Effects of the substituents Y in reactions of compounds of the type (Me3Si)3CSiH(C6H4Y-p)I. Evidence against the SN2(intermediate) mechanism for methanolysis of (Me3Si)3CSiMe2I and (Me3Si)3CSiHPhI

The rates of methanolysis of the iodides TsiSiH(C₆H₄Y-p)I (Y  MeO, Me, H, Cl, or CF₃) in 1/1 v/v MeOH/dioxane have been shown to be increased by electron withdrawal by Y and correspondingly decreased by electron release. This is taken to imply that the methanol is covalently involved in the transition state, and thus that, contrary to an earlier suggestion, the reaction cannot have an S_N2(intermediate) mechanism. No explanation can at present be offered for the fact that methanolysis of TsiSiHPhI (like that of TsiSiMe₂X with X  I, OClO₃, or OSO₂CF₃) is not accelerated by NaOMe whereas that of some other TsiSiHPhX compounds (e.g. X  Br, ONO₂, or OSO₂Me) is so accelerated, with its implications of a duality of mechanism within an S_N2 range. The reactions of the iodides TsiSiH(C₆H₄Y-p)I with KSCN in MeCN are also accelerated by electron withdrawal by Y, whereas those with AgOAc in MeCO₂H are accelerated by electron release.     

Carbamoyl and alkoxycarbonyl complexes of palladium(II) and platinum(II)

Carbamoyl and alkoxycarbonyl complexes of palladium(II) and platinum(II) of the type M(pnp)(CONHR)Cl (pnp = 2,6-bis(diphenylphosphinomethyl)pyridine; M Pd, R  C₆H₅, p-CH₃C₆H₄, p-CH₃OC₆H₄, C₆H₁₁, t-Bu; M  Pt, R  C₆H₅), Pd(pnp)[CON(Pr)₂]Cl (Pr = propyl), M(pnp)(COOR)Cl (M  Pd, R  C₆H₅, CH₃; M  Pt, R  CH₃), Pd(pnp)(COOCH₃)₂ result from reaction of M(pnp)Cl₂ with carbon monoxide and amines or alkoxides at room temperature and atmospheric pressure.The carbamoyl complexes react with bases to give urethane or diphenylurea depending upon the experimental conditions.     

Alkylidenverbrückte diphosphane und dichlalkogenodiphosphorane als liganden in kationischen cyclopentadienyleisencarbonyl-komplexen

Oxidative cleavage of the FeFe bond in [C₅H₅Fe(CO)₂]₂ in the presence of alkylide-bridged diphosphanes LL (LL = (C₆H₅)₂P(CH₂)_n(P(C₆H₅)₂; n = 1–3), (C₆H₅)₂PCH₂As(C₆H₅)₂ and dichalcogenodiphosphoranes (X)LL(X) ((X)LL(X) = (C₆H₅)₂P(X)(CH₂)_n(X)P(C₆H₅)₂; X  O, S, Se; n = 1–3) yields the complexes [C₅H₅Fe(CO)₂L′]BF₄ (L′ = LL, (X)LL(X); X  S, Se) in high yield. the complexes react with Ni(CO)₄ under photochemical conditions to form [C₅H₅Fe(CO)₂(μ-L′)Ni(CO)₃]BF₄ in quantitative yield, and lose a CO group under irradiation (λ_max > 300 nm) to form the chelate compounds [C₅H₅Fe(CO)L′]BF₄, which are isolable for L′  LL (P,As ligand) and (X)LL(X) (X = S, Se). Some substitution reactions with phosphanes are described.     

Reactions of organic halides with a trigonal pyramidal nickel(0) complex

The nickel(0) comlex [Ni(np₃)], np₃  tris(2-diphenylphinoethyl)amine, which has a trigonal pyramidal geometry in the solid state, readily reacts in solution with organic halides (CH₃I, C₂H₅Cl, C₃H₇Cl, C₆H₅Cl, C₆H₅Br, C₆H₅I and C₆H₅CH₂Cl) to give nickel(I) species with formula [NiX(np3)], (X  Cl, Br, I). Benezene, biphenyl, o-, m-, p-chlorobiphenyl are the other products from the reaction between the title complex and chlorobenzene.     

