ABSTRACT
Pyridine-2-carboxylic acid, pyridine-2,3-dicarboxylic acid, and pyridine-2,4-dicarboxylic acid or their [(Ph(3)P)(2)N](+) salts react with the triply bonded dirhenium(II) complex Re(2)Cl(4)(mu-dppm)(2) (dppm = Ph(2)PCH(2)PPh(2)) in refluxing ethanol to afford unsymmetrical substitution products of the type Re(2)(eta(2)-N,O)Cl(3)(mu-dppm)(2), where N,O represents a chelating pyridine-2-carboxylate ligand (N,O = O(2)C-2-C(5)H(4)N (1), O(2)C-2-C(5)H(3)N(-3-CO(2)Et) (3), or O(2)C-2-C(5)H(3)N(-4-CO(2)H) (4)). The carboxylate groups in the 3- and 4- positions are not bound to the metal centers; in the case of 3 this group undergoes esterification in the refluxing ethanol solvent. Structure determinations have shown that 1, 3, and 4 possess similar structures in which there is an axial Re-O (carboxylate) bond (collinear with the Re(triple bond)Re bond) and the mu-dppm ligands are bound in a trans,cis fashion to the two Re atoms which have the ligand atom arrangement [P(2)NOClReReCl(2)P(2)]. The tridentate dianionic pyridine-2,6-dicarboxylate ligand (dipic) reacts with Re(2)Cl(4)(mu-dppm)(2) in ethanol at room temperature to give a compound Re(2)(dipic)Cl(2)(mu-dppm)(2) (6) in which the dipic ligand is bound in a symmetrical eta(3)-(O,N,O) fashion to one Re atom, with the N atom in an axial position (collinear with the Re(triple bond)Re bond) and with preservation of the same trans,trans coordination of the mu-dppm ligands that is present in Re(2)Cl(4)(mu-dppm)(2). Under reflux conditions, this kinetic product isomerizes to the thermodynamically favored isomer 5 with an unsymmetrical structure in which the dipic ligand chelates to one Re atom (as in 1, 3, and 4) and uses its other carboxylate group to bridge to the second Re atom. The isomerization of 6 to 5, which also results in a change in the coordination of the pair of mu-dppm ligand to trans,cis, is believed to occur by a partial "merry-go-round" process, a mechanism that probably explains the structures of the thermodynamic products 1, 3, and 4. The reaction of Re(2)Cl(4)(mu-dppm)(2) with pyridine-3-carboxylate gives the trans isomer of Re(2)(mu:eta(2)-O(2)C-3-C(5)H(4)N)(2)Cl(2)(mu-dppm)(2) (2) in which a pair of carboxylate bridges are present and the pyridine N atom is not coordinated. Single-crystal X-ray structural details are reported for 1-6.
ABSTRACT
The triply bonded dirhenium(II) synthons Re(2)X(4)(mu-dppm)(2) (X = Cl, Br; dppm = Ph(2)PCH(2)PPh(2)) react with acetylene at room temperature in CH(2)Cl(2) and acetone to afford the bis(acetylene) complexes Re(2)X(4)(mu-dppm)(2)(mu:eta(2),eta(2)-HCCH)(eta(2)-HCCH) (X = Cl (3), Br(4)). Compound 3 has been derivatized by reaction with RNC ligands in the presence of TlPF(6) to give unsymmetrical complexes of the type [Re(2)Cl(3)(mu-dppm)(2)(mu:eta(2),eta(2)-HCCH)(eta(2)-HCCH)(CNR)]PF(6) (R = Xyl (5), Mes (6), t-Bu (7)), in which the RCN ligand has displaced the chloride ligand cis to the eta(2)-HCCH ligand. The reaction of 3 with an additional 1 equiv of acetylene in the presence of TlPF(6) gives the symmetrical all-cis isomer of [Re(2)Cl(3)(mu-dppm)(2)(mu:eta(2),eta(2)-HCCH)(eta(2)-HCCH)(2)]PF(6) (8). The two terminal eta(2)-HCCH ligands in 8 are very labile and can be displaced by CO and XylNC to give the complexes [Re(2)Cl(3)(mu-dppm)(2)(mu:eta(2),eta(2)-HCCH)(L)(2)]Y (L = CO when Y = PF(6) (9); L = CO when Y = (PF(6))(0.5)/(H(2)PO(4))(0.5) (10); L = XylNC when Y = PF(6) (11)). These substitution reactions proceed with retention of the all-cis stereochemistry. Single-crystal X-ray structure determinations have been carried out on complexes 3, 5, 8, 10, and 11. In no instance have we found that the acetylene ligands undergo reductive coupling reactions.
