69 research outputs found
Synthesis and Study of New Late Metal Complexes Featuring N-Phosphinoamidinate Ligands
No full textN-Phosphinoamidine/amidinate (P,N) ligands have recently been shown to be highly effective for the selective chromium-catalyzed tri-/tetramerization of ethylene. Since this initial report, a joint collaboration between the Chevron-Phillips Chemical Company (CPChem) and the Stradiotto/Turculet research groups at Dalhousie University has reported on the iron-catalyzed hydrosilyation of carbonyl compounds and the cobalt-catalyzed hydroboration of alkenes using (P,N)M(N(SiMe3)2) complexes (M = Fe, Co).
These monoanionic, bidentate P,N-chelating ligands offer a mix of hard and soft donors and the anionic charge promotes tight binding to facilitate the isolation of unusual low-coordinate late metal complexes. The propensity of such species to exhibit unusual bonding motifs, unprecedented reactivity, and their applications in catalysis is the focus of this work. Futhermore, the chemistry of monoanionic P,N-ligands in general is surprisingly underexplored.
Encouraged by the exceptional reactivity of the first-row transition metal complexes mentioned above, the initial goals of this thesis were to explore the synthesis and reactivity of low-coordinate second and third-row transition metal complexes. Coordinatively unsaturated Cp*RuLn complexes have a well-established track record of exhibiting new and unusual metal-centered reactivity with diverse applications in organic synthesis. As such, considerable focus continues to be directed toward developing new and isolable classes of such complexes and exploring their stoichiometric reactivity. In this regard, the synthesis and reactivity of 16-electron Cp*Ru(II) (Cp* = η5-C5Me5) complexes supported by N-phosphinoamidinates is detailed herein.
Intrigued by the ability of related (nacnac)Pt species in supporting low-coordinate reactive complexes, structurally and electronically unique low-coordinate Pt(II) complexes supported by N-phosphinoamidinate ligands were developed in pursuit of unusual bonding motifs and reactivity. The synthesis and reactivity of an isolable, three-coordinate, neutral, 14-electron Pt(II) species along with the synthesis and reactivity of a Pt(II)-η3-benzyl complex that undergoes an unprecedented benzylic borylation reaction is also detailed herein.
Within the spirit of moving toward the use of relatively abundant and inexpensive metals in catalysis, and building on the previous advances in this area by the CPChem/Turculet/Stradiotto team, this thesis also examines the development of the manganese complex (P,N)Mn(N(SiMe3)2). The remarkable ability of this complex to reduce amides, ketones, aldehydes, and esters under mild conditions is described herein
Synthesis of Transition Metal Complexes Supported by Mixed Donor PSiP' Bis-Phosphino Silyl Pincer Ligands
No full textIn an effort to explore new metal mediated reactivity and further the versatility of metal pincer chemistry, research in the Turculet group has targeted the synthesis of novel bis(phosphino)silyl PSiP pincer complexes. Given the profound influence that ligand design can have on the reactivity of the ensuing metal complexes, pincer ligands that feature a mixed neutral donor set have emerged as an intriguing ligand class that offers enhanced control over the steric and electronic features of a metal pincer complex. In this context the synthesis and reactivity of metal complexes supported by unsymmetrical PSiP’ ligation was pursued.
In this work three novel PSiP’ ligands were synthesized: (Cy-PSiP’-Ph)H, (Ph-PSiP*-iPr)H and (Cy-PSiP*-iPr)H. Group 10 complexes of the type (Cy-PSiP’-Ph)MX (M = Pt, Pd, Ni; X = Cl, Me, Ph) were prepared. The Pd and Ni chloride complexes were structurally characterized and found to exhibit approximate square planar coordination geometry in the solid state, with the silyl donor coordinated trans to the chloride ligand. The Me derivatives proved to be surprisingly unreactive with hydrosilanes, which is unlike the related Cy-PSiP analogues previously reported by the Turculet group. Amido complexes of the type (Cy-PSiP’-Ph)M(NHR) (M = Pt, Ni; R = H, Ph) and (Cy-PSiP’-Ph)Pd(NH2) were also synthesized. While the latter complexes proved to be quite stable, related complexes of the type (Cy-PSiP’-Ph)Pd(NHR) (R = Ph, tBu) underwent facile rearrangement processes involving Si-C (sp2) bond cleavage in the ligand backbone. Such processes have previously been reported for related (Cy-PSiP)MX (M = Ni, Pd; X = alkyl, amido) species. Group 10 complexes supported by alternative PSiP’ ligands including (Ph-PSiP*-iPr)PtCl and (Cy-PSiP*-iPr)MCl (M = Pt, Ni) were also synthesized. The complex (Cy-PSiP*-iPr)PdCl was structurally characterized and found to exist as a dimeric species in the solid state, with the CH2PiPr2 ligand arms bridging between Pd centers. Solution NMR data suggests that in some cases, κ3-coordination of Ph-PSiP*-iPr and Cy-PSiP*-iPr is achieved.
