Publications
497 results found
Song Y, Zong H, Trivedi ER, et al., 2009, Synthesis of multimodal MR-optical contrast agents based on porphyrazines, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, Vol: 238, ISSN: 0065-7727
Ali S, Heathcote DA, Kroll SHB, et al., 2009, The Development of a Selective Cyclin-Dependent Kinase Inhibitor That Shows Antitumor Activity, CANCER RESEARCH, Vol: 69, Pages: 6208-6215, ISSN: 0008-5472
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- Citations: 118
Calo F, Bondke A, Richardson J, et al., 2009, Total synthesis and determination of the absolute stereochemistry of the squalene synthase inhibitors CJ-13,981 and CJ-13,982, TETRAHEDRON LETTERS, Vol: 50, Pages: 3388-3390, ISSN: 0040-4039
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- Citations: 8
Calo F, Richardson J, White AJP, et al., 2009, Enantioselective formal total synthesis of (-)-trachyspic acid, TETRAHEDRON LETTERS, Vol: 50, Pages: 1566-1567, ISSN: 0040-4039
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- Citations: 8
Andersen K, Anderson M, Anderson OP, et al., 2009, Star porphyrazines and related multimetallic macrocycles, 16th International Congress of Heterocyclic Chemistry, Publisher: WILEY, Pages: 1013-1042, ISSN: 0022-152X
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- Citations: 49
Crimmin MR, Barrett AGM, Hill MS, et al., 2009, Beta-diketiminate C-H activation with heavier group 2 alkyls, Dalton Trans, Pages: 9715-7, ISSN: 1477-9234
Well defined dialkyls of the heavier alkaline earth elements, [M{CH(SiMe(3))(2)}(2)(THF)(n)] [M = Ca, n = 2; M = Sr, n = 3; M = Ba, n = 3] react to form either the heteroleptic beta-diketiminato alkyl when M = Ca or unusual 'C-H activation' products in which a methyl group of the ligand is deprotonated when M = Sr or Ba.[on SciFinder (R)]
Crimmin MR, Arrowsmith M, Barrett AGM, et al., 2009, Intramolecular Hydroamination of Aminoalkenes by Calcium and Magnesium Complexes: A Synthetic and Mechanistic Study., J. Am. Chem. Soc., Vol: 131, Pages: 9670-9685, ISSN: 0002-7863
The β-diketiminate-stabilized calcium amide complex [{ArNC(Me)CHC(Me)NAr}Ca{N(SiMe3)2}(THF)] (Ar = 2,6-diisopropylphenyl) and magnesium Me complex [{ArNC(Me)CHC(Me)NAr}Mg(Me)(THF)] are reported as efficient precatalysts for hydroamination/cyclization of aminoalkenes. The reactions proceeded under mild conditions, allowing the synthesis of five-, six-, and seven-membered heterocyclic compds. Qual. assessment of these reactions revealed that the ease of catalytic turnover increases (i) for smaller ring sizes (5 > 6 > 7), (ii) substrates that benefit from favorable Thorpe-Ingold effects, and (iii) substrates that do not possess addnl. substitution on the alkene entity. Prochiral substrates may undergo diastereoselective hydroamination/cyclization depending upon the position of the existing stereocenter. Also, a no. of minor byproducts of these reactions, arising from competitive alkene isomerization reactions, were identified. Stoichiometric reactions between the precatalysts and primary amines provided an important model for catalyst initiation and suggested that these reactions are facile at room temp., with the reaction of the calcium precatalyst with benzylamine proceeding with ΔG°(298 K) = -2.7 kcal mol-1. Both external amine/amide exchange and coordinated amine/amide exchange were obsd. in model complexes, and probably these processes occur via low-activation-energy pathways. As a result of the formation of potentially reactive byproducts such as hexamethyldisilazane, calcium-catalyst initiation is reversible, whereas for the magnesium precatalyst, this process is nonreversible. Further stoichiometric reactions of the two precatalysts with 1-amino-2,2-diphenyl-4-pentene demonstrated that the alkene insertion step proceeds via a highly reactive transient alkylmetal intermediate that readily reacts with N-H σ bonds under catalytically relevant conditions. The results of deuterium-labeling studies are consistent with the formation
