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Browsing by Author "McDonald, Robert"

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    Complexes of multifunctional phosphorus ligands. Rhenium(V) complexes of the multidentate phenoxyphosphine ligands bis(o-trimethylsilyloxyphenyl)phenylphosphine and tris(o-trimethylsilyloxyphenyl)phosphine. Stepwise elimination of Me3SiX (X = Cl, OEt) from the metal-ligand system
    (1998) Cavell, Ronald G.; Hilts, Robert; Luo, Hongyan; McDonald, Robert
    The silylated aryloxo ligands bis(o-silyloxyphenyl)phenylphosphine (abbreviated PhP{OT}2) and tris(o-trimethylsilyloxyphenyl)phosphine (abbreviated P{OT}3, where T = Me3Si) were prepared. Complexation reactions with OReCl2(OEt)(PPh3)2 and OReCl3(PPh3)2 proceed by displacement of one PPh3 and the subsequent stepwise replacement of the OEt and/or Cl substituents. The new complex Re(O)Cl2[κ2-(P,O)-(PhP{O}{OT})](PPh3), formed by elimination of Me3SiOEt, exists in diastereomeric cis and trans forms. Elimination of a second equivalent of Me3SiCl gives Re(O)Cl[κ3-(P,O,O)-(PhP{O}2)](PPh3). Similarly P{OT}3 converts Re(O)Cl2(OEt)(PPh3)2 to ReOCl2[κ2-(P,O)-(P{O}{OT}2)](PPh3) (5) (structurally characterized as 5·0.875CH2Cl2): crystal data; triclinic P1̄, a = 14.302(4) Å, b = 18.734(2) Å, c = 17.639(4) Å, α = 80.950(12)°, β = 80.12(2)°, γ = 81.76(2)°, Z = 4. Final R1 and wR2 values are 0.0852 and 0.1525, respectively on Fo2 > 2σ(Fo2) data (or 0.1948 and 0.2019 on all data). The phenoxy phosphine ligand in 5 is bound via P and one O to Re. The P atoms are mutually cis to each other and to the terminal oxygen on Re. Two ortho-trimethylsiloxy substituted phenyl rings dangle from the coordinated phosphorus atom. Complex 5 can be converted to Re(O)Cl[κ3-(P,O,O)-(P{O}2{OT})](PPh3) (6) by treatment with PPN+ Cl- and 6 was also obtained by direct reaction of Re(O)Cl3(PPh3)2 with P{OT}3 at higher temperatures. The complex 6 has been structurally characterized: crystal data triclinic, P1̄, a = 10.1509(6) Å, b = 12.1123(8) Å, c = 16.2142(14) Å, α = 97.851(7)°, β = 94.852(7)°, γ = 96.889(6)°, Z = 2. Final R1 and wR2 values were 0.0303 and 0.0721 on Fo2 > 2σ(Fo2) data (or 0.0348 and 0.0742 on all data). The phenoxyphosphine ligand in 6 is bound facially to Re through P and two of the phenoxy oxygens. The Ph3P group and terminal oxygen atoms are cis to the oxygen atoms of the phenoxy ligands and the Cl lies trans to P. One trimethylsiloxyphenol group dangles. Careful hydrolysis of 6 gave Re(O)Cl[κ3-(P,O,O)-(P{O}2{OH})](PPh3) which was also formed during complexation reactions in moist solvent. Solution 31P{1H} NMR demonstrated cis- or trans-(P,P) geometry for the complexes, which was confirmed in the two aforementioned cases by structure determinations.
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    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.
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    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.
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    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.
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    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.
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    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.