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The complex (4-chloro-2-butenylphosphinidene)pentacarbonyltungsten, as generated from the appropriate 7-phosphanorbornadiene complex at 58 °C in the presence of copper(I) chloride as a catalyst, readily rearranges to give the stable 1-chloro-2-vinylphosphirane complex. According to DFT calculations on similar Cr(CO)5 complexes, a concerted six-electron (σ C−Cl bond, P lone pair, and π C&dbd;C double bond), five-center mechanism could be involved with a low energy barrier of 4.8 kcal mol^-1 in the chromium series.

The reaction of benzyne with 3,4-dimethylphosphole pentacarbonylmolybdenum complexes affords the corresponding 2,3-benzo-7-phosphanorbornadiene complexes through [4+2] cycloaddition. The condensation takes place on the less hindered side of the phosphole ring corresponding to the phosphorus substituent as shown by the X-ray crystal structure analysis of the phenyl derivative (2). The strain at the bridge of 2 (C−P−C angle ca. 80°) induces a variety of splitting reactions. Upon decomplexation by dppe at 110 °C in toluene, phenylphosphinidene is generated and recovered as phenylphosphine. Upon sulfurization under the same conditions, [PhPS2] is formed and trapped as a [4+2] adduct with 2,3-dimethylbutadiene. Potassium tert-butylate attacks the bridge in THF at −78 °C and, after methylation and hydrolytic workup, yields [Ph(Me)P(OH)Mo(CO)5].

The transient phosphinidene complex [PhP−Mo(CO)5], as generated from the appropriate 7-phosphanorbornadiene complex at 110 °C in toluene, selectively reacts with the C&tbd1;C triple bond of 4-phenyl-3-butyn-1-ol to give the corresponding phosphirene complex 4. Upon further heating, this phosphirene evolves via two pathways. The minor pathway involves the formal addition of the OH bond of the alcohol function onto the phosphirene P−C ring bond to give the 3-benzylidene-1,2-oxaphospholane complex 5. The major pathway involves the reaction of a second molecule of [PhP−Mo(CO)5] with the OH group of 4, giving an intermediate phosphirene with an additional secondary alkoxyphosphine functionality (7). An intramolecular hydrophosphination of one P−C bond of the phosphirene ring then immediately takes place to give the cis-1,2-bis(phosphino)ethene [Mo(CO)4] complex 8 as a mixture of two diastereomers. After methylation of the PH group of 8, decomplexation can be efficiently achieved by reaction with sulfur. Structures have been ascertained by X-ray analysis for 5, 8, and the disulfide 10.

Transient 2H-phospholes are easily obtained from 1-R-1H-phospholes by a [1,5]-shift of the R-substituent from phosphorus to the α-carbons of the ring. They display cyclopentadiene-like chemistry:  [4+2]-cycloaddition reactions with alkenes, alkynes, conjugated dienes and aldehydes, deprotonation to give the aromatic phospholide ions, and reaction with transition metal derivatives to give η⁵-phospholyl complexes. The resulting products have found some use in homogeneous and asymmetric catalysis and show some promise in the field of electroconducting polymers.

Nonviral gene vectors remain inefficient in vivo largely because of their rapid clearance from the circulation and also their nonspecific association with the extracellular matrix. To overcome such drawbacks, cationic lipoplexes are now frequently coated with hydrophilic polymers such as PEGs to reduce nonspecific interactions, and ligands are also linked to their surface to obtain cell-specific gene transfer. In view of the development of vectors for systemic gene delivery, we have designed and studied lipoplexes that carry a triantennary galactosyl ligand attached to the distal end of a (PEG)45-conjugated lipid. We incorporated this targeted PEGylated lipid into lipoplexes using two strategies of formulation, i.e., using either preformed micelles or liposomes. We demonstrated that the incorporation of PEG chains stabilized lipoplexes and masked, but only partially, the positive charges exposed on the surface of the particles. We have also shown that incorporation into lipoplexes of a lipidated PEG chain, bearing a ligand at its distal end, yielded particles that exhibited an accessible ligand throughout the whole range of cationic lipid to DNA ratios. We obtained a targeted transfection in HepG2 cells with one of the formulations. Our results strengthen the validity of using a ligand carried by a long PEG spacer arm for targeted gene transfer.

