Browsing by Author "Cowie, Martin"

Now showing 1 - 13 of 13
  • Thumbnail Image
    Item
    An unusual example of allyl-to-alkynyl migration in a phenylacetylide-bridged heterobinuclear complex of rhodium and iridium
    (1999) George, Darren S. A.; Hilts, Robert; McDonald, Robert; Cowie, Martin
    The reactivity of the alkynyl-bridged complex [RhIr(CO)2(μ2-η1:η2-C2Ph)(dppm)2][X] (X = BF4 (1a), SO3CF3 (1b); dppm = Ph2PCH2PPh2) with electrophiles has been demonstrated. Protic acids HX (X = BF4, SO3CF3) first yield the oxidative-addition products [RhIr(X)(CO)2(μ-H)(μ-C2Ph)(dppm)2][X], which under carbon monoxide result in displacement of the weakly coordinating BF4- or SO3CF3- anions and subsequent conversion to the vinylidene-bridged [RhIr(CO)4(μ-CC(H)Ph)(dppm)2][X]2. Reaction of 1 with allyl halides yields the allyl vinylidene-bridged compounds [RhIr(Y)(CO)(μ-CC(Ph)CH2CHCH2)(μ-CO)(dppm)2][X] (Y = Br (5), Cl (6)), by coupling of the alkynyl and allyl groups at the β-position of the alkynyl moiety. NMR studies at low temperatures show coordination of allyl halide at Ir at −80 °C, followed by allyl halide loss and subsequent oxidative addition at −50 °C. The oxidative-addition intermediates, [RhIr(η1-CH2CHCH2)(CO)2(μ-Y)(μ-C2Ph)(dppm)2][X] (Y = Br (9), Cl (10)), rearrange to the allylvinylidene products (5 and 6) at ambient temperature. Although halide removal from compounds 5 and 6, using AgBF4, does not result in destabilization of the allylvinylidene fragment, resulting instead in replacement of halide by fluoborate ion, the reaction of 1 with allyl halide in the presence of a silver salt does not lead to coupling of the allyl and alkynyl moieties, but gives [RhIr(η3-C3H5)(CO)(μ-C2Ph)(μ-CO)(dppm)2][X]2 (13). Addition of halide ion to this η3-allyl complex at ambient temperature again leads to formation of 5 or 6. On the basis of these results a mechanism is proposed for the allyl/alkynyl coupling reaction.
  • Thumbnail Image
    Item
    Dialkyl and trialkyl heterobinuclear complexes of rhodium and iridium: models for adjacent-metal involvement in bimetallic catalysts
    (2005) Hilts, Robert; Oke, Okemona; Ferguson, Michael J.; McDonald, Robert; Cowie, Martin
    The heterobinuclear dialkyl complexes [RhIr(R)2(μ-CO)(dppm)2] (dppm = μ-Ph2PCH2PPh2; R = CH3 (2), CH2Ph (3)) have been prepared. Both A-frame-like compounds have one alkyl group terminally bound to each metal and a bridging carbonyl ligand. Some subsequent reactivity studies of 2 are reported. Reaction of 2 with CO yields [RhIr(CO)3(dppm)2] and acetone. If this reaction is monitored at low temperature by NMR spectroscopy, the dicarbonyl species [RhIr(CH3)2(CO)2(dppm)2] (4) is first observed, followed by [RhIr(CH3)2(CO)3(dppm)2] (5). In both products, both methyl groups are bound to Ir. Warming to ambient temperature under CO yields acetone and [RhIr(CO)3(dppm)2]. Crossover experiments suggest that acetone arises primarily from an intramolecular process. We propose that migratory insertion of a CO and a methyl group occurs on Ir; presumably reductive elimination also occurs from this metal. Compound 2 reacts with H2 at −78 °C to yield [RhIrH(CH3)2(μ-H)(μ-CO)(dppm)2] (6), in which one methyl group is bound to Rh while the other, together with a hydride ligand, is terminally bound to Ir. This latter species reacts with CO at 0 °C to yield [RhIrH(C(O)CH3)(CH3)(μ-H)(μ-CO)(dppm)2] (7), in which migratory insertion involving CO and the Rh-bound methyl group has yielded a Rh-bound acetyl group. At ambient temperature, under an atmosphere of CO, [RhIr(CO)3(dppm)2] is formed, together with acetaldehyde and methane. Crossover experiments support a predominantly intramolecular process for acetaldehyde formation but are equivocal on the formation of methane. Compound 2 oxidatively adds CH3I or n-C4H9I, yielding [RhIr(CH3)2(R)(μ-I)(μ-CO)(dppm)2] (R = CH3, n-C4H9), in which the added alkyl group in each case is bound to Ir. The n-butyl product reacts with CO to yield [RhIr(n-C4H9)(CH3)2(μ-CO)2(dppm)2][I], in which the n-butyl group has migrated to Rh. A similar product, [RhIr(CH3)3(μ-CO)2(dppm)2][CF3SO3], is obtained in the reaction of 2 with methyl triflate in the presence of CO.
