Diphosphane Complexes Research Articles

Cationic Rhodium Diphosphane Complexes as Efficient Catalysts for the Semi‐Hydrogenation of Dehydroisophytol

AbstractThe selective reduction of terminal alkynes to alkenes was investigated using common cationic diphosphane rhodium complexes of the type [Rh(PP)(diolefin)]X (PP=diphosphane, X=anion). The effectiveness of the catalyst was demonstrated in the semi‐hydrogenation of dehydroisophytol (DIP), an industrial produced intermediate of vitamin E. The present study highlights the high activity and good selectivity of this simple catalytic system. However, deactivation increases at higher DIP concentrations. Several strategies to circumvent the deactivation are presented.

Tunable from Blue to Red Emissive Composites and Solids of Silver Diphosphane Systems with Higher Quantum Yields than the Diphosphane Ligands.

PMMA composites and solids of complexes of formulas [AgX(P-P)]n [n = 1 and 2; X = Cl, NO3, ClO4, CF3COO, and OTf; P-P = dppb, xantphos, (PR2)2C2B10H10 (R = Ph and iPr)] display the whole palette of colors from blue to red upon selection of the anionic ligand (X) and the diphosphane (P-P). The diphosphane seems to play the most important role in tuning the emission energy and thermally activated delayed fluorescence (TADF) behavior. The PMMA composites of the complexes exhibit higher quantum yields than that of the diphosphane ligands and those with dppb are between 28 and 53%. Remarkably, instead of blue-green emissions which dominate the luminescence of silver diphosphane complexes in rigid phases, those with carborane diphosphanes are yellow-orange or orange-red emitters. Theoretical studies have been carried out for complexes with P-P = dppb, X = Cl; P-P = dppic, X = NO3; P-P = dppcc, X = Cl, NO3, and OTf and the mononuclear complexes [AgX(xantphos)] (X = Cl, Br). Optimization of the first excited triplet state was only possible for [AgX(xantphos)] (X = Cl and Br). A mixed MLCT and MC nature could be attributed to the S0 → T1 transition in these three-coordinated complexes.

Influence of highly basic phosphine ligand on the reactivity and hydrolysis of P4 and P4S3 supported by ruthenium fragments

Substitution of PPh3 in [RuCp(PPh3)2Cl] with highly basic PMe3 gave a remarkable change in the reactivity towards P4 and unexpectedly only the bimetallic complex cation [{RuCp(PMe3)2}2(μ,η1:1-P4)]2+ (3) was formed which was characterized by NMR spectroscopy and single crystal X-ray diffraction analysis. The equimolar reaction between the synthon [RuCp(PMe3)2]+ and the mixed cage P4S3 is highly selective quantitatively yielding only the product with η1-Pbasal coordination to ruthenium. On the other hand, the related [RuCp(PPh3)2]+ cation gave a 2:1 mixture of mono-η1-Pbasal and bimetallic complex. The solid state structure of [RuCp(PMe3)2(η1-Pbasal-P4S3)]+ (4) was solved by X-ray diffraction and represents the first example of X-ray structure of intact P4S3 coordinated to a mononuclear ruthenium organometallic fragment. Hydrolysis of the P4 ligand in 3 resulted mainly in two products, i.e. free H3PO3 and the diphosphane complex cation [{RuCp(PMe3)2}2(μ,η1:1-P2H4)]2+ (9), while in the presence of methanol two mononuclear complexes [RuCp(PMe3)2{P(OH)3}]+ (8) and [RuCp(PMe3)2{P(OCH3)3}]+ (10) in (2:1) ratio were selectively formed.

Synthesis and antiproliferative activity of a series of new platinum and palladium diphosphane complexes.