Acyl-platinum(II) and -palladium(II) complexes derived from 2-hydroxybenzaldehyde derivatives. X-ray structure of [Pt(OC6H4CO) (P(p-CH3C6H4)3)2]

Platinum(II) and palladium(II) complexes containing chelating acyl ligands have been synthesized from salicylaldehyde, 2-hydroxynaphthaldehyde and 2-hydroxy-3-methoxybenzaldehyde. The platinum(II) complexes [Pt(acyl)L₂], acyl  OC₆H₄CO, OC₁₀H₆CO, O(m-CH₃OC₆H₃CO), L  tertiary phosphine, 1/2 diphenylphosphinoethane, can be isolated with both monodentate and chelating diphosphines, whereas for palladium only the compounds with chelating phosphines are readily obtainable. The reactions of [Pt(OC₆H₄CO)L₂] with HCl afford trans-[PtCl(OHC₆H₄CO)L₂], L  monodentate tertiary phosphine and cis-[PtCl(OHC₆H₄CO)L₂], L2  1,2-bis-diphenylphosphinoethane, in which the metal—carbon bond remains intact. The structure of [Pt(OC₆H₄CO)-(P(p-CH₃C₆H₄)₃)₂] has been determined by X-ray diffraction methods and found to have the expected square planar structure. Some relevant bond lengths and angles are: PtP; 2.271(4) and 2.348(5) Å; PtC; 1.96(2) Å and PtO; 2.07(1) Å; PPtP  101°, CPtO  82°.     

Structural study of iron carbonyl derivatives: IV. Synthesis and crystal and molecular structure of syn-[μ-(SCH3)Fe(CO)2P(CH3)3]2

Dimeric palladium(I) complexes of the type [μ-(η³-C₅H₅)-μ-XPd₂(PR₃)₂](X  Br, R  i-Pr, Ph, Cy; X  Cl, I, R  i-Pr) have been prepared by reduction of the complexes [(ν⁵-C₅H₅)(PR₃)PdX] with a variety of reducing agents (Mg,Na/Hg, LiAlH(t-BuO)₃, LiAlH₄, NaBH₄, n-BuMgBr). PMR and IR data and some properties of the new complexes are reported.     

The partial hydrogenation of small unsaturated molecules by osmium cluster compounds. The reaction of diispropylcarbodiimide with H2Os3(CO)10

The products (μ-H)[μ-η²-(CH₃)₂CHNHCNCH(CH₃)₂]Os₃(CO)₁₀, I, and (μ-H)- [μ-η²-(CH₃)₂CHNHCO]Os₃(CO)₉[CNCH(CH₃)₂], II have been obtained from the reaction of H₂Os₃(CO)₁₀ with diisopropylcarbodiimine. Both products have been investigated by infrared and ¹H NMR spectroscopies, and by single crystal X-ray diffraction analyses. For I: Space group, P2₁/c, a12.840(4), b  15.724(4), c 12.638(4) Å, β 106.91(2)°, V  2441(2) ų, Z4, ? calc  2.66 g/cc. For 2869 reflections, R  0.051 and R_w  0.052. I contains an N-hydrido, N-isopropylamidinyl ligand bridging one edge of a triangular cluster of three osmium atoms. It was apparently formed by the incorporation of one carbodiimide molecule into the coordination sphere of the cluster followed by the transfer of one hydride ligand to one of the nitrogen atoms. For II: Space group P2 ₁/n;a  13.936(7), b  12.146(2), c  15.509(6) Å, β  105.20(4)°, V  2533(3) Å, Z  4, ?calc  2.57 g/cc. For 3065 reflections, R  0.052 and R_w  0.057. II contains an N-hydrido, N-isopropylformamido ligand bridging one edge of a triangular cluster of three osmium atoms and an isopropylisocyanide ligand. The molecule appears to have been formed by the cleavage of an NCH(CH₃)₂ moeity from one carbodiimide molecule and the transfer of it together with one hydride ligand to the carbon atom of a carbonyl group. The resultant formamido ligand bridges an edge of the cluster. The remaining fragment of the carbodiimide molecule bonds to one of the metal atoms of the cluster as a terminal isocyanide ligand. When heated, I loses one mole of carbon monoxide and forms the new cluster complex (μ-H)[μ₃-η²-(CH₃)₂CHNHCNCH-(CH₃)₂]Os₃(CO)₉ III. On the basis of electron counting schemes, III is believed to contain a triply-bridging amidinyl ligand serving as a five electron donor. Most importantly, no II was formed from I indicating that it is not a precursor -to II. A mechanism for the formation of I and II is presented and discussed.     

