Search

The synthesis and characterization of [Pt{4′-(R)trpy}(CN)]X (R = Ph, X = BF4 or SbF6; R = o-CH3C6H4, X = SbF6; R = o-ClC6H4, X = SbF6; or R = o-CF3C6H4, X = SbF6) are described where trpy = 2,2′:6′,2″-terpyridine. Single crystals of [Pt{4′-(Ph)trpy}(CN)]BF4·CH3CN were grown by vapour diffusion of diethyl ether into an acetonitrile solution of [Pt{4′-(Ph)trpy}(CN)]BF4. An X-ray crystal structure determination of the solvated complex confirms the near linear coordination of the cyanide ligand to the platinum centre. The cation is almost planar as evidenced by a twist of only 1.9° of the phenyl group out of the plane of the terpyridyl moiety. Cyclic voltammograms were recorded in DMF/0.1 M TBAH for the [Pt{4′-(R)trpy}(CN)]+ cations. Two quasi-reversible one-electron reduction (cathodic) waves are observed with E1/2 values that show the trend expected for an increasingly lower energy of the trpy-based LUMO of the complex i.e., [Pt{4′-(Ph)trpy}(CN)]+ ∼ [Pt{4′-(o-CH3C6H4)trpy}(CN)]+ < [Pt{4′-(o-ClC6H4)trpy}(CN)]+ < [Pt{4′-(o-CF3C6H4)trpy}(CN)]+. All the [Pt(4′-(R)trpy}(CN)]+ cations are photoluminescent in dichloromethane. Emission by [Pt{4′-(Ph)trpy}(CN)]+ is from an excited state with largely 3MLCT orbital parentage, but with some intraligand 3π–π* character mixed-in (τ = 0.1 µs). In contrast, the other three cations display emission that appears exclusively intraligand 3π–π* in origin (τ ∼ 0.8 µs). Emission spectra have been recorded in a low concentration frozen DME {1 : 5 : 5 (v/v) DMF–MeOH–EtOH} glass. For the R = o-CH3C6H4, o-ClC6H4 and o-CF3C6H4 cations the envelope of vibronic structure and energies of the vibrational components are essentially the same as that recorded in dichloromethane. However, for the [Pt{4′-(Ph)trpy}(CN)]+ cation, there is a blue-shift in the energies of the vibrational components as compared to that recorded in dichloromethane, as well as a change in the envelope of vibronic structure to a more “domed” pattern; this has been interpreted in terms of a higher percentage of intraligand 3π–π* character in the emitting state for the glass. Increasing the concentration of the glass invariably leads to aggregation of the cations and the consequent development of new low energy bands, such that at 0.200 mM broad peaks centred at ca. 650 and 700 nm dominate the spectrum; these bands are assigned to excimeric 3π–π* and 3MMLCT emission, respectively.

Reaction of [Pt(bipy)Cl2] (bipy = 2,2′-bipyridine) with an excess of silver triflate in refluxing acetonitrile readily affords [Pt(bipy)(MeCN)2](CF3SO3)2 as a yellow, crystalline solid. A single crystal X-ray diffraction study shows that the cations are arranged in a zig-zag manner in rows parallel to the b axis of the monoclinic unit cell. Consideration of the crystal structures of related bipyridyl ligand complexes of platinum(II), leads to the conclusion that a stacked structure with intermolecular Pt…Pt interactions for the title compound is prevented by the electrostatic repulsion between adjacent cations that are doubly charged.

The synthesis and characterisation of 4′-(2‴-chlorophenyl)-2,2′:6′,2″-terpyridine [4′-(o-ClC6H4)trpy] and [Pt{4′-(o-ClC6H4)trpy}Cl]SbF6 are described. An X-ray crystal structure determination of the salt reveals columns of cations and anions with the cations stacked parallel and head-to-tail. At 295 K the Pt⋯Pt distances alternate between 3.374(1) and 3.513(1) A while the perpendicular separation between the mean planes comprising the platinum and three bonded nitrogen atoms remains constant at 3.35 A. As evidenced by crystal structure determinations at 260, 240 and 180 K, the shorter Pt⋯Pt distances become systematically shorter and the longer Pt⋯Pt distances become systematically longer as the temperature of the crystal is lowered. Structural evidence is presented that shows that this trend is a consequence of the more closely separated platinum atoms slipping into line with respect to a perpendicular to the above planes; at the same time the more widely separated platinum atoms fall out-of-line as the temperature is lowered. Emission spectra measured on a polycrystalline sample of the salt at 40 K intervals from 280 to 80 K comprise a single, asymmetric and featureless band [λmaxem = 609 nm at 280 K] that systematically increases in intensity as the temperature is lowered. There is a slight blue shift in the wavelength of the emission maximum as the temperature is lowered to 240 K but, below this temperature, the emission maximum gradually and systematically shifts to the red [λmaxem = 642 nm at 80 K]. This behaviour is rationalised in terms of 3MMLCT emission, the energy of which being determined by subtle changes in the extent of dz2−dz2 orbital overlap between adjacent platinum atoms separated by the shorter distance on one hand, and between platinum atoms separated by the longer distance on the other.

The synthesis and structure of the Ru(I) dimer [Ru(bpy)(CO)2(CH3CN)]2(PF6)2 (1; bpy = 2,2‘-bipyridine) are described. The electrochemical properties of this complex have been examined. The irrevers...

The crystal structure of [Pt(trpy)(MeCN)](SbF6)2, where trpy denotes 2,2‘:6‘,2‘‘-terpyridine, shows that the platinum complex packs as a monomer; however, the 3π−π* emission of the solid occurs at surprisingly long wavelengths at room temperature. At lower temperatures new, shorter-wavelength maxima appear. Of the known salts with the composition [Pt(trpy)Cl]A, the A = SbF6- system is the lone example that exhibits a temperature-independent emission maximum. In these platinum(II) terpyridines, energy migration to defects or trap sites is one of the phenomena responsible for the temperature dependence of the solid-state emission spectrum. If trap emission is evident, the low-temperature spectral data are most representative of the bulk material.