Electrochemical reduction of phosphole P-W(CO)5 complexes affords the free phospholes in good yields. This technique allows the decomplexation of a 2-ethoxy-4-keto-4,5-dihydrophosphole, which has been characterized by X-ray crystal structure analysis of its P-sulfide.

The thermolysis of P-functionalized 7-phosphanorbornadiene tungsten complexes 3a−d in o-xylene at 120 °C in the presence of various carbonitriles and dimethyl acetylenedicarboxylate (DMAD) has been investigated. The reaction of complex 3a, 1-piperidino carbonitrile, and DMAD yielded a product mixture, whereby 2H-1,2-azaphosphole complex 6 was formed in ca. 40−45% yield together with diazaphosphole complexes 7 (ca. 10−15%) and 8 (ca. 10−15%) and other nonidentified products (ca. 30%). Unfortunately, none of these products could be separated by column chromatography. In marked contrast, reactions of 7-phosphanorbornadiene tungsten complexes 3a−d with triphenylphosphane-imino carbonitrile and DMAD led to P-functionalized 2H-1,2-azaphosphole complexes 11a−d in good to excellent yields. Preliminary investigations of decomplexation reactions revealed a remarkable thermal stability of 11a−d:  no reaction occurred with bis(diphenylphosphino)ethane (DPPE) at 140 °C. Preliminary studies of exocyclic P−C bond cleavage reactions of 2H-1,2-azaphosphole complexes 11a,b using potassium tert-butanolate (KOtBu) showed instantaneous reactions and color change from yellow to dark red; an intermediate was detected by ³¹P NMR spectroscopy. Treatment with an excess of methyl iodide led to one major product, which, most probably, is the N-methyl-substituted 1H-1,2-azaphosphole complex 13; unfortunately, chromatography failed and it could only be observed by ³¹P NMR spectroscopy. A comparative study on P−C bond cleavage/methylation reactions using monofunctional 2H-1,3,2-diazaphosphole complex 14 and the system KOtBu/methyl iodide showed the selective formation of the P-methyl-substituted 2H-1,3,2-diazaphosphole complex 16; complexes 14 and 16 were prepared using the Cu(I)Cl route. Complexes 11a−d, 14, and 16 were characterized by elemental analyses, NMR, UV/vis, IR, and mass spectroscopy and, in addition, by single-crystal X-ray diffraction in the case of 11a−d. Additionally, we investigated selected isomers of lithium and potassium 1,2-azaphospholides by ab initio calculations using HF and MP2/6-311++G(2d,p) level of theory; stability, structure, and aromaticity aspects are discussed.

A 2-(phosphirenyl)ethylphosphinidene [W(CO)5]2 complex undergoes an original phosphinidene + phosphirene self-condensation to yield the tricyclic compound 5 with an unusual 2,4-diphosphabicyclobutane “butterfly” structure. The product has been characterized by X-ray crystal structure analysis and its formation studied from a theoretical standpoint at the B3LYP/6-311+G(d,p) level.

The McMurry coupling of a 2-acetylphosphacymantrene with the TiCl4/Zn couple preferentially provides the Z-alkene as a mixture of the rac and meso diastereomers. The coupling of the 2-benzoylphosphacymantrene mainly gives the E-alkene together with the 2-benzyl reduction product. The alkene stereochemistries have been established by X-ray crystal structure analyses. A titanium−carbene intermediate is suggested in the second case.

The electron localization function (ELF), calculated at the DFT/B3LYP level of theory, has been used to analyze various phosphaferrocenes and azaferrocenes. The analysis of the bonding situation and electronic structure in the complexes reveals the importance of the shape of the heteroelement lone pair. Thus, the electron-withdrawing capability of the heteroatom-substituted ring is not only a consequence of electronegativity but also a result of the extension of the lone pair. Our data allow a model of the electrophilic reactivity of these complexes to be proposed.

