Complexes Tp Research Articles

Cyclization Reactions of Coordinated Alkynes in Tungsten(II) Complexes

Displacement of a CO ligand from [Tp‘(CO)2W{HC⋮CH}][OTf] with iodide leads to the neutral parent acetylene complex Tp‘(CO)(I)W{HC⋮CH} (2). Deprotonation of 2 followed by methylation is regioselective and yields a single isomer of the propyne complex Tp‘(CO)(I)W{HC⋮CCH3} (3). Deprotonation of 3 followed by alkylation with RI (R = Me, I(CH2)n (n = 3−7)) is also regioselective and leads to a single isomer, Tp‘(CO)(I)W{RC⋮CCH3} (4−9). Deprotonation of Tp‘(CO)(I)W{I(CH2)nC⋮CCH3} (n = 5 (7), 7 (9)) leads to an η2-allenyl intermediate which undergoes intramolecular alkylation (i.e. endocyclic cyclization) to form Tp‘(CO)(I)W{cyclooctyne} (10) and Tp‘(CO)(I)W{cyclodecyne} (11), respectively. The exocyclic cyclization precursor Tp‘(CO)(I)W{PhC⋮C(CH2)5I} (12) was obtained by deprotonation of the propargyl carbon of Tp‘(CO)(I)W{PhC⋮CCH3} followed by alkylation with I(CH2)4I. The cyclopentyl derivative Tp‘(CO)(I)W{PhC⋮C(cyclopentyl)} was generated by deprotonation of 12 followed by intramolecular alkylation (i.e. exo...

Fluoro[eta(3)-hydrotris(3-R-5-methylpyrazol-1-yl)borato]zinc(II): The First TpZnF Complexes, Convenient Precursors to Zinc Hydride Complexes(,).

Fluoro[eta(3)-tris(3-R-5-methylpyrazol-1-yl)hydroborato]zinc(II) complexes, Tp(R,Me)ZnF (with R = p-Tol, t-Bu), have been prepared by metathesis of Tp(p-)()(Tol,Me)ZnOAc with KF in MeOH/THF and by reaction of KTp(t-)()(Bu,Me) with Zn(ClO(4))(2) and KF in MeOH. The molecular structure of Tp(p-)()(Tol,Me)ZnF has been determined by X-ray crystallography. Crystal data: a = 11.8719(12), c = 37.051(3) Å; trigonal, space group R3c (No. 161); Z = 6. The complex contains tetrahedrally coordinated Zn(II). The tolyl rings deviate by 21 degrees from coplanarity with the pyrazolyl plane. The reaction of Tp(p-)()(Tol,Me)ZnF with py.BF(3) leads to the tetrafluoroborate salt [Tp(p-)()(Tol,Me)Zn(py)](+)BF(4)(-). The analogous reaction with Et(2)O.BF(3) probably gives a solvent complex [Tp(p-)()(Tol,Me)Zn(Et(2)O)](+)BF(4)(-) that however could not be isolated. Triethylsilane reacts with Tp(p-)()(Tol,Me)ZnF to yield the zinc hydride Tp(p-)()(Tol,Me)ZnH. Trimethylsilyl derivatives Me(3)Si-X (X = Cl, Br, I, NCO, OAc) similarly give Tp(p-)()(Tol,Me)ZnX, whereas bis(trimethylsilyl) malonate yields the bridged complex Tp(p-)()(Tol,Me)Zn-O-C(O)-CH(2)-C(O)-O-ZnTp(p-)()(Tol,Me).

Synthesis and Deprotonation/Alkylation Reactions of the Chiral Carbene Complex Tp‘(CO)(NO)MoC(OMe)(Me)

The Fischer carbene complex Tp‘(CO)(NO)MoC(OMe)(Me) (1) has been synthesized, and functionalization of the carbene methyl substituent has been achieved via deprotonation/alkylation reaction sequences. The chiral metal center produced moderate diastereoselectivity. Isomeric, geometric, and thermodynamic features are discussed for the complexes Tp‘(CO)(NO)MC(OMe)(R) (M = W, R = Me; M = Mo, R = Me, Et, Ph, −CH2CH2CHCH2, −C(H)(Me)CH2CHCH2), and evidence of a substantial metal carbene rotational barrier is presented. Important structural features for Tp‘(CO)(NO)MoC(OMe)(Ph) (7), which was characterized by single-crystal X-ray crystallography, include a short molybdenum−carbon bond distance to the carbene (2.085(4) Å) and a carbene carbon−oxygen bond distance of 1.356(5) Å.