Treatment of [{Ru 2 [µ-η 2 -OC(R)O] 2 (CO) 4 } n ] or its acetonitrile adduct [Ru 2 {µ-η 2 -OC(R)O} 2 (CO) 4 (MeCN) 2 ] (R = H, Me or Et) with a two-fold molar equivalent of the phosphorus–nitrogen ligands 2-diphenylphosphinopyridine (dppy), 2-diphenylphosphinoquinoline (dpquin) and 6-diphenylphosphino-2,2′-bipyridine (dpbipy) in alcohol under reflux resulted in the formation of dinuclear products of the type [Ru 2 {µ-η 2 -OC(R)O} 2 (CO) 4 (PPh 2 R′) 2 ] (R′ = pyridyl, quinolyl or bipyridyl) in which the PPh 2 R′ ligands are monodentate, co-ordinating axially through the phosphorus donor atoms, as established X-ray crystallographically for [Ru 2 {µ-η 2 -OC(Me)O} 2 (CO) 4 (dppy) 2 ]. On the other hand reaction of [{Ru 2 [µ-η 2 -OC(R)O] 2 (CO) 4 } n ] with 2 molar equivalents of dppy or dpquin in toluene under reflux in the presence of NH 4 PF 6 and under a slight pressure of carbon monoxide afforded products of the type [Ru 2 {µ-η 2 -OC(R)O}(CO) 4 (µ-dppy) 2 ]PF 6 or [Ru 2 {µ-η 2 -OC(R)O}(CO) 4 (µ-dpquin) 2 ]PF 6 in which the dppy or dpquin ligands adopt the bridging co-ordination mode, this mode of co-ordination being confirmed through a crystal structure determination on [Ru 2 {µ-η 2 -OC(H)O}(CO) 4 (µ-dppy) 2 ]PF 6 . Reaction of [{Ru 2 [µ-η 2 -OC(R)O] 2 (CO) 4 } n ] with dpbipy in n-butanol under reflux likewise afforded products, isolated as their hexafluorophosphate salts, in which the phosphorus–nitrogen ligands are bridging, viz. [Ru 2 {µ-η 2 -OC(R)O}(CO) 2 (µ-dpbipy) 2 ]PF 6 , the structure of [Ru 2 {µ-η 2 -OC(Me)O}(CO) 2 (µ-dpbipy) 2 ]PF 6 being established X-ray crystallographically.

The high-pressure (1300 psi CO, 120°C) reactions of Ru3(CO)12 with the diphosphines R2PCH2PR2; R = CH3 (dmpm), C6H5 (dppm), and C6H11 (dcypm), are reported. In the case of dppm, the disphosphinebridged dinuclear ruthenium complex [Ru2(μ-dppm)2(μ-CO)(CO4] was obtained. The corresponding reaction with dcypm afforded the mononuclear chelated diphosphine complex [Ru(dcypm)(CO)3]. The mixed ligand system [Ru2(μ-dmpm)(μ-dmpm)(μ-CO)(CO)4] was obtained by employing a 1:1 mixture of dppm and dmpm. The crystal and molecular structures of [Ru2(μ-dppm)2(μ-CO)(CO)4] and [Ru(dcypm)(CO)3] were also determined.

Treatment of [Cu(MeCN)4]PF6 in acetonitrile with 2,6-bis(diphenylphosphino)pyridine [(Ph2P)2py] afforded a colourless crystalline material characterised as [Cu2gm-(Ph2P)2PY3][PF612. An X-ray diffraction study confirmed that the three ligands bridge the two copper atoms bonding solely through the phosphorus atoms, each copper being trigonally coordinated; a cavity thus exists in the centre of the dinuclear dication bounded by the nitrogen donor atoms, the Cu… Cu distance and the diameter of the cavity being 4.744(2) and ca 4.9 A, respectively. Measurements of the solution emission spectra of [Cu2{μ-(Ph2P)2PY}3] [PF6]2 in the presence and absence of Cu+ and Ag+ ions suggest that these ions are trapped in the cavity on their addition to an acetonitrile solution of the complex. Addition of (Ph2P)2PY to [Cu(η2-bipy)(MeCN)2]PF6 (bipy = 2,2′-bipyridyl) in acetone afforded a yellow crystalline solid characterised as [Cu2{μ-(Ph2P)2py}2(η2-bipy)2][PF6]2. A crystal structure determination revealed that the two copper atoms are bridged by the two (Ph2P)2PY ligands bonding solely through the phosphorus atoms, with the irregular tetrahedral coordination at each copper being completed by the nitrogen atoms of the chelating bipyridyl ligands. The Cu… Cu distance is 6.806(2) A.

Reaction of 6-diphenylphosphino-2,2′-bipyridine (Ph2Pbipy) with copper(I) precursors such as [Cu(MeCN)4]+ and [Cu(2,2′-bipy)(MeCN)2]+ affords dinuclear phosphorusbipyridyl ligand-bridged dicopper products and in particular [Cu2(μ-Ph2Pbipy)2 (MeCN)2]2+ (1 and [Cu2(2,2′-bipy)(μ-Ph2Pbipy)2]2+ (2), respectively. The ligand coordinates head-to-tail in 1, and head-to-head in 2, as established by single crystal X-ray diffraction studies.

Homochiral catalysts, [Rh (norbornadiene)-(homochiral diphosphine)]+ X−/H2, were tested to assess possible enantiocontrol in the aldol-type coupling of activated vinyl components with aldehydes. A related approach, via in situ rhodium silyl enolates, was also investigated.

Thermolysis of [Ru2(µ-CO)(CO)4{µ-(RO)2PN(Et)P(OR)2}2], [Ru2H2(CO)4{µ-(RO)2PN(Et)P(OR)2}2] or [Ru2{µ-OC(O)}(CO)4{µ-(RO)2PN(Et)P(OR)2}2](R = Me or Pri) under appropriate reaction conditions affords the formally unsaturated species [Ru2(CO)4{µ-(RO)2PN(Et)P(OR)2}2], which have been established by X-ray crystallography for both R = Me and R = Pri to contain two complementary semi-bridging carbonyl groups as well as two terminal carbonyls. These compounds are highly labile and react under mild conditions with a range of small molecule nucleophiles and electrophiles including carbon monoxide, isonitriles, nitrosyl ions, alkynes, sulfur, hydrogen sulfide, dioxygen, sulfur dioxide, tin(II) chloride, dihydrogen, protons, halogens and carbon tetrachloride. The compound [Ru2H2(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2], the product of the reaction involving dihydrogen and the tetraisopropoxy-diphosphazane derivative and in which, as determined by X-ray crystallography, the hydrogens are situated equatorially and trans to each other on different ruthenium atoms, is also highly reactive, typically reductively eliminating dihydrogen in its reactions with nucleophiles including alkynes.

