Über gemischte bindungen in der IV. hauptgruppe: III. Octaphenylpropan-analoga Ph3SnSiPh2SnPh3 und Ph3SnGePh2SnPh3, korrelation zwischen geminalen NMR-kopplungen 2J(SnMSn) und nicht-bindenden Sn⋯Sn-abständen

Reaction of Ph₃SnLi with Ph₂SiCl₂ or Ph₂GeCl₂ at −78°C in THF yields (Ph₃Sn)₂SiPh₂ (1) and (Ph₃Sn)₂GePh₂ (2). The crystal structure of 1 (R = 0.075) exhibits SnSi distances of 257.2(4) and 257.9(5) pm, an SnSiSn angle of 118.5(2)°, and a central C₃SnSiC₂SnC₃ molecular skeleton with symmetry close to C₂. The geminal NMR coupling ²J(¹¹⁹Sn ⋯ ¹¹⁹Sn) in 1, and in a tri-, tetra- and pentastannane series shows a linear correlation to their respective non-bonded d(Sn ⋯ Sn) distances (I(t-Bu₂Sn)₄I: 20 Hz/496 pm; 1: 724 Hz/443 pm).     

Group IB Organometallic chemistry : XV. Arylcopper compounds ArnCun as intermediates in organometallic synthesis. One-step synthesis of triorganotin halides of the type Ar3SnX and Ar3-nRnSnX

A new method for the one-step preparation of triorganotin halides is described. Triphenyltin halides are synthesized via the reaction of pure phenylcopper with SnX₄ or with Ph₂SnX₂. Me₂NCH₂, Me₂N and OMe-substituted phenylcopper react with Me₂(or Ph₂)SnBr₂ to give novel (substituted-phenyl)-diorganotin bromides in high yields. The selective arylation of tin halides by organocopper compounds is based upon the low reactivity of RCu towards the SnX bond in triorganotin halides. The selectivity of the arylation by the corresponding phenyllithium derivatives is connected with intra- or inter-molecular SnN (or O) coordination and/or of steric factors exerted by substituents ortho to the SnC(phenyl) bond.     

Skew-trapezoidal bipyramidal diorganotin(IV) bischelates. Crystal structure of dimethylbis(2-pyridinethiolato-N-oxide)tin(IV)

Dimethylbis(2-pyridinethiolato-N-oxide)tin(IV), Me₂Sn(2-SPyO)₂, crystallizes in space group P2₁/c with a 9.877(3), b 11.980(4), c 13.577(3) Å, β 109.1(2)° and Z = 4. The structure was refined to R_F = 0.036 for 2263 Mo-K_α observed reflections. The coordination geometry at tin is a skew-trapezoidal bipyramid, with the oxygen [SnO 2.356(3), 2.410(4) Å] and sulfur [SnS 2.536(1), 2.566(1) Å] atoms of the chelating groups occupying the trapezoidal plane and the methyl groups [SnC 2.106(6), 2.128(7) Å] occupying the apical positions. The methyl-tin-methyl skeleton is bent [CSnC 138.9(2)°]. The SSnS angle is 77.8(1)°, but the OSnO angle is opened to 136.7(1)° to accommodate the intruding methyl groups. The carbontincarbon angles predicted from quadrupole splitting (^119mSn Mössbauer) and one-bond ¹¹⁹Sn¹³C coupling constant (solution ¹³C NMR) data agree closely with the experimental value.     

The crystal structure of triphenyltin isothiocyanate

The crystal structure of Ph₃SnNCS has been determined by single crystal X-ray diffraction. The crystals are monoclinic, P2₁, a = 19.02(3), b = 11.67(2), c = 15.49(2)Å;, β = 95.64(10)°, Z = 8. The molecules are arranged in infinite zig-zag S…SnNCS…Sn&.sbnd; chains similar to those in Me₃SnNCS, but with slightly longer SnN, shorter SnS bonds, and almost planar SnC₃ units. Principal mean bond lengths and angles are: SnN, 2.22(5); NC, 1.17(8); CS, 1.58(7); SSn, 2.92(1); SnC, 2.09(3); CC, 1.38(2)Å; SnNCm 161(4); CSSn, 97(3); SSnN, 175(3) and CSnC, 119.8(1.5)°.     

