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S Bruce Wild

Publications and source records attributed to S Bruce Wild.

9 recordsLinked to original sources
PubMed2006

Inorganic asymmetric synthesis: asymmetric synthesis of a two-bladed propeller, octahedral metal complex.

A C2 hexadentate, in which two pyridine-2-aldehyde 2'-pyridylhydrazone (PAPHY) groups are linked to a chiral auxiliary derived from (R,R)-tartaric acid, (R,R)-1, reacts with iron(II) benzenesulfonate to give the two-bladed propeller, octahedral complex (P(Fe))-[Fe{(R,R)-1}](PhSO3)2 with complete diastereoselectivity, as determined by 1H NMR spectroscopy and X-ray crystallography. Saponification of the ester linkages and deprotonation of the hydrazone-NH groups in the configurationally pure diastereomer affords the complex (P(Fe))-[Fe(5-HOCH2PAPY)2] with 85% retention of configuration at the iron stereocenter, as determined by reprotonation of the neutral complex with enantiomerically pure (aR)-binaphthyl phosphoric acid and analysis of the 1H NMR spectrum of the mixture of diastereomeric salts produced. This is the first asymmetric synthesis of a two-bladed propeller, octahedral metal complex by the classical organic methodology of chiral auxiliary-directed, asymmetric synthesis.

Journal Article↗
PubMed2006

Asymmetric transformation of a double-stranded, dicopper(I) helicate containing achiral bis(bidentate) Schiff bases.

Reactions of the bis(bidentate) Schiff-bases N,N'-bis(6-alkyl-2-pyridylmethylene)ethane-1,2-diamine (where alkyl = H, Me, iPr) (L) with tetrakis(acetonitrile)copper(I) hexafluorophosphate and silver(I) hexafluorophosphate afforded, respectively, the double-stranded, dinuclear metal helicates [T-4-(R,R)]-(+/-)-[M2L2](PF6)2 (M = Cu, Ag). The helicates were characterized by 1H and 13C NMR spectroscopy, conductivity, microanalysis, and single-crystal X-ray structure determinations on selected compounds. Intermolecular ligand exchange and intramolecular inversion rates for the complexes were investigated by 1H NMR spectroscopy. Reversible intermolecular ligand exchange between two differently substituted helicates followed first-order kinetics. The rate constants (k) and corresponding half-lives (t(1/2)) for ligand exchange for the dicopper(I) helicates were k = (1.6-1.8) x 10(-6) s(-1) (t(1/2) = 110-120 h) in acetone-d6, k = 4.9 x 10(-6) s(-1) (t(1/2) = 40 h) in dichloromethane-d2, and k > 2 x 10(-3) s(-1) (t(1/2) < 5 min) in acetonitrile-d3. Ligand exchange for the disilver(I) helicates occurred with k > 2 x 10(-3) s(-1) (t(1/2) < 5 min). Racemization of the dicopper(I) helicate by an intramolecular mechanism was investigated by determination of the coalescence temperature for the diastereotopic isopropyl-Me groups in the appropriate complex, and DeltaG() >> 76 kJ mol(-1) was calculated for the process in acetone-d6, nitromethane-d3, and dichloromethane-d2 with DeltaG() = 75 kJ mol(-1) in acetonitrile-d3. Complete anion exchange of the hexafluorophosphate salt of a dicopper(I) helicate with the enantiomerically pure Delta-(-)-tris(catecholato)arsenate(V) ([As(cat)3]-) in the presence of Dabco gave the two diastereomers (R,R)-[Cu2L2][Delta-(-)-[As(cat)3]]2 and (S,S)-[Cu2L2][Delta-(-)-[As(cat)3]]2 in up to 54% diastereomeric excess, as determined by (1)H NMR spectroscopy. The diastereomerically and enantiomerically pure salt (R,R)-[Cu(2)L2][Delta-(-)-[As(cat)3]]2 crystallized from the solution in a typical second-order asymmetric transformation. The asymmetric transformation of the dicopper(I) helicate is the first synthesis of a diastereomerically and enantiomerically pure dicopper(I) helicate containing achiral ligands.

