Methoxy Carbene Complexes Research Articles

Syntheses, characterizations and structures of ruthenium carbene and allenylidene complexes supported by 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3tacn) ligands

Treatment of ruthenium(II) precursor [(Me3tacn)Ru(dmso)Cl2] (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane, dmso = dimethylsulfoxide) (1) with concentrated HCl in the presence of air afforded the ruthenium(III) complex [(Me3tacn)RuCl3·H2O] (2), from which a series of bipyridine-ruthenium(II) complexes [(Me3tacn)Ru(R-bpy)(H2O)](PF6)2 (bpy = 2,2′-bipyridine) was obtained according to our previous work. Reactions of [(Me3tacn)Ru(R-bpy)(H2O)](PF6)2 and 1,1-diphenylpropargyl alcohol afforded ruthenium(II) methoxycarbene complexes [(Me3tacn)(R-bpy)Ru=C(OMe)CHCPh2](PF6)2 (R = H,3; 4,4′-Me2, 5; 5,5′-Me2, 7; 4,4′-di-tBu, 9) and ruthenium(II) allenylidene complexes [(Me3tacn)(R-bpy)Ru=C=CCPh2](PF6)2 (R = H,4; 4,4′-Me2, 6; 5,5′-Me2, 8; 4,4′-di-tBu, 10) under different solvent conditions. Complexes 3‒10 were well characterized by infrared, UV/Vis, mass spectrometry, and NMR spectroscopies. The molecular structures of complexes 5, 7, and 8 have been also established by single-crystal X-ray diffraction.

Experimental Evaluation of (L)Au Electron-Donor Ability in Cationic Gold Carbene Complexes.

29 Si NMR spectroscopy was employed to evaluate the electron donor properties of the (L)Au fragments in the cationic gold (β,β-disilyl)vinylidene complexes [(L)Au=C=CSi(Me)2 CH2 CH2 Si(Me)2 ]+ B(C6 F5 )4- [L=P(tBu)2 o-biphenyl or NHC] relative to the p-substituted aryl group in the α-aryl-(β,β-disilyl)vinyl cations [(p-C6 H4 X)-C= CSi(Me)2 CH2 CH2 Si(Me)2 ]+ B(C6 F5 )4- . Similarly, 19 F NMR was employed to evaluate the σ- and π-electron donor properties of the (L)Au fragments in the neutral gold fluorophenyl complexes (L)Au(C6 H4 F) and in the cationic (fluorophenyl)methoxycarbene complexes [(L)AuC(OMe)(C6 H4 F)]+ SbF6- [L=P(tBu)2 o-biphenyl or IPr] relative to the p-substituted aryl group of the protonated monofluorobenzophenones [(p-C6 H4 X)(C6 H4 F)COH]+ OTf- . The results of these studies indicate that relative to p-substituted aryl groups, the gold (L)Au fragments [L=P(tBu)2 o-biphenyl or NHC] are significantly more inductively electron donating and are comparable π-donors and for this reason, the extent of (L)Au→C1 electron donation in gold carbene complexes appears to exceed that provided by a p-(dimethyamino)phenyl group. Furthermore, the [L=P(tBu)2 o-biphenyl]Au fragment is a nominally stronger electron donor than the (IPr)Au fragment, and both are significantly more inductively electron donating than the (PPh3 )Au and [P(OMe)3 ]Au fragments.

Chemistry of transition metal carbene complexes: nucleophilic substitution reactions of cyanamide anion to Fischer carbene complexes

