Rhenium complex isoelectronic

Chiral rhenium complexes, such as 1 and 4, are isoelectronic to the a-alkoxy vinyl-iron complexes discussed above and they exhibit analogous chemistry in many respects. Like the iron complexes, they are prepared as the Z-isomer and are readily alkylated by primary iodoalkanes and (bromomethyl)benzene with efficient 1,3-asymmetric induction97. Subsequent, spontaneous loss of halomethane produces the elaborated rhenium-acyl complexes. Two examples of the stereocontrolled preparation of diastereomeric rhenium-acyl complexes via this methodology are illustrated. 

Under the influence of water, cationic manganese compounds decompose immediately, as in organic donor solvents such as acetone and tetrahydrofuran. In contrast to isoelectronic compounds of the chromium group, diolefin technetium and rhenium complexes have cis structures. In aqueous solution, the cation [Re(CO)4 ( 2114)2] is stable the Re —C2H4 bond in [Re(CO)5 ( 2114)] is also stable. There is no exchange between free ethylene and the ethylene in the complex. 

Rhenium forms a large number of mononuclear nonoxo complexes in oxidation states I through VI. The redox potentials of selected examples are included in Table 1. The majority of compounds are octahedral. However, notable exceptions include the pentagonal bipyra-midal Re(CN)y3-/ - (E° = -0.64 V) and the square antiprismatic Re(CN)g (ii =+1.64V) couples [23]. The latter complexes are similar in behavior to the isoelectronic Mo species. 

Rhenium-acyl complexes, such as 1, are isoelectronic with the iron-acyl complexes discussed above and many reactivity patterns are common to the two groups of compounds. Treatment of complex 1 with strong bases, such as butyllithium or lithium diisopropylamide, results in abstraction of a cyclopentadienyl proton which is followed by rapid migration of the acyl ligand to the cyclopentadienyl ring to produce the metal-centered anion 384. Alkylation of 3generates a metal-alkyl species, such as 4. 

This is, as expected, the rarest oxidation state as far as non-organometallic complexes of rhenium are concerned. The dirhenium phosphite complex Re2[P(OMe)3]10 has been prepared12,13 in low yield by several methods, viz. the potassium-potassium iodide reduction of ReOCl3(py)2 or an ReCLj-pyridine complex, followed by treatment with trimethyl phosphite. This yellow complex displays a 31P H) NMR spectrum that appears as a first order AB4 pattern, and is isoelectronic with Re2(CO)l0. It reacts with H2 upon photolysis in THF solution to produce hydridorhenium(III) and other species.13 The related triphenyl phosphite derivative Re2[P(OPh)3]l0 has been described14 as a product of the reaction between ReH3(PPh3)4 and P(OPh)3. 

Why has it taken a period of more than twenty years since the discovery of Mimoun type complexes that the quality of isoelectronic rhenium 0x0 complexes for catalytic O-transfer reactions has been recognized and proven The key to success with 2 lies in its organometallic functionality. More polar Re-X groups (X = OR, NR2, Cl, etc.) are generally more rapidly protolyzed to give catalytically inactive compounds than the relatively nonpolar Re-R unit in 2, which is stable... 

In these rhenium nitrosyl complexes the nitrosyl ligand takes different functions (1) as an ancillary NO ligand mimicking isoelectronic metal carbonyls (2) as a frans-influence ligand to activate donor ligands for atom or group transfer reaction. 

Ligand-metal bifunctional catalysis provides an efficient method for the hydrogenation of various unsaturated organic compounds. Shvo-type [83-85] Ru-H/OH and Noyori-type [3-7] Ru-H/NH catalysts have demonstrated bifimctionality with excellent chemo- and enantioselectivities in transfer hydrogenations and hydrogenations of alkenes, aldehydes, ketones, and imines. Based on the isoelectronic analogy of H-Ru-CO and H-Re-NO units, it was anticipated that rhenium nitrosyl-based bifunctional complexes could exhibit catalytic activities comparable to the ruthenium carbonyl ones (Scheme 29) [86]. 

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