Reactions of the dirhenium(II) complexes Re2X4(dppm)2 (X = Cl or Br; dppm = Ph2PCH2PPh2) with isocyanides. 4. Isomerism in mixed carbonyl-isocyanide complexes of stoichiometry [Re2Cl3(dppm)2(CO)2(CNR)]n+ (n = 0 or 1) and [Re2Cl3(dppm)2(CO)(CNR)2]+ (R = tert-Bu or xylyl), which possess edge-shared bioctahedral structures
Abstract:281ChemInform Abstract The multiply bonded dirhenium isocyanide complexes (I) react with CO (II) in the presence of TlPF6 to yield the cationic isocyanide-carbonyl species (III). These undergo thermal isomerization to the isomers (IV) which contain an all-cis arrangement of CO and isocyanide ligands. (IIIa) and (IV) can also be obtained from corresponding CO analogues (VIa) and isocyanides (V) or (VIb) and CO. The spectroscopic (IR, NMR, electronic absorption) and electrochemical properties of (III) and (IV), … Show more
“…Up to three π-acceptor ligands have been incorporated into the dimetal complex in a stepwise fashion as shown in Scheme ; in the case of compounds of types Re 2 X 4 (μ-dppm) 2 L, Re 2 X 4 (μ-dppm) 2 LL‘, and [Re 2 X 3 (μ-dppm) 2 LL‘L‘‘] + , structural isomerism has been encountered with certain combinations of X, L, L‘, and L‘‘. ,,− In the present report, we describe the first instances of the coordination of four π-acceptor ligands to the (Re⋮Re) 4+ core to give complexes which exist in different isomeric forms. This behavior demonstrates the remarkable resistance of the [Re 2 (μ-dppm) 2 ] 4+ moiety to cleavage and disruption of the Re−Re bonding. 1 Products from the Reactions of Re 2 X 4 (μ-dppm) 2 with Carbon Monoxide and Organic Isocyanides a a CO and the RNC ligands are represented by L, L‘, and L‘‘.…”
The complexes Re 2 Cl 4 (µ-dppm) 2 and Re 2 Br 4 (µ-dppm) 2 have proven to be very effective synthons in the development of the reaction chemistry of the electron-rich triple bond (σ 2 π 4 δ 2 δ* 2 electronic configuration). 2 One noteworthy aspect of this chemistry is the ability of Re 2 X 4 (µ-dppm) 2 to be complexed by π-acceptor ligands, especially CO and organic isocyanides, to afford dinuclear species in which the dppm ligand bridges play a pivotal role in stabilizing the dimetal unit, 2,3 thereby permitting the development of novel dimetal redox chemistry. 4 In the absence of the µ-dppm units, fragmentation to mononuclear species can readily occur, as happens in the case of the triply bonded complexes Re 2 X 4 (PR 3 ) 4 , 5,6 which contain monodentate rather than bridging bidentate phosphines.Up to three π-acceptor ligands have been incorporated into the dimetal complex in a stepwise fashion as shown in Scheme 1; in the case of compounds of types Re 2 X 4 (µ-dppm) 2 L, Re 2 X 4 (µ-dppm) 2 LL′, and [Re 2 X 3 (µ-dppm) 2 LL′L′′] + , structural isomerism has been encountered with certain combinations of X, L, L′, and L′′. 1,3,[7][8][9][10][11][12][13] In the present report, we describe the first instances of the coordination of four π-acceptor ligands to the (RetRe) 4+ core to give complexes which exist in different isomeric forms. This behavior demonstrates the remarkable resistance of the [Re 2 (µ-dppm) 2 ] 4+ moiety to cleavage and disruption of the Re-Re bonding.We established previously 9 that the monocarbonyl complex Re 2 Cl 4 (µ-dppm) 2 (CO), 1, reacts with XylNC in acetonitrile to afford the open bioctahedral complex Re 2 Cl 4 (µ-dppm) 2 (CO)-(CNXyl), 2, which in turn reacts with a further equivalent of XylNC in dichloromethane, in the presence of Tl + , to give salts of the [Re 2 Cl 3 (µ-dppm) 2 (CO)(CNXyl) 2 ] + cation, 3. We have now found that the reactions of the neutral complex 2 and the triflate salt of 3 with equimolar mixtures of TlO 3 SCF 3 and XylNC afford the salt [Re 2 Cl 2 (µ-dppm) 2 (CO)(CNXyl) 3 ](O 3 -SCF 3 ) 2 in two different isomeric forms (complexes 4 and 5 in Scheme 2). 14,15 We have not found any thermal conditions by