ABSTRACT
The pseudotetrahedral complexes [Cu(NN)(DPEphos)]BF(4), where DPEphos = bis[2-(diphenylphosphino)phenyl]ether and NN = 1,10-phenanthroline (1), 2,9-dimethyl-1,10-phenanthroline (2), 2,9-di-n-butylphenanthroline (3), or two dimethylcyanamides (4), and NiCl(2)(DPEphos) (5) have been synthesized and structurally characterized by X-ray crystallography and their solution properties examined by use of a combination of cyclic voltammetry, NMR spectroscopy, and electronic absorption spectroscopy. Complexes 1-4 possess a reversible Cu(II)/Cu(I) couple at potentials upward of +1.2 V versus Ag/AgCl. Compounds 1-3 exhibit extraordinary photophysical properties. In room-temperature dichloromethane solution, the charge-transfer excited state of the dmp (dbp) derivative exhibits an emission quantum yield of 0.15 (0.16) and an excited-state lifetime of 14.3 mus (16.1 mus). Coordinating solvents quench the charge-transfer emission to a degree, but the photoexcited dmp complex 2 retains a lifetime of over a microsecond in acetone, methanol, and acetonitrile.
ABSTRACT
The substitution of the mu-acetato ligands in cis-Re(2)(mu-O(2)CCH(3))(2)Cl(2)(mu-dppm)(2) (1, dppm = Ph(2)PCH(2)PPh(2)) and trans-Re(2)(mu-O(2)CCH(3))(2)Cl(2)(mu-dppE)(2) (2, dppE = Ph(2)PC(=CH(2))PPh(2)) by [4-Ph(2)PC(6)H(4)CO(2)](-) occurs with retention of stereochemistry to give cis-Re(2)(mu-O(2)CC(6)H(4)-4-PPh(2))(2)Cl(2)(mu-dppm)(2) (3) and trans-Re(2)(mu-O(2)CC(6)H(4)-4-PPh(2))(2)Cl(2)(mu-dppE)(2) (6), respectively. The uncoordinated phosphine groups in complexes 3 and 6 have been used to form mixed-metal assemblies with Au(I) and Pd(II), including the Re(2)Pd(2) complex cis-Re(2)(mu-O(2)CC(6)H(4)-4-PPh(2))(2)Cl(2)(mu-dppm)(2)(Pd(2)Cl(4)) (5), in which the planar [(P)ClPd(mu-Cl)(2)PdCl(P)] unit has the unusual cis structure. The crystal structures of 3 and 5 have been determined.
ABSTRACT
This report describes new, readily accessible copper(I) complexes that can exhibit unusually long-lived, high quantum yield emissions in fluid solution. The complexes are of the form [Cu(NN)(POP)]+ where NN denotes 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (dmp) or 2,9-di-n-butyl-1,10-phenanthroline (dbp) and POP denotes bis[2-(diphenylphosphino)phenyl] ether. Modes of characterization include X-ray crystallography and cyclic voltammetry. The complexes each have a pseudotetrahedral coordination geometry and a Cu(II)/Cu(I) potential upward of +1.2 V vs Ag/AgCl. In room-temperature dichloromethane solution, charge-transfer excited states of the dmp and dbp derivatives exhibit respective emission quantum yields of 0.15 and 0.16 and corresponding excited-state lifetimes of 14.3 and 16.1 mus, respectively. Despite the fact that coordinating solvents usually quench charge-transfer emission from copper systems, the photoexcited dmp (dbp) complex retains a lifetime of 2.4 mus (5.4 mus) in methanol.
ABSTRACT
The quadruply bonded dirhenium(III) complex (n-Bu(4)N)(2)Re(2)Cl(8) reacts with tridentate ligands that contain essentially planar P,O,P donor sets to afford the complexes Re(2)Cl(6)(eta(3)-L(1)) (3) (L(1) = bis[2-(diphenylphosphino)phenyl]ether) and (n-Bu(4)N)[Re(2)Cl(7)(eta(1)-L(2))] (4) (L(2) = 4,6-bis(diphenylphosphino)dibenzofuran). Spectroscopic and electrochemical data support the unsymmetrical structure Cl(4)ReReCl(2)(eta(3)-L(1)) in the case of 3, while 4 contains monodentate P-bound L(2) both complexes contain Re---Re bonds. The synthon cis-Re(2)(mu-O(2)CCH(3))(2)Cl(4)(H(2)O)(2) reacts with ligands L(1), L(2), 2,6-bis(diphenylphosphinomethyl)pyridine (L(3)), bis[2-(diphenylphosphino)ethyl]amine (L(4)), and N,N-bis[2-(diphenylphosphino)ethyl]trimethylacetamide (L(5)) to give the paramagnetic complexes Re(2)(mu-O(2)CCH(3))Cl(4)(eta(3)-L(n)) (5-9) with Re bonds. The lability of the mu-acetato ligands in 5-9 has been demonstrated by the reactions of compounds 5 (n = 1) and 7 (n = 3) with 4-Ph(2)PC(6)H(4)CO(2)H, 2-Ph(2)PC(6)H(4)CO(2)H, and quinoline-4-carboxylic acid to give complexes 10-12 (from 5) and 13-15 (from 7), respectively. These products contain uncoordinated donor atoms that can be used to produce mixed-metal assemblies. Compounds 5 and 7 also react with terephthalic acid (1,4-C(6)H(4)(CO(2)H) to give [Re(2)Cl(4)(eta(3)-L(1))](2)(mu-O(2)CC(6)H(4)CO(2)) (16) and [Re(2)Cl(4)(eta(3)-L(3))](2)(mu-O(2)CC(6)H(4)CO(2)) (17) in which electronic coupling between the paramagnetic sets of dirhenium units is very weak. Single-crystal X-ray structure determinations have been carried out on complexes 5-8, 11, 12, and 14-16.
