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Phosphane, PH3—a highly pyrophoric and toxic gas—is frequently contaminated with H2 and P2H4, which makes its handling even more dangerous. The inexpensive metal–organic framework (MOF) magnesium formate, α-[Mg(O2CH)2], can adsorb up to 10 wt % of PH3. The PH3-loaded MOF, PH3@α-[Mg(O2CH)2], is a non-pyrophoric, recoverable material that even allows brief handling in air, thereby minimizing the hazards associated with the handling and transport of phosphane. α-[Mg(O2CH)2] further plays a critical role in purifying PH3 from H2 and P2H4: at 25 °C, H2 passes through the MOF channels without adsorption, whereas PH3 adsorbs readily and only slowly desorbs under a flow of inert gas (complete desorption time≈6 h). Diphosphane, P2H4, is strongly adsorbed and trapped within the MOF for at least 4 months. P2H4@α-[Mg(O2CH)2] itself is not pyrophoric and is air- and light-stable at room temperature., Angewandte Chemie. International Edition, 62 (13), ISSN:1433-7851, ISSN:1521-3773, ISSN:0570-0833

Bismesitoylphosphinic acid, (HO)PO(COMes)2 (BAPO-OH), is an efficient photoinitiator for free-radical polymerizations of olefins in aqueous phase. Described here are the structures of various copper(II) and copper(I) complexes with BAPO-OH as the ligand. The complex CuII (BAPO-O)2 (H2 O)2 is photoactive, and under irradiation with UV light in aqueous phase, it serves as a source of metallic copper in high purity and yield (>80 %). Simultaneously, the radical polymerization of acrylates can be initiated and allows the preparation of nanoparticle/polymer nanocomposites in which the metallic Cu nanoparticles are protected against oxidation. The determination of the stoichiometry of the photoreductions suggests an almost quantitative conversion from CuII into Cu0 with half an equivalent of BAPO-OH, which serves as a four-electron photoreductant.

Keywords: phosphorus; photoinitiators; polymers; radical polymerization; surface modification Thumbnail image of graphical abstract Got a light? An efficient method for the synthesis of phosphorus functionalized bis(acyl)phosphaneoxides (BAPOs) was developed which allows the preparation of photoactive polymers or grafting of these photoinitiators to various surfaces. Irradiation in the presence of polymerizable monomers leads to coatings that can be deposited imagewise.

Pentaphenylcyclopentaphosphane, c-(P5Ph5) is conviently prepared from PhPCl2 and thermally activated zinc powder in thf. Hydrolysis of c-(P5Ph5) in the presence of ZnCl2 gives to an equimolar distribution of PhPH2, PhP(=O)H2, and PhP(=O)(OH)H. Reaction of c-(P5Ph5) with CuICl leads to the tetranuclear copper(I) chloride complex [Cu4(μ4-Cl)2(μ2-Cl)2{c-(P5Ph5)}2] with a Cu4(μ4-Cl)2(μ2-Cl)2 cluster core and the hexanuclear [Cu6(μ3-Cl)2(μ2-Cl)2{c-(P5Ph5)}2(thf)2]. Hydrolysis of the copper c-(P5Ph5) complexes leads to significantly higher amounts of the primary phosphane oxide PhP(=O)H2.

The chiral tetrachelating amino−olefins (R,R)-N,N‘-bis(5H-dibenzo[a,d]cyclohepten-5-yl)-1,2-diaminocyclohexane ((R,R)-trop2dach) and (S,S)-N,N‘-bis(5H-dibenzo[a,d]cyclohepten-5-yl)-1,2-diphenyl-1,2-ethylenediamine ((S,S)-trop2dpen) were prepared and used as ligands in the complexes (R,R)-[Rh(trop2dach)]OTf and (S,S)-[Rh(trop2dpen)]OTf (OTf- = CF3SO3-). Quasi-reversible reductions, d8-[RhI(trop2diamine)]+ + e- → d9-[Rh0(trop2diamine)] and d9-[Rh0(trop2diamine)] + e- → d10-[Rh-I(trop2diamine)]-, at rather negative potentials (trop2diamine = trop2dach, E1/21 = −1.83 V, E1/22 = −2.27 V; trop2diamine = trop2dpen, E1/21 = −1.78 V, E1/22 = −2.24 V; vs Fc+/Fc) indicate the donor capacity of the amine functions. One NH group in (R,R)-[Rh(trop2dach)]OTf (pKa = 15.7(2), NH bond dissociation energy (BDE) 317(2) kJ mol-1) is easily deprotonated to give the neutral amide (R,R)-[Rh(trop2dach-H)], which is quasi-reversibly oxidized at E° = −0.34 V (vs Fc/Fc+) to the radical cation (R,R)-[Rh(trop2dach-H)]•+. The pKa and B...

