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Garth R. Giesbrecht

Bio: Garth R. Giesbrecht is an academic researcher from Tel Aviv University. The author has contributed to research in topics: Ligand & Pyridine. The author has an hindex of 22, co-authored 39 publications receiving 1239 citations. Previous affiliations of Garth R. Giesbrecht include University of British Columbia & Lawrence Berkeley National Laboratory.

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TL;DR: A DFT (Density Functional Theory) study of a samarium imido complex has provided insight into the electronic and steric factors that may be necessary to support these unusual reactive groups.
Abstract: In stark contrast to the transition metals, examples of imido or alkylidene complexes of the lanthanides remain scarce. A recent literature survey reveals that only nine examples of lanthanide imido complexes have been reported, and the majority of these have arisen serendipitously. Concrete examples of species containing lanthanide–carbon multiple bonds are even more sparse. Recently, some rational approaches to the synthesis of lanthanide complexes containing LnX functionalities have been detailed (X = C, N). Additionally, a DFT (Density Functional Theory) study of a samarium imido complex has provided insight into the electronic and steric factors that may be necessary to support these unusual reactive groups. This Perspective reviews the work in this field and offers some suggestions to expand this potentially useful class of compounds.

167 citations

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TL;DR: In this article, an X-ray structural analysis reveals an unassociated complex with a four-coordinate lanthanum center, with a single guanidinate ligand and two phenoxide groups.
Abstract: La[N(SiMe3)2]3 reacted with 1,3-dicyclohexylcarbodiimide in refluxing toluene to yield the mono-guanidinate complex La[CyNC(N(SiMe3)2)NCy](N(SiMe3)2)21. Compound 1 is monomeric in solution; X-ray structural analysis reveals an unassociated complex in the solid state, with a four-coordinate lanthanum center. Complex 1 reacts with 2,6-di-tert-butylphenol (2 equivalents) in cold pentane to yield the bis(phenoxide) complex La[CyNC(N(SiMe3)2)NCy](OC6H3tBu2-2,6)2. X-Ray analysis indicates a similar structure to that of 1, with a four-coordinate lanthanum center coordinated by a single guanidinate ligand and two phenoxide groups. This compound catalyses the ring-opening polymerization of D,L-lactide to polylactide. Although high molecular weight polymer is obtained, polydispersities are broad and no control over the stereochemistry of the polymer is observed.

143 citations

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TL;DR: The coordination chemistry of ancillary amidinate ligands with a pendant pyridine functionality is described in this article, where the authors show that these ligands are monomeric.

80 citations

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TL;DR: The first dialkyl-substituted scandium phosphine complexes with two hydrocarbyl groups were reported in this article, showing that they are mononuclear in the solid state.

80 citations

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TL;DR: In this paper, Density functional theory calculations have been carried out to gain a better understanding of the nature of the bonding interactions within complex 2 and indicate that the 5d metal acceptor orbitals play a significant role in stabilizing π-donation from the imido groups to the samarium centers within the Sm2N2 core.

76 citations


Cited by
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TL;DR: Hydroamination of Alkenes and Alkynes under Microwave Irradiation and Nitromercuration Reactions 3878 9.8.4.5.
Abstract: 8.4.5. Nitromercuration Reactions 3878 9. Hydroamination of Alkenes and Alkynes under Microwave Irradiation 3878 * To whom correspondence should be addressed. Phone: +49 241 8

1,685 citations

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TL;DR: A review of recent developments in the preparation and use of new initiators for the ring opening polymerization of lactide is presented in this article, where the authors compare different classes of initiators including metal complexes, classed according to their group in the periodic table, and carbon-based initiators/organocatalysts.
Abstract: The review summarizes recent developments in the preparation and use of new initiators for the ring opening polymerization of lactide. The review compares different classes of initiator including metal complexes, classed according to their group in the periodic table, and carbon‐based initiators/organocatalysts. Emphasis is placed on the polymerization kinetics and the control exhibited by the different types of initiators. Where useful properties, such as high rates or stereocontrol, have been observed a more detailed examination of the initiator is provided. A further focus of the review is initiators displaying low toxicity and biocompatibility.

638 citations

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TL;DR: Guanidines have attracted increasing attention as electronically and sterically flexible ligands as mentioned in this paper, exhibiting a variety of coordination modes and a range of donor properties leading to compatibility with a remarkably wide range of metal ions from all parts of the periodic table.