Rate constants for the reactions of cyanamide anion N≡C-NH(-) with Fischer carbene complexes of the type (CO)(5)M=C(XR)C(6)H(4)Z with M = Cr and W, XR = SMe and OMe, Z = NMe(2), OMe, Me, H, F, Cl and CF(3) in 50% MeCN-50% water (v/v) at 25 °C are reported. N≡C-NH(-) shows a much higher reactivity towards these carbene complexes than OH(-), primary aliphatic amines (e.g. n-butylamine) or secondary alicyclic amines (e.g. piperidine) but is slightly less reactive than thiolate ions (e.g. HOCH(2)CH(2)S(-)). The alkoxy carbene complexes were found to react faster than the thiomethyl derivatives, consistent with previous findings for alkoxide ion, CH(CN)(2)(-), OH(-), amine and thiolate ion nucleophiles. Hammett ρ values are 3.00 ± 0.08 (k(1)) and 2.98 ± 0.08 (k(2)) for Cr-OMe-Z-N≡C-NH(-) reactions and 0.94 ± 0.05 (k(1)) for Cr-SMe-Z-N≡C-NH(-) reactions. The ρ values for the reaction of Cr-OMe-Z and Cr-SMe-Z with CH(CN)(2)(-) and DABCO (1,4-diazabicyclo[2.2.2]octane) (in 50% MeCN-50% H(2)O (v/v) are comparable to the present reactions. The much higher reactivity and hence much higher ρ value for methoxy carbene complexes over the corresponding thiomethyl derivatives is best explained by considering the substituent effects not only on the transition state (TS) but also on the reactant, and consistent with the previously observed pattern. Higher k(1)(W)/k(1)(Cr) ratios for (thiomethyl)carbene complexes as well as methoxy and ethoxycarbene complexes are related to the intrinsic rate constant which is higher for tungsten-carbene complexes than the corresponding Cr ones resulting in an enhanced ratio. This can also be explained by considering the electronegativity of Cr and W, which is higher for the latter; as a result the negative charge on the central metal atom is more localized in case of W causing destabilization of the TS and hence higher reactivity.

Synthesis and structure of {{amino(triorganosilyl)carbene}pentacarbonyltungsten(0)} complexes and attempted synthesis of {[2-bis(trimethylsilyl)methyl-3-triorganosilyl-2 H-azaphosphirene-κ P]pentacarbonyltungsten(0)}

First examples of tungsten aminocarbene complexes [(OC 5)W{C(SiR 1 nR 2 3-n)NH 2}] 2a– d (R 1 = Ph, R 2 = Me) were synthesized via ammonolysis of the corresponding methoxycarbene complexes 1a– d. They were characterized by NMR spectroscopy, MS, IR, UV/Vis and elemental analysis, and in the case of the C-triphenylsilyl derivative 2a by single-crystal X-ray structure analysis. The reaction of P-chloro alkylidenephosphane 3 with complexes 2a– d, meant to give 2 H-azaphosphirene complexes, was monitored by 31P NMR spectroscopy to reveal the formation of the products 4– 7, which were presumably formed via decomposition of the transient complexes 10a– d.

Ruthenium Carbene and Allenylidene Complexes Supported by the Tertiary Amine−Aromatic Diimine Ligand Set: Structural, Spectroscopic, and Theoretical Studies

Ruthenium−methoxycarbene and −allenylidene complexes bearing 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3Tacn) and 1,10-phenanthroline (phen), [(Me3Tacn)(phen)Ru═C(OMe)R]2+ (R = CH2Ph (1), CH═CPh2 (2), CH═C(C6H4Cl-4)2 (3), CH═C(C6H4Me-4)2 (4)), and [(Me3Tacn)(phen)Ru═C═C═CR2]2+ (R = Ph (5), C6H4OMe-4 (6)) have been prepared. The molecular structures of 1(PF6)2 and 2(PF6)2 reveal Ru−C distances of 1.917(3) and 1.906(4) Å, respectively. The lowest-energy dipole-allowed absorptions for complexes 1−4 (λmax ≈ 435 nm) are assigned as dπ(RuII) → π*(phen) metal-to-ligand charge transfer (MLCT) transitions, while those for complexes 5 and 6 (λmax = 530 and 585 nm, respectively) are assigned as metal-perturbed π−π* [Ru═C═C═CR2] intraligand transitions. Complexes 1−4 are emissive in glassy MeOH/EtOH at 77 K: excitation at λ = 430 nm produces emission at λmax = 570−620 nm, which are tentatively assigned as dπ(RuII) → π*(phen) 3MLCT in nature. Density functional theory (DFT) calculations, charge decomposition analysis (CDA), and natural bond orbital (NBO) analysis on complexes 1, 2, 5, and 6 suggest that allenylidene ligands are better electron donors and poorer acceptors compared with methoxycarbene ligands, and the Ru−C interactions in ruthenium−allenylidene and −methoxycarbene complexes can be depicted by the polarized formulation Ruδ+═Cδ− and nonpolarized formulation Ru═C, respectively. The methoxycarbene/allenylidene rotational barriers on 1, 2, and 5 are calculated to be 8.3, 6.3, and 1.5 kcal mol−1, respectively.