The tetra-chelating ligands 1,2-bis[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphanyl]-ethane, bis(troppPh)ethane, and 1,3-bis[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphanyl]-propane, bis(troppPh)propane, were synthesised. For the binding of transition metals, these ligands offer two olefin moieties and two phosphorus centres and form mixtures of diastereomers with a R,S-configuration at the phosphorus centres (meso), or a R,R(S,S)-configuration (rac), respectively. meso/rac-bis(troppPh)ethane was separated by fractional crystallisation and reacted with [Ir(cod)2]OTf (cod=cylcooctadiene, OTf−=CF3SO3 −) to give the penta-coordinated complex-cations meso/rac-[Ir(bis(troppPh)ethane)(cod)]+, where the bis(troppPh)ethane serves as tridentate ligand merely. One olefin unit remains non-bonded, however, a slow intra-molecular exchange between this olefin and the coordinated olefin unit was established (meso-[Ir(bis(troppPh)ethane)(cod)]+: k

The redox chemistry of the stable tetracoordinated 16 valence electron d8-[Ir+I(troppPh)2]+(PF6)- and pentacoordinated 18 valence d8-[Ir+I(troppPh)2Cl] complexes was investigated by cyclic voltammetry (troppPh=dibenzotropylidenyl phosphine). The experiments were performed using a platinum microelectrode varying scan rates (100 mV/s-10 V/s) and temperatures (- 40 to 20 °C) in tetrahydrofuran, THF, or acetonitrile, ACN, as solvents. In THF, the overall two-electron reduction of the 16 valence electron d8-[Ir+I(troppPh)2]+(PF6)- proceeds in two well separated slow heterogeneous electron transfer steps according to: d8-[Ir+I (troppPh)2]++e-d9-[Ir0(troppPh)2]+e-d10-[Ir-I(troppPh)2]-, [ks1=2.2×10-3 cm/s for d8-Ir+I/d9-Ir0 and ks2=2.0×10-3 cm/s for d9-Ir0/d10-Ir-I]. In ACN, the two redox waves merge into one two-electron wave [ks1, 2=7.76×10-4 cm/s for d8-Ir+I/d9-Ir0 and d9-Ir0/d10-Ir-I] most likely because the neutral [Ir0(troppPh)2] complex is destabilized. At low temperatures (ca. - 40 °C) and at high scan rates (ca. 10 V/s), the two-electon redox process is kinetically resolved. In equilibrium with the tetracoordianted complex [Ir+I(troppPh)2]+ are the pentacoordinated 18 valence [Ir+I(troppPh)2L]+ complexes (L=THF, ACN, Cl-) and their electrochemical behavior was also investigated. They are irreversibly reduced at rather high negative potentials (- 1.8 to - 2.4 V) according to an ECE mechanism 1) [Ir+I(troppPh)2(L)]+e-[Ir0(troppPh)2(L)] ; 2) [Ir0(troppPh)2(L)][Ir(troppPh)2]+L, iii) [Ir0(troppPh)2]+e-[Ir-I(troppPh)2]-. Since all electroactive species were isolated and structurally characterized, our measurements allow for the first time a detailed insight into some fundamental aspects of the coordination chemistry of iridium complexes in unusually low formal oxidation states.

The new tetrachelating diphosphanes 1,2-[(5H-dibenzo[a,d]cyclohepten-5-yl)phenylphosphano]ethane, R,S-11 [R,S-bis(troppPh)], and the corresponding enantiomers R,R-bis(troppPh), R,R-12, and S,S-bis(troppPh), S,S-12, were synthesised from 1,2-bis(phenylphosphano)ethane (9), and 5-chloro-5H-dibenzo[a,d]cycloheptene (10). With the meso form R,S-11, the rhodium(I) complex [Rh{R,S-bis(troppPh)}]PF6 (15), and the iridium(I) complex [Ir(cod){R,S-bis(troppPh)}]O3SCF3 (16), were prepared. The cation of the 16-electron rhodium complex 15 has a square planar structure, which is markedly distorted towards a square pyramid with the rhodium centre in the apex. The structure of the cation of the 18-electron complex of 16 is trigonal bipyramidal and unprecedented a phosphorus and an olefin unit occupy the axial positions. Cyclic voltammetry data of 15 indicate, that considerable strain energy (ca. 30 kJ mol−1) is build up when the [Rh{R,S-bis(troppPh)}]+ cation is reversibly reduced in THF by one electron to the paramagnetic neutral complex [Rh{R,S-bis(troppPh)}]0.