Barrett AGM, Casely IJ, Crimmin MR, et al., 2009, Beta-diketiminato calcium and magnesium amides; model complexes for hydroamination catalysis, Inorg Chem, Vol: 48, Pages: 4445-53, ISSN: 1520-510X
In a study relevant to group 2-mediated hydroamination catalysis, the reaction of the beta-diketiminato magnesium alkyl complex [{ArNC(Me)CHC(Me)NAr}Mg((n/s)Bu)] (Ar = 2,6-(i)Pr(2)C(6)H(3)) with benzylamine, 2-methoxyethylamine, pyrrolidine, and 2-methyl-4,4-diphenylpyrrolidine has been shown to yield the corresponding magnesium amide complexes [{ArNC(Me)CHC(Me)NAr}Mg(NR(1)R(2))] (R(1) = H, R(2) = CH(2)Ph, CH(2)CH(2)OMe; R(1) = R(2) = -(CH(2))(4)-, -CH(Me)CH(2)CPh(2)CH(2)-) within the first point of analysis (30 min) at room temperature in near quantitative yield as monitored by (1)H NMR spectroscopy. Reactions proceeded non-reversibly, and the products have been characterized in both solution and the solid state. While single crystal X-ray diffraction analysis demonstrated that the magnesium amides are dimeric in the solid state, with aggregation occurring via mu(2)-coordinated amide ligands, NMR studies suggest that for more sterically crowded amide ligands discreet monomeric species exist in solution. In contrast, the calcium complex [{ArNC(Me)CHC(Me)NAr}Ca{N(SiMe(3))(2)}(THF)] reacted reversibly with benzylamine at room temperature to form an equilibrium mixture of a calcium benzylamide and bis(trimethylsilyl)amide. A series of Pulsed-Gradient Spin-Echo NMR studies upon beta-diketiminato calcium amides were consistent with the formation of a dimer in solution. A van't Hoff analysis performed on this mixture allowed DeltaH degrees = -51.3 kJ mol(-1) and DeltaS degrees = -134 J mol(-1) of the protonolysis/dimerization reaction to be derived and the Gibbs' free energy to be calculated as DeltaG degrees (298 K) = -11.4 kJ mol(-1).[on SciFinder (R)]
Barrett AGM, Brinkmann C, Crimmin MR, et al., 2009, Heavier group 2 metals and intermolecular hydroamination: a computational and synthetic assessment, J Am Chem Soc, Vol: 131, Pages: 12906-7, ISSN: 1520-5126
A density functional theory assessment of the use of the group 2 elements Mg, Ca, Sr, and Ba for the intermolecular hydroamination of ethene indicated that the efficiency of the catalysis is dependent upon both the polarity and the deformability of the electron density within the metal-substituent bonds of key intermediates and transition states. The validity of this analysis was supplemented by a preliminary study of the use of group 2 amides for the intermolecular hydroamination of vinyl arenes. Although strontium was found to provide the highest catalytic activity, in line with the expectation provided by the theoretical study, a preliminary kinetic analysis demonstrated that this is possibly a consequence of the increased radius and accessibility of this cation rather than a reflection of a reduced barrier for rate-determining alkene insertion.[on SciFinder (R)]
Barrett AGM, Crimmin MR, Hill MS, et al., 2009, Catalytic 2,3,4-hexatriene formation by terminal alkyne coupling at calcium, Chem Commun (Camb), Pages: 2299-301, ISSN: 1359-7345
Heteroleptic calcium amides effect the catalytic dimerisation of the terminal alkyne CH(3)OCH(2)C[triple bond, length as m-dash]CH to the hexatriene (CH(3)OCH(2))CH[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]CH(CH(2)OCH(3)) under mild conditions; the reaction is proposed to occur via a dimeric calcium acetylide intermediate and to be promoted by polarisation of the electron density within the alkynide C[triple bond, length as m-dash]C bonds.[on SciFinder (R)]
Calo F, Richardson J, Barrett AGM, 2008, Total synthesis of citrafungin A., J Org Chem, Vol: 73, Pages: 9692-9697
The antifungal natural product citrafungin A was synthesized using, as key steps, an asymmetric aldol reaction of a chiral oxazolidinone, diastereoselective alkylation of a chiral 1,3-dioxolan-2-one, semihydrogenation of an enyne, and selective methyl ester deprotection.