Electrochemical and chemical reductions of Rh^(I) complexes of LP4 (a macrocycle containing four phosphinine rings) and of LP2S2 (a macrocycle containing two phosphinine rings and two thiophene rings) lead, in liquid solution, to EPR spectra exhibiting large hyperfine couplings with ³¹P nuclei. An additional coupling (27 MHz) with ¹⁰³Rh is detected, in the liquid state, for the spectrum obtained with [LP2S2Rh⁽⁰⁾]; moreover, resolved ³¹P hyperfine structure is observed in the frozen solution spectrum of this latter complex. DFT calculations performed on Rh^(I) complexes of model macrocycles L‘P4 and L‘P2S2 indicate that, in these systems, the metal coordination is planar and that one-electron reduction induces a small tetrahedral distortion. The calculated couplings, especially the dipolar tensors predicted for [L‘P2S2Rh⁽⁰⁾], are consistent with the experimental results. Although the unpaired electron is mostly delocalized on the ligands, the replacement of two phosphinines by two thiophenes tends to increase the rhodium spin density (ρRh =0.35 for [L‘P2S2Rh⁽⁰⁾]). It is shown that coordination to Rh as well as one-electron reduction of the resulting complex provoke appreciable changes in the geometry of the macrocycle.

Several 1,2-disubstituted 3,6-bis(trimethylsilyl)-1,2-dihydro-1,2-diphosphinine complexes were prepared in a series of reactions starting from the palladium-catalyzed head-to-head dimerization of a 1-(2-ethoxycarbonylethyl)-2-trimethylsilylphosphirene W(CO)5-complex. The P−CH2CH2CO2Et bonds were cleaved by ^tBuOK in THF to give the corresponding P-anions. The most significant products were the PCl−P(CH2CH2CO2Et) (4), PH−P(OH) (5), and PH−P(CH2Ph) (8) complexes. The thermolysis of the P(CH2Ph)−P(CH2Ph) complex (9) led to the corresponding phosphole complex 11 by extrusion of one phosphorus unit. Apparently, the postulated aromatic 1,2-diphosphinines are able to evolve toward other products via low-energy pathways.

The reduction of [(η⁵-C4Me4P)2ZrCl2] (1) by magnesium in THF affords a transient octamethyl-1,1‘-diphosphazirconocene which can be trapped by CO, bis(trimethylsilyl)acetylene, and 2-butyne to give the corresponding dicarbonyl 2, zirconacyclopropene 3, and zirconacyclopentadiene 4; all of these products have been characterized by X-ray analyses. An assessment of the π-basicity of the η⁵-C4Me4P ligand has been made by several methods: (a) a comparison of the IR carbonyl stretching frequencies of 2 and of other dicarbonylzirconocene complexes, (b) a correlation of the ¹³C NMR and IR data in 3 and in similar zirconacyclopropenes, and (c) an electrochemical study on 1. All these experiments confirm that the η⁵-C4Me4P ligand is a poorer π-base than the Cp ligand.

4,5-Dimethyl-2-bromophosphinine reacts with [Ru(η⁵-C5Me5)(η⁴-C6H10)Cl], in the presence of AgBF4, to afford depending on the reaction conditions complexes resulting from the substitution of the chloride or the diene ligand. Under the same experimental conditions, reactions with the more sterically hindered 2,6-bis(trimethylsilyl)phosphinines yield the sandwich [Ru(η⁵-C5Me5)(η⁶-phosphinine)][BF4] cationic complexes.

Reduction of the [Ru(Cp*)(tmbp)Cl] complex (tmbp = 4,4‘,5,5‘-tetramethyl-2,2‘-biphosphinine) with 1 and 2 equiv of sodium naphthalenide respectively yield a dimeric [Ru(Cp*)(tmbp)]2 complex and a [Ru(Cp*)(tmbp)][Na(DME)2] complex which were both structurally characterized. Trapping the Ru(0) complex with MeI, Ph3SnCl, Me3SnCl, or H⁺ affords the corresponding Ru(II) derivatives.

