Reactions of the dirhenium(II) complexes Re2X4(dppm)2 (X= Cl, Br; dppm = Ph2PCH2PPh2) with isocyanides. Part IX. New isomeric forms of the mixed carbonyl-isocyanide dirhenium(II) Complexes Re2 Cl4(dppm)2(CO)(CNxyl) and [Re2Cl3(dppm)2(CO)(CNxyl)2]O3SCF3 The X-ray crystal structure of [(xyl NC)2ClRe(?-dppm)2ReCl2(CO)] O3SCF3
“…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
“…All reactions were performed under an atmosphere of dry nitrogen. IR spectra, 1 H and 31 P{ 1 H} NMR spectra, and cyclic voltammetric measurements were determined as described previously. , Elemental microanalyses were performed by Dr. H. D. Lee of the Purdue University Microanalytical Laboratory.…”
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.…”
Section: Introductionmentioning
confidence: 99%
“…One system which exemplifies the range of isomers that can be obtained is the mixed carbonyl−xylyl isocyanide dirhenium cation [Re 2 Cl 3 (μ-dppm) 2 (CO)(CNXyl) 2 ] + (Xyl = xylyl), ,,, which has been definitively identified in at least three distinct structural forms. In this communication, we report details of the structural characterization of a fourth isomer of this complex cation.…”
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.
“…The genesis of this work was our discovery that an extensive series of stable geometrical isomers can be isolated and characterized from the reactions of the triply bonded dirhenium(II) complexes Re 2 X 4 (μ-dppm) 2 (X = Cl, Br; dppm = Ph 2 PCH 2 PPh 2 ) with various combinations of CO and RNC ligands. − An especially noteworthy example is the [Re 2 Cl 3 (μ-dppm) 2 (CO)(CNXyl) 2 ] + cation (Xyl = 2,6-dimethylphenyl), whose salts have been identified in three distinct isomeric forms 1 − 3 (see Scheme ). ,,, Of the two edge-sharing bioctahedral isomers 1 and 2 , the most thermodynamically stable form is 2 , ,, but neither converts to or is formed from 3 , which is prepared by a quite different synthetic route . We have now found that the thermolysis of 3 converts it quantitatively to the new isomeric form 4 (see Scheme ).…”
In the course of studying the factors which control the stereochemistry of multiply metal-metal bonded complexes with structures based on open bioctahedral and edge-sharing bioctahedral geometries (A and B, respectively; P-P represents a bridging bidentate phosphine), we have identified a reaction that is unprecedented in metal-metal multiple bond chemistry, 2 involving a simple isomerization in which a complex of type A converts to an isomeric form of type B with complete loss of the metal-metal bond.The genesis of this work was our discovery that an extensive series of stable geometrical isomers can be isolated and characterized from the reactions of the triply bonded dirhenium-(II) complexes Re 2 X 4 (µ-dppm) 2 (X ) Cl, Br; dppm ) Ph 2 PCH 2 -PPh 2 ) with various combinations of CO and RNC ligands. [3][4][5][6][7][8] An especially noteworthy example is the [Re 2 Cl 3 (µ-dppm) 2 -(CO)(CNXyl) 2 ] + cation (Xyl ) 2,6-dimethylphenyl), whose salts have been identified in three distinct isomeric forms 1-3 (see Scheme 1). 3,4,6,8 Of the two edge-sharing bioctahedral isomers 1 and 2, the most thermodynamically stable form is 2, 3,4,8 but neither converts to or is formed from 3, which is prepared by a quite different synthetic route. 6 We have now found that the thermolysis of 3 converts it quantitatively to the new isomeric form 4 (see Scheme 1). This isomerization represents the transformation of diamagnetic triply bonded compound to a paramagnetic isomer in which there is no metal-metal bond present.The transformation of the orange-brown isomer 3 to the blue isomer 4 occurs upon heating solutions of the triflate salt of 3 in 1,2-dichloroethane for 24 h. 9 This thermal isomerization can also be carried out in benzene or acetonitrile but requires longer reaction times. The analogous bromo analogue of 3 can, in a similar fashion, be converted to the di-µ-bromo complex [(XylNC)(OC)Re(µ-Br) 2 (µ-dppm) 2 ReBr(CNXyl)]O 3 SCF 3 . 10 In contrast to the open bioctahedral structure of 3, 6 the cation of 4 has a di-µ-halo-bridged edge-sharing bioctahedral geometry. The structure of the dirhenium cation is shown in Figure 1. 11 A plausible mechanism for the conversion of 3 to 4 is the type of "merry-go-round" process shown in Scheme 1. 12 This mechanism has previously 13 been used to explain the fluxionality of the multiply bonded edge-sharing bioctahedral complex Re 2 -Cl 4 (µ-dppm) 2 (CO) 2 . We have not found any conditions under which 4 converts to 1, 2, or 3.Complex 4 has IR-active ν(CO) and ν(CN) modes which agree with the presence of terminal CO and XylNC ligands.(1) Part 12. Reactions of the Dirhenium Complexes Re2X4(µ-dppm)2 (X ) Cl, Br; dppm ) Ph2PCH2PPh2) with Isocyanides. For the previous paper in this series, see: Wu, W.; Subramony, J. A.; Fanwick, P. E.; Walton, R.(9) A typical procedure is as follows. A sample of 3 as its triflate salt (133 mg, 0.079 mmol) was dissolved in 45 mL of 1,2-C2H4Cl2 and the resulting orange-yellow solution heated at reflux for 24 h. The solution changed color to green and, finally, to...
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