Phosphine complexes rhenium

The coordination chemistry of the hydrido/phosphine rhenium complexes can be extended to phosphonite and phosphite complexes. This has been demonstrated for monodentate ligands such as P(OEt)3, P(OCH2)3CEt and PPhtORE (R = Me, Et, Pri),2S8779,809,iii8 chelating phos-... 

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 rhenium complex 76 related to 74b was also prepared recently by Labinger and Bercaw using another synthetic strategy. 2 In this case, the pendant borane moieties were introduced by hydroboration of unsaturated phosphines in the coordination sphere of the metal. The cationic rhenium complex 75 featuring two diphenyl(vinyl)phosphines was readily converted into the corresponding bis(phosphine-borane) complex 76 (Scheme 45). The coordination mode of 76 was substantiated spectroscopically (5 nB = 87.7 ppm) and crystallographically. 

Abstract This review presents a comprehensive overview of the most significant developments in the chemistry of technetium and rhenium complexes anchored by heterofunc-tionalized phosphines and by hard and soft scorpionates. The main goal is to provide the reader with chemical,radiochemical and biological knowledge which is expected to enhance the application of these types of compounds in the development of target-specific radiopharmaceuticals. 

Scheme 11 Reactions of rhenium complexes with silylated phosphine proligands...

A suspension of 3.83 g (5.4 mmol) of mer-trichlorotris(dimethylphenyl-phosphine)rhenium(HI) (or its benzene solvate)1 and 2.48 g (65 mmol) of sodium tetrahydroborate(l —) in 100 mL of absolute ethanol is heated under nitrogen on a steam bath until the orange complex dissolves to give a colorless suspension. The solvent is evaporated under reduced pressure, and the residue is extracted with three 75-mL portions of benzene. The benzene extract is evaporated, and the residue is crystallized from 60 mL of absolute ethanol to give prisms of tris(dimethylphenylphosphine)pentahydrido-rhenium(V) the yield is 2.2 g (67%). Anal. Calcd. for C24H38P3Re C, 47.59 H, 6.32 P, 15.34. Found (checkers values) C, 47.60 H, 6.24 P, 15.51. 

In principle, steric control may be exercised by a chiral transition metal catalyst in which the metal center is the asymmetry origin rather than the phosphine or its substituents. Gladysz and coworkers have separated the enantiomers of rhenium complexes using HPLC. 

Oxo-rhenium complexes can catalyze various OAT reactions between suitable oxo-donors (XO = sulfoxides (R2SO) tertiary amine A-oxides (R3NO) pyridine A-oxide (C5H5NO, PyO) triphenyl-phosphine, -arsine, or -stilbene oxide (R3AO) (A = P, As, Sb) peroxides (Bn OOH, H2O2) ... 

Complexes of the general formula /ac-Re(a-diimine)(CO)3X and Re(a-diimine)(CO)2XX (where ot-diimine = bpy, phen, substituted bpy or phen, etc. and X, X = halide, solvent, alkyl, benzyl, monodentate phosphine, CO, etc.), have attracted interest since the mid-1970s [51-53]. Many of these complexes show emission from their lowest long-lived MLCT state at room temperatme in solution. Their catalytic properties for CO2 reduction have also been investigated. Electrolysis of a solution containing/uc-Re(bpy)(CO)3 Cl and 0.1 M BU4NPF6 in freshly distilled C02 saturated MeCN at —1.5 V (vs. SCE) produces both CO and C03 with cmrent efficiencies of 98 and 110 %, respectively [54]. Further, yhc-Re(bpy)(CO)3X (X = Cl, Br ) has been used successfully as a photocatalyst for CO2 reduction to CO with TEOA in DMF [55-58]. When X = Cl , a quantiun yield of 0.14 has been measured in the presence of excess Cl". A formato-rhenium complex,/ac-Re(bpy)(C0)3(02CH), has been isolated in the absence of excess Cl". 

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