Finally preliminary studies revealed that Group 8 and 9 complexes supported by such PSiP’ ligands are synthetically viable
Synthesis of Phosphino(Silyl) Ligated Nickel and Manganese Complexes for the Catalytic Hydrofunctionalization of Alkenes
No full textTransition metal catalysts play a key role in the synthesis of value-added products from abundant raw materials. While homogeneous catalysts that feature scarce metals such as Pd, Pt, Rh, and Ru have proven effective, recent focus on sustainability has led to interest in utilizing Earth-abundant 3d-metals such as Mn, Fe, Co, and Ni. Multidentate phosphino(silyl) ligands under investigation in the Turculet group have proven useful in 3d-metal mediated catalysis. This document details the development of new tridentate PSiN and bidentate PSi supported Ni and Mn complexes for application in hydrofunctionalization catalysis.
Nickel complexes supported by a new PSiN ligand that features a quinolyl donor, as well as complexes supported by the bidentate CyPSi (CyPSi = κ2-(2-Cy2PC6H4)SiiPr2) ligand were shown to be effective pre-catalysts for alkene tandem isomerization-hydroboration. Deuterium labeling experiments support a Ni-mediated alkene chain-walking mechanism involving reversible alkene insertion/β-hydride elimination. Borylation occurs exclusively at a terminal position, affording high selectivity. Nickel complexes supported by a new PSiInd ligand featuring an indolyl backbone were also pursued, and these complexes along with (CyPSi)Ni species were screened in alkene hydrogenation catalysis. A variety of sterically hindered, unfunctionalized alkenes were readily hydrogenated under mild conditions. Deuteration experiments highlight the occurrence of background chain-walking, similar to that observed in the previous hydroboration studies.
The synthesis of chiral phosphino(silyl) Ni complexes for application in asymmetric catalysis was also targeted. In this regard, a new (BIPHEN-SilaPhos)Ni(η3-C8H13) complex is described. This complex and the previously synthesized ((S,S)-TADDOL-SilaPhos)Ni(η3-C8H13) were applied in the asymmetric hydrogenation of (Z)-2-acetamido-3-arylacrylates to access chiral α-amino acid esters. SilaPhos ligation represents a new approach to chiral ligands featuring chirality at a Si donor. The (S,S)-TADDOL-SilaPhos ligated Ni complex afforded the desired products in near quantitative yields with excellent enantioselectivity (up to 98:2 er). Both direct and transfer hydrogenation with iPrOH as the hydrogen source are shown to be viable pathways for this reactivity.
Progress towards the synthesis of Mn complexes supported by multidentate phosphino(silyl) ligation is also described. Mn(I) tricarbonyl complexes supported by CyPSiP (CyPSiP = κ3-(2-Cy2PC6H4)2SiMe) and PSiN ligation were synthesized and structurally characterized. The utility of Mn pre-catalysts in alkyne semi-hydrogenation and alkene hydrogenation was investigated. In situ generated Mn(II) dialkyl complexes featuring CyPSiP and PSiN ligation are shown to be active in the catalytic hydrogenation of a range of terminal alkenes
Synthesis and Reactivity of Group 10 Silyl Pincer Complexes
No full textIn an effort to explore new metal mediated reactivity and further the versatility of metal pincer chemistry, research in the Turculet group has targeted the synthesis of novel bis(phosphino)silyl PSiP pincer complexes. In this context, the synthesis and reactivity of Group 10 complexes featuring [Cy-PSiP] ([Cy-PSiP] = [?3-(2-Cy2PC6H4)2SiMe]⁻) ligation is described herein. The central silyl donor is anticipated to promote the formation of electron rich metal species capable of diverse and challenging reactivity.