Syntheses of octaethyldiphosphaferrocene 4 and tetraethylphosphaferrocene 5 are presented. Tetraethylzirconacyclopentadiene 1 reacts with PCl3 in dichloromethane to yield the 1-chlorotetraethylphosphole 2, which upon reduction by lithium in excess, yields the teraethylphospholide anion 3. Anion 3 was subsequently converted into 4 or 5 by treatment with FeCl2 or with [Fe(η⁶-C9H12)(η⁵-C5H5)][PF6] respectively. The structure of diphosphaferrocene 4 was determined. Two conformations are present in the cell:  a C2 conformation (α = 51.1°) in which the P atom of each ring is located above the α-carbon atom of the other ring, and a C2h conformation (α = 180°) in which P atoms point in opposite directions. Reaction of ligand 4 with [Pd(dba)2] yields the bis(octaethyldiphosphaferrocene)palladium(0) complex 6. An X-ray crystallographic study reveals that the overall geometry around palladium is nearly tetrahedral and that both ligands, whose geometry is not significantly perturbed, adopt a bridging mode involving a side-on coordination of the lone pairs. Complex 6 behaves as an efficient catalyst for the coupling reaction between phenylboronic acid and 4-bromoacetophenone in refluxing toluene. A conversion of 98% was obtained with 1 × 10^-4% of catalyst (TON = 9.80 × 10⁵). The catalytic activity of 6 in coupling reactions between phenylboronic acid and 3-bromothiophene, 2-bromoanisole, and bromobenzene was also investigated.

Phosphorus-31 1D NMR spectra of a stationary powder sample of a phosphole tetramer containing two phosphorus spin pairs have been obtained at 4.7 T and 9.4 T. In order to separate 31P-31P spin-spin coupling from anisotropic chemical shielding, 2D spin-echo NMR spectra have been acquired. Phosphorus-31 CPMAS NMR experiments indicate that the two spin pairs of the tetramer are equivalent and each may be treated as an isolated spin pair. Within a given spin pair, the difference between the isotropic chemical shifts of two directly bonded phosphorus nuclei is 1.7 ppm. As well, they are spin-spin coupled by both the indirect and direct interactions, 1J(31P, 31P) = -362 Hz and RDD= 1.80 kHz, respectively. The principal components and relative orientation of the two phosphorus chemical shielding tensors have been determined using the dipolar-chemical shift technique; however, since the dipolar tensor is axially symmetric, ambiguities in the chemical shielding tensor orientation relative to the molecular framework result. Using ab initio calculations and simulations of the 2D spin-echo spectra, many of these ambiguities have been resolved. The spans and skews of the phosphorus shielding tensors for all four three-coordinate phosphorus nuclei are the same within experimental error, 115 ppm and 0.70, respectively. Combined experimental and theoretical results indicate that the phosphorus shielding tensor orientations are dictated by the local environment. For both shielding tensors, the most shielded component, 33, is approximately 78° from the P-P bond and in the phosphole ring plane. The relative orientation of the 33components is described by a dihedral angle of 82°, similar to the dihedral angle of approximately 76° defining the twist of the phosphole rings about the bridging P-P bond.Key words: solid-state 31P NMR, phosphorus chemical shielding tensors, phosphole tetramer, 31P—31P spin pairs, ab initio calculations.

