Detection of σ-alkane complexes of manganese by NMR and IR spectroscopy in solution: (η5-C5H5)Mn(CO)2(ethane) and (η5-C5H5)Mn(CO)2(isopentane)

Irradiation of CpMn(CO)₃ in liquid ethane at 135 K at 355 nm yields a photoproduct that exhibits ν(CO) bands in the IR spectrum shifted to low wavenumber with respect to CpMn(CO)₃ that are indicative of a Mn(i) dicarbonyl. Parallel experiments employing in situ irradiation within an NMR probe (133 K, 355 nm photolysis) reveal the ¹H NMR signals of this product and confirm its formulation as the σ-ethane complex CpMn(CO)₂(η²-C1–H-ethane). The resonance of its coordinated C–H group is observed at δ –5.84 and decays with lifetime of ca. 360 s. Analogous photolysis experiments in isopentane solution with IR detection produce CpMn(CO)₂(η²-C–H-isopentane) with similar IR bands to those of CpMn(CO)₂(η²-C–H-ethane). ¹H NMR spectra of the same species were obtained by irradiation of CpMn(CO)₃ in a 60 : 40 mixture of propane and isopentane; three isomers of CpMn(CO)₂(η²-C–H-isopentane) were detected with coordination of manganese at the two inequivalent methyl positions and at the methylene group, respectively. The lifetimes of these isomers are ca. 380 ± 20 s at 135 K and do not vary significantly from each other. These σ-complexes of manganese are far more reactive than those of related CpRe(CO)₂(alkane) complexes which are stable in solution at 170–180 K. The room temperature lifetimes of CpMn(CO)₂(η²-C–H-ethane) and CpMn(CO)₂(η²-C–H-isopentane), as determined by TRIR spectroscopy, are 2.0 ± 0.1 and 28 ± 1 μs, respectively.     

Synthetic and structural studies of monocyclopentadienyl cyclometalated aryl tantalum(V) compounds

Cyclometalated aryl tetra- or trichlorido cyclopentadienyl tantalum complexes [TaXCl(3){C(6)H(4)(2-CH(2)NMe(2))-κ(2)C,N}] (X = Cl 1, η(5)-C(5)H(5)2, η(5)-C(5)H(4)(SiMe(3)) 3, η(5)-C(5)Me(5)4) containing a five-membered TaC(3)N chelate ring were synthesized by reaction of the TaXCl(4) (X = Cl, η(5)-C(5)H(5), η(5)-C(5)H(4)(SiMe(3)), η(5)-C(5)Me(5)) with the appropriate lithium aryl reagent [Li{C(6)H(4)(2-CH(2)NMe(2))}]. The reported complexes were studied by IR and NMR spectroscopy and the X-ray molecular structures of compounds 2, 3 and 4 were determined by diffraction methods. These compounds were theoretically analyzed by the DFT method and their structures were rationalized. The preferential coordination of the 2-{(dimethylamino)methyl}phenyl ligand was justified by an analysis of the molecular orbitals of the Ta(η(5)-C(5)H(5))Cl(3) and C(6)H(4)(2-CH(2)NMe(2)) fragments. In addition, the exchange pathways that account for the NMR equivalency of the Me(2)N- methyl groups and -CH(2)- hydrogen atoms of the coordinated C(6)H(4)(2-CH(2)NMe(2))-κ(2)C,N ligand were theoretically studied.     

Carbon dioxide coordination and activation by niobium oxide molecules

Carbon dioxide coordination and activation by niobium oxide molecules were studied by matrix isolation infrared spectroscopy. It was found that the niobium monoxide molecule reacted with carbon dioxide to form the niobium dioxide carbonyl complex NbO(2)(η(1)-CO) spontaneously on annealing in solid neon. The observation of the spontaneous reaction is consistent with theoretical predictions that this carbon dioxide activation process is both thermodynamically exothermic and kinetically facile. In contrast, four niobium dioxide-carbon dioxide complexes exhibiting three different coordination modes of CO(2) were formed from the reactions between niobium dioxide and carbon dioxide, which proceeded with the initial formation of the η(1)-O bound NbO(2)(η(1)-OCO) and NbO(2)(η(1)-OCO)(2) complexes on annealing. The NbO(2)(η(1)-OCO) complex rearranged to the η(2)-O,O bound NbO(2)(η(2)-O(2)C) isomer under visible light irradiation, while the NbO(2)(η(1)-OCO)(2) complex isomerized to the NbO(2)(η(1)-OCO)(η(2)-OC)O structure involving an η(2)-C,O ligand under IR excitation. In these niobium dioxide carbon dioxide complexes, the η(1)-O coordinated CO(2) ligand serves as an electron donor, whereas both the η(2)-C,O and η(2)-O,O coordinated CO(2) ligands act as electron acceptors.     

