Chloride-bridged Dimer Research Articles

Manganese(II) complexes of a set of 2-aminomethylpyridine-derived ligands bearing a methoxyalkyl arm: syntheses, structures and magnetism

Four new ligands, N-(2-methoxyethyl)- N-(pyridin-2-ylmethyl)amine (mepma), N-(3-methoxypropyl)- N, N-bis(pyridin-2-ylmethyl)amine (mpbpa), N-(2-methoxyethyl)- N, N-bis(pyridin-2-ylmethyl)amine (mebpa) and 2-{[(2-methoxyethyl)(pyridin-2-ylmethyl)amino]methyl} phenol (Hmepap), and four of their complexes with manganese(II) halides, [MnCl 2(mepma) 2] ( 1), [MnCl(μ-Cl)(mpbpa)] 2 ( 2), [MnBr 2(mebpa)] ( 3) and [MnBr 2(MeOH)(Hmepap)] ( 4) have been synthesized and characterized. Single-crystal Xray studies revealed that in all four complexes, the Mn(II) coordination spheres are distorted octahedral. In 1 and 2, the ether oxygen atom does not coordinate to the Mn(II) centre, but in 3 and 4 it does. The mononuclear molecules of 1 are linked by double hydrogen bonds to form linear chains. Temperature dependent magnetic susceptibility measurements revealed that the Mn(II) ions in 1 interact antiferromagnetically, with J=−1.06 cm −1. Compound 2 crystallizes as a double chloride-bridged dimer in which there is a weak ferromagnetic interaction ( J=0.55 cm −1) between the Mn(II) pair. The solution EPR spectrum of 2 suggests that in methanol compound 2 decomposes to a great extent to mononuclear species. In compound 3, mebpa acts as a tetradentate ligand with all of its nitrogen and oxygen atoms coordinated to the Mn(II) ion. Unexpectedly, in complex 4, the phenolic oxygen of Hmepap remains protonated and does not coordinate to the metal ion. Instead the oxygen from a methanol molecule coordinates the manganese centre. Hydrogen bonds between one of the two bromide ions, and the methanol and phenol hydroxyl groups, respectively, connect the mononuclear molecules of 4 into chains. No magnetic interactions were observed between the Mn(II) ions in 3 or 4.

Synthesis and characterization of phosphorescent cyclometalated platinum complexes.

The synthesis, electrochemistry, and photophysics of a series of square planar Pt(II) complexes are reported. The complexes have the general structure C(wedge)NPt(O(wedge)O),where C(wedge)N is a monoanionic cyclometalating ligand (e.g., 2-phenylpyridyl, 2-(2'-thienyl)pyridyl, 2-(4,6-difluorophenyl)pyridyl, etc.) and O(wedge)O is a beta-diketonato ligand. Reaction of K(2)PtCl(4) with a HC(wedge)N ligand precursor forms the chloride-bridged dimer, C(wedge)NPt(mu-Cl)(2)PtC(wedge)N, which is cleaved with beta-diketones such as acetyl acetone (acacH) and dipivaloylmethane (dpmH) to give the corresponding monomeric C(wedge)NPt(O(wedge)O) complex. The thpyPt(dpm) (thpy = 2-(2'-thienyl)pyridyl) complex has been characterized using X-ray crystallography. The bond lengths and angles for this complex are similar to those of related cyclometalated Pt complexes. There are two independent molecular dimers in the asymmetric unit, with intermolecular spacings of 3.45 and 3.56 A, consistent with moderate pi-pi interactions and no evident Pt-Pt interactions. Most of the C(wedge)NPt(O(wedge)O) complexes display a single reversible reduction wave between -1.9 and -2.6 V (vs Cp(2)Fe/Cp(2)Fe(+)), assigned to largely C(wedge)N ligand based reduction, and an irreversible oxidation, assigned to predominantly Pt based oxidation. DFT calculations were carried out on both the ground (singlet) and excited (triplet) states of these complexes. The HOMO levels are a mixture of Pt and ligand orbitals, while the LUMO is predominantly C(wedge)N ligand based. The emission characteristics of these complexes are governed by the nature of the organometallic cyclometalating ligand allowing the emission to be tuned throughout the visible spectrum. Twenty-three different C(wedge)N ligands have been examined, which gave emission lambda(max) values ranging from 456 to 600 nm. Well-resolved vibronic fine structure is observed in all of the emission spectra (room temperature and 77 K). Strong spin-orbit coupling of the platinum atom allows for the formally forbidden mixing of the (1)MLCT with the (3)MCLT and (3)pi-pi states. This mixing leads to high emission quantum efficiencies (0.02-0.25) and lifetimes on the order of microseconds for the platinum complexes.