A synthetic approach toward mixed phosphinine−phosphole and phosphinine−phosphaferrocene tridentate ligands has been studied. In the first step, the metallacycle transfer reaction from 2,5-bis(trimethylsilyl)zirconacyclopentadienes to the corresponding phospholes has been investigated. Three metallacycles 2a−c, bearing different groups at the β-positions of the ring (a, R = Ph; b, R = n-Bu; c, R = Me), have been synthesized. Whereas the reaction of PCl3 with 2a,b respectively leads to 1-P chlorophosphirenes 3a,b, complex 2c is readily transformed into the corresponding 1-P bromophosphole 4 upon reaction with PBr3 in dichloromethane. This approach was extended to the synthesis of the bis(dimethylpropynylsilyl)zirconacyclopentadiene compound 5, which was then further converted into the corresponding 1-P chlorophosphole 6. Phospholyl anion 7 was obtained from the reaction of 6 with lithium in THF at room temperature. Three 1-R-2,5-bis(dimethylpropynylsilyl)phospholes (8a, R = CH2CH2Cl; 8b, R = CH2CH2CN; 8c, R = CH2CH2CO2Et) have been obtained from the reaction of anion 7 with the corresponding species RCH2CH2X (X = Cl, Br). The X-ray crystal structure of compound 8b has been determined. The reaction of anion 7 with [FeCp(η⁶-C9H12)][PF6] and FeCl2 respectively yielded the monophosphaferrocene 9 and the diphosphaferrocene 10. The X-ray crystal structure of 10 has been determined. The three phosphinine−phosphole tridentate ligands 12a−c have been assembled by reacting phospholes 8a−c with diazaphosphinine 1 followed by reaction of the 2,5-bis(dimethyl(1,2-azaphosphininyl)silyl)phospholes 11a−c with (trimethylsilyl)acetylene in excess. Ligands 12b,c have been converted into the anion 13 upon reaction with LDA at low temperature. The 2,5-bis(dimethyl(phosphininyl)silyl)phosphaferrocene ligand 15, which was structurally characterized, has been prepared by following the strategy devised for the synthesis of ligands 12. Reaction of ligands 12a and 15 with [Rh(COD)Cl]2 gave respectively the corresponding Rh chloride complexes 16 and 17. Both complexes adopt a square-planar geometry, and complex 17 has been structurally characterized.

The reduction of 4,4‘,5,5‘-tetramethyl-2,2‘-biphosphinine (tmbp) with excess Li, Na, or K affords the corresponding dianions. Reaction of these anions with metal halides gives (tmbp)metal(0) complexes.

The uses of phospholes for building phosphorins, carbon-phosphorus saturated heterocycles and phosphinidene generators are described.

The protonation of phospholyl anions yields P-unsubstituted 1H-phospholes. Between -50° and -20°C, the 1H-phospholes rearrange to give 2H-phospholes which instantly dimerize. The hydrolysis of 3,4-dimethylphospholyllithium W(CO)5- or Cr(CO)5- complexed leads to stable 3,4-dimethyl-2H-phosphole complexes.

Results obtained with semiempirical MO methods support a mechanism for the pyrolysis of vinylphosphirane yielding phosphapropyne in which extrusion of ethylene leads to a vinylphosphinidene intermediate. A pathway from vinylphosphinidene to phosphapropyne involving 2H-phosphirene and 2-phosphapropenylidene intermediates is predicted from high level ab initio results to have a higher energy barrier than that for direct rearrangement. A higher energy pathway from vinylphosphirane is the migration of a hydrogen atom forming methyl(1-phosphiranyl)methylene, followed by loss of ethylene to yield the phosphaalkyne product. However, since fragmentation of 1-phosphiranylmethylene, once formed, has a low predicted barrier, its generation emerged as a new route to phosphaalkynes. (Trimethylsilyl)(1-phosphiranyl)diazomethane was synthesized, and its pyrolysis yields Me3SiC&tbd1;P.

The Tungstaphosphirenes, Phosphaalkenes, Phosphahexatrienes, η4-phosphabutadiene complexes and 1,2-dihydrophosphete ring have been synthesized by coupling reactions of carbyne or carbene complexes with the transient phenyl phosphinidene pentacarbonyl tungsten [PhP=W(CO) 5]. The preparation of other heterocycles such as Dihydrodiphosphetes and Dihydrophosphepines has been realized from the vinylphosphinidene complexes via a 4π-electrocyclization and a Phospha-Cope rearrangement respectively.

The synthesis of 3,4-dimethylphosphaferrocene (1) complexes of rhodium ([Rh(1)3Cl], 2, and [Rh(1)4][BF4], 3) and iridium ([Ir(1)3(COD)][BF4], 4) are reported. An X-ray crystal structure analysis of the homoleptic derivative 3 reveals that ligands arrange around the rhodium center without apparent steric congestion. Complex 4, which was also structurally characterized, adopts a trigonal bipyramid geometry in the solid state. The reaction of 4 with H2 under pressure yields the [Ir(1)4H2]⁺ complex.