Treatment of [Ru2(µ-CO)(CO)4{µ-(RO)2PN(Et)P(OR)2}2](R = Me or Pri) with AgSbF6 in methanol, ethanol or tetrahydrofuran–water resulted in the formation of the solvento species [Ru2(CO)5(R′OH){µ-(RO)2PN(Et)P(OR)2}2][SbF6]2 which is isolable for R′= H but which spontaneously deprotonates to the alkoxycarbonyl-bridged derivative [Ru2{µ-η2-OC(OR′)}(CO)4{µ-(RO)2PN(Et)P(OR)2}2]SbF6 for R′= Me or Et. The aqua species [Ru2(CO)5(H2O){µ-(RO)2PN(Et)P(OR)2}2][SbF6]2 was readily deprotonated in consecutive steps by appropriate bases to afford respectively the hydroxycarbonyl-bridged species [Ru2{µ-η2-OC(OH)}(CO)4{µ-(RO)2PN(Et)P(OR)2}2]SbF6 and the adduct [Ru2{µ-η2-OC(O)}(CO)4{µ-(RO)2PN(Et)P(OR)2}2] in which the carbon dioxide molecule adopts a novel bridging co-ordination mode; this deprotonation is reversible and treatment of the latter with HBF4·OEt2 leads to stepwise regeneration of the aqua species. The co-ordinated water molecule in [Ru2(CO)5(H2O){µ-(PriO)2PN(Et)P(OPri)2}2][SbF6]2 was readily displaced by acids HA derived from conjugate bases with potential co-ordinating properties such as thiolate ions R″S–(R″= H or Ph) or carboxylate ions R‴CO2–(R‴= H, Me, Ph or CF3), to produce monocationic pentacarbonyl species of the type [Ru2A(CO)5{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6; detection of an intermediate, presumably [Ru2(CO)5(HA){µ-(PriO)2PN(Et)P(OPri)2}2][SbF6]2, was possible for HA = HCO2H and MeCO2H. The sulfido derivatives [Ru2(SR″)(CO)5{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6(R″= H or Ph) rapidly decarbonylate in solution to afford the tetracarbonyl products [Ru2(µ-SR″)(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6 in which the sulfido group bridges the two ruthenium atoms. On the other hand the carboxylato derivatives [Ru2{OC(O)R‴}(CO)5{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6(R‴= H, Me, Ph or CF3) are stable to decarbonylation in solution at room or elevated temperatures but can be decarbonylated to the carboxylato-bridged products [Ru2{µ-η2-OC(R‴)O}(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6 by irradiation with ultraviolet light. The water molecule in [Ru2(CO)5(H2O){µ-(PriO)2PN(Et)P(OPri)2}2][SbF6]2 was also readily displaced by the conjugate bases of the above acids HA, but in contrast to that observed for the carboxylic acids R‴CO2H (R‴= H, Me or Ph), reaction of the aqua species with the corresponding carboxylate ions R‴CO2– led to direct formation of the carboxylato-bridged species [Ru2{µ-η2-OC(R‴)O}(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6. Possible mechanisms for the formation of the various products are discussed as are the structures of [Ru2(CO)5(H2O){µ-(PriO)2PN(Et)P(OPri)2}2][SbF6]2·OCMe2, [Ru2{µ-η2-OC(OEt)}(CO)4{µ-(MeO)2PN(Et)P(OMe)2}2]SbF6, [Ru2{µ-η2-OC(Me)O}(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2]PF6 and [Ru2{µ-η2-OC(O)}(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2], established X-ray crystallographically.

Cyclic voltammetric studies in benzonitrile, dichloromethane and acetone show that the oxidation of the di-iron derivatives [Fe2(μ-CO)(CO)4(μ-R2PYPR2)2] (Y = CH2, R = Me or Ph; Y = NEt, R = OMe, OEt, OiPr or OPh) generally proceeds via an EEC mechanism, the only exception being the oxidation of the Y = CH2, R = Ph derivative in acetone, which proceeds via an EE mechanism. The chemical step in the EEC mechanism involves solvent attack at an iron atom with formation of a dicationic solvento species of the type [Fe2(CO)5(solvent)(μ-R2PYPR2)2]2+. The electrochemical oxidation of the diruthenium tetramethoxydiphosphazane ligand-bridged derivative [Ru2(μ-CO)(CO)4{μ-(MeO)2PN(Et)-P(OMe)2}2] only proceeds via an EEC mechanism in the very weakly coordinating solvent dichloromethane; in benzonitrile and acetone oxidation is via an ECE mechanism for which the potential required to remove the second electron is lower than that for the removal of the first electron giving rise to an overall 2e-transfer reaction. Again the end-product of the oxidation process is a dicationic solvento species. Electrochemical oxidation in all three solvents of the diruthenium tetraisopropoxydiphosphazane ligand-bridged derivative [Ru2(μ-CO)(CO)4{μ-(iPrO)2PN(Et)P(OiPr)2}2] is proposed to proceed via an ECEC mechanism for which the first chemical step involves a structural rearrangement and the second solvent attack at a ruthenium atom to form the dicationic solvento species. Significantly, the separation between the potentials required to remove the first and second electrons is small, i.e., < 0.5 V. Two pathways are utilized in the electrochemical oxidation of the mixed-ligand complex [Ru2(μ-CO)(CO)4{μ-(MeO)2PN(Et)P(OMe)2}{μ-(iPrO)2PN(Et)P(OiPr)2}], their nature being dependent on the choise of solvent. The ECE mechanism is adopted in all three solvents benzonitrile, acetone and dichloromethane; however, in the first solvent the second pathway is the EEC process whereas the second pathway adopted in acetone and dichloromethane is the ECEC process. Thus, the overall mechanism proposed for the electrochemical oxidation of the above derivatives of [Fe2(CO)9] and [Ru2(CO)9] allows for three pathways to a dicationic solvento species, the pathway adopted being dependent on the metal, the bridging ligand, in particular on its size, and on the coordinating ability of the solvent.

Reaction of [Ru3(CO)12] with PPhH2 in toluene under reflux affords a range of higher nuclearity as well as trinuclear products, two of which have been characterised as the π-toluene derivatives [Ru5(μ4-PPh)(CO)12(η6-C6H5Me)] and [Ru7(μ4-PPh)2(CO)15(η6-C6H5Me)]. Crystal structure determinations have revealed that the structures of these two compound are based on those of their parents, [Ru5(μ4-PPh)(CO)15] and [Ru7(μ4-PPh)2(CO)18], with three carbonyls on one of the ruthenium atoms of each cluster having been replaced by a π-toluene ring.