On the Ligating Properties of Sulfonate and Perchlorate Anions Towards Zinc

Attempts are reported to incorporate sulfonate and perchlorate anions as ligands in zinc complexes of tripodal ligands. Using tris(benzimidazolylmethyl)amine (BIMA) only the aqua complexes [ (BIMA)Zn-OH2](RSO3)(ClO4) and [(BIMA)Zn-OH2](RSO3)2(RCH3, CF3, p-tolyl) were accessible. Using substituted pyrazolylborates (Tp*), the same three sulfonate anions were found to be ligands in the complexes Tp*Zn-OSO2R. Spectroscopic evidence for perchlorate coordination in Tp*ZnClO4 · 2 DMSO conflicts with crystallograpic evidence against it in Tp*ZnClO4 · pyridine. The crystal structures of [(BIMA)Zn-OH2](CH3SO3)2, TpCum,MeZn-OS02CH3, TPtBu,MeZn-OSO2C6H4-p-CH3, and [TpCum,MeZn · NC5H5]ClO4 were determined.

Correlation of EPR Parameters with Electronic Structure in the Homologous Series of Low-Symmetry Complexes Tp*MoOX2 (Tp* = Hydrotris(3,5-dimethylpyrazol-1-yl)borate; X = F, Cl, Br)

Correlation of EPR Parameters with Electronic Structure in the Homologous Series of Low-Symmetry Complexes Tp*MoOX₂ (Tp* = Hydrotris(3,5-dimethylpyrazol-1-yl)borate; X = F, Cl, Br)

Chemical Interconversions in the System TP*Zn/CO2/Alcohol [Tp* = Substituted Tris(pyrazolyl)borate

AbstractThe zinc hydroxide complexes Tp*Zn–OH with TpCum,Me = tris(3‐cumenyl‐5‐methylpyrazolyl)borate and TptBu,Me = tris(3‐tert‐butyl‐5‐methylpyrazolyl)borate can be converted to the alkyl carbonate complexes Tp*Zn–OCOOR by reaction with dialkyl dicarbonates or with alcohol and CO2. An alternative formation reaction is the treatment of the pyrazolyl borate with zinc perchlorate and potassium carbonate in alcohol. The interconversion between TpCum,MeZn–OH and TpCum,MeZn–OCOOMe in methanol‐containing solution can be repeatedly performed in both directions by bubbling either CO2 or N2 through the solution. The alkyl carbonate complexes show a variable sensitivity towards hydrolytic destruction with reformation of the hydroxide complexes. The complexes TptBu,MeZn–OCOOR (R = Me, Et) release CO2 under high vacuum to form the alkoxide complexes TptBu,Me‐Zn–OR, which could not be obtained pure due to their extreme water sensitivity. Indirect evidence for their existence is also obtained by the reaction between TpCum,MeZn–OCOOMe and methyl iodide, forming TpCum,MeZn–I and dimethyl ether. The Zinc hydroxide complexes catalyse the formation of diethyl carbonate from ethanol and CO2.

Hydrotris(pyrazolyl)borate molybdenum chemistry: spin triplet 16-electron carbonyl derivatives of molybdenum (II), and the X-ray structure of the Mo(V) oxo compound {HB(3,5-Me 2C 3N 2H) 3} MoOI 2

The hydrotris(3,5-dimethylpyrazolyl)borate complexes Tp ∗ Mo( CO) 2 X ( X = Cl, I) are rare examples of 16-electron carbonyl derivatives with a spin triplet ground state, which exhibit relatively sharp contactshifted 1H NMR spectra. Oxidation of Tp ∗MoI(CO) 2 led to the isolation and crystallographic characterization of Tp ∗MoOI 2.

Regular paper

Solution studies by 1H and 13C NMR and IR spectroscopy of rhodium(I) complexes Tp PhRh(NBD) 1, Tp PhRh(COD) 2 and Tp PhRd(CO) 2 3 (NBD = 2,5-norbornadiene, COD = 1,5-cyclooctadiene) show that these compounds exist as mixtures of two isomeric square-planar complexes containing the Tp Ph ligand in a bidentate k 2-bonded form, with the third uncoordinated pyrazolyl ring occupying an equatorial position, form A, or an axial position, form B. In the solid state the complexes are tetracoordinated, as proved by X-ray crystallography: 1 (monoclinic, space group P2 1/ c) and 2 (orthorhombic, space group P2 12 12 1), whose structures correspond to forms B and A respectively. Changes in the A/ B ratio in the solid complex Tp PhRh(CO) 2 3 were observed after several months.

