Reactions of the Dirhenium(II) Complexes Re2X4(μ-dppm)2 (X = Cl, Br; dppm = Ph2PCH2PPh2) with Isocyanides. 16.1 Complexes of the Type [Re2(μ-Br)2(μ-dppm)2Br(CO)(CNXyl)2]Y (Y = O3SCF3, PF6) That Exist in Isomeric Forms with Boat and Chair Conformations for the [Re2(μ-dppm)2] Unit
“…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. ,− …”
Section: Discussionmentioning
confidence: 79%
“…Up to three π-acceptor ligands (designated L, L‘ and L‘ ‘) can be incorporated into the coordination sphere of the triply bonded dirhenium(II) synthons Re 2 X 4 (μ-dppm) 2 (X = Cl, Br; dppm = Ph 2 PCH 2 PPh 2 ) as shown in the following sequence of reaction steps In the case of L = CO and L‘ = L‘ ‘ = XylNC (Xyl = 2,6-dimethylphenyl), a remarkable variety of structural isomers have been encountered with structures which are based upon open bioctahedral ( A ) and edge-sharing bioctahedral ( B ) geometries (L represents the halide, CO, or XylNC ligands) 1,3-11 with, in one instance, both boat and chair conformers for the [Re 2 (μ-dppm) 2 ] unit. , …”
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. ,− …”
Section: Discussionmentioning
confidence: 79%
“…Up to three π-acceptor ligands (designated L, L‘ and L‘ ‘) can be incorporated into the coordination sphere of the triply bonded dirhenium(II) synthons Re 2 X 4 (μ-dppm) 2 (X = Cl, Br; dppm = Ph 2 PCH 2 PPh 2 ) as shown in the following sequence of reaction steps In the case of L = CO and L‘ = L‘ ‘ = XylNC (Xyl = 2,6-dimethylphenyl), a remarkable variety of structural isomers have been encountered with structures which are based upon open bioctahedral ( A ) and edge-sharing bioctahedral ( B ) geometries (L represents the halide, CO, or XylNC ligands) 1,3-11 with, in one instance, both boat and chair conformers for the [Re 2 (μ-dppm) 2 ] unit. , …”
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 reactions of Re 2 Cl 4 (μ-dppm) 2 (dppm = Ph 2 PCH 2 PPh 2 ) with CO lead to the incorporation of up to three of these ligands into the dimetal coordination sphere to afford the complexes Re 2 Cl 4 (μ-dppm) 2 (CO), , Re 2 Cl 4 (μ-dppm) 2 (CO) 2 , and [Re 2 Cl 3 (μ-dppm) 2 (CO) 3 ] + . In addition, several extensive series of dirhenium(II) complexes have been isolated and structurally characterized which contain a combination of CO along with up to three xylyl isocyanide ligands, viz., Re 2 Cl 4 (μ-dppm) 2 (CO)(CNXyl), , [Re 2 Cl 3 (μ-dppm) 2 (CO)(CNXyl) 2 ] + , − and [Re 2 Cl 2 (μ-dppm) 2 (CO)(CNXyl) 3 ] 2+ . , Several of the analogous bromo complexes are also known. ,, These compounds exist in a variety of stable isomeric forms that are notable for the dependence of the Re−Re bond order on the structure of the isomer, and the rich metal-based redox chemistry that they exhibit. ,− …”