The reversible adduct formation of group III trialkyls with relatively involatile phosphines; X-ray crystal structures of (Me3M)2·(Ph2PCH2)2 (M = Al,Ga, In) and (Me3Al)3·(Ph2PCH2CH2)2PPh

The following adducts of Group III trialkyls with phosphines have been prepared, either by direct reaction in hydrocarbon solution or by displacement of ether from the metal trialkyl etherate: Me₃M·PPh₃ (M = Ga, In); Me₃In·P(2-MeC₆H₄)₃; (R₃M)₂·(Ph₂PCH₂)₂ (R = Me, M = Al, Ga, In; R = Et, M = Ga, In; R = Buⁱ, M = Al); (Me₃M)₃·(Ph₂PCH₂CH₂)₂PPh (M = Al, Ga, In) and (Me₃M)₄·(Ph₂PCH₂CH₂PPhCH₂)₂ (M = Al, Ga, In). The compounds were analysed by ¹H and ³¹P NMR spectra of (Me₃M)₂·(Ph₂PCH₂)₂ (M = Ga, In) showed little change between 193 K and room temperature. Thermal dissociation of the adducts in vacuo gave the free metal trialkyl with no detectable contamination by the respective phosphine. Crystals of (Me₃M)₂·(Ph₂PCH₂)₂ (M = Al, Ga, In) are iso-structural and the molecules contain two distorted tetrahedral metals bridged by the (Ph₂PCH₂)₂; the MP distances are 2.544(4), 2.546(4) and 2.755(4) Å, respectively. The X-ray crystal structure of (Me₃Al)₃·(Ph₂PCH₂CH₂)₂PPh shows the molecule to contain distorted tetrahedral aluminium atoms bonded to each of the three phosphorus atoms, with AlP distances of 2.536(9) and 2.510(9) Å for the terminal and central moieties, respectively; the unit cell contains two such molecules plus one benzene molecule (the crystallizing solvent).     

Synthese und strukturuntersuchungen von zwei stannylwolframpentacarbonylen R2Sn-W(CO)5 (R = (o-dimethylaminomethyl)phenyl bzw. (o-diphenylphosphinomethyl)phenyl)

The compounds [o-C₆-H₄CH₂E]₂Sn-W(CO)₅, (E = NMe₂ (1) or PPh₂ (2)) have been prepared by reaction of o-LiC₆H₄CH₂E with pentacarbonyltungsten tin(II) chloride (CO)₅WSnCl₂. The complexes were characterized by ¹³C, ³¹P, and ¹¹⁹Sn NMR spectroscopy and by X-ray diffraction analyses. 1 crystallizes monoclinically in the space group C/c (no. 15) with a 1310.2(4), b 1552.1(4), c 1202.9(4) pm, β 90.11(4)°, and Z = 4. 2 crystallizes monoclinically in the space goup P2₁/n (no. 14) with a 2108.1(4), b 1707.7(4), c 1283.7(3) pm, β 97.47(2)° and Z = 4. The structures were refined to final R values of 0.029 and 0.039, respectively.The SnW bond distances of 274.9 and 276.2 pm are very similar in both complexes. The Sn atoms are penta-coordinated by 2C, 2N and W in 1 and by 2C, 2P and W in 2. The penta-coordination comprises one SnW and two SnC single bonds, and either a SnN (in 1) or a SnP bond (in 2) of bond order 0.45. In the stannyl group of 1 the SnN bond distances both are identical by symmetry (256.4 pm), whereas the two SnP bond lengths of 2 differ to some extent (283.1 and 301.2 pm).     

Über polystannane: IV. Vergleich von abständen d(SnSn), NMR-Kopplungen 1J(Sn) und Valenzschwingungen ν(SnSn) in acetat-verbrücketen distannanen Ph4Sin2(X3CCO2) (X = H,Cl, F)

The three compounds Ph₄Sn₂(X₃CCO₂)₂ were synthesized from Ph₂SnH₂ and X₃CCOOH (X = H, Cl) or by cleavage of two phenyl groups in Ph₆Sn₂ with Stoichiometric amounts of X₃CCOOH (X = Cl, F). The crystal structures (R = 0.041, 0.030, 0.058) show that the Ph₄Sn₂ units are bridged by two isobidentate acetates resulting in five-coordinated tin atoms. Five crystallographically independent centrosymmetric molecules form three distinct conformers. Bonding parameters (compared with Ph₆Sn₂): distances d(SnSn) 269, 271, 272, 277 pm; NMR couplings (CDCl₃ solution) ¹J(SnSn) 16870, 9443, 12915, 4480 Hz; stretching vibrations ν(SnSn) 152, 155, 157, 159 cm⁻. The ion pairs [Ph₄Sn₂]²⁺ [(X₃CCO₂)₂]²⁻ are discussed.     