Reaction des phosphorines avec les cymantrenes. Synthese d'un complexe sandwich η5-cyclopentadienyl-η6-phosphorine-manganese

σ-Phosphorin-manganese complexes are easily obtained from RCpMn(CO)₂ (THF) and phosphorins. Photolysis of CpMn(CO)₂ (triphenylphosphorin) yields a sandwich complex : (η⁵-cyclopentadienyl)(η⁶-triphenylphosphorin) manganese , which displays a particularly high field resonance in its ³¹P NMR spectrum. By photolysis of RCpMn(CO)₂(4,5-dimethyl 2-phenylphosphorin), two additional products are obtained, to one of which the structure of a σ-π complex has been assigned.     

A beneficial kinetic effect of an η(5)-C5Me4H ligand

C-H activation of benzene at 26 °C by (η(5)-C(5)Me(5))W(NO)(CH(2)CMe(3))(η(3)-CH(2)CHCHMe) results after 4 h in the production of five new organometallic complexes, only two of which are isomers of the desired (η(5)-C(5)Me(5))W(NO)(C(6)H(5))(η(3)-CH(2)CHCHMe) compound. In contrast, the identical reaction involving the η(5)-C(5)Me(4)H analogue affords only the phenyl complexes during the first 24 h, thereby facilitating their isolation in good yields. This striking difference in reactivity can be attributed to the lesser steric demands of the η(5)-C(5)Me(4)H ligand that result in its complexes reacting at a significantly slower rate.     

A homobimetallic complex of chromium(0) with a σ-borane component

The synthesis, characterization, and reactivity of a chromium(0) complex bearing an amine-borane moiety (η(6)-C(6)H(5)CH(2)NMe(2)·BH(3))Cr(CO)(3) (2) is reported. Photolysis of complex 2 results in the elimination of a CO ligand followed by the formation of an intramolecular σ-borane complex (η(1)-(η(6)-C(6)H(5)CH(2)NMe(2)·BH(2)-H))Cr(CO)(2) (3). This species was characterized in solution by NMR spectroscopy. Reaction of complex 2 with photochemically generated (OC)(5)Cr(THF) affords a novel homobimetallic σ-borane complex (OC)(3)Cr(η(6)-C(6)H(5)CH(2)NMe(2)·BH(2)-H-Cr(CO)(5)) (4), wherein one of the BH moieties is bound to the chromium center in an η(1)-fashion. The σ-borane complex 4 was isolated in moderate to good yield (72%). The BH(3) fragment in the complexes 3 and 4 are highly dynamic involving exchange of the BH hydrogen bound to the metal with the terminal BH hydrogen atoms. The dynamics has been studied using variable-temperature NMR spectroscopy. Complexes 2 and 4 have been characterized by X-ray crystallography.     

Vinylidene complexes of transition metals : IV. The transfer of the phenylvinylidene ligand from manganese to rhenium. the novel binuclear complex Cp2MnRe(μ-CCHPh)(CO)4

The novel complex Cp₂MnRe(μ-CCHPh)(CO)₄ (I) containing the bridging phenylvinylidene ligand and MnRe bond was obtained in the reaction of CpMn(CCHPh)(CO)₂ with CpRe(CO)₂·THF. Complex I turns into CpRe(CCHPh)(CO)₂ under normal conditions. This is the first example of the transfer of the vinylidene ligand from one transition metal to another.     