Soorukram D, Qu T, Barrett AGM, 2008, Four-component benzyne coupling reactions: A concise total synthesis of dehydroaltenuene B, ORGANIC LETTERS, Vol: 10, Pages: 3833-3835, ISSN: 1523-7060
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- Citations: 44
Navarro I, Basset J-F, Hebbe S, et al., 2008, Biomimetic synthesis of resorcylate natural products utilizing late stage aromatization:: Concise total syntheses of the marine antifungal agents 15G256ι and 15G256β, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 130, Pages: 10293-10298, ISSN: 0002-7863
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- Citations: 71
Callens E, Burton AJ, White AJP, et al., 2008, Mechanistic study on benzylic oxidations catalyzed by bismuth(III) salts: X-ray structures of two bismuth-picolinate complexes, TETRAHEDRON LETTERS, Vol: 49, Pages: 3709-3712, ISSN: 0040-4039
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- Citations: 24
Song Y, Zong H, Kohlmeir EK, et al., 2008, INOR 513-Synthesis of high-relaxivity magnetic resonance contrast agents via click chemistry, 235th American-Chemical-Society National Meeting, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Sholto A, Lee S, Hoffman BM, et al., 2008, Spectroscopy, binding to liposomes and production of singlet oxygen by porphyrazines with modularly variable water solubility, PHOTOCHEMISTRY AND PHOTOBIOLOGY, Vol: 84, Pages: 764-773, ISSN: 0031-8655
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- Citations: 25
Jogalekar AS, Snyder JP, Liotta DC, et al., 2008, Pyrazolopyrimidinamine compounds as selective inhibitors for cyclin-dependent kinases and their preparation, pharmaceutical compositions and use in the treatment of CDK-mediated diseases, PCT Int. Appl. (2008), 201pp. CODEN: PIXXD2 WO 2008151304 A1 20081211
This invention provides a class of compds. of formula I which are useful for specifically inhibiting cyclin-dependent kinases. This class of compds. of formula I finds use in treating diseases resulting from inappropriate activity of cyclin-dependent kinases. Moreover, certain members of this class are particularly useful for inhibiting cyclin-dependent kinase 7 and are esp. useful for the treatment of breast cancer. Compds. of formula I wherein R is C1-6 hydrocarbyl; R1 is OH, alkoxy, H and halo; R2 is H, alkyl, amino, sulfanyl, and sulfonyl; R3 is H, SO2NH2 and derivs., halo, alkoxy, etc.; R4 is H, halo, alkoxy, OH, (un)substituted C1-6 hydrocarbyl; R5 is H, OH, alkoxy, halo, and linear, branched or cyclic chain with between 1 - 8 carbon atoms; X is H, C1-4 hydrocarbyl, halo, (un)substituted hydroxyalkyl, (un)substituted aminoalkyl, (un)substituted alkoxyalkyl, etc.; are claimed. Example compd. II was prepd. by amination of 3-isopropyl-5,7-dichloropyrazolo[1,5-a]pyrimidine; the resulting N-benzyl-5-chloro-3-isopropylpyrazolo[1,5-a]pyrimidin-7-amine underwent Boc-protection with Boc-anhydride to give the corresponding Boc-protected amine, which underwent amination with isopropylamine to give tert-Bu benzyl-3-isopropyl-5-(isopropylamino)pyrazolo[1,5-a]pyrimidin-7-ylcarbamate, which underwent hydrolysis to give compd. II. All the invention compds. were evaluated for their cyclin-dependent kinase inhibitory activity (data given).
Liotta DC, Snyder JP, Jogalekar A, et al., 2008, Processes for preparing 5,7 diaminopyrazolo[1,5-〈] pyrimidine compounds, WO 2009-US67627 20091211. Priority: US 2008-121850 20081211.