Studies on some mono-η5-cyclopentadienyliron derivatives with chelate diphosphine ligands

The reactions between Fe(η⁵-C₅H₅)(LL)I (where LL = Ph₂PCH₂CH₂PPh₂, Me₂PCH₂CH₂PMe₂ or ()-DIOP) and TIBF₄ or TIPF₆ inpresence of olefins are described. Evidence is presented that the diphosphine ligands give rise to steric restrictions against coordination of olefins to the metal center.     

Highly reduced organometallics: XII. The reaction of a carbonyltungstate anion with triphenyltin chloride resulting in a phenyltin bond cleavage. X-ray structural characterization of the novel salt: [Me4N][(Ph3Sn)2{(Ph2Sn)2O-i-Pr}W(CO)3]

The reaction of a highly reduced tricarbonyltungstate species with triphenyltin chloride results in an unprecedented phenyl-tin cleavage and the formation of an unusual substituted carbonyl anion. The X-ray structure of [Me₄N][(Ph₃Sn)₂-{(Ph₂Sn)₂O-i-Pr}W(CO)₃] shows the presence of seven coordinate tungsten bound to three terminal carbonyl groups, two triphenyltin units and a previously unknown isopropoxo-bis(diphenyltin) bidentate ligand. The seven ligating atoms are disposed in an approximate 4 : 3 piano stool arrangement about the central tungsten atom. Crystal data: Space group P2₁/c, a 22.580(10), b 14.162(4), c 23.070(10) Å, β 114.21(4)°, Z = 4, V 6728(1) ų, ?(calc) 1.626 g cm^?3.     

Stannylierungsexperimente mit NH-funktionellen Aminoiminophosphoranen. Synthese und Struktur der tricyclischen Stannaphosphazene [Me2Sn(tBu2PN)NH]2 und [nBu2Sn(Ph2PN)2NH]2

Stannylation Experiments with NH-functional Aminoiminophosphoranes. Synthesis and Structure of the Tricyclic Stannaphosphazenes [Me₂Sn(^tBu₂PN)NH]₂ and [ⁿBu₂Sn(Ph₂PN)₂NH]₂ Aminoiminophosphoranes ^tBu₂P(NH)NH₂ ( 1 ) and (H₂NPPh₂)N(Ph₂PNH) ( 2 ) react with diaminostannanes R₂Sn(NEt₂)₂ by cyclocondensation to give cyclostannaphosphazenes [Me₂Sn(^tBu₂PN)NH]₂ ( 3 ) and [R₂Sn(Ph₂PN)₂NH]₂ ( 4 a , b ) ( a : R = Me, b : R = ⁿBu). With 2 and Me₃SnNEt₂ the ring compound Me₂Sn(Ph₂PN)₂NSnMe₃ ( 5 ) besides Me₄Sn is formed by per-N-stannylation and Sn-methyl group transfer. The crystal structures of 3 and 4 b were determined by X-ray structure analysis. 3 forms a planar heterotricyclus containing three four-membered rings with two pentacoordinated tin atoms (space group P 1 (No. 2); Z = 1). 4 b consists of a tricyclic molecule with two puckered six-membered rings and one planar four membered tin-nitrogen ring with two pentacoordinated tin atoms (space group P 1 (No. 2); Z = 1).     

The crystal structure of bromotris(tetracarbonylcobalt)tin(IV)

Crystal of BrSn[Co(CO)₄]₃ are hexagonal, a = 10.20, c = 11.81 å, space group P6₃. The molecule comparises a central tin atom, surrounded tetrahedrally by the bromine atom and three Co(CO)₄ groups. The SnCo bond length is 2.60 å.     

Die kristallstruktur des trimethylbleiazids,Me3PbN3

Me₃PbN₃ crystallizes as colourless needles in the space group P3₁21 (or P3₂21) with a 664.6 ± 5 pm; c 1378 ± 1 pm; V 527.2 »³; Z = 3; d_c 2.781 g cm^?3. With 122 independent reflections (7 non-observed by I < o(I)) and anisotropic temperature factors for the lead atom the structure was refined to a conventional R-value (without hydrogen atoms) R = 0.042. Planar Me₃Pb groups are linked by linear N₃ groups in a 3₁ (or 3₂) screw, rendering the lead atoms an almost perfect trigonal bipyramidal coordination sphere (PbN 258 pm; PbC 225 pm). The Me₃Pb units are ordered in a skew conformation; since the lead atoms are positioned 65 pm away from the screw axes the packing of the methyl groups is not influenced (Pb·Pb 474 pm).     