The reactions of three different tetracoordinated Ir complexes, [Ir(troppph)2]n (n=+1, 0, −1), which differ in the formal oxidation state of the metal from +1 to −1, with proton sources and dihydrogen were investigated (tropp=5-(diphenylphosphanyl)dibenzo[a,d]cycloheptene). It was found that the cationic 16-electron complex [Ir(troppph)2]+ (2) cannot be protonated but reacts with NaBH4 to the very stable 18-electron IrI hydride [IrH(troppph)2] (5), which is further protonated with medium strong acids to give the 18-electron IrIII dihydride [IrH2(troppph)2]+ (6; pKs in CH2Cl2/THF/H2O 1 : 1 : 2 ca. 2.2). Both, the neutral 17-electron Ir0 complex [Ir(troppph)2] (3) and the anionic 18-electron complex [Ir(troppph)2]− (4) react rapidly with H2O to give the monohydride 5. In reactions of 3 with H2O, the terminal IrI hydroxide [Ir(OH)(troppph)2] (8) is formed in equal amounts. All these complexes, apart from 5, which is inert, do react rapidly with dihydrogen. The complex 2 gives the dihydride 6 in an oxidative addition reaction, while 3, 4, and 8 give the monohydride 5. Interestingly, a salt-type hydride (i.e., LiH) is formed as further product in the unexpected reaction with [Li(thf)x]+[Ir(troppph)2]− (4). Because 3 undergoes disproportionation into 2 and 4 according to 2 3⇄2+4 (Kdisp=2.7⋅10−5), it is likely that actually the diamagnetic species and not the odd-electron complex 3 is involved in the reactions studied here, and possible mechanisms for these are discussed.

A synthesis of the new ligand 5-diphenylphosphanyl-10-methyl-5H-dibenzo[a,d]cycloheptene (metroppph) was developed in order to prepare highly distorted tetra-co-ordinated rhodium(+I) complexes. The ligand metroppph contains a cycloheptatriene ring in a rigid boat conformation such that a Ph2P and an olefinic binding site are perfectly arranged for transition metal complexation. Four equivalents of metroppph react with [Rh2(μ-Cl)2(cod)2] in the presence of KPF6 to yield almost quantitatively [Rh(+I)(metroppph)2]PF6, which was isolated in the form of dark red-violet crystals. A crystal structure analysis reveals that the co-ordination sphere of the rhodium centre in [Rh(+I)(metroppph)2]+ deviates strongly from a square planar arrangement (φ = 42°). One methyl group in [Rh(+I)(metroppph)2]+ can be deprotonated by KOBut to give the allyl complex [Rh(allyltroppph)(metroppph)]. This complex has a structure that may be best described as a distorted trigonal bipyramid. The boron hydride [BEt3H]− and organolithium reagents, LiR, react with [Rh(allyltroppph)(metroppph)] in allylic alkylation reactions to yield anionic rhodate complexes [Rh(RCH2troppph)(metroppph)]− (R = H, Me, n-Bu, Ph) that formally have a d10 valence electron configuration. The rhodate [Rh(metroppph)2]− can be obtained directly by reduction of cation [Rh(metroppph)2]+ with alkali metals. In a sym-proportionation reaction [Rh(metroppph)2]+ and [Rh(metroppph)2]− give the neutral d9-[Rh(metroppph)2] radical (K = 1.1 × 107), which is not stable but decomposes with loss of H2 to give the allyl complex [Rh(allyltroppph)(metroppph)]. The structures in solution of [Rh(metroppph)2]+, [Rh(allyltroppph)(metroppph)], and [Rh(nBuCH2troppph)(metroppph)]− were determined by NMR techniques, which reveal that (i) they match the solid state structures and (ii) are rather similar to each other. This fact may explain the remarkable electronic flexibility of the rhodium centre, which changes reversibly its formal oxidation state from + I to 0 to − I at rather low negative potentials (ΔE01 = − 0.882 V; ΔE02 = − 1.298 V).