Diastereoselective Cyclopropanation of Ketone Enols with Fischer Carbene Complexes

Treatment of aryl/heteroaryl methoxycarbene complexes of chromium with -substituted ketone lithium enolates between -78 degrees C and room temperature resulted in the diastereoselective synthesis of 1,2,2,3-tetrasubstituted cyclopropanols. An exception has been observed in the reaction with cyclohexanone lithium enolate that yielded a bicyclic 2-buten-4-olide. 1,2-Dimethoxycyclopropanes and 1-methoxy-2-trimethylsilyloxycyclopropanes were isolated by quenching the reactions with MeOTf or Me3SiCl, respectively. This novel cyclopropanation process involves formation of lithium (3-oxoalkyl)pentacarbonylchromate intermediates which on warming undergo intramolecular addition to the carbonyl group. This cyclization is equivalent to the cyclopropanation in smooth conditions of electron-rich alkenes with Fischer carbene complexes.

Carbene Ligands in Diiron Complexes.

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Transition Metal Carbene Chemistry. 4. Nucleophilic Attachment of DABCO to Fischer Carbene Complexes in MeCN

Rate constants for the attachment of DABCO (1,4-diazabicyclo[2.2.2]octane) to Fischer carbene complexes of the type (CO)(5)Cr=C(XR)C(6)H(4)Z (X = O and S) in dry MeCN at 25 degrees C are reported. Hammett rho values are 2.18 +/- 0.13 and 0.89 +/- 0.07 for DABCO reactions with (CO)(5)Cr=C(OMe)C(6)H(4)Z (10-Cr-Z) and (CO)(5)Cr=C(SMe)C(6)H(4)Z (11-Cr-Z), respectively. The rho values for the reaction of 10-Cr-Z and 11-Cr-Z with CH(CN)(2)(-) in 50% MeCN-50% H(2)O (v/v) are comparable to the present reactions. The reaction of DABCO with 10-Cr-Z is more closely related to the reaction of (n-Bu)(3)P with (CO)(5)W=C(OMe)C(6)H(5)-Z (23) which also provided a rho value 2.22. The much higher rho values and hence much higher reactivity of methoxy carbene complexes over the corresponding thiomethyl derivatives fit a pattern observed previously for alkoxide ion, OH(-), amine, and thiolate ion nucleophiles, and a rational explanation comes from the consideration of the substituent effects not only on the transition state but also on the reactant. A major difference between 10-Cr-Z and 11-Cr-Z is that the pi-donor effect of the methoxy group is much stronger than that of thiomethyl group. This leads to a substantial contribution of the zwitterionic form to the structure of 10-Cr-Z with much more localized positive charge on the methoxy group than the negative charge on the (CO)(5)Cr moiety. This leads to overall destabilization by an electron-withdrawing phenyl substituents resulting an increase in reactivity. The ethoxycarbene complexes are somewhat less reactive than their methoxy counterparts due to the somewhat more ground state stabilization through its stronger pi donor effect and partly due to steric crowding exerted by the slightly larger ethoxy group in the transition state. Higher k(1)(W)/k(1)(Cr) ratios for (thiomethyl)carbene complexes than methoxy or ethoxycarbene complexes are related to the intrinsic rate constant which is higher for ((thiomethyl)carbene)tungsten complexes than the corresponding Cr ones resulting in an enhanced ratio.

Polymer-Bound Fischer Tungsten Carbene Complexes: Synthesis and Reactivity

The solid-phase synthesis of polymer-bound tungsten Fischer carbene complexes of the types 8 and 16 is described. Starting with isocyanide ligands 5 and 14, readily available from the Merrifield resin 1, the pentacarbonyl(isocyanide)tungsten complexes 7 and 15 are efficiently formed. The synthesis of the corresponding methoxycarbene complexes 8a,b and 16a,b (a, R = Me; b, R = Ph) is undertaken under standard Fischer conditions. The solid-phase amination, methyl acrylate cyclopropanation, and C−H insertion arise as preliminary studies related to their reactivity.