Syntheses, structure and reactivity of η1, η3-phosphaallyliron complexes [η1P-(η3-RP-CH=CHR')Fe(CO) (Cp)]W(CO)5.

Some recent developments of the chemistry of phos-phirenes are reviewed. They include two new syntheses of the ring, a preliminary investigation on the reactivity of 1-chlorophosphirenes and various ring expansions.

Efficient synthetic routes are described, leading to novel η6-phosphinine- (1) and η6-1,3-diphosphinine (4, 5) iron(0) complexes. 1 is a catalyst for pyridine formation by a [2+2+2]-cyclic addition reaction of nitriles and alkynes and s4 is a useful source of unsaturated free four and six membered organophosphorus rings.

The chemistry of pyramidal phospholes is governed by their low aromaticity and the strong σ,π overlap between the P-R exocyclic bond and the dienic system. Hence, functionalisation of the ring is difficult but [1,51 sigmatropic shift of R is easy. These two complementary aspects of phosphole chemistry are explored. Two routes to α-functional phospholes are described. They involve either a C-Br to C-Li exchange reaction or the allylic metallation of 3,4-dimethylphosphole-borane complexes. The influence of the atom connected to P (sp2C, spC, N, O, S) and the substitution pattern of the phosphole ring upon the [1,5] sigmatropic migration is discussed. Finally, several applications of this chemistry for the synthesis of water-soluble phosphines and polyphospha-macrocycles are described.

Heating 1-Z-3,4-dimethylphospholes with potassium tert-butoxide in THF at ca. 150−160 °C affords the corresponding potassium 2-Z-3,4-dimethylphospholides (Z = 1-methyl-2-pyrrolyl and 2-(diphenylphosphino)phenyl) via a [1,5]-sigmatropic shift of Z. The first anion can be used to prepare the corresponding bis(pyrrolyl)-1,1‘-diphosphaferrocene, and the second anion is able to chelate palladium(II) between its phospholide and PPh2 functionalities.

Transient terminal phosphinidene complexes [RP→W(CO)5] (R = Ph, Me, Bz, allyl), as generated from the corresponding 7-phosphanorbornadiene complexes, react with substituted butadiynes to afford the corresponding 3-alkynyl-1,2-dihydro-1,2-diphosphete complexes by insertion of a second phosphinidene unit into the alkynyl-substituted P-C ring bond of the initially formed phosphirene complexes. According to the X-ray analysis of one of the products, the stereochemistry of the substituents on the P-P bond is cis.

Thermal reactions of 4,6-di-tert-butyl-1,3,2-diazaphosphinine 1a, obtained from the reaction of the corresponding diazatitanacycle with PCl3 in the presence of NEt3, with various functional alkynes are dicussed. Phosphinines are produced in good yields (from 55 to 75%) via two [4 + 2] cycloaddition−cycloreversion sequences with extrusion of two molecules of pivalonitrile from 1a. Two 2-diethoxymethyl-substituted, 3 and 4, one 3-propynyl-substituted, 6, and two examples of 3-monosubstituted and 3,5-disubstituted ferrocenylphosphinines, 8 and 9, have been synthesized. The X-ray structure of the 2,6-bis(trimethylsilyl)-3,5-bis(ferrocenyl)phosphinine 9 has been determined. Due to a strong steric crowding between the silyl and ferrocenyl groups, the ring adopts a twisted geometry with a dihedral angle of 11.65°. Upon reaction of 1a with bis(diphenylphosphino)acetylene, a 2,3-bis(diphenylphosphino)-substituted, 11, and the 2,3,5,6-tetrakis(diphenylphosphino)-substituted, 12, phosphinines have been obtained. Reactions of 1a with 1,n-diynes (n > 3) also provides easy access to Ph−P-, (CH2)3-, and SiMe2-, linked bis(phosphinines) 14, 16, and 18, respectively. A SiMe2 linked tris(phosphinine) has also been prepared using a two step sequence which involves the preliminary synthesis of a 2,6-bis(phenylethynyl)dimethylsilylphosphinine 20. Reaction of 2 equiv of 1a with 1 equiv of 20 and then with 2 equiv of (trimethylsilyl)acetylene gave the tris(phosphinine) 22. This methodology has also been extended to the synthesis of arsinine derivatives. In a similar way, the first example (4,6-di-tert-butyl) of a 1,3,2-diazaarsinine 1b has been prepared (yield 20−25% relative to Cp2TiMe2) from the reaction of the corresponding diazatitanacycle with AsCl3 in the presence of Et3N. Similar to its phosphorus counterpart 1a, 1b reacts with alkynes by the same cycloaddition−cycloreversion sequence to give tetrafunctional arsinines (yields from 40 to 50%). The 2,6-bis- and 2,3,5,6-tetrakis(trimethylsilyl), 23 and 24, respectively, derivatives have been obtained from reaction of 1b with phenyl(trimethylsilyl)acetylene and bis(trimethylsilyl)acetylene, respectively. The reaction of 1b with bis(diphenylphosphino)acetylene gave a 2,6-bis(diphenylphosphino)arsinine 25, which has also been characterized by an X-ray diffraction study.