Many catalytic active transition metal complexes contain phosphines as ligands which control decisively the activity and selectivity of the catalyst. Therefore synthetic methods which allow the preparation of highly functionalized phosphines are needed to match the increasing demands for higher activity and selectivity in catalytic processes. In this report we introduce a simple general new method for the synthesis of phosphines, arsines, and stibines. This allowed for example the preparations of phosphines based on serine and thymine derivatives (SerPhos and ThymPhos, respectively).

A pocket suitable for bonding transition metals is formed by the 5-phosphanyl group and the olefinic unit of the central seven-membered ring, which has a rigid boat conformation, of the ligand troppPh (1). This new ligand system allows the synthesis and isolation of stable d9 and d10 rhodium complexes 2 and 3, respectively.

Dibenzocycloheptatrienyl phosphanes (dibenzotropylidene phosphanes=TROPPR) 11a–c may be easily prepared from dibenzocycloheptatrienyl chloride 8 and the secondary phosphanes R2PH [9a: R=Ph; 9b: R=4-Me-C6H4; 9c: R=cyclohexyl (Cyc)] in good yields. Alternatively, the di(tert-butyl)phosphanyl substituted TROPPBut derivative 4 was obtained along with the phosphane 5 by a mechanistically still unknown rearrangement of a strained phosphorus ylide I. The conformations of these new phosphanes were established by X-ray analyses performed for the compounds TROPPBut4 and TROPPPh11a. The R2P moiety is bonded to an axial position of the central seven-membered ring, which adopts a boat conformation. Thereby a rigid concave binding site containing a phosphane and an olefin function is formed, which should allow the synthesis of a wide range of transition metal complexes. In order to test how far the particular shape of the TROPP-type ligands enforces metal–olefin interactions, the coinage metal complexes [(TROPPPh)Cu(µ2-Cl)]2, 13, [(TROPPPh)Ag(µ2-O2SOCF3)]2, 16, [(TROPPPh)2Ag][O3SCF3], 17 and [(TROPPPh)AuCl], 19 were prepared. These were completely characterized by multinuclear NMR experiments in solution and the solid state, as well as by X-ray analyses. The structural and NMR data show that the interaction between the metal center M and the olefin moiety of the TROPP ligand is weak and decreases in the order Cu>Ag>Au. Indeed, for 19 (M=Au) no interaction could be observed. In the silver complex 17, coupling between an Ag nucleus and a proton of a bonded olefin was determined for the first time [J(109/107AgH)=0.4 Hz]. In solution the complexes derived from TROPP-type ligands seem to have an enhanced (kinetic) stability.

Die oligomeren homoleptischen Kupfer(I)-chalkogenolat-Verbindungen [CuS(2,4,6-iPr3C6H2)]x=4,8 (1, 2) und [CuSe(2,4,6-iPr3C6H2)]6 (3) wurden mit 2,2′-Bipyridin (Bipy) zu dem tetranuklearen Kupferkomplex [CuS(2,4,6-iPr3C6H2)]4(Bipy)2 (4) und dem dinuklearen Komplex [CuSe(2,4,6-iPr3C6H2)]2(Bipy)2 (5) umgesetzt, deren Strukturen durch Einkristall-Rontgenstrukturanalysen bestimmt wurden. In dem achtgliedrigen Cu4S4-Ring von 4 mit Sesselkonformation sind die Kupferatome uber μ2-verbruckende Thiolat-Liganden verknupft, wobei nur 2 Kupferatome von 2,2′-Bipyridin koordiniert werden. Der entsprechende Kupfer(I)-selenolat-Komplex (5) bildet einen gefalteten viergliedrigen Cu2Se2-Ring mit μ2-verbruckenden Selenolat-Liganden. Der CuCu-Abstand ist mit 2.52 A relativ kurz. Im Gegensatz zu der Umsetzung mit 2,2′-Bipyridin entsteht aus 1 bzw. 2 und Phenantrolin (Phen) ein dinuklearer Komplex [CuS(2,4,6-iPr3C6H2)] 2(Phen)2 (10). Wahrend 5 sich offensichtlich ohne Zerfall lost, wie NMR-spektroskopische und kryoskopische Untersuchungen zeigen, dissoziiert 4 in Losung in kleinere Aggregate, die miteinander im Gleichgewicht stehen. Das elektrochemische Verhalten von 4, 5 und 10 wurde in CH2Cl2 studiert. In allen Fallen wurden keine reversiblen Redoxprozesse beobachtet. Synthesis and Structure of Copper(I)Chalcogenolate-2,2′-Bipyridine Complexes [CuS(2,4,6-iPr3C6H2)]4(Bipy)2 and [CuSe(2,4,6-iPr3C6H2)]2(Bipy)2 The oligomeric homoleptical copper(I) chalcogenolate compounds [CuS(2,4,6-iPr3C6H2)]x=4,8 and [CuSe(2,4,6-iPr3C6H2)]6 react with 2,2′-bipyridine (Bipy) to yield the tetranuclear complex [CuS(2,4,6-iPr3C6H2)]4(Bipy)2 (4) and the dinuclear complex [CuSe(2,4,6-iPr3C6H2)]2(Bipy)2 (5). The structures of 4 and 5 were determined by X-ray analysis. In the eight-membered Cu4S4 core of 4 with chair conformation the copper atoms are linked by μ2-bridging selenolate ligands. Only two copper atoms are coordinated by 2,2′bipyridine. The corresponding copper(I) selenolate complex (5) forms a folded four-membered Cu2Se2 ring with μ2-bridging selenolate ligands. The CuCu distance of 2.52 A is relatively short. In contrast to the reaction performed with 2,2′-bipyridine, addition of phenantroline to 1 respectively 2 yields a dinuclear complex [CuS(2,4,6-iPr3C6H2)]2(Phen)2 (10). NMR spectroskopic and cryoscopic measurement of 4 show that this complex dissociates into smaller fragments in solution which undergo rapid exchange reactions. However, corresponding investigations performed on 5 indicate that the solid state structure is maintained in solution. The electrochemical behaviour of 4, 5 and 10 was studied in CH2Cl2 and in any case no reversible redox processes could be observed.