Journal Article↗
PubMed2005

Reactivity of cyclooligophosphanes: synthesis and structural characterisation of cyclo-1,4-(BH3)2(P4Ph4CH2) and cyclo-1,2-(BH3)2(P5Ph5).

The borane complexes cyclo-1,4-(BH3)2(P4Ph4CH2) (3) and cyclo-1,2-(BH3)2(P5Ph5) (4) were prepared by reaction of cyclo-(P4Ph4CH2) and cyclo-(P5Ph5) with BH3(SMe2). Only the 2:1 complexes 3 and 4 were isolated, even when an excess of the borane source was used. In solution, 3 exists as a mixture of the two diastereomers (R(P)*,S(P)*,S(P)*,R(P)*)-(+/-)-3 and (R(P)*,R(P)*,R(P)*,R(P)*)-(+/-)-3. However, in the solid state the (R(P)*,S(P)*,S(P)*,R(P)*)-(+/-) diastereomer is the major stereoisomer. Similarly, while only one isomer of 4 is observed in its X-ray structure, NMR spectroscopic investigations reveal that it forms a complex mixture of isomers in solution. 3 may be deprotonated with tBuLi to give the lithium salt cyclo-1,4-(BH3)2(P4Ph4CHLi) (3 x Li), though this could not be isolated in pure form.

Boranes↗
PubMed2003

Diastereoselectivity and molecular recognition in the self-assembly of double-stranded dinuclear metal complexes of the type [M2[(R,S)-tetraphos]2](PF6)2 (M = Ag and Au).

The ligand (R,S)-Ph(2)PCH(2)CH(2)P(Ph)CH(2)CH(2)P(Ph)CH(2)CH(2)PPh(2), (R,S)-tetraphos, combines with silver(I) and gold(I) ions in the presence of hexafluorophosphate to diastereoselectively self-assemble the head-to-head (H,H) diastereomers of the double-stranded, dinuclear metal complexes [M(2)[(R,S)-tetraphos](2)](PF(6))(2) in which the two chiral metal centers in the complexes have M (R end of phosphine) and P (S end of phosphine) configurations. The crystal and molecular structures of the compounds have been determined: (H,H)-(M,P) -[Ag(2)[(R,S)-tetraphos](2)](PF(6))(2), monoclinic, P2(1)/c, a = 10.3784(2), b = 47.320(1), c = 17.3385(4) A, beta = 103.8963(5) degrees, Z = 4; (H,H)-(M,P)-[Au(2)[(R,S)-tetraphos](2)](PF(6))(2), monoclinic, P.2(1) (No. 4, c unique axis), a = 24.385(4), b = 46.175(3), c = 14.820(4) A, Z = 8. The complexes crystallize as racemic compounds in which the unit cell in each case contains equal numbers of enantiomorphic molecules of the cation and associated anions. The cations in both structures have similar side-by-side structures of idealized C(2) symmetry, the bulk helicity of each molecule in the solid state being due solely to the twist of the central ten-membered ring containing the two metal ions of opposite configuration, which has the chiral twist-boat-chair-boat conformation. When 1 equiv each of (R,S)-tetraphos, (R,R)-(+/-)-tetraphos, (S,S)-(+)-tetraphos, 2 equiv of Ph(2)PCH(2)CH(2)PPh(2) (dppe), and 7 equiv of [AuCl(SMe(2))] in dichloromethane are allowed to react for several minutes in the presence of an excess of ammonium hexafluorophosphate in water (two phases), the products are the double-stranded digold(I) complexes in which each ligand strand has recognized itself by stereoselective self-assembly, together with [Au(dppe)(2)]PF(6).

Journal Article↗
PubMed2003

Photoluminescence properties of four-coordinate gold(I)-phosphine complexes of the types [Au(diphos)2]PF6 and [Au2(tetraphos)2](PF6)2.