“…Up to three π-acceptor ligands have been incorporated into the dimetal complex in a stepwise fashion as shown in Scheme ; in the case of compounds of types Re 2 X 4 (μ-dppm) 2 L, Re 2 X 4 (μ-dppm) 2 LL‘, and [Re 2 X 3 (μ-dppm) 2 LL‘L‘‘] + , structural isomerism has been encountered with certain combinations of X, L, L‘, and L‘‘. ,,− In the present report, we describe the first instances of the coordination of four π-acceptor ligands to the (Re⋮Re) 4+ core to give complexes which exist in different isomeric forms. This behavior demonstrates the remarkable resistance of the [Re 2 (μ-dppm) 2 ] 4+ moiety to cleavage and disruption of the Re−Re bonding. 1 Products from the Reactions of Re 2 X 4 (μ-dppm) 2 with Carbon Monoxide and Organic Isocyanides a a CO and the RNC ligands are represented by L, L‘, and L‘‘.…”
The complexes Re 2 Cl 4 (µ-dppm) 2 and Re 2 Br 4 (µ-dppm) 2 have proven to be very effective synthons in the development of the reaction chemistry of the electron-rich triple bond (σ 2 π 4 δ 2 δ* 2 electronic configuration). 2 One noteworthy aspect of this chemistry is the ability of Re 2 X 4 (µ-dppm) 2 to be complexed by π-acceptor ligands, especially CO and organic isocyanides, to afford dinuclear species in which the dppm ligand bridges play a pivotal role in stabilizing the dimetal unit, 2,3 thereby permitting the development of novel dimetal redox chemistry. 4 In the absence of the µ-dppm units, fragmentation to mononuclear species can readily occur, as happens in the case of the triply bonded complexes Re 2 X 4 (PR 3 ) 4 , 5,6 which contain monodentate rather than bridging bidentate phosphines.Up to three π-acceptor ligands have been incorporated into the dimetal complex in a stepwise fashion as shown in Scheme 1; in the case of compounds of types Re 2 X 4 (µ-dppm) 2 L, Re 2 X 4 (µ-dppm) 2 LL′, and [Re 2 X 3 (µ-dppm) 2 LL′L′′] + , structural isomerism has been encountered with certain combinations of X, L, L′, and L′′. 1,3,[7][8][9][10][11][12][13] In the present report, we describe the first instances of the coordination of four π-acceptor ligands to the (RetRe) 4+ core to give complexes which exist in different isomeric forms. This behavior demonstrates the remarkable resistance of the [Re 2 (µ-dppm) 2 ] 4+ moiety to cleavage and disruption of the Re-Re bonding.We established previously 9 that the monocarbonyl complex Re 2 Cl 4 (µ-dppm) 2 (CO), 1, reacts with XylNC in acetonitrile to afford the open bioctahedral complex Re 2 Cl 4 (µ-dppm) 2 (CO)-(CNXyl), 2, which in turn reacts with a further equivalent of XylNC in dichloromethane, in the presence of Tl + , to give salts of the [Re 2 Cl 3 (µ-dppm) 2 (CO)(CNXyl) 2 ] + cation, 3. We have now found that the reactions of the neutral complex 2 and the triflate salt of 3 with equimolar mixtures of TlO 3 SCF 3 and XylNC afford the salt [Re 2 Cl 2 (µ-dppm) 2 (CO)(CNXyl) 3 ](O 3 -SCF 3 ) 2 in two different isomeric forms (complexes 4 and 5 in Scheme 2). 14,15 We have not found any thermal conditions by
“…Background. The yellow isomeric form of the salts [Re 2 Cl 3 (μ-dppm) 2 (CO)(CNXyl) 2 ]Y (Y = Cl ( 1a ), O 3 SCF 3 ( 1b ), PF 6 ( 1c ), ReO 4 ( 1d )) 5,9 has previously been assigned the edge-sharing bioctahedral structure as depicted in structure 1 , based upon the similarity of the spectroscopic and electrochemical properties of these salts to those of analogous bis(carbonyl)−monoisocyanide complexes of composition [Re 2 Cl 3 (μ-dppm) 2 (CO) 2 (CNR)]Y (R = i -Pr, t -Bu, Xyl), , the structures of which have been established by X-ray crystallography (structure 2 ). This assignment of the structure of 1 is now known to be incorrect (vide infra) .…”
Section: Resultsmentioning
confidence: 99%
“…The yellow isomeric forms of the complex [Re 2 Cl 3 (μ-dppm) 2 (CO)(CNXyl) 2 ]Y, viz. [(XylNC)ClRe(μ-Cl)(μ-CNXyl)(μ-dppm) 2 ReCl(CO)]Y (Y = Cl ( 1a ), O 3 SCF 3 ( 1b ), or PF 6 ( 1c )), , and the compounds [( t -BuNC)ClRe(μ-Cl)(μ-CNXyl)(μ-dppm) 2 ReCl(CO)]PF 6 ( 8 ) 7 and [(η 5 -C 5 H 5 ) 2 Fe]PF 6 were prepared according to literature procedures. 2,6-Dimethylphenyl isocyanide, XylNC, was purchased from Fluka Chemical, Corp., and (η 5 -C 5 H 5 ) 2 Co and tert -butyl isocyanide ( t -BuNC) were purchased from Aldrich Chemical, Co.…”