  • Thumbnail Image
    Item
    Diphosphine-bridged, heterobimetallic complexes containing iridium and osmium. Reversible orthometalation of a bridging bis(diphenylphosphino)methane group at the iridium center promoted by the adjacent osmium center
    (1991) Hilts, Robert; Franchuk, Roberta; Cowie, Martin
    The compound (PPN)[HOs(CO)4] reacts readily with [IrCl(i)1 2-dppm)2] (PPN+ = (Ph3P)2N+, dppm = Ph2PCH2PPh2) at ambient temperature, yielding the heterobinuclear complex [IrOs(H)2(CO)3(#t2-’?3-(oCeH^PhPCI^PPh^(dppm)] (1), in which one phenyl group is ortho-metalated at the Ir center. Treatment of 1 with the electrophile sources HBF4-Et¡>0 or [AuPPh3]BF4 reverses the ortho metalation to give the hydrido-bridged species, [IrOs(CO)3Gt-H)(M-X)(dppm)2][BF4] (X = H (2), AuPPh3 (3)). Deprotonation of 2 with use of NaH regenerates compound 1. The AuPPh3 group in 3 is readily replaced by an iodo group in the reaction with I2 to give [IrOs(CO)3^-H)(/¿-I)(dppm)2] [BF4] (4). Under a CO atmosphere, compound 2 yields [IrOs(CO)6(dppm)2] [BF4] (5), and reaction of 5 with Me3N0-2H20 results in loss of one carbonyl group from the Ir center to yield [IrOs(CO)4(dppm)2] [BF4] (6). The structure of 5 has been determined by X-ray techniques. This compound crystallizes, together with 1.5 equiv of CH2C12, in the monoclinic space group P2,/c, with cell parameters o = 12.063 (2) Á, b = 22.725 (3) Á, c = 22.050 (3) Á, ß = 101.66 (1)°, V = 5920 A3, and Z = 4. The structure has refined to R = 0.043 and f?w = 0.063 on the basis of 5515 unique observations with 444 parameters varied. Compound 5 has a trans-bridging arrangement of diphosphine ligands and has two carbonyls bound to Ir and three on Os. The carbonyl and phosphine arrangement on Os suggests a trigonal bipyramidal (TBP) arrangement characteristic of Os(0), which then forms a dative Os Ir bond to the Ir(+I) center, giving it a TBP geometry also. The Os-Ir separation of 2.9652 (4) A is at the long end of the range expected for a normal single bond.