New organometallic complexes [M(dppe)(R)2] {where M = Pt or Pd, dppe = 1,2-bis(diphenylphosphano)ethane, and R = C6F4H-x (x = 6,5,4), C6F3H2-3,5, C6F3H2-5,6, C6F3H2-3,6, C6F4(OMe)-4, and C6F4(cyclo-C5H10N)-4, the numbers x refer to the positions of the protons in the polyfluoroaryl ligands} were synthesised either through transmetalation from the dichlorido complexes [M(dppe)Cl2] or through ligand exchange using [M(diene)Cl2] precursor complexes with diene = 1,5-cyclooctadiene (cod) or 1,5-hexadiene (hex). Alternatively, [M(dppX)Cl(R)] complexes with dppX = dppm (1,1-bis(diphenylphosphano)methane), dppe, dppp (1,3-bis(diphenylphosphano)propane), and dppb (1,4-bis(diphenylphosphano)butane) were prepared in decarboxylation reactions from thallium(i) carboxylates Tl(O2CR). The different preparative methods were compared in terms of yield and purity. Structural and spectroscopic data are reported for the new dppX- and diene-M(R)2 complexes. Antiproliferative activity was investigated for these new complexes against the HT-29 (colon carcinoma) and MCF-7 (breast adenocarcinoma) cell lines, and the active compounds of this first series together with organometallic dppX or hex PtII or PdII complexes were then included in cell tests using L1210 (leukaemia cells) and the cisplatin-resistant L1210/DDP cell line. Remarkably, promising antiproliferative results were found for a few PtII and PdII complexes, while structurally closely related compounds were essentially nontoxic.

Ethyl lactate from dihydroxyacetone by a montmorillonite-supported Pt(II) diphosphane complex

The Lewis-acidity of a series of bis-cationic Pt(II)(aqua) complexes bearing phosphane ligands was exploited to catalyze the conversion of dihydroxyacetone to ethyl lactate. The Pt(II) complex bearing 1,2-bis(diphenylphosphanyl)ethane and triflate as counter anion showed high catalytic activity (TOF=530h−1) and chemoselectivity (>96%) at 70°C. On intercalating the latter precatalyst between the lamellae of Na-montmorillonite by a cationic exchange process, high chemoselectivity for ethyl lactate (>99%) at 70°C was observed, which was maintained in three consecutive catalytic runs.

Asymmetric 1,3-dipolar cycloaddition reactions between enals and nitrones catalysed by half-sandwich rhodium or iridium diphosphane complexes

The aqua complexes [(η5-C5Me5)M(PP*)(H2O)][SbF6]2(M = Rh, Ir; PP* = chiral diphosphane) catalyse the asymmetric 1,3-dipolar cycloaddition of nitrones to α,β-unsaturated aldehydes. Enantioselectivity up to 99% ee was achieved.

ChemInform Abstract: An Easy Route Toward Enantio‐Enriched Polycyclic Derivatives via an Asymmetric Domino Conjugate Reduction—Aldol Cyclization Catalyzed by a Chiral Cu(I) Complex.

AbstractThe intramolecular reductive aldol cyclization of diketo esters in the presence of a silane as reducing agent and a copper/chiral diphosphane complex allows the synthesis of manifold bi‐ and tricyclic adducts with high levels of diastereo‐ and enantiocontrol.

Mechanistic Study of the Oxidative Carbonylation of Methanol Catalyzed by Palladium Diphosphane Complexes with Nitrobenzene as Oxidant

AbstractThe reactivity of Pd complexes having bidentate diarylphosphane ligands was studied in the oxidative carbonylation of CH3OH to dimethyl carbonate/oxalate (DMC/O) with PhNO2 as the oxidant. Different ligands were employed with variation in backbone length and aryl ring substituent, and the acidity, CO pressure, or the partial pressure of H2 was varied. At two different stages in the catalytic cycle, one equivalent of DMC/O may evolve for every equivalent of PhNO2 reduced, which means that the efficiency with which nitrobenzene can function as the oxidant for the oxidative carbonylation of methanol (EOC) can potentially be 200 % relative to nitrobenzene conversion. The selectivity for DMC relative to DMO is thought to be determined by a species of the type [P2PdC(O)OCH3(R)]; the DMO/DMC ratio can be increased by increasing the CO pressure, by addition of an acid, or by using a ligand with a relatively large bite angle. On the basis of the collected results, we conclude that an ideal catalyst for oxidative carbonylation would have a relatively acidic palladium center and be sterically undemanding in the axial positions but sterically demanding in the equatorial positions of palladium. The Pd complex of bis(diphenylphosphanyl)ferrocene meets these criteria and was found to function most efficiently with PhNO2 as oxidant for the oxidative carbonylation of methanol among the series of compounds studied, that is, with about 50 % of the theoretical maximum efficiency EOC.

