Insertion Reactions of Carbon Disulfide into Mg‐C and Mg‐N Bonds: Syntheses and Structural Determinations of Mg(S2CY)2(THF)n(Y=NEt2, NiPr2, iPr,Ph) and BrMg(S2CZ)(THF)3(Z=Ph,iPr)

The insertion reaction of CS₂ with Mg(NR₂)₂ (R= Et, ⁱPr), MgR′₂ (R′= Et, Ph) and R″MgBr (R″= ⁱPr, Ph) respectively lead solid products, Mg(S₂CNR₂)₂(THF)_n ( 1 : R= Et, n=2; 2 : R= ⁱPr, n=1), Mg(S₂C′R)₂(THF)₂ ( 3 : ′R= Et, 4 : ′R= Ph), BrMg(S₂C″R) (THF)₃ ( 5 : ″R= ⁱPr, 6 : ″R= Ph) in which the inserted carbon disulfides act as terminal chelating ligands. These compounds were characterized with ¹H, ¹³C NMR, IR spectroscopy, mass spectrometry, elemental analyses, and X‐ray crystallography.     

Unsymmetrische Triorganobismutane mit β-funktionalisierten Alkylsubstituenten

Unsymmetrical Triorganobismuthanes Containing β-Functionalized Alkylsubstituents Sodium diorganobismuthide, was treated with strained ring systems such as propyleneoxide, styreneoxide, ethylene-sulfide or propyleneimine to produce unsymmetrical triorganobismuthanes R₂BiCH₂CH(R′)XH (R = Me, Et, Ph, pTol; R′ = H, Me, Ph; X = O, S, NH) in good yields.     

Synthesis and Characterization of Alkyltris(2-pyridyl)phosphonium Salts

Alkytris(2-pyridyl)phosphonium salts [(2-Py) ₃ PR]X 1 [1a, R = Et, X = Br; 1b, R = Pr, X = Br; 1c, R = Bu, X = Br; 1d, R = CH₂Ph, X = Br; 1e, R = CH ₂ Ph, X = Cl] were synthesised from (2-Py) ₃ P and an excess of RCl. 1c and 1e were found to rapidly decompose in hot acetone to 2,2′-bipyridinium(+1) bromide 2 and (2-Py)P(O)(CH ₂ Ph)C(OH)Me ₂ 3, respectively. A reaction mechanism for both products is proposed. All compounds were fully characterized, including X-ray crystallography for 1a and 3 with 1a being the first representative of this class of compounds characterized by this technique.     

Hypervalent Organoselenium(II) Compounds with Organophosphorus Ligands. Crystal and Molecular Structure of [2‐(iPr2NCH2)C6H4]Se[S2PR′2] (R′ = Ph,OiPr)

Redistribution reactions between diorganodiselenides of type [2‐(R₂NCH₂)C₆H₄]₂Se₂ [R = Et, iPr] and bis(diorganophosphinothioyl disulfanes of type [R′₂P(S)S]₂ (R = Ph, OiPr) resulted in the hypervalent [2‐(R₂NCH₂)C₆H₄]SeSP(S)R′₂ [R = Et, R′ = Ph ( 1 ), OiPr ( 2 ); R = iPr, R′ = Ph ( 3 ), OiPr ( 4 )] species. All new compounds were characterized by solution multinuclear NMR spectroscopy (¹H, ¹³C, ³¹P, ⁷⁷Se) and the solid compounds 1 , 3 , and 4 also by FT‐IR spectroscopy. The crystal and molecular structures of 3 and 4 were determined by single‐crystal X‐ray diffraction. In both compounds the N(1) atom is intramolecularly coordinated to the selenium atom, resulting in T‐shaped coordination arrangements of type (C,N)SeS. The dithio organophosphorus ligands act monodentate in both complexes, which can be described as essentially monomeric species. Weak intermolecular S ··· H contacts could be considered in the crystal of 3 , thus resulting in polymeric zig‐zag chains of R and S isomers, respectively.     