The intact deposition of a complex into carbon powder allows the construction of an organometallic fuel cell (OMFC) that efficiently converts alcohols into carboxylic acids. This method may provide a way for the synthesis of fine chemicals from renewable resources under waste-free conditions.

The chlorido-bridged dimeric complex [Rh 2 (μ-Cl) 2 (trop 2 -NH) 2 ] [trop 2 NH =bis(benzo[a,d]cycloheptenyl)amine] or the acetonitrile complexes [Rh(trop 2 NH)(MeCN) 2 ] + (CF 3 SO 3 - ) and [IrCl(MeCN)(trop2NH)] are well-suited precursor complexes for phenanthroline-type complexes [M(trop2NH)(R,R-phen)] + A - (M = Rh, Ir; R = H, Me, Ph substituents in the 4,7-or 5,6-positions of the phen ligand, A - = CF 3 SΟ 3 - , PF 6 - ). These complexes contain 18-valence-electron configured metal centers in a trigonal-bipyramidal coordination sphere with the amino (NH) group in an axial position and each of the olefinic C=C trop units is in an equatorial position. The cationic amino complexes [M(trop 2 NH)(R,R-phen)] + are sufficiently acidic (pK a in dmso: 18.2-19.0) to be quantitatively deprotonated by one equivalent of KOtBu to give neutral amido complexes [M(trop2N)(R,R-phen)] (M = Rh, Ir). These can be easily oxidized to give aminyl radical complexes [M(trop 2 N - )(R,R-phen)] + A - , which for M = Rh can be isolated as green crystals. The iridium complex [Ir(trop 2 N . )(phen)] + is unstable. High-resolution pulse EPR spectroscopy was used to gain insight into the electronic structure of the aminyl radical complexes. Remarkably, the rhodium and iridium complexes have a very similar electronic structure, as revealed by their EPR parameters ([Rh(trop 2 N . ](phen)] + : g 1,2,3 = 2.084(2), 2.049(2), 2.027(2); lA iso l = 45.4 (N1), 10.4 (N 2 ), 3.1 (N3) 27.0 (Rh) MHz; [Ir(trop 2 N . )(phen)] + : g 1,2,3 = 2.140(2), 2.107(2), 2.015(2); lA iso l = 47 (N1), 7.9 (N2), 3.5 (N3), 26.8 (Ir) MHz} and these show that about 60 % of the spin population is localized on the nitrogen center (N1) of the trop 2 N ligand. In reactions with stannanes (R 3 SnH) and thiols (RSH), H-atom transfer to the trop 2 N nitrogen atom is observed, [M(trop 2 N . ](phen)] + + EH→ [M(trop 2 NH)(phen)] + + 1/2HE-EH.

(Chemical Equation Presented) A little goes a long way: An iridium-nitrogen-radical complex is a highly active and selective catalyst for the dehydrogenation (oxidation) of primary alcohols to aldehydes in the presence of the oxidant benzoquinone (see simplified scheme). With only 0.01 mol% of the complex, turnover frequencies of up to 150 000 s-1 are reached. © 2007 Wiley-VCH Verlag GmbH and Co. KGaA.