  • Thumbnail Image
    Item
    Dithiophosphinate-bridged ruthenium(I) and ruthenium(II) complexes. The structure of [(Ru2(CO)4(.mu.-S2PMe2)2(PPh3)2].cntdot.1/2CH2Cl2
    (1990) Hilts, Robert; Cowie, Martin
    Replacement of the bridging acetate groups in [Ru2(C0)4(M-02CMe)2(PR'2R")2] (R', R" = Ph, Me) by the dithiophosphinate anions R2PS2‘ (R = Me, Ph) yields a new class of dithiophosphinate-bridged Ru(I) complexes, [Ru2(CO)4(m-S2PR2)2(PR'2R")2]· Although the Ru-Ru bond in these species can be reversibly protonated, it does not react with [Au(PPh3)][BF4], diazomethane, or dimethyl acetylenedicarboxylate. Reaction of the related acetate-bridged species [Ru2(C0)4(M-02CMe)2(NCMe)2] with NaS2PMe2 does not yield the expected dithiophosphinate-bridged product but instead gives the mononuclear species [Ru- (CO)2();2-S2PMe2)2] along with Na2S, Na02CMe, MeCN, and Me2P(S)P(S)Me2. An X-ray structure determination of [Ru2- (CO)4(M-S2PMe2)2(PPh3)2]>1/2CH2Cl2 confirms the dithiophosphinate-bridged formulation and shows a long Ru-Ru separation of 2.9000 (6) A and a twisting about the metal-metal axis by ca. 39°. This compound crystallizes in the monoclinic space group P2,/c with cell parameters a = 15.182 (3) A, b = 18.230 (4) A, c = 18.082 (4) A, ß = 94.23 (2)°, and Z = 4. Refinement has converged at R = 0.054 and /?w = 0.082 on the basis of 5928 unique reflections and 365 parameters varied.
  • Thumbnail Image
    Item
    Double activation of the geminal carbon−hydrogen bonds in 1,3-butadiene by a diiridium complex
    (2000) Ristic Petrovic, Dusan; Torkelson, Jeffrey R.; Hilts, Robert; McDonald, Robert; Cowie, Martin
    The binuclear complex [Ir2(CH3)(CO)2(dppm)2][CF3SO3] (1) (dppm = Ph2PCH2PPh2) reacts with 1,3-butadiene at ambient temperature over a 48 h period to give the vinylvinylidene-bridged product [Ir2(CH3)(H)(CO)2(μ-H)(μ-CC(H)C(H)CH2)(dppm)2][CF3SO3] (2). At −55 °C the same reactants yield the 1,3-butadiene adduct [Ir2(CH3)(CO)2(μ-η2:η2-H2CC(H)C(H)CH2)(dppm)2][CF3SO3] (3), in which the diolefin binds in an s-trans geometry on one face of the complex. A proposal is advanced rationalizing the conversion of 3 to 2 upon warming.
  • Thumbnail Image
    Item
    Formation, x-ray structure, and deprotonation of an S,S'-methylene-bridged P2N4S2 ring
    (1992) Chivers, Tristram; Cowie, Martin; Edwards, Mark; Hilts, Robert
    There is an extensive chemistry of binary sulfur-nitrogen (S- N) anions, several of which are shown only in coordination complexes with metals. Although there is polarographic evidence for the formation of S4N4(2-) at low temperatures, this dianion has only been characterized in Ira and Pt5b complexes as a tridentate (N,S,S’) ligand formed by insertion of the metal into an S-N bond of S4N4. Anions of diphosphadithiatetrazocines 1 are unknown, but Pt0 or Pd0 compounds readily undergo oxidative addition with these norganic heterocycles to give ŋ2- S4ZS1-metal complexes.(6)
  • Thumbnail Image
    Item
    Heterobinuclear Hydrido, Alkyl, and Related Complexes of Rh/Os. Site-Specific Reductive Elimination of Methane from a Rh/Os Core and the Structures of [RhOs(CH2CN)(CO)3(dppm)2] and [RhOs(CH3)(CO)3(dppm)2]
    (1995) Sterenberg, Brian T.; Hilts, Robert; Moro, Giovanni; McDonald, Robert; Cowie, Martin