Lanthanide and Transition Metal Complexes of Dialkyl α-Hydroxyiminophosphonates

Abstract

α-Hydroxyiminophosphonic acid derivatives are widely known not only as intermediates in the synthesis of the important aminophosphonic acids,^1,2 but also as phosphorylating agents,³ potential metalloenzyme inhibitors,⁴ and as compounds having fungicidal activity.⁵ In this work the scope of these compounds has been extended considerably by the synthesis of a number of novel dialkyl derivatives. Novel lanthanide (La^III, Pr^III, Nd^III, Gd^III and Dy^III) and transition metal (Co^II and Ni^III) complexes of dialkyl α-hydroxyiminophosphonates (RO)₂P(O)C(R')N(OH) where R = Et. Prⁱ and R′ = Me, Et have been prepared and the NMR shift properties of the Pr^III complex (R = Et; R′ = Et) indicate the potential of these compounds as NMR shift reagents for the analysis of geometric isomers.^6,7 X-ray crystal structure analysis of [Ni(L¹)₂C1₂] (L¹: R = Et; R′ = Et) shows a distorted cis octahedral coordination at the nickel atom giving two symmetry related diethyl-(E)-α-hydroxyiminopropanephosphonate ligands and two chlorine donors, and those of [Pr(L²)₃Cl₃] and [Nd(L²)₂(NO₃)₃(H₂O)] (L²: R = Prⁱ; R′ = Et) show nine-coordination geometries with asymmetric bidentate and monodentate L² bonding respectively. Thus the metal complexes show unusual coordination ambivalence, changing from symmetrically bidentate to asymmetrically bidentate and then to monodentate bonding modes, to accommodate the different steric requirements of the coordinating anions in facilitating neutral complex formation.     

Spectroscopic Studies of Mixed Phosphoric-Carboxylic Imides

Abstract

IR spectroscopic studies of hydrogen bonding (intra- vs intermolecular) in selected mixed phosphoric-carboxylic imides (RO) ₂P(O)NR′C(O)R″ 1, R = Et, R′ = H, alkyl, R″ = OEt, Ph, are presented.     

Selektive Darstellung zweifach diorganophosphido-verbrückter Metallatetrahedrane [Re2(MPR3)2(μ-PR2)2(CO)6] mit Re2M2-Metallgerüst (M = Au,Ag)

Selective Preparation of Twofold Diorganophosphido-bridged Metallatetrahedranes [Re₂(MPR₃)₂(μ-PR₂)₂(CO)₆] with Re₂M₂ Metal Core (M = Au, Ag) The reaction of the in situ prepared salt Li[Re₂(AuPR)(μ-PR₂)(CO)₇Cl] (R = R′ = Cy ( 1 a ), R = Cy, R′ = Ph ( 1 b ), R = Ph, R′ = Cy ( 1 c ), R = Ph, R′ = Et ( 1 d ), R = Ph, R′ = Ph ( 1 e )) with one equivalent HPR in methanolic solution at room temperature yields the neutral cluster complexes [Re₂(AuPR)(μ-PR₂)(CO)₇(ax-HPR) (R = R′ = R″ = Cy ( 2 a ), Ph ( 2 b ), R = R′ = Cy, R″ = Et ( 2 c ), R = Cy, R′ = R″ = Ph ( 2 d ), R = Cy, R′ = Ph, R″ = Et ( 2 e ), R = R″ = Ph, R′ = Et ( 2 f ), R = Ph, R′ = Cy, R″ = Et (2 g)). Photochemically induced these complexes react in the presence of the organic base DBU in THF solution to give the doubly phosphido bridged anions Li[Re₂(AuPR)(μ-PR₂)(μ-PR)(CO)₆], which were characterized as salts PPh₄[Re₂(AuPR)(μ-PR₂)(μ-PR)(CO)₆] (R = R′ = R″ = Ph ( 3 a ), R = R′ = Ph, R″ = Cy ( 3 b ), R = Ph, R′ = Cy, R″ = Et ( 3 c ), R = R″ = Ph, R′ = Et ( 3 d )). These precursor complexes 3 then react with one equivalent of ClMPR (M = Au, Ag) to doubly phosphido bridged metallatetrahedranes [Re₂(MPR₃)₂(μ-PR₂)(μ-PR)(CO)₆] (M = Au, R = R′ = R″ = Ph ( 4 a ), M = Au, R′ = Et, R = R″ = Ph ( 4 b ), M = Au, R = R′ = Ph, R″ = Cy ( 4 c ), M = Au, R = Cy, R′ = Ph, R″ = Et ( 4 d ), M = Ag, R = R′ = R″ = Ph ( 4 e )). All isolated cluster complexes were characterized and identified by the following analytical methods: NMR- (¹H, ³¹P) and ν(CO) IR-spectroscopy and, additionally, complexes 2 b , 4 a and 4 e by X-ray structure analysis.     