Dimeric rhodium(III), iridium(III) and ruthenium(II) thiosalicylate complexes

Reactions of the chloride-bridged dimers [LMCl(μ-Cl)] 2 (M=Rh, Ir; L=Cp*=η 5-C 5Me 5; M=Ru, L=η 6- p-cymene) with two mole equivalents of thiosalicylic acid (HSC 6H 4CO 2H, H 2tsal) and excess base gives the dimeric rhodium(III), iridium(III) and ruthenium(II) thiosalicylate complexes [LM(tsal)] 2. Reaction of the complex [Cp*RhCl 2(PPh 3)] with one equivalent of H 2tsal and triethylamine in dichloromethane gives a mixture of the dimer [Cp*Rh(tsal)] 2 and the phosphine complex [Cp*Rh(tsal)(PPh 3)]; upon recrystallisation, pure dimer is obtained. A single-crystal X-ray diffraction study on the rhodium and ruthenium dimers reveals the expected thiolate-bridged M 2(μ-S) 2 unit. Electrospray mass spectrometry (ESMS) is a useful technique in studying the chemistry of the thiosalicylate complexes, all complexes giving strong [M+H] + ions. With added thiosalicylic acid, cations of the type [(LM) 2(Htsal) 3] + were detected in the mass spectra.

Synthesis and characterization of phosphorescent cyclometalated iridium complexes.

The preparation, photophysics, and solid state structures of octahedral organometallic Ir complexes with several different cyclometalated ligands are reported. IrCl3.nH2O cleanly cyclometalates a number of different compounds (i.e., 2-phenylpyridine, 2-(p-tolyl)pyridine, benzoquinoline, 2-phenylbenzothiazole, 2-(1-naphthyl)benzothiazole, and 2-phenylquinoline), forming the corresponding chloride-bridged dimers, CwedgeN2Ir(mu-Cl)2IrCwedgeN2 (CwedgeNis a cyclometalated ligand) in good yield. These chloride-bridged dimers react with acetyl acetone (acacH) and other bidentate, monoanionic ligands such as picolinic acid (picH) and N-methylsalicylimine (salH), to give monomeric CwedgeN2Ir(LX) complexes (LX = acac, pic, sal). The emission spectra of these complexes are largely governed by the nature of the cyclometalating ligand, leading to lambda(max) values from 510 to 606 nm for the complexes reported here. The strong spin-orbit coupling of iridium mixes the formally forbidden 3MLCT and 3pi-pi* transitions with the allowed 1MLCT, leading to a strong phosphorescence with good quantum efficiencies (0.1-0.4) and room temperature lifetimes in the microsecond regime. The emission spectra of the CwedgeN2Ir(LX) complexes are surprisingly similar to the fac-IrCwedgeN3 complex of the same ligand, even though the structures of the two complexes are markedly different. The crystal structures of two of the CwedgeN2Ir(acac) complexes (i.e., CwedgeN = ppy and tpy) have been determined. Both complexes show cis-C,C', trans-N,N' disposition of the two cyclometalated ligands, similar to the structures reported for other complexes with a "CwedgeN2Ir" fragment. NMR data (1H and 13C) support a similar structure for all of the CwedgeN2Ir(LX) complexes. Close intermolecular contacts in both (ppy)2Ir(acac) and (tpy)2Ir(acac) lead to significantly red shifted emission spectra for crystalline samples of the ppy and tpy complexes relative to their solution spectra.