Bond energies and thermal decomposition of [Pt(X)(CH3)(P(C2H5)3)2] complexes

The thermal decomposition of the complexes trans-[Pt(X)(CH₃)L₂] (L  P(C₂H₅)₃; X  Cl, Br, I, CN) in decalin at 170 and 200°C affords methane platinum metal and [Pt(X)₂L₂]. The kinetics of the decomposition of the complexes were determined by monitoring the appearance of methane by GLC. The observed first-order rate constant was found to be independent on the nature of the ligand X. The thermal decomposition of the trideuteriomethyl complexes [Pt(X)(CD₃)L₂] (X  I, CN) in decalin-d₁₈ at 170 and 200°C was studied by GLC/MS. The thermolysis affords CD₃H and CD₄ in ratios which are independent of the nature of X and of the temperature used. The mass spectra of the complexes were also examined. A relative scale of platinum-to-methyl bond dissociation energies has been established by measuring the appearance potential of the fragment ion [Pt(X)L₂]⁺ and the ionization energies in the series [Pt(X)(CH₃)L₂]. Ionization potentials and PtCH₃ bond energies show a clear dependence on the nature of X which is not reflected in corresponding changes in the decomposition rates.     

Insertion of isocyanides into the palladium-(2-pyridyl) bond

The reaction of the pyridyl-bridged binuclear complex [PdBr(μ-2-C₅H₄N)(PPh₃)]₂ with isocyynides CNR (R  p-C₆H₄OMe, Me, C₆H₁₁) yields the complex $\text{PdBr}${(&2.dbnd;NR)C(&2.dbnd;NR) (2-C₅H₄N)}(PPh₃)] containing a C,N-chelated 1,2-bis(imino)-2-(2-pyridyl)ethyl group, which results from successive insertions of two isocyanides molecules into the palladium2-pyridyl bond. The mononuclear compound trans-[PdBr(2-C₅H₄N)(PMePh₂)₂] readily reacts with various CNR ligands (R  p-C₆H₄OMe, Me, C₆H₁₁, CMe₃) to give the imino(2-pyridyl)methylpalladium(II) derivatives, trans-[Pdbr{C(=NR)(2-C₅H₄N)} (PMePh₂)₂].     