Treatment of [Ru2(µ-CO)(CO)4{µ-(RO)2PN(Et)P(OR)2}2](R = Me or Pri) with halogens results in the ready formation of [Ru2X(CO)5{µ-(RO)2PN(Et)P(OR)2}2]+(X = Cl, Br or I) with the halogen atom co-ordinating terminally. These pentacarbonyl species, isolated as their hexafluorophosphate salts, decarbonylate in solution, rapidly in the presence of trimethylamine N-oxide dihydrate but slowly in the absence of this decarbonylating agent, to produce the tetracarbonyl species [Ru2(µ-X)(CO)4{µ-(RO)2PN(Et)p(OR)2}2]+ in which the halogen bridges the two ruthenium atoms. Substitution of the carbonyl groups in these tetracarbonyl species can be effected further by halide ions, either photochemically or by promoting the process using Me3NO·2H2O and thus reaction of [Ru2(µ-X)(CO)4{µ-(RO)2PN(Et)P(OR)2}2]+ with chloride, bromide or iodide ions in the presence of Me3NO·2H2O readily affords [Ru2(µ-X)X(CO)3{µ-(RO)2PN(Et)P(OR)2}2]. Significantly, treatment of [Ru2I(CO)5{µ-(RO)2PN(Et)P(OR)2}2]I3, or [Ru2I(CO)5{µ-(RO)2PN(Et)P(OR)2}2]PF6 in the presence of iodide ions, with an excess of Me3NO·2H2O leads solely to the neutral tetracarbonyl derivative [Ru2I2(CO)4{µ-(RO)2PN(Et)P(OR)2}2]. On the basis of an X-ray crystallographic study on [Ru2(µ-I)I(CO)3{µ-(PriO)2PN(Et)P(OPri)2}2], the tricarbonyl derivatives have structures related to that of [Ru2(µ-X)(CO)4{µ-(RO)2PN(Et)P(OR)2}2]+ with an axial carbonyl group having been replaced by a halide ion.

Treatment of [Ru2(μ-CO)(CO)4{μ-(RO)2PN(Et)P(OR)2}2] (R = Me or Pri), electron-rich derivatives of [Ru2(CO)9], with a twice molar amount of a silver(I) salt in aprotic, weakly co-ordinating solvents such as acetone, acetonitrile or benzonitrile leads to the formation of the solvento species [Ru2(CO)5(solvent)- {μ-(RO)2PN(Et)P(OR)2}2]2+. The structure of the benzonitrile derivative, [Ru2(CO)5(PhCN){μ-(PriO)2PN(Et)P(OPri)2}2](SbF6)2, has been established by X-ray crystallography. The acetone molecule in [Ru2(CO)5(acetone){μ- (RO)2PN(Et)P(OR)2}2]2+ is readily replaced by various nucleophiles to afford products of the type [Ru2(CO)5L{μ-(RO)2PN(Et)P(OR)2}2]2+, where L is a neutral ligand such as CO, Me2C6H3NC, PhCN, C5H5N, H2O, Me2S or SC4H8, [Ru2Y(CO)5{μ-(RO)2PN(Et)P(OR)2}2]2+, where Y− is an anionic ligand such as Cl−, Br−, I−, CN−, SCN−, MeCO2−, CF3CO2− or [Ru2(μ-Y)(CO)4{μ-(RO)2- PN(Et)P(OR)2}2]+ where Y− is an anionic ligand such as Cl−, Br−, I−, SPh−, S2CNEt2−, MeCO2− or CF3CO2−.

The reaction of [Ru3(CO)12] with PPh2H in toluene under reflux affords a range of products, the nature and yields of which depend on the reaction times and the molar ratios employed. Compounds isolated include not only the trinuclear species [Ru3(μ2-PPh2)2(μ2-H)2(CO)8], [Ru3(μ2-PPh2)3(μ2-H)(CO)7], [Ru3(μ2-PPh2)3(μ2-H)(CO)6(PPh2H)], [Ru3(μ3-PPh)(μ-H)2(CO)9] and [Ru3(μ-PPh)(μ-PPh2)2(CO)7] but also condensation products, such as [Ru4(μ4-PPh)2(μ2-CO)(CO)10], [Ru5(μ4-PPh)(CO)15], [Ru6(μ4-PPh)2(μ3-PPh)2(CO)12] and [Ru7(μ4-PPh)2(CO)18], previously isolated from the reaction of [Ru3(CO)12] with PPhH2, as well as the highly unusual octaruthenium derivative [Ru8(μ8-P)(μ2-η1,η6-CH2Ph)(μ2-CO)2(CO)17] and the fragmentation product [Ru2(μ-PPh2)2(CO)6]. The molecular stereochemistries of [Ru2(μ-PPh2)2(CO)6], [Ru3(μ2-PPh2)3(μ2-H)(CO)7], [Ru3(μ2-PPh2)3(μ2-H)(CO)6(PPh2H)] and [Ru8(μ8-P)(μ2-η1,η6-CH2Ph)(μ2-CO)2(CO)17] have been established by X-ray crystallography. The eight ruthenium atoms in the latter adopt a square antiprismatic geometry and encapsulate a phosphorus atom derived from the diphenylphosphine. The benzyl group in this compound exhibits an unusual mode of coordination with the benzene ring functioning as a hexahapto ligand towards one of the ruthenium atoms and with the benzylic carbon bonding directly to an adjacent ruthenium atom.

Protonation of [Co2(CO)4{µ-(RO)2PN(Et)P(OR)2}2](R = Me or Pri) proceeds without CO loss to give [Co2(µ-H)(CO)4{µ-(RO)2PN(Et)P(OR)2}2]+. Proton n.m.r. spectroscopic data, as well as an X-ray structure determination of [Co2(µ-H)(CO)4{µ-(MeO)2PN(Et)P(OMe)2}2]BPh4, confirm the presence of a bridging hydride ligand. Both cobalt atoms are trigonal bipyramidal but the overall conformation is staggered as evidenced by P–Co–Co–P torsion angles of 34.7(1) and 35.7(1)°. Attempts to form a dihydrido species by addition of H– merely served to deprotonate the cation with formation of the starting complex and H2.