C−H Activation Induced by Water. Monocyclometalated to Dicyclometalated: C∧N∧C Tridentate Platinum Complexes

Metalation of 2,6-diphenylpyridine (1) by potassium tetrachloroplatinate in acetic acid gives a monocyclometalated chloride-bridged dimer 4. This dimer is split with CO to give a kinetic product 9t with the incoming CO trans to the orthometalated carbon. The kinetic product of cleavage is shown to be 16 kJ mol-1 higher in energy than the thermodynamic product 9c, which has the CO trans to the pyridine nitrogen. The isomerization of 9t to 9c is shown not to take place via an associative mechanism and, with analogue 11, is effectively suppressed when excess chloride is added, implying that it takes place via a chloride dissociation. The monocyclometalated 9 undergoes a second cyclometalation to give the C∧N∧C dicyclometalated complex 15 in high yield. This second cyclometalation is brought about by the simple expedient of adding water to the monocyclometalated precursor. The addition of water is rationalized on the basis of needing to ionize the HCl byproduct of the reaction. Using a substituted pyridine (5...

Halide-Bridged Palladium(II) Dimers of Orthometalated (S)-(+)-N,N-Dimethyl-α-methylbenzylamine and (S)-(+)-N,N-Dimethyl[1-(2-naphthyl)ethyl]amine: Solution and Solid-State Structures and Reactions with 3,4-Dimethyl-1-phenylphosphole and Allyldiphenylphosphine

Activation thermodynamics for the cis ⇌ trans isomerization of the chloride-, bromide-, and iodide-bridged palladium(II) dimers of orthometalated (S)-(+)-N,N-dimethyl-α-methylbenzylamine (TMBA) and (S)-(+)-N,N-dimethyl[1-(2-naphthyl)-ethyl]amine (TMNA) have been determined by variable-temperature 1H NMR spectroscopy. The chloride-bridged dimers are cleaved regioselectively by 3,4-dimethyl-1-phenylphosphole (DMPP) and allyldiphenylphosphine (ADPP) to form the mononuclear products and (R3P = DMPP, ADPP), with the phosphine exclusively trans to nitrogen. The chloride-bridged dimers react with NaPF6 or AgClO4, DMPP, and CH3CN to produce and (X = PF6-, ClO4-). They react with NaPF6 or AgClO4 and excess DMPP to form [Pd(DMPP)4](X)2 (X = PF6-, ClO4-). When X = PF6-, this complex undergoes two thermal [2+2] dimerizations of the coordinated DMPP ligands in the solid state to form {Pd(DMPP2-[2+2])2}(PF6)2. The complex reacts with AgClO4 and ADPP at 75 °C to form an unusual chloride-bridged tetrapalladium(II) macroc...

Two novel zinc(II) complexes of the 1,8-cross-bridged cyclam ligand and their structures

Without special precautions to exclude moisture or protic solvents, cross-bridged cyclam ligand 1 was found to readily complex zinc dichloride and yield two types of cis-folded complexes in the solid-state; one a chloride-bridged dimer and the other an aqua complex featuring a coordinated [ZnCl 4] 2− counterion.

Bis(cyclopentadienyl)titanium(III) Chloride

Bis(cyclopentadienyl)titanium(III) chloride 1 - Nugent's reagent - exists as a chloride-bridged dimer in its solid state, but dissociates to its monomeric species in the presence of donor solvents (e.g. THF) to afford a loosely solvated `transition-metal-centred-radical'. The very mild nature of Nugent's reagent, and its selective one-electron reduction of epoxides results in its compatibility with highly functionalised compounds. The reactivity of the carbon-centred radical formed by initial C-O homolysis of the epoxide can be tuned depending on the reacting partner.