Synthesis and reactivity with amines of new diiron alkynyl methoxy carbene complexes

The new diiron alkynyl methoxy carbene complexes [Fe 2{μ-CN(Me)(R)}(μ-CO)(CO){C(OMe)C CR′}(Cp) 2] + (R = 2,6-Me 2C 6H 3 (Xyl), R′ = Tol, 3a; R = Xyl, R′ = Ph, 3b; R = Xyl, R′=Bu n , 3c; R = Xyl, R′=SiMe 3, 3d; R = Me, R′ = Tol, 3e; R = Me, R′ = Ph, 3f) are obtained in two steps by addition of R′C CLi (R′ = Tol, Ph, Bu n , SiMe 3) to the carbonyl aminocarbyne complexes [Fe 2{μ-CN(Me)(R)}(μ-CO)(CO) 2(Cp) 2] + (R = Xyl, 1a; Me, 1b), followed by methylation of the resulting alkynyl acyl compounds [Fe 2{μ-CN(Me)(R)}(μ-CO)(CO){C(O)C CR′}(Cp) 2] (R = Xyl, R′ = Tol, 2a; R = Xyl, R′ = Ph, 2b; R = Xyl, R′ = Bu n , 2c; R = Xyl, R′ = SiMe 3, 2d; R = Me, R′ = Tol, 2e; R = Me, R′ = Ph, 2f). Complexes 3 react with secondary amines (i.e., Me 2NH, C 5H 10NH) to give the 4-amino-1-metalla-1,3-dienes [Fe 2{μ-CN(Me)(R)}(μ-CO)(CO){C(OMe)CH C(R′)(NMe 2)}(Cp) 2] + (R = Xyl, R′ = Tol, 4a; R = Xyl, R′ = Ph, 4b; R = Me, R′ = Ph, 4c) and [Fe 2{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(OMe)CH C(Tol)(NC 5H 10)}(Cp) 2] +, 5. The addition occurs stereo-selectively affording only the E-configured products. Analogously, addition of primary amines R′NH 2 (R′ = Ph, Et, Pr i ) affords the 4-( NH-amino)-1-metalla-1,3-diene complexes [Fe 2{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(OMe)CH C(R)(NHR′)}(Cp) 2] + (R = Ph, 6a; Et, 6b; Pr i , 6c). In the case of 6a, only the E isomer is formed, whereas a mixture of the E and Z isomers is present in the case of 6b, c, with prevalence of the latter. Moreover, the two isomeric forms exist under dynamic equilibrium conditions, as shown by VT NMR studies. Complexes 6 are deprotonated by strong bases (e.g., NaH) resulting in the formation of the neutral vinyl imine complexes [Fe 2{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(OMe) CHC( NR)(Tol)}(Cp) 2] (R = Ph, 7a; Et, 7b; Pr i , 7c); the reaction can be reverted by addition of strong acids. X-ray crystal structures have been determined for 3a[CF 3 SO 3 ] · Et 2 O, 4c[CF 3 SO 3 ], 6a[BF 4 ] · CH 2 Cl 2 , 6c[CF 3 SO 3 ] · 0.5Et 2 O and 7a · CH 2 Cl 2 .

Ruthenium Tris(pyrazolyl)borate Complexes. Part 20 [1]. Synthesis, Characterization, and Reactivity of Neutral Trispyrazolylborate Ruthenium Vinylidene Complexes

The reaction of RuTp(COD)Cl (1) with PPh2Pri and terminal alkynes HC≡CR (R=C6H5, C4H3S, C6H4OMe, Fc, C6H4–Fc, C6H9) affords the neutral vinylidene complexes RuTp(PPh2Pri) (Cl)(=C=CHR) (2a–2f) in high yields. These complexes do not react with MeOH to give methoxy carbene complexes of the type RuTp(PPh2Pri)(Cl)(=C(OMe)CH2R), but react with oxygen to yield the CO complex RuTp(PPh2R)(Cl)(CO) (3). The structures of 2b, 2f, and 3 have been determined by X-ray crystallography.

Solvent‐Controlled Diastereoselective Synthesis of Cyclopentane Derivatives by a [3 + 2] Cyclization Reaction of α,β‐Disubstituted (Alkenyl)(methoxy)carbene Complexes with Methyl Ketone Lithium Enolates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Solvent-controlled diastereoselective synthesis of cyclopentane derivatives by a [3 + 2] cyclization reaction of alpha,beta-disubstituted (alkenyl)(methoxy)carbene complexes with methyl ketone lithium enolates.

Reaction of alpha,beta-unsaturated methoxycarbene complexes 1 and 11 with methyl ketone lithium enolates 2 leads to the corresponding five-membered carbocyclic compounds 4 or diast-4 and 12. The influence of the solvent and/or cosolvent (PMDTA), which turned out to be crucial to direct the reaction to 4 or diast-4, is studied, and a tentative mechanism according to these facts is proposed. In addition, the reaction of carbene complex 1a with alkynyl methyl ketone lithium enolates can be directed to the formal [3 + 2] or [4 + 1] cyclization products by a slight variation of the reaction conditions. Finally, consecutive three-component coupling reactions with carbene complex 1a, lithium enolates 2, and aldehydes 18 to give, in a diastereoselective way, hydroxy carbonyl compounds 19 and tricyclic polyethers 20 are presented.