Processes for the prepn. of certain 5,7-diaminopyrazolo[1,5-〈]pyrimidine compds. comprising the reaction of a primary or secondary amine and a protected 5-halo-7-aminopyrazolo[1,5-〈]pyrimidine compd. in solvent system comprising water and one or more org. solvents, optionally in the presence of an exogenous base.
Liotta DC, Synder JP, Jogalekar AS, et al., 2008, Processes for preparing 5,7-diaminopyrazolo[1,5-α]pyrimidine derivatives via regioselective aminations of dichloro(pyrazolo)pyrimidines with primary and secondary amines, WO 2010068838 A2, Priority Dec 11, 2008 US 2008-121850
The invention relates to processes for the prepn. of 5,7-diaminopyrazolo[1,5-α]pyrimidine compds. of formula I comprising the reaction of a primary or secondary amine of formula R3R4NH and a protected 5-halo-7-aminopyrazolo[1,5-α]pyrimidine compd. of formula II in solvent system comprising water and one or more org. solvents, optionally in the presence of an exogenous base, followed by deprotection. 5,7-Diaminopyrazolo[1,5-α]pyrimidine compds. of formula I or salts thereof wherein R1 = H, halo, alkyl, haloalkyl, cycloalkyl, alkenyl, alkynyl, heterocyclyl, heterocyclylalkyl, aryl, aralkyl, heteroaryl, heteroaralkyl, amino; R2 = alkyl, haloalkyl, cycloalkyl, alkenyl, alkynyl, heterocyclyl, heterocyclylalkyl, aryl, aralkyl, heteroaryl, heteroaralkyl, amino; R3 = H, alkyl, aryl, cycloalkyl; R4 = alkyl, alkenyl, aryl, arylalkyl, arylalkenyl, cycloalkyl, heterocyclyl, heterocyclylalkyl, heteroaryl, and heteroarylalkyl, are claimed. Protected 5-halo-7-aminopyrazolo[1,5-α]pyrimidine compd. of formula II wherein R8 = C1-8 alkyl, C6-14 aryl, C7-20 arylalkyl, C4-7 heterocyclic, C5-15 heterocyclicalkyl, C4-7 heteroaryl, C5-15 heteroaralkyl, C1-8 alkoxy, C6-14 aryloxy, C7-20 arylalkoxy, C4-7 heterocyclicoxy, C5-15 heterocyclicalkoxy, C4-7 heteroaryloxy, or C5-15 heteroaralkyloxy; X = F, Cl, Br, or I; R1 is as defined above; and R2 is as defined above and is optionally, protected with a protecting group, are claimed. Primary or secondary amines of formula R3R4NH wherein R3 is as defined above and is optionally, protected with a protecting group; R4 is as defined above and is optionally, protected with a protecting group; in a solvent system comprising water and one or more org. solvents, optionally in the presence of a base, are claimed. Thus, 5,7-dichloro-3-isopropylpyrazolo[1,5-α]pyrimidine (prepn. shown) underwent regioselective amination with benzylamine to afford N-benzyl-5-chloro-3-isopropylpyrazolo[1,5-α]pyrimidin-7-amine, which unde
Fuchter MJ, Zhong C, Zong H, et al., 2008, Porphyrazines: Designer macrocycles by peripheral substituent change, AUSTRALIAN JOURNAL OF CHEMISTRY, Vol: 61, Pages: 235-255, ISSN: 0004-9425
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- Citations: 54
Barrett AGM, Crimmin MR, Hill MS, et al., 2008, Reversibility in the protonolysis of a beta-diketiminate stabilised calcium bis(trimethylsilyl)amide with benzylamine, Dalton Trans, Pages: 1292-4, ISSN: 1477-9226