Thermolysis of 2,2‘,5,5‘-tetra-tert-butyl-1,1‘-biphosphole with Co2(CO)8 gives good yields of (2,5-di-tert-butylphospholyl)dicarbonylcobalt (1), a compound which provided access to a range of cobalt phospholyl complexes. Thermolysis with trimethyl phosphite produced C12H20PCo(CO)P(OMe)3 (2), while photolysis with 1,3-cyclohexadiene and 1,5-cyclooctadiene gave the corresponding complexes C12H20PCo(diene) (3, 4). In the absence of a donor ligand, a metal−metal doubly bridged dimer 6 was obtained; this reacted classically with ethyl diazoacetate to give the bridging complex {C12H20PCo(CO)}2(μ-CHCO2Et) (7). Prolonged heating of 1 with 3-hexyne in xylene gave the cyclotrimerization product C6Et6; an initial attempt to prepare pyridines by cocyclization of PrCN with PhC&tbd1;CΗ gave the cyclobutadiene complex C12H20PCo(1,2-C4H2Ph2) (5).

[RuCp*(η⁴-C6H10)Cl] (Cp* = C5Me5; 1) reacts with the tmbp ligand (2; tmbp = 4,4‘,5,5‘-tetramethyl-2,2‘-biphosphinine) in THF to afford the [RuCp*(tmbp)Cl] complex 3, which has also been characterized by a single-crystal X-ray diffraction study. Complex 3 crystallizes with one THF molecule. The environment about the Ru atom corresponds to that of a classical three-legged piano-stool structure. Reaction of 3 with LiBr and KCN in CH2Cl2/MeOH afforded [RuCp*(tmbp)Br] (4) and [RuCp*(tmbp)CN] (5), respectively. 3 also reacts in CH2Cl2, in the presence of NH4PF6, with various monodentate ligands to produce a series of stable cationic complexes of the type [RuCp*(tmbp) (L)]⁺[PF6]^- (L = acetonitrile (6), pyridine (7), trimethyl phosphite (8), triphenylphosphine (9), 2-bromo-4,5-dimethylphosphinine (10), tert-butyl isocyanide (11), cis-cyclooctene (12), norbornene (13)). All complexes were obtained in good yields and have been characterized by a combination of elemental analyses and spectroscopic methods (IR and ³¹P, ¹H, and ¹³C NMR). The redox chemistry of 3 has been investigated by cyclic voltammetry in MeCN. Complex 3 is reversibly oxidized in [RuCp*^III(tmbp)Cl] at +0.49 V (vs SCE). The first irreversible monoelectronic reduction wave, which occurs at −1.82 V vs SCE, indicates the formation of the [Ru^ICp*(tmbp)] complex with the loss of Cl^-. The second reversible reduction wave at −2.24 V was assigned to the formation of the anionic [Ru⁰Cp*(tmbp)]^- complex, which is stable within the time scale of the cyclic voltammetry.