Zur Kenntnis der Chemie der Metallcarbonyle und der Cyano-Komplexe in flüssigem ammoniak : XL. Über die Reaktion kationischer Cyclopentadienyl-carbonyl-nitrosyl-Komplexe des Mangans und Rheniums mit flüssigem Ammoniak

The reactions of the cationic complexes [CpMn(CO)₂NO]⁺, [MeCpMn(CO)₂NO]⁺ (Cp = η⁵-C₅H₅, MeCp = η⁵-C₅H₄CH₃), [CpRe(CO)₂NO]⁺, [CpMn(CO)(L)NO]⁺ (L = PPh₃, PEt₂Ph, AsPh₃, CNMe, CNEt), {[CpMn(CO)NO]₂Me₂PC₂H₄PMe₂}²⁺ and {CpMn(CO)NO]₂Ph₂PC₂H₄PPh₂}²⁺ with liquid NH₃ yield the neutral carbamoyl complexes CpMn(CO)(NO)CONH₂, MeCpMn(CO)(NO)CONH₂, CpRe(CO)(NO)CONH₂, CpMn(L)(NO)CONH₂ (L = PPh₃, PEt₂Ph, AsPh₃, CNMe, CNEt), [CpMn(NO)CONH₂]₂Me₂PC₂H₄PMe₂ and [CpMn(NO)CONH₂]₂Ph₂PC₂H₄PPh₂. Properties and reactions of these new compounds are described.     

Vinylidene complexes of transition metals : III. Derivatives of cyclopentadienyltricarbonyl rhenium with phenylvinylidene ligands. Crystal and molecular structure of Cp(CO)2Re[CC(Ph)C(Ph)CH2]Re(CO)2Cp

The novel complexes CpRe(CCHPh)(CO)₂ and Cp₂Re₂(μ-CCHPh)(CO)₄ containing a terminal and a bridging phenylvinylidene ligand respectively and the binuclear complex Cp(CO)₂Re[CC(Ph)C(Ph)CH₂]Re(CO)₂Cp were obtained in the reaction of CpRe(CO)₃ with PhCCH.According to an X-ray study of the latter complex the unusual bridging ligand is η¹-bonded to one Re atom and η²-bonded to the other.     

N-heterocyclic carbene stabilized dichlorosilylene transition-metal complexes of V(I), Co(I), and Fe(0)

Reactions of N-heterocyclic carbene stabilized dichlorosilylene IPr·SiCl(2) (1) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with (η(5)-C(5)H(5))V(CO)(4), (η(5)-C(5)H(5))Co(CO)(2), and Fe(2)(CO)(9) afford dichlorosilylene complexes IPr·SiCl(2)·V(CO)(3)(η(5)-C(5)H(5)) (2), IPr·SiCl(2)·Co(CO)(η(5)-C(5)H(5)) (3), and IPr·SiCl(2)·Fe(CO)(4) (4), respectively. Complexes 2-4 are stable under an inert atmosphere, are soluble in common organic solvents, and have been characterized by elemental analysis and multinuclear ((1)H, (13)C, and (29)Si) NMR spectroscopy. Molecular structures of 2-4 have been determined by single crystal X-ray crystallographic studies and refined with nonspherical scattering factors.     

Synthesis and structure of distanna and tristanna ansa half-sandwich complexes of ruthenium and nickel

The synthesis and structural characterization of the first tin-bridged ansa half-sandwich complexes via a two-step protocol from Na[η(5)-C(5)H(5)Ru(CO)(2)] and in situ generated Na[η(5)-C(5)H(5)Ni(CO)] are presented. Both compounds are characterized by multinuclear NMR spectroscopy and single-crystal diffraction.     

Facile η5-η3 hapticity interconversion in pentamethylcyclopentadienyl ruthenium(II) complexes containing a phenylmethallyl ("open indenyl") ligand

The indenyl effect has been introduced to pentadienyl ("open cyclopentadienyl") chemistry by preparation of the phenylmethallyl ("open indenyl") ligand oInd(Me). The reaction of its potassium salt K(oInd(Me)) with [(η(5)-C(5)Me(5))RuCl](4) afforded the sandwich complex [(η(5)-C(5)Me(5))Ru(η(5)-oInd(Me))] (1), which, upon treatment with PMe(3), CO, and 2,6-dimethylphenyl isocyanide (CN-o-Xy), easily underwent η(5)-η(3) hapticity interconversion and formed the complexes [(η(5)-C(5)Me(5))Ru(η(3)-oInd(Me))(L)] (2, L = PMe(3); 3, L = CO; 4, L = CN-o-Xy). In these complexes, the η(3)-bound phenylmethallyl ligand adopts an anti-conformation with regard to the relative positions of the phenyl and methyl substituents. For the PMe(3) complex anti-2, slow conversion to the syn-isomer was observed, and this equilibrium reaction was monitored by NMR spectroscopy at 50 °C to determine a first order rate constant of k(323 K) = 6.57 × 10(-6) (± 0.02 × 10(-6)) s(-1) and an activation barrier of ΔG° = 26.8 kcal mol(-1). DFT calculations afforded a stabilization of syn-2 and syn-3 by ΔG(298) = -1.54 and -1.74 kcal mol(-1) over the respective anti-isomer.     