New η-allyl η-cyclopentadienylcobalt cations

[Co(R-η-C₃H₄)(η-C₅H₅)I] is a good precursor for the preparation of some new cationic complexes as the iodide can easily be replaced; thus addition of PEt₃ to the iodo-complex (R  H) gives [Co(η-C₃H₅)(η-C₅H₅)(PEt₃)]⁺. The reactions of [Co(R-η-C₃H₄)(η-C₅H₅))I] (R  H or 2-Me) with AgBF₄ give solutions containing the coordinatively unsaturated species [Co(R-η-C₃H₄)(η-C₅H₅)⁺. The presence of traces of water leads to the formation of [Co(R-ηC₃H₄)-(η-C₅H₅)(H₂O)]⁺. The addition of monodentate ligands L  PEt₃ PPh₃, AsPh₃, SbPh₃, CNCH₃ and bidentate ligands LL  Ph₂PCH₂CH₂PPh₂(dppe) and o-C₆H₄(AsMe₂)₂(diars), gives, respectively mononuclear [Co(2-Me-ηC₃H₄)-(η-C₅H₅)L]⁺ and binuclear ligand-bridged [(2-Me-ηC₃H₄)(η-C₅H₅)CoLLCo(2-Me-ηC₃H₄)(η-C₅H₅))]²⁺ complexes. Crystals of [Co(2-Me-ηC₃H₄)(η-C₅H₅)-(H₂O)]⁺[BF₄]^- are monoclinic, space group P2₁/c, with a 7.858(3), b 10.262(4), c 15.078(4) Å, β 98.36(1)°. The molecular structure contains the cobalt atom bonded to planar 2-Me-allyl and cyclopentadienyl substituents, which are almost parallel with the H₂O molecule in a staggered conformation with respect to the 2-Me group.     

Spectroscopic investigations on the structure and fluxionality of the trihaptocycloheptatrienyl complexes [MX(CO)2(LL)(η3-C7H7)] (M  Mo,W; X  I,Cl; LL  bisphosphine or diamine) and synthesis of the tetracyanoethene adducts [WI(CO)2{Ph2P(CH2)nPPh2}{η3-C9H7(CN)4}] (n = 1 or 2)

Spectroscopic investigations, including ³¹P, ¹H and ¹³C NMR studies, on the formally 6-coordinate bisphosphine complexes [MX(CO)₂{Ph₂P(CH₂)_nPPh₂}(η³-C₇H₇)] (M  Mo, W; X  I, Cl; n = 2 (dppe), n = 1 (dppm); C₇H₇  cycloheptatrienyl) reveal a structure with no molecular plane of symmetry in which inequivalent P-donor atoms are arranged cis-cis and cis-trans to the two mutually cis-carbonyl groups. The dppe complexes exhibit a fluxional process which interconverts inequivalent phosphorus environments. Low temperature ¹H and ¹³C NMR studies on the diamine derivatives [MCl(CO)₂(H₂NCH₂CH₂NH₂)(η³-R)] (M  Mo, W, R  C₇H₇; M  Mo, R  C₃H₅ (allyl)) imply that the non-symmetric structure of the bisphosphine analogues is adopted. The adducts [WI(CO)₂{Ph₂P(CH₂)_n-PPh₂} {η³-C₉H₇(CN)₄}] (n = 1 or 2) are formed by tetracyanoethene addition to the trihapto-bonded cycloheptatrienyl ring of the tungsten complexes [WI(CO)₂-{Ph₂P(CH₂)_nPPh₂}(η³-C₇H₇)] (n = 1 or 2).     

Fulvene—platinum complexes: x-ray crystal structure of [Pt(η2-C5H4CPh2)(PPh3)2]