Protonolysis of the beta-diketiminate calcium bis(trimethylsilyl)amide [{ArNC(Me)CHC(Me)NAr}Ca{N(SiMe3)2}(THF)] with benzylamine is reversible and forms a quantifiable equilibrium mixture.[on SciFinder (R)]
Barrett AGM, Crimmin MR, Hill MS, et al., 2008, Insertion reactions of β-diketiminate-stabilised calcium amides with 1,3-dialkylcarbodiimides., Dalton Trans., Pages: 4474-4481, ISSN: 1477-9226
A series of heteroleptic β-diketiminate-stabilized calcium amides [(ArN:CMeCHCMe:NAr)Ca(NR1R2)(THF)] (Ar = 2,6-iPr2C6H3; 2 R1 = H, R2 = 2,6-iPr2C6H3; 3 R1 = R2 = Ph; 4 R1 = H, R2 = CH2CH2OMe) undergo addn. of the amido group at the carbon atom of 1,3-dialkylcarbodiimides, R3N:C:NR3 (R3 = Cy, iPr), to yield the corresponding guanidinate β-diketiminates [(ArN:CMeCHCMe:NAr)Ca[(R3N)2CNR1R2](THF)] (5-8, resp.) at room temp. in hydrocarbon solns. These latter compds. contain both β-diketiminate and guanidinate ligands bound to calcium. Solid-state data are consistent with the guanidinate ligands adopting a no. of binding modes including κ2 through κ3 coordination, with varying degrees of delocalization of the non-bound guanidinate nitrogen lone-pair across the π-framework of the ligand. DFT computational studies have been conducted to address these variations in coordination behavior. [on SciFinder(R)]
Barrett AGM, Boorman TC, Crimmin MR, et al., 2008, Heavier group 2 element-catalysed hydroamination of isocyanates, Chem Commun (Camb), Pages: 5206-8, ISSN: 1359-7345
The heteroleptic calcium amides [{ArNC(Me)CHC(Me)NAr}Ca(NR(2))(THF)] (Ar=2,6-di-iso-propylphenyl, R=SiMe(3), Ph) and the homoleptic heavier alkaline earth amides, [M{N(SiMe(3))(2)}(2)] (M=Ca, Sr and Ba) are reported as pre-catalysts for the hydroamination of isocyanates.[on SciFinder (R)]
Lee S, Vesper BJ, Zong H, et al., 2008, Synthesis and Biological Analysis of Thiotetra(ethylene glycol) monomethyl Ether-Functionalized Porphyrazines: Cellular Uptake and Toxicity Studies., Met Based Drugs, Vol: 2008, ISSN: 0793-0291
The porphyrazines (pzs), a class of porphyrin analogues, are being investigated for their potential use as tumor imaging/therapeutic agents. We here examine six peripherally-functionalized M[pz(AnB4-n)] pzs with n=4, 3, or 2 (in a trans conformation) and M = H2 or Zn, where A is an [S((CH2)2O)4Me]2 unit and B is a fused beta,beta'-diisopropyloxybenzo group. Cell viability/proliferation assays and fluorescence microscopy were carried out in both tumor and normal cells. Dark toxicity studies disclosed that four of the compounds exhibited toxicity in both normal and tumor cells; one was nontoxic in both normal and tumor cells, and one was selectively toxic to normal cells. Additionally, three of the pzs showed enhanced photo-induced toxicity with these effects in some cases being observed at treatment concentrations of up to ten-fold lower than that needed for a response in Photofrin. All six compounds were preferentially absorbed by tumor cells, suggesting that they have potential as in vitro diagnostic agents and as aids in the isolation and purification of aberrant cells from pathological specimens. In particular, two promising diagnostic candidates have been identified as part of this work.