The dissociation kinetics of energy-selected CpMn(CO)(3)(+) ions studied by threshold photoelectron-photoion coincidence spectroscopy

Threshold photoelectron-photoion coincidence spectroscopy has been used to investigate the dissociation kinetics of the cyclopentadienyl manganese tricarbonyl ion, CpMn(CO)(3)(+). The ionization energy of CpMn(CO)(3) was measured from the threshold photoelectron spectrum to be 7.69 +/- 0.02 eV. The dissociation of the CpMn(CO)(3)(+) ion proceeds by the sequential loss of three CO molecules. The first and third CO loss reactions were observed to be slow (lifetimes in the microsecond range). By simulating the resulting asymmetric time-of-flight peak shapes and breakdown diagram, 0 K onsets for three product ions were determined to be 8.80 +/- 0.04, 9.43 +/- 0.04, and 10.51 +/- 0.06 eV, respectively. Combined with the adiabatic ionization energy, the three successive Mn-CO bond energies in the CpMn(CO)(3)(+) were found to be alternating with values of 1.11 +/- 0.04, 0.63 +/- 0.04, and 1.08 +/- 0.06 eV, respectively. Using a scaled theoretical Cp-Mn(+) bond energy of 3.10 +/- 0.10 eV and the combined results from theory and experiment, the 298 K gas-phase heat of formation of CpMn(CO)(3) is suggested to be -419 +/- 15 kJ/mol. Based on this value, the 298 K heats of formation of CpMn(CO)(3)(+), CpMn(CO)(2)(+), CpMnCO(+), and CpMn(+) are 325 +/- 15, 546 +/- 15, 719 +/- 15, and 938 +/- 15 kJ/mol, respectively. By scaling theoretical calculated neutral bond energies with the experimental information derived in this study, the successive Mn-CO bond energies were estimated to be 1.88, 1.10, and 1.03 eV, respectively, while the Cp-Mn bond energy was found to be 2.16 eV. Comparison between the quantum chemical calculations and experimental values shows that the loss of CO groups follows the lowest energy adiabatic path, in which electronic spin on the metal center is not conserved.     

Diastereoselective proton transfer: a route to enantiomerically pure half-sandwich rhenium complexes

The diastereomeric methyl rhenium complex [CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}(CH3)] was prepared in two steps from chiral racemic [CpRe(NO)(CO)(NCMe)]BF4 and the chiral racemic phosphine P(Me)(Ph)(2-C6H4NMe2). The unlike diastereomer reacts preferentially with MeSO3H to give the ring-closed ionic complex unlike-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}]MeSO3 along with unreacted like-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}(CH3)], which is easily separated and converted to like-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}]MeSO3. Starting from (R)-P(Me)(Ph)(2-C6H4NMe2), the diastereomerically and enantiomerically pure complexes (RRe,SP)-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}]MeSO3 and (SRe,SP)-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}]MeSO3 were obtained. Thus, this reaction sequence demonstrates a highly diastereoselective proton transfer from a functionalized chiral phosphine to a transition metal. Furthermore, it provides efficient access to enantiomerically pure half-sandwich rhenium complexes.     

Insight into binding of alkanes to transition metals from NMR spectroscopy of isomeric pentane and isotopically labeled alkane complexes

Alkane complexes of the type Cp'Re(CO)2(alkane) (Cp' = cyclopentadienyl or (isopropyl)cyclopentadienyl; alkane = isotopomers of n-pentane and cyclopentane) have been characterized using NMR spectroscopy following photolysis of Cp'Re(CO)3 in the appropriate alkane at 163-193 K. In the case of n-pentane, three different complexes are observed corresponding to binding of the three different types of carbon in this alkane. ROESY NMR experiments indicate that these isomeric complexes are slowly interconverting intramolecularly at 173 K. The order of the energetically preferred site of coordination is methylene (C2) approximately central methylene (C3) > methyl (C1) but with a spread of <0.2 kcal mol-1. Isotopic perturbation of resonance (IPR) experiments, conducted on several isotopomers of (i-PrCp)Re(CO)2(1-pentane), showed a large shielding of the 1H NMR chemical shift of the proton in a bound CHD2 moiety (delta -3.62) and CH2D (delta -2.64) compared with that of a bound CH3 moiety (delta -1.99). Likewise, the value of 1JCH for the coordinated methyl group of isotopomers of (i-PrCp)Re(CO)2(1-pentane) reduces in the order CH3 > CH2D > CHD2. This suggests that the alkane coordinates in an eta2-C,H fashion with a rapid exchange of bound hydrogen or deuterium within a methyl or methylene group, and that binding of a hydrogen atom is preferred over a deuterium by an amount of 0.23 +/- 0.03 kcal mol-1.     