In einer Tasche gebunden, die aus der 5-Phosphanylgruppe und der Olefineinheit des zentralen, in starrer Wannenkonformation vorliegenden siebengliedrigen Ringes gebildet wird, ist das Rh-Zentrum in den mit dem troppPh-Liganden 1 einfach zuganglichen d9- und d10-Rh-Komplexen 2 bzw. 3.

The reaction of phenyldichlorophosphane, PhPCl2, a commercially important precursor for organophosphorus compounds, with lithium and sodium as reducing metals was re-investigated with the aim to well-characterize the resulting oligophosphandiides, [M2(PnPhn)(solv)x] (M = Li, Na). Experimental conditions for the optimal formation of these compounds were found for both series with M = Li and M = Na and several of these were crystallized and characterized by X-ray diffraction studies. As a result, we find that sodium strongly prefers ion triple structures [M2(PnPhn)(solv)x] over solvent-separated ion pairs, [M(solv)m]+[MPnPhn(solv)n]?, which have a higher tendency to form with M = Li. Also, while [Na2(P4Ph4)(solv)x] retains its structure in thf solution, [Li2(P4Ph4)(solv)x] partially dissociates into the radical anion (Ph2P2).? which is detected by EPR spectroscopy. The knowledge about the structures and the behavior of the alkali metal diphosphandiides allows us to propose a reaction mechanism for their formation., Chimia, 59 (3), ISSN:0009-4293

Copper phosphide or arsenide complexes, [Cu(EPh(2))(neo)] (E = P, As, neo = 2,9-dimethyl-1,10-phenanthroline; trivial name: neocuprine) react selectively with the N-protected brominated serine derivatives, 2-(S)-(alkoxycarbonylamino)-3-bromomethylpropionates ((ROCO)SerBr, : R = PhCH(2), : tBu, : Me) to give the corresponding phosphanylated or arsanylated amino acids, (ROCO)SerPhos (: Phos = PPh(2)) and (Z)SerArs (Ars = AsPh(2), Z = PhCH(2)OCO). The dipeptide (Z)AlaSerPhos was likewise prepared. The phosphanes , and the arsane reacted cleanly with [Rh(2)(micro-Cl)(2)(cod)(2)] to give the rhodium(I) complexes [RhCl(cod)((Z)SerPhos)] , [RhCl(cod)((Boc)SerPhos)] (Boc = tBuOCO), [RhCl(cod)((Z)AlaSerPhos)] , and [RhCl(cod)((Z)SerArs)] which were characterized by X-ray diffraction studies. A common structural feature is an intramolecular (N)H[dot dot dot]Cl(Rh)-hydrogen bridge which according to NMR investigations remains intact in solution. The abstraction of chloride from the coordination sphere of Rh(I) in or has a profound structural impact. While in and , the ligands bind in a monodentate fashion, via the phosphorus atom only, they serve as bidentate ligands via the phosphorus centre and the peptidic C=O group in [Rh(cod)(kappa(2)-(Z)SerPhos)]PF(6) and [Rh(cod)(kappa(2)-(Z)AlaSerPhos)]PF(6). This causes also the amino acid residue structures to change from alpha-helix type in and to a beta-sheet type in both. Addition of chloride to and fully re-establishes the structures of both. The complexes [RhCl(cod)((Z)SerPhos)] and [RhCl(cod)((Boc)SerPhos)] show good activities in homogeneously catalyzed hydrogenations of olefins while the dipeptide complex is less active. Phosphane addition to greatly diminishes the catalytic activity. The cationic complex [Rh(cod)(kappa(2)-(Z)AlaSerPhos)]PF(6) shows low activity which, however, is greatly increased by addition of one equivalent of phosphane.

Metal-stabilized phenoxyl radicals appear to be important intermediates in a variety of enzymatic oxidations. We report that transition metal coordination also supports an aminyl radical, resulting in a stable crystalline complex: [Rh(I)(trop 2 N . )(bipy)] + OTf – (where trop is 5-H-dibenzo[a,d]cycloheptene-5-yl, bipy is 2,2′-bipyridyl, OTf – is trifluorosulfonate). It is accessible under mild conditions by one-electron oxidation of the amide complex [Rh(I)(trop 2 N)(bipy)], at a potential of –0.55 volt versus ferrocene/ferrocenium. Both electron paramagnetic resonance spectroscopy and density functional theory support 57% localization of the unpaired spin at N. In reactions with H-atom donors, the Rh-coordinated aminyl behaves as a nucleophilic radical.