Pincer and Diamine Ru and Os Diphosphane Complexes as Efficient Catalysts for the Dehydrogenation of Alcohols to Ketones

The ruthenium and osmium complexes [MCl(2)(diphosphane)(L)] (M=Ru, Os; L=bidentate amino ligand) and [MCl(CNN)(dppb)] (CNN=pincer ligand; dppb=1,4-bis-(diphenylphosphino)butane), containing the N−H moiety, have been found to catalyze the acceptorless dehydrogenation of alcohols in tBuOH and in the presence of KOtBu. The compounds trans-[MCl(2)(dppf)(en)] (M=Ru 7, Os 13; dppf=1,1'-bisdiphenylphosphino)ferrocene; en=ethylenediamine) display very high activity and different substrates, including cyclic and linear alcohols, are efficiently oxidized to ketones by using 0.8-0.04 mol % of catalyst. The effect of the base and the comparison of the catalytic activity of the Ru versus Os complexes are reported. The ruthenium complex 7 generally leads to a faster conversion into ketones with respect to the osmium complex 13, which displays better activity in the dehydrogenation of 5-en-3β-hydroxy steroids. The synthesis of new Ru and Os complexes [MCl(2)(PP)(L)] (PP=dppb, dppf; L=(±)-trans-1,2-diaminocyclohexane,2-(aminomethyl)pyridine, and 2-aminoethanol) of trans and cis configuration is also reported.

Dinitrosylbis[tris(4-methylphenyl)phosphane]iron

The title compound, [Fe(NO)2(C21H21P)2], belongs to the family of metal dinitrosyl compounds with the general formula Fe(NO)2(L)x, referred to collectively as ‘dinitrosyl iron compounds’ (DNICs). Herein we report the structure of a dinitrosyl iron diphosphane complex, [Fe(NO)2 L 2], with L = P(C6H4-p-CH3)3. There are two crystallographically independent but chemically equal mol­ecules per asymmetric unit. The iron atom in each mol­ecule is tetra­hedrally coordinated by two phosphane ligands and two NO groups, with Fe—N—O angles in the range 173.84 (15)–179.31 (16)°.

Dinitrosylbis[tris(4-fluorophenyl)phosphane]iron chloroform monosolvate

The title compound, [Fe(NO)2(C18H12F3P)2]·CHCl3, belongs to the family of metal dinitrosyl compounds with the general formula Fe(NO)2(L)x, referred to collectively as ‘dinitrosyl iron compounds’ (DNICs). Herein we report the structure of a dinitrosyl iron diphosphane complex, (Fe(NO)2 L 2, with L = P(C6H4-p-F)3. The structure includes one metal complex mol­ecule and one chloro­form solvent mol­ecule. The iron atom is tetra­hedrally coordinated with two phosphane ligands and with two NO groups with Fe—N—O angles of 178.1 (2) and 177.0 (2)°.

Dinitrosylbis[tris(4-chlorophenyl)phosphane]iron

The title dinitrosyl iron diphosphane complex, [Fe(NO)2(C18H12Cl3P)2] or Fe(NO)2 L 2 [L = P(C6H4-p-Cl)3] belongs to the family of metal dinitrosyl compounds with the general formula Fe(NO)2(L)x, referred to collectively as dinitrosyl iron compounds (DNICs). The iron atom is tetra­hedrally coordinated by two phosphane ligands and two NO groups with Fe—N—O bond angles of 178.76 (15) and 177.67 (14)°.

Mixed Isobutylphobane/N‐Heterocyclic Carbene Ruthenium‐ Indenylidene Complexes: Synthesis and Catalytic Evaluation in Olefin Metathesis Reactions

AbstractTwo new second generation ruthenium(II) dichloride‐indenylidene complexes [RuCl2(9‐isobutylphosphabicyclo[3.3.1]nonane)(NHC)(3‐phenyl‐1‐indenylidene)], where NHC=1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene (SIMes) or its unsaturated imidazol‐2‐ylidene analogue (IMes), were isolated in high yields upon heating a tetrahydrofuran (THF) solution of the diphosphane complex [RuCl2(isobutylphobane)2(3‐phenyl‐1‐indenylidene)] with a two‐fold excess of the corresponding imidazol(in)ium‐2‐carboxylate zwitterions. Both products were characterized by 1H, 13C, and 31P NMR spectroscopy, and the molecular structure of [RuCl2(isobutylphobane)(SIMes)(3‐phenyl‐1‐indenylidene)] was determined by X‐ray diffraction analysis. A close inspection of the packing structure revealed the presence of different types of intra‐ and intermolecular interactions that enhanced the global stability of the crystals, while low temperature NMR experiments showed the existence of two distinct rotational isomers due to the unsymmetrical nature of the phobane ligand. The catalytic activity of both compounds was assessed in olefin metathesis using benchmark ring‐opening metathesis polymerization, ring‐closing metathesis (RCM), and cross‐metathesis reactions, and compared with those of related first and second generation ruthenium‐benzylidene and indenylidene catalyst precursors. Kinetic studies confirmed the high thermal stability of the mixed isobutylphobane/N‐heterocyclic carbene complexes, which suffered from a slow initiation efficiency compared to other catalytic systems based on the tricyclohexylphosphane ligand. However, the remarkable robustness of [RuCl2(isobutylphobane)(SIMes)(3‐phenyl‐1‐indenylidene)] was beneficial for performing the RCM of diethyl 2,2‐bis(2‐methylallyl)malonate. Monitoring the formation of the ruthenium‐methylidene active species [RuCl2(isobutylphobane)(SIMes)(CH2)] derived from this precursor further demonstrated its ability to sustain long reaction times and high temperatures required to carry out the RCM of tetrasubstituted olefins.