Carbyne-fluoro complexes of rhenium. Single-pot synthesis of trans-[ReF(CCH2R)-(Ph2PCH2CH2PPh2)2][BF4]

Treatment of a THF solution of trans-[ReCl(N₂)(dppe)₂] (dppe = Ph₂PCH₂CH₂PPh₂) with a 1-alkyne HCCR (R =^tBu, CO₂Me, CO₂Et, or C₆H₄Me-4), in the presence of Tl[BF₄]/[NH₄][BF₄], under sunlight, affords the corresponding carbyne-fluoro complexes trans-[ReF(CCH₂R)(dppe)₂][BF₄] in an unprecedented single-pot synthesis. Further reaction with [BU₄N]OH leads to the vinylidenefluoro compounds trans-[ReF(=C=CHR)(dppe)₂] (R = CO₂Me, CO₂Et, or C₆H₄Me-4).     

Isolation and Characterization of intermediate in the Synthesis of α-Fluorodiesters

The anion [(EtO)₂P(O)CFCO₂Et]^?Li⁺, pregenerated from its precursor diethyl (carboethoxyfluoromethyl)phosphonate (EtO)₂P(O)CFHCO₂Et and n-butyllithium, was added via syringe to a THF solution of ethyl oxaiyl chloride to yield an acylated phosphonate (EtO)₂P(O)CF(COCO₂Et)CO₂Et. In situ reaction with Grignard reagents RMgX produces the α-fluorodiesters (E,Z)-R(CO₂Et)C=CFCO₂Et in good yields. In contrast, addition of ethyl oxalyl chloride to a THF solution of diethyl (carboethoxyfluoromethyl)phosphonate anion gives an isolated intermediate (EtO)₂P(O)CFCO₂Et(CO₂Et)C=CFCO₂Et. Subsequent reaction of this isolated intermediate with Grignard reagents also affords a one-pot synthesis of the α-fluorodiesters with high E-stereoselectivity. The E-stereoselectivity increases when HMPT or DMPU is used as a cosolvent in the preparation of diethyl 2-fluoro-3-phenylfumarate (E,Z)-Ph(CO₂Et)C=CFCO₂Et.     

Synthese und Kristallstrukturen von [Cu4(As4Ph4)2(PRR′2)4], [Cu14(AsPh)6(SCN)2(PEt2Ph)8], [Cu14(AsPh)6Cl2(PRR′2)8], [Cu12(AsPh)6(PPh3)6], [Cu10(AsPh)4Cl2(PMe3)8], [Cu12(AsSiMe3)6(PRR′2)6] und [Cu8(AsSiMe3)4(PtBu3)4] (R,R′ = organische Gruppen)