Crimmin MR, Barrett AGM, Hill MS, et al., 2008, Heavier Group 2 Element Catalyzed Hydrophosphination of Carbodiimides., Organometallics, Vol: 27, Pages: 497-499, ISSN: 0276-7333
Amides of the heavier Group 2 elements Ca, Sr, and Ba are effective precatalysts for the atom-efficient addn. of phosphine P-H bonds to carbodiimides, e.g. >99% CyNHC(PPh2):NCy. A no. of intermediates within the catalytic cycle were identified by in situ NMR methods and by stoichiometric synthesis; the crystal and mol. structures of [[ArN:C(Me)CHC(Me):NAr]Pt(iPrN:C(PPh2)NiPr)(THF)] (Ar = 2,6-iPr2C6H3) were detd. by x-ray crystallog. [on SciFinder(R)]
Barrett AGM, Crimmin MR, Hill MS, et al., 2008, Synthesis, Characterization, and Solution Lability of N-Heterocyclic Carbene Adducts of the Heavier Group 2 Bis(trimethylsilyl)amides., Organometallics, Vol: 27, Pages: 3939-3946, ISSN: 0276-7333
N-heterocyclic carbene (NHC) adducts of the heavier Group 2 bis(trimethylsilyl)amides, [(L1)M{N(SiMe3)2}2], [(L2)Ca{N(SiMe3)2}2], and [(L1)Ca{N(SiMe3)2}Cl] (L1 = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene and L2 = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, M = Ca, Sr, and Ba), were synthesized by either the addn. of the group 2 amide to the appropriate imidazolium salt or direct addn. of the carbene to the solvent-free, homoleptic, metal amide. X-ray diffraction studies of the reaction products revealed the formation of monomeric three-coordinate alk. earth metal species in which the NHC binds via conventional σ-donation of the lone pair to the electrophilic metal center. Although 1H, 13C, and NOESY NMR expts. suggest this coordination is retained in soln., reactions with protic substrates such as 2-methoxyethylamine, diphenylamine, and di-p-tolylphosphine demonstrate the lability of the NHC under catalytically-relevant conditions. Furthermore, reactions of [L1Ca{N(SiMe3)2}2] with Lewis bases suggest that the strength of the interaction between the metal and neutral ligand decreases across the series Ph3P:O > NHC ≈ THF > PPh3. In the case of Ph3P:O the structure of the reaction product, [(Ph3P:O)2Ca{N(SiMe3)2}2], was confirmed by independent synthesis from addn. of Ph3P:O to [Ca{N(SiMe3)2}2]. [on SciFinder(R)]
Lachs JR, Barrett AGM, Crimmin MR, et al., 2008, Heavier group-2-element catalyzed hydroamination of carbodiimides., Eur. J. Inorg. Chem., Pages: 4173-4179, ISSN: 1434-1948
The heteroleptic calcium amide [{ArNC(Me)CHC(Me)NAr}Ca{N(SiMe3)2}(THF)] (Ar = 2,6-diisopropylphenyl) and the homoleptic heavier alk. earth amides, [M{N(SiMe3)2}2(THF)2] (M = Ca, Sr and Ba) are reported as competent precatalysts for the hydroamination of 1,3-carbodiimides. Reactions of arom. amines RNH2 (R = 2-FC6H4, Ph, 1-naphthyl, etc.) with 1,3-dialkylcarbodiimides R1N:C:NR2 (R1 = i-Pr, c-Hex, t-Bu; R2 = i-Pr, c-Hex, t-Bu, Et) in most cases proceed rapidly in hydrocarbon solvents at room temp. with catalyst (heavier group-2 guanidinate complexes) loadings as low as 0.2 mol-%. The guanidine reaction products R1NHC(NHR2):NR crystallize directly from the reaction mixt. [on SciFinder(R)]
Barrett AGM, Crimmin MR, Hill MS, et al., 2008, Triazenide complexes of the heavier alkaline earths: synthesis, characterization, and suitability for hydroamination catalysis., Inorg. Chem. (Washington, DC, U. S.), Vol: 47, Pages: 7366-7376, ISSN: 0020-1669