In the course of this work, it was found that [Cy-PSiP] ligation supports the synthesis of square planar PtII alkyl complexes that can mediate Si-H and Si-Cl bond cleavage chemistry. A cationic PtII species was accessed by treatment of [Cy-PSiP]PtMe with B(C6F5)3. The latter complex underwent B-C bond cleavage in the [MeB(C6F5)3]⁻ counteranion to produce [Cy-PSiP]Pt(C6F5). Examples of Si-C bond cleavage reactions at Pt0 and PtII centers were also observed. Related alkyl complexes of Ni and Pd were observed to undergo rearrangement processes involving net Si-C(sp2) and Si-C(sp3) bond cleavage. In the case of Ni these Si-C bond cleavage steps are reversible on the NMR timescale. Attempts to prepare a terminal hydride complex of the type [Cy-PSiP]MH (M = Pd, Pt) resulted in the isolation of ?2-Si-H coordination complexes of the type [Cy-PSi(µ-H)P]M, which were shown to undergo insertion of CO2 to form the corresponding formate species. In the presence of B(C6F5)3, these ?2-Si-H complexes were capable of mediating the catalytic reduction of CO2 to CH4 using hydrosilanes as the reducing agent.
The synthesis and characterization of terminal, monomeric Pt hydroxide and alkoxide complexes of the type [Cy-PSiP]Pt(OR) (R= H, Ph, tBu) was achieved, and these complexes were shown to readily deprotonate relatively acidic C-H bonds in phenylacetylene and acetonitrile. A rare example of hydrogenolysis of the Pt-OR linkage with H2 was documented, as was an unusual example of Si-H addition across the Pt-OR bond to form Pt silyl species. While terminal anilido Pt complexes of the type [Cy-PSiP]Pt(NHAr) (Ar = Ph, 2,6-Me2C6H3, 2,6-iPr2C6H3) proved readily isolable, related Ni and Pd anilido species underwent rearrangement processes similar to those observed in their alkyl analogues. Terminal phosphido complexes supported by [Cy-PSiP] ligation were successfully isolated and characterized for all Group 10 metals. Lastly, the Pt and Pd coordination chemistry of a new PSiN pincer derivative was explored, and the amino donor arm of this pincer ligand was demonstrated to exhibit hemilabile coordination to the metal center
Synthesis, Characterization, and Reactivity of Transition Metal Complexes Supported by Heteropolydentate Ligation
No full textPincer complexes of the platinum group metals have been the subject of intense research in recent years, owing to the remarkable stoichiometric and catalytic reactivity exhibited by such complexes. In this context, research previously reported by the Turculet group has focused on developing the reactivity of new bis(phosphino)silyl pincer complexes that feature tridentate ligands of the type [R-PSiP] (R = alkyl or aryl). In an effort to further expand the scope of silyl pincer ligation, the study of complexes supported by new PSiN mixed donor ligands of the type [R-PSiN-R’] (R, R’ = alkyl or aryl) has been undertaken. This document details the synthesis of such PSiN ligand precursors, as well as the synthesis, characterization, and reactivity of platinum group metal complexes featuring such PSiN ligands.
In an effort to further expand the scope of silyl pincer ligation to non platinum-group metals, the study of Co complexes supported by PSiP ligation was undertaken. It was anticipated that such Co complexes featuring highly donating PSiP ligands could be able to mimic two-electron redox chemistry of the platinum group metals. The synthesis and characterization of [Cy-PSiP]Co complexes in both the CoI and CoII oxidation states is described, as well as an investigation of the ability of [Cy-PSiP]CoI to undergo two-electron oxidative addition reactions with substrates such as iodobenzene, and H2.