Syntheses and Crystal Structures of [Cu₄(As₄Ph₄)₂(PRR′₂)₄], [Cu₁₄(AsPh)₆(SCN)₂(PEt₂Ph)₈], [Cu₁₄(AsPh)₆Cl₂(PRR′₂)₈], [Cu₁₂(AsPh)₆(PPh₃)₆], [Cu₁₀(AsPh)₄Cl₂(PMe₃)₈], [Cu₁₂(AsSiMe₃)₆(PRR′₂)₆], and [Cu₈(AsSiMe₃)₄(P^tBu₃)₄] (R, R′ = Organic Groups) Through the reaction of CuSCN with AsPh(SiMe₃)₂ in the presence of tertiary phosphines the compounds [Cu₄(As₄Ph₄)₂(PRR′₂)₄] ( 1 – 3 ) ( 1 : R = R′ = ⁿPr, 2 : R = R′ = Et; 3 : R = Me, R′ = ⁿPr) and [Cu₁₄(AsPh)₆(SCN)₂(PEt₂Ph)₈] ( 4 ) can be synthesised. Using CuCl instead of CuSCN results to the cluster complexes [Cu₁₄(AsPh)₆Cl₂(PRR′₂)₈] ( 5–6 ) ( 5 : R = R′ = Et; 6 : R = Me, R′ = ⁿPr), [Cu₁₂(AsPh)₆(PPh₃)₆] ( 7 ) and [Cu₁₀(AsPh)₄Cl₂(PMe₃)₈] ( 8 ). Through reactions of CuOAc with As(SiMe₃)₃ in the presence of tertiary phosphines the compounds [Cu₁₂(AsSiMe₃)₆(PRR′₂)₆] ( 9 – 11 ) ( 9 : R = R′ = Et; 10 : R = Ph, R′ = Et; 11 : R = Et, R′ = Ph) and [Cu₈(AsSiMe₃)₄(P^tBu₃)₄] ( 12 ) can be obtained. In each case the products were characterised by single‐crystal‐X‐ray‐structure‐analyses. As the main structure element 1 – 3 each have two As₄Ph₄^2–‐chains as ligands. In contrast 4 – 12 contain discrete AsR^2–ligands.     

Effect of Microwave Irradiation on Reaction of Arylaldehyde Derivatives with Some Active Methylene Compounds in Aqueous Media

Abstract

The effect of microwave irradiation on the condensation reactions of arylaldehydes 1 and active methylene compounds 2 in aqueous media was studied and compared with “classical” conditions. The results show that the condensation was carried out only under microwave irradiation in the presence of ammonium chloride as a catalyst, followed by dehydration, to afford (E)‐olefins 3. The protocol was used to synthesize coumarins by a condensation reaction of salicylaldehyde or its derivatives with various derivatives of ethylacetate 5 (e.g., R³CH₂CO₂Et; R³: CO₂Et, CO₂Me, COMe, CN) in high yields. These investigations will contribute to the development of environmentally friendly and inexpensive processes in organic synthesis.     

Formation of T‐Shaped versus Charge‐Transfer Molecular Adducts in the Reactions Between Bis(thiocarbonyl) Donors and Br2 and I2

The reactions of 4,5,6,7‐tetrathiocino‐[1,2‐b:3,4‐b′]‐1,3,8,10‐tetrasubstituted‐diimidazolyl‐2,9‐dithiones (R₂,R′₂‐todit; 1 : R=R′=Et; 2 : R=R′=Ph; 3 : R=Et, R′=Ph) with Br₂ exclusively afforded 1:1 and 1:2 “T‐shaped” adducts, as established by FT‐Raman spectroscopy and single‐crystal X‐ray diffraction in the case of complex 1? 2 Br₂. On the other hand, the reactions of compounds 1 – 3 with molecular I₂ provided charge‐transfer (CT) “spoke” adducts, among which the solvated species 3? 2 I₂ ? (1?x)I₂ ? x CH₂Cl₂ (x=0.94) and ( 3 )₂ ? 7 I₂ ? x CH₂Cl_2, (x=0.66) were structurally characterized. The nature of all of the reaction products was elucidated based on elemental analysis and FT‐Raman spectroscopy and supported by theoretical calculations at the DFT level.     

Chelatkomplexe LM/n von Übergangsmetallen mit Iminophosphin-säureamidato-Liganden R2P(NR′)2– (= L)