    This paper reports the synthesis and characterization of a series of hydrido, alkyl, alkenyl, and related heterobimetallic complexes of Rh and Os and the site-specific reductive elimination of methane from hydrido methyl complexes. Reaction of[RhOs(C0)3(NCMe)&-H)(dppm)~]~+ (3, dppm= PhzPCHzPPhz) with NaCGCH in acetonitrile yields the acetylide complex [RhOs(CzH)(CO)3(dppm)~] (6) and the cyanomethyl complex [RhOs(CHz- CN)(CO)3(dppm)z] (7). The same reaction under CO instead results in deprotonation of one dppm group to give [RhOs(CO)4(dppm-H)(dppm)] (8, dppm-H = bis(dipheny1phosphino)methanide). The methanide carbon can be alkylated to give [RhOs(CO)4(PhzPCH(CH3)PPhz)(dppm)]+ (9) or protonated to give the known compound [RhOs- (C0)4(dppm)z]+ (2). The methyl complex [RhOs(CH3)(C0)3(dppm)z] (10) is prepared by several routes, and upon protonation yields [R~OS(CO)~&-H)&*-)~-(O-C~H~)P~PCHZPP~~)(~~~~)]+ (14) via methane loss. If the reaction is carried out at -80 "C and slowly warmed, three hydrido methyl intermediates are observed at different temperatures, yielding information about the reductive elimination from these heterobinuclear species, which appears to occur from the Os center. An alkenyl complex analogous to the alkyl species 7 and 10 can be obtained by the reaction of [RhOsH(CO)3(dppm)z] (1) with dimethyl acetylenedicarboxylate resulting in insertion into the Os-H bond and migration of the resulting alkenyl group to Rh yielding [Rh0s(MeO~CC=C(H)COzMe)(C0)3(dppm)~l (18). Protonation of 18 yields [RhOs(R)(C0)3&-H)(dppm)z]+ (19) and alkylation yields [RhOs(R)(CH3)(C0)3(dppm)~]+ (20, R = MeOZCC=C(H)COzMe). Compound 20 has the vinylic moiety bound to Rh with the methyl group on Os. The structures of 7 and 10 have been established by X-ray crystallography. Compound 7 crystallizes in the monoclinic space group C2/c with a = 18.313(3) A, b = 13.279(2) A, c = 22.492(5) A, ,8 = 115.89(1)', and Z = 4; compound 10 crystallizes in the triclinic space group Pi with a = 11.102(2) A, b = 11.684(3) A, c = 10.954(3) A, a = 111.79(2)", ,8 = 93.16(2)', y = 68.18(2)', and Z = 1. Both compounds are disordered at an inversion center, although only the metals and the carbonyl and alkyl groups are disordered. Both models refined acceptably: R = 0.046, R, = 0.058 (7); R = 0.047, R, = 0.077 (10). The geometries of the two complexes are almost identical, having the cyanomethyl or methyl group terminally bound to Rh and having the three carbonyls on Os. One carbonyl forms a semibridging interaction with Rh.
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
    Polymeric ruthenium( I) and binuclear ruthenium(1) and osmium(1) carboxylate-bridged complexes containing diphosphine, diarsine, arsinophosphine, diphosphine chalcogenide, and dithioether ligands: the structure of [Ru2( CO) 4( p-02CMe) 2( MeSCH2SMe)l2.THF
    (1990) Steyn, Margo M. de V.; Hilts, Robert; Sherlock, Stephen J.; Cowie, Martin; Singleton, Eric