Chemoselective methoxycarbonylation of terminal alkynes catalyzed by Pd(ii)-TROPP complexes

The mono-phosphanes 5-(diphenyl)-phosphanyl-5H-dibenzo[a,d]cycloheptene (TROPP(Ph)) and 5-((2-methoxy)phenyl)-phosphanyl-5H-dibenzo[a,d]cycloheptene (TROPP((2-MeOPh))) have been employed to coordinate PdCl(2), yielding [PdCl(2)(TROPP(Ph))] (1a) and [PdCl(2)(TROPP((2-MeOPh)))] (1b), respectively. The corresponding tosylate (OTs) complexes [Pd(OTs)(2)(TROPP(Ph))] (2a) and [Pd(OTs)(2)(TROPP((2-MeOPh)))] (2b) have been successfully applied in the p-benzoquinone (BQ)-assisted methoxycarbonylation of terminal alkynes to give chemoselectively the corresponding alkynylcarboxylic acid methyl ester with high TOF (up to 980 h(-1)). Unlike 2a/b, the Pd(II)-(tosylate)-diphosphane complexes [Pd(OTs)(H(2)O)(dppp)](OTs) 2c (dppp = 1,3-bis-di(phenylphosphanyl)propane and [Pd(H(2)O)(2)(MeO-dppp)](OTs)(2) 2d (MeO-dppp = 1,3-bis(di(2-methoxyphenyl)phosphanyl)propane) preferentially catalyzed a double alkyne insertion. The "in situ" spectroscopic observation of the Pd-methoxycarbonyl compound [Pd(COOMe)(TROPP(Ph))](OTs) (3a) in conjunction with the evidence of the fast beta-hydride elimination reaction of TROPP-based Pd-catalysts in the dimerization reaction of ethene are indicative for a strongly electrophilic metal centre. The X-ray crystal structures of 1a x 0.5 C(2)H(4)Cl(2) and of the neutral and cationic Pd-alkyl complexes [Pd(Me)(Cl)(TROPP(Ph)) (7a x 0.5 CH(2)Cl(2)) and [Pd(CH(2)CH(2)COMe)(TROPP(Ph))](PF(6)) (10a x 0.5 C(6)H(6)), respectively, confirm unambiguously the bidentate coordination mode of TROPP-ligands to Pd(II), that persists even in the presence of CO pressure.

Sterically‐Directed Consecutive and Size‐Selective Self‐Assembly of Palladium Diphosphane Complexes with an Ar‐BIAN Ligand: Unexpected Formation of Pentameric and Hexameric Aggregates