Section: Methodsmentioning
confidence: 99%
“…The ability of the triply bonded dirhenium(II) synthons Re 2 X 4 (μ-dppm) 2 (X = Cl, Br; dppm = Ph 2 PCH 2 PPh 2 ) to react with carbon monoxide and organic isocyanides, with incorporation of up to three of these ligands into the coordination sphere of the dimetal unit, is well-established (see Table ). − In several instances, these complexes have been shown to exist as structural isomers. ,− ,, The scope of this chemistry is currently under investigation in our laboratory, a principle aim of which is to identify new classes and types of isomers in redox-active dimetal systems which contain metal−metal bonds.…”
A yellow form of the dirhenium salts of the type
[Re2Cl3(μ-dppm)2(CO)(CNXyl)2]Y
(Y =
Cl, O3SCF3, PF6,
ReO4) has been shown to have the μ-CNXyl-bridged
structure [(XylNC)ClRe(μ-Cl)(μ-CNXyl)(μ-dppm)2ReCl(CO)]+
on the basis of an X-ray crystal structure determination of its neutral paramagnetic congener. The Re−Re bond
length in the structure of
Re2Cl3(μ-dppm)2(CO)(CNXyl)2
is 2.7155(9) Å, in accord with the presence of a formal
Re−Re bond order of 1.5. This particular cation constitutes the fourth
isomer of
[Re2Cl3(μ-dppm)2(CO)(CNXyl)2]+ to have been structurally
characterized.
“…As part of a study concerned with the consequences of electron transfer in bimetallic transition metal complexes, the redox behavior of ESBO [Re 2 (μ-NCS) 2 (NCS) 8 ] 3- has been investigated. , Like many ESBO dirhenium compounds, − the aforementioned complex has been found to display extensive redox chemistry in nonaqueous solvents; a series of sequential one-electron processes was observed, in addition to an overall two-electron process. Each of these processes has been examined by in situ spectroelectrochemical measurements, which reveal that both the one-electron oxidized and one-electron reduced products are remarkably stable and retain the ESBO structure.…”
Electrochemical and spectroelectrochemical studies have shown that
the edge-shared bioctahedral
[Re2(μ-NCS)2(NCS)8]3- anion can be reversibly
oxidized and reduced (in one-electron steps) with retention of
structure to give
the even electron species
[Re2(μ-NCS)2(NCS)8]2-
and
[Re2(μ-NCS)2(NCS)8]4-.
A second oxidation of [Re2(μ-NCS)2(NCS)8]3-
is however only partially reversible, the
[Re2(μ-NCS)2(NCS)8]1-
ion being of limited stability.
Further irreversible oxidation of this latter species can be
achieved in what appears to be a ligand-based process
yielding cyanide-containing species. An irreversible two-electron
reduction of
[Re2(μ-NCS)2(NCS)8]4-
culminates
in structural rearrangement to the direct metal−metal-bonded ion
[Re2(NCS)8(NCS)2]6-,
as shown by voltammetric
and spectroelectrochemical measurements. Re-oxidation of
[Re2(NCS)8(NCS)2]6-
results in the quantitative re-formation of the edge-shared structure
[Re2(μ-NCS)2(NCS)8]4-.
This reversible structural interconversion occurs
in both noncoordinating and coordinating solvents, as well as in the
presence of a high concentration of free
Cl-.
The redox behavior of
[Re2(NCS)8]2-
has also been reinvestigated, and the relationship between the direct
metal−metal-bonded and edge-shared bioctahedral structures established.
Oxidation of
[Re2(NCS)8]2-
at room temperature
results in the formation of
[Re2(μ-NCS)2(NCS)8]2-
and NCS--depleted products.
[Re2(NCS)8]2-
reacts immediately
with 2 mol equiv of NCS- to give
[Re2(μ-NCS)2(NCS)8]4-,
which is susceptible to aerial oxidation. At low
temperature, however, the one-electron oxidation and reduction of
[Re2(NCS)8]2-
become reversible on the time
scale of the IR spectroelectrochemical experiment, such that
[Re2(NCS)8]1-
and
[Re2(NCS)8]3-
have been
characterized in situ. Further reduction of
[Re2(NCS)8]3-
to
[Re2(NCS)8]4-
is partially reversible under these
conditions thus permitting characterization of the latter
species.
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