    The addition of 1 molar equiv of the bidentate ligands L~L, R'2P(CH2)„PR'2, R'2As(CH2)„AsR'2, Ph2P(CH2)2AsPh2, Ph2PCH2P(S)Ph2, Ph2P(S)CH2P(S)Ph2, and R'SCH2SR' (R' = Me, Ph; = 1-4), to THF/acetone solutions of either the polymer [Ru2(CO)4(g-02CMe)2]ilor the dimers [Ru2(CO)40i-O2CR)2(NCMe)2] (R = Me, Et) affords a new class of polymeric species, [Ru2(CO)4(m-02CR')2(L L)]„, in which the carboxylate-bridged dimeric units are linked by the bidentate L~L ligands. The use of 2 molar equiv of either Ph2PCH2PPh2 (dppm) or Ph2PCH2P(S)Ph2 (dppmS) in the reaction with the acetate-bridged dimer yields complexes of the type [Ru2(C0)4(^-02CMe)2(7j1-Ph2PCH2P(X)Ph2)2] (X = S, electron pair). The osmium analogues [0s2(C0)4(u-02CMe)2(V-Ph2PCH2P(X)Ph2)2] can be obtained by heating [0$2(00)6(µ-020 ß)2] with 2 equiv of dppm or dppmS in CHCI3. The pendant PPh2 moieties of [0s2(C0)4(M-02CMe)2(7j1-dppm)2] can be oxidized to P(0)Ph2 groups by treatment with 2 molar equiv of H202. The structure of the dithioether species [Ru2(CO)40i-O2CMe)2(MeSCH2SMe)]2-THF has been determined by an X-ray diffraction study and has been shown to consist of a polymeric chain of [Ru2(C0)4(g-02CMe)2] units linked by MeSCH2SMe ligands. Each dimer unit has a sawhorse-like arrangement in which the four carbonyls are opposite the bridging acetate groups. The independent Ru-Ru bonds are 2.682 (1) and 2.684 (1) Á. This compound crystallizes in the space group P\ with a = 15.838 (2) A, b = 17.562 (2) A, c = 8.238 (2) A, a = 102.55 (l)°,/3 = 101.87 (1)°, = 68.17 (1)°, V = 2056.3 A3, and Z = 2. The asymmetric unit contains two [Ru2(C0)4(M-02CMe)2(MeSCH2SMe)] moieties. On the basis of 3533 unique observations and 435 parameters varied, the structure was refined to R = 0.046 and Rw = 0.055.
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
    Reactions of triethylammonium salts of the [(.mu.-CO)(.mu.-RS)Fe2(CO)6]- anion with alkyl-, aryl-, and vinylmercuric halides. Formal C-alkylation of the bridging CO ligand
    (1991) Seyferth, Dietmar; Archer, Colin M.; Ruschke, David P.; Cowie, Martin; Hilts, Robert
    The reaction of alkyl- and arylmercuric halides with [Et3NH][(µ-CO)(p-RS)Fe2(CO)6] gives bridging acyl complexes, (p-R'C=0)(µ-RS)Fe2(CO)6. In the case of vinylmercuric halides the bridging acyl complexes are less stable and, in some cases (CH2=CHHgBr, PhCH=CHHgCl, ClCH=CHHgCl), they undergo decarbonylation to give the µ- , -vinyl complexes, (p-CH=CH2)(p-RS)Fe2(CO)6 in the case of CH2=CHHgBr. Methyl substituents on the vinyl carbon atoms stabilize the µ-acyl complex. The reaction of CH3OCH2CH2HgCl with [Et^NH] [µ-CO) (p-RS)Fe2(CO)g] gave the bridging carboxylato complex (µCH3C02)(p-RS)Fe2(C0)e. Such compounds are more readily prepared by the reaction of Hg(02CR')3 with [ 3 ][(µ-00)(µ- 8) ß2(00)6]. The reaction of Hg(SCH3)2 witii [Et3NH][Oi-CO)(p-PhS)Fe2(CO)6] resulted in formation of (p-CH3S)(p-PhS)Fe2(CO)6. Possible mechanisms of these reactions are discussed. The structure of (p-CH3C02)(p-t-Bu8)Fe2(C0)6 has been determined by X-ray techniques. This compound crystallizes in the triclinic space group Pi with a = 13.608 (2) Á, b = 16.945 (1) Á, c = 8.599 (1) A, a = 98.52 (1)°, ß = 99.00 (1)°, y = 113.03 (1)°, V = 1753.8 Á3, and Z = 4. Refinement has converged at R = 0.055 and Rw = 0.093 on the basis of 325 parameters varied and 3310 unique observations. Both independent molecules have essentially identical geometries in which the Fe2(CO)6 moiety is bridged by a 1,1-dimethylethanethiolate and an acetate ligand.