Bis(cycloocta-1,5-diene)platinum reacts with 2,3,4,5-tetraphenylfulvene to afford the complex [Pt(η²-CH₂C₅Ph₄)(cod)] (cod  C₈H₁₂) in which the metal atom is coordinated to the exo-cyclic double bond of the fulvene. Related compounds [Pt(η²-CH₂C₅Ph₄L₂] (L  PPh₃, PMePh₂, PMe₂Ph, AsPh₃ or CNBu^t have also been prepared and characterised. Reaction of the complexes [Pt(C₂H₄)₂(L)] (L  P(cyclo-C₆H₁₁)₃, PPh₃ or AsPh₃) with 2,3,4,5-tetraphenylfulvene yields the compounds [Pt(C₂H₄)(η²-CH₂C₅PH₄)(L)]. NMR data for the new species are reported and discussed. 6,6-Diphenylfulvene reacts with [Pt(cod)₂] and PPh₃ ($\text{1}\text{2}$ mol ratio) to give the complex [Pt(η²-C₅H₄CPh₂)-(PPh₃)₂] in which the metal atom is bonded to carbon atoms C(2) and C(3) of the fulvene ring. This was established by an X-ray diffraction study. Crystals are monoclinic, space group P2₁/n, with Z  4 in a unit cell of dimensions a  13.761(4), b  21.653(13), c  17.395(6) Å, β,  104.46(2)°. The structure has been solved and refined to R  0.064 (R′  0.064) for 3139 independent diffracted intensifies measured at room temperature. The platinum atom is in a trigonal environment formed by the two ligated phosphorus atoms and the CC bond of the fulvene which is elongated to 1.52(3) Å. The c₅ fulvene ring is planar, and makes an angle of 108° with the coordination plane around the platinum. In this plane the metal atom is slightly asymmetrically bonded with PtC 2.15(2) and 2.24(2) Å, and PtP 2.280(6) and 2.301(6) Å.     

Bonding in the ground state and excited states of copper-alkene complexes

The ground state and ¹B₂ excited state of Cu(C₂H₄)⁺ and of CuX(C₂H₄) (X  F, Cl) have been investigated by the Hartree-Fock-Slater (HFS) method. The main metal-ligand interactions in the ground state are ethene π → Cu 4s donation and Cu 3d_π → ethene π^* backdonation, which have comparable contributions to the metal-ligand bond strength. The excitation of CuX(C₂H₄) does not involve an alkene π → metal charge transfer (LMCT), but instead is metal 3d → alkene π^* charge transfer (MLCT) in character. The implications for the photochemistry of olefin-copper(I) complexes are discussed.     

Basische metalle : XXXVI. Die synthese stabiler hydrido(olefin)rhodium-komplexe und von[C5H5Rh(PMe3)(η3-CH3CHC6H5)]PF6

The complexes C₅H₅Rh(PMe₃)C₂H₃R′ (R′  H, Me, Ph) and C₅H₅Rh(PR₃)C₂H₄(PR₃  PMe₂Ph, PPrⁱ₃) are prepared by reaction of[PMe₃(C₂H₃R/t')RhCl]₂ or [PR₃(C₂H₄)RhCl]₂ and TlC₅H₅, respectively. They react with HBF₄ in ether/propionic anhydride to form the BF₄ salts of the hydrido(olefin)rhodium cations [C₅H₅RhH(C₂H₃R′)PR₃]⁺(R  Me; R′  H, Me and R  Prⁱ; R′  H). From C₅H₅Rh(PMe₃)C₂H₃Ph and CF₃COOH/NH₄PF₆ the η³-benzyl complex [C₅H₅Rh(PMe₃)(η³-CH₃CHC₆H₅)]PF₆ is obtained. The reversibility of the protonation reactions is demonstrated by temperature-dependent NMR spectra and by deuteration experiments. The complexes C₅H₅Rh(PMe₃)C₂H₃R′ (R′  H, Ph) and C₅H₅Rh(PMe₂Ph)C₂H₄ react with CH₃I in ether to give the salts [C₅H₅RhCH₃(C₂H₃R′)PR₃]I which in THF or CH₃NO₂ yield the neutral compounds C₅H₅RhCH₃(PR₃)I.     