Rhenium Complexes with Weakly Coordinating Solvent Ligands, cis-[Re(PR3)(CO)4(L)][BArF], L = CH2Cl2, Et2O, NC5F5: Decomposition to Chloride-Bridged Dimers in CH2Cl2 Solution

The solvent-coordinated complexes [cis-Re(CO)4(PR3)(S)][BArF] (R = Ph, iPr, Cy, BArF = [B(3,5-(CF3)2C6H3)4]-) for S = Et2O, CH2Cl2, and NC5F5 have been prepared from reaction of the neutral methyl precursors, cis-Re(CO)4(PR3)(Me), with either [H(OEt2)2][BArF] or [Ph3C][BArF] in the appropriate solvent. A crystal structure of the complex [cis-Re(CO)4(PiPr3)(ClCH2Cl)][BArF] shows that the dichloromethane ligand is coordinated through one chlorine, with an Re−Cl distance of 2.554(2) A. The first example of a structurally characterized pentafluoropyridine complex of rhenium was also determined, [cis-Re(CO)4(PiPr3)(NC5F5)][BArF], with an Re−N distance of 2.319(5) A. Activation of C−Cl bonds in the dichloromethane complexes result in the formation of the chloride-bridged dimers, {[cis-Re(CO)4(PR3)]2(μ-Cl)}{BArF}, and the X-ray structures of the Ph and Cy derivatives were determined.

Synthesis of bis(diphenylphosphinocyclopentadienyl) yttrium chloride complexes and heterodimetallic derivatives. X-ray structure of bis[(μ-chloro)bis(diphenylphosphinocyclopentadienyl) yttrium(III)

Reaction of lithium diphenylphosphinocyclopentadienide with YCl 3 or YCl 3(THF) 3 and working lead to the formation of three yttrocene phosphines: the lithium metal adduct isolated as (Ph 2PC 5H 4) 2Y(μ-Cl) 2Li(THF) 2 · 0.5 LiCl ( 1), the chloride-bridged dimeric species {(Ph 2PC 5H 4) 2Y(μ-Cl)} 2 ( 2), and the coordinated monometal species [(Ph 2PC 5H 4) 2YCl(THF)] ( 3). The X-ray structure of 2 is remarkable in that the crystal exhibits two independent chloride-bridged dimers that differ in the arrangement ( syn, anti) of the diphenylphosphino groups. Chelation of phosphorus atoms to a molydenum carbonyl moiety is also reported.

Synthesis of 2,7-Disubstituted Derivatives of 1,8-Naphthalenediol. Unusual Structure of a Chlorotitanium 1,8-Naphthalenediolate

A variety of 2,7-disubstituted derivatives of 1,8-naphthalenediol (2) of potential value as ligands for the complexation of transition metals can be prepared from 1,8-naphthalenediyl bis(diethylcarbamate) (3) and 1,8-bis(methoxymethoxy)naphthalene (9) by directed ortho-metalation and subsequent functionalization. The reaction of TiCl4 with 1,8-naphthalenediol (2) in the presence of diisopropyl ketone produced an adduct of a novel chloride-bridged dimer of [1,8-naphthalenediolato(2-)-O,O‘]dichlorotitanium (16; R = H). Its unusual structure indicates that complexes derived from 1,8-naphthalenediols can have features not normally observed in complexes derived from simple phenols.