476 citations

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TL;DR: 96 Samarium diiodide acted as reducing agent in the reaction with (phenylenebis(3,5-tBu4-salicylidene)iminato)sodium, which resulted in formation of the THF adduct {P2N2}YCH2SiMe3(THF), whereas the THf-free compound could only be isolated as a highly reactive oily material.
Abstract: ion upon treatment with B(C6F5)3 in THF to generate the cationic species [(MAC)Y(CH2SiMe3)][B(C6F5)3(CH2SiMe3)]. However, this salt was found to be highly unstable and could not be isolated as a pure material.97 Fryzuk et al. have developed a remarkable organoyttrium chemistry around the phosphorus-containing macrocycle syn-{P2N2} ({P2N2} ) [PhP(CH2SiMe2NSiMe2CH2)2PPh]). The starting material was the chloride-bridged dimer [{P2N2}Y(μ-Cl)]2, which can be prepared in 95% yield by the reaction of synLi2(THF){P2N2} with YCl3(THF)3 in THF solution. Straightforward metathesis using the very bulky alkyllithium reagent LiCH(SiMe3)2 according to eq 29 (methyl groups on Si omitted for clarity) afforded the monomeric yttrium alkyl species {P2N2}YCH(SiMe3)2 in 92% yield. Use of the less sterically hindered alkyl moiety CH2SiMe3 followed by addition of THF resulted in formation of the THF adduct {P2N2}YCH2SiMe3(THF), whereas the THF-free compound could only be isolated as a highly reactive oily material.98 A quite remarkable samarium alkyl complex of complicated molecular structure was reported by Gambarotta et al.99 Samarium diiodide acted as reducing agent in the reaction with (phenylenebis(3,5-tBu4-salicylidene)iminato)sodium, (3,5tBu4salophen)Na2(THF)3, to give dimeric [Sm2(SBSB)(THF)3]‚2toluene (SB-SB ) C-C bonded 3,5tBu4salophen dimer). The new ligand resulted from the reductive coupling of two imino functional groups of two 3,5-tBu4salophenSm units. Subsequent treatment with MeLi resulted in a novel oxo-bridged dimer (24), featuring alkylation of both samarium atoms and arising from cleavage of the C-C bond connecting the two units, as well as complete reduction of the imine groups of the salophen ligands and THF deoxygenation. In the formula drawing depicted here the bridging phenylene rings are omitted for clarity.99 Carbene complexes of the lanthanide elements have first become available through the use of the stable Arduengo-type carbenes.100,101 Organolanthanide derivatives are readily accessible by adding the heterocyclic carbene ligands to various diand trivalent rare earth complexes such as decamethylsamarocene. Cyclopentadienyl-free derivatives have been obtained by reacting 1,3,4,5-tetramethylimidazol-2-ylidene with the tris(2,2,6,6-tetramethylheptane-3,5-dionato) complexes of yttrium and europium, Ln(THD)3 (Ln ) Y, Eu). The two carbene complexes 25 were isolated as white solids in quantitative yield. The europium complex was structurally characterized by X-ray analysis. Despite the differences in the ionic radii of the two metals 7-coordinate monocarbene adducts are formed in both cases. With 266.3(4) pm the Eu-C distance in (1,3,4,5-tetramethylimidazol-2-ylidene)Eu(THD)3 is comparable to Pr(III)-C and Sm(III)-C distances reported for some isonitrile complexes.102,103 In the 13C NMR spectrum of the yttrium complex the resonance for the former carbene carbon is at δ 199.38 (cf. δ 214 for the free carbene ligand) and shows a 13C-89Y coupling of 33 Hz which indicates that the Y-C bond does not dissociate rapidly on the NMR time scale.101 The bulkier 1,3-diisopropyl-4,5dimethylimidazol-2-ylidene (iPr-Carb) has been used to synthesize a mixed carbene-THF alkyl Lu(CH2SiMe3)3(THF)(Pr-Carb) (26).22d Due to its higher steric demand, the carbene ligand occupies an equatorial position (Lu-C(Carb) ) 249 pm). Somewhat related to the carbene complexes is a highly unusual monomeric samarium bis(iminophosphoranyl) chelate complex which has been reported by Cavell et al.104 Addition of H2C(Ph2PdNSiMe3)2 to a toluene solution of samarium tris(dicyclohexylamide) afforded bright yellow [κ-C,N,N′-C(Ph2Pd NSiMe3)2]Sm(NCy2)(THF) (27). The core of the molecule consists of two nearly planar, fused fourmembered rings with a Sm-C shared edge. With 246.7(4) pm the Sm-C bond length is considerably shorter (10%) than the average samarium-carbon distances, indicating that 27 can be formulated as a carbene complex. Non-Cyclopentadienyl Organolanthanide Complexes Chemical Reviews, 2002, Vol. 102, No. 6 1865

438 citations

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TL;DR: In this paper, a review of the non-Cp organometallic chemistry of the ligands which have so far been explored for this purpose, commenting on the fine balance of steric and electronic properties necessary to stabilize monomeric, base-free organometall compounds of these metals.

397 citations