In order to further develop the applications of heteropolydentate ligands in transition metal chemistry, N-phosphinoamidine/amidinate ligands were identified as targets of inquiry. The exploration of the ability of sterically demanding N-phosphinoamidine/amidinate ligands to support reactive, low-coordinate complexes for use in catalytic applications is detailed. Of particular interest was the design of low-coordinate complexes that will be active in the iron and cobalt catalyzed reduction of unsaturated substrates. This thesis details the synthesis of novel sterically demanding N-phosphinoamidine/amidinate ligands and their corresponding low-coordinate iron and cobalt complexes. The remarkable activity of such iron and cobalt complexes in the catalytic hydrosilylation of carbonyl substrates as well as the catalytic hydroboration of alkenes is also discussed
Life tables for the CONCORD-2 study
No full textThe CONCORD-2 study has initiated worldwide surveillance of population-based cancer survival, a metric designed to assess the overall effectiveness of health systems in managing cancer, and to inform global policy on cancer control. Patient data were obtained from 279 population-based cancer registries in 67 countries. Centralised quality control and analysis was performed on individual tumour records for 25·7 million adults (age 15-99 years) and 75,000 children (age 0-14 years) diagnosed with one of 10 cancers during 1995-2009. Net survival up to five years from diagnosis was estimated as the survival probability after compensation for background mortality from other causes. The background mortality is contained in life tables. More than 12,000 life tables are provided, classified by Continent, Country, Registry (Region), Race/Ethnicity (selected populations), Calendar year and Sex. Each life table contains the central all-cause mortality rate per 100,000 person-years, the probability of death, and the probability of survival by single year of age (0-99 years). Researchers must complete a CSG User Registration Form to gain access
Synthesis and Characterization of Palladium Complexes Supported by an NPN-Phosphido Ancillary Ligand
No full textMono-, Di-, and Trinuclear Complexes Featuring the New Bis(phosphido) Ligand 4,5-Bis(<i>tert</i>-butylphosphido)-9,9-dimethylxanthene ([POP]<sup>2−</sup>)
No full textThe synthesis of the new dianionic xanthene-derived bis(phosphido) ligand 4,5-bis(tert-butylphosphido)-9,9-dimethylxanthene ([POP]2−) is described. Coordination chemistry studies reveal that this versatile new ancillary ligand is capable of supporting electronically and coordinatively unsaturated Zr species (4), as well as rationally assembled heteropolynuclear ZrRh (5) and ZrRh2 (6) complexes
Zirconium Amide, Halide, and Alkyl Complexes Supported by Tripodal Amido Ligands Derived from <i>cis,cis</i>-1,3,5-Triaminocyclohexane
No full textZirconium complexes containing the chelating triamido ligands [cis,cis-1,3,5-(C6F5N)3C6H9]3-
and {cis,cis-1,3,5-[3,5-(CF3)2C6H3N]3C6H9}3- are reported. The dimethylamido complexes [cis,cis-1,3,5-(C6F5N)3C6H9]ZrNMe2(NHMe2) (3) and {cis,cis-1,3,5-[3,5-(CF3)2C6H3N]3C6H9}ZrNMe2(NHMe2) (4) were prepared from Zr(NMe2)4 and cis,cis-1,3,5-(C6F5NH)3C6H9 (1) or
cis,cis-1,3,5-[3,5-(CF3)2C6H3NH]3C6H9 (2), respectively. As determined by X-ray crystallography, an ortho fluorine atom in the triamido ligand of complex 3 is coordinated to the
zirconium center. The zirconium chloride complexes [cis,cis-1,3,5-(C6F5N)3C6H9]ZrCl (5) and
{cis,cis-1,3,5-[3,5-(CF3)2C6H3N]3C6H9}ZrCl(THF)2 (6) were prepared from Np3ZrCl and 1 or
2, respectively. Compound 5 reacts with MeMgBr, LiCH(SiMe3)2, LiCH2SiMe3, and PhCH2MgCl to give the corresponding alkyl derivatives [cis,cis-1,3,5-(C6F5N)3C6H9]ZrMe(Et2O) (7),
[cis,cis-1,3,5-(C6F5N)3C6H9]ZrCH(SiMe3)2 (8), [cis,cis-1,3,5-(C6F5N)3C6H9]ZrCH2SiMe3 (9), and
[cis,cis-1,3,5-(C6F5N)3C6H9]ZrCH2Ph (10). An X-ray crystallographic study of 8 reveals the
presence of an α-agostic interaction, as well as the coordination of two ortho fluorines to the
metal center. These interactions persist in solution, as indicated by NMR studies. Compound
6 reacts with MeMgCl and LiCH(SiMe3)2 to give the corresponding alkyl derivatives {cis,cis-1,3,5-[3,5-(CF3)2C6H3N]3C6H9}ZrMe(THF)2 (11) and {cis,cis-1,3,5-[3,5-(CF3)2C6H3N]3C6H9}ZrCH(SiMe3)2(THF) (12). The methyl derivative 7 reacts with 3 equiv of xylyl isocyanide to
yield (15), which was structurally characterized. Complex 15 features three molecules
of xylyl isocyanide that have been coupled to give a diazazirconacycle with an exocyclic
ketenimine group. The alkyl derivatives 7−12 react with hydrogen at elevated temperatures
to yield ZrF species derived from the activation of the fluorinated substituents on the triamido
ligands, presumably via reactive hydride intermediates
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