  • Thumbnail Image
    Item
    Sulfur–carbon bond formation and bond cleavage in alkynyl-bridged heterobinuclear complexes of rhodium and iridium
    (2000) George, Darren S. A.; Hilts, Robert; McDonald, Robert; Cowie, Martin
    The phenylacetylide-bridged heterobinuclear complexes [RhIr(CO)2(μ-η1:η2-C2Ph)(dppm)2][X] (X=BF4, SO3CF3; dppm=Ph2PCH2PPh2) (1) react with carbon disulfide to give several products. At temperatures between −60 and −80°C the first product, [RhIr(CO)(η2-CS2)(μ-CO)(μ-η1:η2-C2Ph)(dppm)2][X] (2), is the result of CS2 coordination at Ir. Upon warming, two products are formed as a result of condensation of two CS2 groups. In [RhIr(CO)(μ-η1:η3-CC(Ph)SCSCS2)(μ-CO)(dppm)2][X] (3), the resulting C2S4 fragment has also condensed at the β-carbon of the acetylide group to give a heteroatom-substituted vinylidene group. The other identified product, [RhIr(CO)(C2S4)(μ-C2Ph)(μ-CO)(dppm)2][X] (4), is very similar to 3 apart from the absence of coupling of the C2S4 moiety and the acetylide group. Compound 3 appears to be formed independently of 4, but also slowly transforms into 4 by cleavage of a C-S bond. The reaction of 1 with nBuNCS at −80°C yields [RhIr(CO)(η2-SCNnBu)(μ-CCPh)(μ-CO)(dppm)2][X] (5), analogous to 2, and upon warming this rearranges to the isothiocyanate-bridged product [RhIr(CCPh)(CO)2(μ-SCNnBu)(dppm)2][X] (6). Compound 6 undergoes S-C bond cleavage to yield [RhIr(CCPh)(CO)(CNnBu)(μ-S)(μ-CO)(dppm)2][X] (7), slowly at ambient temperature or within hours under reflux. Although no simple adducts analogous to 5 and 6 were observed with tBuNCS, refluxing 1 in the presence of an excess of this substrate yields [RhIr(CCPh)(CO)(CNtBu)2(μ-S)2(dppm)2][X] (9) as the major product along with smaller amounts of [RhIr(CCPh)(CO)(CNtBu)(μ-S)(μ-CO)(dppm)2][X] (8), analogous to compound 7. Refluxing 1 in the presence of excess nBuNCS also yields some of the bis-n-butylisocyanide product, analogous to 9. The X-ray structures of compounds 3 (SO3CF3 − salt), 7 (BF4 − salt) and 9 (BF4 − salt) are reported.
  • Thumbnail Image
    Item
    Synthesis and reactions of the [(.mu.-Ph2P)Fe2(CO)6]- anion
    (1992) Seyferth, Dietmar; Brewer, Karen S.; Wood, Timothy G.; Cowie, Martin; Hilts, Robert
    The action of 2 molar equiv of LiBE^H on 0i-CH3C=O)0i-Ph2P)Fe2(CO)6 gives a reactive species which IR spectroscopic evidence suggests to be Li[(/i-Ph2P)Fe2(CO)6]. This species reacts with acid halides, RC(0)C1, Me2NC(S)Cl, Me2P(S)Cl, and chlorophosphines; neutral products of type 0t-E)0i-Ph2P)Fe2(CO)6 (E = RC=0, Me2NC=S, Me2P=S, R^) were obtained in good yield. Reaction with CS2 and RNCS gave anionic products, 0t-SC==S)0t-Ph2P)Fe2(CO)6 and Ot-RÑO=S)Ot-Ph2P)Fe2(CO)6. The [Oi-Ph2P)Fe2(CO)8]~ reagent is much more reactive than the known [^-CO)(p-Ph2P)Fe2(CO)6]~. The structure of (µCH3)2P==S)0t-PhS)Fe2(CO)6 (18b) has been determined by X-ray techniques. Compound 18b crystallizes in the orthorhombic space group P212121 with o = 12.494 (2) k,b- 17.075 (2) Á, c = 8.7909 (9) k,V1944.7 (7) Á3, and Z = 4. The two Fe(CO)3 groups in the complex are bridged by the benzenethiolate and the dimethylphosphino sulfide groups, the latter of which is S-bound to one metal and P-bound to the other. Within the SPMe2 ligand the P—S distance of 2.030 (2) A lies intermediate between that of a single (2.18 A) and a double (1.95 A) bond.