Numerous reports describe the photoluminescence of two- and three-coordinate gold(I)-phosphine complexes, but emission in their analogous four-coordinate complexes is almost unknown. This work examines the luminescence of tetrahedral gold(I) complexes of the types [Au(diphos)(2)]PF(6) (diphos = 1,2-bis(diphenylphosphino)ethane, 1) and [Au(2)(tetraphos)(2)](PF(6))(2) (tetraphos = (R,R)-(+/-)/(R,S)-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane, (R,R)-(+/-)/(R,S)-2). Although nonemitting in solution, these complexes luminesce with an intense yellow color (lambda(max) 580-620 nm) at 293 K in the solid state or when immobilized as molecular dispersions within solid matrixes. The excited-state lifetimes of the emissions (tau 4.1-9.4 micros) are markedly dependent on the inter- and intramolecular phenyl-phenyl pairing interactions present. At 77 K in an ethanol glass, two transitions are observed: a minor emission at lambda(max) 415-450 nm and a major emission at lambda(max) 520-595 nm. For [Au(1)(2)]PF(6), lifetimes of tau 251.0 +/- 20.5 micros were determined for the former transition and tau 14.9 +/- 4.6 micros for the latter. Density functional theory (DFT) calculations and comparative studies indicate that the former of these emissions involves triplet LMCT pi(Ph) --> Au(d)-P(p) transitions associated with individual P-phenyl groups. The latter emissions, which are the only ones observed at 293 K, are assigned to LMCT pi(Ph-Ph) --> Au(d)-P(p) transitions associated with excited P-phenyl dimers. Other tetrahedral gold(I)-phosphine complexes containing paired P-Ph substituents display similar emissions. The corresponding phosphine ligands, whether free, protonated, or bound to Ag(I), do not exhibit comparable emissions. Far from being rare, luminescence in four-coordinate Au(I)-phosphine complexes appears to be general when stacked P-phenyl groups are present.

Journal Article↗
PubMed2002

Phosphine-stabilized arsenium salts: water-stable, labile, coordination complexes.

A series of air- and water-stable tertiary phosphine-stabilized arsenium salts of the type R(3)P-->AsR(2)(+)PF(6)(-) has been isolated. In the crystal structures of two chiral triarylphosphine complexes of prochiral methylphenylarsenium hexafluorophosphate, the stereochemistry around arsenic is trigonal pyramidal with the phosphorus atom occupying the apical position, the As-P bond being orthogonal to the plane of the trigonal (lone-pair included) arsenium ion: Ph(3)P-->AsMePh(+) PF(6)(-), P2(1)/c, a = 10.7775(2) A, b = 17.7987(3) A, c = 13.3797(2) A, beta = 109.066(1) degrees, V = 2425.78(7) A(3), T = 200 K, Z = 4; Ph(2)(2-MeOC(6)H(4))P-->AsMePh(+) PF(6)(-), P1, a = 10.8077(2) A, b = 10.9741(2) A, c = 13.5648(2) A, alpha = 99.0162(9) degrees, beta = 105.2121(9) degrees, gamma = 116.4717(9) degrees, V = 1318.11(5) A(3), T = 200 K, Z = 2. The arsenium ion in each case appears to be further stabilized by conjugation of the lone pair with the phenyl group, with which the arsenic and methyl-carbon atoms are almost coplanar. In the crystal structure of the 2-(methoxymethylphenyl)diphenylphosphine adduct of methylphenylarsenium hexafluorophosphate, there operates a counteractive chelate effect in which anchimeric oxygen coordination to arsenic destabilizes the arsenic-phosphorus bond in the six-membered chelate ring. Although they are stable, phosphine-stabilized arsenium salts undergo rapid phosphine exchange and attack at arsenic by anionic carbon and oxygen nucleophiles to give tertiary arsines and arsinous acid esters, respectively, with liberation of the phosphine.

Journal Article↗
PubMed2002

Synthesis and resolution of (R,R)-(+/-)-1,1,4,7,10,10-hexaphenyl-1,10-diarsa-4,7-diphosphadecane: new ligand for the stereoselective self-assembly of dicopper(I), disilver(I), and digold(I) helicates.