Synthesis and Characterization of Linked Clusters Capped by Alkylidyne

1 INTRODUCTION Constructing higher nuclearity clusters with well-defined dimensions and structures provide a rather active field of chemistry with potential applications in areas including nanotechnology, molecular recognition and catalysis[1~4]. A continuing effort has been directed toward developing a better methodology for systematic synthesis of supracluster compounds through molecular design [5,6]. On the basis of extensive investigation on the metal exchange reaction in cluster com…     

A reactive Ru-binaphtholate building block with self-tuning hapticity

A versatile Ru-BINO building block is reported, which offers a straightforward entry point into the chemistry of atropisomeric binaphtholate complexes of ruthenium. Reaction of RuCl(2)(PPh(3))(3)6a with Tl(2)((S)-BINO) affords Ru((S)-BINO)(PPh(3))(2)7 as a mixture of isomers: in 7', the BINO ligand is bound via η(3)-CCO,η(1)-O' donors, and in symmetrical 7″, via η(3)-CCO,η(3)-O'C'C' interactions. The bis(enolate) BINO bonding mode in the latter, not previously observed for any metal, underscores the remarkable geometric and electronic flexibility of the binaphtholate moiety. The BINO ligand proves able to stabilize complexes containing as few as two, and as many as four, additional ligands in 7 and its derivatives, enabling a synthetic versatility that contrasts with that of the superficially similar o-catecholate complex Ru(o-cat)(PPh(3))(3). As with the important achiral Ru precursor 6a, complex 7 undergoes facile transformation into a range of products under mild conditions, including acetonitrile, pyridine, and vinylidene derivatives. Single-crystal X-ray structures are reported for three of these complexes: Ru(η(3),η(3)-(S)-BINO)(PPh(3))(2)7″, Ru(η(3),η(1)-(S)-BINO)(PPh(3))(2)(MeCN) 9, and Ru(η(3),η(1)-(S)-BINO)(PPh(3))(py)(2)11. (13)C{(1)H} NMR signatures are proposed for new and known BINO coordination modes (η(1)-O,η(1)-O'; η(1)-C1,η(1)-O'; η(3)-CCO,η(3)-O'C'C'; η(3)-CCO,η(1)-O'; η(6)-C(6),η(1)-O'), as a potential aid to further developments in late-metal BINO chemistry.     

Lewis base character of the phosphorus atom in phosphanido-niobocene complexes. Synthesis of new early-early homo- and heterobimetallic entities

The reaction of phosphanido complexes [Nb(η(5)-C(5)H(4)SiMe(3))(2)(L)(PPh(2))] [L = CO (1), CNXylyl (2)] with early transition metal halides in high oxidation states has been carried out. New bimetallic niobocene complexes [{Nb(η(5)-C(5)H(4)SiMe(3))(2)(L)}(μ-PPh(2))(MCl(5))] [M = Nb, L = CO (3), L = CNXylyl (4); M = Ta, L = CO (5), L = CNXylyl (6)] have been successfully synthesized by the reaction with [MCl(5)](2) (M = Nb or Ta). In a similar way [{Nb(η(5)-C(5)H(4)SiMe(3))(2)(L)}(μ-PPh(2))(MCl(4))] [M = Ti, L = CO (13), CNXylyl (14); M = Zr, L = CO (15), CNXylyl (16)] were synthesized using MCl(4) (M = Ti or Zr). Solutions of complexes 4-6 in chloroform produced new ionic derivatives [Nb(η(5)-C(5)H(4)SiMe(3))(2)(P(H)Ph(2))(L)] [MCl(6)] [M = Nb, L = CO (7), L = CNXylyl (8); M = Ta, L = CO (9), L = CNXylyl (10)]. Ionic complexes [Nb(η(5)-C(5)H(4)SiMe(3))(2)(P(Cl)Ph(2))(L)] [NbCl(4)O(thf)] [L = CO (11), CNXylyl (12)] were formed from solutions in thf - rapidly in the case of 3 but more slowly for 4. New heterometallic complexes [Nb(η(5)-C(5)H(4)SiMe(3))(2)(L)(μ-PPh(2)){(Ti(η(5)-C(5)R(5))Cl(3)}] [R = H, L = CO (17), CNXylyl (18); R = CH(3), L = CO (19), CNXylyl (20)] were synthesized by the reaction of 1 or 2 with [Ti(η(5)-C(5)R(5))Cl(3)] (R = H or CH(3)). All of these compounds were characterized by IR and multinuclear NMR spectroscopy, and the molecular structures of 9 and 12 were determined by single-crystal X-ray diffraction.     

