Alkaline and alkaline earth metals

Hill, Michael S.

doi:10.1039/c1ic90016a

Cited by 4 publications

(6 citation statements)

References 171 publications

(164 reference statements)

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“…21 The nature of the end-groups capping the PCL or PLLA chains was examined by NMR analyses of the polymer samples recovered after precipitation. In particular, 1 that the other hydroxyl end-capping group is formed upon deactivation of the active metal-oxygen bond. [45][46][47][48][58][59][60][61][62][63] In light of our already published studies on strontium analogues, 24 DFT calculations on the initiation step of the ROP of ε-CL were carried out.…”

Section: Dalton Transactions Papermentioning

confidence: 99%

“…SEC traces of the polymers all exhibited a unimodal and symmetrical peak. The molar masses of short-chain polymer samples were determined by 1 H NMR analysis in CDCl 3 from the relative intensities of the signals of the PCL or PLLA main-chain methylene protons for PCL (-CH 2 OC(O), δ 4.04 ppm) or methine protons for PLLA (-CHCH 3 C(O), δ 5.15 ppm), and those of the chainend methylene protons (-CH 2 OH, δ 3.65 ppm).…”

Section: Dalton Transactions Papermentioning

confidence: 99%

“…There is significant increasing interest in the coordination and organometallic chemistry of the heavier alkaline earth metals (Ca, Sr, Ba). [1][2][3][4][5][6] Within these series, calcium compounds remain the most largely investigated. 4,5,7 Although calcium is an inexpensive and non-toxic element present in significant amount in the human body, access to its organometallic and coordination compounds is often limited by their kinetic lability with detrimental Schlenk-type equilibria.…”

Section: Introductionmentioning

confidence: 99%

“…1 H NMR (d 8 -THF, 300.13 MHz): δ 0.41 (q, br, 8 H, BH 4 , 1 J H-B = 82 Hz) ppm 11. B NMR (d 8 -THF, 96.29 MHz): δ −36.6 (qt,1 J H-B = 82 Hz) ppm. [Cp*Ca(BH 4 )(THF) n ] 2 (2a).…”

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confidence: 99%

“…The residue was washed with 15 mL of n-pentane and dried in vacuum to obtain a pale yellow solid. Yield: 188 mg (56%) 1. H NMR (d 8 -THF, 300.13 MHz): δ 2.00 (s, 15 H, CH 3 ), −0.44 (q, 4 H, BH 4 , 1 J H-B = 83 Hz) ppm.…”

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confidence: 99%

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Organometallic calcium and strontium borohydrides as initiators for the polymerization of ε-caprolactone and l-lactide: combined experimental and computational investigations

et al. 2013

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[Ca(BH4)2(THF)2] (1a), a known compound, was easily prepared following a convenient new procedure from [Ca(OMe)2] and BH3·THF in THF. Reaction of 1a with KCp* (Cp* = (η(5)-C5Me5)) and K{(Me3SiNPPh2)2CH} in a 1 : 1 ratio in THF resulted in the corresponding dimeric heteroleptic mono-borohydride derivatives [Cp*Ca(BH4)(THF)n]2 (2a) and [{(Me3SiNPPh2)2CH}Ca(BH4)(THF)2] (3a), respectively. Both compounds were fully characterized and the solid-state structure of 3a was established by single crystal X-ray diffraction. Compounds 1a, 2a, and 3a, together with the earlier reported compounds [Sr(BH4)2(THF)2] (1b), [Cp*Sr(BH4)(THF)2]2 (2b), and [{(Me3SiNPPh2)2CH}Sr(BH4)(THF)2] (3b), were used as initiators for the ROP of polar monomers. The general performances of the complexes in the ROP of ε-caprolactone and l-lactide demonstrate a relatively good control of the polymerization under the operating conditions established. α,ω-Dihydroxytelechelic poly(ε-caprolactone)s (PCLs) and poly(lactide)s (PLAs) were thus synthesized. DFT calculations on the initiation step of the ROP of ε-CL were carried out. Gibbs free energy profiles were determined for the three calcium complexes highlighting slightly more active calcium complexes as compared to strontium analogues, in agreement with experimental findings.

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Section: Dalton Transactions Papermentioning

confidence: 99%

Section: Dalton Transactions Papermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…1 H NMR (d 8 -THF, 300.13 MHz): δ 0.41 (q, br, 8 H, BH 4 , 1 J H-B = 82 Hz) ppm 11. B NMR (d 8 -THF, 96.29 MHz): δ −36.6 (qt,1 J H-B = 82 Hz) ppm. [Cp*Ca(BH 4 )(THF) n ] 2 (2a).…”

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confidence: 99%

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confidence: 99%

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Organometallic calcium and strontium borohydrides as initiators for the polymerization of ε-caprolactone and l-lactide: combined experimental and computational investigations

et al. 2013

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Alkali Metals: Organometallic Chemistry

