Reactions of the Dirhenium(II) Complexes Re2X4(μ-dppm)2 (X = Cl, Br; dppm = Ph2PCH2PPh2) with Isocyanides. 13.1 Identification of a New Structural Isomer of the Dirhenium Cation [Re2Cl3(μ-dppm)2(CO)(CNXyl)2]+ and Its Isomerization Behavior. Structural Characterization of (XylNC)ClRe(μ-Cl)(μ-CNXyl)(μ-dppm)2ReCl(CO)
Abstract: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
[Re2C… Show more
“…The second one-electron reductions to 5 ‘ ‘ and 6 ‘ ‘, give compounds which are structurally similar to 5a ‘ and 6a ‘. These coupled redox/isomerization processes, as well as the discovery that solutions of 6a ‘ and 6 ‘ ‘ in acetonitrile and benzene slowly isomerize to additional isomeric forms ( 7a ‘ and 8 ‘ ‘, respectively), reveal a dimension to the isomer chemistry of multiply bonded dirhenium compounds that contain the [Re 2 (μ-dppm) 2 ] moiety which we have not encountered in our previous studies of the [Re 2 Cl 3 (μ-dppm) 2 (CO)(CNXyl) 2 ] + cation. ,− …”
The reactions of the multiply bonded dirhenium(II) complexes Re(2)Cl(4)(&mgr;-dppm)(2)(CO), Re(2)Cl(4)(&mgr;-dppm)(2)(CO)(CNXyl), and [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)]O(3)SCF(3) (dppm = Ph(2)PCH(2)PPh(2); Xyl = 2,6-dimethylphenyl) with the requisite number of equivalents of TlO(3)SCF(3) and XylNC lead to three, non-interconvertible, structural isomers of the complex [Re(2)Cl(2)(&mgr;-dppm)(2)(CO)(CNXyl)(3)](O(3)SCF(3))(2) (4a, 5a, and 6a; a signifies a triflate salt). Each of these complexes undergoes two reversible one-electron reductions which afford the redox pairs 4a'/4' ', 5a'/5' ', and 6a'/6' ', respectively. While 4a' and 4' ' have structures which are very similar to that of 4a, the complexes 5a'/5' ' and 6a'/6' ' have structures which differ from 5a and 6a, thereby establishing the existence of coupled redox/isomerization reactions. Solutions of 6a' in acetonitrile and 6' ' in benzene slowly convert to the new isomers 7a' and 8' ', respectively, which are in turn found to be members of the redox series 7'/7' ' and 8/8'/8' '. In all, the [Re(2)Cl(2)(&mgr;-dppm)(2)(CO)(CNXyl)(3)](n+) species (n = 2, 1, or 0) have been found to exist in seven distinct structural forms which possess Re-Re bond orders of 3, 2, 1.5, 1, or 0 depending on the specific bioctahedral structure which is assumed and the charge on the complex. Single-crystal X-ray structure determinations have been carried out on the seven complexes 4' ', 5a, 6a, 6a', 6' ', 7a', and 7' '.
“…The second one-electron reductions to 5 ‘ ‘ and 6 ‘ ‘, give compounds which are structurally similar to 5a ‘ and 6a ‘. These coupled redox/isomerization processes, as well as the discovery that solutions of 6a ‘ and 6 ‘ ‘ in acetonitrile and benzene slowly isomerize to additional isomeric forms ( 7a ‘ and 8 ‘ ‘, respectively), reveal a dimension to the isomer chemistry of multiply bonded dirhenium compounds that contain the [Re 2 (μ-dppm) 2 ] moiety which we have not encountered in our previous studies of the [Re 2 Cl 3 (μ-dppm) 2 (CO)(CNXyl) 2 ] + cation. ,− …”
The reactions of the multiply bonded dirhenium(II) complexes Re(2)Cl(4)(&mgr;-dppm)(2)(CO), Re(2)Cl(4)(&mgr;-dppm)(2)(CO)(CNXyl), and [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)]O(3)SCF(3) (dppm = Ph(2)PCH(2)PPh(2); Xyl = 2,6-dimethylphenyl) with the requisite number of equivalents of TlO(3)SCF(3) and XylNC lead to three, non-interconvertible, structural isomers of the complex [Re(2)Cl(2)(&mgr;-dppm)(2)(CO)(CNXyl)(3)](O(3)SCF(3))(2) (4a, 5a, and 6a; a signifies a triflate salt). Each of these complexes undergoes two reversible one-electron reductions which afford the redox pairs 4a'/4' ', 5a'/5' ', and 6a'/6' ', respectively. While 4a' and 4' ' have structures which are very similar to that of 4a, the complexes 5a'/5' ' and 6a'/6' ' have structures which differ from 5a and 6a, thereby establishing the existence of coupled redox/isomerization reactions. Solutions of 6a' in acetonitrile and 6' ' in benzene slowly convert to the new isomers 7a' and 8' ', respectively, which are in turn found to be members of the redox series 7'/7' ' and 8/8'/8' '. In all, the [Re(2)Cl(2)(&mgr;-dppm)(2)(CO)(CNXyl)(3)](n+) species (n = 2, 1, or 0) have been found to exist in seven distinct structural forms which possess Re-Re bond orders of 3, 2, 1.5, 1, or 0 depending on the specific bioctahedral structure which is assumed and the charge on the complex. Single-crystal X-ray structure determinations have been carried out on the seven complexes 4' ', 5a, 6a, 6a', 6' ', 7a', and 7' '.
“…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
“…The reactions of the dirhenium(II) synthons Re 2 X 4 (μ-dppm) 2 (X = Cl, Br; dppm = Ph 2 PCH 2 PPh 2 ) with various combinations of CO and organic isocyanide ligands have led to several series of bioctahedral complexes which have structures based upon open bioctahedral ( A ) and edge-sharing bioctahedral ( B ) geometries. In some instances, structural isomers have been isolated, the most striking instances being in the case of the salts of the [Re 2 X 3 (μ-dppm) 2 (CO)(CNXyl) 2 ] + cations (Xyl = 2,6-dimethylphenyl), which have been identified in at least six different structural forms (Chart ). − The identity of all but one of these (structure 6 ) have been confirmed by single-crystal X-ray structure determinations. During the course of our studies on the synthesis and characterization of the dirhenium cation 5 (X = Br), which we isolated as its O 3 SCF 3 - and PF 6 - salts, we obtained spectroscopic evidence for the existence of this complex in two very similar structural forms.…”
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