The coordination properties of N,N'-bis[4-(4-pyridyl)phenyl]acenaphthenequinonediimine (L(1)) and N,N'-bis[4-(2-pyridyl)phenyl]acenaphthenequinonediimine (L(2)) were investigated in self-assembly with palladium diphosphane complexes [Pd(P;P)(H(2)O)(2)](OTf)(2) (OTf = triflate) by using various analytical techniques, including multinuclear ((1)H, (15)N, and (31)P) NMR spectroscopy and mass spectrometry (P;P = dppp, dppf, dppe; dppp = bis(diphenylphosphanyl)propane, dppf = bis(diphenylphosphanyl)ferrocene, and dppe = bis(diphenylphosphanyl)ethane). Beside the expected trimeric and tetrameric species, the interaction of an equimolar mixture of [Pd(dppp)](2+) ions and L(1) also generates pentameric aggregates. Due to the E/Z isomerism of L(1), a dimeric product was also observed. In all of these species, which correspond to the general formula [Pd(dppp)L(1)](n)(OTf)(2n) (n = 2-5), the L(1) ligand is coordinated to the Pd center only through the terminal pyridyl groups. Introduction of a second equivalent of the [Pd(dppp)](2+) tecton results in coordination to the internal, sterically more encumbered chelating site and induces enhancement of the higher nuclearity components. The presence of higher-order aggregates (n = 5, 6), which were unexpected for the interaction of cis-protected palladium corners with linear ditopic bridging ligands, has been demonstrated both by mass-spectrometric and DOSY NMR spectroscopic analysis. The sequential coordination of the [Pd(dppp)](2+) ion is attributed to the dissimilar steric properties of the two coordination sites. In the self-assembled species formed in a 1:1:1 mixture of [Pd(dppp)](2+)/[Pd(dppe)](2+)/L(1), the sterically more demanding [Pd(dppp)](2+) tectons are attached selectively to the pyridyl groups, whereas the more hindered imino nitrogen atoms coordinate the less bulky dppe complexes, thus resulting in a sterically directed, size-selective sorting of the metal tectons. The propensity of the new ligands to incorporate hydrogen-bonded solvent molecules at the chelating site was confirmed by X-ray diffraction studies.

An Atropo‐Stereogenic Diphosphane Ligand with a Proximal Cationic Charge: Specific Catalytic Properties of a Palladium Complex Thereof

AbstractA class of cationic diphosphane ligands combining phosphane and amidiniophosphane moieties is illustrated on the N‐methyl,N‐naphthylbenzimidazolium framework. The palladium(II) complex thereof is described and compared to the corresponding complex of the analogous neutral diphosphane. Contrary to first‐level expectations, the N2C–P and N2CP–Pd bonds in the cationic diphosphane complex are not longer than those occurring in its neutral counterpart. In the cationic ligand, the proximal positive charge is indeed conjugated to one phosphanyl group, and the coordination scheme is tentatively interpreted by resonance of the phosphane→metal dative bond (+N2C–P:→[Pd]) with a carbene→phosphenium dative bond (N2C:→[+P:→Pd]). Despite this peculiar structural feature, the electronic σ donation (vs. π acceptation) towards the palladium centre remains lowered in the cationic ligand. This specific property can be a priori valuable in a catalytic process where oxidative addition is not the limiting step. It is indeed shown that although the neutral complex is more active in Suzuki coupling reactions, the cationic complex is more active in Sonogashira‐type coupling reactions involving predissociated halide substrates, namely an acyl chloride. These likely atropo‐chiral ligands deserve to be resolved for application in asymmetric catalysis.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

On the Influence of “Arm‐on, Arm‐off” Processes on Alkene Hydrogenation Catalysed by a Rhodium Triphos Complex

AbstractThe influence of phosphane “arm‐on, arm‐off” association/dissociation in rhodium catalysed alkene hydrogenation using [Rh(COD)(κ3‐triphos)]PF6 {1, COD = cyclooctadiene, triphos = 1,1,1‐tris(diphenylphosphanylmethyl)ethane} has been investigated by comparison of the activity of 1 to mixtures of the related diphosphane complex, [Rh(COD)(κ2‐dppp)]PF6 {2, dppp = 1,3‐bis(diphenylphosphanyl)propane} and triphenylphosphane (THF, 50 °C, 1 bar H2). These investigations are supplemented by a demonstration of the κ2–κ3 fluxionally of the triphos coordination in 1 by reversible reaction with [RuCl2(p‐cymene)]2 at room temperature in CH2Cl2. The product of this reaction, the bimetallic complex [(p‐cymene)Cl2Ru{(PPh2CH2)CMe(CH2PPh2)2}Rh(COD)]PF6, was isolated and fully characterized, including determination of the solid‐state structure by X‐ray diffraction analysis. Despite this evidence for facile arm‐off dissociation of the triphos ligand in 1, complex 2, with or without triphenylphosphane, was found to be more efficient for the hydrogenation of styrene and cyclohexene. Notably, use of triphenylphosphane together with 2 was found to have beneficial effects – increasing the rate of styrene hydrogenation (in some cases) and helping to stabilise the metal center during cyclohexene hydrogenation. These observations are supported by mercury poisoning experiments and reactivity experiments with 2 in medium pressure sapphire NMR tubes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Heterobimetallic cuboidal [Mo 3NiS 4] and [W 3NiS 4] cluster diphosphane complexes as molecular models in hydrodesulfurization catalysis