Chemistry of Ti(OiPr)Cl3 with Chloride and Oxygen-Containing Ligands: The Roles of Alkoxide and Solvents in the Six-Coordinate Titanium Complexes

Ti(OiPr)Cl3 reacts easily with various ligands to form a series of six-coordinate complexes, [Ti(OiPr)Cl5]2-(HAm+)2 (Am = NEt3 (7a) or NC5H5 (7b)), Ti(OiPr)Cl3L2 (L = THF (8) or PhCHO (9)), Ti(OiPr)Cl3(PhCHO)(Et2O) (10), and [Ti(OiPr)Cl2(μ-Cl)(PhC(O)OMe)]2 (11). Upon dissolution of 7a in THF, 8 was obtained. When 1 mol equiv of HNEt3Cl was added to 8, [Ti(OiPr)Cl4(THF)]-(HNEt3)+ (12) was obtained. With the addition of another 1 mol equiv of HNEt3Cl, 12 was converted to 7a. One THF in 8 can be removed in vacuo to give the chloride-bridged dimer [Ti(OiPr)Cl2(μ-Cl)(THF)]2 (13) which can be converted back to 8 by dissolving in THF. 13 was found to react with 2 mol equiv of HNEt3Cl or PhCHO to give 12 and Ti(OiPr)Cl3(PhCHO)(THF) (14), respectively. The molecular structures of 7b, 8, and 10−13 show short Ti−OiPr distances, and the relative bonding order of -OiPr > Cl- > THF > Et2O > PhCHO > μ-Cl- > RC(O)OMe is discussed based on the solid state structures. This bonding sequence is very useful for the prediction...

Studies on organolanthanide complexes. Part 55. Synthesis of furan-bridged bis(cyclopentadienyl) lanthanide and yttrium chlorides, and ligand and metal tuning of reactivity of organolanthanide hydrides (in situ)

Four new complexes [{Ln[[graphic omitted]CH(CH2C5H4)]Cl}2](Ln = Y, Yb, Sm or Nd) were synthesised by using furan-bridged bis(cyclopentadienes) as ancillary ligands and characterized by elemental analyses, mass, IR and 1H NMR spectroscopy. The spectra indicate that these complexes are chloride-bridged dimers and the two furan-bridged cyclopentadienyl rings co-ordinate to each metal in a chelating fashion with in transolecular co-ordination between the oxygen atom and the metal. The effects of the bridging chain and the central metal upon the reactivity of organolanthanide hydrides generated in situfrom the [Ln(C5H5)2Cl]–NaH system were investigated. The reactivity can be tuned not only by varying the ligands but also by taking advantage of the lanthanide contraction. The ligand tunability varies for different reactions. More reactive organolanthanide hydride species (in situ) can be obtained by both ‘ligand tuning’ and ‘metal tuning’, i.e. by selecting the appropriate ancillary ligands and the early lanthanide metals.

Organolanthanoids XVIII. The synthesis and X-ray crystal structure of di[η-chlorobis(diphenylphosphino-η 5-cyclopentadienyl)ytterbium(III)

Reaction of the divalent phosphinoytterbocene Yb(C 5H 4PPh 2) 2(THF)(THF = tetrahydrofuran) with mercuric chloride in THF or toluene yields mercury metal and the lanthanoid(III) complex Yb(C 5H 4PPh 2) 2Cl. An X-ray crystal structure of the compound revealed the presence of two independent chloride-bridged dimers (one centrosymmetric, one non-centrosymmetric, in a ratio of 1:2) with uncoordinated Ph 2P groups and pseudo-tetrahedral eight coordination (two η 5-C 5H 4PPh 2 and two η-Cl ligands) at ytterbium. The dimers differ in the arrangement ( syn, anti) of the Ph 2P groups. Solution spectroscopic data suggest that there is P-Yb bonding in toluene.

Studies on organolanthanide complexes: XLVI. Synthesis and characterization of N-containing ring-linked biscyclopentadienyl lanthanide and yttrium chlorides

Four new title complexes, [CH 3N(CH 2CH 2C 5H 4) 2LnCl] 2 (Ln = Y, Yb, Sm, Nd), were synthesized by using amine-linked biscyclopentadiene, CH 3N(CH 2CH 2C 5H 5) 2, as ancillary ligands and fully characterized by elemental analyses, MS, IR and 1H NMR. Their spectroscopies indicate that these complexes are chloride-bridged dimers and the two amine-linked cyclopentadienyl rings coordinate to one metal in a chelating fashion with intramolecular coordination from the nitrogen atom to the metal.