Triazenide complexes of the heavier alk. earths, Ca, Sr, and Ba, were synthesized by either protonolysis or salt metathesis routes. Although complexes [{Ar2N3}M{N(SiMe3)2}(THF)n] (M = Ca, n = 2; M = Sr, n = 3; Ar = 2,6-diisopropylphenyl) and [{Ar2N3}Ca(I)(THF)2]2 could be isolated and characterized by x-ray crystallog., soln. studies revealed the propensity of these species to undergo Schlenk-like redistribution with the formation of [{Ar2N3}2M(THF)n] (M = Ca, n = 1; M = Sr, n = 2). The latter compds. were synthesized independently. In the case of the large Ba dication, attempts to synthesize the heaviest analog of the series, [{Ar2N3}2Ba(THF)n], failed and led instead to the isolation of the K barate complex [K{Ar2N3}Ba{N(SiMe3)2}2(THF)4]. Single crystal x-ray diffraction studies demonstrated that, although in all the aforementioned cases the triazenide ligand binds to the electrophilic Group 2 metal centers via sym. κ2-N,N-chelates, in the latter compd. an unprecedented bridging mode is obsd. in which the triazenide ligand coordinates through both terminal and internal N centers. D.-functional theory computational expts. were undertaken to assist in the authors' understanding of this phenomenon. In further expts., the Ca and Sr amide derivs. [{Ar2N3}M{N(SiMe3)2}(THF)n] (M = Ca, n = 2; M = Sr, n = 3) proved to be catalytically active for the intramol. hydroamination of 1-amino-2,2-diphenylpent-4-ene to form 2-methyl-4,4-diphenylpyrrolidine, with the Ca species demonstrating a higher turnover no. than the Sr analog (2a, TOF = 500 h-1; 2b, TOF = 75 h-1). In these instances, because of ambiguities in the structural characterization of the precatalyst in soln., such quantification holds little value and detailed catalytic studies were not conducted. [on SciFinder(R)]
Crimmin MR, Barrett AGM, Hill MS, et al., 2008, Bis(trimethylsilyl)methyl derivatives of calcium, strontium and barium: potentially useful dialkyls of the heavy alkaline earth elements, Chemistry, Vol: 14, Pages: 11292-5, ISSN: 1521-3765
Barrett AGM, Crimmin MR, Hill MS, et al., 2008, β-Diketiminato Calcium Acetylides: Synthesis, Solution Dimerization, and Catalytic Carbon-Carbon Bond Formation., Organometallics, Vol: 27, Pages: 6300-6306, ISSN: 0276-7333
The β-diketiminate-stabilized calcium amide [{ArNC(Me)CHC(Me)NAr}Ca{N(SiMe3)2}(THF)] (1) reacts with terminal acetylenes in hydrocarbon solvents to yield the corresponding calcium acetylide complexes [{ArNC(Me)CHCN(Me)Ar}Ca{C≡CR1}]2 (R1 = n-Bu, t-Bu, Ph, 4-MeC6H4, ferrocenyl, Ar = 2,6-di-isopropylphenyl, 2a-e). Although in all instances solid and soln. state data were consistent with the reaction products existing as dimeric species with aggregation occurring via three-center-two-electron bridging acetylide units, a further reaction of 1 with HC≡CSi(iPr)3 demonstrated that both monomeric solvated [{ArNC(Me)CHC(Me)NAr}Ca{C≡CSi(iPr)3}(THF)2] (3b) or dimeric acetylide [{ArNC(Me)CHC(Me)NAr}Ca{C≡CSi(iPr)3}]2 (3a) species could be isolated from the reaction depending upon the exact conditions of the crystn. of the reaction product from soln. Further soln. studies demonstrated the presence of a monomer-dimer equil. in soln. A van't Hoff anal. allowed ΔG°(298 K) for the dimerization reaction to be calcd. as +27.0 kJ mol-1. The reaction of these hydrocarbon-sol. kinetically stabilized calcium acetylides with 1,3-dialkylcarbodiimides gave the corresponding heteroleptic calcium C-propargyl amidinate complexes [{ArNC(Me)CHCN(Me)Ar}Ca{(R2N)2CC≡CR1}(THF)n] (R1 = 4-MeC6H4, n = 0, 4a; 4-MeC6H4, n = 1, 4a·THF; R2 = iPr; R1 = Si(iPr3), R2 = Cy, n = 1, 4b·THF) via insertion of the carbodiimide into the calcium-carbon σ-bond. The latter complexes have been characterized in both soln. and the solid state including single-crystal x-ray anal. of 4a·THF. Extension of this reactivity to catalytic systems has allowed the application of amide 1 (5 mol %) to the catalytic hydroacetylenation of 1,3-di-isopropylcarbodiimide with phenylacetylene, yielding the corresponding propargyl amidine in 59% yield following crystn. from hexane soln. [on SciFinder(R)]
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