Reactions and properties of some trimethyleneplatinum(IV) complexes: X. Reaction with iodide and thiocyanate ions

The reaction between the platinacyclobutanes [$\text{PtX}{}_2\text{(CH}{}_2\text{CRR′C}$H₂)L₂] (X  Cl, Br; L  C₅H₅N, 4-CH₃C₅H₄N; R, R′  H, CH₃; R  H, R′  CH₃, C₆H₅) and iodide and thiocyanate ions in methyl cyanide solution has been studied. The C₃ moiety is eliminated as the cyclopropane and the process is first order with respect to the platinacyclobutanes and zero to half order with respect to the salt (MY). With the iodides the rate increases in the order Li < Na < K, Et₄N, and methyl substitution in the cyclobutane ring reduces the rate of reaction with Et₄NI. Added pyridine retards the reaction when L  C₅H₅N (X  Cl; R, R′  H) and added dimethylsulphoxide accelerates it.The mechanism suggested involves dissociation of an L ligand and attack of Y^? ions and of M⁺Y^? ion pairs on the five-coordinate intermediate formed.     

Primary photochemical process in norbornadienechromium tetracarbonyl

Low-temperature photolysis of NbdCr(CO)₄(I) (Nbd  norbornadiene) in the presence of triphenylphosphine yields trans-NbdCr(CO)₃[P(C₆H₅)₃]. The quantum yields of the room-temperature photoinduced conversion of I in the presence of H₂, of P(C₆H₅)₃ and of both reagents, are respectively 0.140, 0.105 and 0.104. Primary photoinduced formation of monodentate I is shown to account for these observations.     

Errata

Treatment of 1,1,4,4-tetramethyl-1,4-distanna-2,5-cyclohexadiene with organoboron dihalides or boron trihalides generally leads to organoboron polymers and (CH₃)₂SnX₂ (X  Cl, Br). Ferrocenyldibromoborane, FcBBr₂ (Fc  (C₅H₅)Fe(C₅H₄)), reacts atypically with formation of FcB(CH  CH)₂BFc, which on controlled methanolysis affords CH₃OB(CH  CH)₂BOCH₃. The new 1,4- dibora-2,5-cyclohexadienes are characterized as nickel complexes Ni[FcB(CH  CH)₂BFc](CO)₂ and Ni[CH₃OB(CH CH)₂BOCH₃]₂, respectively.     

Protonation of the metal—metal bond in Fe2(μ-A)(μ-A′)(CO)4L2 complexes (A  A′ SC6H5, P(C6H5)2, P(CH3)2; A  SC6H5, A′ z.dbnd; P(C6H5)2; L z.dbnd; P(C6H5)3-n(CH3)n). : III. Experimental study of the influence of the A and A′ bridges on the basicity of the metal—metal bond

In order to check the influence of the bridges on the basicity of the metal—metal bond in Fe₂(μ-A)(μ-A′)(CO)₄L₂ complexes, the compounds with A  A′ SC₆H₅, P(C₆H₅)₂; P(CH₃)₂; A  SC₅H₅, A′ P(C₆H₅)₂ and L  P(CH₃)_3-n (C₆H₅)_n (n  0—3) have been prepared. IR and PMR spectroscopic results are interpreted in structural terms, and show that the Fe₂(SC₆H₅)(P(C₆H₅)₂.)-(CO)₄L₂ complexes are non rigid on the NMR time scale for n = 0, 1. Replacement of the first SC₆H₅ bridge by a P(C₆H₅)₂ bridge markedly increase the basicity of the metal—metal bond, but replacement of the second SC₆H₅ bridge has no significant effect.     

μ-Oxo-bis(triorganoantimon- und -bismutsulfonate). Kristallstruktur von {(CH3)3SbOH2]2}O3SC6H5)2