The synthesis and characterisation of 4′-(2‴-methylphenyl)-2,2′:6′,2″-terpyridine [4′-(o-CH3–Ph)trpy] and 4′-(2‴-trifluoromethylphenyl)-2,2′:6′,2″-terpyridine [4′-(o-CF3–Ph)trpy] are described. Reaction of these ligands with [Pt(PhCN)2Cl2] in the presence of the appropriate silver salt afforded [Pt{4′-(o-CH3–Ph)trpy}Cl]A and [Pt{4′-(o-CF3–Ph)trpy}Cl]A (A = BF4 or SbF6). The crystal structure of the SbF6− salt of the [Pt{4′-(o-CH3–Ph)trpy}Cl]+ cation consists of columns of cations and anions with the cations stacked parallel and head-to-tail and with a constant Pt⋯Pt distance [3.368(1) A] and interplanar spacing (3.36 A) along the stack. Crystals of the BF4− salt also contain columns of cations and anions with the cations stacked parallel and head-to-tail. However, the platinum atoms of successive cation pairs are offset to different extents with respect to a line drawn perpendicular to the stack. As a result the Pt⋯Pt distances along the stack alternate between 3.573(1) and 3.827(1) A while the interplanar spacing is within experimental error, constant at an average value of 3.42 A. The [Pt{4′-(o-CF3–Ph)trpy}Cl]SbF6 salt exhibits the same packing motif but with alternating Pt⋯Pt distances of 3.629(1) and 3.685(1) A and an average interplanar spacing of 3.46 A. The variable temperature emission spectra recorded on microcrystalline samples of these compounds reflect the environments of the cations in the crystals. The red [Pt{4′-(o-CH3–Ph)trpy}Cl]SbF6 salt exhibits 3MMLCT (MMLCT = metal–metal–ligand-charge-transfer) emission [λ(em)max = 616 nm] that is distinguished by a large red-shift of ca. 60 nm in the emission maximum when the sample is cooled from room temperature to 80 K; such a red-shift is associated with strong platinum dz2–dz2 orbital interactions perpendicular to the cation stack. The other three salts are yellow with broad featureless emission spectra that do not change position when the temperature is lowered but which are red-shifted when compared to the low temperature dilute glass spectrum recorded for [Pt{4′-(o-CH3–Ph)trpy}Cl]SbF6 in a dimethylformamide/methanol/ethanol (1 ∶ 5 ∶ 5) mixture; this is interpreted in terms of excimeric emission consistent with the presence of π–π interactions in the solid. The roles of the ortho-substituents (CH3 and CF3) and the anions (SbF6− and BF4−) in determining the precise arrangements of the cations in the crystals and hence the photoluminescence properties of these materials are briefly discussed.

Treatment of [M(η-C5H5)(CO)32] (M = Mo or W) with diiodine in ethanol at O°C in the presence of Na[B(C6H5)4] produces the iodine-bridged derivative [(M(η-C5H5)(CO)32(μ-I)] [B(C6H5)4] [IV-B(C6H5)4]. IV is an intermediate in the formation of [M(η-C5H5)(CO)3I] from [(M(η-C5H5)(CO)32] and I2 in dichloromethane as shown by monitoring with IR and, consistent with this, iodide attack on this bridged species gives [M(η-C5H5)(CO)3I]. IV is also susceptible to nucleophilic attack by neutral donors such as acetone, pyridine, P(C6H5)3 and P(OCH3)3. The reaction of the substituted derivatives [Mo(η-C5H5)(CO)2P(OCH3)32] with an equimolar amount of diiodine in ethanol in the presence of Na(B(C6H5)4] also affords a bridged iodo product, viz. [Mo(η-C5H5)(CO)2P(OCH3)3 2(μ-I)[B(C6H5)4] although if an excess of diiodine is employed the molybdenum (IV) species [Mo(η-C5H5)(CO)P(OCH3)3I3] is formed. Bromination and chlorination of [(M(η-C5H5)(CO)32] and [Mo(η-C5H5)(CO)2P(OCH3)32] always gives rise to molybdenum (IV) derivatives, [M(η-C5H5)(CO)2X3] or [Mo(η-C5H5)(CO)P(OCH3)3X3], as well as the molybdenum (II) products [M(η-C5H5)(CO)3X] or [Mo(η-C5H5)(CO)2 P(OCH3)3X] (X = Br or Cl), irrespective of the molar ratios employed. The tertiary phosphinemolybdenum (IV) compounds [Mo(η-C5H5)(CO)LX3] L = P(C2H5)3 or P(CH3)2C6H5, L ≠ P(C6H5)3; X = Cl Br or I are produced by treatment of the corresponding molybdenum (II) derivatives [Mo(η-C5H5)(CO)2LX] with the appropriate dihalogen. A mechanism for the halogenation of [(M(η-C5H5)(CO)2L2] (L = CO or P(OCH)3)3) is proposed.

The synthesis of [Mo(η-C 5 H 5 )(CO) 2 LI] (L = CO or P(OCH 3 ) 3 ) and [W(η-C 5 H 5 )(CO) 3 I] by iodination of [{Mo(η-C 5 H 5 )(CO) 2 L} 2 ] and [{W(η-C 5 H 5 )(CO) 5 } 2 ], respectively, is shown to proceed via iodide bridged intermediates, [{M(η-C 5 H 5 )(CO) 2 L} 2 I] + (M = Mo or W); treatment of [Mo(η-C 5 H 5 )(CO) 2 LX] {X = CI, Br or I; L =CO, P(C 2 H 5 ) 3 , P(CH 3 ) 2 C 6 H 5 or P(OCH 3 ) 3 ; L ≠ P(C 6 H 5 ) 3 } with excess halogen leads to the formation of the molybdenum(IV) derivatives, [Mo(η-C 5 H 5 )(CO)LX 3 ].

Protonation of the dinuclear compounds [M 2 (μ-CO)(CO) 4 (μ-R 2 PYPR 2 ) 2 ] by HBF 4 or HPF 6 leads to the formation of crystalline cationic hydrido products [M 2 H(CO) 5 (μ-R 2 PYPR 2 ) 2 ]X and [M 2 (μ-H)(μ-CO)(CO) 4 (μ-R 2 PYPR 2 ) 2 ]X (X = BF 4 or PF 6 ) in which the hydride ligand is terminal for M = Ru, Y = N(Et) and R = OMe or OPr i and bridging for M = Fe, Y = CH 2 and R = Me or Ph, for M = Fe, Y = N(Et) and R = OMe, OEt, OPr i or OPh and for M = Ru, Y = CH 2 and R = Ph; the fluxional behaviour of [Ru 2 H(CO) 5 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ] + (R = Me or Pr i ) in solution is described.

[Ru4(μ4-PPh)2(μ2-CO)(CO)10], in which an essentially square planar array of ruthenium atoms is capped by two phenylphosphinidene groups, readily and reversibly adds carbon monoxide to afford the tridecacarbonyl derivative [Ru4(μ3-PPh)2 (CO)13] ; crystal structure determinations on this compound and its arsenic analogue reveal that the CO addition is accompanied by a re arrangement of the cluster framework, and that these compounds can be considered as dirivatives of [Ru3(μ3-XPh)2(CO)9] (X  P or As) in which an Ru(CO)4 unit has been inserted into one of the three RuP or RuAs bonds.