Co-complexation of Lithium Gallates on the Titanium Molecular Oxide {[Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-CH)

Amide and lithium aryloxide gallates [Li(+){RGaPh(3)}(-)] (R = NMe(2), O-2,6-Me(2)C(6)H(3)) react with the μ(3)-alkylidyne oxoderivative ligand [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-CH)] (1) to afford the gallium-lithium-titanium cubane complexes [{Ph(3)Ga(μ-R)Li}{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-CH)] [R = NMe(2) (3), O-2,6-Me(2)C(6)H(3) (4)]. The same complexes can be obtained by treatment of the [Ph(3)Ga(μ(3)-O)(3){Ti(η(5)-C(5)Me(5))}(3)(μ(3)-CH)] (2) adduct with the corresponding lithium amide or aryloxide, respectively. Complex 3 evolves with formation of 5 as a solvent-separated ion pair constituted by the lithium dicubane cationic species [Li{(μ(3)-O)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-CH)}(2)](+) together with the anionic [(GaPh(3))(2)(μ-NMe(2))](-) unit. On the other hand, the reaction of 1 with Li(p-MeC(6)H(4)) and GaPh(3) leads to the complex [Li{(μ(3)-O)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-CH)}(2)][GaLi(p-MeC(6)H(4))(2)Ph(3)] (6). X-ray diffraction studies were performed on 1, 2, 4, and 5, while trials to obtain crystals of 6 led to characterization of [Li{(μ(3)-O)(3)Ti(3)(η(5)-C(5)Me(5))(3)(μ(3)-CH)}(2)][PhLi(μ-C(6)H(5))(2)Ga(p-MeC(6)H(4))Ph] 6a.     

Oligomeric allyl-palladium(II) complexes of β-substituted ethylselenolates: syntheses, structures and thermal decomposition

Tri-nuclear allyl-palladium complexes, [Pd(μ-SeCH(2)CH(2)COOR)(η(3)-C(3)H(4)R')](3) (R = H, Me, Et and R' = H, Me), have been synthesized by the reaction of [Pd(2)(μ-Cl)(2)(η(3)-C(3)H(4)R')(2)] with NaSeCH(2)CH(2)COOR. These complexes exist in a dynamic equilibrium with a dimeric form in solution and are fluxional at room temperature as shown by variable temperature (1)H NMR spectroscopy. The DFT calculations indicate that there is a negligible energy difference between the dimer and the trimer, and suggest that the delicate balance between the steric factors and angular strain decides the reaction products. These complexes (with R' = H) on treatment with [Pd(2)(μ-Cl)(2)(η(3)-C(3)H(5))(2)] afforded hetero-bridged complexes [Pd(2)(μ-Cl)(μ-SeCH(2)CH(2)COOR)(η(3)-C(3)H(5))(2)] (R = Me, Et). All the complexes have been characterized by NMR ((1)H, (13)C, (77)Se) spectroscopy. The molecular structure of [Pd(μ-SeCH(2)CH(2)COOEt)(η(3)-C(3)H(5))](3) revealed a chair conformation of the six-membered Pd(3)Se(3) ring, in which all the allyl groups lie at one side of the ring (similar to three axial 1,3,5-hydrogens of cyclohexane). Thermolysis of [Pd(μ-SeCH(2)CH(2)COOEt)(η(3)-C(3)H(5))](n) in diphenyl ether or hexadecylamine (HDA) yielded Pd(7)Se(4) as characterized by powder XRD.