Rhenium phosphines

Introduction of the desired metal complex into the polymer film was accomplished by performing electrochemistry in an 0.2 M TBAH/CH2CI2 electrolyte solution which was 5 nM in complex. Solutions of the osmium and rhenium phosphines were protected from light due to their photolytic instability. All solutions were degassed using a stream of Cl C -saturated nitrogen. An N2 blanket was maintained during the course of the experiment to prevent subsequent aeration. 

ALKYNE-DERIVED CARBYNES 2.1. Rhenium Phosphinic Complexes... 

The chemistry of technetium(II) and rhenium(II) is meagre and mainly confined to arsine and phosphine complexes. The best known of these are [MCl2(diars)2], obtained by reduction with hypophosphite and Sn respectively from the corresponding Tc and Re complexes, and in which the low oxidation state is presumably stabilized by n donation to the ligands. This oxidation state, however, is really best typified by manganese for which it is the most thoroughly studied and, in aqueous solution, by far the most... 

The diamagnetic ylide complexes 34 have been obtained from the reaction of electron-deficient complexes [MoH(SR)3(PMePh2)] and alkynes (HC=CTol for the scheme), via the formal insertion of the latter into the Mo-P bond. The structural data show that 34 corresponds to two different resonance-stabilized ylides forms 34a (a-vinyl form) and 34b (carbene ylide form) (Scheme 17) [73]. Concerning the group 7 recent examples of cis ylide rhenium complexes 36 cis-Me-Re-Me) have been reported from the reaction of the corresponding trans cationic alkyne derivatives 35 with PR" via a nucleophilic attack of this phosphine at the alkyne carbon. 

The vast majority of phosphine/phosphite-substituted products involve F-ligand ligation at late transition metals. In contrast, phosphite ligands displaced rhenium-coordinated CO or acetylene in [RePt3(/i-dppm)3(CO)3(L)l", - which are the... 

Platinum-bound phosphine and rhenium-ligated carbonyl irreversibly exchange on w arming a solution of Re2Pt(/r-H)2(CO)j (PPh3)2l above 213 a mix-... 

Complexity in the manganese and rhenium pentarbonyl halides substitution arises from the fact that these decompose in inert solvents to form the halogen-bridged dimers [M(CO)4X]2. Both monomers and dimers react with phosphines, arsines, pyridine, aniline etc. to give the disubstituted compounds M(CO)3XL2. Thus three final products or any mixture of them may be obtained, depending upon the precise reaction conditions... 

Saladino R, Crestini C, Costanzo G, DiMauro E (2005) On the Prebiotic Synthesis of Nucle-obases, Nucleotides, Oligonucleotides, Pre-RNA and Pre-DNA Molecules. 259 29-68 Santos I, Paulo A, Correia JDG (2005) Rhenium and Technetium Complexes Anchored by Phosphines and Scorpionates for Radiopharmaceutical Applications. 252 45-84 Santos M, see Szathmdry E (2005) 259 167-211... 

An interesting approach to rhenium bioconjugate formation that has been developed but apparently has yet to be fully evaluated from the standpoint of applicability and stability is the use of chelating and nonchelating phosphine imine and phosphine oxide ligands [110]. For... 

A rapid reaction between dioxorhenium(VII) and PPh3 was proposed in Eq. (11) for sake of consistency with the kinetic data. For reasons to be presented subsequently, this is shown as the addition of the phosphorus to an oxo oxygen. In effect, this is the reduction of rhenium(VII) with the concomitant creation of a rhenium(V) complex ligated by a phosphine oxide,... 

The results presented in Section IV.D.l show that the net loss of the dioxorhenium(VII) species, and the ultimate formation of the phosphate R3PO, must occur in two stages because the rate of reaction (17) shows a direct first-order phosphine dependence. That said, the chemical mechanism is still open to discussion does the first step entail abstraction of an oxo oxygen or addition to it If the former, the cycle is completed by PR3 coordination to a four-coordinate rhenium intermediate if the latter, the addition step is then followed by yet another ligand substitution reaction. The alternatives are presented in Schemes 1 and 2. 

Independent of this study, it has been shown that PPh3 is oxidized by Eh OOH more rapidly than MeSTol, when 1 catalyzes both reactions. Nonetheless, addition of 1.0 mM PPh3, along with 34 mM MeSTol, reduces t-i/2 from 3900 to 1900 s. Owing to these complications it was not possible to present a closed-form expression for the reaction rate. We do note the strong inhibition by phosphine, which inevitably remains coordinated to rhenium in a generally less active form, at least until oxidized. 

Scheme 11. Suggested mechanism for rhenium-catalyzed phosphine oxidation.

We conclude that only one phosphine attacks a ji-S group of 20. Indeed, the phosphine sulfide product from dmpm is Me2P(S)CH2PMe2, not a bis(sulfide).The other phosphine implicated by Eqs. (32) and (33), whether from a second PR3 or from a di-phosphine, adds as a Lewis base to rhenium. The basis for this is that a pyridine easily replaced one of the phosphines in the mechanism. This proposed mechanism should steer the reaction directly towards formation of 21, but owing to the dilemma posed in point (c), an intermediate likely intervenes. It can partition to the slowly-reacting 21 or to 23, the latter step requiring additional phosphine Scheme 13 shows the postulated mechanism. The dual role for phosphine and the use of Py in its place and the proposal for partitioning are shown in Scheme 14. 

The existence of the neutral rhenium carbonyl [Re(C0)4] was first claimed in 1965 206 but, although it is easily sublimed, it has not yet been characterized by mass spectrometry and the value of n is still not known. This colourless substance [v (CO) 2055 and 1995 cm-1 in CHC13] has been obtained as a by-product in the synthesis of Re2(CO)i0 starting from Re2S7, copper powder, and carbon monoxide at 85 atm, 200 °C206>. There has also been a report of the compound Re4(CO)10(PPh2Me)6, which can be considered to be a substitution product of the hypothetical species, Re4(CO)i6 it has been obtained by a photochemical reaction between Re2(CO)j0 and PPh2Me194. In both cases, and particularly in the phosphine derivative, a tetrahedral structure seems improbable because of steric constraints. 

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