Chemistry Surrounding Chiral Tungsten(II) η1-Imine Complexes

Chiral tungsten(II) η1-imine complexes [Tp‘(CO)(PhC⋮CMe)W(NHCRR‘)]+ (Tp‘ = hydridotris(3,5-dimethylpyrazolyl)borate) have been prepared by oxidation of the corresponding amido complexes Tp‘(CO)(PhC⋮CMe)W(NHCHRR‘) (R/R‘ = Ph/Ph, Ph/Me, Me/Et, and H/CHMePh) with elemental iodine. These oxidations also result in formation of amine complexes which have been independently synthesized. Oxidation in the presence of a weak base suppresses amine formation. However, when R = Ph, deprotonation of the imine product forms the neutral azavinylidene complex Tp‘(CO)(PhC⋮CMe)W(NCRR‘). Protonation of the azavinylidene complex provides a clean route to the desired imine complex. Crystal structures of a representative complex from each category of nitrogen donor ligand have been determined: cationic imine complex [Tp‘(CO)(PhC⋮CMe)W(NHCMeEt)][BAr‘4] (2a), cationic amine complex [Tp‘(CO)(PhC⋮CMe)W(NH2CH2CHMePh)][I3] (4d), neutral amido complex Tp‘(CO)(PhC⋮CMe)W(NHCHMeEt) (1a), and neutral azavinylidene complex Tp‘(CO)(PhC⋮CMe...

Modelling transition state analogues and enzyme-inhibitor complexes of zinc-containing class II aldolases and metalloproteases

The zinc complex Tp ∗ZnOH ( 1: Tp ∗ = hydrotris-(3- cumyl,5- methyl-pyrazolyl)borate ) which is a model of hydrolytic zinc enzymes was reacted with hydroxamic acids and hydroxyketones. Two hydroxamates Tp ∗Zn-Hya ( 2: Hya = acetohydroxamate, 3: Hya = 2-hydroxamato-4-methylpentanoyl-alanyl-glycylamide ) and two ketoalcoholates Tp ∗Zn-Kea ( 4: Kea = hydroxyacetonate, 5: Kea = cumoylacetonate ) were obtained. Crystal structure determinations of 2, 3 and 5 have revealed distorted ZnN 3O 2 coordinations in each case. The immediate environment of the zinc ion in the hydroxamates closely resembles that in enzyme-(hydroxamate)inhibitor complexes of zinc-containing metalloproteases like collagenases and thermolysin or of class II aldolases like fuculose-1-phoshate aldolase. Like in the enzymes the hydroxamates and the ketoalcoholates can serve as transition state analogues of the enzyme-catalysed reactions.

Iridapyrrole Complexes via Formal 3 + 2 Cycloaddition of Iridium Alkenyls to Acetonitrile

Under appropriate conditions, the bis(ethylene) derivative Tp*Ir(C2H4)2 (Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate) reacts with MeCN to provide the Ir(III) complex Tp*Ir(CHCH2)(C2H5)(NCMe) (1). In the presence of catalytic amounts of water, 1 undergoes intramolecular coupling of the vinyl and acetonitrile ligands, with formation of a compound (2a) that contains a delocalized, five-membered iridapyrrole ring. This unusual cycloaddition reaction can be extended to other related alkenyl complexes of iridium.

Competition between π Donation and α-C−H Agostic Interactions in Complexes of the Type Tp‘Ta(CH-t-Bu)(X)(Y) (X = Halide; Y = Halide, NR2, OR; Tp‘ = Hydrotris(3,5-dimethylpyrazolyl)borate)

The compounds Tp‘Ta(CHC(CH3)3)X2 (2 (X = Cl), 3 (X = Br)) (Tp‘ = hydrotris(3,5-dimethylpyrazolyl)borate), have been synthesized by the reaction of KTp‘ with Ta(CHC(CH3)3)X3(thf)2 in THF. One Cl ligand in 2 can be substituted with OR- (R = i-Pr, Me) or NMe2-. The values of 1JC-H for the alkylidene carbon are uniformly low due to the α-H agostic interaction between the metal center and the alkylidene proton. The magnitude of 1JC-H in these compounds depends upon the π donor properties of the remaining ligands. Attempted synthesis of monoarylamide complexes by displacement of Cl- from 2 with N(H)Ar- results in proton transfer from N to C and formation of the imido complexes Tp‘Ta(CH2C(CH3)3)(NAr)Cl (Ar = 2,6-i-PrC6H3 (7), Ph (8)). When 2 reacts with KN(Me)Ph, proton transfer occurs from the Me group to the alkylidene carbon giving the imine complex Tp‘Ta(η2-CH2NPh)(CH2CMe3)Cl (9). A single-crystal X-ray diffraction study of 9 confirmed the structure and suggested that 9 is best described as an azametallacycl...