Synthesis and Structures of two Bulky Gallium Chlorides

Abstract The bulky gallium chlorides, (t-BuGaCl2)2 (1) and (Cy2GaCl)2 (Cy = C6H11) have been prepared via the reaction of GaCl3 with t-BuLi and CyMgCl, respectively. The structures of 1 and 2 have been determined by X-ray methods. Crystals of 1 are monoclinic, space group P21/c, with a = 6.937(4), b = 6.877(5), c = 17.11(1) Å, β = 95.65(6)[ddot], Z = 2; crystals of 2 are monoclinic, space group P21/c, with a = 10.389(2), b = 11.580(3), c = 11.198(2) Å, β = 95.96(2)[ddot], Z = 2. The R values for 1 and 2 are 0.0617 and 0.0681, respectively. The solid state structures of 1 and 2 consist of chloride-bridged dimers.

Reduction of tungsten complexes with primary phosphines and lithium dialkyl phosphides. X-ray crystal structures of [(Cp*WCl 2) 2·( t-Bu 2PP t-Bu 2) 2], [(Cp*WCl 4)(H 2PPh)], [{(PhN)WCl 2(PMe 3) 2} 2(μ-N 2)] and trans-WCl 4(H 2P t-Bu) 2 (Cp* = η 5-C 5Me 5)

The reduction of several high oxidation state tungsten halide complexes by lithium organophosphides and primary phosphines is described. Reaction of Cp*WCl 4 (Cp* = η5-C 5Me 5) with t-Bu 2PLi (4 equiv.) results in reduction of the metal and coupling of t-Bu 2P units to form a mixture of [Cp*WCl 2] 2 and t-Bu 2PP t-Bu 2 which co-crystallize as [(Cp*WCl 2) 2·( t-Bu 2PP t-Bu 2) 2] ( 1). There are no close intermolecular contacts between the tungsten(III) chloride-bridged dimer (Cp*WCl 2) 2 and ( t-Bu 2PP t-Bu 2) in the solid state. In the crystal structure of 1 the diphosphine exists in the gauche conformation found in other structurally characterized diphosphines. The (Cp*WCl 2) 2 dimer has all four chloride ligands in bridging positions. Reaction of [Cp*WCl 4] 2 with 2 equiv. of Ph(H)PLi forms the monomeric phosphine adduct (Cp*WCl 4) (H 2PPh)] ( 2) in 50% yield. The reaction of WCl 6 wi th excess t-BuPH 2 in dichloromethane gives trans-WCl 4(H 2P t-Bu) 2 ( 3). Reaction of [(PhN)Cl 3W(PMe 3) 2] with t-Bu 2PLi (2 equiv.) under nitrogen leads to reduction and formation of the μ-N 2 bridged W(IV) dimer [{(PhN)WCl 2(PMe 3) 2} 2(μ-N 2)] ( 4) in which the WNNW core is virtually linear. Crystal data for 1: C 52H 102P 4Cl 4W 2, M = 1360.8, monoclinic, P2 1/ n (No. 14), a = 8.309(9), b = 24.50(1), c = 15.117(8) Å, β = 95.98(1)°, U = 3060.5 Å 3, Z = 2, R = 0.0385, R w = 0.0474. Crystal data for 2: C 16H 21PCl 4W, M = 569.98, monoclinic, P2 1/ c (No. 14), a = 8.776(9), b = 16.310(6), c = 16.580(1) Å, β = 101.21(6)°, U = 2327.8 Å 3, Z = 4, R = 0.046, R w = 0.069. Crystal data for 3: C 8H 20 P 2Cl 4W, M = 503.85, monoclinic, C2 (No. 5), a = 11.1 36(5), b = 8.218(7), c = 9.832(8) Å, β = 93.20(6)°, U = 898.29 Å 3, Z = 1, R = 0.0330, R w = 0.0369. Crystal data for 4: C 24H 46P 4Cl 4N 4W 2, M = 1024.07, monoclinic, P2 1/ c (No. 14), a = 15.702(2), b = 12.580(2), c = 19.416(4) Å, β = 94.41(1)°, U = 3823.9 Å 3, Z = 4, R = 0.043, R w = 0.051.