The reaction of [Ru3(CO)12] with PPhH2 in toluene under reflux affords a range of products, the nature and yields of which are dependent on the reaction times and the molar ratios employed. Compounds isolated and characterised include not only the trinuclear derivatives [Ru3(µ-PPhH)(µ-H)(CO)10], [Ru3(µ3-PPh)(µ-H)2(CO)9], and [Ru3(µ3-PPh)2(CO)9] but the tetra-, and penta-, and hexanuclear species [Ru4(µ4-PPh)2(µ-CO)(CO)10], [Ru4(µ4-PPh)2(µ-PPhH)2(CO)8], [Ru5(µ4-PPh)(CO)15], [Ru6(µ-PPh)2(CO)n](n= 14 or 15), [Ru6(µ4-PPh)2(µ3-PPh)2(CO)12], and [Ru6(µ4-PPh)3(µ3-PPh)2(CO)12] as well as the pentanuclear by-product [Ru5(µ4-PPh){µ-PPh(OPrn)}(µ-H)(CO)13]. Crystal-structure determinations have revealed that [Ru4(µ4-PPh)2(µ-CO)(CO)10] contains an approximately square-planar array of ruthenium atoms capped on both sides by phenylphosphinidene ligands, that [Ru6(µ4-PPh)2(µ3-PPh)2(CO)12] and [Ru6(µ4-PPh)3(µ3-PPh)2(CO)12] have distorted trigonal-prismatic skeletal geometries, and that the ruthenium atom framework in [Ru5(µ4-PPh){µ-PPh(OPrn)}(µ-H)(CO)13] adopts a square-pyramidal configuration with the basal plane being capped by a phenylphosphinidene ligand and a basal edge being bridged by a phosphido group.

The diphosphazane ligand (CH 2 O) 2 PN(Et)P(OCH 2 ) 2 reacts readily with [Co 2 (CO) 8 ] to form the red-black complex [Co 2 (CO) 4 μ-(CH 2 O) 2 PN(Et)P(OCH 2 ) 2 2 ]. A single crystal X-ray diffraction study of this complex shows the two cobalt atoms linked by a metalmetal bond of length 2.635(2) A, and by two bridging diphosphazane ligands. Both cobalt atoms are five-coordinate with an identical set of ligands, comprising the other cobalt atom, two carbonyl groups and two phosphorus donor atoms. However, one cobalt atom has near trigonal-bipyramidal coordination while the other has highly distorted square-pyramidal coordination, the apical positions in both cases being occupied by phosphorus atoms. Significantly, the different coordination at each cobalt atom is achieved by the twisting of each diphosphazane ligand about the CoCo bond; the CoPPCo torsion angles are 29 and 40°. Indeed, in solution, rapid twisting of the diphosphazane ligands renders the phosphorus atoms equivalent on the NMR time scale, as evidenced by a single peak in the 31 P 1 H NMR spectrum of the molecule. The solution and solid state structures of the title compound are compared with those previously reported for teh closely-related complex [Co 2 (CO) 4 μ-(MeO) 2 PN(Et)P(OMe) 2 2 ].

Reaction of [Ru 3 (CO) 12 ] with an equimolar amount of PPh 2 H affords a range of products including an octaruthenium species [Ru 8 (μ 8 -P)(μ 2 -η 1 ,η 6 -CH 2 C 6 H 5 )(μ 2 -CO) 2 (CO) 17 ], in which, as established X-ray crystallographically, a phosphorus atom is encapsulated in a square anti-prism of ruthenium atoms and a benzyl group is coordinated to two of these rutheniums through all seven carbon atoms.

Reaction of [Ru 3 (CO) 12 ] with a two molar proportion of (RO) 2 PN(Et)P(OR) 2 (R = Me or Pr i ) in benzene under reflux affords a number of products including [Ru 3 (CO) 10 {μ-(RO) 2 PN(Et)P(OR) 2 }], [Ru 3 (CO) 9 {μ-(RO) 2 PN(Et)P(OR) 2 }{η 1 -(RO) 2 PN(Et)P(OR) 2 }] and, as the major species, the tetranuclear derivative [Ru 4 (μ 3 -η 2 -CO)(CO) 9 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ]. An X-ray diffraction study of [Ru 4 (μ 3 -η 2 -CO)(CO) 9 {μ-(MeO) 2 PN(Et)P(OMe) 2 } 2 ] has revealed that the skeletal framework adopts a butterfly structure and that one of the carbonyl groups functions as a triply bridging four-electron donor ligand capping the two wing-tip and one of the hinge ruthenium atoms.

Treatment of [M 2 (μ-CO)(CO) 4 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ] (M  Fe or Ru; R  Me, Pr i or Ph) with halogens gives [M 2 X(CO) 5 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ]X (X  Cl, Br or I) which can be readily decarbonylated to [M 2 (μ-X)(CO) 4 {μ-(RO) 2 -PN(Et)(OR) 2 } 2 ]X (M  Fe or Ru), [M 2 (μ-X)X(CO) 3 {μ-(RO) 2 PN(Et)-P(OR) 2 } 2 ] (M  Ru) and [M 2 (μ-X) 2 (CO) 2 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ] (M  Ru) under appropriate reaction conditions; the structures of [Fe 2 I(CO) 5 {μ-(MeO) 2 PN(Et)P(OMe) 2 }]PF 6 and [Ru 2 (μ-I)I(CO) 3 {μ-(Pr i O) 2 PN(Et)P(OPr i ) 2 } 2 ] have been established X-ray crystallographically.

Dissolution of [Fe 2 (μ-CO)(CO) 4 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ] (R = Me, Pr i or Ph) and [Ru 2 (μ-CO)(CO) 4 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ](R = Me or Pr i ) in CCl 4 leads to the rapid formation of [Fe 2 (μ-Cl)(CO) 4 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ]Cl and [Ru 2 Cl 2 (CO) 4 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ], respectively, with the latter isomerising in dichloromethane or chloroform solution to [Ru 2 (μ-Cl)(Cl(CO) 4 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ]Cl, which in turn decarbonylates to [Ru 2 (μ-Cl)Cl(CO) 3 {μ-(RO) 2 PN(Et)P(OR) 2 } 2 ]; the structure of [Ru 2 Cl 2 (CO) 4 {μ-(MeO) 2 PN(Et)P(OMe) 2 } 2 ] has been established X-ray crystallographically.

