, 3 was converted (t1/2 ≈ 120 min) to a 78:22 equilibrium mixture of 2:3. Photolysis of 3 in a Rayonet photoreactor (maximum emission 300 nm) resulted in CO loss and formation of Cp*(CO)Re(μ-η2,η2-CH3O2CC⋮CCO2CH3)(μ-CO)Re(CO)Cp* (4). Compounds 2, 3, and 4 were characterized by X-ray crystallography: 2, orthorhombic, Pcba, a = 14.480(3) A, b = 16.246(3) A, c = 26.027(3) A, Z = 8, Dc = 1.946 Mg/m3; 3, monoclinic, C2/c, a = 12.854(2) A, b = 14.729(3) A, c = 16.650(3) A, β = 108.188(12)°, Z = 4, Dc = 1.989 Mg/m3; 4, trigonal, P3(2), a = 16.277(2) A, b = 16.277(2) A, c = 9.408(3) A, α = 90°, β = 90°, γ = 120°, Z = 3, Dc = 2.005 Mg/m3.

The deuterioformylation of 1-hexene catalyzed by (chelating diphosphine)rhodium catalysts gave nearly exclusive formation of CH{sub 3}(CH{sub 2}){sub 3}CHDCH{sub 2}CDO and CH{sub 3}(CH{sub 2}){sub 3}CH(CH{sub 2}D)CDO, with the deuterium label at the {beta}-carbon and at the aldehyde carbon. Very little deuterium was incorporated into recovered hexenes. These results establish that the regiochemistry of aldehyde formation is set by a largely irreversible addition of a rhodium hydride to complexed 1-hexene to produce an alkylrhodium intermediate that is committed to aldehyde formation. Plausible steric explanations for the increased n:i aldehyde regioselectivity seen for diequatorial chelates compared with apical-equatorial chelates are considered. However, such steric explanations are not supported by molecular mechanics calculations of probable transition states. 26 refs., 3 figs., 5 tabs.