The preparation of imidazolidinone and oxazolidinone chelated carbene complexes

Abstract The synthesis of several internally chelated imidazolidinone and oxazolidinone Fischer carbene complexes of the type (CO)4M=CC(R1)NCO(CHR2CHR3X) are reported where the M=chromium, tungsten; R1=methyl, ethyl, iso-propyl, phenyl, trans-propenyl, iso-propenyl, iso-butenyl, cyclohexenyl and 1-propynyl; R2=H, Ph, Bn, Me, Cy; R3=H, Me, Ph; X=O, NMe. Four different methods are used for the synthesis of these complexes. The imidazolidinone complexes are best prepared by adding an imidazolidinone or lithiated imidazolidinone to a methoxy carbene complex or to an in-situ generated acetoxy carbene complex. α,β-Unsaturated imidazolidinone complexes are prepared by aldol condensations of alkyl imidazolidinone complexes or by alkylaltion of these complexes with bromomethyl methyl ether and then elimination of methanol. The oxazolidinone complexes are best made by a two-step procedure that involves the addition of an β-aminoalcohol to a methoxy or acetoxy complex followed by closure of the resulting amino carbene complex to the oxazolidinone complex with phosgene.

ChemInform Abstract: Diastereoselective Intermolecular Cyclopropanation of Simple Alkenes by Fischer Alkenyl and Heteroaryl Carbene Complexes of Chromium: Scope and Limitations.

The intermolecular cyclopropanation of simple alkyl-substituted alkenes with Fischer methoxycarbene complexes under thermal conditions is reported. The scope and limitations of this [2 + 1] cycloaddition with respect to the nature of the carbene complex, substitution pattern of the electron neutral olefin, and functional group tolerance in the electron neutral olefin are described in detail. This methodology provides functionalized cyclopropanes in good to excellent yields and generally with high diastereoselectivity. A mechanism involving the initial formation of a chelated tetracarbonyl complex intermediate is proposed to account for the observed results.

Diastereoselective Intermolecular Cyclopropanation of Simple Alkenes by Fischer Alkenyl and Heteroaryl Carbene Complexes of Chromium: Scope and Limitations

The intermolecular cyclopropanation of simple alkyl-substituted alkenes with Fischer methoxycarbene complexes under thermal conditions is reported. The scope and limitations of this [2 + 1] cycloaddition with respect to the nature of the carbene complex, substitution pattern of the electron neutral olefin, and functional group tolerance in the electron neutral olefin are described in detail. This methodology provides functionalized cyclopropanes in good to excellent yields and generally with high diastereoselectivity. A mechanism involving the initial formation of a chelated tetracarbonyl complex intermediate is proposed to account for the observed results.

Ruthenium Benzylidene and Vinylidene Complexes in a Sulfur-Rich Coordination Environment

Interaction of Ru(CHPh)(PCy3)2Cl2 (Cy = cyclohexyl) with K[N(PPh2S)2] affords air-stable Ru(CHPh)[N(PPh2S)2]2, 1, which has been characterized by X-ray diffraction. The Ru−Cα and average Ru−S distance for 1 are 1.88(2) and 2.377 A, respectively. Reaction of 1 with CO gives cis-Ru(CO)2[N(PPh2S)2]2. Complex 1 undergoes metathesis with ethyl vinyl ether to give the methoxycarbene complex Ru(CHOEt)[N(PPh2S)2]2, 3. Treatment of Ru(CHPh)(PCy3)2Cl2 with K[N(PPh2Se)2] affords Ru(CHPh)[PPh2NP(Se)Ph2]2, 4, which has been characterized by X-ray crystallography. The Ru−C, average Ru−P, and average Ru−Se distances are 1.873(8), 2.383, and 2.450 A, respectively. Reactions of Ru(CHPh)(PCy3)2Cl2 with K[P(OR)2S2] afford cis-Ru(CHPh)(PCy3)[P(OR)2S2]2 (R = Et (6) and i-Pr (7)). Reaction of Ru(CHPh)(PCy3)2Cl2 with 1,4,7-trithiacyclononane ([9]aneS3) gives [([9]aneS3)Ru(CHPh)(PCy3)Cl]Cl, 8. Treatment of Ru(CCHPh)(PCy3)2Cl2 with K[N(PPh2S)2] or [9]aneS3 affords cis-Ru(CCHPh)(PCy3)[N(PPh2S)2]2 (9) or ([9]aneS3)Ru(PCy3)Cl2 (10),...