Cyclic voltammetric studies in acetone and benzonitrile show that the oxidation of [M2(η-CO)(CO)4(η-R2PYPR2)2] (M  Fe, Y  CH2, R  Ph or Me; M  Fe, Y  NEt, R  OMe, PRri or OEt; M  Ru, Y  NEt, R  OPri) generally proceeds via an EEC mechanism, whereas oxidation of [Ru2(η-CO)(CO)4 {η-(MeO)2PN(Et)-P(OMe)2}2] proceeds via an ECE mechanism, for which removal of the second electron is easier than the first, giving rise to an overall 2e-transfer reaction. In both mechanisms the chemical step involves solvent attack.

The reaction of [{Rh(µ-Cl)(CO)2}2] with PPh2H in benzene affords the mononuclear complex [RhCl(CO)(PPh2H)2] for a molar ratio of 1 : 4 and the trinuclear derivative [Rh3(µ-PPh2)3(µ-Cl)2(µ-CO)(CO)3], for a molar ratio of 1 : 2. The structure of the trinuclear derivative has been determined by X-ray crystallography. It crystallises in the monoclinic space group P21/n, with a= 12.461(5), b= 32.867(5), c= 11.149(5)A, β= 99.29(1)°, Z= 4, and R= 0.085. The metal atoms adopt a triangular configuration with each edge of the triangle being bridged by a diphenylphosphido-group as well as by either a chloro or a carbonyl group. In spite of this compound being a 50-electron system, all of the Rh–Rh distances correspond with those normally associated with a formal rhodium–rhodium bond. The chloro-groups in this compound can be extracted as radicals by the addition of NEt2H, affording, in the presence of CO, [Rh3(µ-PPh2)3(CO)5], or displaced as chloride ions by treatment of the complex with AgSbF6; the former reaction is a reversible process with dissolution of [Rh3(µ-PPh2)3(CO)5] in CCl4 resulting in the regeneration of the title complex. [Rh3(µ-PPh2)3(µ-Cl)2(µ-CO)(CO)3] is only moderately stable in solution and converts slowly to an insoluble species formulated as [{Rh(µ-PPh2)(µ-Cl)(CO)}n].

Treatment of [Ru4(μ4-PPh)2(μ2-CO)(CO)10] with NaBH4 leads to the formation of [Ru4(μ4-PPh)2(μ2-H)(μ2-CO)2(CO)8]− which readily adds protons and carbon monoxide to produce [Ru4(μ3-PPh)2(μ2-H)2(CO)12]; X-ray crystallographic studies have revealed that while the Ru4P2 framework adopts a closo octahedral geometry in [Ru4(μ4-PPh)2(μ2-H)(μ2-CO)2(CO)8]−, it adopts a closo trigonal prismatic one in [Ru4(μ3-PPh)2(μ2-H)2(CO)12]

The pentacoordinate rhodium nitrosyl complexes [RhBr2(NO)L2 [L = P(OPh)2Ph, P(OMe)Ph2 or P(OPri)Ph2] have been synthesized and the structures of [RhBr2(NO){P(OMe)Ph2}2] and [RhBr2(NO){P(OPri)Ph2}2] have been determined X-ray crystallographically. Both of these latter compounds are tetragonal pyramidal with the nitrosyl group apical. The methoxydiphenylphosphine ligands in [RhBr2(NO){P(OMe)Ph2}2] are cis-disposed whereas the larger cis-propoxydiphenylphosphine ligands in [RhBr2(NO){P(OPri)Ph2}2] are mutually trans. The nitrosyl group in trans-[RhBr2(NO){P(OPri)Ph2}2] eclipses an Rh-P axis but in cis-[RhBr2(NO){P(OMe)Ph2}2] it is staggered with respect to the P-Rh-P linkage. The isomeric behaviour of nitrosyl complexes of type [RhX2(NO)L2] (X = halogen, L = phosphorus donor ligand) is rationalized in terms of the size of the ligand L.

Treatment of [Mn(MeC5H4)(CO)2(SEt)]–, prepared in situ from [Mn(MeC5H4)(CO)2(thf)] and [SEt]–, with perchloric acid in aqueous tetrahydrofuran leads to the formation of the unusual monothio-bridged derivative [{Mn(MeC5H4)(CO)2}2(SEt)][ClO4], in which the manganese atoms are joined by a metal–metal bond (MeC5H4=η-methylcyclopentadienyl). A crystal structure determination by the heavy-atom method from diffractometer data of this complex reveals the cyclopentadienyl groups to be trans, and Mn–Mn 2.930(1)A. Crystals are monoclinic, space group P21/n, Z= 4, a= 8.676(5), b= 16.062(5), c= 15.872(5)A, β= 104.45(20)°, and the structure was refined to R 0.51 for 1 785 observed reflections. The compound undergoes two reversible one-electron reductions as established by cyclic voltammetry and polarography.

Treatment of closo -[Ru 4 (μ 4 -PPh) 2 (μ 2 -CO)(CO) 10 ] with acetylene under ambient conditions leads to the insertion of the acetylene into the skeletal framework of the cluster and the formation of [Ru 4 (μ 4 -PPh){μ 4 -η 3 -P(Ph)CHCH}(μ 2 -CO)(CO) 10 ], the structure of which has been determined X-ray crystallographically.

The tertiary alkyl phosphites P(OR) 3 (R = CH 3 , C 2 H 5 , n-C 4 H 9 and C 3 H 5 ) react with π-C 5 H 5 Fe(CO) 2 Cl in benzene to give in addition to neutral π-C 5 H 5 Fe(CO)P(OR) 3 Cl and ionic [π-C 5 H 5 Fe(CO) 2 P(OR) 3 ]Cl complexes, neutral phosphonate derivatives of formula π-C 5 H 5 Fe(CO) 2 [P(O)(OR) 2 ] and π-C 5 H 5 Fe(CO)-[P(OR) 3 ][P(O)(OR) 2 ]. The corresponding reactions involving the tertiary phosphonite P(OC 3 H 5 ) 2 C 6 H 5 and the tertiary phosphinite P(OC 3 H 5 )(C 6 H 5 ) 2 yield similar type products. In contrast compounds of the type [π-C 5 H 5 Fe(CO)P(OR) 3 ]I are the sole products from the reactions of P(OR) 3 (R = CH 3 and C 2 H 5 ) with π-C 5 H 5 Fe(CO) 2 I. The formation of π-C 5 H 5 Fe(CO) 2 [P(O)(OR) 2 ] is shown to occur via [π-C 5 H 5 Fe(CO) 2 P(OR) 3 ]Cl as intermediate and to involve a Michaelis-Arbuzov rearrangement. The reactions of π-C 5 H 5 Fe(CO) 2 X (X = Cl and I) with the tertiary phosphines PR 3 (R = C 2 H 5 and C 4 H 9 ) are also described.