Cluster synthesis by photolysis of R3PAuN3 IV. Synthesis and structure of [(Ph3PAu)4Mn(CO)4]PF6

Photolysis of R₃PAuN₃ in the presence of Mn₂(CO)₁₀ yields the cationic cluster compounds [(Ph₃PAu)₄Mn(CO)₄]⁺ (1) and [(Ph₃PAu)₆Mn(CO)₃]⁺ (2), which can be separated by column chromatography. Compound 1 crystallizes from CH₂Cl₂-diisopropylether after addition of PF₆⁻ as 1 · PF₆· 0.5CH₂Cl₂ in the triclinic space group P1&#x0304; with a = 1709.8(6) pm, b = 2017.3(7) pm, c = 1180.3(7) pm, α = 106.42(3)°, β = 98.81(4)°, γ = 102.82(4)°, V = 3704.9 × 10⁶ pm³, Z = 2. The central unit of 1 is a trigonal bipyramid Au₄Mn with the manganese atom in equatorial position. The AuAu distances are in the range 277.3 to 292.2 pm. The manganese atom forms two short bonds of 263.3 and 264.0 pm to the axial gold atoms and two longer bonds of 272.3 and 273.3 pm to the equatorial neighbors. A d²sp³ hybridization can be assumed for the manganese atom. Four of the orbitals are used for the MnCO σ-bonds. The remaining two are then pointing approximately to the center of the Au₃ triangular faces.     

Über polystannane: II. I(t-Bu2Sn)4I,ein 1,4-difunktionelles tetrastannan

The compound I(t-Bu₂Sn)₄I has been synthesized by controlled cleavage of the related cyclotetrastannane (t-Bu₂Sn)₄ with iodine in toluene. Both compounds have been investigated by mass, NMR and vibrational spectra. I(t-Bu₂Sn)₄I: δ(¹¹⁹Sn_terminal) 67.7, δ(Sn_central) 17.4 ppm; ¹J(SnSn) 2199 (terminal-central) and 1575 (central-central), ²J(SnSn) 20 (terminal-central), ³J (SnSn) 307 Hz (terminal-terminal); ν(SnSn) 119, ν(SnI) 167 cm^?1. (t-Bu₂Sn)₄: δ(Sn) 87.4 ppm; ν(SnSn) 125 cm^?1. The crystal structure of I(t-Bu₂Sn)₄I has been determined (R = 0.071): bond lengths SnSn 289.5(1) (terminal-central) and 292.4(1) (central-central), SnI 275.3(1) pm. The conformation of the chain ISn₄I is all trans.     

The crystal and molecular structure of tris[(triphenylstannyl)methyl]methane

The title compound, C₅₈H₅₂Sn₃, belongs to the triclinic space group P$\text{1}$, with a 10.165, b 13.365, c 18.670 Å, α 96.28, β 93.88, γ 103.15°, V = 2443.8 ų, f_w = 1105.1, Z = 2, D_calc 1.501 g cm^?3, m.p. 206.5–208°C, λ(Mo-K_$\text{α}$) 0.71069 Å. The structure was refined on 2684 nonzero reflections to an R factor of 0.044. The crystal contains molecules in which the (SnCH₂)₃CH core possesses an approximate C₃ symmetry. The three SnC(H₂) bonds are gauche to the C(4)-H bond. Repulsive interactions involving the bulky Ph₃Sn substituents lead to large SnC(H₂)C(H) angles (av. 117.3°), whereas the C(H₂)C(H)C(H₂) angles at the tertiary carbon average 111.3°. Little distortion of the Ph₃Sn groups themselves is present, since the PhSnPh angles (av. 109.8°) are almost equal to the C(H₂)SnPh angles (av. 109.9°). The molecule as a whole has no symmetry because the aromatic rings in the three Ph₃Sn groups have different orientations. The phenyl groups create a pocket in the middle of the molecule which encloses and shields the tertiary hydrogen atom. The resulting inaccessibility of this hydrogen accounts in part for the low reactivity of the title compound in redox reactions.     