Chelate Complexes LM/n of Transition Metals with Phosphinoimidic Amidato Ligands R₂P(NR′)₂^– (= L) Reaction of LLi with metal halides or metal halide complexes affords chelate complexes LM/n (L = R₂P(NR′)₂^–; M = Cr⁺⁺⁺, Co⁺⁺, Ni⁺⁺, Zn⁺⁺). With the bulky ligand t-Bu₂P(NSiMe₃)₂^– and Ni(PPh₃)₂Cl₂ or Ni(dme)Br₂ (dme = dimethoxyethane) only halide bridged chelates [LNiHal]₂ (Hal = Cl, Br) containing tetrahedral chromophors NiN₂Hal₂ were obtained. Main objects of investigation were the bischelates L₂Ni 2 . 2 a (R = i-Pr, R′ = Me) and 2 c (R = Ph, R′ = Et) are planar, 2 b (R = i-Pr, R′ = Et) and 2 d–g (R, R′ = i-Pr, i-Pr; Ph, i-Pr; Et, SiMe₃; Ph, SiMe₃) tetrahedral. In solutions of 2 b and 2 c a conformational equilibrium planar (diamagnetic) tetrahedral (paramagnetic) exists that is shifted to the right with increasing temperature and is dominated by the tetrahedral ( 2 b ) or planar conformer ( 2 c ) at room temperature. As is the case with the isovalence electronic compounds [R₂P(S)NR′]₂Ni small substituents R′ apparently favour the planar state and in contrast to some complexes [R₂P(O)NR′]₂Ni no paramagnetic planar species 2 have yet been observed. These findings that are derived from the results of magnetic measurements and of UV/VIS as well as NMR spectroscopy are confirmed by crystal structure determinations: 2 a was found to be planar (orthorhombic; a = 3382.8(11), b = 1124.0(4), c = 8874(3); P2₁2₁2; Z = 6), and 2 g to be tetrahedral (monocline; a = 1268.4(2), b = 1806.8(2), c = 1971.6(2), P2₁/n; Z = 4). The bite angle NNiN of the chelate ligand in 2 a (ca. 77°) is similar to those in paramagnetic planar complexes [R₂P(O)NR′]₂Ni (NNiO 74–77°) and shows that a small chelate bite does not necessarily imply paramagnetism of planar Ni(II) complexes.     

Formation and Stability of Difluoromethylene Phospho-Raiies,R3P=CF2

Abstract

Carbonyl compounds react with CBr₂F₂ in the presence of phosphanes, RP (R = Ph, NR;), and metals (M = Zn, Cd, Pb) forming geminal difluoroolefins (eq. 1)¹.

R′CHO + CBr₂F₂ + R₃P + M → R′CH=CF₂ + MBr₂ + R₃PO (1)

Without any doubt this reaction has to occur via the intermediate formation of difluoromethylene phosphoranes, which then undergo the Wittig reaction with carbonyl compounds (eq. 2). R₃P=CF₂ + R′CHO → R₃PO + R′CH=CF₂ (2).     

Metal complexes of hybrid oxygen-arsenic ligands. Part V. A study of the products fromo-R2AsC6H4CO2M and CrO3 (M = H)/trans-[CrCl2(OH2)4]Cl · 2H2O (M = Na) in acetone

Summary A change of the reported medium of reaction oftrans- [CrCl₂(OH₂)₄]Cl · 2H₂O witho-R₂AsC₆H₄CO₂M (M = Na), from 95% ethanol to acetone, results in the change of an hydroxo — to an oxo — group (R = Ph), in the number of water molecules (R = Et or C₆H₁₁) and/or of ligand molecules (R =p-tolyl) in chromium(III)-arsine complexes. However, for R = Me, the same complex is obtained in each case. I.r. spectral data of these complexes favour the chelation of the carboxylate ion and non-coordination of arsenic(III) except for CrO(o-Ph₂AsC₆H₄CO₂) · 2.5 H₂O in which arsenic(III) of the monotertiary arsine group appears to coordinate to chromium(III). This would seem to be the first example of this type. On the other hand, the reaction of CrO₃ witho-R₂As- C₆H₄CO₂M (M = H) in 14.5 molar ratio in acetone yields only one type of complex,viz., [Cr₃O₃(o-R₂As(O)C₆H₄-CO₂)₂(o-R₂AsC₆H₄CO₂)(H₂O)₆] · n H₂O (n = 2, R = Me, C₆H₁₁ or Ph; n = O, R = Et). The arsine oxide molecules appear to chelate through As = 0 and the carboxylate oxygens while the arsine ligand binds only through the carboxylate oxygens leaving arsenic(III) uncoordinated as reported for the complexes obtained from the same reactants in 95% ethanol.     