The preparation of the title compound is reported. Crystals are monoclinic, a= 9·527(4), b= 15·381(6), c= 15·518(7)A, β= 105·09(5)°, Z= 4, space group P21/c. The structure was determined by Patterson and Fourier methods from diffractometer data and refined by least-squares methods to a final R of 0·032 for 2048 reflections. The ruthenium atom is sandwiched between the cyclopentadienyl ring and one of the phenyl rings of the tetraphenylborate anion. The rings are planar, parallel, and 3·52 A apart.

X-ray diffraction shows that [Rh 2 (CO) 3 {(PhO) 2 PN(Et)P(OPh) 2 } 2 ], synthesised by reduction of [{RhCl(CO)(PhO) 2 PN(Et)P(OPh) 2 } 2 ] with amalgamated zinc in the presence of carbon monoxide, has an unusual structure with one rhodium atom square planar and the other trigonal bipyramidal.

The structure of one isomer of [Rh 3 Fe{P(C 6 H 5 ) 2 } 3 (CO) 8 ], synthesised by treatment of [ {Rh(CO) 2 Cl} 2 ] with [Fe(CO) 4 {P(C 6 H 5 ) 2 H} ] in the presence of a base, has been determined by single crystal X-ray diffration. This species rearranges in solution to a second isomer whose structure has been elucidated by 31 P NMR spectral measurements. The reactions of these compounds with carbon monoxide are described.

The reaction of [{Rh(CO) 2 Cl} 2 ] with PPh 2 H in benzene in the presence of a base affords a green product [Rh 3 (μ-PPh 2 ) 3 (CO) 5 ], the structure of which has been determined by X-ray crystallography.

Reaction of [{Rh(μ-Cl)(CO)2}2] with PPh2H in CO-saturated ethanol yields [Rh3(μ-PPh2)3 (CO)6 (PPh2H)], a red trinuclear cluster of rhodium containing a near-planar six-membered Rh3P3 ring; this compound reversibly undergoes elimination of CO and PPh2H to afford [Rh3(μ-PPh2)3(CO)5].

Treatment of [{Rh(diene)Cl}2](diene = C8H12 or C7H8) with the ditertiary phosphite (PhO)2PN(Et)P(OPh)2(etdp) in benzene leads to successive replacement of the diene ligands and the formation of [Rh2(diene)(etdp)Cl2] and [{Rh(etdp)Cl}2]. The corresponding bromo- and iodo- derivatives [{Rh(etdp)X}2](X = Br or I) are produced analogously. Reactions of [{Rh(C8H12)Cl}2] with excess of etdp in ethanol or methanol in the presence of a suitable counter ion effects not only the displacement of the diene ligands but also the halogens as halide ions to afford [Rh(etdp)2][A](A = BPh4 or SbF6). Carbon monoxide reacts reversibly with [Rh(etdp)2]+ and [Rh(C8H12)(etdp)]+ obtained by treatment of [Rh(C8H12)(solvent)x]+ with etdp, to yield [Rh(etdp)2(CO)]+ and [Rh(C8H12)(etdp)(CO)]+ respectively. Reaction of [Rh(etdp)2]+ with HBr and Br2 gives trans-[Rh(etdp)2H(Br)]+ and [Rh(etdp)2Br2]+ respectively, although the former degrades to [Rh(etdp)2]+ in solution.

Tetraethyl diphosphite (L1) forms complexes [M2Cl4L12](M = Pd or Pt), [Pt2Cl4L1(PMe2Ph)2](2), and [Pt2L12(PMe2Ph)4][BPh4]4 in which it forms bidentate bridges between two metal atoms. Bis(OO′-ethylene) diphosphite (L2) is unidentate in cis-[MCl2L22](M = Pd or Pt) and bridging in (2) and in similar complexes. 1,1,3,3-Tetraethoxy-2-ethyldiphosphazane (L4) and 2-ethyl-1,1,3,3-tetraphenoxydiphosphazane (L5) form chelate complexes [MCl2L](M = Pt, L = L4; M = Pd or Pt, L = L5). Explanations are offered for the differences in stoicheiometry of the complexes formed by these ligands.

Reaction of [{Rh(µ-Cl)(CO)2}2] with PPh2H in benzene affords, in the presence of a base and under an atmosphere of CO, a yellow crystalline product, believed to be [Rh3(µ-PPh2)3(CO)9] and which degrades to an orange-red species, characterised as the heptacarbonyl [Rh3(µ-PPh2)3(CO)7], on recrystallisation from methanol under CO at 15 °C. The same reaction in ethanol, also under an atmosphere of CO but in the absence of a base, gave an orange-red crystalline derivative established to be [Rh3(µ-PPh2)3(CO)6(PPh2H)]. All three complexes are unstable under any atmosphere but CO and are readily and reversibly decarbonylated, with loss of PPh2H as well in the case of [Rh3(µ-PPh2)3(CO)6(PPh2H)], to a green crystalline species characterized as [Rh3(µ-PPh2)3(CO)5]. The latter condenses slowly in polar solvents to afford the tetranuclear cluster [Rh4(µ-PPh2)4(µ-CO)2(CO)4] while it reacts with Cl2 to give the 50-electron species [Rh3(µ-PPh2)3(µ-Cl)2(µ-CO)(CO)3]. Crystal structure determinations on [Rh3(µ-PPh2)3(CO)5][monoclinic, space group P21/n, a= 14.003(5), b= 17.471 (5), c= 16.523(5)A, β= 103.76(5)°, and Z= 4], [Rh3(µ-PPh2)3(CO)7][monoclinic, space group P21/c, a= 18.16(1), b= 17.935(10), c= 13.119(10)A, β= 103.5(1)°, and Z= 4], and [Rh3(µ-PPh2)3(CO)6(PPh2H)][monoclinic, space group P21/c, a= 12.515(5), b= 11.843(5), c= 37.102(5)A, β= 94.6(1)°, and Z= 4] have revealed that addition of PPh2H and/or CO to the pentacarbonyl compound is accompanied by an expansion of the Rh3P3 ring from an average Rh–Rh distance of 2.766 A to one of 3.15 A for [Rh3(µ-PPh2)3(CO)7] and one of 3.165 A for [Rh3(µ-PPh2)3(CO)6(PPh2H)].