[(Ph3PCH2)(Ph3P)PtCl][AlCl4], ein in CH2Cl2-lösung dreifach koordinierter kationischer platin(II)-komplex

The interaction of cis-[(Ph₃PCH₂)(Ph₃P)PtCl₂] with aluminium(III) chloride in CH₂Cl₂ affords the three coordinate cationic platinum(II) complex [(Ph₃PCH₂)(Ph₃P)PtCl][AlCl₄] which is a useful starting material for platinum complexes with four different ligands. With Ph₃As and Me₂S the cationic phosphorus ylide complexes [(Ph₃PCH₂)(Ph₃P)(Ph₃As)PtCl][AlCl₄] and [(Ph₃PCH₂)(Ph₃P)(Me₂S)PtCl][AlCl₄] are formed. 851 V 3     

Neue Phosphaniminato‐Komplexe von Molybdän und Wolfram. Die Kristallstrukturen von [(μ‐S2N2){MoCl4(NPPh3)}2], [Mo(NPPh3)4][BF4]2, [W(S)2(NPPh3)2] und [Ph3PNH2]+[SCN]–

New Phosphoraneiminato Complexes of Molybdenum and Tungsten. Crystal Structures of [(μ‐S₂N₂){MoCl₄(NPPh₃)}₂], [Mo(NPPh₃)₄][BF₄]₂, [W(S)₂(NPPh₃)₂], and [Ph₃PNH₂]⁺[SCN]^– The binuclear molybdenum(V)phosphoraneiminato complex [(μ‐S₂N₂){Mo^VCl₄(NPPh₃)}₂] ( 1 ) has been prepared by the reaction of the chlorothionitreno complex [Mo^VICl₄(NSCl)]₂ with Me₃SiNPPh₃ in dichloromethane forming green crystals. The temperature dependent magnetic susceptibility in the range of 2–30 K shows ideal behaviour according to the Curie law with a magnetic moment of 1.60 B.M. According to the crystal structure determination 1 forms centrosymmetric molecules in which the molybdenum atoms are connected by the nitrogen atoms of the S₂N₂ molecule. In trans‐position to it the nitrogen atoms of the phosphoraneiminato groups (NPPh₃^–) are coordinated with Mo–N bond lengths of 171(1) pm. The tetrakis(phosphoraneiminato) complex [Mo(NPPh₃)₄]‐ [BF₄]₂ ( 2 ) has been obtained as colourless crystal needles by the reaction of MoN(NPPh₃)₃ with boron trifluoride etherate in toluene solution. In the dication the molybdenum atom is tetrahedrally coordinated by the nitrogen atoms of the (NPPh₃^–) groups with Mo–N bond lengths of 179,8–181,0(3) pm. The dithio‐bis(phosphoraneiminato) tungsten complex [W(S)₂(NPPh₃)₂] ( 3 ) is formed as yellow crystals as well as [Ph₃PNH₂]⁺[SCN]^– ( 4 ) from the reaction of WN(NPPh₃)₃ with carbon disulfide in tetrahydrofurane in the presence of traces of water. 3 has a monomeric molecular structure with tetrahedrally coordinated tungsten atom with bond lengths W–S of 214.5(5) pm and W–N of 179(1) pm. In the structure of 4 the thiocyanate ions are associated by hydrogen bonds of the NH₂ group of the [Ph₃PNH₂]⁺ ion to give a zigzag chain. 1 : Space group Pbca, Z = 4, lattice constants at –80 °C: a = 1647.9(3), b = 1460.8(2), c = 1810.4(4) pm; R₁ = 0.0981. 2 : Space group P1, Z = 2, lattice constants at –80 °C: a = 1162.5(1), b = 1238.0(1), c = 2346.2(2) pm; α = 103.14(1)°, β = 90.13(1)°, γ = 97.66(1)°; R₁ = 0.0423. 3 : Space group Fdd2, Z = 8, lattice constants at –80 °C: a = 3310.1(4), b = 2059.7(2), c = 966,7(1) pm; R₁ = 0.0696. 4 : Space group P2₁2₁2₁, Z = 4, lattice constants at –80 °C: a = 1118.4(1), b = 1206.7(1), c = 1279.9(1) pm; R₁ = 0.0311.     