Heavier halides of early transition elements by halide-exchange reactions. Crystal and molecular structure of [Ph3C]2[Hf2Cl10

The decahalogenodimetalates of zirconium(IV) and hafnium(IV) as their triphenylmethyl derivatives [Ph3C]2[M2Cl10] have been obtained by the reaction of M(BH4)4 with the appropriate Ph3CX or by addition of Ph3CX to MX4. The crystal and molecular structure of [Ph3C]2[Hf2Cl10] has been studied by X-ray diffraction methods: triclinic, space group P, a= 15.965(3), b= 12.907(3), c= 10.526(3)A, α= 99.75(2), β= 84.84(2), γ= 102.64(2)°, and Z= 2. The structure consists of [Ph3C]+ cations and [Hf2Cl10]2– anions, the latter having crystallographic symmetry. The chloride-bridged dimers have a distorted octahedral co-ordination while the [Ph3C]+ cations have a trigonal-planar geometry around the central carbon. The heavier halides of niobium(V) and tantalum(V) have been prepared from the chlorides by exchange reactions with PriBr (in the case of NbBr5) or with HX in EtBr solution (in the cases of NbI5 and TaX5).

Reactions of cyclopalladated compounds. Part 24. Reactivity of the Pd–C bond of cyclopalladated compounds towards isocyanides and carbon monoxide. Role of the donor group

The Pd–C bond of a series of Cyclopalladated compounds of general formula [P[graphic omitted]Me)2(µ-Cl)2], obtained through direct palladation of thioether ligands, is remarkably reactive towards insertion of one isocyanide as compared to the corresponding compounds in which the SMe unit has been replaced by a NMe2 moiety. The most reactive compound of the series is that derived from orthopalladation of benzyl methyl thioether, which leads either to chloride-bridged dimers with benzyl- or phenyl-isocyanide or to imino-bridged dimers with t-butyl isocyanide. With the other cyclopalladated compounds, insertion of the isocyanides also takes place in the presence of 2 equivalents of isocyanides per palladium atom though less readily as in the previous case, affording new imino units σ-bonded to palladium via their imino carbon atom. Carbon monoxide is readily inserted into the Pd-C bond of most of these cyclopalladated compounds to afford new palladated acyl groups, this reaction being reversible.

Reactivity of cyclopalladated compounds: XXI. Direct palladation of the prochiral CH 2 group of the α-trimethylsilyl-8-methylquinoline ligand by palladium(II), and reactions of the resulting PdC bond with alkynes

The reaction between α-trimethylsilyl-8-methylquinoline and palladium acetate, followed by metathesis of the acetato groups with lithium chloride, gave a mixture of chloride-bridged cyclopalladated dimers [{P dCHRC 9H 6N(μ-Cl)}] 2 ( 2, R  H; 3, R  SiMe 3) through cleavage of a CSi and a CH bond, respectively. In the presence of internal alkynes, compound 2 gave a stable chloride-bridged dimer by insertion of one molecule of dimethyl acetylenedicarboxylate (DMAD) into its PdC bond, and a monomeric compound by regioselective insertion of two molecules of ethyl-3-phenylpropiolate (EPP) into its PdC bond. In contrast, the reactions of 3 with both DMAD and EPP gave organometallic compounds containing η 3-allylic moieties; these were formed through insertion of the alkynes into the PdC bond of 3 followed by a 1,3-sigmatropic shift of the SiMe 3 group to the terminal carbon atom of the C(3) unit bridging the quinoline ring and the palladium atom.