(Hydrotris(3,5-dimethylpyrazolyl)borato)niobium Alkyne Complexes: Dichloro and Dialkyl Derivatives and Formation of a Butadienyl Complex with an α-Agostic Interaction

A high-yield one-pot synthesis of Tp*NbCl2(alkyne) is described [Tp* = hydrotris(3,5-dimethylpyrazolyl)borate; alkyne = PhC⋮CCH3 (1a), PhC⋮CCH2CH3 (1b), PhC⋮CCH2CH2CH3 (1c), CH3C⋮CCH3 (1d), PhC⋮CPh (1e)]. It involves treatment of NbCl3(DME) (DME = 1,2-dimethoxyethane) with first an alkyne and then with KTp*. The dimethyl derivatives Tp*Nb(CH3)2(alkyne) (alkyne = PhC⋮CCH3 (2a), PhC⋮CCH2CH3 (2b), PhC⋮CCH2CH2CH3 (2c)) and the dibenzyl complex Tp*Nb(CH2Ph)2(PhC⋮CCH3) (3a) have been obtained from the appropriate dichloro complex and 2 equiv of either methyllithium or benzylmagnesium chloride, respectively. These 16-electron niobium(III) d2 complexes, 1a-e, 2a-c, and 3a, have been characterized spectroscopically. In all cases the alkyne is shown to occupy the molecular mirror plane. The barrier to alkyne rotation is high and could be measured only in the case of 1d (68 kJ mol-1 at 358 K). On the basis of qualitative arguments, the structure of these complexes is basically governed by steric interactions. A comparison with the isoelectronic cyclopentadienyl derivatives is provided. When 1a is treated with 2 equiv of ethylmagnesium chloride, the formal dehydrogenation of an ethyl group results in the alkyne-coupled product Tp*Nb(CH2CH3)[C(Ph)C(CH3)CHCH2] (4a), which has been spectroscopically characterized. 1H and 13C NMR data suggest that an α-agostic interaction is present in the ethyl group in this complex.

Reduction of ketones by dihydrogen or hydrogen transfer catalysed by a ruthenium complex of the hydridotris (3,5-dimethyl)pyrazolyl borate ligand

The hydride complexes Tp∗RuH(H 2) 2 ( 1) and Tp∗RuH(COD) ( 2) (Tp∗ = hydridotris(3,5-dimethyl)pyrazolyl borate) show good catalytic activity for the reduction of unactivated ketones either by dihydrogen or by hydrogen transfer from alcohols in basic media.

Nitrene Transfer to Trimethylphosphine from Cationic Tungsten Tosylnitrene Complexes [Tp'(CO)2W(NTs)][X

Reaction of Tp{prime}(CO){sub 3}WH(Tp{prime}=hydridotris(3.5-dimethyl-1-pyrazolyl)borate) with tosyl azide in THF at reflux affords the amido complex Tp{prime}(CO){sub 2}W(N(H)Ts) (1). Crystals of 1 are monoclinic, space group P2{sub 1}/n, with cell parameters a = 12.4855(11) A, b=20.5976(16){Angstrom}, c= 12.7311(11){Angstrom}, {beta}=96.510(10){degrees}, V=3253.0(5) {Angstrom}{sup 3}, and D{sub calcd}=1.591 g cm{sup {minus}3} for Z = 4. Least-squares refinement led to final R and R{sub w} values of 0.038 and 0.046, respectively. Complex 1 undergoes oxidation by silver triflate or iodine to give the imido complexes [Tp{prime}-(CO){sub 2}W(NTs)]X (X=OTf, 2a; X=I{sub 3},2b). The single crystal X-ray structure of 2b is also reported (orthorhombic, space group Pcab, a= 15.1764(16) {Angstrom}, b = 16.8890(14) {Angstrom}, c=26l909(3) {Angstrom}, V=6897.2(13) {Angstrom}{sup 3}, and D{sub calcd}= 2.094 g cm{sup {minus}3} for Z=8; R=0.044, R{sub 2}=0.052). The cationic nitrene complex 2 reacts with LiBH{sub 4} to regenerate the amido compound 1. Addition of trimethylphosphine to solutions of 2 leads to the formation of three species the phosphinimine TsN=PMe3 (3) and two tungsten complexes, [Tp{prime}(CO){sub 2}W(PMe{sub 3}){sub 2}][X](X = OTf, 4a; X=I{sub 3}, 4b) and [Tp{prime}(CO)(PMe{sub 3})W(NTs)][X] (X=OTf, 5a; X=I{sub 3}, 5b). Complex 5b undergoes substitution by iodide to produce the tungsten monocarbonyl Tp{prime}(CO)IW(NTs) (6).