Structural chemistry of organotin carboxylates: I. The crystal structure of di-n-butylbis(thiophenoxyacetato)tin(IV): nBu2Sn(O2CCH2SC6H5)2

A crystal structure study of ⁿBu₂Sn(O₂CCH₂SC₆H₅)₂ reveals the compound to be monomeric with the tin atom situated on a crystallographic 2-fold axis in a skew-trapezoidal bipyramidal geometry. The basal plane is defined by two asymmetrically chelating carboxylate groups; SnO 2.134(4) and 2.559(5) Å and the ⁿBuSnⁿBu angle is 140.7(2)°. The sulphur atoms do not participate in any significant interactions to the tin atom. Crystals are monoclinic with space group C2 and unit cell dimensions a 18.668(6), b 15.761(6), c 5.106(5) Å, β 117.55(5)°; Z = 2. The structure was refined by a full-matrix least-squares procedure to final R = 0.034 and R_w = 0.033 for 1294 reflections with I ≥ 2.5σ(I).     

Destruktive Komplexierung des dimeren Diorganylzinn(IV)‐hydroxids [Me2Sn(A)(μ‐OH)]2 (HA = Benzol‐1,2‐disulfonsäureimid): Bildung und Strukturen der Einkernkomplexe [Me2Sn(A)2(OPPh3)2] und [Me2Sn(phen)2]2⊕ · 2 A⊖ · MeCN

Polysulfonylamines. CXVI. Destructive Complexation of the Dimeric Diorganyltin(IV) Hydroxide [Me₂Sn(A)(μ‐OH)]₂ (HA = Benzene‐1,2‐disulfonimide): Formation and Structures of the Mononuclear Complexes [Me₂Sn(A)₂(OPPh₃)₂] and [Me₂Sn(phen)₂]^2⊕ · 2 A^⊖ · MeCN Destructive complexation of the dimeric hydroxide [Me₂Sn(A)(μ‐OH)]₂, where A^⊖ is deprotonated benzene‐1,2‐disulfonimide, with two equivalents of triphenylphosphine oxide or 1,10‐phenanthroline in hot MeCN produced, along with Me₂SnO and water, the novel coordination compounds [Me₂Sn(A)₂(OPPh₃)₂] ( 3 , triclinic, space group P 1) and [Me₂Sn(phen)₂]^2⊕ · 2 A^⊖ · MeCN ( 4 , monoclinic, P2₁/c). In the uncharged all‐trans octahedral complex 3 , the heteroligands are unidentally O‐bonded to the tin atom, which resides on a crystallographic centre of inversion [Sn–O(S) 227.4(2), Sn–O(P) 219.6(2) pm, cis‐angles in the range 87–93°; anionic ligand partially disordered over two equally populated sites for N, two S and non‐coordinating O atoms]. The cation occurring in the crystal of 4 has a severely distorted cis‐octahedral C₂N₄ coordination geometry around tin and represents the first authenticated example of a dicationic tin(IV) dichelate [R₂Sn(L–L′)₂]^2⊕ to adopt a cis‐structure [C–Sn–C 108.44(11)°]. The five‐membered chelate rings are nearly planar, with similar bite angles of the bidentate ligands, but unsymmetric Sn–N bond lengths, each of the longer bonds being trans to a methyl group [ring 1: N–Sn–N 71.24(7)°, Sn–N 226.81(19) and 237.5(2) pm; ring 2: 71.63(7)°, 228.0(2) and 232.20(19) pm]. In both structures, the bicyclic and effectively C_S symmetric A^⊖ ions have their five‐membered rings distorted into an envelope conformation, with N atoms displaced by 28–43 pm from the corresponding C₆S₂ mean plane.     

Strukturuntersuchungen an mono- und bis-alkoxy(triphenylsilyl)-carben-komplexen des rheniums

Steric and electronic influences on bond lengths and angles at the carbene carbon atoms of cis-Re₂(CO)₉C(OR)SiPh₃ (I: R = CH₃, II, R = C₂H₅) and cis,trans-Re₂(CO)₈[C(OEt)SiPh₃]₂ (III) are discussed based on their structural analyses. I (ReRe 305.2(1) pm; ReC(carbene) 209(2) pm) and II (two independent molecules; ReRe 305.0(3) and 305.2(4) pm; ReC (carbene) 208(5) and 210(5) pm) differ by the cis and trans positions of the alkyl groups at the partial C(carbene)O double bonds. The change in configuration affects the bond angles at the carbene carbon. In III the carbene ligands are bonded to different rhenium atoms; cis to one Re atom and trans to the other Re atom (ReRe bond 309.1(2) pm). The ReC(carbene length of the trans- carbene ligand is significantly shorter (185(3) pm) than that of the cis-carbene ligand (208(3) pm).