Iridium(I) complexes containing a (5H-dibenzo[a,d]cyclohepten-5-yl)-phosphane (tropp(R); R = phosphorus-bound substituent = Ph, Cyc) as a rigid, concave-shaped, mixed phosphane olefin ligand were prepared and tested as catalyst precursors in the hydrogenation of imines. With the complex [Ir(tropp(Cyc))(cod)]OTf, turnover frequencies (TOFs) of >6000 h(-1) were reached in the hydrogenation of N-phenyl-benzylidenamine, PhN==CHPh. Lower activities (TOF>80 h(-1)) are observed with N-phenyl-(1-phenylethylidene)amine, PhN==CMePh. Chiral tropp-type ligands were prepared in few simple steps. Monosubstitution of the olefinic unit in the dibenzo[a,d]cycloheptenyl moiety with (R)- or (S)-mentholate gave mixtures of diastereomers that could be separated and isolated in enantiomerically pure form. Iridium(I) complexes with these ligands are rare examples of side-on bonded enolether complexes. In catalytic imine hydrogenations, complete conversion (>98 %) was reached in all cases (conditions: p[H(2)] = 50 bar, T = 50 degrees C, t = 2 h, substrate/catalyst 100:1). The best enantiomeric excess (ee = 86 % S isomer) was reached with PhN==CMePh as substrate and the R,R form of the (10-menthyloxy-5H-dibenzo[a,d]cyclohepten-5-yl)diphenylphosphane ligand. The iridium(I) complex containing the same phosphane gave a 60 % ee (S isomer) with the enamide N-(1-phenylvinyl)acetamide as substrate (conditions: p[H(2)] = 4 bar, T = 50 degrees C, t = 18 h, substrate/catalyst = 50:1). These reactions constitute the first examples in which chiral olefins have been used as steering ligands in catalytic enantioselective hydrogenations.

The formation of adducts of the square-planar 16-electron complexes trans-[M(tropp(ph))(2)](+) and cis-[M(tropp(ph))(2)](+) (M=Rh, Ir; tropp(Ph)=5-diphenylphosphanyldibenzo[a,d]cycloheptene) with acetonitrile (acn) and Cl(-), and the redox chemistry of these complexes was investigated by various physical methods (NMR and UV-visible spectroscopy, square-wave voltammetry), in order to obtain some fundamental thermodynamic and kinetic data for these systems. A trans/cis isomerization cannot be detected for [M(tropp(ph))(2)](+) in non-coordinating solvents. However, both isomers are connected through equilibria of the type trans-[M(tropp(ph))(2)](+)+L==[ML(tropp(ph))(2)](n)==cis-[M(tropp(ph))(2)](+)+L, involving five-coordinate intermediates [ML(tropp(ph))(2)](n) (L=acn, n=+1; L=Cl(-), n=0). Values for K(d) (K(f)), that is, the dissociation (formation) equilibrium constant, and k(d) (k(f)), that is, the dissociation (formation) rate constant, were obtained. The formation reactions are fast, especially with the trans isomers (k(f)1x10(5) m(-1) s(-1)). The reaction with the sterically more hindered cis isomers is at least one order of magnitude slower. The stability of the five-coordinate complexes [ML(tropp(ph))(2)](n) increases with IrRh and Cl(-)acn. The dissociation reaction has a pronounced influence on the square-wave (SW) voltammograms of trans/cis-[Ir(tropp(ph))(2)](+). With the help of the thermodynamic and kinetic data independently determined by other physical means, these reactions could be simulated and allowed the setting up of a reaction sequence. Examination of the data obtained showed that the trans/cis isomerization is a process with a low activation barrier for the four-coordinate 17-electron complexes [M(tropp(ph))(2)](0) and especially that a disproportionation reaction 2 trans/cis-[M(tropp(ph))(2)](0)--[M(tropp(ph))(2)](+)+[M(tropp(ph))(2)](-) may be sufficiently fast to mask the true reactivity of the paramagnetic species, which are probably less reactive than their diamagnetic equilibrium partners.