Hydrogen tunneling in the activation of dioxygen by a tris(pyrazolyl)borate cobalt complex

The activation of dioxygen by coordination to metals plays an important role in living organisms as well as artificial oxidation catalysts. We have previously described the dioxygen complex Tp[prime]Co[sup II](O[sub 2]) (Tp[prime] = hydridotris (3-tert-butyl-5-methylpyrazolyl)borate) and its reaction with Tp[prime]Co[sup I](N[sub 2]) to yield Tp[prime]Co[sup II]OH, the apparent product of hydrogen atom abstraction by a highly reactive cobalt - oxo complex. Herein we report related chemistry of the Tp[double prime]Co-moiety (Tp[double prime] = hydridotris (3-isopropyl-5-methylpyrazolyl) borate), including the observation of an intermediate and evidence for a tunneling contribution to hydrogen atom abstraction from the ligand. 16 refs., 1 fig.

Mononuclear bis-aminocarbyne complexes of tungsten with Tp′ ligands; theory of metal-centred carbyne-carbyne coupling

An efficient procedure for the synthesis of mononuclear bis-aminocarbyne complexes of tungsten is reported starting from Tp′(CO) 2WCN (R)Et ( 1a: R  Me; 1b: R  Et) (Tp′= hydrido(3,5-dimethylpyrazol-1-yl)borate). In the first step oxidative decarbonylation of 1a and 1b with Br 2 occurs to afford the six-coordinate aminocarbyne complexes Tp′(Br) 2WCN(R)Et ( 2a, 2b) in high yield. Similarly, complexes 1a and 1b are converted by I 2 into the diiodo derivatives Tp′(I) 2WCN(R)Et ( 3a, 3b). Reductive dehalogenation of 3a and 3b by Na/Hg in the presence of EtNC gives the electron-rich mono-aminocarbyne complexes Tp′(EtNC) 2WCN(R)Et ( 4a, 4b), which are finally alkylated with [Et 3O]BF 4 at one isocyanide-nitrogen to yield the bis- aminocarbyne complexes {Tp′(EtNC)W[ ▪CN(R)Et][ ▪CNEt 2]}BF 4 ( 5a, 5b). Extended-Hückel calculations on the hypothetical 18e bis-carbyne complex [CpW(CO)(CH) 2] + predict a spontaneous rearrangement to the energetically favoured 16e acetylene complex [CPW(CO)(HCCH)] + and show, in full agreement with the experimental work, that introduction of amino-substituents on both carbyne-carbons stabilizes the bis-carbyne form relative to the alkyne isomer. The solid-state structure of 2b was determined by a single- crystal X-ray diffraction study revealing a distorted octahedral complex with a short WC carbyne bond. The short C carbyne N bond and the planar amino-nitrogen indicate a high degree of π-bonding between the carbyne-carbon and the amino-nitrogen.

Acyl, carbene, vinyl, and azavinylidene ligands in tungsten(II) hydridotris(3,5-dimethylpyrazolyl)borate alkyne complexes