Harvey

2014

Encyclopedia of Inorganic and Bioinorganic Chemistry

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Organolithium complexes, such as the organomagnesium Grignard reagents, are important reactants in organic synthesis. The similarity in structure, bonding, and reactivity of organolithium and ‐magnesium compounds exemplifies the common chemistry exhibited by representative elements that appear in the same diagonal in the periodic table. Although much debate exists over the degree of covalency within lithium–carbon bonding interactions—the presence of some covalent characters in Li–C bonds of alkyllithium compounds is widely accepted. The bonding interactions within organoalkali metal complexes of the heavier alkali metals are generally considered to be strongly electrostatic or ionic in nature. This is supported by a large collection of evidence, consisting primarily of solution NMR data, single‐crystal X‐ray analyses, and gas‐phase computational studies. Many of the organolithium compounds are soluble in hydrocarbons, but organometallic compounds of the heavier Group 1 metals generally require more polar media to dissolve. In general, the reactivity of the alkali metals and the reactivity of the organometallic compounds of these metals increase as the group descends. Although organoalkali metal compounds are similar to Grignard reagents, they are more reactive and are both air‐ and moisture‐sensitive and sometimes pyrophoric. In addition, organoalkali metal compounds will react as Brønsted bases with protic reagents. Specific details regarding the synthesis, reactivity, and structures of various types of organoalkali metal compounds are discussed.

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Organometallic Strontium Borohydrides: Synthesis, X‐ray Structures, Catalytic Polymerization of ε‐Caprolactone, and Density Functional Calculations

et al. 2012

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In the last few years a number of research groups started significant activity in the exploration of the coordination and organometallic chemistry of the heavier alkaline-earth metals. [1] Most of this work is focused on calcium, [2] an inexpensive and non-toxic element present in significant amounts in the human body. Indeed, synthetic access to such large alkalineearth metal complexes is often limited by their kinetic lability with detrimental Schlenk-type equilibria. [3] Within this reserach not only the synthesis of new compounds but also the structures, [4] the reactivity, [5] and some catalytic applications were investigated. [6] Among these latter the ring-opening polymerization (ROP) of cyclic esters such as e-caprolactone (e-CL) and lactide (LA), allows access to polymers with controlled molar mass and molar mass distribution and especially, in some cases, controlled stereochemistry. [2a, 7] In contrast to this well-established chemistry, the application of structurally characterized strontium compounds as initiators in ROP remains very rare. Besides ill-defined amino isopropoxyl strontium, [8] phenoxide ligated cationic strontium complexes [9] and some phenoxide strontium amides [10] were only very recently used for the ROP of LA.Whereas in related rare-earth chemistry, borohydrides such as [Ln(BH 4 ) 3 (thf) 3 ] [11] or its derivatives have become well-established initiators for the ROP of cyclic esters and carbonates, [12] comparable chemistry of alkaline-earth elements was only first published recently by Cushion and Mountford (e.g. on calcium). [13] This is rather surprising because [Ca(BH 4 ) 2 (thf) 2 ] is commercially available for applications in materials science. [14] In contrast, such borohydride chemistry involving strontium is even less developed. Although, the synthesis and the solidstate structure of [Sr(BH 4 ) 2 (thf) 2 ] (1) were already reported in 1995, [15] there is to date, to the best of our knowledge, no structurally characterized coordination or organometallic strontium borohydride compound known.Herein, we describe the synthesis and structural characterization of the half-sandwich [Cp*Sr(BH 4 )(thf) 2 ] 2 (Cp* = h 5 -C 5 Me 5 ; 2) and the bis(phosphinimino)methanide [{(Me 3 SiNPPh 2 ) 2 CH}Sr-(BH 4 )(thf) 2 ] (3) complexes, as well as their application as initiators for the ROP of e-CL. The starting material 1 was prepared according to a literature procedure from [Sr(OEt) 2 ] and a solution of BH 3 in THF. [15] Reaction of 1 with KCp* and K[(Me 3 SiNPPh 2 ) 2 CH] [16] resulted in the corresponding heteroleptic monoborohydride derivatives 2 and 3, respectively (Scheme 1).The new complexes 2 and 3 have been characterized by standard analytical/spectroscopic techniques and the solidstate structures were established by single-crystal X-ray analysis. The 1 H NMR spectra show the expected resonance for the Cp* ligand of 2 at d = 1.98 ppm and a broad signal for the methine group of the bis(phosphinimino)methanide ligand of 3 at d = 1.72 ppm. The BH 4 À groups are observed as...

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Alkaline and alkaline earth metals

Cited by 4 publications

References 171 publications

Organometallic calcium and strontium borohydrides as initiators for the polymerization of ε-caprolactone and l-lactide: combined experimental and computational investigations

Organometallic calcium and strontium borohydrides as initiators for the polymerization of ε-caprolactone and l-lactide: combined experimental and computational investigations

Alkali Metals: Organometallic Chemistry

Organometallic Strontium Borohydrides: Synthesis, X‐ray Structures, Catalytic Polymerization of ε‐Caprolactone, and Density Functional Calculations

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