ABSTRACT
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' '.
ABSTRACT
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.
ABSTRACT
The reaction of the open bioctahedral form of Re(2)Cl(4)(&mgr;-dppm)(2)(CO)(CNXyl) (1), where XylNC = 2,6-dimethylphenyl isocyanide, with TlO(3)SCF(3) in the presence of acetonitrile proceeds with retention of stereochemistry at the dirhenium unit to afford the complex [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(NCCH(3))]O(3)SCF(3) (3). The single-crystal X-ray structure determination of 3 shows that a Re&tbd1;Re bond is retained (the Re-Re distance is 2.378(3) Å) and that it is the chloride ligand trans to the XylNC ligand of 1 which is labilized. Complex 1 reacts with TlO(3)SCF(3) in a noncoordinating solvent to produce the unsymmetrical complex [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)]O(3)SCF(3) (2), through loss of this same chloride ligand of 1 and CO transfer from the adjacent Re center. The acetonitrile ligand of 3 is very labile and is readily displaced by XylNC and t-BuNC, with retention of stereochemistry, to produce complexes of stoichiometry [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(CNR)]O(3)SCF(3) (R = Xyl, 4a; R = t-Bu, 4b). In a noncoordinating solvent, the nitrile ligand of 3 is lost and 2 is formed following CO transfer; this conversion is reversed upon the reaction of 2 with acetonitrile. When 3 is treated with CO, the acetonitrile ligand is again displaced, but in this instance the reaction is accompanied by a structure change to produce an edge-sharing bioctahedral complex of the type [Re(2)(&mgr;-CO)(&mgr;-Cl)(&mgr;-dppm)(2)Cl(2)(CO)(CNXyl)]O(3)SCF(3) (5).
ABSTRACT
The reactions of the unsymmetrical, coordinatively unsaturated dirhenium(II) complexes [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)]Y (XylNC = 2,6-dimethylphenyl isocyanide; Y = O(3)SCF(3) (3a), PF(6) (3b)) with XylNC afford at least three isomeric forms of the complex cation [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](+). Two forms have very similar bis(&mgr;-halo)-bridged edge-sharing bioctahedral structures of the type [(CO)BrRe(&mgr;-Br)(2)(&mgr;-dppm)(2)Re(CNXyl)(2)]Y (Y = O(3)SCF(3) (4a/4a'), PF(6) (4b/4b')), while the third is an open bioctahedron [(XylNC)(2)BrRe(&mgr;-dppm)(2)ReBr(2)(CO)]Y (Y = O(3)SCF(3) (5a), PF(6) (5b)). While the analogous chloro complex cation [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](+) was previously shown to exist in three isomeric forms, only one of these has been found to be structurally similar to the bromo complexes (i.e. the isomer analogous to 5a and 5b). The reaction of 3a with CO gives the salt [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3) (7), in which the edge-sharing bioctahedral cation [(XylNC)BrRe(&mgr;-Br)(&mgr;-CO)(&mgr;-dppm)(2)ReBr(CO)](+) has an all-cis arrangement of pi-acceptor ligands. The Re-Re distances in the structures of 4b', 5a, and 7 are 3.0456(8), 2.3792(7), and 2.5853(13) Å, respectively, and accord with formal Re-Re bond orders of 1, 3, and 2, respectively. Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](PF(6))(0.78)(ReO(4))(0.22).CH(2)Cl(2) (4b') at 295 K: monoclinic space group P2(1)/n (No. 14) with a = 19.845(4) Å, b = 16.945(5) Å, c = 21.759(3) Å, beta = 105.856(13) degrees, V = 7038(5) Å(3), and Z = 4. The structure was refined to R = 0.060 (R(w) = 0.145) for 14 245 data (F(o)(2) > 2sigma(F(o)(2))). Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)]O(3)SCF(3).C(6)H(6) (5a) at 173 K: monoclinic space group P2(1)/n (No. 14) with a = 14.785(3) Å, b = 15.289(4) Å, c = 32.067(5) Å, beta = 100.87(2) degrees, V=7118(5) Å(3), and Z = 4. The structure was refined to R = 0.046 (R(w) = 0.055) for 6962 data (I > 3.0sigma(I)). Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3).Me(2)CHC(O)Me (7) at 295 K: monoclinic space group P2(1)/n (No. 14) with a = 14.951(2) Å, b = 12.4180(19) Å, c = 40.600(5) Å, beta = 89.993(11) degrees, V = 7537(3) Å(3), and Z = 4. The structure was refined to R = 0.074 (R(w) = 0.088) for 6595 data (I > 3.0sigma(I)).