Diphenylvinylarsine oxide reacts with 1,2-bis(phenylphosphino)ethane in the presence of potassium tert-butoxide to give the anti-Markovnikov product (R,R)-(+/-)/(R,S)-1,1,4,7,10,10-hexaphenyl-1,10-diarsa-4,7-diphosphadecane dioxide-1AsO,10AsO, which, upon reduction with HSiCl(3)/NEt(3) in boiling acetonitrile, affords in 84% overall yield the di(tertiary arsine)-di(tertiary phosphine) (R,R)-(+/-)/(R,S)-diphars. After separation of the diastereomers by fractional crystallization, the (R,R)-(+/-) form of the ligand was resolved by metal complexation with (+)-di(mu-chloro)bis[(R)-1-[1-(dimethylamino)ethyl]-2-phenyl-C(2),N]dipalladium(II): (R,R)-diphars, mp 87-88 degrees C, has [alpha](D)(21) = -18.6 (c 1.0, CH(2)Cl(2)); (S,S)-diphars has [alpha](D)(21) = +18.4 (c 1.0, CH(2)Cl(2)). The crystal and molecular structures of the complexes (M)-[M(2)[(R,R)-diphars](2)](PF(6))(2) (M = Cu, Ag, Au) have been determined: [M-(S(Cu),S(Cu))]-(-)-[Cu(2)[(R,R)-diphars](2)](PF(6))(2), orthorhombic, P2(1)2(1)2(1) (No. 19), a = 16.084(3) A, b = 18.376(3) A, c = 29.149(6) A, Z = 4; [M-(S(Ag),S(Ag))]-(+)-[Ag(2)[(R,R)-diphars](2)](PF(6))(2), triclinic, P1, a = 12.487(2) A, b = 12.695(4) A, c = 27.243(4) A, alpha = 92.06 degrees, beta = 95.19 degrees, gamma = 98.23 degrees, Z = 2; [M-(S(Au),S(Au))]-(-)-[Au(2)[(R,R)-diphars](2)](PF(6))(2), orthorhombic, P2(1)2(1)2(1) (No. 19), a = 16.199(4) A, b = 18.373(4) A, c = 29.347(2) A, Z = 4. In the copper(I) and gold(I) helicates, each ligand strand completes 1.5 turns of an M helix in a parallel arrangement about the two chiral MAs(2)P(2) stereocenters of S configuration. The unit cell of the silver(I) complex contains one molecule each of the parallel helicate of M configuration and the conformationally related double alpha-helix of M configuration in which each ligand strand completes 0.5 turns of an M helix about two metal stereocenters of S configuration. Energy minimization calculations of the three structures with use of the program SPARTAN 5.0 gave results that were in close agreement with the core structures observed.

Journal Article↗
PubMed2002

Configurationally homogeneous diastereomers of a linear hexa(tertiary phosphine): enantioselective self-assembly of a double-stranded parallel helicate of the type (P)-[Cu(3)(hexaphos)(2)](PF(6))(3).

Three configurationally homogeneous diastereomers of the linear hexa(tertiary phosphine) Ph(2)PCH(2)CH(2)P(Ph)CH(2)CH(2)P(Ph)CH(2)CH(2)P(Ph)CH(2)CH(2)P(Ph)CH(2)CH(2)PPh(2) (hexaphos) have been isolated in enantiomerically pure form, namely (R,S,S,R)-, (R,S,S,S)-, and (S,S,S,S)-hexaphos. The strongly helicating (R,S,S,R)-(-) form of the ligand combines with copper(I) ions to generate by stereoselective self-assembly the P enantiomer of a parallel helicate of the type [Cu(3)(hexaphos)(2)](PF(6))(3), which has been characterized by x-ray crystallography. Theoretical modeling of the cation indicates that it is the relationship between the helicities of the two 10-membered rings containing the three copper ions, each of which has the twist-boat-chair-boat conformation, and the configurations of the three chiral, tetrahedral copper stereocenters of P configuration that determines the stereochemistry of the parallel and double alpha-helix conformers of the double-stranded trinuclear metal helicate.

Cations↗