UV–visible spectroscopy for zirconocene activation by MAO in olefin polymerization: activity versus wavenumber

Activation of ansa‐zirconocenes of the type Rac [Zr{1‐Me₂Si(3‐R‐(η⁵‐C₉H₅))(3‐R′‐(η⁵‐C₉H₅))}Cl₂] [R = Et, R′ = H ( 1 ); R = Pr, R′ = H ( 2 ); and R = Et, R′ = Pr ( 3 ), R, R′ = Me ( 4 ) and R, R′ = Bu ( 5 )] by MAO has been studied by UV–visible spectroscopy. Compounds 1–3 have been tested in the polymerization of ethylene at different Al:Zr ratios. UV–vis spectroscopy was used to determine a correlation between the electronic structures of ( 1–5 ) and their polymerization activity. Copyright © 2009 John Wiley & Sons, Ltd.     

The synthesis and spectroscopic properties of some (π-allyl) dicarbonyl-semicarbazonatohalogenomolybdenum(II) complexes

Reaction of [MoX(CO₂(NCMe)₂(η³-C₃H₄R)] in CH₂Cl₂ at room temperature with an equimolar quantity of (R′R″)CNNHCONH₂ gave high yields of the bidentate coordinated semicarbazone complexes [MoX(CO)₂{(R′R″)CNNHCONH₂}(η³-C₃H₄R)] (X = Cl, Br or I; R = H or Me; R′,R″ = H or Me and Me, Et, ⁿPr or Ph) via displacement of two acetonitrile ligands.     

The First Butyltin(IV) Homo- and Heterobimetallic Diethanolaminates

Equimolar reactions of BuSn(OPrⁱ)₃ with diethanolamines, RN(CH₂CH₂ OH) ₂ (abbreviated as RdeaH₂, where R = H or Me), afford dimeric isopropoxo-bridged six-coordinate butyltin(IV) complexes [{Bu(η³-Rdea)Sn(μ-OPrⁱ)}₂] (R = H ( 1 ), Me ( 2 )). Interactions between BuSn(OPrⁱ)₃ and diethanolamines (RdeaH₂) in a 1:2 molar ratio yield monomeric derivatives of the type [BuSn(Rdea)(RdeaH)] (R = H ( 3 ), R = Me ( 4 )). These homometallic complexes on 1:1 reactions with an appropriate metal alkoxide form monomeric heterobimetallic complexes of the type [BuSn (Rdea)₂ {M(OR′)_n}] (R = H, M = Al, R′ = Prⁱ, n = 2 ( 5 ); R = H, M = Ti, R = Prⁱ, n = 3 ( 6 ); R = H, M = Zr, R′ = Prⁱ, n = 3 ( 7 ); R = Me, M = Al, R′ = Prⁱ, n = 2 ( 8 ); R = Me, M = Ti, R′ = Prⁱ, n = 3 ( 9 ); R = Me, M = Ge, R′ = Et, n = 3 ( 10 )). The driving force behind this work was (i) to explore the utility of homometal complexes ( 1 ) –( 4 ) in assembling a metal alkoxide fragment via a condensation reaction and (ii) to gain insights into the structures of new compounds by NMR spectral data. All of these derivatives have been characterized by elemental analysis, spectroscopic (IR, NMR; ¹H, ²⁷Al, and ¹¹⁹Sn) studies, and molecular weight measurements. ¹¹⁹Sn NMR spectral studies indicate that both the homometallic ( 3 ) and ( 4 ) and heterobimetallic ( 5 ) – ( 9 ) complexes exist in a solution in an equilibrium of six- and five-coordinated tin(IV) species.     

Mass spectra of some (Z)-α-Phenyl-β-(2-thienyl)acrylonitriles

The mass spectra of some (Z)α-(4-R′-phenyl)-β-(2-thienyl-5-R)acrylonitriles (R = H, CH₃, Br; R′ = H, CH₃O, CH₃, Cl, NO₂) at 70 eV are reported. Mass spectra exhibit pronounced molecular ions. The compound's where R = H, and CH₃ are characterized by the occurrence of a strong [M - H]⁺ peak. Moreover, in all the compounds a m/z 177 peak occurs. In the compounds where R = H, [M - HS]* and [M - CHS]* ions are present except the nitroderivatives. Where R = CH₃, [M - HS]⁺ ion occurs.     

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.