μ-Oxo-bis(triorganoantimony- and -bismuthsulfonates) (R₃MO₃Sr′)₂O[M  Sb, R  Ph, benzyl, M  Bi, R  Ph; R′  Me, CH₂CH₂OH, CF₃, Ph, 4-CH₃C₆H₄, 2,4-(NO₂)₂C₆H₃] and (Me₃SbO₃SR′)₂O · nH₂O (n  2, R′  CF₃, Ph, 4-CH₃C₆H₄; n  0, R′  CH₃, CH₂CH₂OH) have been prepared by reaction of (Ph₃SbO)₂ and Me₃Sb(OH)₂, respectively, with appropriate sulfonic acids or with (R₃MX)₂O (R  Ph, benzyl; X  Br) and R′SO₃H in the presence of Ag₂O. The anhydrous compounds (Me₃SbO₃SR′)₂O are obtained by heating the hydrates. Me₃Sb(OH)₂ and 2,4-(NO₂)₂C₆H₃SO₃H react to give the hydroxosulfonate Me₃Sb(OH)O₃SR′. CH₃OH solvolyzes the products. A covalent structure, with pentacoordinated Sb or Bi atoms, unidentate O₃SR′ ligands and μ-oxygen in apical, and R in equatorial positions, is inferred from the vibrational data for all nonhydrated sulfonate compounds. A correlation between ν_as(SbOSb) vibration and SbOSb bond angles in hexaphenyl distiboxans was established, which indicates that the SbOSb bridges are linear in (Ph₃SbO₃SR′)₂O (R′  2,4-(NO₂)₂C₆H₃, 2,4,6-(NO₂)₃C₆H₂) and bent in the other compounds. Data also indicate that there is a linear BiOBi bridge in (Ph₃BiO₃SCH₂CH₂OH)₂O. The hydrated compounds have a distinctly different ionic structure one H₂O being coordinated apically to each of the pentacoordinated Sb atoms in the cation [(Me₂SbOH₂)₂O]²⁺. This proposal is verified by the crystal structure determination of (Me₃SbO₃SPh)₂O · 2H₂O which revealed an ionic structure: [(Me₃SbOH₂)₂O](O₃SPh)₂. The angles μ-OSbO(H₂O) of 171.7(2) and 171.0(2)° and μ-OSbC(CH₃) of 98.3° (mean) reflect the distortion of the trigonal bipyramidal surrounding of the Sb atoms, and the long SbO(H₂O) distance of 244.4(5) pm (mean) the rather weak bonding of the water molecules to Sb. The distances S [144.6(6) pm (mean)] and the angles OSO [112.6(4)° (mean)] in the sulfonate anion are essentially identical. Hydrogen bonds exist between the water ligands and O atoms of the anions.     

Synthesis and characterization of mono- and dinuclear aryl palladium(II) complexes: oxidative additions of 1,4-dihalogenated benzene or 4,4′-dibromobiphenyl to Pd(PR3)4

Mononuclear palladium(II) complexes 1–12, (C₆H₄X-4)PdX?(PR₃)₂ (X?=?I, Br, or Cl; X??=?I or Br; R?=?Ph, Cy, Et, or Me), were synthesized by oxidative addition of 1,4-dihalogenated benzene to Pd(PR₃)₄; dinuclear palladium(II) complexes 13–15, (Me₃P)₂XPd(C₆H₄-1,4)PdX?(PMe₃)₂ (X, X??=?I or Br), could be obtained only using trimethylphosphine. Another method to prepare 13–15 is via re-oxidative addition of the corresponding mononuclear palladium(II) complexes and Pd(PMe₃)₄. Using 4,4′-dibromobiphenyl as the starting material, the mononuclear palladium(II) complexes [C₆H₄(C₆H₄Br-4)-4]PdBr(PPh₃)₂ (16) and [C₆H₄(C₆H₄Br-4)-4]PdBr(PCy₃)₂ (17) with bulky phosphines could be synthesized at relative low temperature, while dinuclear 18, (Cy₃P)₂BrPd(C₆H₄C₆H₄-4,4?)PdBr(PCy₃)₂, was prepared by bis-oxidative addition at higher temperature. The re-oxidative addition of 16 and Pd(PMe₃)₄ gave dinuclear 19, (Me₃P)₂BrPd(C₆H₄C₆H₄-4,4?)PdBr(PMe₃)₂, accompanying phosphine exchange. X-ray diffraction analysis revealed that formation of dinuclear palladium(II) complexes depends on the reaction temperature, phosphine ligands, and bridging groups.