Treatment of the cationic, incomplete cubane-type sulfido clusters [M 3S 4X 3(diphos) 3] + (M = Mo, W; X = Cl, Br; diphos = dmpe (1,2-bis(dimethylphosphanyl)ethane), dppe (1,2-bis(diphenylphosphanyl)ethane)) with an excess of [Ni(cod) 2] (cod = 1,5-cyclooctadiene) afforded the heterobimetallic single cube clusters [M 3NiS 4X 3(diphos) 3(CH 3CN)] + as PF 6 - salts. The acetonitrile ligand could be substituted by pyridine, tetrahydrothiophene and carbon monoxide in CH 2Cl 2 at room temperature, modelling the catalytic sites of heterogeneous Ni–MoS 2 hydrodesulfurization catalysts. X-ray crystal structure analyses of [Mo 3NiS 4Cl 3(dmpe) 3(CH 3CN)]BPh 4 and [W 3NiS 4Br 3(dmpe) 3(CO)]PF 6 are reported. Electrochemical studies by cyclic voltammetry reported for all heterobimetallic [M 3NiS 4] clusters show two quasireversible oxidation processes, the molybdenum complexes being ca. 0.2 V more difficult to oxidize than the tungsten analogues.

Polymerisation of Acrylates Catalysed by Methylaluminoxane Activated Ditertiary Phosphine Complexes of Iron and Cobalt Dichlorides

AbstractSummary: Diphosphane complexes of iron(II) are active catalysts for the polymerisation of methyl acrylate (MA) monomers in the presence of methylaluminoxane (MAO). High molar mass atactic MA polymers ($\overline M _{\rm n}$ ∼ 200 kg/mol) were obtained under mild conditions with relatively narrow polydispersities (PDI ∼ 2). Polymerisation activity and polymer molar masses are strongly dependent on the ligand frame. The polymerisation requires the coordination of MA to a vacant coordination site at the metal centre, and processes with chain‐transfer to aluminium. Cobalt analogues proved to be less efficient catalysts, giving activities in the range of 50–250 kg/mol · h instead of 200–450 kg/mol · h for the iron complexes. MAO activated FeCl2 and CoCl2 salts also perform the polymerisation of MA with low activity.Ditertiary phosphine complex of iron(II) chloride as methyl acrylate polymerisation catalyst.imageDitertiary phosphine complex of iron(II) chloride as methyl acrylate polymerisation catalyst.

The complete delineation of the initiation, propagation, and termination steps of the carbomethoxy cycle for the carboalkoxylation of ethene by Pd-diphosphane catalysts.

Drent and Budzelaar have proposed two catalytic cycles for cationic Pd–diphosphane complex catalyzed CO–alkene coupling reactions such as CO–ethene copolymerization and methoxycarbonylation of ethene. The hydride cycle is initiated by alkene insertion into a Pd–hydride bond whilst the carbomethoxy cycle is initiated by CO insertion into a Pd–methoxy bond. The two cycles may operate in parallel, for example, CO–alkene copolymerization, or one cycle may dominate, for example, the Lucite process for the methoxycarbonylation of ethene to methylpropanoate. Where the two cycles operate in tandem there exists the possibility of crossover between the cycles which has been inferred from chain end-group analysis. 2] Product selectivity is determined in both the initiation and termination step(s). The chainpropagation steps, insertion of CO into a metal–alkyl bond, and insertion of alkene into a metal–acyl, bond have been extensively investigated, whilst van Leeuwen has recently discussed termination by alcoholysis of the Pd–alkyl and Pd–acyl intermediates. We have recently (1) fully characterized the intermediates in and (2) delineated the initiation process of the hydride cycle. The hydride cycle is thus well established, however, a complete cycle for the Pd–carbomethoxy mechanism has not yet been demonstrated because of the absence of suitable Pd–carbomethoxy precursors. We report herein a simple, general procedure for the preparation of the key cationic monocarbomethoxy Pd–diphosphane compounds and present an NMR study that characterizes, for the first time, all the intermediates in the carbomethoxy cycle. We also report (1) the delineation of the propagation steps of the hydride cycle for this catalyst, and (2) for the first time, characterization of all the complexes involved in termination of the hydride cycle with concomitant crossover and initiation of the carbomethoxy cycle. It should be noted that ligands of the type used in this work give highly active catalysts in this field of chemistry.