The 17-electron complexes [M(tropp(ph))2] (M=Co0, Rh0, Ir0) were prepared and isolated (tropp = tropylidene phosphane). A structural analysis of [Co(tropp(ph))2] revealed this complex to be almost tetrahedral, while the heavier homologues have more planar structures. Partially deuterated tropp complexes [D6][M(tropp(ph))2] were synthesised for M = Rh and Ir in order to enhance the resolution in the EPR spectra. This synthesis involves a four-fold intramolecular C-H activation reaction, whereby alkyl groups are transformed into olefins. Dihydrides were observed as intermediates for M = Ir. The electronic and geometric structures of all complexes [M(tropp(ph))2] (M = Co, Rh, Ir) and [D6][M(tropp(ph))2] (M = Rh, Ir) were investigated by continuous wave (CW) and echo-detected EPR in combination with pulse ENDOR and ESEEM techniques. In accord with their planar structures, cis and trans isomers were detected for [M(tropp(ph))2] (M = Rh0, Ir0) for which a dynamic equilibrium was established. The thermodynamic data show that the cis isomer is slightly preferred by deltaH(o) = -4.7 +/- 0.3 kJ mol(-1) (M = Rh) and delta H(o) = -5.1 +/- 0.5 kJ mol(-1); (M = Ir). The entropies for the process trans-[M(tropp(ph))2] cis-[M(tropp(ph))2] are also negative [deltaS(o) = -5 +/- 1.5 J mol(-1) (M = Rh); deltaS(o) = -17 +/- 3.7 J mol(-1) (M = Rh)], indicating higher steric congestion in the cis isomers. The cobalt(0) and irdium(0) complexes show rather large g anisotropies, while that of the rhodium(0) complex is small (Co: g(parallel) = 2.320, g(perpendicular) = 2.080; cis-Rh: g(parallel) = 2.030, g(perpendicular) = 2.0135; trans-Rh: g(parallel) = 2.050, g(perpendicular) = 2.030; cis-Ir: g(parallel) = 2.030, g(perpendicular) = 2.060; trans-Ir: g(parallel) = 1.980, g(perpendicular) = 2.150). The g matrices of [M(tropp(ph))2] (M = Co, Rh) are axially symmetric with g(parallel) > g(perpendicular), indicating either a distorted square planar structure (SOMO essentially d(x2 - y2) or a compressed tetrahedron (SOMO essentially d(xy)). Interestingly, for [Ir(tropp(ph))2] the inverse ordering, g(perpendicular) > g(parallel) is found; this cannot be explained by simple ligand field arguments and must await a more sophisticated analysis. The hyperfine interactions of the unpaired electron with the metal nuclei, phosphorus nuclei, protons, deuterons and carbon nuclei were determined. By comparison with atomic constants, the spin densities on these centres were estimated and found to be small. However, the good agreement of the distance between the olefinic protons and the metal centres determined from the dipolar coupling parameter indicates that the unpaired electron is primarily located at the metal centre.

Using the tropp(Ph) ligand 1, stable monomeric d(8)-Ir+I, d(9)-Ir-0 and d(10)-Ir-I complexes could be isolated and structurally characterized; in all complexes, the metal centre lies within a coordination sphere intermediate between a square plane and a tetrahedron.

A pocket suitable for bonding transition metals is formed by the 5-phosphanyl group and the olefinic unit of the central seven-membered ring, which has a rigid boat conformation, of the ligand tropp

Halide abstractions from P-chlorinated phosphorus ylides 9a–c either by AlCl3 or SnCl2 yield unsymmetrical methylene phosphonium ions 10a–c in which energy barriers > 83 kJ mol–1 for the rotation around the PC have been estimated by NMR techniques. The salts with AlCl4– counteranions are stable, but compounds with SnCl3– anions decompose stereoselectively to unsymmetrical methylene phosphanes, SnCl2, and ButCl.

CO 2 reacts with hexyne(−3) in a catalytic reaction under formation of tetraethyl-2-pyrone, when the catalytic system alkyl 3 P/acetonitrile/nickel(0) is used. The selectivity of this homogeneous-catalytic reaction can be increased to values of 96% when phosphanes of high basicity and small cone angle are used. The investigation of the system Ni(COD) 2 /tricyclohexylphosphane/acetonitrile shows that acetonitrile can act as ligand in complexes of nickel(0). A yellow-brown tetranuclear complex was isolated, the structure of which was determined by X-ray diffraction studies. Acetonitrile acts as bridging ligand and is coordinated alkyne-analogously to one nickel center with its triple bond. The free electron pair of the nitrogen atom is bonded to a second nickel atom. Some reaction steps of this selective catalytic reaction are discussed. This reaction represents the first example of a selective homogeneous-catalytic co-oligomerization between CO 2 and an unsaturated substrate which takes place under CC linkage with a 3 d -transition metal.