Convenient routes to mono- and dinuclear (C 5Me 5)iron(II) complexes bearing acyl, alkynyl, aryl and thienyl ligands

Treatment of the cations [Fe(C 5Me 5)(CO) 2(L)][PF 6] ( 1a, L=CO; 1c, L=PPh 3) with LiCCSiMe 3 gives the corresponding acyl derivatives [Fe(C 5Me 5)(CO) 2{C(O)CCSiMe 3}] ( 2) and [Fe(C 5Me 5)(CO)(PPh 3){C(O)CCSiMe 3}] ( 4), respectively. The nucleophile adds at the carbonyl ligand, but in the case of 1a, competitive attack occurs at the metal centre leading to the formation of the alkynyl complex [Fe(C 5Me 5)(CO) 2{CCSiMe 3}] ( 3). The latter species is formed as the only product from the acetonitrile complex [Fe(C 5Me 5)(CO) 2(CH 3CN)][PF 6] ( 1b), under the same conditions. Similarly, the dinuclear bis(acyl) complex [Fe(C 5Me 5)(CO) 2{μ-η 1,η 1′-C(O)-] 2(2,2′-C 4H 2S) ( 6) is obtained from 1a by using 0.5 equivalents of the dilithium salt 2,2′-Li 2C 4H 2S/TMEDA. Complete decarbonylation by UV irradiation of 3 or 6 in the presence of dppe affords the corresponding disubstituted complexes [Fe(C 5Me 5)(dppe){CCSiMe 3}] ( 5) and [Fe(C 5Me 5)(dppe)] 2{μ-η 1,η 1′-2,2′-C 4H 2S} ( 7), respectively. Complexes [Fe(C 5Me 5)(CO) 2{CH(OMe)C 6H 4- p-Br}] ( 9) and [Fe(C 5Me 5)(CO) 2{CH(OMe)-2-C 4H 3S}] ( 10) are synthesised from the methoxycarbene complex [Fe(C 5Me 5)(CO) 2(CHOMe)][PF 6] ( 8); the nucleophilic addition of the organolithium reagents occurs at the carbene ligand. Dinuclear complexes such as the thiophene derivative [Fe(C 5Me 5)(CO) 2{μ-η 1,η 1′-CHOMe-] 2(2,2′-C 4H 2S) ( 11) and the biphenylene complex [Fe(C 5Me 5)(CO) 2{μ-η 1,η 1′-CHOMe-] 2( p-C 6H 4-C 6H 4) ( 12) are obtained by using the appropriate dilithiated nucleophiles. Protonolysis of 12 gives the bis(carbene) complex [Fe(C 5Me 5)(CO) 2{μ-η 1,η 1′-CH-] 2( p-C 6H 4-C 6H 4) ( 13), which is stable at −50°C.

Chemoselective synthesis of (allyloxy)carbene chelate complexes of iron

Chelate (allyloxy)carbene complexes [F e(C 5H 5)(CO){η 2-C(OCH 2CHC HPh)C 6H 4- o-X}][OTf] ( 4a–b) ( a, X=OMe; b, X=Cl) are readily accessible from methoxycarbene complexes 2 and 3 containing a hemilabile or labile ligand. The facile coordination of the alkenyl group, due to the presence of a potential vacant coordination site, allows the selective formation of 4.

Organotransition metal modified sugars 4. Carbene complex functionalized acyclic carbohydrates

A synthetic strategy based on a combination of sugar electrophiles and transition metal nucleophiles allows the metal carbene functionalization of acyclic carbohydrates. Following this methodology the per- O-acetylated methoxycarbene complexes 8–14 are prepared in moderate to good yields. Upon reaction with ammonia they undergo aminolysis to give the aminocarbene complexes 16–18. 1H-NMR studies indicate that in solution the d-galacto and l-arabino complexes adopt extended planar zigzag conformations. A similar conformational preference is observed for the solid state as established by X-ray studies on the d-galacto derivatives 8 and 15.