A study of the reactions between the triply bonded dirhenium(II) complexes Re2Cl4(mu-LL)2, where LL = Ph2PCH2PPh2 (dppm), Ph2PC(=CH2)PPh2 (dppE), or Cy2PCH2PCy2 (dcpm), with the isocyanides t-BuNC and XylNC (Xyl = 2,6-dimethylphenyl) show that complexes of the type Re2Cl4(mu-LL)2(CNR), Re2Cl4(mu-LL)2(CNR)2, and [Re2Cl3(mu-LL)2(CNR)3]+ are formed sequentially. Several of these have been structurally characterized by X-ray crystallography: Re2Cl4(mu-dppm)2(CNXyl) (2), Re2Cl4(mu-dcpm)2(CNXyl) (11), Re2Cl4(mu-dppE)2(CN-t-Bu)2 (6), Re2Cl4(mu-dcpm)2(CN-t-Bu)2 (12), and [Re2Cl3(mu-dppE)2(CN-t-Bu)3]Cl (7). Complex 2 has an A-frame-like structure with a single mu-Cl bridging ligand, whereas for 11 the structure is like that of 2 but without this bridge, viz., Cl2Re(mu-dppm)2ReCl2(CNXyl) with a Re-Cl bond approximately collinear with Re identical to Re. The symmetrical complexes 6 and 12 are essentially isostructural and have an anti-arrangement of the two t-BuNC ligands. Complex 7 has the open bioctahedral structure [(t-BuNC)2ClRe(mu-dppE)2ReCl2(CN-t-Bu)]+, which is quite different from that of the edge-sharing bioctahedron found in salts of the [Re2Cl3(mu-dppm)2(CNXyl)3]+ cation and its neutral congener Re2Cl3(mu-dppm)2(CNXyl)3; preliminary crystallographic data for the latter compound show the structure to be (XylNC)ClRe(mu-Cl)(mu-CNXyl)(mu-dppm)2ReCl(CNXyl) with an all-cis arrangement of XylNC ligands. The Re-Re bond distances of 2, 6, 7, 11, and 12 occur in the range 2.289-2.380 A and are consistent in all instances with the retention of a Re identical to Re bond, albeit weakened by some degree of Re-->CNR(pi*) back-bonding.
“…The incorporation of up to four π-acceptor ligands about the coordination sphere of the [Re 2 (μ-dppm) 2 ] 4+ unit (dppm = Ph 2 PCH 2 PPh 2 ) has been accomplished − in the following reaction sequence which utilizes the triply bonded dirhenium(II) complex Re 2 Cl 4 (μ-dppm) 2 as the starting material: Several of the analogous bromo complexes have also been isolated and characterized. ,,− …”
Section: Introductionmentioning
confidence: 99%
“…These systems are noteworthy for the remarkably large number of stable structural isomers that can be isolated, the dependence of the Re−Re bond order on the structure of the isomer, and the rich reversible redox chemistry that many of these complexes possess. − For example, our most recent study 1,15 has led to the isolation of four structurally distinct, noninterconvertible isomers of the [Re 2 Cl 2 (μ-dppm) 2 (CO)(CNXyl) 3 ] 2+ cation, each of which exhibits reversible redox chemistry that leads in two instances to coupled redox/isomerization processes. In all, the [Re 2 Cl 2 (μ-dppm) 2 (CO)(CNXyl) 3 ] n+ species ( n = 2, 1, or 0) exist in seven structural variants, which possess Re−Re bond orders of 3, 2, 1.5, 1 or 0.…”
Three of the five known isomers of Re(2)Cl(2)(&mgr;-dppm)(2)(CO)(CNXyl)(3) (labeled 4' '-8' ' in accord with earlier work) react with 1 equiv each of XylNC and TlO(3)SCF(3) in benzene to produce the symmetrical dirhenium(I) complex [Re(2)(&mgr;-Cl)(&mgr;-CO)(&mgr;-dppm)(2)(CNXyl)(4)]O(3)SCF(3) (I) in good yield. Isomers 4' ', 6' ', and 8' ' are converted to I, while 5' ' gives an unidentified mixture and isomer 7' ' is unreactive. When the reactions of 4' ', 5' ', 6' ', and 8' ' with TlO(3)SCF(3) are carried out in acetonitrile in the absence of XylNC, the compound [Re(2)Cl(&mgr;-dppm)(2)(CO)(CNXyl)(3)(NCCH(3))]O(3)SCF(3) can be isolated in three stable isomeric forms (A-C). Isomer B is unreactive, while A and C react with XylNC in benzene to afford I. Single-crystal X-ray structure determinations have been carried out on compounds I and B.
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