Reaction of [Tp'(CO)[sub 2]W(PhC[sub 2]Me)][BF[sub 4]] with LiCuR[sub 2] (R = Ph, Me) generates neutral [eta][sup 1]-acyl complexes Tp'(CO)(PhC[sub 2]Me)W([eta][sup 1]-C(O)R) in which the alkyne ligand remains as a four-electron donor. Deprotonation of the alkyne methyl in Tp'(CO)PhC[sub 2]MeW([eta][sup 1]-C(O)Me) produces a nucleophilic propargyl synthon which reacts with MeI to yield an ethyl alkyne complex. Protonation or methylation of the neutral [eta][sup 1]-acyl complexes at the acyl oxygen results in the formation of Fischer-type hydroxy- or methoxycarbene cations, [Tp'(CO)(PhC[sub 2]Me)W=C(OE)R][sup +] (E = H, Me; R = Me, Ph, n-C[sub 4]H[sub 9]). Crystals of the methoxybutylcarbene complex belong to the orthorhombic space group P2[sub 1]2[sub 1]2[sub 1], Z = 4, with unit cell dimensions of a = 15.090(6), b = 16.562(4), and c = 14.624(4) A. Refinement of 273 variables over 2187 reflections led to an R value of 6.4% with R[sub w] = 6.7%. The alkyne ligand aligns itself parallel to the cis metal-carbonyl axis and perpendicular to the plane of the carbene ligand. Reaction of [Tp'(PhC[sub 2]Me)W=C(OMe)Me]CF[sub 3]SO[sub 3] with NaOH in MeOH generates a neutral [sigma]-vinyl complex, Tp'(CO)(PhC[sub 2]Me)W([eta][sup 1]-C(OMe)=CH[sub 2]), via deprotonation of the carbene methyl group. Reaction of [Tp'(CO)(PhC[sub 2]Me)W=C(OMe)Ph][CF[sub 3]SO[sub 3]] with 2 equivmore » of KCN in MeOH yields a neutral azavinylidene complex, Tp'(CO)(PhC[sub 2]Me)WN=C(CN)CH(OMe)Ph, in which the lone pair of electrons on the nitrogen of the azavinylidene ligand competes with the alkyne [pi] donor orbital for donation to the lone vacant metal d[pi] orbital. 35 refs., 2 figs., 3 tabs.« less

Organometall‐Oxide — Höhervalente Derivate der d‐Metall‐Säuren, 6. Tris(3,5‐dimethyl‐1‐pyrazolyl)boranato‐substituierte Alkyl(dioxo)1‐, Methylenphosphoranyl(dioxo)1‐ und s̀1‐Allyl(dioxo)1‐Komplexe des Molybdäns und Wolframs

Organometallic Oxo Complexes — Highervalent Derivatives of the d‐Metal Acids, 6. — Hydrotris(3,5‐dimethyl‐1‐pyrazolyl)borato‐Substituted Alkyl(dioxo)1‐, Methylenephosphoranyl(dioxo)1‐, and s̀1‐Allyl(dioxo) Complexes of Molybdenum and TungstenTp*MoO2Cl (1) and Tp*WO2Cl (2) [Tp* = κ31‐HB(3,5‐Me2pz)3] react with trimethyl aluminium to form the corresponding dioxo(methyl) complexes Tp*MO2(CH3), MMo (3), W (4). An X‐ray crystal structure analysis of 3 is performed. The less oxidizing tungsten complex 2 is alkylated by Grignard reagents to yield alkyl complexes of the type Tp*WO2R 5–7 [RCH2SiMe3, CH2tBu and CH2C(Me)Ph2] and the s̀1‐2‐methallyl complex Tp*WO2(CH2CMeCH2) 8. Reactions of 2 with methylenephorphoranes R3PCH2 (RiPr, Ph) give transylidation products Tp*WO2(CHPiPr3) (9) and Tp*WO2(CH‐PPh3) (10). Hydrolysis of 10 leads to a trioxotungstate [Tp*WO3]– (11), stabilized by a hydroxyphosphonium cation.

Übergangsmetall-Carbin-Komplexe: CIII. Aktivierung von Ethylisocyanid an elektronenreichen Metallzentren; Synthese von einkernigen Wolfram-Aminocarbin-Komplexen des Typs Tp′(CO) 2 WCN(R)Et (R  Me, Et)

A large-scale, high-yield synthesis of the aminocarbyne complexes Tp′(CO) 2WCN(R)Et (5: R  Me; 6: R  Et) [Tp′ = hydridotris(3,5-dimethylpyrazol-1-yl)borate] is reported, starting from Tp′W(CO) 3I ( 2). The first step of the synthetic procedure involves thermal decarbonylation of 2 with EtNC to give cis-Tp′W(CO) 2(CNEt)I ( 3). Complex 3 is then reduced with Na/Hg to give the metallate Na[Tp′W(CO) 2(CNEt)] ( 4). Finally, complex 4 is alkylated with RI (R  Me, Et) exclusively at the isocyanide nitrogen to give the aminocarbyne complexes 5 and 6. In contrast, the metallates Na[(η 5-C 5R′ 5)W(CO) 2(CNEt)] (R′  H, Me) undergo alkylation with RI at the metal centre to afford the W II alkyl complexes cis/ trans-(η-C 5R′ 5)W(CO) 2(CNEt)R. This difference in reactivity is ascribed to the steric demands of the Tp′ ligand, which shields the metal centre from the incoming electrophile.